Powering the Future: A Scientist's Guide to Energy Independence
Page 17
More recently, photovoltaic thin films have been developed, and some are in commercial production. (These make up almost 40% of the devices sold.) These use very small amounts of certain rare metal compounds, including cadmium telluride (a compound of cadmium and tellurium), CIGS (a chemical compound of copper, indium, gallium, and selenium), and a noncrystalline form of silicon.
At the time of this writing, some research is also exploring organic compounds that emit electricity when exposed to light, and there has been research over many years to try to take chlorophyll from green plants and use that in nonliving materials to generate electricity. But the majority of research and development of active solar energy is with inorganic photovoltaic systems.3
How much energy does solar provide now?
The amazing thing about commercially available photovoltaics is how efficient they are—how much of the energy they receive as sunlight goes out a wire as useful electricity. The record so far is 24% from crystalline silicon, and the thin films have reached 18% and 19%. Compare this to green plants that on average fix a miserly 3%.
By the end of 2007 there were many large installations, called solar energy parks. The 25 largest of these each had an electrical generating capacity of 5 megawatts or more from photovoltaic cells. Eleven of the largest installations were in Spain, ten in Germany, one each in Portugal and Japan, and only two in the United States.4 These 25 largest solar parks by themselves have a generating capacity of more than 225 megawatts, enough to provide electricity for more than 225,000 homes. Worldwide, 880 photovoltaic power plants, each with at least 200-kilowatt capacity, are in operation, with a total capacity of 955 megawatts. Most of these large-scale plants are in Germany (390), the United States (225), and Spain (130).5
Although these individual systems are impressive both visually and in their electrical generation, they are dwarfed by the largest solar thermal plants. In fact, the largest solar energy installation of any kind operating today is Solar Energy Generating Systems (SEGS) in the Mojave Desert, the same region where Solar One was built. This is actually nine individual solar thermal plants with a combined capacity of 310 megawatts. Its 400,000 mirrors occupy 1,000 acres (about 1.6 square miles).6 Operated by Florida Power & Light and Southern California Edison, its capacity is larger than the sum of the 25 largest photovoltaic installations in the world.
What contribution do these systems make to the total energy supply? In the United States, total energy generated from all sources in 2005 was 29,590 kilowatt-hours.7 (This is the standard value we are using throughout this book.) In 2008, the most recent year for which data are available, electricity generated in the U.S. totaled 4,119 billion kilowatt-hours. Solar energy provided just 0.02% (two-hundredths of a percent) of the electricity and 0.003% (three-thousandths) of the total energy from all sources. Wind provided much more: 1.34% of the electricity and 0.86% (almost 1%) of the total energy from all sources. So together, these two kinds of renewable energy provided a very small amount of the electricity and of the total energy. The situation is similar worldwide. At present, solar photovoltaic electricity provides less than 1% of the world’s electrical energy and only about 0.1% of the world’s energy.8 So the take-home lesson here is that today solar photovoltaic systems provide a very small percentage of the world’s electrical energy and therefore of the world’s total energy use.
How much energy could solar energy provide?
The short answer: a huge amount. I got interested in this several years ago when what was then the largest photovoltaic system in the world, the one in Bavaria, began operating. I made calculations, based on installed facilities—not theoretical possibilities—for a variety of sites established by PowerLight Corporation (now part of U.S. SunPower Corp.). Here I need to make a disclaimer. My son, Jonathan Botkin, is an engineer at this company and has been especially helpful in making sure that my calculations are correct. When I gave a talk about solar energy to some journalists a few years ago and mentioned this, they seemed to think I was therefore lobbying and advertising for that corporation. Although I do think this company is doing a good job, I’m not touting them, just turning to someone I trust implicitly to make sure my figures are correct.
Here are some of the calculations I made. Although the largest solar energy parks are in Spain, it wasn’t very long ago, in 2005, that the world’s largest solar energy facility started producing electricity in what would seem an unlikely place, the small city of Mühlhausen, in Germany’s Bavaria (Figure 7.5). Mühlhausen is famous for Johann Christian Bach’s life there as an organist, but although it’s a picturesque tourist destination, it probably wouldn’t go on your list of sunbathing resorts. Still, in 2005, one of the best answers to our energy crisis was right there, in farm fields where sheep grazed beneath an unusual crop: an array of rectangles mounted on long metal tubes that rotate slowly during the day, following the sun like mechanical sunflowers. Yes, this was, a few years ago, the world’s largest solar electric installation, generating 10 megawatts on 62 acres. Scaled up to just 3.5% of Germany’s land area, this kind of solar power could provide all the energy used in Germany—by cars, trucks, trains, manufacturing, everything!
