STUDY UNIT 3: SOLAR ENERGY SYSTEMS

3.1. LEARNING OUTCOMES

Upon completion of the course on solar energy systems, students should be able to:
 Understand the fundamental principles of solar energy, including the photovoltaic effect, solar
radiation, and the conversion of sunlight into electricity.
 Demonstrate knowledge of various solar energy technologies, including photovoltaic (PV)
systems, concentrating solar power (CSP), and solar thermal systems.
 Analyze and evaluate the performance and efficiency of solar energy systems, considering
factors such as solar resource assessment, system design, and component selection.
 Design and optimize solar energy systems for different applications, such as residential,
commercial, and utility-scale installations, taking into account factors like system sizing,
orientation, shading analysis, and energy storage integration.
 Demonstrate knowledge of relevant policies, regulations, and standards related to solar
energy systems, both at the national and international levels.
 Analyze case studies and real-world examples of successful solar energy projects,
understanding the challenges, technological advancements, and best practices in the field.
 Communicate effectively about solar energy systems, both in written reports and oral
presentations, demonstrating a deep understanding of the technical, economic, and
environmental aspects of solar energy technology.

3.2. INTRODUCTION

In this unit, we will explore the fascinating realm of solar energy systems for both heating and
electricity generation. By delving into the principles, technologies, and applications of solar thermal
and photovoltaic systems, you will gain a comprehensive understanding of harnessing solar energy
for diverse energy needs.
Solar energy offers immense potential not only for generating electricity but also for meeting heating
demands in various sectors. By studying solar energy systems for heating and electricity, you will be
equipped to contribute to the development of sustainable and efficient energy solutions.
In the initial part of this unit, we will focus on solar thermal systems for heating applications. We will
explore the principles of solar thermal energy conversion and investigate different types of solar
collectors, such as flat-plate collectors, evacuated tube collectors, and concentrating collectors. You
will learn how solar thermal systems can be used for space heating, water heating, and industrial
processes, and gain insights into system design, performance evaluation, and integration with existing
heating systems.
Next, we will shift our focus to solar photovoltaic (PV) systems for electricity generation. We will delve
into the physics behind the photovoltaic effect and examine the various types of PV technologies,
including monocrystalline, polycrystalline, thin-film, and emerging technologies. You will gain a deep
understanding of PV system components, such as solar modules, inverters, and balance-of-system
components, as well as the design and optimization considerations for grid-connected, off-grid, and
hybrid PV systems.
Throughout this unit, we will emphasize the integration of solar energy systems for heating and
electricity generation into existing energy infrastructure. We will explore grid interconnection
requirements, net metering policies, and energy management strategies for maximizing the utilization
of solar energy. Additionally, we will discuss the challenges and opportunities associated with the
integration of solar energy systems into district heating networks and microgrids.
Furthermore, we will analyze case studies and real-world examples of solar energy systems for
heating and electricity. By examining successful projects and best practices, you will gain valuable
insights into the practical implementation, performance optimization, and economic considerations of
solar energy systems in action.
As students, this study unit will provide you with a solid foundation and a multidimensional
understanding of solar energy systems for heating and electricity. You will be prepared to analyze
design trade-offs, evaluate system performance, and contribute to the advancement of sustainable
energy solutions in both domestic and industrial settings.
So, let us embark on this enlightening journey into the world of solar energy systems for heating and
electricity. Together, we will explore the principles, technologies, integration challenges, and real-world
applications of harnessing solar energy to meet our heating and electricity needs. By acquiring the
knowledge and skills in this unit, you will contribute to a future powered by clean, renewable, and
sustainable energy sources.

3.3. SOLAR ENERGY SYSTEMS

Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies
such as solar power to generate electricity, solar thermal energy (including solar water heating), and
solar architecture. It is an essential source of renewable energy, and its technologies are broadly
characterized as either passive solar or active solar depending on how they capture and distribute
solar energy or convert it into solar power. Active solar techniques include the use of photovoltaic
systems, concentrated solar power, and solar water heating to harness the energy. Passive solar
techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or
light-dispersing properties, and designing spaces that naturally circulate air.
Let's explain the concept of "Solar Energy Resources" to students, focusing on South Africa as an
example. We will provide relevant formulas and data specific to solar energy resources [1]:
 Solar Irradiance and Power Calculation: Solar irradiance is the amount of solar power
received per unit area on a surface exposed to the sun. The power available from solar
energy can be calculated using the following formula:
P=A*G*η
Where:
P represents the power available from solar energy
A is the area of the solar panel (in m²)
G is the solar irradiance (in W/m²)
η is the overall system efficiency
 South Africa's Solar Resource: South Africa has abundant solar energy resources due to its
geographic location and high levels of sunlight. The country has favorable solar conditions for
the deployment of solar power systems. Let's consider an example of a solar panel
installation in South Africa:
Location: Upington, Northern Cape
Average annual solar irradiance: 2,600 kWh/m²
Area of solar panel: 10 m²
Overall system efficiency: 0.15 (15%)
Using the given data, we can calculate the power available from solar energy at this location:
P = A * G * η = 10 m² * 2,600 kWh/m² * 0.15 = 3,900 kWh or 3.9 MWh
Therefore, in Upington, Northern Cape, with an average annual solar irradiance of 2,600
kWh/m², a solar panel installation with an area of 10 m² and an overall system efficiency of
15% can potentially generate around 3.9 MWh of power annually.
 Solar Resource Assessment in South Africa: Solar resource assessment involves
analyzing solar radiation data to evaluate the solar energy potential of a particular location.
The South African Solar Radiation Database provides comprehensive solar radiation data
across the country. It includes information on direct normal irradiance (DNI), global horizontal
irradiance (GHI), and diffuse horizontal irradiance (DHI). This data helps engineers assess the
solar energy resources and design effective solar power systems.
  Solar Energy Potential in South Africa: South Africa has immense solar energy potential,
especially in the Northern Cape region, which experiences high levels of solar irradiance. The
country's solar energy potential can be harnessed through various technologies, such as
photovoltaic (PV) systems and concentrated solar power (CSP). Solar energy can contribute
significantly to South Africa's electricity generation mix and support the transition to cleaner
and renewable energy sources.
By considering solar irradiance, power calculation formulas, and specific data for South Africa,
students can evaluate the solar energy resources in the country. They can utilize this information to
identify suitable locations for solar power projects, estimate power generation potential, and design
efficient solar energy systems.

Fig. 3.1: Solar map South Africa [2]

There are several measured types of solar irradiance:

 Total solar irradiance (TSI) is a measure of the solar power over all wavelengths per unit
area incident on the Earth's upper atmosphere. It is measured perpendicular to the incoming
sunlight. The solar constant is a conventional measure of mean TSI at a distance of one
astronomical unit (AU).
 Direct normal irradiance (DNI), or beam radiation, is measured at the surface of the Earth at
a given location with a surface element perpendicular to the Sun direction. It excludes diffuse
solar radiation (radiation that is scattered or reflected by atmospheric components). Direct
irradiance is equal to the extraterrestrial irradiance above the atmosphere minus the
atmospheric losses due to absorption and scattering. Losses depend on time of day (length of
light's path through the atmosphere depending on the solar elevation angle), cloud cover,
moisture content and other contents. The irradiance above the atmosphere also varies with
time of year (because the distance to the Sun varies), although this effect is generally less
significant compared to the effect of losses on DNI.
 Diffuse horizontal irradiance (DHI), or diffuse sky radiation is the radiation at the Earth's
surface from light scattered by the atmosphere. It is measured on a horizontal surface with
 radiation coming from all points in the sky excluding circumsolar radiation (radiation coming
from the sun disk). There would be almost no DHI in the absence of atmosphere.
 Global horizontal irradiance (GHI) is the total irradiance from the Sun on a horizontal
surface on Earth. It is the sum of direct irradiance (after accounting for the solar zenith angle
of the Sun z) and diffuse horizontal irradiance.
 Global tilted irradiance (GTI) is the total radiation received on a surface with defined tilt and
azimuth, fixed or Sun-tracking. GTI can be measured or modeled from GHI, DNI, DHI. It is
often a reference for photovoltaic power plants, while photovoltaic modules are mounted on
the fixed or tracking constructions.
 Global normal irradiance (GNI) is the total irradiance from the Sun at the surface of Earth at
a given location with a surface element perpendicular to the Sun.

3.4. THERMAL ENERGY

3.4.1. Water heating

Solar hot water systems use sunlight to heat water. In middle geographical latitudes (between 40
degrees north and 40 degrees south), 60 to 70% of the domestic hot water use, with water
temperatures up to 60 °C (140 °F), can be provided by solar heating systems [3] The most common
types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors
(34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to
heat swimming pools.

