CHAPTER 9

RENEWABLE ENERGY SUPPLY

9.1 INTRODUCTION

Renewable energy can be defined initially as any energy source that is derived directly or indirectly
from solar energy. In the broadest sense, however, almost all of the energy we use today, including fossil
fuels, can be considered a form of solar energy. The most familiar forms of energy, such as wood, oil, gas,
and coal, are embodied forms of solar energy gathered, stored, and transformed by natural processes.

Climate change due to emissions of GHGs, particularly CO2, becomes an issue when stored solar
energy is converted to useable forms of energy (heat, electricity, fuels, chemicals) at a rate far exceeding
the rate of formation. For coal, oil, and natural gas, the ratio of time between formation and use is on the
order of 1 million to one: that is, the world uses in one year what took natural processes one million years
to create. Only biomass among these stored forms has a time ratio that is within a human time frame of
years or decades. Renewable energy can now be defined as forms of solar energy that are available and
replenished in time scales no longer than human lifetimes.

Given this definition of renewable energy, it becomes clearer why renewable energy is an important
option for mitigating climate change. Because renewable energy creates little if any net greenhouse gas
emissions, its use will not disrupt the radiative energy balance of the earth's atmosphere and will permit
sustainable, long-term mitigation of climate change. The renewable energy option will allow climate
change mitigation, energy use, and economic development to proceed in synergy rather than in opposition.

The remainder of this chapter will discuss what information, data, and analytic tools are needed
to identify, screen, and characterize renewable energy options. The information and data needed include:

$ economic and social development goals and needs

$ energy end uses and tasks to be performed
$ characteristics of energy needs
- scale (total requirements, grid/off-grid, centralized/distributed, etc.)
- timing of energy needs (duration, seasonality, diurnal, etc.)
$ available energy resources
$ technology characterization

Once energy needs are defined within the larger context of economic and social development
needs and plans, renewable energy resources and technologies can be identified and evaluated for
incorporation into this larger context. The analytical tools needed include systematic methods to inventory
renewable energy resources and to evaluate the most appropriate applications of these resources.

This chapter presents an overview of renewable energy options and discusses resource
assessment and characterization of renewable energy technologies. Methods for analyzing renewable
energy options within an integrated framework are discussed in Chapter 3. Policy options for encouraging
adoption of renewable energy technologies are briefly described at the end of this chapter.

9.2 MITIGATION TECHNOLOGY OPTIONS

Renewable energy supplies encompass a broad range of resources, and numerous technologies
can be used to tap those resources. Table 9-1 lists the major technologies and the following discussion
briefly describes each technology and its applications. Although many of these technologies are still under
development, most have entered commercial markets around the world at some level. Some, such as
hydropower and biomass technologies, have achieved sizeable market penetration, while others (e.g.,
 Chapter 9 Renewable Energy Supply 9-3

Table 9-1. Renewable Energy Technologies

END-USE APPLICATION
RESOURCE TECHNOLOGY Electricity a
Industry Buildings Transport

Photovoltaics - Flat Plate T

Photovoltaics - Concentrator T

Solar Thermal Parabolic Trough T T

Solar Thermal Dish/Stirling T

Solar Thermal Central Receiver T T

Solar Ponds T T T

Passive Heating T

Active Heating T
Solar Daylighting T

Horizontal Axis Turbine T

Wind Vertical Axis Turbine T

Direct Combustion T T T

Gasification/Pyrolysis T T T

Anaerobic Digestion T T T
Biomass Fermentation T

Dry Steam T

Flash Steam T

Binary Cycle T

Heat Pump T
Geothermal Direct Use T T

Conventional T

Pumped Storage T
Hydropower Micro-hydro T

Tidal Energy T
Ocean
Thermal Energy Conversion

a
Electricity generated by any of these methods can be used in the remaining end-use applications either to meet power demands
directly (e.g., industrial electricity inputs, buildings lighting demand, or electric vehicles) or as an input to end-use fuel production (e.g.,
hydrogen produced via electrolysis).
9-4 Greenhouse Gas Mitigation Assessment: A Guidebook

photovoltaics) are used in important but relatively limited applications today. Research and development
activities continue to improve all of these systems to enhance their ability to meet future energy
requirements, and new systems that are still in the early stages of development may provide additional
opportunities.

9.2.1 Solar Energy

Solar technologies use the sun's energy directly to generate energy for industrial processes,
buildings, and transportation as well as electricity for general consumption in all three of these end-use
sectors. Given the large size of the solar resource, these technologies are not constrained by feedstock
requirements but rather by costs and "institutional" obstacles such as performance (e.g., intermittent
operation), perceived risks, and siting issues.

$ Photovoltaics

Photovoltaic (PV) devices convert the energy contained in sunlight directly into electricity-
using modules composed of multiple PV cells. Two broad categories of PV devices exist:
flat-plate and concentrating. Concentrator systems uses lenses to focus radiation onto
just a few, highly efficient PV cells and only use direct beam sunlight, while flat-plates
utilize the whole of the incident solar radiation, including diffuse (scattered) and direct
insolation.

Today's annual PV market is only about 50 MW worldwide, but market growth during the
last few years has been 25% per year. PV systems are currently cost-effective in some
consumer products (e.g., watches and calculators) and distributed and remote power
generation (e.g., village power). For example, over 2000 small residential PV systems
have been installed in the Dominican Republic under a unique revolving credit system that
permits rural clients to borrow funds to purchase these systems and pay the loans back
as they save money from avoided kerosene purchases. Similarly, 15,000-20,000 systems
have been installed in Mexico under the government's rural development program. As
costs continue to decline in the next 5-15 years, opportunities for PV systems will expand,
allowing them to compete with large-scale conventional power generation in the next
century.

