The Big Picture

Alternative energy sources to fossil fuels are available to meet the world's energy needs. These renewable sources of energy include solar power, geothermal power, wind power, water power, hydrogen fuel, and biomass fuels. These sources are all potentially large in available energy: each day, more solar energy hits the Earth than the entire world's human population could use in 27 years! It is not possible to use all of this available energy, however, because much of the sunlight falls on the ocean, where people do not live. But, even if a tiny fraction could be used to power our electric devices and machines, we could greatly reduce our reliance on polluting fossil fuels. The major obstacle to instituting these alternative and renewable sources of energy is economic, not technological. For example, as described in the case study, the Luz International Solar Electric Facility has reduced the cost of a solar-generated electric power from $0.12 per kilowatt-hour to $0.08 per kilowatt-hour. Other sources of electric power sell for $0.06 per kilowatt-hour. A new facility planned by Luz would have brought the cost down even more, to $0.065 per kilowatt-hour, but Luz was forced to file for bankruptcy before that facility could be built. The bankruptcy occurred because sources of US government funding were eliminated; in contrast, the polluting fossil fuels and nuclear energy industry enjoy the continued support of the government. These non-renewable sources are allowed to pollute, which causes everyone to pay for the clean-up and is thus an external cost that is not factored into the price of electricity. The Luz plant was technologically successful, meeting the electricity needs of 350,000 people, but it was not cost-competitive on the uneven playing field formed by our nation's inconsistent energy policies. Nonetheless, solar and renewable energy sources are becoming more widely used: the USA uses 71 trillion BTUs of solar energy each year, 60 trillion BTUs for residential and commercial use alone (1 BTU is equivalent to 90 pounds of coal or 8 gal of gasoline). Solar can come in a variety of forms: photovoltaics (PV) can be used in off-the-grid homes and remote applications (84 megawatts of PV panels were manufactured in the USA 1995); solar-thermal-electric can produce large-scale utility power (the Luz facility was 354 megawatts); solar water heating can produce heat for commercial or home use, and passive solar building design. Another renewable energy source is wind power, which is contributing electricity right now to the USA's electric grid (1600 megawatts installed capacity in massive wind farms in California and elsewhere). The wind farms meet the energy needs of 1 million people at a cost of $0.04 per kilowatt-hour to $0.07 per kilowatt-hour. Geothermal is also extremely promising, currently providing 7 % of California's electricity (2700 megawatts) at a cost of between $0.05 per kilowatt-hour and $0.075 per kilowatt-hour. Hydroelectricity supplies the biggest part of the USA's renewable energy, with 92,000 megawatts of installed capacity. This all suggests that the future of renewable sources of energy is good. In this chapter, the authors explain the pros and cons of each of these renewable energy technologies.

Frequently Asked Questions

• The renewable energy sources are solar (active, passive, direct, indirect, solar-thermal and photovoltaics), geothermal, wind power, hydropower, ocean thermal, hydrogen fuel, and biomass fuels.
• Making electricity from renewable sources normally involved heating water beyond the boiling point, where it can be used to spin turbines and generators. That is, it is the same as fossil fuel electricity production, except the way the water is heated is different.
• Most renewables (except biomass fuels) do not release CO₂ into the atmosphere, making them attractive from the standpoint of avoiding global warming. Even biomass fuels do not produce excess CO₂, because the plants grown to make the biomass fuel are taking CO₂ out of the atmosphere when they grow.

• Economics are normally against them. Any new technology is costly at first, but the cost per unit of output drops over time.
• Eventually, these renewable sources of energy will be cost-competitive, especially if fossil fuel prices rise in response to scarcity and as a function of their pollution costs.

• Geothermal is the use of earth heat or heated rocks to heat buildings or make electricity.
• In geothermal electrical generation, water is pumped into the Earth; the temperature of water is raised above the boiling point, which creates steam that can be used to spin a turbine and a generator to make electricity.
• Geothermal can be considered a non-renewable resource if heat is extracted from the rocks faster than the Earth produces it. This is happening at the Geysers Geothermal facility in California (See Figure 17.2 in text), which is experiencing a decrease in geothermal energy output each year.
• Geothermal resources occur in specific areas of the world, where the Earth's tectonic plates collide.
• There are 2,700 megawatts of geothermal produced worldwide, about 2,000 MW comes from the Geysers plant alone. The Geysers produces about 7 % of California's energy needs.
• In geothermal groundwater systems, a geothermal heat pump is used to warm the air in a building. The temperature difference between the surface air and the ground water is usually great enough in the summer to cool a home and warm enough in the winter to warm it. Ground water stays a constant 13 ^oC (55 ^oF) all year, but the air temperature fluctuates.

