Renewable Energey: Solar

The sun is the primary energy source of the earth. All renewable energies such as wind, wave, hydroelectricity, biomass, as well as the nonrenewable fossil fuels are all secondary solar resources. The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850 ZJ (10^21) per year, or current 8000 times of world energy consumption. Photosynthesis captures less than 1/1000 of that energy in biomass.

Free and abundant and omnipresent, however, this solar energy must be harnessed and converted into other form, such as electricity and heat to do useful work.
Three main solar technologies are photovoltaic (PV), Concentrating Solar Power (CSP), and Solar Heating and Lighting (SHL).

CSP is used in building solar power plant. Solana, the largest solar power plant, with a 280 megawatts capability on “concentrating solar power” technology, will be online in 2011 at Arizona. It occupies 1900 acres, using square meter to light a 40 watt light bulb (more accurately, 36.4 watt). To cover all electricity use in America, it takes 27000 square km or the size of Maine. A kind reminder: Arizona is the sunny part.

PV is the technology for the commonly known solar panels. It has both industrial and residential applications. The “Rote Jahne,” the thin-film solar power plant in Germany, has a output capacity of 6 megawatts on 16.5 acres.

A home solar system includes solar panels, a battery (if off-grid) or an inverter (on-grid). A 1 kWp (watt peak, power measure of the panel under standard conditions) generates 1-2 kWh per year of energy depending on the sunniness. It cost around $10000 and the return period is around 20 years.

Today PV can do 20-35 cents/kWh and CSP 12-15 cents/kWh, both targeting at 10 cents/kWh in 2020. The retail price is about 10 cents to residential, 6 cents to industrials.