$ Solar Thermal - Electric

Solar thermal technologies collect the sun's radiant energy to create a high-temperature
heat source that can be converted into electricity via a number of thermodynamic
conversion cycles. Parabolic trough technologies employ a field of parabolically-shaped
solar collectors that focus the sun's energy onto specially-coated metal pipes surrounded
by glass tubes containing a heat transfer fluid (such as synthetic oil). Parabolic dish
systems use a modular mirror system that approximates a parabola and creates a high
energy flux at the focal point where an external combustion Stirling engine converts the
heat into electricity. Central receivers use a large field of sun-tracking mirrors (heliostats)
that reflect the incident radiation onto a tower-mounted thermal receiver. Finally, solar
pond systems collect and store solar energy in a liquid medium (usually a large basin of
water with a salt gradient to suppress heat loss), which can then be converted to electricity
using a closed Rankine Cycle engine.

Solar thermal technologies are currently in the development/demonstration phase, with

projects designed to prove the reliability and operation of such facilities in numerous
Chapter 9 Renewable Energy Supply 9-5

locations worldwide. Many systems employ thermal storage devices or energy backup
(so-called "hybrid" systems) to overcome issues associated with the intermittent nature of
the solar resource (e.g., power generation during cloudy weather). Likely applications for
these technologies will be village power (especially the parabolic dish/Stirling systems)
and centralized electricity generation in the late 1990s and early 21st century.

$ Solar Thermal - Industrial Process Heat

Solar thermal technologies for industrial process heat (IPH) utilize technologies and
principles similar to solar thermal electric technologies in generating a high- or medium-
temperature heat source. The heat generated from these systems can then be used to
supply energy for general industrial processing needs or for specialty processes, such as
the detoxification of hazardous wastes.

Development and deployment opportunities for these technologies are closely tied to
those for solar thermal electric systems since they employ similar thermodynamic and
physical principles.

$ Solar Building Technologies

Solar building technologies include active and passive heating and cooling systems, as
well as daylighting. Today, there are more than two million solar water heaters installed
in Japan and 600,000 in Israel; significant numbers are also found in many other
countries, notably the United States, Kenya, China, Turkey, and Papua New Guinea.
Active heating systems provide hot water and space heating for residential or commercial
buildings utilizing a collector that receives or absorbs the incident solar energy and
transfers it to a working fluid (water, oil, or air) for direct use or storage. Active solar
cooling technologies include solar desiccant systems that use a drying agent to adsorb
water vapor in building circulation air; solar heat is then used to dry or regenerate the
desiccant for re-use. Another cooling technology, the solar absorption system, is based
on traditional refrigeration technologies but uses solar heat to provide much of the energy,
although some mechanical assistance is typically required.

Passive heating and cooling systems use little or no mechanical assistance, relying rather
on the design of the building to achieve specific thermal requirement goals. Passive space
heating uses natural heat transfer processes to collect, store, and distribute heat.
Techniques in practice today include direct gain systems (e.g., south-facing windows),
thermal storage walls, attached sunspaces (e.g., greenhouses), roof storage using water
that collects heat and is distributed via convection, and convective loops based on a
thermosiphon principle common in solar hot water heaters but using air as the working
fluid.

Conventional passive cooling techniques maximize natural ventilation, incorporate well-

insulated and low-emissivity building materials, and utilize advantageous landscaping
methods (e.g., shade tree planting). More advanced practices involve earth cooling tubes
that use lower underground soil temperature to cool incoming air, evaporative cooling
using water, and ice ponds (in which ice from the winter months is used to cool circulating
air as it melts).

Finally, daylighting simply involves the effective use of natural light to provide illumination.
This is primarily achieved through building design although advanced optical switching
9-6 Greenhouse Gas Mitigation Assessment: A Guidebook

materials and low-emissivity coatings for windows can further the effective use of
daylighting.
9.2.2 Wind Energy

Wind technologies convert the energy of moving air masses at the earth's surface to rotating shaft
power that can be directly used for mechanical energy needs (e.g., milling or water pumping) or converted
to electric power in a generator. Two major types of turbines exist and are defined based on the axis of
blade rotation: horizontal-axis (which currently dominate commercial markets) and vertical-axis turbines.

Wind energy has proven the most cost-competitive renewable electricity technology for the bulk
power market to date; however, its use is also very well-suited to remote and distributed applications.
Hybrid applications, in which a wind turbine is coupled with another renewable energy source (e.g., PV)
and/or a conventional back-up unit (e.g., diesel generator), are attracting much interest in the remote power
market. For example, the fishing village of Xcalac in Mexico uses a hybrid system composed of six 10 kW
wind turbines, an 11.2 kW PV array, and a diesel backup generator to provide 100% of its power.

As of 1994, there were over 1700 MW of installed wind turbines in the world, the majority of which
are located in California in the U.S. Most of these are in the 50-150 kW size range and are providing power
to the electric utilities in that state. Newer turbines being installed today for bulk power are closer to the
150-300 kW range, and systems in the future are expected to be much larger, reaching sizes over 500 kW.

