Solar Energy

The modern age of solar power arrived in 1954 when researchers at Bell Laboratories developed a photovoltaic cell capable of converting light into electricity. This breakthrough marked a fundamental change in how power is generated. Since then, efficiencies of solar cells have improved from 6 percent to 15 percent, with experimental cells reaching efficiencies over 40 percent. Along with these increases in efficiency, prices for PV modules have fallen from $300 per watt to less than $3 per watt, making them increasingly competitive.

The Earth receives 174 petawatts of incoming solar radiation (insolation) at the upper atmosphere at any given moment. When it meets the atmosphere, 6 percent of the insolation is reflected and 16 percent is absorbed. Average atmospheric conditions (clouds, dust, pollutants) further reduce insolation traveling through the atmosphere by 20 percent due to reflection and 3 percent via absorption. These atmospheric conditions not only reduce the quantity of energy reaching the Earth's surface, but also diffuse approximately 20 percent of the incoming light and filter portions of its spectrum. After passing through the Earth's atmosphere, approximately half the insolation is in the visible electromagnetic spectrum with the other half mostly in the infrared spectrum (a small part is ultraviolet radiation).

Architecture and Urban Planning

Solar architecture controls the use of solar energy to provide comfortable temperatures, lighting and air quality. The basic elements of solar architecture are building orientation, proportion, thermal mass, and window placement. The solar architecture and design process tailors these elements to the local climate and environment.