U19EE918

RENEWABLE ENERGY SOURCES

 UNIT 2

SOLAR ENERGY SYSTEMS

 UNIT 2

SOLAR ENERGY SYSTEMS

Solar Energy Systems
 Solar radiation & its measurements

 Solar energy collectors

 Solar energy storage systems

 Solar pond & applications

 Applications of solar energy

 Solar pumping
 Solar cooking
 Solar Distillation
 Solar Greenhouse
 Solar Radiation
• Introduction
– Solar radiation is the Electromagnetic rays emitted by the sun

– Solar radiation depends on

• Geographic location
• Time of day
• Season
• Local landscape
• Local weather

– Solar radiation that reaches earth’s surface

• Direct beam radiation
• Diffuse radiation
 Solar Radiation
• Solar radiation at the earth’s surface
– Beam of solar radiation
• Absorbed
– Ozone absorbs UV rays
– CO2 and water vapour absorb IR rays
• Scattered
– By Dust particles, pollutants, water vapour

– Direct Beam radiation

• Radiation that is neither scattered nor absorbed
– Directly reach the earth’s surface

– Diffuse radiation
• Scattered radiation that reaches earth’s surface from all directions
 Solar Radiation
• Solar radiation at the earth’s surface
 Solar Radiation
• Solar radiation at the earth’s surface
 Solar Radiation
• Terminology
– Solar insolation (incident solar radiation)
• Solar radiation received on a flat horizontal surface on earth

– Global radiation
• Sum of beam and diffuse radiation

– Solar constant
• Energy received from sun per unit time, on unit area of surface
perpendicular to direction of rays I  I [1  0.033 cos( 360n )]
ext sc
365
– Solar time (Local apparent time)
• Energy received from sun per unit time, on unit area of surface
perpendicular to direction of rays
 Solar Radiation
• Geometry of Solar radiation
– Expressed by the following terms
• Angle of latitude

• Declination angle

• Hour angle

• Inclination angle (altitude)

• Zenith angle

• Solar Azimuth angle

• Slope (Tilt angle)

• Surface azimuth angle

• Angle of incidence
 Solar Radiation
• Angle of Latitude (ϕ)
– To indicate location of the considered point on earth

– Angle made by
• Line joining location (P) and centre of earth with
• Its projection on equator plane

– Northern hemisphere: positive

– Southern hemisphere: negative
 Solar Radiation
• Angle of Latitude (ϕ)
– Angle made by
• Line joining location (P) and centre of earth with
• Its projection on equator plane
 Solar Radiation
• Angle of Latitude (ϕ)
– Angle made by
• Line joining location (P) and centre of earth with
• Its projection on equator plane
 Solar Radiation
• Declination angle (δ)
– Angular displacement of the sun from the plane of earths equator
 Solar Radiation
• Declination angle (δ)
– Angular displacement of the sun from the plane of earths equator
Solar Radiation
 Solar Radiation
• Slope / Tilt angle (β)
– Angle between
• Collector’s inclined plane surface and
• The horizontal plane

• Surface Azimuth angle (γ)

– Angle in horizontal plane between
• Line along south direction and
• Horizontal projection of Normal to collector’s incline plane

• Angle of incidence (θi)

– Angle on horizontal plane between
• Sun’s ray incident on incline surface of collector and
• Normal (perpendicular) to that surface
 Solar Radiation
• Angle of incidence (θi)
– Angle on horizontal plane between
• Sun’s ray incident on incline surface of collector and
• Normal (perpendicular) to that surface
 Solar Radiation
• Hour angle (ω)
– Hour angle at any moment is the angle through which the earth must turn to
bring the median of the observer directly in line with sun’s rays
 Solar Radiation Measurement
• Actinometer
– Instrument used to measure intensity (heating power) of radiation

– Device that determines number of photons in a beam

– Used in meteorology to measure solar radiation

• Measurement of solar radiation

– Pyranometer

– Pyrheliometer

– Net radiometer
 Pyranometer
Solar Radiation Measurement
• Construction of Pyranometers
– Thermopile:
• Thermocouple: a temperature sensor that is measured thru’ voltage variation

• Thermopiles: Thermocouples connected in series

 Pyranometer
Solar Radiation Measurement
• Construction of Pyranometers
– Thermopile:
 Pyranometer
Solar Radiation Measurement
• Construction of Pyranometers
– Glass dome
• Hemispherical glass dome

• Shields thermopile from wind, rain and convection

 Pyranometer
Solar Radiation Measurement

• Working Principle
– based on measurement of temperature difference between

• dark surface: black coating absorbs the solar radiation

• clear surface: reflects the radiation; hence less heat is

absorbed.