Figure 7.5 The Bavaria Solarpark, in 2005 the world’s largest solar energy installation, lies within a picturesque landscape famous in history but not especially sunny. (Courtesy of SunPower Corporation)
Here are some U.S. examples. Based on already installed photovoltaic systems in San Francisco’s Bay Area, one acre covered by a photovoltaic system provides enough electricity for 379 houses.9 San Francisco covers 46 square miles and in 1990 had a population of 723,959. Figuring about three people per house, this is equivalent to 241,320 houses, and just 1,910 acres of solar collectors would be enough to provide all the domestic electricity for the residents. Thus, solar photovoltaic devices would occupy only 6.5% of the city’s land area, and if the solar collectors were on house roofs, it is quite likely that the existing roofs would provide adequate area for domestic electricity needs.
Let’s use the same basic information for Arizona, even though it actually gets a lot more sunlight than San Francisco, but just to be on the conservative side. Arizona occupies 113,642 square miles of land, or 72,730,880 acres. At the installed energy yield I have been discussing—enough to provide electricity for 379 houses per acre—the entire state could provide electric power for 27 to 28 billion houses, and at an average of 3 people per house, that’s enough for 81 billion people, or 13 times the population of the Earth. If 1% of Arizona’s land area were used for photovoltaics, enough electricity could be produced for more than 275 million houses, which is considerably more houses than exist in the United States. At an average of three people per house, this area of photovoltaics would provide electricity for 837 million people, or about 28% of the world’s population.
Other people have made similar calculations—for example, Professor Nathan Lewis of Caltech, a expert on energy supply. He writes that in 1990 the total world energy demand was 10 billion kilowatts, and that using reasonable estimates of the increase in the human population and the increase in the demand for energy, by 2050 the demand could more than double, so that 28 billion kilowatts might be required to meet all energy demands.
Professor Lewis also points out that our planet receives 120,000 billion kilowatts of energy continuously, on average, from the sun. So current world energy use by people is just two-hundredths of the total energy our planet receives from the sun.
This means that all the energy used by the world’s people in 1990 could have been provided by covering just 0.1% of Earth’s area (and just 5.5% of the United States) with photovoltaics that were just 10% efficient, and that the estimated energy demand in the year 2050 could be met by the same photovoltaics covering 0.16% of Earth’s surface, or 8.8% of the United States.10 Indeed, the total energy demand in the United States alone could be met if photovoltaics occupied 1.7% of the land. In about 20 years of collecting solar energy in this way, we would have collected a
s much energy as is contained in all known fossil-fuel reserves—and that’s assuming a conservative efficiency of 10% in transferring solar energy to electrical output.
In short, the United States could become a net exporter of energy, either in the form of electricity or in the form of a fuel made with that electrical energy, such as hydrogen or a small hydrocarbon derived from hydrogen and carbon dioxide. And even if things did not work out exactly as suggested here, and required twice as much land area, we are still talking about a small portion of the land area of a nation and of the world.
Another approach: solar energy off the grid
There is an ongoing debate between proponents of on-the-grid and off-the-grid alternative energy. On-the-grid refers to solar energy whose electricity is put directly onto the electrical grid and becomes part of a major energy system for a region and for an entire nation, and in this way contributes to the world energy supply. Off-the-grid refers to solar energy whose use is local, ranging from providing power to a single house, to individual housing developments, to small villages, or small industries.
One can make the case that the on-the-grid/off-the-grid debate goes back to the very origins of the development of electrical energy during Thomas Edison’s time. After inventing the lightbulb and helping with the invention and development of electric motors and generators, Edison promoted a direct-current system. But the problem was, direct current could not be transmitted efficiently over a long distance; there was just too much power loss. Edison lost out in the advancement of electricity when the first large hydroelectric plants were installed at Niagara Falls and the electricity was transmitted long distances as alternating current.
Later, the establishment of the Bonneville Power Administration and the Tennessee Valley Authority in the 1930s to build large hydroelectric dams enhanced and increased a regional, centralized electrical production and distribution system. It was viewed as government providing a service to all the people, but was also consistent with a large-scale, big-industrial approach to providing energy.
A different political philosophy with a different technological approach, could have taken the same money and promoted local production of electricity. But the technology wasn’t really ready for that. Only now, with the development of late-20th-century and early-21st-century wind and solar energy technologies, can this kind of intense off-the-grid electrical generation be seen as a competitive approach to energy production.
Off-the-grid solar energy for rural areas, for the poor, for single-family homeowners, and for less-developed nations
Like wind power, solar energy is useful for those who lack easy access to other forms of energy or simply prefer to be energy-independent. The potential for off-the-grid, locally generated solar energy to help people in developing nations led to the development of solar cookers, but the earliest versions did not become widely used. These early solar stoves concentrated sunlight enough to cook food, but they were unfamiliar devices, out of context for the cultures and rural societies they were supposed to help, and have been referred to as solutions in search of a problem. It would probably be more accurate to say they were a Western male engineer’s concept of a device to be used in non-Western civilizations by rural women used to cooking in traditional ways.