Fig.3.2: Solar hot water diagram [3]

Here's an explanation of the operation theory and relevant formulas:

  Solar Radiation Incident on the Collector: Solar water heaters utilize solar radiation as an
energy source. The amount of solar radiation incident on the collector surface can be
estimated based on factors like location, time of year, and orientation of the collector. Solar
radiation data and models can be used to determine the solar irradiance (G) in Watts per
square meter.
 Absorption of Solar Radiation: The solar collector absorbs a portion of the incident solar
radiation. The absorbed energy (Q_absorbed) can be calculated using the following formula:
Q_absorbed = α * G * A_c
Where:
α is the absorptivity of the collector surface, representing the fraction of incident radiation
absorbed. It is typically a value between 0 and 1.
G is the solar radiation incident on the collector surface.
A_c is the surface area of the collector.
 Heat Loss from the Collector: Heat loss from the collector occurs through various
mechanisms, including conduction, convection, and radiation. The specific formula for heat
loss depends on the design, construction, and insulation of the collector. The heat loss
(Q_loss) can be estimated using appropriate heat transfer equations for each mechanism.
 Heat Transfer to the Water: The absorbed heat energy in the collector is transferred to the
water in the storage tank. The rate of heat transfer (Q_transfer) can be calculated using the
following formula:
Q_transfer = m * c * (T_out - T_in)
Where:
m is the mass flow rate of the heat transfer fluid in kilograms per second.
c is the specific heat capacity of the heat transfer fluid in Joules per kilogram per degree
Celsius.
T_out is the temperature of the heat transfer fluid leaving the collector.
T_in is the temperature of the heat transfer fluid entering the collector.
 Energy Balance Equation: The energy balance equation for the solar water heater system
can be expressed as: Q_in - Q_out = Q_loss
Where:
Q_in is the total energy input into the water heater system. It includes the energy absorbed by
the collector (Q_absorbed) and any additional energy input from backup heating sources.
Q_out is the energy output from the system. It is the energy transferred to the water in the
storage tank (Q_transfer).
Q_loss is the energy lost from the system due to heat losses through the collector, pipes, and
storage tank.

3.4.2. Sizing solar water heating

Here is a detailed methodology for solar water heater sizing, specifically tailored for students studying
solar energy, with a numerical example case in South Africa [3]:
 Determine Hot Water Demand: Assess the hot water demand for the application or site in
South Africa. Consider factors such as the number of occupants, their bathing habits, water
usage patterns, and the desired temperature of the hot water. Determine the required amount
of hot water in liters per day or liters per hour.
Example: Hot water demand is 200 liters per day.
 Analyze Solar Resource: Obtain solar resource data specific to the location in South Africa.
Use reliable sources such as the South African Solar Radiation Database or solar radiation
maps specifically designed for South Africa. Consider variations in solar irradiation throughout
the year and any shading effects from nearby objects or structures.
Example: Average daily solar irradiation in Johannesburg, South Africa is 5.5 kWh/m².
 Assess Collector Efficiency: Determine the efficiency of the solar thermal collectors to be
used in the solar water heater system. This efficiency depends on factors such as the
 collector type (flat plate, evacuated tube), design, tilt angle, orientation, and any shading or
soiling effects. The collector efficiency indicates the percentage of solar energy that can be
converted into heat.
Example: Assume a collector efficiency of 70%.
 Calculate Energy Requirement: Calculate the energy required to heat the water to the
desired temperature. This calculation takes into account the specific heat capacity of water
and the temperature rise required. The energy requirement can be expressed in kilowatt-
hours (kWh) or joules.
Example: Assuming a desired temperature rise of 40°C, the energy requirement can be
calculated using the formula:
Energy (kWh) = Volume of Water (liters) x Specific Heat Capacity of Water x Temperature
Rise / 3600
Energy (kWh) = 200 L x 4.18 kJ/kg°C x 40°C / 3600 = 9.31 kWh
 Determine Solar Fraction: Define the solar fraction, which represents the percentage of the
total energy requirement that will be provided by the solar water heater system. The solar
fraction depends on factors such as the solar resource, collector efficiency, storage capacity,
and hot water demand. It indicates the system's ability to meet the hot water demand using
solar energy.
Example: Assume a solar fraction of 80%.
 Calculate Required Solar Energy: Calculate the amount of solar energy that needs to be
collected by the solar water heater system to meet the hot water demand. Multiply the total
energy requirement (Step 4) by the solar fraction (Step 5) to obtain the required solar energy.
Example: Required solar energy = Energy requirement (9.31 kWh) x Solar fraction (0.8) =
7.45 kWh
 Determine Collector Area: Calculate the required collector area to collect the necessary
solar energy. Divide the required solar energy (Step 6) by the product of the solar irradiation
(Step 2) and the collector efficiency (Step 3).
Example: Required collector area = Required solar energy (7.45 kWh) / (Average daily solar
irradiation (5.5 kWh/m²) x Collector efficiency (0.7)) = 2.44 m²
 Select Solar Water Heater System: Select a suitable solar water heater system based on
the calculated collector area, hot water demand, and specific requirements. Consider factors
such as system type (direct, indirect, or thermosiphon), storage capacity, backup heating
options, and manufacturer specifications. Ensure that the selected system meets the sizing
requirements and is appropriate for the South African context.
Example: Choose a solar water heater system with a collector area of approximately 2.5 m², a
storage capacity of 200 liters, and suitable backup heating options.
 Conduct Economic Analysis: Perform an economic analysis to assess the financial viability
of the solar water heater system in South Africa. Consider factors such as the initial
investment cost, expected energy savings, payback period, return on investment (ROI), and
any available incentives or subsidies for solar thermal installations specific to South Africa.
Evaluate the economic feasibility and long-term benefits of the solar water heater system.
Example: Suppose the initial investment cost for the solar water heater system is $2,000, and
the cost of alternative heating methods is $500 per year. With an estimated energy savings of
$400 per year, the payback period can be calculated by dividing the initial investment cost by
the annual savings, which would be approximately 5 years.
 Documentation and Reporting: Document the entire solar water heater sizing process,
including the data collected, calculations performed, assumptions made, and results obtained.
Present the findings in a clear and concise manner, including graphs, tables, and illustrations
as needed. Provide a comprehensive report that outlines the system design, performance
estimates, economic analysis, and any recommendations or future research considerations
specific to the South African context.
 Example: Prepare a detailed report that includes information about the chosen solar water
heater system, collector area, estimated energy savings, economic analysis results, and
recommendations for optimizing the system design for the specific location in South Africa.
By following this detailed methodology with the provided numerical example in South Africa, students
can gain a thorough understanding of the solar water heater sizing process and apply it to real-world
situations in a specific geographical context.

3.4.3. Heating, cooling and ventilation

In the South Africa, heating, ventilation and air conditioning (HVAC) systems account for a significant
portion of the energy used in commercial and residential buildings. Solar heating, cooling and
ventilation technologies can be used to offset a portion of this energy. Use of solar for heating can
roughly be divided into passive solar concepts and active solar concepts, depending on whether
active elements such as sun tracking and solar concentrator optics are used [4].
Here's an explanation of the operation theory for each aspect:
 Solar Heating: Solar heating systems utilize solar energy to provide space heating. The basic
principle involves collecting solar radiation and converting it into heat energy. The operation
theory and formulas for solar heating can be summarized as follows:
Solar Collector: A solar collector, such as a flat-plate collector or evacuated tube collector,
absorbs solar radiation and converts it into heat. The collector's absorber plate is typically
coated with a dark material to enhance heat absorption.
Heat Transfer Fluid: A heat transfer fluid, such as water or a heat transfer oil, circulates
through the collector and absorbs the heat energy. The fluid carries the heat to a heat
exchanger or storage system.
Heat Transfer and Storage: The heat transfer fluid transfers its heat to a heat exchanger or
storage system. The heat transfer rate and energy storage capacity depend on factors like the
flow rate of the fluid, specific heat capacity, and temperature difference. The formulas used for
heat transfer and storage calculations depend on the specific system configuration and
design.
Distribution: The stored heat energy is distributed throughout the building using various
methods, including radiant heating systems, forced-air systems, or hydronic systems. The
distribution system design and formulas depend on the specific heating method employed.
 Solar Cooling: Solar cooling systems use solar energy to provide cooling and air
conditioning. The operation theory and formulas for solar cooling can be summarized as
follows:
Solar Thermal Cooling: Solar thermal cooling systems use solar energy to drive an absorption
or adsorption refrigeration cycle. The solar collector provides the thermal energy required for
the cooling process. The formulas for solar thermal cooling depend on the specific
refrigeration cycle used and may involve equations related to thermodynamics and heat
transfer.
Photovoltaic (PV) Cooling: PV cooling systems use solar photovoltaic panels to generate
electricity, which powers cooling devices such as electric compressors or fans. The formulas
for PV cooling involve electrical equations for power generation, efficiency calculations, and
thermodynamic equations for the cooling process.
 Solar Ventilation: Solar ventilation systems utilize solar energy to improve indoor air quality
and provide ventilation. The operation theory and formulas for solar ventilation can be
summarized as follows:
Solar Air Collectors: Solar air collectors absorb solar radiation and heat up the air passing
through them. The heated air can be used for ventilation or as a preheated air source for
space heating. The formulas for solar air collectors involve heat transfer equations and fluid
dynamics principles.
Natural Ventilation: Solar energy can also be utilized to drive natural ventilation processes.
Techniques such as solar chimneys or solar-powered fans can enhance air movement and
 exchange in a building. The formulas for natural ventilation depend on factors like airflow
rates, pressure differentials, and heat transfer coefficients.

