Harvesting Sunlight- Concentrator PV Modules Richard Perez Solar concentrators work like a magnifying glass- gathering light from a large area and focusing it on a smaller area. If that small area is a PV cell, then the power output of the cell increases. In fact, focusing two square units on sunlight on a one square unit PV cell will double the output of the cell. This two times concentration is called "two suns". If you put ten suns on a PV cell, then it will produce ten times the power. Here's some info on a concentrator that does NINETY suns! Sound like the free lunch? Hardly, it's just more effective use of our best natural resource- sunlight . Concentrator PV Modules Over the years many concentrating schemes have been used on PVs- most of them hopelessly high tech. The major problem is heat. When you concentrate sunlight , in addition to the visible and near ultraviolet portions, the infrared (heat) portion also gets concentrated also. And PV cells don't like running hot. It reduces their output and shortens their lifetime. Most concentrator designs called for coolants, pumps and heat exchangers. All adding complexity and expense to the system. When at the Midwest Renewable Energy Fair, I was surprised to see concentrator PV modules that used no active cooling system. And they are affordable. The Midway Labs Concentrator PV Modules This design uses two stage optical concentration to achieve 91 suns on each PV cell. The first stage of concentration is an acrylic Fresnel lens (289 sq. cm. area) for each PV cell. The second stage of concentration is a glass lens, directly over the cell, which focuses the sunlight on a PV cell about the size of a silver dollar (0.79 inches in diameter). The PV cells used are single crystal silicon cells (made by Solarex or Astropower). The cells are heatsunk to a welded aluminum framework that hold the cells and the concentrating optics. The entire array is actively tracked via a Robbins tracker. The equatorial mount tracks the daily east/west motion of the sun and also weekly changes in the Sun's north/south direction. This Midway module, called the PowerSourceª, measures 70 inches long, by 21 inches wide, by 11 inches deep. It produces 75 Watts of power (4.7 Amperes at 16 VDC). Up to ten of these modules can be tracked by a single Robbins active tracker. The entire works mounts into the ground on steel pipes set in concrete. The economic advantage of concentration is more effective use of expensive highly refined silicon. The PowerSource module uses about 20 times LESS PV material than a conventional unconcentrated module. It also makes about 50% MORE power. The combined area of all the silicon PV cells in a single PowerSource module is about 30 square inches and it generates 75 Watts. The combined cell area in a conventional panel is about 575 square inches of expensive hyperpure silicon to produce about 50 Watts of power. Since highly refined silicon is the most expensive component in PV panels, concentrating sunlight pays off big time in lower cost per watt. Consider an average (cycling 5 to 6 kiloWatt-hours daily) home system which requires a PV array with peak power of 750 Watts. The cost of using ten PowerSource modules, and their active Robbins tracker is about $4,500. The cost of an equivalent conventional setup- tracked, but unconcentrated, 750 Watt PV array (Å15 panels) is about $5,700. While I haven't yet tried the PowerSource and compared its performance with other more conventional PV setups, I am eager to do so. Midway Labs' warranty on the PowerSource is ten years. If in fact, the PowerSource lives up to its maker's claims, then concentrating and tracking PV arrays will become less expensive than conventional arrays. Access Richard Perez. C/O Home Power, POB 130, Hornbrook, CA 96044 ¥ 916- 475-3179. The PowerSourceª is made by: Midway Labs, 2255 East 75th St., Chicago, IL 60649 ¥ 312-933-2027.