All that has changed rapidly. In recent years, the most famous proponent of solar cooking for developing nations is Margaret Owino, director of Solar Cookers International, East Africa, who has successfully promoted the use of these cookers in Southern Africa. More than 10,000 women in Kenya have learned how to use and promote them, and there are many testimonials about how they are helping. For example, Elizabeth Leshom, who lives in Kajiado about 50 miles south of Nairobi, has found that the solar cooker has cut her family’s use of charcoal in half and considerably reduced her use of firewood.
Solar cookers come in two major types, simple hot boxes (Figure 7.6, top) and parabolic mirrors that concentrate sunlight onto a point (Figure 7.6, bottom). Hot boxes simply heat up enough to cook food. Their advantages are that a number of pots can fit into one box and they are cheap. The least expensive of these are made of waxed cardboard cartons with foil surfaces and can heat up to 275°F. In Kenya, these have sold for the equivalent of $5.60 to $7.90. Worldwide, these are the most widely used individual solar cookers, with several hundred thousand in use in India alone.11
Figure 7.6 (Top) A hot-box solar cooker (Solar Cookers International) and (Bottom) a parabolic solar cooker, whose mirror concentrates the heat at a point. (Maarten Olthof/Vajra Foundation).
Opportunities for entrepreneurs
According to an article in the Wall Street Journal, some companies are beginning to see a market in small and inexpensive solar energy devices for the Third World, including lighting. One company, Cosmos Ignite, sells solar-powered MightyLights for US$40, about the cost of a few months’ supply of kerosene. This company came about as a project in a class at Stanford Business School, where the students were asked to develop a cheap alternative to artificial lighting for developing countries. One of the students, Matt Scott, developed a light and founded this company. In India alone, 10,000 of these have been sold.12
To give you a clear picture of the potential, here are some basic facts. In full sunlight, a square meter (think a little bigger than a square yard) receives 1,000 watts of sunlight, enough energy to light ten 100-watt lightbulbs. A silicon chip 4 inches square generates 1 watt of electricity in full sunlight at ordinary outdoor temperatures. A small photovoltaic system that generates 50 watts in full sun provides enough energy “for four or five small fluorescent bulbs, a radio, and a 15-inch black-and-white television set for up to 5 hours a day,” according to Robert Foster of the Southwest Technology Development Institute at New Mexico State University.13
In Kenya, more than 200,000 small solar-electric systems have been sold. These include basic array of photovoltaic units, a storage battery, and whatever wiring and electronic devices were necessary to make a system work.14 These have provided home lighting and power for radios, televisions, computers, and so on at a cost of a few hundred dollars for the smallest system (less than 16 watts output) to more than $800 for larger systems (more than 45 watts).15 The cost to install these systems worked out to be $15 to $18 per watt, and of course there were no monthly fuel costs. By comparison, a gasoline electrical generator cost at least $500 to install and required $64 worth of fuel per month to run. Rural Kenyans without electrical generating systems buy kerosene for lighting and dry-cell batteries to operate radios, at a cost of $5 to $10 a month. Thus, a small photovoltaic system pays for itself in two years or so. Many small companies have started up in Kenya to sell, install, and maintain these systems.
By the end of the 20th century, only 62,000 Kenyan households—less than 1% of the total in that nation—were on an electrical grid.16 A good argument can be made that in nations with economic situations similar to Kenya’s, an electrical grid is not cost-effective and is unlikely to be developed; therefore, local, off-the-grid small systems will be the major way for their citizens to have access to computers, radio, television, and other modern technology. Small solar energy systems like those described above are helping.
For example, on the Philippine Island of Mindanao, U.S. AID (Agency for International Development) has funded the installation of solar cells (and small hydropower systems) to provide electricity where it was difficult to establish an electrical grid. I was a Peace Corps volunteer on that island in the 1960s. We lived in Marawi City, the capital of Mindanao Province, on the shores of beautiful Lake Lanao. About 30 miles down the river that flowed out from that lake, at the city of Iligan, was a hydroelectric power plant at Maria Christina Falls. The city of Iligan, on the coast and right near the falls, had a good electrical supply, but Marawi City had no grid system and no electricity except for individual gasoline and diesel generators. At the university where I was teaching, there were three engines: an electrical generator, a water pump, and a refrigerator. One day all three brok
e down, reminding all of us of the benefits of an electrical power system with some redundancies.
There were telephone lines that had been constructed when the Philippines was a U.S. territory, but with the renewal of fighting between people of Mindanao and the central Philippine government, the system had fallen into disrepair, and we were told that bandits had stolen the telephone wires to sell the copper. More recently, fighting between the Mindanao Muslims and the central government also made it impossible to develop an electrical grid. As a result, the Alliance for Mindanao Off-grid Renewable Energy (AMORE) began a new program that has electrified more than 500 villages with these small local systems.17
Other definitely off-the-grid solar technologies