Fig.3.3: Heating, cooling and ventilation [4]

3.4.4. Cooking
Solar cookers use sunlight for cooking, drying, and pasteurization. They can be grouped into three
broad categories: box cookers, panel cookers, and reflector cookers. The simplest solar cooker is the
box cooker first built by Horace de Saussure in 1767. A basic box cooker consists of an insulated
container with a transparent lid. It can be used effectively with partially overcast skies and will typically
reach temperatures of 90–150 °C (194–302 °F). Panel cookers use a reflective panel to direct sunlight
onto an insulated container and reach temperatures comparable to box cookers. Reflector cookers
use various concentrating geometries (dish, trough, Fresnel mirrors) to focus light on a cooking
container. These cookers reach temperatures of 315 °C (599 °F) and above but require direct light to
function properly and must be repositioned to track the Sun [5].
Here's an explanation of the operation for solar cooking:
 Solar Radiation: Solar cooking harnesses the energy from solar radiation to cook food. The
operation theory involves capturing and utilizing the sun's energy. The amount of solar
radiation incident on the cooking device can be estimated based on factors such as location,
time of day, and weather conditions. Solar radiation data and models can be used to
determine the solar irradiance (G) in Watts per square meter.
 Absorption and Conversion of Solar Energy: The solar cooking device, such as a solar
cooker or solar oven, is designed to absorb and convert solar energy into heat for cooking.
The device typically consists of a reflective surface, such as a mirrored or reflective panel, to
focus and concentrate solar radiation onto the cooking vessel.
The absorbed solar energy (Q_absorbed) can be calculated using the following formula:
Q_absorbed = α * G * A_c
Where:
α is the absorptivity of the solar cooking device, representing the fraction of incident radiation
absorbed.
G is the solar radiation incident on the cooking device.
A_c is the surface area of the cooking device.
 Heat Transfer and Cooking: The absorbed solar energy is transferred to the cooking vessel
or container, which contains the food to be cooked. The rate of heat transfer (Q_transfer) can
be calculated using appropriate heat transfer formulas, which depend on factors such as the
thermal conductivity of the cooking vessel, the surface area of contact, and the temperature
difference between the cooking vessel and the food.
The specific formulas for heat transfer and cooking depend on the design and configuration of
the solar cooking device, as well as the characteristics of the cooking vessel and food being
 cooked. Advanced studies at the level may involve more complex heat transfer models and
computational simulations to analyze the cooking performance and optimize the design for
efficiency.
 Cooking Time Estimation: To estimate the cooking time required, various factors need to be
considered, including the initial temperature of the food, the desired final temperature, the
heat transfer characteristics of the cooking vessel, and the solar irradiance. Mathematical
models or empirical correlations can be employed to estimate the cooking time based on
these factors. Additionally, it's important to consider factors such as the angle and orientation
of the solar cooking device, the presence of shading or clouds, and the efficiency of the
reflective surfaces to ensure effective utilization of solar energy for cooking.

Fig. 3.4: Solar cooking [5]

3.4.5. Water treatment

Solar water treatment involves the use of solar energy to purify or disinfect water, making it safe for
consumption. Here's an explanation of the operation theory for solar water treatment [6]:
 Solar Disinfection (SODIS): Solar disinfection, or SODIS, is a simple and low-cost method of
water treatment that utilizes solar energy for disinfection purposes. The operation theory
involves the combined effects of solar radiation and temperature on microbial inactivation.
The following factors contribute to the effectiveness of SODIS:
Solar Radiation: Solar radiation, particularly ultraviolet (UV) radiation, plays a crucial role in
disinfection. UV radiation damages the DNA of microorganisms, rendering them unable to
reproduce and causing their inactivation.
Exposure Time: The exposure time required for effective disinfection depends on the intensity
of solar radiation, the type and concentration of microorganisms present in the water, and the
desired level of disinfection. Longer exposure times are generally required under less intense
solar radiation conditions.
Water Depth: The depth of the water in the container or bottle used for SODIS affects the
penetration of UV radiation. Thinner layers of water allow for better UV penetration and more
efficient disinfection.
 Solar Water Purification: Solar water purification methods involve the utilization of solar
energy for various purification processes, including distillation and desalination. The operation
theory and formulas for solar water purification depend on the specific purification method
employed:
Solar Distillation: Solar distillation involves the use of solar energy to evaporate water and
subsequently condense the vapor to obtain purified water. The operation theory revolves
 around the phase change of water from liquid to vapor and then back to liquid. The formulas
for solar distillation include heat transfer equations, mass transfer equations, and
thermodynamic principles.
Solar Desalination: Solar desalination utilizes solar energy to remove salt and other impurities
from saline water. The operation theory and formulas for solar desalination methods, such as
solar stills or solar-powered reverse osmosis, involve a combination of heat transfer, mass
transfer, and thermodynamic principles.
 Solar Water Treatment Efficiency: The efficiency of solar water treatment systems can be
evaluated using various parameters, such as disinfection efficiency, purification efficiency,
energy efficiency, or specific energy consumption. These parameters quantify the
performance of the system in terms of its ability to treat water effectively while utilizing solar
energy efficiently. The formulas used to calculate these efficiencies depend on the specific
system design, operational parameters, and performance indicators.

Fig.3.5: Solar water treatment [6]

3.4.6. Molten salt technology

Solar molten salt systems are advanced solar thermal energy storage systems that use molten salt as
a heat transfer fluid and thermal energy storage medium. These systems are typically employed in
concentrated solar power (CSP) plants. At the level, the operation of solar molten salt systems can be
explored in detail. Here's an explanation [7]:
 Fig.3.6: Solar molten salt [7]
 Operation Theory: Solar molten salt systems operate based on the following key principles:
Solar Collector: Concentrated solar radiation is focused onto a solar collector, which typically
consists of mirrors or heliostats that track the sun's movement. The concentrated solar energy
is absorbed by a receiver, which contains the molten salt.
Heat Transfer Fluid: The molten salt, often a eutectic mixture of sodium nitrate and potassium
nitrate, acts as a heat transfer fluid. It absorbs the concentrated solar energy in the receiver
and carries it to the thermal storage system or directly to the power cycle.
Thermal Energy Storage: The molten salt can store the thermal energy for later use, enabling
continuous power generation even when there is no direct sunlight. The hot molten salt is
stored in insulated tanks or reservoirs, maintaining its high temperature until it is needed.
Power Generation: When electricity is required, the stored thermal energy is used to generate
steam, which drives a turbine connected to an electric generator. The steam generation can
occur directly by passing the molten salt through a heat exchanger or indirectly through a heat
transfer fluid (e.g., water/steam) in a secondary loop.
 Heat Transfer and Storage: The operation of solar molten salt systems involves heat
transfer formulas and calculations. Some important formulas include:
Heat Transfer Rate: The rate at which heat is transferred from the solar collector to the molten
salt can be calculated using the following formula:
Q = m * Cp * ΔT
Where:
Q is the heat transfer rate (in watts or kilowatts)
m is the mass flow rate of molten salt (in kilograms per second)
Cp is the specific heat capacity of the molten salt (in joules per kilogram-kelvin)
ΔT is the temperature difference between the hot and cold sides of the heat exchanger or
receiver (in kelvin or degrees Celsius)
Thermal Energy Storage: The amount of thermal energy stored in the molten salt system can
be calculated using the following formula:
E = m * Cp * ΔT
Where:
E is the thermal energy stored (in joules or kilojoules)
m is the mass of the molten salt stored (in kilograms)
Cp is the specific heat capacity of the molten salt (in joules per kilogram-kelvin)
ΔT is the temperature difference between the stored molten salt and the ambient temperature
(in kelvin or degrees Celsius)
Activity 3.1.
Please watch the available videos from the following links to acquire a comprehensive understanding
of solar thermal systems. Afterward, kindly respond to the subsequent questions:
https://www.youtube.com/watch?v=DhDNRD823XU
https://www.youtube.com/watch?
v=n4tVuv5SYPk&list=PLg8QoV0J4dTPz1_t_vSvosYr0TASvZDgE&index=2
https://www.youtube.com/watch?
v=mHRcTKHsleU&list=PLg8QoV0J4dTPz1_t_vSvosYr0TASvZDgE&index=3
 Explain the different types of solar collectors used in solar thermal systems and discuss their
advantages and disadvantages.
 Describe the design and working principles of a parabolic dish solar collector.
 Discuss the various heat transfer mechanisms involved in a solar thermal system.
 Explain the concept of optical concentration in solar thermal systems and its impact on
system efficiency.
 What are the different types of thermal energy storage systems used in solar thermal
applications? Compare their characteristics and suitability for different scenarios.
 Discuss the role of phase-change materials (PCMs) in thermal energy storage for solar
thermal systems.
 Explain the factors that affect the performance and efficiency of a solar thermal power plant.
 Discuss the challenges and potential solutions for integrating solar thermal systems with
conventional power grids.
 Describe the concept of hybrid solar thermal systems and their advantages in terms of energy
generation and efficiency.
 Discuss the current research trends and advancements in solar thermal technology, including
novel materials and system designs.
 Explain the concept of exergy analysis and its application in evaluating the performance of
solar thermal systems.
 Discuss the economic implications and cost-effectiveness of implementing solar thermal
systems.
 Describe the environmental impacts and sustainability aspects associated with solar thermal
energy generation.
 Discuss the potential applications of solar thermal systems beyond electricity generation,
such as industrial process heat and space heating.
 Explain the concept of solar thermal desalination and discuss its potential for addressing
water scarcity issues.