9.2.3 Biomass Energy

Biomass energy is a term that includes all energy materials derived from biological sources,
including wood wastes, agricultural residues, food industry wastes, sewage, municipal solid waste (MSW),
and dedicated herbaceous or woody energy crops. The potential size of the biomass resource is quite
large on a global scale, and the ability to utilize existing residue streams that may provide low-cost
feedstocks offers attractive near-term opportunities for biomass use. In the longer term, the development
of sustainable, dedicated biomass energy plantations may further expand the resource base and help
reduce the costs of energy produced from biomass.

$ Biomass Electric Technologies

Cogeneration of biomass in the industrial sector provides the largest share of biomass-
derived electricity today. Low-cost feedstocks are often critical to the economic viability
of biomass energy use in these markets, and thus waste materials such as agricultural
and forest products residues, food processing wastes, and MSW can be attractive
feedstocks for direct combustion in boiler systems. Dedicated electricity generation also
benefits from the use of waste materials although the development of dedicated biomass
energy crops may provide low-cost feedstocks in the long term while simultaneously
extending the resource base.

The energy, environmental, and economic performance of biomass electric technologies

can also be enhanced by moving to advanced conversion technologies, such as
gasification/gas turbine technologies. Gasifiers convert biomass to a synthetic gasoline
(syngas) containing chiefly CO and hydrogen, which can then be combusted in an
aeroderivative gas turbine. The theoretical efficiency of such a process is much higher
than that of the conventional direct combustion/steam turbine process, thereby reducing
feedstock requirements and enhancing the economics of power generation.
Chapter 9 Renewable Energy Supply 9-7

Biomass energy systems are emerging as an economically viable option for satisfying
power needs in both industrialized and developing countries (on-grid and off-grid). Where
the resource conditions are favorable, power systems based on feedstocks grown on
short-rotation forestry (SRF) plantations can produce electricity at costs that are
comparable with conventional fossil-based alternatives (see Carpentieri et al., 1993;
Russell et al., 1992; and Perlack et al., 1991). Potential SRF biomass-to-electricity
projects include:

- the conversion of agricultural processing facilities (e.g., sugar mills, rice mills,
sawmills) to cogenerate heat and power for on-site processing needs and export
of excess power to the local distribution grid using a combination of mill wastes
and plantation grown biomass;

- the conversion of fossil-fired electric generation facilities to burn or co-fire

plantation-grown biomass; and

- and the development of stand-alone biomass-based power generation relying

exclusively on SRF plantation-grown feedstocks.

The interest in biomass-to-electricity projects comes not only from its potential as a low-
cost supply of power but for its potential to mitigate a host of environmental concerns such
as reducing the rate of CO2 buildup in the atmosphere by sequestering carbon, by
substituting for fossil fuels, and by replacing wood use from existing forests. When SRF
feedstocks are grown renewably, biomass contributes no net buildup of atmospheric
carbon because the carbon released during burning is extracted from the atmosphere
during photosynthesis.

Direct combustion technologies can continue to improve and expand their market share
in industrial cogeneration and utility markets, and the advanced power cycles discussed
above are likely to move out of the demonstration phase and into commercial operation
near the turn of the century.

$ Biomass Heating Technologies

The most common use of biomass is direct combustion for residential space heating and
cooking and for industrial process heating. In the residential sector, improved wood
cooking and heating stoves can offer advantages in terms of reduced fuel requirements
(thus, lower costs or less time spent collecting biomass) and improved emissions
characteristics. In industrial processes (e.g., the sugar cane industry or pulp and paper
industry), biomass wastes can be used more effectively by increasing boiler efficiencies
and enhancing residue collection activities.

$ Biomass Transportation Fuels

Fuels produced from biomass feedstocks for transportation applications include ethanol,
methanol, and their ethers, ETBE and MTBE, as well as hydrogen, syngas, biodiesel, and
jet fuels. Ethanol is produced from sugar (e.g., sugar cane), starch (e.g., corn), or
cellulosic feedstocks (wood, herbaceous material, and MSW). The conversion process
involves the biochemical conversion of the feedstock into its constituent glucose chains,
which are then fermented to produce alcohol.
9-8 Greenhouse Gas Mitigation Assessment: A Guidebook

Methanol is produced from biomass by first gasifying the feedstock to form a syngas, a
subsequent gas-shift reaction to adjust the chemical composition of the gas, cleaning, and
finally the conversion to methanol in the presence of a catalyst. Hydrogen can also be
manufactured via the gasification of biomass followed by gas-shift reactions and
separation of the hydrogen component of the syngas.

Synthetic hydrocarbon fuels (gasoline, diesel, and jet fuel) can be created from biomass
by pyrolizing the feedstock to form an intermediate biocrude liquid product and then
catalytically converting the biocrude to a traditional hydrocarbon fuel formulation.
Alternative methods convert the oils extracted from certain plant seeds to diesel fuel by
isolating the hydrocarbon portion of the carbon chain.

Currently, ethanol is the only biofuel that has achieved noticeable market success,
particularly in Brazil and, to an extent, in the U.S. The advanced technologies associated
with producing ethanol from low-cost feedstocks (i.e., lignocellulosic biomass) may help
enlarge the ethanol market after the turn of the century. Similarly, biomass-methanol
production technologies might be commercially available in the first decade of the 21st
century, particularly if gasification technologies continue to advance in the electric power
sector. Finally, current research experience indicates that cost-effective hydrogen and
synfuel production might also reach commercial levels sometime in the first decade of the
21st century.

