the United States, and Spain are aggressive wind developers and presently lead the world in total installed power capacity, each with fifteen thousand megawatts or more (a typical coal-fired power plant is five hundred to a thousand megawatts; a thousand megawatts might power one million homes). India and China are close behind with six to eight thousand megawatts. Canada, Denmark, Italy, Japan, the Netherlands, Portugal, and the United Kingdom all have installed capacities of one thousand megawatts or more. Altogether, at least forty countries worldwide are now developing wind farms,153 and all of these numbers are growing quickly.
The reasons for this rapid growth are many. To start, wind is free. Wind turbines are relatively cheap, consume no fuel or water, emit no greenhouse gases, and, aside from the permitting process, can be installed quickly. Because wind farms are comprised of many turbines, it is possible to start small, then grow capacity over time. At present, wind power is one of the cheapest renewable energies, averaging around $0.05 per kilowatt- hour,154 putting it closest to conventional fossil-fuel electricity prices ($0.02-$0.03/ kWh). The main concerns with wind power are bird and bat deaths, conflicts over land use, and aesthetics. Most wind farms today are on land, but offshore installations are also gathering investors’ interest. While it’s harder to install turbines and grid connections in the ocean, offshore winds are stronger, so they produce more electricity, and there is less competition for the space. In 2010 the Obama administration approved the United States’ first offshore wind farm near Cape Cod, Massachusetts.
The wind power industry has a thirty-year legacy and is now reaping double-digit growth. Depending on the choices we make,155 our global wind power capacity is expected to grow anywhere from tenfold to over fiftyfold by the year 2050, cornering 2%-17% of the world’s electricity market.
That leaves solar energy. The Sun, in principle, offers us more inexhaustible clean power than we could ever possibly use. One hour of sunlight striking our planet contains more energy than all of humanity uses in a year. It absolutely dwarfs all other possible energy sources, even if we add up all of the world’s coal, oil, natural gas, uranium, hydropower, wind, and photosynthesis combined. It is nonpolluting, carbonless, and free. Panels of solar photovoltaic cells have been powering satellites for over half a century, and we see their familiar shape all around us—encrusted on streetlights, garden lamps, and pocket calculators. Why, then, is our total world production of solar photovoltaic electricity equivalent to that of just one very large coal-fired power plant?
For all its largesse, sunlight has a fundamental problem. Although vast in total, its energy density is low. Unlike a power-packed coal nugget, sunlight is diffuse, low-grade stuff. Getting significant power out of it requires covering a large area, either with mirrors to focus the Sun’s rays, or with panels of photovoltaic (PV) cells that directly convert solar photons into electricity. Both are expensive (especially photovoltaics) and efficiencies are low.
Theoretically,156 PV cells can convert sunlight to electricity with efficiencies as high as 31%, but most are considerably lower, around 10%-20%. If that sounds pathetic to you, then consider that the efficiency of plant photosynthesis, after three billion years of evolution, is just 1%. Nonetheless, a typical silicon-based solar photovoltaic panel, with 10% efficiency and a manufacturing cost of around three hundred dollars per square meter, produces electricity that costs around thirty-five cents per kilowatt-hour. That’s seven to seventeen times greater than coal-fired electricity. So sunlight, despite being far and away the world’s biggest energy source, is also the most expensive.
Finding a cheaper way to hijack sunlight is thus the single greatest barrier to the widespread use of solar power. Most photovoltaic panels are made of sliced wafers of extremely pure silicon that are highly polished, fitted with electrical contacts, sealed into a module, and encased in transparent glass. They are heavy, cumbersome, and expensive to make, and become even more costly when the price of silicon goes up. As ardent renewable-energy enthusiast Chris Goodall points out, installing large solar panels on the roof of his Oxford home costs about ?12,000, yet the total market value of the electricity they produce after four years is just ?300. While it makes sense for governments to subsidize such investments initially, eventually the technology must become competitive with fossil fuels in order to take hold.
That means the cost of PVs must fall to about one-fifth of what they are today, a huge challenge. It’s a materials-science problem and there is much exciting research under way, particularly in the area of “thin-film” photovoltaics that abandon heavy silicon panels in favor of exotic coatings of semiconductors like cadmium telluride, or even carbon nanotubes.157 The conversion efficiencies of these materials would probably be lower than that of traditional silicon PV cells (8%-12%), but if they could be manufactured cheaply—even printed as shrink-wrap for buildings, for example—the cost of PV electricity would tumble and we could start enshrouding the planet in electricity-making paints and films.