3.5. ELECTRICITY PRODUCTION

3.5.1. Photovoltaic system

Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity,
either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells
convert light into an electric current using the photovoltaic effect. Concentrated solar power systems
use lenses or mirrors and solar tracking systems to focus a large area of sunlight to a hot spot, often
to drive a steam turbine [8].
Photovoltaics were initially solely used as a source of electricity for small and medium-sized
applications, from the calculator powered by a single solar cell to remote homes powered by an off-
grid rooftop PV system. Commercial concentrated solar power plants were first developed in the
1980s. Since then, as the cost of solar electricity has fallen, grid-connected solar PV systems'
capacity and production have grown more or less exponentially, doubling about every three years.
Millions of installations and gigawatt-scale photovoltaic power stations continue to be built, with half of
the new generation capacity being solar in 2021.
In 2022, solar generated 4.5% of the world's electricity, compared to 1% in 2015, when the Paris
Agreement to limit climate change was signed. Along with onshore wind, in most countries, the
cheapest levelised cost of electricity for new installations is utility-scale solar.
Almost half the solar power installed in 2022 was rooftop. Low-carbon power has been recommended
as part of a plan to limit climate change. The International Energy Agency said in 2022 that more effort
was needed for grid integration and the mitigation of policy, regulation and financing challenges.

3.5.1.1. Photovoltaic cell

Understanding the physics behind a photovoltaic (PV) cell is fundamental for studying solar energy
conversion. Here's an explanation of the physics principles involved in a PV cell:
 Semiconductor Materials: A PV cell consists of semiconductor materials, primarily made of
silicon (Si) or other compound semiconductors. Semiconductors have an energy band
structure that allows them to exhibit both conducting and insulating properties, depending on
the energy levels of electrons within the material.
 Energy Bands: In a semiconductor, there are two important energy bands: the valence band
and the conduction band. The valence band is the energy band filled with electrons, while the
conduction band is the energy band above the valence band that contains unoccupied energy
states.
 Band Gap: The energy difference between the valence band and the conduction band is
called the band gap. This band gap determines whether the semiconductor is an insulator, a
semiconductor, or a conductor. In an insulator, the band gap is large, whereas in a conductor,
the band gap is zero. In a semiconductor, the band gap is moderate.
 Photovoltaic Effect: The key physics principle behind a PV cell is the photovoltaic effect.
When a semiconductor material is exposed to photons (particles of light), the energy from the
photons can be absorbed by the semiconductor. If the energy of the absorbed photons is
equal to or greater than the band gap energy of the semiconductor, electron-hole pairs
(excitons) are generated.
 Generation of Electron-Hole Pairs: The absorbed photons transfer their energy to the
electrons in the valence band, allowing them to overcome the band gap energy and move to
the conduction band. This results in the creation of free electrons in the conduction band and
positively charged holes in the valence band.
 Charge Separation: Once the electron-hole pairs are generated, an electric field within the
PV cell causes the electrons to move towards the n-type region (which is negatively charged)
and the holes to move towards the p-type region (which is positively charged). This charge
separation creates a voltage potential across the cell.
 PN Junction: A typical PV cell consists of a PN junction, where the n-type region has an
excess of electrons and the p-type region has an excess of holes. The PN junction acts as a
diode, allowing the flow of current in one direction (from the n-type to the p-type region) while
hindering it in the reverse direction.
 External Circuit: To harness the generated electric potential, an external circuit is connected
to the PV cell. When the circuit is closed, electrons flow from the n-type region through the
external circuit to the p-type region, creating an electric current.
 Efficiency and Power Output: The efficiency of a PV cell is determined by its ability to
convert incoming sunlight into electrical energy. Factors such as the band gap energy,
material quality, and cell design impact the efficiency. The power output of a PV cell depends
on the intensity of the incident light, the cell's efficiency, and its surface area.
 Further Considerations: PV cells can be interconnected to form PV modules, and multiple
modules can be connected to create PV arrays. PV arrays are commonly used in solar
energy systems to generate electricity for various applications.
As a student studying photovoltaic (PV) cells, you would typically encounter various types of PV cells.
Here are some common types of PV cells that you may come across:
  Monocrystalline Silicon (Mono-Si) Cells: These PV cells are made from a single crystal
structure, providing high efficiency and uniform appearance. Mono-Si cells have a high purity
level and are known for their excellent performance, especially in high-temperature
environments. They are commonly used in residential and commercial applications.
 Polycrystalline Silicon (Poly-Si) Cells: Poly-Si cells are made from multiple silicon crystals,
resulting in a grainy appearance. They are less expensive to produce compared to mono-Si
cells but typically have slightly lower efficiency. Poly-Si cells are widely used in large-scale PV
installations due to their cost-effectiveness.
 Thin-Film Solar Cells: Thin-film solar cells are made by depositing thin layers of
semiconductor materials onto a substrate. Common thin-film technologies include amorphous
silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS). Thin-film
cells are flexible, lightweight, and can be produced in large areas, making them suitable for
various applications such as building-integrated PV systems and portable devices.
 Multijunction Cells: Multijunction cells are composed of multiple semiconductor layers with
different band gaps. Each layer is optimized to absorb different portions of the solar spectrum,
increasing efficiency. Multijunction cells are commonly used in concentrated photovoltaic
(CPV) systems and space applications where high efficiency is required.
 Organic Photovoltaic (OPV) Cells: OPV cells use organic (carbon-based) materials as the
active layer. They are lightweight, flexible, and can be manufactured using low-cost processes
such as printing. OPV cells have lower efficiency compared to traditional PV technologies but
offer the potential for applications in portable electronics, wearable devices, and building-
integrated PV.
 Perovskite Solar Cells: Perovskite solar cells are a rapidly emerging PV technology. They
use a perovskite material, typically a hybrid organic-inorganic lead halide, as the light-
absorbing layer. Perovskite cells have achieved high efficiency in a relatively short time and
offer the potential for low-cost manufacturing. However, stability and durability in real-world
conditions are still areas of active research.
 Tandem or Multi-junction Solar Cells: Tandem solar cells combine multiple PV
technologies, such as silicon and perovskite, to achieve higher efficiency. By utilizing different
materials that absorb different portions of the solar spectrum, tandem cells can capture more
sunlight and convert it into electricity more efficiently.
These are some of the prominent types of PV cells that you may encounter as a student studying
photovoltaics. Each type has its advantages, disadvantages, and specific applications, and
understanding their characteristics can help you analyze and optimize their performance for various
solar energy conversion systems.
Fig. 3.7: Reported timeline of research solar cell energy conversion efficiencies (National Renewable
Energy Laboratory) [8]

Fig. 3.8: From solar cell to PV system [8]