$ Biomass Energy Systems: General Considerations

In addition to the direct power and environmental benefits, biomass energy systems offer
numerous other potential benefits, especially for developing countries. Some of these
benefits include off-season employment of underutilized labor (tree planting and
maintenance, use of tree co- and by-products); increased agricultural productivity through
soil stabilization, reduced water runoff, and improved microclimates; and increased
opportunities for industrial development through the availability of peak (wet season) and
base load (dry season) power. In power deficit areas, the availability of power can
encourage the development of small-scale industries and rural commerce, increase the
productivity of agriculture through irrigation and post-harvest processing, make modern
conveniences (e.g., lighting and potable water pumping) available to many more rural
residents, and promote general well-being.

What separates the evaluation and implementation of biomass energy projects apart from
other renewable and conventional energy systems is that resource or feedstock
management is an integral part of a total energy, environmental, and economic system.
Moreover, the complexity of the evaluation and possible implementation is further
compounded by a high dependency of the biomass energy system on adaptation to local
environmental, economic, social, and institutional considerations. Evaluation of this option
must address a complex array of issues: competitiveness with other sources of energy
supply, costs, emissions, financing, energy regulatory policies, food and fiber production,
employment and impacts on agriculture, biodiversity and habitat, land ownership and
tenure, flood and erosion control, pollution remediation, plantation sustainability, and
logistics of resource supply and distribution.
 Chapter 9 Renewable Energy Supply 9-9

9.2.4 Geothermal Energy

Geothermal energy systems tap the heat originating from the earth's molten interior and the decay
of radioactive materials in the crust. The potential size of the resource is very large although conversion
technologies for fully accessing the estimated 100 million quads of available worldwide resource are yet
to be proven. Geothermal energy is currently being used in various locations around the world to produce
electricity at costs competitive with conventional sources and provide energy directly for space heating, food
and industrial processing, refrigeration, and aquaculture.

$ Geothermal Electric Technologies

Hydrothermal resources, consisting of water and/or steam trapped in fractured or porous

rocks, are currently the only type of geothermal energy being accessed on a commercial
scale. Electricity is produced via one of three major routes: dry steam, flash steam, and
binary conversion. Dry steam systems use the geothermal steam directly to drive a
turbine-generator while flash steam technologies first convert hot geothermal liquids to
steam by quickly reducing its pressure. Finally, binary cycle systems are used for
generating power from lower-temperature liquids by using the hot geothermal waters to
vaporize a secondary working fluid which then drives a turbine-generator unit.

The state of California in the U.S. currently receives 6% of its electricity from geothermal
energy, and installed units exist in the Philippines, Mexico, Italy, Japan, New Zealand, and
other countries. Advances in methods for locating, drilling, and extracting geothermal
energy coupled with improvements in conversion technologies can help geothermal
electricity expand its current market share further, effectively competing with fossil-
powered sources in the baseload power market.

$ Geothermal Heating Technologies

In some regions of the world, low-temperature geothermal energy is being used directly
for space heating, such as in several cities in Iceland where steam/hot water lines carry
geothermal fluid through the district heating system. Another promising technology is the
geothermal heat pump (GHP). GHPs operate like a conventional heat pump (a
refrigerator, for example, is a one-way heat pump) and use the heat gradient between the
earth's surface and groundwater or soil several hundred feet below the surface to power
the pump. Because GHPs are reversible, they can provide space heating in the winter and
space cooling in the summer as well as supplement domestic hot water needs year-round.
More than 100,000 of these systems have been installed in the U.S. to date and sales
continue to grow at significant rates.

9.2.5 Hydropower

Hydropower facilities exploit the kinetic energy in flowing or falling water to generate electricity.
Conventional hydropower facilities use water from a river, stream, canal, or reservoir to continually produce
electrical energy, and water releases from single-purpose reservoirs (i.e., dedicated to power production)
can be quickly adjusted to match electricity loads. Multipurpose reservoirs are not capable of following load
9-10 Greenhouse Gas Mitigation Assessment: A Guidebook

as closely; however, they can be simultaneously used for irrigation, flood control, navigation, recreation, and
water supply.

Pumped storage plants operate similarly, but instead of tapping free-flowing water, the facility uses
recycled water. During off-peak hours, water is pumped to an upper reservoir using low-cost resources,
where it can be re-used to provide peak power on demand. Pumped hydropower facilities are net energy
consumers (typically 1.25-1.40 kWh is required to pump the water to the upper reservoir for each kWh
generated); however, they provide significant economic and operational benefits to utilities because of their
ability to meet transient peak power demands.

Finally, mini-hydro facilities (30 MW or less in size) offer opportunities for distributed or remote
power generation with minor environmental impacts, low operating costs, and high reliability. Installation
of these systems is usually quite rapid and can use local labor.

Hydropower technology is currently mature and widely available. Almost 15% of the world's
electrical energy comes from hydroelectric facilities operating in over 80 countries (Moreira and Poole
1993). Only a fraction of the available resource has been exploited to date, in large part because of siting
constraints, environmental pressures against large-scale systems, and competition with other interests for
water resource use. The increased development and use of micro-hydro technologies may permit
additional resources to be accessed without encountering the barriers that have traditionally constrained
conventional hydropower development. In Nepal, for example, the Agricultural Development Bank has
financed the purchase of more than 650 small hydro systems by farmers, who use income from milling
operations and electricity sales to pay back the loans.