– potential difference is created in the thermopile

• Due to temperature gradient between the two surfaces

– voltage measured using a potentiometer

 Pyranometer
Solar Radiation Measurement
• Advantages
– Very small temperature coefficient
– More accurate measurements
– Longer response time than a photovoltaic cell
– Integrated measurement of the total available short-wave solar
energy under all conditions.

• Applications
– Predicting insulation requirements for building structures
– Establishment of greenhouse locations
– Designing photovoltaic systems
– Meteorological and climatological studies
– Measurement of solar intensity data.
 Pyrheliometer
Solar Radiation Measurement
• Construction of Pyrheliometer

 Based on thermopile

 Measures beam of direct radiation

 Needs a tracker mechanism to measure all day

 Pyrheliometer
Solar Radiation Measurement
Construction of Pyrheliometer
– Shape: Collimator tube
• Collimator: device that narrows a beam or
particle; usually consists of a long narrow tube &
lens / other absorbing surface
– Ex : Telescope is an optical collimator (has a lens
and long tube to narrow visible light)

• Black coated insides: To absorb most of the

radiation (at various angles)

• Sealed with dry air: To avoid absorption of

radiation by water-vapour within tube
 Pyrheliometer
Solar Radiation Measurement

Construction of Pyrheliometer
– Measurement: Thermopile
• Wire wound thermopile

• Placed behind sensor plate

• Thermocouple: a temperature sensor that is

measured thru’ voltage variation

• Thermopiles: Thermocouples connected in

series
 Pyrheliometer
Solar Radiation Measurement

• Working Principle
– The direct radiation is channelized in the tube
• And absorbed due to the black coating

– based on measurement of temperature difference in thermopile

– potential difference is created in the wire-wound thermopile

• Due to temperature gradient

– Measured voltage is then converted to radiation data

 Pyrheliometer
Solar Radiation Measurement

• Angstrom type Pyrheliometer

– Pyrheliometer designed by Angstrom

– Simplest and most accurate

– Construction
• 2 similar strips: S1 and S2 of area A

• 1 end of thermocouple connected to S1 and other end to S2

• Sensitive galvanometer (G) is connected to thermocouple

• Strip S2 is connected to an external electric circuit

 Pyrheliometer
Solar Radiation Measurement

• Angstrom type Pyrheliometer

– Working Principle
• When both S1 and S2 are shielded from radiation
– Both junctions are at same temperature

– So, NO deflection in galvanometer

• S1 is exposed and S2 is shielded with cover M

– Temperature of S1 rises as it receives solar radiation

– Galvanometer shows deflection

• Current allowed to pass thru’ S2

– Until the galvanometer shows NO deflection

– Now S1 and S2 are at same temperatures

 Pyrheliometer
Solar Radiation Measurement

• Angstrom type Pyrheliometer

– Working Principle
• Heat absorbed by S1 is equal to Heat produced in S2
– Heat absorbed by S1 = Q.A.a

Q: heat radiation absorbed per unit area

A: area of strip
a: absorption coefficient

– Heat produced in S2 = V.I

Q.A.a = V.I

Q = V.I / A.a
 Sunshine Measurement
• Sunshine Recorder
– Instrument used to record amount of sunshine at a given location

– Also called heliograph

– Provides info about weather, climate and temperature of a location

– Used in meteorology, science, agriculture, tourism and other fields

 Sunshine Recorder
• Construction
– Glass sphere: Mounted on its axis parallel to that of earth

– Inside a Spherical bowl section (semi-circular brass bar)

– Sunshine card: special paper with timescale (placed inside groove of bowl)
 Sunshine Recorder
Working Principle
– Focussing sun’s rays:
• bowl and glass sphere are placed such that sun’s rays are focussed at a point
on the card

– Burnt path on the card:

• As sun moves,

• Focussed sunshine burns a path along the card

• Length of trace is duration of sunshine

– 3 overlapping pairs of grooves – for various seasons

Solar Energy Collectors
 Need for Solar Collectors

 Performance Indices of Solar Collectors

 Types of Solar Collectors

 Flat plate
 Concentrating type
 Need for Solar Collectors
• Introduction

Solar Energy Utilization

Solar Photovoltaic Solar Thermal

– Solar Photovoltaic
• directly converts solar energy into electricity thru’ PV cells