3.5.1.2. Components
 Solar array: Conventional c-Si solar cells, normally wired in series, are encapsulated in a
solar module to protect them from the weather. The module consists of a tempered glass as
cover, a soft and flexible encapsulant, a rear backsheet made of a weathering and fire-
resistant material and an aluminium frame around the outer edge. Electrically connected and
mounted on a supporting structure, solar modules build a string of modules, often called solar
panel. A solar array consists of one or many such panels. A photovoltaic array, or solar array,
is a linked collection of solar modules. The power that one module can produce is seldom
enough to meet requirements of a home or a business, so the modules are linked together to
 form an array. Most PV arrays use an inverter to convert the DC power produced by the
modules into alternating current that can power lights, motors, and other loads. The modules
in a PV array are usually first connected in series to obtain the desired voltage; the individual
strings are then connected in parallel to allow the system to produce more current. Solar
panels are typically measured under STC (standard test conditions) or PTC (PVUSA test
conditions), in watts. Typical panel ratings range from less than 100 watts to over 400 watts.
The array rating consists of a summation of the panel ratings, in watts, kilowatts, or
megawatts.
 Mounting: Modules are assembled into arrays on some kind of mounting system, which may
be classified as ground mount, roof mount or pole mount. For solar parks a large rack is
mounted on the ground, and the modules mounted on the rack. For buildings, many different
racks have been devised for pitched roofs. For flat roofs, racks, bins and building integrated
solutions are used. Solar panel racks mounted on top of poles can be stationary or moving,
see Trackers below. Side-of-pole mounts are suitable for situations where a pole has
something else mounted at its top, such as a light fixture or an antenna. Pole mounting raises
what would otherwise be a ground mounted array above weed shadows and livestock, and
may satisfy electrical code requirements regarding inaccessibility of exposed wiring. Pole
mounted panels are open to more cooling air on their underside, which increases
performance. A multiplicity of pole top racks can be formed into a parking carport or other
shade structure. A rack which does not follow the sun from left to right may allow seasonal
adjustment up or down.
 Cabling: A solar cable is the interconnection cable used in photovoltaic power generation.
Solar cables interconnect solar panels and other electrical components of a photovoltaic
system. Solar cables are designed to be UV resistant and weather resistant. They can be
used within a large temperature range. Specific performance requirements for material used
for wiring a solar panel installation are given in national and local electrical codes which
regulate electrical installations in an area. General features required for solar cables are
resistance to ultraviolet light, weather, temperature extremes of the area and insulation
suitable for the voltage class of the equipment. Different jurisdictions will have specific rules
regarding grounding (earthing) of solar power installations for electric shock protection and
lightning protection.
 Tracker: A solar tracking system tilts a solar panel throughout the day. Depending on the type
of tracking system, the panel is either aimed directly at the Sun or the brightest area of a
partly clouded sky. Trackers greatly enhance early morning and late afternoon performance,
increasing the total amount of power produced by a system by about 20–25% for a single axis
tracker and about 30% or more for a dual axis tracker, depending on latitude. Trackers are
effective in regions that receive a large portion of sunlight directly. In diffuse light (i.e. under
cloud or fog), tracking has little or no value. Because most concentrated photovoltaics
systems are very sensitive to the sunlight's angle, tracking systems allow them to produce
useful power for more than a brief period each day. Tracking systems improve performance
for two main reasons. First, when a solar panel is perpendicular to the sunlight, it receives
more light on its surface than if it were angled. Second, direct light is used more efficiently
than angled light. Special anti-reflective coatings can improve solar panel efficiency for direct
and angled light, somewhat reducing the benefit of tracking.
Trackers and sensors to optimise the performance are often seen as optional, but they can
increase viable output by up to 45%. Arrays that approach or exceed one megawatt often use
solar trackers. Considering clouds, and the fact that most of the world is not on the equator,
and that the sun sets in the evening, the correct measure of solar power is insolation – the
average number of kilowatt-hours per square meter per day. For the weather and latitudes of
the United States and Europe, typical insolation ranges from 2.26 kWh/m2/day in northern
climes to 5.61 kWh/m2/day in the sunniest regions.
 For large systems, the energy gained by using tracking systems can outweigh the added
complexity. For very large systems, the added maintenance of tracking is a substantial
detriment. Tracking is not required for flat panel and low-concentration photovoltaic systems.
For high-concentration photovoltaic systems, dual axis tracking is a necessity. Pricing trends
affect the balance between adding more stationary solar panels versus having fewer panels
that track.
As pricing, reliability and performance of single-axis trackers have improved, the systems
have been installed in an increasing percentage of utility-scale projects. According to data
from WoodMackenzie/GTM Research, global solar tracker shipments hit a record 14.5
gigawatts in 2017. This represents growth of 32 percent year-over-year, with similar or greater
growth projected as large-scale solar deployment accelerates.
 Inverter: Systems designed to deliver alternating current (AC), such as grid-connected
applications need an inverter to convert the direct current (DC) from the solar modules to AC.
Grid connected inverters must supply AC electricity in sinusoidal form, synchronized to the
grid frequency, limit feed in voltage to no higher than the grid voltage and disconnect from the
grid if the grid voltage is turned off. Islanding inverters need only produce regulated voltages
and frequencies in a sinusoidal waveshape as no synchronisation or co-ordination with grid
supplies is required.
A solar inverter may connect to a string of solar panels. In some installations a solar micro-
inverter is connected at each solar panel. For safety reasons a circuit breaker is provided both
on the AC and DC side to enable maintenance. AC output may be connected through an
electricity meter into the public grid. The number of modules in the system determines the
total DC watts capable of being generated by the solar array; however, the inverter ultimately
governs the amount of AC watts that can be distributed for consumption. For example, a PV
system comprising 11 kilowatts DC (kWDC) worth of PV modules, paired with one 10-kilowatt
AC (kWAC) inverter, will be limited to the inverter's output of 10 kW. As of 2019, conversion
efficiency for state-of-the-art converters reached more than 98 percent. While string inverters
are used in residential to medium-sized commercial PV systems, central inverters cover the
large commercial and utility-scale market. Market-share for central and string inverters are
about 44 percent and 52 percent, respectively, with less than 1 percent for micro-inverters.
 Maximum power point tracking (MPPT) is a technique that grid connected inverters use to
get the maximum possible power from the photovoltaic array. In order to do so, the inverter's
MPPT system digitally samples the solar array's ever changing power output and applies the
proper impedance to find the optimal maximum power point.
 Anti-islanding is a protection mechanism to immediately shut down the inverter, preventing it
from generating AC power when the connection to the load no longer exists. This happens,
for example, in the case of a blackout. Without this protection, the supply line would become
an "island" with power surrounded by a "sea" of unpowered lines, as the solar array continues
to deliver DC power during the power outage. Islanding is a hazard to utility workers, who
may not realize that an AC circuit is still powered, and it may prevent automatic re-connection
of devices. Anti-Islanding feature is not required for complete Off-Grid Systems.
 Battery: Although still expensive, PV systems increasingly use rechargeable batteries to store
a surplus to be later used at night. Batteries used for grid-storage also stabilize the electrical
grid by leveling out peak loads, and play an important role in a smart grid, as they can charge
during periods of low demand and feed their stored energy into the grid when demand is high.
Common battery technologies used in today's PV systems include the valve regulated lead-
acid battery – a modified version of the conventional lead–acid battery – nickel–cadmium and
lithium-ion batteries. Compared to the other types, lead-acid batteries have a shorter lifetime
and lower energy density. However, due to their high reliability, low self-discharge as well as
low investment and maintenance costs, they are currently (as of 2014) the predominant
technology used in small-scale, residential PV systems, as lithium-ion batteries are still being
developed and about 3.5 times as expensive as lead-acid batteries. Furthermore, as storage
 devices for PV systems are stationary, the lower energy and power density and therefore
higher weight of lead-acid batteries are not as critical as, for example, in electric
transportation. Other rechargeable batteries considered for distributed PV systems include
sodium–sulfur and vanadium redox batteries, two prominent types of a molten salt and a flow
battery, respectively. In 2015, Tesla Motors launched the Powerwall, a rechargeable lithium-
ion battery with the aim to revolutionize energy consumption.
 MPPT: PV systems with an integrated battery solution also need a charge controller, as the
varying voltage and current from the solar array requires constant adjustment to prevent
damage from overcharging. Basic charge controllers may simply turn the PV panels on and
off, or may meter out pulses of energy as needed, a strategy called PWM or pulse-width
modulation. More advanced charge controllers will incorporate MPPT logic into their battery
charging algorithms. Charge controllers may also divert energy to some purpose other than
battery charging. Rather than simply shut off the free PV energy when not needed, a user
may choose to heat air or water once the battery is full.
 Monitoring and metering: The metering must be able to accumulate energy units in both
directions, or two meters must be used. Many meters accumulate bidirectionally, some
systems use two meters, but a unidirectional meter (with detent) will not accumulate energy
from any resultant feed into the grid. In some countries, for installations over 30 kWp a
frequency and a voltage monitor with disconnection of all phases is required. This is done
where more solar power is being generated than can be accommodated by the utility, and the
excess cannot either be exported or stored. Grid operators historically have needed to
provide transmission lines and generation capacity. Now they need to also provide storage.
Initially storage was used so that baseload generators could operate at full output. With
variable renewable energy, storage is needed to allow power generation whenever it is
available, and consumption whenever needed.

Fig. 3.9: Component of PV system [9]

3.5.1.3. Solar array arrangements

The solar arrays are the subsystems which convert incoming light into electrical energy. They
comprise a multitude of solar panels, mounted on support structures and interconnected to deliver a
power output to electronic power conditioning subsystems. The majority are free-field systems using
ground-mounted structures, usually of one of the following types:
  Fixed Tilt Arrays: Fixed tilt arrays are the simplest and most common solar array
arrangement. In this configuration, solar panels are fixed at a predetermined tilt angle,
typically based on the latitude of the installation site. The tilt angle is fixed and remains
constant throughout the year. Fixed tilt arrays are easy to design, install, and maintain.
However, their energy capture is optimized for specific times of the year, and their overall
energy production may be slightly lower compared to other configurations.
 Seasonal Tilt Arrays: Seasonal tilt arrays involve adjusting the tilt angle of solar panels at
different times of the year to maximize energy capture. The tilt angle is changed manually or
automatically to optimize solar energy absorption during different seasons. For example,
panels can be set at a steeper angle in winter to capture more sunlight during low solar
elevation angles and set at a shallower angle in summer to capture more sunlight during
higher solar elevation angles. Seasonal tilt arrays can enhance energy production compared
to fixed tilt arrays.
 Tracking Arrays: Tracking arrays consist of solar panels that move or track the sun's position
throughout the day to maximize energy capture. There are two main types of tracking
systems:
Single-Axis Tracking: Single-axis tracking systems adjust the tilt angle of the solar panels in
one axis (typically the horizontal axis) to follow the sun's east-west movement. This allows the
panels to face the sun more directly, increasing energy capture compared to fixed tilt arrays.
Single-axis tracking is commonly used in utility-scale installations.
Dual-Axis Tracking: Dual-axis tracking systems adjust the tilt angle of the solar panels in two
axes (both horizontal and vertical) to track the sun's movement more accurately throughout
the day. This configuration provides the highest energy capture as it maximizes the panels'
exposure to sunlight. However, dual-axis tracking systems are more complex, require more
maintenance, and are typically used in specialized applications or research projects.
 Building-Integrated Arrays: Building-integrated arrays integrate solar panels into the
building's structure, such as rooftops, facades, or shading elements. These arrays can take
various forms, including solar tiles, solar shingles, solar glass, or solar awnings. Building-
integrated arrays offer aesthetic appeal as they blend with the building design while
generating clean energy. However, their energy capture may be influenced by shading,
orientation, and other architectural considerations.
 Floating Arrays: Floating arrays are installed on water bodies such as reservoirs, ponds, or
lakes. These arrays use specially designed floating structures that support the solar panels.
Floating arrays have several advantages, such as reduced land use, potential for increased
energy production due to the cooling effect of water, and reduced evaporation from water
bodies. They are commonly used in large-scale installations and can be combined with
tracking systems for enhanced performance.
Understanding the different solar array arrangements is crucial for optimizing energy capture,
maximizing system efficiency, and adapting PV systems to specific installation sites. Each
arrangement has its advantages and considerations, and as a student, you can explore their design
principles, performance analysis, and application suitability based on factors such as site location,
climate conditions, and energy requirements.