9.2.6 Ocean Energy

Numerous systems have been conceived of for capturing the energy of the ocean's waves, tides,
and temperature gradients. Of these, ocean thermal energy conversion (OTEC) and tidal power systems
have received the greatest attention to date. OTEC uses the temperature difference between the surface
of the ocean and depths of up to 1000 meters to generate electricity in either a closed-loop (using a
secondary working fluid) or open-loop cycle (using seawater as the working fluid).

Tidal power uses the same principle employed in hydroelectric power generation to extract energy
from a difference in hydrostatic head created by the rising and falling tides. A minimum difference of 5
meters between low and high tides is often cited as the limit required to effectively produce electricity,
although developments in micro-hydro technology may permit additional resources with lower ranges to
be accessed.

OTEC and tidal power are still primarily in the development stage, and technical, cost, and siting
constraints continue to limit the progress of these systems.

9.2.7 Screening Mitigation Options

The first step in screening renewable energy options for further analysis is to conduct a preliminary
resource assessment. For many countries, such an assessment may have already been conducted with
sufficient accuracy to allow a screening out of those options that are unlikely to be of interest because
adequate resources are lacking, or are too small to make a significant national contribution. Alternately,
the study team can conduct its own preliminary assessment, drawing on appropriate experts in the country.
For assessment of biomass resources, the energy sector analyst should work together with the forestry
and agricultural analysts.
 Chapter 9 Renewable Energy Supply 9-11

For those technologies for which exploitable resources appear to be available, a screening should
be conducted using the criteria listed in Table 2-1 in Chapter 2. It is particularly important to consider the
potential for indirect economic benefits such as local employment creation and foreign exchange savings.

9.3 RESOURCE ASSESSMENT1

Use of renewable energy requires careful matching of conversion technology to resource

availability and to energy demand. Although it is usually obvious to the inhabitants of an area that one form
of renewable energy is more plentiful than another, it is important to conduct an inventory of renewable
energy resources before selecting technologies that may be deployed to convert these resources to usable
energy forms. Some countries may have progressed beyond what is discussed below on resource
assessment, while others may not have.

Resource assessment requires determination of the quantity and quality of resources found in a
given region at a given time. It may involve exploration and monitoring to determine whether a particular
site is suitable for a particular renewable energy technology.

An inherent difference between renewable and conventional energy resources is that renewable
sources are determined by their "flow" whereas conventional sources are "fixed" in stock. Renewable
energy resources vary by time of day, and some of them, such as solar radiation and wind, vary by night
and day. Most renewable energy sources vary seasonally, and all of them vary from year to year. Sunlight
and wind are variable in place, also. The rate at which renewable energy resources can be expended is
generally fixed by the flow and not, as with conventional resources, by demand. These inherent resource
characteristics make it essential to carefully evaluate energy needs when considering renewable energy
systems. Some renewable energy resources, such as biomass resources, have competing uses that must
be considered. Furthermore, crops can be grown for energy as well as agricultural uses, and in cases such
as bagasse from sugar cane, there are mutual benefits in using a biomass resource for both agricultural
and energy applications.

Data availability for renewable energy resources varies widely. Furthermore, most of the data
available have been collected primarily for other purposes such as agriculture, airline operations, flood
control, timber harvests, waste management, and the protection of life and property (weather forecasts).
Such data are valuable for those purposes, but they do not always provide the information required to
make accurate assessments of renewable energy resources. The collection of data specifically for
assessing renewable energy resources is quite limited. In addition, data that are available for renewable
energy resources are generally lacking in accuracy and spatial (geographic) and temporal (time) resolution.
The poor spatial resolution (lack of data at most locations) is the direct result of the small number of
locations at which resource measurements have been made. The lack of temporal resolution means that
it is not possible to accurately estimate the flow characteristics of renewable resources on time scales
capable of resolving hourly, daily, monthly, and annual variations.

1
The discussion on resource assessment is taken from Maxwell and Renne (1994).
9-12 Greenhouse Gas Mitigation Assessment: A Guidebook

9.3.1 Solar Radiation

Most measures of solar radiation resources are given in terms of the total energy received (in Btu,
kWh, or megajoules) each hour and/or day at the measurement location. Monthly and annual averages
are computed from the hourly or daily data, and these are used to prepare tabular data sets and maps of
average daily energy. These data tables and maps provide a first-level indication of resource availability.
More detailed assessment requires resolving the temporal characteristics of solar radiationCchanges that
take place over time scales ranging from minutes to decades. Experience has shown that short-term
changes in the flow of solar energy requires measurement intervals of 5 minutes or less. Monitoring long-
term changes associated with climate change, volcanic eruptions, and atmospheric pollution requires a
continuous measurement program. Typically, solar radiation data have been collected at intervals from
one minute to one day, with the most common interval being one hour. Hourly data are adequate for most
applications. The short-term (e.g., five-minute) variability of solar radiation at a given site can usually be
determined from one to three years of data.

For initial screening of solar radiation resources and to produce solar resource maps at the
national level, monthly average daily totals of the global horizontal radiation are available on Internet from
a database at NASA-Langley at a resolution of 280 km by 280 km grids. These data are available for all
locations. These data can be processed to obtain finer spatial (to 30 km grids) and temporal resolution,
but such work will require specific effort by experts. These data should be validated by ground-based
observations before they are applied to evaluate the suitability of solar energy technologies or projects to
meet specific end uses or needs. International solar radiation data are available from the World Radiation
Data Center (WRDC) in St. Petersburg, Russia, and from the World Radiation Monitoring Center in Zurich.
Data from the WRDC will be available in the near future from The National Renewable Energy Laboratory
(NREL) on Internet.

