Solar cells ( also called photovoltaics) absorb sunlight and convert it directly to electricity. Solar cells are very thin ( about 1/ 100th of an inch thick). Most are rectagular or circular wafers made of silicon ( sand), but some sonsist of a thin film that is mounted on glass or thin matal.
Irradiance is a measure of the sunpower available at surface of the earth and has an averages of 1000 wats per square meter(m2) with typical crystalline solar cells effetive around 14-17% that means we can only expect to generate about 140-170w per square meters of solar cells placed in full sun.
Most solar cells are used in a first generation devices based on crystalline silicon wafers.”Second generation” or thin film solar cells, used in semiconductor materials only and are few micrometers thick. The performance of a solar cell is measured in terms of its efficiency at turning light in to electricity.
The efficiency for first generation cells are around 15 percent that is about one-sixth of the light striking the cell and turns it into electricity. The efficiency for second generation products that are being manufactured today,range from three to 7 percent.
Chemistry based third generation cells close to eight percent efficiency.
SINGLE CRYSTAL SILICON:
Sliced from single crystal boules of grown silicon. These wafers/cells are cut as thin as 200 microns. Research cells are reaching nearly 24 precent efficiency. Commercial modules of single-crystal cells exceed 15 percent.
Sliced from blocks of cost silicon these wafers/cells are both less expensive to manufacture and less efficient than single e-crystall silicon cells. Research cells approach 18 percent efficiency and the commercial modules approach 14 precent efficiency.