• Benefits: Relatively clean, no CO₂ emissions, free heat source, no transportation of fuel
• Costs: Noise, gas emissions, may be non-renewable, hot wastewaters are thermal pollutants and are often corrosive. Many Hawaiians believe in Pele, the goddess of fire, and think this practice offends her and "steals her breath and water". This opposition is based on culture, not science, however.
• Cost per kilowatt-hour: $0.05 - $0.075

• Indirect solar is basically all forms of renewable energy - even fossil fuels are indirectly due to solar energy. Trees and plants are natural solar collectors. See Figure 17.3 for a breakdown of how all renewable energy can be traced back to the sun.
• Direct solar is using the sun's energy to heat water, air or make electricity at or near the point of use. There are several kinds of direct solar energy: Passive solar design, active solar water heating, active solar electric (photovoltaics and solar-thermal).

• Passive solar energy systems are normally designed into buildings when they are built. Simple design features include having windows face south with overhangs above the windows to block summer sunlight, but allow winter sunlight in.
• Active solar systems use pumps or fans to circulate the warmed water, fluids, and air in a building. An area is set up to collect solar energy and the heat is pumped away from that area to heat water for bathing, boil water to make electricity, or simply heat the air in a building.

• A building can be designed so that it catches the sun's light most of the day. In the northern hemisphere, that means having the major glazed surfaces facing south (See Figure 17.4 in text)
• Overhangs can prevent sunlight from entering during the summer when the sun is high overhead; in the winter, the sun is low in the sky, so sunlight can pass through the windows.
• The walls and floor in a south-facing room with many windows (called a sunspace) can be lined with brick, stone, tile or other masonry. The masonry walls will store the heat during the day and re-radiate it during the night. Water tanks will also store solar energy.
• Landscaping with trees can be used to minimize sunlight input during the summer and allow it to enter in winter (deciduous trees lose their leaves during the winter).
• Solar-heat collecting walls (glass enclosed brick or water filled trombe walls) collect heat and pass it through without a window being present.

• Benefits: Low cost over life of building, although up front costs are high; little or no fuel required for heat, heating and summer cooling costs are lower than without the design; fossil fuel and CO₂ releases are minimized.
• Costs: The sun is an intermittent source of power (none at night or during cloudy days), so back up heaters are still needed. Thus total costs of the system exceed standard heating systems by 20 %.

• Solar collectors are flat panels with glass covered cases with black interior surfaces (See Figure 17.5 in text)
• Water or anti-freeze (ethylene glycol) is pumped through a convoluted tube inside the enclosed airspace within the collector, and heat is absorbed by the fluid, reaching 38 - 93 ^oC (100-200 ^oF).
• The heated water can be used directly for showering or washing, or if anti-freeze fluid is used in the tube, the heat from the fluid is released within a large water heater tank and this water is used for household hot water.

• Benefits: Although up-front costs are higher than a regular water heater ($1000 - $5000 versus under $1000), the system pays for itself in 7 - 10 years; little or no fuel required to reach the 140 ^oF required by most dishwashers, heat, water heating costs (which are 25 % of utility bills) are much lower than without the design; fossil fuel and CO₂ releases are minimized (50 tons less of CO₂ over the lifetime of the equipment) .
• Costs: The sun is an intermittent source of power (none at night or during cloudy days), so back up heaters are still needed. Over the entire lifetime, a natural gas heater is still more economical (but it releases CO₂).

• Photovoltaics are electricity-producing solar cells most people have seen on watches, calculators, satellites, remote lighting systems, and navigation buoys.
• Photovoltaics operate on the principle of excited electrons in solid semiconductor materials, which move from one material (silicon) to another (boron) in the presence of sufficient sunlight. Other cells are made of gallium arsenide.
• Panels are becoming standardized and mass produced.
• The amount of electricity produces is not great, but if the surface area covered with photovoltaics is large enough, they can produce up to 5000 kW of power.
• Utility companies are exploring the possibility of getting electricity this way "onto the grid". Most applications now are "off-the-grid".
• A new record of efficiency was recently set at 16.8 % of the sun's energy converted to electricity.

• Benefits: There are numerous benefits, they could work forever, there is no maintenance once installed, no moving parts to break, free fuel (the sun) and minimal pollution during production and no CO₂ released during use.
• Costs: It's still more costly than fossil fuels or other forms of electricity to produce. During cloudy days and at night, 12 volt car batteries must be used to power lights and other appliances. All new electronics must be purchased that run on DC not AC (many can be converted). The batteries are recharged during sunny days, but the batteries need to be replaced and are filled with lead/acid, which causes lead pollution to increase. Some pollution will result during manufacture of the cells.