9.3.2 Wind Energy

Because the power of the wind is proportional to the cube of the wind speed, a small change in
wind speed can represent a large change in wind power at any given time. Wind power density is
calculated by summing the average wind power of several ranges of wind speed over a specified period
of time (month, season, or year). The power for each range is multiplied by the frequency of occurrence
of wind speeds within that range, and the results are summed over all ranges to obtain the wind power
density. Maps based on such wind speed ranges to define wind power classes are available but at such
large scales that even initial screening at the national level for most countries will be difficult. Wind atlases
for many parts of the world are available but vary in quality and consistency. Grubb and Meyer (1993)
survey data availability at the national and continental levels. Since wind speed is highly variable and is
affected by surface roughness and topography, regional or local data are desirable for screening purposes.

Similar to solar radiation, wind speed has not generally been measured for the purpose of
assessing wind energy resources. For these reasons and others, most of the wind data available today are
not as reliable as one would like for estimating wind energy resources. Wind resources, including the
turbulence characteristics of the resource, can vary significantly over small distances, particularly in very
mountainous terrain or in coastal or lake-shore regions. When no wind data are available, topographic and
vegetative indicators, or numerical models, might be used to estimate wind resources.
 Chapter 9 Renewable Energy Supply 9-13

9.3.3 Hydropower

The hydropower resources for a given river basin or catchment area can be estimated from three
sources of information: hydrographic records, which define the rate of flow of water at a certain point within
the river basin, measurements or estimates of precipitation falling on the catchment area, and the
topographic characteristics of the catchment basin. Recording rain gauges are standard for virtually all
weather service stations around the world.

The prospects of developing any site also depend on numerous engineering, environmental, and
economic considerations which have not been fully assessed and which can change over time. In those
areas of the world with rapid population growth or areas that are prone to periodic severe droughts, there
can be intense competition for the available freshwater supply. As with other renewable resources, the cost
of energy derived from a hydropower project can vary considerably, even within regions where the resource
is generally abundant.

9.3.4 Geothermal

Geothermal energy resources fall into four categories: hydrothermal (hot water and steam), hot
dry rock, geopressured hot water with dissolved CO4, and magma. Only hydrothermal resources have
been commercially developed to date. Palmerini (1993) provides an overview of global geothermal
resources and extraction technologies.

The main characteristics of a geothermal reservoir that determine the usefulness of its energy are
its volume, the water state (liquid and/or steam), temperature, pressure, depth, water chemistry, and
recharge rate. High-temperature steam sources are of greatest value for generating electricity. Lower
temperature liquid sources (T< 90°C) are typically used for heating buildings and for process heat. The
depth and pressure, particularly for liquid resources, will affect the cost of getting the resource to the
surface. The chemistry of the liquid or steam will affect construction and operational costs, according to
the measures required to remove harmful minerals or mitigate their effects. The rate at which the hot water
or steam is replenished (naturally and by injecting spent fluids) determines the quantity of energy that the
source is capable of supplying on a continuous basis.

9.3.5 Biomass

Biomass is by far the most complex of the renewable energy resources and presents the most
difficult assessment problems. This complexity is due primarily to the multiple sources of
biomassCincluding energy crops (e.g., trees, corn, sugarcane, microalgae); standing crops (mostly forests)
grown for other purposes; litter and dead or non-commercial trees (standing waste) in forests; and forest
and agricultural wastes (field and mill or factory)Cand to the many energy conversion processes that are
possible, including direct combustion, gasification, liquefaction, and biochemical processing. The first step
(after determining end-use needs) is to inventory sources of biomass and their availability. Hall, et al.
(1993) reviews biomass resources at the national and continental levels.

Once the sources and availability are identified, harvesting rates, transportation, storage, and
conversion issues must be considered. For example, microalgae might be harvested on a daily basis,
agricultural crops and agricultural waste from one to three times per year, trees grown for energy use every
three to five years. It may be economical to harvest litter and standing waste only in conjunction with a
9-14 Greenhouse Gas Mitigation Assessment: A Guidebook

timber harvest, which may occur as infrequently as once every 10 to 50 years. Given the variety of biomass
resources, several resource assessment methods will be needed. Assessment of biomass resources for
the energy sector should be coordinated with the non-energy part of the mitigation assessment.

Biomass resources are also difficult to assess because they consist of both flow and fixed stock
components. Standing crop and litter in a mature forest represent a fixed stock waiting to be harvested.
Annual growth in young forests, agricultural crops, and harvesting and production wastes all represent flow
resources that are subject to change seasonally and from year to year. With the exception of crops grown
for energy use, there is little consensus regarding the proportion of most biomass resources that is available
for energy use. Competing uses of biomass for food, clothing, and shelter also complicates resource
assessment. Competition for many biomass waste products is also important to consider. Wastes from
both forest and agricultural crops are essential to stabilize and replenish soils. Straw and wood chips are
used for bedding material for animals, and some waste products, such as bean pods and sugar beet pulp,
are used as animal feed. In general, the amount of waste that could be diverted to sustainable energy
production is not well known.

