Flat-plate PV collectors contain an array of individual cells, connected in a series/parallel circuit and encapsulated within a sandwich structure, the front of which is glass or plastic. Unlike thermal collectors, the backside of the collectors is not insulated because for best performance, they need to be cooled by the atmosphere. If this energy loss can be eliminated in new designs, the conversion efficiency could be much improved. Flat PV collectors can also track the sun by being tilted about their axis.
Today the energy payback period of PV collectors for thin-film PV systems (the energy required for manufacturing expressed as the time required to collect the equivalent amount of solar energy to the energy needed to produce and assemble the particular PV collector and its support structure) is three years; four years for multi-crystalline silicon PV systems. As manufacturing techniques improve, these payback periods are likely to drop to one to two years. With a minimum life span of 25 years, the ratio of energy obtained to energy invested is 10:1 for solar energy. This compares favorably to oil shale for example, which has a ratio of only 4:1.
The carbon dioxide emission payback period (the time required to compensate for the carbon dioxide emission that occurs during the manufacturing of the collectors if they are manufactured using fossil-fuel-generated energy—400 kg CO2 per sq. m of collector—by the emission avoidance gained by using PV collector-generated energy) is three years. Because solar collectors have already operated for over 25 years and their life span is likely to increase, this ratio is also about 10:1.
Who Are the Solar Power Leaders?The nations with the largest installed capacity of solar collectors are China (36 gW [gigawatts]), Japan (9 gW), Turkey (7 gW), Germany (3.5 gW), Greece (3.5 gW), U.S. 1.5 gW). On a per capita basis, the leading users of solar energy are Cyprus, Israel and Greece. According to the International Energy Agency, 40 % of all the PV installations today are in Germany, and 13% are in the U.S. The magazine Solar Generationreported in its September 2006 issue that the total solar energy generation commitment in the U.S. by 2020 is 7.3 gW. Of this, California is committed to 3 gW and New Jersey to 1.5 gW.
|About the Author|
Béla Lipták, PE, former adjunct professor at Yale University, is also editor of the Instrument Engineer’s Handbook, 4th Ed., and recipient of the ISA’s Life Achievement Award and a member of Control’s Automation Hall of Fame. He can be reached at email@example.com.