A Germany research organization has developed reference cells that will help to reduce the cost of using solar photovoltaic power.
FREIBURG, Germany, DE, 2001-04-05 <SolarAccess.com> The Fraunhofer Institute for Solar Energy Systems (ISE) offers reference cells and measurement technology in an electronic shop for a broad range of applications. The unit can accurately predict the amount of electricity that will be generated by a PV system, thereby allowing manufacturers and designers of PV systems to minimize costs by eliminating the need for expensive safety margins. Germany introduced a law last April that pays 99 Pfennig for every kilowatt-hour sold to the grid from renewable energy generators. The law has prompted a boom for photovoltaics in the country, says the Institute’s calibration laboratory. CalLab says competition has increased between PV suppliers to reduce costs, and it has discovered ways to help. The lab found that only one of 25 systems from various PV manufacturers that it monitored actually supplied the amount of electricity it had specified, while the remainder were to 20 percent below spec. The heavy fines imposed for breach of contract under the government law has forced system planners to design extra capacity, but a 20 percent cushion can cost DM 20,000 in the case of a 10 kW system. CalLab has developed calibrated reference cells to monitor the efficiency of PV modules during production, which it says can track the specified performance of the module as it is produced. The objective is to allow system planners to avoid additional capacity. The reference cells have been measured by ISE CalLab and serve as radiation sensors, or a form of yardstick for the balance of production. During calibration, the electrical current from a reference cell is related to solar radiation, which is difficult to measure, to determine the precise performance of PV cells or modules. ISE CalLab, the calibration laboratory at Fraunhofer ISE, was formed in 1986 and is one of three PV measurement labs. It works with the Physical-Technical Federal Office in Braunschweig and the Technical Monitoring Association in Rhineland, both of which have their reference cells calibrated by CalLab. CalLab has four solar simulators, two monochromators and an outdoor test stand with a solartracker. The lab can measure anything that converts light to electricity by the photovoltaic process, and it is involved with dye-sensitised solar cells, thin-film PV or tandem cells for optical concentration. While the cell is illuminated with a solar simulator, its current-voltage characteristic is recorded to determine its spectral response, which is needed to correct the measurement with the solar simulator to correspond to the internationally defined standard conditions. Sunlight is comprised of many colours and different cells react differently to various colours, and simulators are not able to reproduce the standard spectrum exactly. A calibrated cell claims accuracy of within 2 percent of performance output.