9.3.6 Municipal Solid Waste

Municipal solid waste (MSW) can be defined as the post-consumer solid waste generated by
residential, commercial, and institutional (schools, hospitals, offices, etc.) sources (OTA 1989). Industrial
sources are not included because industrial wastes are usually discarded separately from municipal
wastes. Some of these solid wastes are combustible and are being used in some areas as a renewable
source of energy. The feasibility of using MSW for energy production in a given area depends on a number
of factors, including population, availability of landfills, the general economy of the area, and the demand
for thermal or electrical energy.

An estimate of the national resource base requires an estimate of the materials flow of paper and
paperboard, plastics, yard trimmings, rubber and leather, textiles, wood, food wastes, and other categories
of MSW that could be used as an energy resource. Estimates of MSW resources for individual
municipalities requires measurements of the MSW at the dump site or the point of generation. At the dump,
the total weight could be determined by weighing the trash collection trucks before and after dumping.
Measuring the composition of the MSW is more costly and time-consuming. A certain percentage of the
trash trucks must be randomly selected and their contents dumped and sorted into categories such as
paper and paperboard, plastics, wood, metal, etc. Each category must then be weighed separately.
Similar to any other measurement process, the accuracy and reliability of MSW sampling is dependent on
the design of the sampling program (e.g., number of samples, distribution in time, and length of sampling
period) and its execution. Currently, there is no standard method for collecting such data; in fact, there is
no general agreement on the categories to be used to define MSW (Kahn and Sable 1988).

9.4 TECHNOLOGY CHARACTERIZATION

After renewable energy resources are assessed to the degree possible with the available data, the
next step is to characterize technologies that can convert the resources to usable forms. Renewable
energy technologies are as varied as the resources they convert to electricity, heat, and fuels, and the
information required to evaluate them differs somewhat among technologies. In general, however, the
types of data listed in Table 8-11 for conventional energy supply technologies (engineering performance,
economic parameters, environmental impacts) also apply for renewable energy technologies.
 Chapter 9 Renewable Energy Supply 9-15

The National Renewable Energy Laboratory (NREL) in the U.S. has prepared technical and
economic descriptions (technology characterizations) of selected renewable energy technologies for the
IPCC that include performance and cost data. These technology characterizations include those
renewable energy technologies considered by the Energy and Industry Subgroup of the IPCC to be
commercially available in the near-term (<10 yrs) and suited for limiting the levels or growth rates of
greenhouse gas emissions in developing and transitional economies. The technologies characterized and
their applications are:

$ flat-plate photovoltaics (electricity)

$ solar thermal (heat, electricity)
$ salt-gradient ponds (electricity, space and process heat, desalinization)
$ wind turbines (electricity, water pumping)
$ small-scale hydro (electricity)
$ geothermal (electricity)
$ MSW (electricity, heat)
$ biomass: direct-fire steam turbine, gasification-gas turbine cycles (electricity)
$ pelletized wood (space and process heating).

Additional cost information on photovoltaics, solar thermal electric, and biomass energy (electricity
and liquid fuels) is available in Ahmed (1994).

An important set of technologies not included in the IPCC work so far is that to produce liquid fuels
from biomass. Technology characterizations of these and other energy systems listed in Table 9-1 are
available from NREL.

9.5 CONSTRUCTING BASELINE AND MITIGATION SCENARIOS

After potentially applicable renewable energy technologies are identified, a method to select the
most suitable technologies is needed. There are two general ways to make this selection. One way is to
use optimization or other models that can integrate renewable energy technologies into the overall energy
2
supply system once assumptions on costs and performance are made. The second way is to use a
decision analysis tool that explicitly accounts for subjective and non-quantifiable factors. An example of
such a tool is the Analytical Hierarchy Process (AHP), which has been applied for evaluation of renewable
energy technologies in Mexico (Corbus et al. 1993).

Specific options can be further analyzed by identifying market opportunities and exploring market
penetration options. In doing so, attention should be paid to some of the unique characteristics of

2
Many models assess the availability of resources (e.g., oil, gas, coal) through pricing. As the resource becomes
more scarce, the fuel price of a technology increases and the deployment of the technology is therefore constrained.
For many renewables, fuel price does not exist (i.e., solar or wind technologies) and there is no way for the model to
automatically limit deployment based on resource availability. In these instances, a "cap" may need to be applied to the
model.
9-16 Greenhouse Gas Mitigation Assessment: A Guidebook

renewable supply technologies. Renewables offer important benefits in terms of reduced environmental
impact beyond climate change mitigation, energy independence and diversity, and economic and social
development. These benefits are often not readily modeled but are essential elements of a comprehensive
assessment.

A particularly promising area for renewables deployment is distributed or off-grid power generation.
Accounting for these opportunities requires a way of evaluating the trade-off between grid extension and
off-grid remote power generation. In many instances, a utility line extension can be more costly than
deploying a renewable technology as a stand-alone system.

For on-grid applications, a key issue for renewable energy is integrating the technologies into the
existing energy network. Many of the renewable technologies operate intermittently, which is to say that
they only produce power part of the time (when the sun is out or the wind is blowing). Some of the outages
can be predicted (e.g., the time that the sun will set is known), while others cannot (e.g., a large bank of
clouds passing overhead). As a result, electric utilities consider most solar and wind technologies as non-
dispatchable since they cannot be turned on whenever they are required. Considerable research and
experience has been devoted to assessing how utilities can deal with this uncertainty. One method has
been to increase the knowledge of the resource through resource assessment to reduce the uncertainty
about when the resource is available (i.e., "predict" when the wind will come up). Other techniques include
the use of backup and storage systems, promoting system diversity, and load management.