3.5.1.4. PV sizing
PV system sizing involves determining the appropriate capacity and configuration of the photovoltaic
(PV) system based on energy requirements, available space, and other factors. Here are the details
of PV system sizing for a comprehensive understanding:
 Gather Data: Collect relevant data specific to South Africa. This includes the energy demand
of the application or site, location coordinates (latitude and longitude) of the installation site in
South Africa, solar resource data (solar irradiation levels) specific to the location, available
area for PV panel installation, and any specific requirements or constraints.
Example: Energy demand: 15,000 kWh per year
 Location: Johannesburg, South Africa (latitude: -26.2041°, longitude: 28.0473°)
Solar irradiation data: Average daily solar irradiation of 5.5 kWh/m²
Determine Energy Demand: Analyze the energy demand by assessing the electrical loads
that need to be powered by the PV system. Consider factors such as lighting, appliances,
electronics, HVAC systems, and any other electrical equipment. Determine the total energy
consumption in kilowatt-hours (kWh) over a specific period, such as daily, monthly, or
annually.
Example: Energy demand is 15,000 kWh per year.
 Assess Solar Resource: Obtain solar resource data specific to the location in South Africa.
Use reliable sources such as the South African Solar Radiation Database or solar radiation
maps specifically designed for South Africa. Consider variations in solar irradiation throughout
the year and any shading effects from nearby objects or structures.
Example: Average daily solar irradiation in Johannesburg, South Africa is 5.5 kWh/m².
 Calculate System Capacity: Calculate the required PV system capacity to meet the energy
demand. Divide the total energy consumption (15,000 kWh) by the average daily solar
irradiation (5.5 kWh/m²) at the site. This provides an estimate of the average daily energy
production required from the PV system.
Example: Required average daily energy production = 15,000 kWh / 365 days = 41.10 kWh
per day.
 Consider Performance Losses: Account for performance losses that affect the overall
efficiency of the PV system. These losses may include shading, panel soiling, temperature
effects, wiring losses, inverter inefficiencies, and other system losses. Apply a performance
ratio or derating factor to account for these losses and adjust the total PV system capacity
accordingly.
Example: Assuming a performance ratio of 0.8, the adjusted average daily energy production
required from the PV system would be 41.10 kWh / 0.8 = 51.38 kWh per day.
 Select PV Panels: Select PV panels based on their specifications, efficiency, and suitability
for the installation site in South Africa. Consider factors such as panel type (monocrystalline,
polycrystalline, thin-film), efficiency, temperature coefficient, and manufacturer warranties.
Higher efficiency panels typically generate more energy per unit area, but they may also be
costlier.
Example: Choose a monocrystalline PV panel with an efficiency of 18% and a rated power
output of 300 W.
 Size the Inverter: Choose an inverter with an appropriate capacity based on the PV panel
configuration and energy output. Consider factors such as inverter efficiency, maximum power
point tracking (MPPT) capability, and the type of inverter (string inverter, micro-inverter, or
power optimizer). Ensure that the inverter capacity matches or slightly exceeds the maximum
power output of the PV panels.
Example: Choose an inverter with a capacity of 3 kW to accommodate the selected PV
panels.
 Balance of System Components: Determine the requirements for balance of system
components specific to South Africa. This includes mounting structures, wiring, combiner
boxes, charge controllers (for off-grid systems), batteries (for energy storage systems), and
other necessary equipment. Consider factors such as system voltage, wiring losses, safety
considerations, and compliance with relevant codes and standards specific to South Africa.
Example: Determine the wiring requirements, such as appropriate wire gauge and cable
length, based on the distance between the PV panels and the inverter.
 Validate the Design: Validate the system design using simulation software or PV system
design tools specific to South Africa. These tools utilize the collected data, such as location,
solar resource, panel specifications, and system configuration, to estimate the energy output
and performance of the PV system in the South African context. They can help optimize the
panel orientation, tilt angle, and system configuration for maximum energy production.
 Example: Use software like PVsyst or SAM (System Advisor Model) to simulate and validate
the PV system design for the specific location in South Africa.
 Conduct Economic Analysis: Perform an economic analysis to assess the financial viability
of the PV system in South Africa. Consider factors such as the initial investment cost,
expected energy savings, payback period, return on investment (ROI), and any available
incentives or subsidies for solar installations specific to South Africa. Evaluate the economic
feasibility and long-term benefits of the PV system.
Example: Suppose the initial investment cost for the PV system is $10,000, and the electricity
tariff in South Africa is $0.15/kWh. The expected energy savings would be the average daily
energy production (51.38 kWh) multiplied by 365 days and the electricity tariff, resulting in
annual savings of $935.67. The payback period can be calculated by dividing the initial
investment cost by the annual savings, which would be approximately 10.7 years.
 Documentation and Reporting: Document the entire PV system sizing process, including
the data collected, calculations performed, assumptions made, and results obtained. Present
the findings in a clear and concise manner, including graphs, tables, and illustrations as
needed. Provide a comprehensive report that outlines the system design, performance
estimates, economic analysis, and any recommendations or future research considerations
specific to the South African context.
Example: Prepare a detailed report that includes information about the chosen PV panel,
inverter capacity, estimated energy production, economic analysis results, and
recommendations for optimizing the system design for the specific location in South Africa.
By following this detailed methodology with the provided numerical example in South Africa, students
can gain a thorough understanding of the PV system sizing process and apply it to real-world
situations in a specific geographical context.

Activity 3.2.
Please watch the available videos from the following links to acquire a comprehensive understanding
of solar photovoltaic systems. Afterward, kindly respond to the subsequent questions:
https://www.youtube.com/watch?v=L_q6LRgKpTw
https://www.youtube.com/watch?v=Yxt72aDjFgY
 Explain the photovoltaic effect and how it relates to the generation of electricity in a PV cell.
 Describe the structure and composition of a typical PV cell.
 What is the role of semiconductors in PV technology?
 Explain the process of electron-hole pair generation and separation in a PV cell.
 Discuss the concept of a bandgap energy and its significance in PV cell operation.
 Describe the working principles of different types of PV cell technologies, such as crystalline
silicon, thin-film, and multi-junction cells.
 Compare the advantages and disadvantages of different PV cell materials and technologies.
 Explain the concept of doping and its role in PV cell performance.
 Discuss the factors that influence the efficiency and performance of a PV cell.
 Describe the operation of anti-reflection coatings and how they improve the performance of
PV cells.
 Explain the relationship between the incident solar radiation and the electrical output of a PV
cell.
 Discuss the effect of temperature on the operation and efficiency of PV cells.
 Describe the behavior of a PV cell in terms of its current-voltage (I-V) characteristics.
 Explain the concept of the maximum power point (MPP) and its importance in PV system
design.
 Discuss the role of shading and its impact on the performance of PV cells and arrays.
  Explain the concept of series and parallel connections of PV cells and their effect on the
voltage and current of a PV system.
 Describe the operation of bypass diodes in PV arrays and their role in mitigating shading
effects.
 Discuss the concept of spectral response in PV cells and its dependence on the incident solar
radiation spectrum.
 Explain the concept of quantum efficiency and its relationship to the absorption and
conversion of photons in a PV cell.
 Describe the challenges and opportunities associated with emerging PV technologies, such
as perovskite solar cells or tandem cells.

Activity 3.3.
Project Title: Design and Optimization of a Standalone Photovoltaic (PV) System for a South
African Case Study using HOMER

Project Overview
The objective of this project is to design and optimize a standalone PV system for a specific location
in South Africa using HOMER software. The project will involve analyzing the solar resource in South
Africa, determining the optimal system configuration, assessing the economic viability, and evaluating
the system's performance. The project will culminate in presenting a comprehensive report outlining
the optimized PV system design and its feasibility in the South African context.