• Solar thermal electric is using the sun's concentrated energy to heat fluids to very high levels, and using it to boil water and make steam. Then a steam turbine generator is used to make electricity. There are three basic designs:
• Parabolic mirrors - The Luz Solar-electric generating system in the Mojave desert is the most successful attempt to date at generating large-scale electricity for the grid (See Figure 17.8 in the text). It was successful because it combined natural gas heaters as a back up for nighttime and cloudy days. This insures uninterrupted power generation.
• Power tower - By having a tower with sun-tracking mirrors (heliostats) surrounding it, electrical energy can be generated in a manner similar to the parabolic mirror solar electric system. They have not proven to be as economically successful as the Luz system, but they do work to make electricity during the day.
• Solar pond -This is a shallow pond with a vertical salt water gradient, so that the denser saltier water stays at the bottom of the pond and does not mix with the upper layer of fresher water. Consequently, the lower salty layer gets very hot (70 - 85 ^oC or 158 - 185 ^oF). This heat can be used to make electricity (with additional heating from traditional sources), provide energy for desalination, and to supply energy space heating in buildings.

• Advantages: Free fuel, no CO₂ releases
• Disadvantages: Needs large land area; not cost effective yet. But Luz was close to breaking the fossil fuel low-cost barrier.

• The southwestern USA has the best solar potential, with over 26,000 kJ/m² solar energy hitting the Earth each year (See Figure 17.9 in text)

• Ocean thermal relies on a temperature difference between surface waters (28 ^oC , 82 ^oF) and bottom waters (1 -3 ^oC, 35-38 ^oF) to generate heat or cause the expansion of ammonia gas that can turn a generator and make electricity. This energy source is largely in the experimental stage, so cost estimates are very high.

• In a hydrogen fuel cell, hydrogen gas is allowed to oxidize, forming water and releasing energy. So much energy is released that hydrogen gas can be explosive. In most applications, this is avoided by using an electrolyte solution in which to mix the gases; the result is an electric current that can run an electric motor.

• Advantages: It is non-polluting; water is the only waste product; it can be used like a battery to store electricity made form any source, including photovoltaics and other solar sources. The electricity is run through water, producing hydrogen gas which is stored for later use. Can be used to power electric vehicles (see Figure 17.10 in text).
• Disadvantages: It is dangerous to have hydrogen gas around, so safe storage is a major hurdle.
• Cost will be $3 - $5 per gallon, similar to fossil fuels (taxes on gasoline need to be raised).

• Dams are created to store a head of water (potential energy), which is released through water turbines, which turn generators to make electricity. (See Figure 17.11 in text). A micro-hydropower facility is a small scale hydroelectric facility that can make a significant contribution to the electric needs of a small building or be sold "on the grid" to an electric cooperative.

• Similar to hydroelectric power, a head of water is created after the tide has entered an estuary or bay. The dam flood gates are then closed, and as the tide recedes, a water elevation difference occurs, head is generated, and water is released over turbines to make electricity.

• Advantages: It does not pollute or produce CO₂. It is cost-competitive with fossil fuels.
• Disadvantages: The dams and reservoirs cause the deaths of many young anadromous fishes, especially salmon migrating downstream after hatching. These young smolts are susceptible to predators and nitrogen gas bubble disease. Also humans and wildlife are displaced when the river is flooded. Most of the places where a dam could be built in the USA already have hydroelectric dams. Dams also trap sediments, starving beaches of a sediment source and filling up the reservoir basin in the process. Tidal power can only work in a few estuaries where there is a sufficiently large change in tidal height.

• Using wind energy to turn large propeller-like windmills and turbines. (See Figure 17.13 in text)
• There is great potential for wind energy and it has been installed in many places; 82 % of the capacity is in just three windfarms in California. (See Figure 17.14 in text)

• Advantages: Cost competitive now with fossil fuels; no CO₂ or pollution during operation.
• Disadvantages: It can only be successful in certain constantly windy areas (although there are lots of such areas). Windmills kill migrating birds, including some endangered species like falcons, hawks, and bald eagles; vibrations and noise are produced; wind turbines can interfere with radio and TV reception. They may also cause aesthetic values for an area to decline.