– Solar Thermal Systems

• thermal energy produced is used for various purposes
– Heating, cleaning, power generation plant etc.
 Need for Solar Collectors

• Need for Solar Collectors

– Solar Energy
• Low density per unit area due to diffusion

– Solar Collectors
• First unit of a solar thermal system
• For maximum utilization of solar energy
– Solar energy is absorbed as heat

– Transferred to heat up fluid

– Fluid delivers heat to next system for utilization

Classification of Solar Collectors
Non-Concentrating type (Flat Plate) Collectors

• Characteristic
– Absorb radiation as received on the collector surface
• Absorb both beam and diffuse radiation

• Construction
– Simple and robust
• Back surface: to absorb the incident radiation
• Glazing cover: to prevent radiative & convective heat loss from surface
• Heat exchanger: to transfer heat absorbed
• Support structure & insulation: to increase the strength & efficiency
Non-Concentrating type (Flat Plate) Collectors
• Positioning of Flat plate collectors
Non-Concentrating type (Flat Plate) Collectors
• Advantages
– Easy to manufacture
– Low cost
– Collect both beam & diffuse radiation
– Permanently fixed
– Little maintenance

• Disadvantages
– High temperatures cannot be obtained
– Heat is lost from large area (due to lack of optical concentration)
 Liquid Flat Plate Collector
• Characteristic: Heat transport medium is a fluid (liquid)
• Construction
– Back surface: usually Cu, Al or steel absorber plate
– Transparent cover: 1 or 2 sheets of glass or plastic
– Heat exchanger: tubes, channels or passages in contact with absorber plate
– Support structure & insulation: weather tight, insulated container
 Liquid Flat Plate Collector
• Components
– Heat exchanger system
 Liquid Flat Plate Collector
• Components: Collector plates
– Pipe & Fin type
• Liquid flows in pipes only
• Low wetted area & liquid capacity
• Used for high temp. applications

– Water sandwich type

• High wetted area & liquid capacity

– Roll bond type

• Also called semi-water sandwiched
• Intermediate between the two

Sandwich type: used for low temp

applications like swimming pool warming
 Flat Plate Air Heating Collector
• Characteristic: Heat transport medium is air

• Applications
– Drying for agricultural & industrial purposes
– Space heating

• Construction
– Similar to liquid flat plate collector: with change in absorber & tube
– Heat transfer coefficient b/w absorber & air is low
 Flat Plate Air Heating Collector

• Types: To improve heat exchange

• The surfaces are roughened

– Fin type
• Longitudinal fins in airflow passage

– Metal Matrix type

– Corrugated type

– Thermal trap type

 Flat Plate Air Heating Collector
• Advantages: Over liquid flat plate collector
– Compact, simple constructions & low maintenance
– Transfer of heat between two or more fluids is not required
• Air is directly used as working fluid

– Corrosion is completely eliminated

– Leakage of air from duct is less severe
– Possibility of freezing of working fluid is eliminated
– Pressure inside collector is always moderate

• Disadvantages
– Large amount of air is to be handled, due to low density
– Heat transfer is poor b/w absorber plate & air
– Less storage capacity due to low heat capacity
 Concentrating type Collectors
• Non-focus type
– Reflects additional radiation onto absorber plate
• Using reflectors to increase concentration of radiation

• Focus type
– Reflects and concentrates entire radiation onto
• A single line: Line focus
• A single point: Point focus
 Modified Flat Plate Collector
• Characteristic
– Reflectors: plane mirrors at the edges of flat plate collector
• Additional radiation is reflected into the collector
• Concentration of radiation is increased (normal & reflected)

– V-trough design: aligned in East-West direction

– Requires periodic tilt adjustment
– Relatively small increase in radiation concentration
• Thus not widely used
 Compound Parabolic Concentrator (CPC)
• Characteristic
– Parabolic mirror segments: at the edges of flat plate collector
• Additional radiation is reflected into the collector (beam & diffuse)
• Concentration of radiation is increased

– Trough like arrangement: aligned in East-West direction

• Does NOT require tracking
Focus Type Collector
• Line Focus
 Cylindrical Parabolic Concentrator
• Characteristic
– Reflectors: cylindrical parabolic trough
– Receiver: tube blackened at outside surface
– Heat transfer: fluid in the receiver tube

– Rotated about one axis to track the sun

 Fixed Mirror Solar Concentrator
• Characteristic
– Concentrator: fixed mirror strips arranged on circular ref. cylinder
– Receiver: tube made to rotate at centre of curvature to track the sun
– Heat transfer: fluid in the receiver tube