Project Phases
 Site Assessment: Gather information about the specific location in South Africa, including
latitude, longitude, and solar irradiance data.
Analyze the solar resource in South Africa using available solar irradiance data for the
location and validate its reliability.
 Load Profile Analysis: Analyze the energy demand for the South African case study by
collecting load data or estimating the load profile based on local energy consumption patterns
and project requirements.
Identify the daily energy consumption pattern and load characteristics specific to the South
African context.
 System Design: Determine the system requirements, considering factors such as desired
autonomy, reliability, and any specific constraints applicable to South Africa.
Select appropriate PV module types and capacities suitable for the South African climate and
available options.
Design the battery storage system (if applicable) considering capacity, depth of discharge,
and round-trip efficiency, taking into account the specific requirements and constraints of the
South African case study.
Choose the inverter capacity suitable for the PV system, considering compatibility with local
grid standards and requirements.
 Financial Analysis: Gather cost data for PV modules, batteries, inverters, and other
necessary system components specific to the South African market and context.
Analyze the project's financial viability by estimating the levelized cost of energy (LCOE), net
present cost (NPC), payback period, and return on investment (ROI) within the South African
economic framework.
Consider factors such as system lifespan, discount rate, maintenance costs, and any local
incentives or subsidies available in South Africa.
 HOMER Simulation and Optimization: Utilize HOMER software to simulate and optimize
the PV system design for the South African case study.
Set the optimization objective (e.g., minimize the total net present cost or minimize the
levelized cost of energy) based on the local financial and energy context.
 Define the constraints, including autonomy, renewable fraction, and system reliability,
considering the specific requirements and constraints of the South African case study.
Run multiple optimization scenarios by varying parameters like PV module capacities and
battery sizes, keeping in mind the local market availability and conditions.
 Sensitivity Analysis:
Perform sensitivity analysis by varying critical parameters relevant to the South African
context, such as solar irradiance levels, battery costs, or load profiles specific to the region.
Evaluate the impact of parameter variations on the system configuration, economic indicators,
and performance metrics within the South African framework.
 Report and Presentation: Prepare a comprehensive report documenting the project
methodology, findings, and optimized PV system design tailored to the South African case
study.
Include analysis results, financial indicators, sensitivity analysis outcomes specific to the
South African context, and recommendations.
Present the project findings, including system design, economic viability, and performance
evaluation, to stakeholders, highlighting the relevance and applicability of the optimized PV
system design for the South African market.
Note: It is essential to consider the specific location within South Africa, local solar resource data,
market availability, and any regulatory or policy considerations relevant to the case study. Access to
HOMER software and accurate data is crucial for an accurate analysis and optimization process.

3.5.2. Concentrated Solar Power

3.5.2.1. Type of CSP
Concentrated Solar Power (CSP) technology encompasses several different types of systems, each
with its unique configuration and operating principles. The main types of CSP systems are [10]:
 Parabolic Trough Systems: Parabolic trough systems are the most mature and widely
deployed CSP technology. They consist of long, parabolic-shaped mirrors that concentrate
sunlight onto a receiver tube located at the focal line. A heat transfer fluid (HTF) flows through
the receiver, absorbing the concentrated solar energy and transferring it to a power block to
generate electricity. Parabolic trough systems are known for their high efficiency and ability to
incorporate thermal energy storage.
 Solar Power Towers: Solar power tower systems, also called central receiver systems, use
an array of mirrors or heliostats to focus sunlight onto a central receiver positioned atop a
tower. The receiver absorbs the concentrated solar energy, typically heating a working fluid,
such as molten salt or steam. The heated fluid is then used to generate electricity in a power
block. Solar power towers offer high-temperature operation, which enables efficient power
generation and energy storage capabilities.
 Dish-Stirling Systems: Dish-Stirling systems use a parabolic dish-shaped reflector to
concentrate sunlight onto a receiver, which contains a Stirling engine. The concentrated solar
energy heats a working fluid within the receiver, causing the Stirling engine to convert the
thermal energy into mechanical power. The mechanical power is then converted into
electricity using a generator. Dish-Stirling systems are known for their high efficiency and
scalability, making them suitable for both small-scale and large-scale applications.
 Linear Fresnel Systems: Linear Fresnel systems use an array of flat mirrors or reflectors to
concentrate sunlight onto a linear receiver. The receiver typically consists of tubes through
which an HTF flows, absorbing the concentrated solar energy. The heated HTF is then used
to generate steam and produce electricity through a conventional power block. Linear Fresnel
systems offer a lower cost alternative to parabolic trough systems while still achieving a
reasonable level of efficiency.
 Solar Dish Systems: Solar dish systems utilize a dish-shaped reflector to concentrate
sunlight onto a receiver positioned at the focal point. The receiver absorbs the concentrated
solar energy and transfers it to a working fluid, which can be used for various applications
 such as electricity generation, thermal applications, or even solar cooking. Solar dish systems
are often used for smaller-scale applications or in remote areas where electricity or heat is
required.

3.5.2.2. CSP components

Concentrated Solar Power (CSP) systems consist of various components that work together to
harness and convert solar energy into electricity. As a student studying CSP, understanding these
components is essential. Here is a description of key CSP components:
 Solar Collectors: Solar collectors, such as mirrors or heliostats, are used to concentrate and
redirect sunlight onto a receiver. These collectors track the movement of the sun to maximize
the amount of solar energy captured. Mirrors are typically arranged in a field or heliostat
layout to form a solar field.
 Receiver: The receiver is a crucial component where solar energy is absorbed and
transformed into thermal energy. It is usually situated at the focal point of the solar collectors.
Receivers can be categorized into two types:

Solar Tower Receiver: In a solar tower system, a central receiver is located at the top of a
tower. It absorbs concentrated sunlight, heats up a heat transfer fluid (HTF), and transfers the
thermal energy to the power block.
Parabolic Trough Receiver: In a parabolic trough system, the receiver is a tube positioned
along the focal line of the parabolic trough-shaped mirrors. The concentrated sunlight heats
the HTF flowing through the tube.
 Heat Transfer Fluid (HTF): The HTF is responsible for capturing and transferring the thermal
energy from the receiver to the power block. It can be a liquid, such as synthetic oil or molten
salt, or a gas, such as air or steam. The selection of the HTF depends on factors such as
operating temperature range, heat transfer efficiency, and cost.
 Thermal Energy Storage (TES): TES allows CSP systems to store excess thermal energy
for later use, which enables continuous power generation even when sunlight is not available.
Common TES mediums include molten salt, which can store and release thermal energy
effectively due to its high heat capacity. TES systems can be integrated with the receiver or
located separately.
 Power Block: The power block converts the thermal energy from the receiver or TES system
into electricity. It typically consists of a steam turbine, generator, condenser, and associated
auxiliary systems. The thermal energy is used to produce high-pressure steam, which drives
the turbine to generate mechanical power. The generator then converts the mechanical power
into electrical power.
 Control and Instrumentation Systems: CSP plants require advanced control and
instrumentation systems to monitor and regulate various parameters. These systems help
optimize the performance of the CSP plant, ensure safety, and enable efficient power
generation. They include sensors, actuators, controllers, and data acquisition systems.
 Power Grid Integration: To supply electricity to the grid, CSP systems need to be integrated
with the power grid. Power conditioning systems, such as inverters and transformers, are
used to convert the generated electricity to the appropriate voltage, frequency, and waveform
for grid compatibility. Grid integration also involves grid connection equipment, protection
systems, and grid control interfaces.
 Auxiliary Systems: CSP plants include various auxiliary systems to support their operation,
such as cooling systems for the power block, pumps or fans for HTF circulation, and
instrumentation for monitoring and control. These systems play a crucial role in maintaining
optimal performance and reliability.

3.5.2.3. Operation principle

Concentrated Solar Power (CSP) systems harness the power of sunlight to generate electricity
through a unique and sophisticated process. In this section, we will delve into the detailed operation
principle of CSP systems, explaining the key components and processes involved in converting solar
energy into electrical power.

Fig.3.10: Operation principle of Concentrated Solar Power [10]