• Biomass fuels are those fuels that can be grown using the sun's energy to produce combustible products. Any organic material is potentially useable as fuel.
• For example, sugar cane can be grown and the sugar fermented to make ethanol. This "biofuel" can power automobiles. Other biofuels include methanol, methane or biocrude.
• Other biomass fuels include wood, wood pulp, peat, kelp, manure, and various kinds of agricultural wastes.
• Municipal solid waste can be burned for energy as well.

• Advantages: Using waste products like solid waste, manure, and agricultural wastes is efficient. No net increase in CO₂ should occur, because plants remove CO₂ from the atmosphere when growing. Later, when they are burned, the CO₂ is replaced. If we used biomass instead of fossil fuels, CO₂ levels would decline.
• Disadvantages: Low net energy yield (it takes a lot of energy to grow crops and then ferment them for biofuels); produces CO₂, although no net increase of CO₂ should occur.

• That would be wind or geothermal, because they are competitive now. Solar thermal is promising as well, but it is currently more costly than fossil fuels.

Ecology In Your Backyard

• Can you make use of more alternative energy in your home or lifestyle? For example, try to purchase solar-powered electric devices whenever you can (calculators, watches, lighting for the outside of your home, personal digital assistants, etc.). The price is usually a little higher than a similar battery-powered product, but you will save money on battery purchases in the long run and not create a toxic waster problem when you dispose of the batteries after they are exhausted.
• Look for the USEPA "Energy Star" label to find the most energy efficient product when you buy anything that consumes electricity or fossil fuels.
• When you design or purchase a new home, do you consider the energy savings that can be obtained by using passive solar design? That is, will your new home save energy by having the glazing of the home facing south (in the northern hemisphere) to take advantage of the sun's (free) energy? You will need to have overhangs or awnings installed to cut down on the summer sun (high angle), but during the winter the sun will warm your home.
• Can you modify you existing home to include more solar power, including adding an after market solar hot water heater or photovoltaic equipment? These devices are typically more expensive in the short run than their fossil fuel equivalents, but in the long-term (more than 8 - 10 years) they are cost competitive or less expensive than fossil fuels. You won't produce nearly the same amount of pollution, however, and CO₂ emissions are dramatically reduced. This helps prevent global warming.
• Purchase a solar-heated camp shower or water bag (a SunshowerÔ or similar product, available at most outdoor stores or in the camping section of many discount department stores) and use it the next time you go sailing, to the beach, or camping. The Sunshower is a simple design: it consists of a plastic bag with a clear side and a black side, a port for filling it, and a tube with a low-flow shower head. The water you put in the bag (about 5 gallons) will be very warm (110 ^oF) within a few hours. It's great for washing off sandy feet at the beach or providing hot water for washing while camping. I use mine all the time when camping.
• Please respond to these questions or send your thoughtful examples and comments to:

Hardcopy Links In The Library

• Keisling, B. 1983. The Homeowner's Handbook of Solar Water Heating Systems, Rodale Press, 1983
• Rosenbaum, M. 1991. Solar hot water for the 90's. Solar Today, September/October 1991, 5(5): p. 20.
• Sklar, S. and Sheinkopf, K. 1991. Consumer Guide to Solar Energy, Bonus Books, Inc., 160 East Illinois Street, Chicago, IL 60611, 1991.
• Solar Industry Journal, Solar Energy Industries Association, 122 C Street, NW, 4th Floor, Washington, DC 20001. Solar Industry Journal has information on commercializing new technologies, case studies of commercially available technologies, and articles on government policies and regulations that affect renewable-energy businesses.
• Solar Today, 2400 Central Avenue, Unit G-1, Boulder, CO, 80301. (303) 443-3130. Solar Today covers all the solar technologies, both mature and emerging, in a general-interest format.

Ecolinks On The Web

• http://www.nrel.gov/ - The U.S. Department of Energy's National Renewable Energy Laboratory Website. Visit this one first. This site is fantastic! Start with "Clean energy basics" and explore from there. You can find links here explaining how photovoltaics work, how to select a home solar hot water heater, how renewable energy can provide for transportation (electric, propane, and transit on demand), how wind energy and solar thermal electric energy can help our country meet its energy needs. This site demonstrates the high level of sophistication of renewable sources of energy that can take the place of fossil fuels right now. There are some outstanding photographic images of solar and renewable energy technologies that you can search and download.

• http://www.fsec.ucf.edu/ - Florida Solar Energy Center. Another great website about solar and renewable energy sources. Check out the alternative fuels for transportation links and the photovoltaic links (both are excellent) and the Space Coast Clean Cities program link: http://www.fsec.ucf.edu/~fsccities/index.htp

• http://www.epa.gov/appdstar/homes/ - EPA's Energy Star Homes Program. Want to buy an energy efficient solar home? Here's how you can do it! ENERGY STAR Homes use at least 30% less energy than required by the national Model Energy Code while maintaining or improving indoor air quality. Are you a builder? Submit you plans to the EPA and get an energy star rating.

