For solar photovoltaic power, the growing consensus among experts is that small really is beautiful. From Southern California to Sydney, Australia, engineers have for years favored modest, distributed installations of perhaps 1 to 1000 kilowatts, affixed to the roofs of the homes or office buildings that receive the sun-generated electricity.
The alternative, "central-station" approach concentrates more generation into fewer, more remote, and much larger installations. It never caught on in most of the developed world for several reasons, chief among them the 10-percent loss of power incurred when distributing solar power on the grid. Furthermore, no one really wants to look at vast agglomerations of solar panels sprawled over dozens of hectares of picturesque countryside.
These facts have not deterred the owners of one of the world's newest and largest photovoltaic (PV) power plants, the Bavarian Solarpark. With 57 600 solar panels covering a total of 25 hectares of farmland, the facility is nearing completion and already starting to soak up the wan southern German sunlight.
Operating as a single financial entity, the 10-megawatt-peak station actually consists of three collector installations located within a 50-kilometer radius: 6.3 MW at Mühlhausen, 1.9 MW at Günching, and another 1.9 MW at Minihof. The solar farms feed into southern Germany's electric grid just as a gas-fired, coal, or nuclear plant would, except that the PV plant's dc power must be converted by inverters into ac power, at a loss of about 5 percent of the power the plant generates. Another 5 percent is lost as the current travels through power lines and into homes and businesses. During peak day hours, solar power displaces power from conventional plants with enough juice for 5000 homes consuming 2 kW each.
PowerLight Corp. of Berkeley, Calif., in partnership with Deutsche Structured Finance in Frankfurt and K&S Consulting Group of Regensburg, Germany, installed the PV system for about ¤45 million (about US $58 million). Mounted on a single-axis tracking system, the panels follow the sun, increasing their exposure to solar radiation by 30 percent in the course of a day compared with static horizontal panels. That's crucial in a region where the sun shines only about 1500 hours on average per year, providing only 60 percent of the sunlight that is available in places like Southern California.
If building a central station PV plant in Bavaria—a region that records on average 180 days with rain and 179 days with fog per year—strikes you as a costly indulgence, you're not alone.
"Bavaria is about the maddest place you could put a photovoltaic power plant," says Vaclav Smil, distinguished professor at the University of Manitoba, in Canada, and author of Energy at the Crossroads: Global Perspectives and Uncertainties (MIT Press, 2003). "You've got cloudy conditions through the year," observes Smil, who grew up in the same gloomy climate across the border in what is now the Czech Republic. "In the fall and in the spring, there are several days in a row where you have no direct solar radiation at all, which means your solar-cell power output goes down to almost nothing."
The German government, a coalition of Social Democrats and Greens, has decreed that the country will wean itself completely from nuclear power by 2020. To do so, it must replace all that nuclear capacity—about 30 percent of Germany's total of more than 500 terawatthours per year—and the coalition has pledged that a substantial amount of it will come from renewables. Germany now gets about 10 percent of its electricity from renewables, and the plan is to increase that share to 20 percent by 2010.
The German Renewable Energy Law, adopted in 2000, compels utilities to buy power from grid-connected renewable sources, such as hydro, wind, and PV, at guaranteed prices for 20 years. The so-called feed-in tariff, which is the rate that the utilities must pay, is ¤0.457 per kilowatt-hour for central station PV in 2004—more than any other renewable source, including wind, which reaps just ¤0.09/kWh. Utilities in turn sell Solarpark's power to the consumer at about ¤0.16/kWh, from which the utilities also must recover their costs for generation, transmission, distribution, and administration. The shortfall of about ¤0.30/kWh gets totaled up across all utilities and is then shared by all German power customers in the form of higher energy bills.
Goal: Partially replace Germany's nuclear and fossil fuel power plants with homegrown solar PV plants
Why it's a loser: The losses due to transmission of central station solar power negate the benefits enjoyed by users of on-site solar generation; plus, it rains every other day in Bavaria
Organizations: PowerLight Corp., Berkeley, Calif.; Deutsche Structured Finance, Frankfurt; and K&S Consulting Group, Regensburg, Germany
Center of activity: Bavaria, Germany
Number of people on the project: 255
Budget: ¤45 million (about US $58 million)