To understand the physics behind the operation principle of Concentrated Solar Power (CSP)
systems, we can examine the underlying equations that govern the relevant physical processes. Let's
explore the key equations associated with each step of the CSP operation:
 Solar Radiation Collection: The amount of solar energy collected by the mirrors (heliostats)
in a CSP system can be determined by the equation:
Solar Energy Flux = Solar Constant * Mirror Reflectivity * Concentration Factor
where:
Solar Energy Flux is the amount of solar energy incident on the mirrors
Solar Constant is the average solar radiation intensity in space (~1367 W/m²)
Mirror Reflectivity is the fraction of incident sunlight reflected by the mirrors
Concentration Factor represents how much the sunlight is concentrated by the mirrors
 Solar Energy Absorption and Heat Transfer:
The absorbed solar energy is transferred to the receiver, and the rate of heat transfer can be
calculated using the equation:
Q = m * Cp * ΔT
where:
Q is the amount of heat transferred
m is the mass flow rate of the heat transfer fluid (HTF)
Cp is the specific heat capacity of the HTF
ΔT is the temperature difference between the receiver and the HTF
The temperature difference ΔT depends on factors like the absorptivity of the receiver
material and the concentration of sunlight.
 Heat Transfer Fluid (HTF) Circulation:
The flow of the HTF in the system can be described by fluid dynamics equations, such as the
Navier-Stokes equations, which govern the conservation of mass, momentum, and energy for
a fluid. These equations consider factors like fluid velocity, pressure, and density, and they
help determine the flow distribution, pressure drop, and heat transfer characteristics of the
HTF within the system.
 Energy Storage (Optional): If thermal energy storage (TES) is incorporated, the physics
involved depends on the type of storage medium used. For example, in a molten salt-based
TES system, the energy storage capacity can be calculated using the equation:
Energy Stored = Mass * Specific Heat Capacity * Temperature Change
 where:
Mass is the mass of the molten salt
Specific Heat Capacity is the heat capacity of the molten salt
Temperature Change is the difference in temperature during the phase change process
The specific heat capacity and the phase change temperature of the molten salt determine its
ability to store and release thermal energy effectively.
 Power Generation: The thermodynamics of power generation in a CSP system can be
described by the Rankine cycle equations. In a steam-based CSP system, the heat transfer
from the HTF to water generates steam, and the power output can be determined using the
following equation: Power Output = η * (m * h1 - m * h2)
where:
Power Output is the electrical power generated
η is the overall efficiency of the power block
m is the mass flow rate of the working fluid (steam)
h1 and h2 are the enthalpies of the working fluid at the turbine inlet and outlet, respectively
The enthalpies depend on the temperature and pressure conditions at those points.
 Power Grid Integration: The physics of power grid integration involves electrical engineering
principles, such as the equations governing power conditioning and control. These equations
consider parameters like voltage, current, frequency, and power factor, and they are used to
regulate and condition the electrical output of the CSP system to meet the requirements of the
power grid.

3.5.2.4. CSP sizing

Sizing a Concentrated Solar Power (CSP) system involves determining the appropriate capacity and
components required to meet the energy needs of a specific location. Here is a detailed methodology
for CSP system sizing, along with a numerical example for South Africa:
 Define Energy Requirements: Start by identifying the energy requirements of the target
location or application. Determine the desired electrical output or thermal energy demand.
Consider factors such as peak power requirements, average energy consumption, and any
specific operational constraints. Example: Let's consider a scenario where the energy
requirement is to generate 20 MW of electrical power.
 Solar Resource Assessment: Conduct a solar resource assessment specific to the location
of interest. Obtain solar irradiance data, including direct normal irradiance (DNI) and global
horizontal irradiance (GHI) values. This data helps estimate the solar energy potential at the
site. Example: In South Africa, assume the location receives an average annual DNI of 2,200
kWh/m².
 System Efficiency Estimation: Estimate the overall efficiency of the CSP system, taking into
account the specific technology and components being considered. This includes the
efficiency of solar collectors, receiver, thermal energy storage (if applicable), power block, and
any auxiliary systems.
Example: Assume an overall system efficiency of 35%.
 Capacity Factor Calculation: Calculate the capacity factor, which represents the actual
energy output of the CSP system over a given period compared to the maximum possible
output. The capacity factor depends on factors like solar resource availability, system
downtime, maintenance, and other operational considerations.
Example: Assume a capacity factor of 25%, considering factors such as maintenance
downtime and grid integration requirements.
 Annual Energy Production Calculation: Determine the annual energy production of the
CSP system by multiplying the energy requirement (step 1) by the reciprocal of the capacity
factor (step 4) and the reciprocal of the system efficiency (step 3).
Annual Energy Production = Energy Requirement / (Capacity Factor * System Efficiency)
Example: Annual Energy Production = 20 MW / (0.25 * 0.35) = 228.57 MWh
  Solar Field Sizing: Based on the solar resource assessment, determine the required size of
the solar field to achieve the desired annual energy production. Consider the solar collector
technology, concentration factor, and solar field layout.
Example: Assume a parabolic trough system with a concentration factor of 80. The required
solar field size can be estimated by dividing the annual energy production (step 5) by the
annual solar radiation received per unit area.
Solar Field Size = Annual Energy Production / (Annual DNI * Concentration Factor)
Solar Field Size = 228,570 MWh / (2,200 kWh/m² * 80) ≈ 164 hectares
 Storage Sizing (if applicable): If thermal energy storage (TES) is incorporated, determine
the required capacity based on factors such as the desired storage duration, discharge rate,
and temperature differential. Consider the specific heat capacity and phase change
temperature of the storage medium. Example: Assume a molten salt TES system with a
desired storage capacity of 8 hours and a temperature differential of 250°C. Use the equation:
Energy Stored = (Annual Energy Production * Storage Duration) / Temperature Differential
Energy Stored = (228,570 MWh * 8 hours) / 250°C ≈ 7,342 MWh
 Power Block Sizing: Size the power block components, such as the steam turbine and
generator, based on the desired electrical output and the specific technology being used.
Consider factors such as steam inlet conditions, pressure, temperature, and turbine efficiency.
Example: Assuming a standard steam-based power block, select a turbine and generator
combination that can handle the desired electrical output of 20 MW.
 Economic Considerations: Assess the economic viability of the sized CSP system,
considering factors such as capital costs, operational costs, maintenance costs, and potential
revenue streams such as power purchase agreements or feed-in tariffs. Conduct a financial
analysis, including calculations for levelized cost of electricity (LCOE) and return on
investment (ROI).
Example: Perform an economic analysis to determine the LCOE and ROI based on the
specific cost data and financial assumptions relevant to the South African context.

Activity 3.4.
Please watch the available videos from the following links to acquire a comprehensive understanding
of CSP systems. Afterward, kindly respond to the subsequent questions:
https://www.youtube.com/watch?v=3KFJHJfnelU
https://www.youtube.com/watch?v=-SsJBobMpAk
 What is Concentrated Solar Power (CSP), and how does it differ from other solar power
technologies such as photovoltaics (PV)?
 Describe the different types of CSP technologies, including parabolic troughs, power towers,
dish/engine systems, and linear Fresnel reflectors.
 Explain the working principles of a parabolic trough CSP system and the role of the collector,
receiver, and heat transfer fluid.
 Discuss the advantages and challenges associated with each CSP technology, considering
factors such as efficiency, scalability, and cost.
 How does thermal energy storage (TES) contribute to the performance and dispatchability of
CSP systems? Explain different TES technologies used in CSP.
 Describe the components and operation of the power block in a CSP system, including the
steam turbine, generator, and auxiliary systems.
 Discuss the role of system integration in CSP projects, including the integration of solar fields,
thermal energy storage, and power generation components.
 Explain the design considerations for selecting the appropriate solar field size and capacity to
meet the energy requirements of a CSP project.
 How can solar resource assessment and modeling techniques be used to optimize the
performance and energy output of a CSP system?
  Evaluate the economic viability of CSP projects, including factors such as capital costs,
operational costs, and potential revenue streams.
 Discuss the environmental benefits and considerations associated with CSP technology,
including its potential for reducing greenhouse gas emissions and water usage.
 Provide examples of real-world CSP projects and their applications, highlighting their impact
and benefits.

3.6. CONCLUSION

In conclusion, the study of solar thermal and photovoltaics provides students with a comprehensive
understanding of two key technologies in the field of solar energy. Throughout this study unit, students
have gained knowledge about the principles, applications, and design considerations of solar thermal
systems and photovoltaic (PV) systems.
Solar thermal systems harness the sun's energy to generate heat for various applications such as
water heating, space heating, and industrial processes. Students have learned about different types of
solar thermal collectors, including flat-plate collectors, evacuated tube collectors, and concentrating
collectors such as parabolic troughs and solar power towers. They have gained insights into the
components of solar thermal systems, including heat transfer fluids, thermal energy storage, and
system integration.
On the other hand, the study of photovoltaics has focused on the conversion of sunlight directly into
electricity using semiconducting materials. Students have delved into the working principles of PV
cells, including the photovoltaic effect and the operation of different PV technologies such as
crystalline silicon, thin-film, and emerging technologies like perovskite solar cells. They have learned
about PV system components, such as modules, inverters, and balance of system components, as
well as the design considerations for grid-connected and off-grid PV systems. Students have also
explored the importance of solar resource assessment, system sizing, and economic analysis for PV
projects.
Throughout the study unit, students have gained practical knowledge through numerical examples,
case studies, and exposure to real-world applications of solar thermal and PV technologies. They
have developed the skills to assess solar resource availability, analyze system performance, optimize
system design, and evaluate the economic and environmental aspects of solar energy projects.
The knowledge acquired in this study unit equips students with the necessary tools and understanding
to contribute to the advancement and implementation of solar thermal and PV technologies. As the
world continues to transition towards renewable energy sources, the expertise gained in this study
unit will enable students to address challenges, develop innovative solutions, and contribute to a
sustainable and clean energy future.
Overall, the study of solar thermal and photovoltaics has provided students with a solid foundation in
these technologies, empowering them to make meaningful contributions to the field of solar energy
through research, development, and practical applications.

3.7. REFERENCES

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[6] Zhang, Ying, Muttucumaru Sivakumar, Shuqing Yang, Keith Enever, and Mohammad
Ramezanianpour. "Application of solar energy in water treatment processes: A review."
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[9] Dobrzański, L. A., A. Drygała, and M. Prokopiuk vel Prokopowicz. "Selection of components for
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