– Overcomes difficulty in manufacturing large parabolic mirrors

 Linear Fresnel Lens Collector
• Characteristic
– Concentrator: Fresnel lens with linear grooves (optical quality plastic)
• behaves as a spherical lens by arranging the angle of grooves accordingly
– Receiver: tube
– Heat transfer: fluid in the receiver tube
Focus Type Collector
• Point Focus
Paraboloidal Dish Collector (Scheffler Solar Concentrator)
• Characteristic
– Concentrator: Parabolic dish with two axis tracking
– Receiver: at the focus point

– Requires 2 axis tracking

 Hemispherical Bowl Mirror Concentrator
• Characteristic
– Concentrator: hemispherical fixed mirror
– Receiver: moved along paraxial line through the centre of curvature

– Requires 2 axis tracking

 Circular Fresnel Lens Concentrator
• Characteristic
– Concentrator: Fresnel lens with several thin circular zones
• Tilt of each zone is adjusted so that the lens resembles a thin spherical lens
– Receiver: at the focal point of the lens
 Central Tower Receiver
• Characteristic
– Concentrator: several heliostats
• Heliostat: independently controlled flat mirrors
– Receiver: at the top of a central tower
Solar Energy Storage Systems
 Need for Energy Storage

 Types of Energy Storage

 Thermal
 Electrical
 Chemical
 Mechanical
 Electromagnetic
Types of Energy Storage
 Thermal Energy Storage
• Storage by: heating, melting or vaporization
• Reused: as heat by reversing the process

• Application: domestic water & space heating;

• Types of Thermal Energy Storage

– Sensible Heat Storage
• Storage by increasing the temp. of a material

– Latent Heat Storage

• Storage by phase change
– Solid to liquid or Liquid to vapour
 Thermal Energy Storage
• Sensible Heat Storage
– Temperature is increased
– No change in phase / state
– Thermal energy capacity of a storage unit:

where, m: mass; Cp: specific heat

– Ability to store thermal energy in a container of volume V:

where, p: density of storage medium

– Materials used:
• Water; rock, gravel, crushed stone; Iron shot; Concrete; refractory materials etc.
 Thermal Energy Storage
• Sensible Heat: Water Storage
– Heat transfer & storage medium: water

– Suitable characteristics of water:

• Inexpensive; readily available
• High thermal storage capacity
• Pumping cost is small
 Thermal Energy Storage
• Sensible Heat: Pebble Bed Storage
– Heat transfer medium: air
– Heat storage: rock, gravel or crushed stone in a bin
• Loosely packed (to allow air flow)

• Direction of air flow is reversed for heat

collection

• Have good heat transfer characteristics

• Used in solar houses or hot air collector

system
 Thermal Energy Storage
• Latent Heat Storage
– Heat is stored: when material melts
– Heat extracted: when material is made to freeze
– Phase change to be accompanied with high latent heat effect

• Ex: Paraffin; fatty acids; water; Glauber’s salt etc.

 Electrical Energy Storage
• Capacitor Storage
– Stored as: Electric Charge
– Store electrical energy at high voltage and low current

– Energy stored in a capacitor:

– Best dielectric material available: Mica

 Electrical Energy Storage
• Inductor Storage
– Stored as: Magnetic flux
– Store electrical energy at low voltage and high current

– Energy stored in an inductor:

– Discharging is a problem:
• as it deals with opening a circuit with high current
 Electrical Energy Storage
• Battery Storage
– Stored: Electrochemically in electrolyte
– Regained as: Electrical energy

– Energy efficiency of a battery:

Ex: Li-ion battery

 Chemical Energy Storage
• Chemical (fuel) Storage
– Stored: Photochemically in converter / storage battery
– Regained as: Electrical energy

– Stored: Methane (produced by anaerobic fermentation of algae)

– Regained as: Heat (released when Methane when reacts with oxygen)
 Chemical Energy Storage
• Thermo Chemical Storage
– Reversible chemical reactions

– Products are recombined to give source – with release of heat

 Mechanical Energy Storage
• Pumped Hydroelectric Storage
– Used by solar power plants (electricity using solar energy)

– Stored as: Potential energy (water in a higher reservoir)

• Electric energy is used to pump water up to reservoir

– Regained as: Electric energy

• Stored water is used to produce hydroelectricty
 Mechanical Energy Storage
• Compressed Air Storage
– Future storage alternative
– Storage: Air pumped into pressurized storage tank
– Re-usage: stored air runs turbine
• To produce electricity

• Flywheel Storage
– Excess energy during off-peak
– Storage: as mechanical (rotational) energy of flywheel
• Driven by motor
– Re-usage: rotational energy used to run a generator
 Electromagnetic Energy Storage
• Energy storage via super conducting magnets
– Uses superconducting materials
• Lose all resistance when cooled below a particular temp.