• http://sel.me.wisc.edu/ - The University of Wisconsin-Madison College of Engineering's Solar Energy Lab (SEL). This is the oldest solar energy research lab in the country. They accept graduate students interested in solar energy engineering and design.

• http://solstice.crest.org/ - Solstice is the Internet information service of the Center for Renewable Energy and Sustainable Technology (CREST), and is your site for Sustainable Energy and Development Information. An excellent source of information about renewable energy, solar energy, and solar hot water heating systems.

• http://eande.lbl.gov/CBS/VH/vh.html - The Home Energy Saver (US EPA Sponsored). The information and interactive tools you'll find here can help you figure out how to save hundreds of dollars on your energy bill, and prevent pollution too. This site is still being developed, but it provided some excellent information about how you can save energy in different regions of the USA. There are rating lists of energy efficient appliances and heat pumps. There is an interactive energy audit (you input data specific to your home) that tells you what your energy bill should be and could be if you made all the improvements that they suggest. A very interesting site for the homeowner (or future homeowner) who wants to save money and energy.

• http://gem.crest.org/ - Global Energy Marketplace. This research-oriented database of energy efficiency and renewable energy information has been sponsored by the US Environmental Protection Agency and created by CREST to promote a more sustainable energy future and mitigate global climate change that results from energy use.

• http://www.sandia.gov/Renewable_Energy/renewable.html - Sandia National Labs Renewable Energy Web Page. Look here for information about research into renewable energy technologies, including solar thermal, geothermal, wind and photovoltaics. Great images of The National Solar Thermal Test Facility (NSTTF), with the Central Receiver Test facility, better known as the power tower, which is an 8 Megawatt solar-thermo-electric generating facility. This technology is expected to be commercially competitive with other energy sources. Also, good photos of a 34-meter wind turbine.

• http://www.demon.co.uk/geosci/igahome.html - International Geothermal Association. An information- filled website about geothermal technologies around the world. Pictures and descriptions of the world's geothermal electric plants.

• Note: If any of these links are not working, please see if alternative links are available at the Ecolink Update Site.

Ecotest Online

1. Each day, more solar energy hits the surface of the Earth than the entire human population of Earth could use in ____________________.

a. 15 days

b. 27 weeks

c. 27 years

d. 10 weeks

2. Which of the following renewable fuels releases CO₂ into the atmosphere in the process of making useable energy?

a. Passive solar

b. Photovoltaics

c. Hydropower

d. Wind power

e. Biomass fuels

3. It has been said that all we are doing when making electricity is "boiling hot water". For which of these renewable energy sources is this not true?

a. Solar -thermal

b. Photovoltaics

c. Geothermal electric

d. Biomass fuels

4. Why was the Luz International Company's solar design different?

a. They used a tower power to generate electricity

b. They used a natural gas heater to augment the solar energy on cloudy days and at night for a continuous output

c. The used passive solar design throughout

d. Photovoltacic pumps were used to pump the hot oil through the tubes

5. The solar energy potential of the ____________________ United States is the best for large scale solar energy.

a. Northeastern

b. Northwestern

c. Southeastern

d. Southwestern

6. A temperature difference between surface and bottom water can be used to pump ammonia down and allow it to expand rapidly as a gas. This expanding gas drives a turbine and makes electricity in a process known as _________________________.

a. solar pond thermal electric

b. hydrogen fuel cells

c. tidal power

d. ocean thermal conversion

7. Which of these is not a disadvantage of hydropower?
a. Dams cause anadromous fish deaths

b. River basin is flooded, displacing wildlife

c. The vibrations of the turbines produce radio and TV interference

d. Sedimentation is filling in behind the dams.

8. If both release CO₂, why is biomass fuel preferred by environmentalists over fossil fuel?

a. It reduces the build up of organic waste products

b. There is no net increase in CO2 in biomass

c. Biomass fuels can be grown in areas unsuitable for human food production

d. Biofuels are cleaner burning than all fossil fuels except natural gas

e. All of these are correct

9. What is a major disadvantage of wind power?

a. It kills endangered birds

b. The windmills produce excess CO2

c. The equipment is unreliable

d. Not cost competitive with fossil fuels.

10. _________________ is the type of design in which the building's design is planned in advance to optimize free solar energy to be used as heat.

a. Indirect solar

b. Direct solar

c. Active solar

d. Passive solar

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