There's no doubt that skylights make for psychologically-nicer buildings, while also reducing the amount of electricity required for daytime artificial lighting. If they let in too much sunlight, however, they can actually increase the amount of electricity needed for air conditioning. California-based EnFocus is attacking the situation from two ends - its Diamond-Power panels diffuse sunlight to keep interior heat down, while also harnessing it to create electricity.

Designed for use in commercial buildings, each weatherproof panel is about the size of a regular skylight, and weighs 100 pounds (45 kg). A series of small lenses in each one focus the sunlight by 400 times, onto strips containing high-efficiency gallium arsenide photovoltaic cells. These lenses are also mounted on a dual-axis tracker, which allows them to pivot with the Sun throughout the day.

Each panel has an electrical output of 288 watts, which the company claims results in 720 kilowatt-hours of power generation annually, while also providing 1,490 kWh-worth of lighting. Additionally, each panel reportedly reduces a building's heat load by 2.1 MBTU (million BTUs) per year ... we can assume these figures are for sunny California.

All told, EnFocus states that its Diamond-Power panels can reduce a building's electrical bills by up to 50 percent, and should pay for themselves within five years. Those figures were apparently enough to impress Google, which is testing the panels at one of its Silicon Valley offices.