At the moment, photovoltaic paint lies in the sweat-soaked dreams of nanotech graduate students. A safer bet for 2050 lies in the expansion of so-called concentrated solar thermal power, or CSP, technology. Like wind power it has been around for years, and is already providing economically viable electricity from a handful of pilot installations. Unlike photovoltaics, CSP does not attempt to convert sunlight into electrons directly. Instead, in much the way that kids fry ants with a magnifying glass, CSP relies on mirrors or lenses to focus the Sun’s rays, heating a fluid like water, mineral oil, or molten salt inside a metal tube or tank. The fluid boils or expands, forcing a mechanical turbine or Stirling engine to move, making electricity. Sound familiar? It’s just plain old-fashioned electricity generation158 driven by a new source. And because CSP plants work best on hot, sunny days—a time when millions of air conditioners drive up the price of electricity—their product commands top dollar. Unlike photovoltaics, CSP requires no silicon wafers, cadmium telluride, or other fancy semiconductors, just a great many polished mirrors, the motorized steel racks to mount them on, and a traditional power plant.
To make the most sense, CSP plants should be located in deserts. Current operations include several in Spain and the U.S. states of California, Nevada, and Arizona. Seventy miles southwest of Phoenix a billion-dollar project is under way to spread mirrors across three square miles of desert, enough to power seventy thousand homes.159 Other projects are operating or planned in Algeria, Egypt, Morocco, Jordan, and Libya.160 In terms of sheer untapped potential, these North African countries are the next Saudi Arabia-in-waiting for solar energy (as is Saudi Arabia). The same goes for Australia, much of the Middle East, the southwestern United States, and the Altiplano Plateau and eastern side of Brazil in South America.
So why, then, haven’t we plastered CSP plants all over our deserts? One reason is that because there are still so few built, the necessary mirrors and other equipment are still specialty products and thus quite expensive. These costs are expected to fall as the industry grows, but at the moment, with electricity prices of at least twelve cents per kilowatt-hour, CSP is still less economical than conventional power plants. Another challenge is the lack of high-voltage transmission lines connecting hot, empty deserts to the places where people actually live. All the electricity production in the world is worthless if it can’t be delivered to customers. This entails running hundreds of miles of high-voltage direct-current (HVDC) power cable, which suffers lower transmission losses than traditional alternating current (AC) transmission lines. HVDC is already used to transmit electricity over great distances in Africa, China, the United States, Canada, and Brazil but, like all major infrastructure, is quite expensive. An undersea HVDC cable between Norway and the Netherlands cost about a million euros per kilometer in 2008.161 So while doable, channeling solar power from the world’s deserts to cities will require major capital investments in infrastructure.
One disadvantage that afflicts not just CSP but all forms of solar and wind energy is energy storage. Few of us marvel that a light beam appears with the simple click of a flashlight button. Yet, imagine if the flashlight were powered not by battery but by hand-crank, with no battery storage whatsoever. Use of this flashlight would require constant hand-cranking (I would simply give up and sit in the dark). Furthermore, for maximum efficiency the turning hand would have to exactly match the electricity requirement at all times: Without battery storage, any excess power generated (i.e., beyond the wattage of the bulb) is lost; any deficit causes the bulb to dim.
Scaling this problem up, we see that meeting society’s volatile electricity needs in a nonwasteful manner poses an enormous challenge. Demand fluctuates by the week, hour, and minute in response to all sorts of things, from business cycles to the commercial breaks of popular television programs. Power utilities must constantly adjust their production of electricity accordingly. Too much capacity wastes money as power plants make unused electricity; too little capacity triggers brownouts or rolling power outages.
It’s hard enough to predict fluctuations on the demand side. Solar and wind sources—because they wither or die on calm days, cloudy days, and at night—add new volatility on the supply side. In a world powered substantially from wind and solar sources, avoiding brownouts will require vast “smart grids,” meaning highly interconnected and communicative transmission networks, plenty of backup capacity from conventional power plants,162 and new ways to store excess electricity for times of deficit.