9.6 MITIGATION POLICIES

Policies to promote adoption of renewable energy options and examples of their application are
briefly described in Table 9-2. These are loosely aligned with the policy options listed in Chapter 8 on
conventional energy supply since many of the same types of policies will serve to enhance renewable
energy supply. Table 9-2 only lists policies and examples that might directly promote the use of renewable
energy; however, most of the options discussed in Chapter 8 can have indirect effects on the use of
renewables. For example, taxes or restrictions on the use of carbon-intensive fuels (e.g., coal) will increase
opportunities for renewable energy. Finally, integrated resource planning offers opportunities for
incorporating renewable energy technologies into utility planning as part of a formal process.

In addition to the policies in Table 9-2, technological transition strategies should be part of an
implementation plan for renewable energy. Hybrid systems such as diesel generator/wind, hydro pumped
storage/wind, and co-firing of renewable and conventional fuels (e.g., biomass and coal) are ways of
integrating renewable and conventional technology options.
Chapter 9 Renewable Energy Supply 9-17

Table 9-2. Policies to Promote Use of Renewable Energy

OPTION DESCRIPTION EXAMPLES

Emissions Controls Limits on emissions of GHG or other pollutants - Emissions cap on new power plants,
- caps by technology transportation vehicles, etc.
- caps by region/sector - Emissions cap from regional utilities,
urban zones (e.g., Aclean cites@), or
segments of the industrial sector

Input Controls Require uses of renewable energy feedstocks - Set-asides for renewable utility
technologies in future capacity
expansion plans
- Payments to operators using renewable
energy for industrial processes

Price Controls Price subsidies for renewable energy fuels - Federal/local subsidies on cost of
and technologies electricity from renewable utility
technologies
- Payments to operators using renewable
energy for industrial processes

Rate-of-Return Regulation Requirements on the rate-of-return calculation - Permit owners/operators of renewable

for energy supply companies electric technologies to achieve
higher rates of return

Permitting Conditions placed on energy supply operations - Preferential siting of renewable energy
supply facilities; reduce siting
constraints

Tradeable Require the acquisition of GHG emission rights - Renewable energy supply technology
Emission Permits by trading with other sources used to offset emissions from non-
renewable sources

Taxes Tax credits/levies for GHG control - Tax credits for renewable energy use
- on products (fuels, electricity, etc.)
- on firms - Taxes on GHG-emitting technologies
- on land and facilities

Tariffs Reduced tariffs for importation of non-GHG - Reduced tariffs on foreign renewable
emitting technologies energy supply technologies (e.g., wind
energy systems) or demand tech-
nologies (e.g., alcohol-fueled vehicles)

Research, Government funding of RD&D in the area of - Government-sponsored research,

Development, and renewable energy including demonstration activities
Deployment

Government Purchase Government purchase of renewable energy - Purchase of alternative-fueled vehicles

technologies for government fleet use
- Cost-sharing with industry and in
purchase of industrial renewable
energy technologies

Information Promote renewable energy technologies with the - Creation of one-stop shopping
Dissemination general public, specific industry groups, and information
energy planners Aclearinghouses@ for renewables
- Sponsorship of technical conferences
with
industry
9-18 Greenhouse Gas Mitigation Assessment: A Guidebook

Cooperatives Promote cooperatives that aggregate demand - Rural electric cooperatives (with focus on
for renewable energy technologies village power)
- Industry-sponsored cooperatives (e.g.,
pulp and paper industry)

REFERENCES

Ahmed, K. 1994: Renewable Energy Technologies: A Review of the Status and Costs of Selected
Technologies, World Bank Technical Paper No. 240, Washington, DC: The World Bank.

Capentieri, A.E., E.D. Larson, and J. Woods. 1993. "Future Biomass-Based Electricity Supply in Northeast
Brazil," Biomass and Bioenergy, 4:149-174.

Grubb, M.J. and N.I. Meyer. 1993: "Wind Energy: Resources, Systems and Regional Strategies", in Johansson,
et al., 1993.

Hall, D.O., et al. 1993: "Biomass for Energy: Supply Prospects", in Johansson, et al., 1993.

Kahn, Z.K. and E. Sable. 1988: APlanning a Program to Determine Physical and Chemical Characteristics of
Municipal Solid Waste,@ Resource Recovery/Cogeneration World, 1:15-18.

Johansson, T.B., et al. 1993: Renewable Energy: Sources for Fuels and Electricity, Washington, DC: Island
Press.

Maxwell, E.L. and D.S. Renne. 1994: Measures of Renewable Energy, National Renewable Energy Laboratory
(NREL/MP-463-6254), Jan. 1994.

Moreira, J.R. and A.D. Poole. 1993: "Hydropower and Its Constraints", in Johansson, et al. 1993.

OTA. 1989: Facing America=s Trash B What Next for Municipal Solid Waste? OTA-O-424, U.S. Congress,
Office of Technology Assessment, Washington, DC: U.S. Government Printing Office.

Palmerini, C.G. 1993: "Geothermal Energy", in Johansson, et al. 1993.

Perlack, R.D., Ranney, J.W. and M. Russell. 1991. Biomass Energy Development in Yunnan Province, China,
Oak Ridge National Laboratory, ORNL/TM-11791, Oak Ridge Tennessee, June 1991.

Russell, M., Jantzen, D. and Z. Shen. 1992. Electricity From Biomass: Two Potential Chinese Projects,
Energy, Environment, and Resources Center, University of Tennessee, Knoxville, 1992.