– Normal conductor
• Any current carrying conductor
• Associated with electromagnetic field
• Energy is stored in this field
• With resistive losses

– Super conductor
• Low or negligible resistive losses
• So, power storage capacity increases

• Ex: Superconducting Magnetic Energy Storage (SMES)

Solar Pond and Applications
 Description & Principle of operation

 Extraction of Thermal Energy

 Applications
 Solar Pond
• What is it?
– Pool of salt water
– Collects and stores solar thermal energy

• Halocline:
– vertical salinity gradient in salt water
– Acts as a virtual insulator of penetrating solar radiation
 Solar Pond
• Zones of a solar pond
– Upper Convective (Surface) Zone:
• Relatively fresh water
• Salinity < 5%
• Temp: 30 deg.C

– Non-Convective (Insulation) Zone:

• Increasing salinity with depth
• Acts as insulator

– Lower Convective (Storage) Zone:

• Fully saturated salt brine
• Salinity ≈ 20%
• Temp: upto 90 deg.C
 Solar Pond: Non-convective
• Principle of operation & description
– Storage:
• Sun’s rays heat up the pond
• Heat is transferred to the lower most layer of the pond (with time)
• Normal pond:
– Heat reduces density of water
– So, hot water rises up & releases heat to atmosphere
– This is why in fresh water lakes & ponds
• Solar pond:
– Hotter salt water is still more dense than less saltier water above it
– So, it doesn’t rise up – so called non-convective
– Heat gets stored in the bottom denser water
– This salinity gradient acts as a virtual insulator
 Solar Pond: Extraction of Thermal Energy
• Hot brine is removed from the bottom of the pond
– Heat stored is used up
 Solar Pond: Applications

• Heating and Cooling of Buildings

– Solar pond: Large heat storage capacity
• Even during cloudy days & at high altitudes
– So, ideal to meet heat & cooling loads

• Industrial Process Heat

– Great alternative for oils and natural gas
– For process heating: heat is directly used
• Ex: crop drying & paper industry
 Solar Pond: Applications
• Production of Power
 Solar Pond: Applications
• Desalination
– Low cost thermal energy
• To desalt or purify water
• To be used for drinking or irrigation

• Heating animal housings and drying crops on farms

– Small scale
• To heat up green houses
• To run dehydration plants

• Heat for biomass conversion

– Heat from solar pond used to
• Convert biomass to alcohol / methane
– Ideal combination of renewable energies
Applications of Solar Energy
 Solar Pumping

 Solar Cooking

 Solar Distillation

 Solar Greenhouse
 Solar Heat Exchanger
• Used in
– Solar power plants; Solar pumps etc
 Solar Pumping
• Solar Pump
– Water pump driven by solar energy
– Greatest need for water pump – summer
• Solar radiation is greatest
• BUT High capital cost
 Solar Pumping
• Working Principle
– Turbine driven pump using Solar energy
 Solar Cooking
• Solar cooker
– Sunlight is converted into heat energy
– This heat energy is stored for cooking

• Types of solar cooker

– Flat plate box type solar cooker with or without reflector
 Solar Cooking
• Types of solar cooker
– Flat plate box type solar cooker with or without reflector
 Solar Cooking
• Types of solar cooker
– Multi reflector type solar oven
 Solar Cooking
• Types of solar cooker
– Parabolic disc concentrator type solar cooker
 Solar Distillation
• Distillation
– process of separating the components or substances from a liquid
mixture by using selective evaporation and condensation
 Solar Distillation
• Working Principle
– Solar radiation enters thru’ the glass cover
– Black surface traps heat and Heats the water
– Vapour when cooled Condenses to droplets on the roof
– Condensed pure water is collected at the end of slope in trough
 Solar Greenhouse
• Greenhouse
– Closed glass structure that provides regulated climatic conditions
• For year long growth of plants
 Solar Greenhouse
• Greenhouse types:
– 2 types
• Summer greenhouse
• Winter greenhouse
– Design types
• Free standing type Pit type

• Attached type
Solar Water Heater