The sun's energy has been used since the beginning of civilization to provide power for essential human needs: cooking food, warming water, and lighting workspaces. These are examples of passive solar energy. The modern world still has a role for passive solar energy, but today's more demanding and sophisticated energy requirements can also be met by converting the sun's energy into electricity through the use of photovoltaics.

Photovoltaics convert sunlight into electricity. When sunlight hits a solar panel, it knocks electrons loose from the atoms of silicon and other materials inside the panels. These free electrons travel from one side of the solar panel to the other, creating electricity (the flow of electrons). That electrical current moves through a wire into a unit called an inverter, which turns it into the kind of current typically used in a household: AC (alternating current). Just like the electricity from the utility company, this can be used to power appliances, heating and cooling equipment, and lights. If not used immediately, the energy can be stores in a battery for later use.

Photovotaics can be small scale - on individual homes in the form of solar panels or solar tiles; or large-scale - in the form of solar plants comprised of many solar panels spread across an open field that can provide dozens of megawatts of electricity to whole communities. A typical home PV roof set-up can cost around $20,000 - expensive, but half the cost it was a decade ago. And financial incentives - from the federal and state governments and from utility companies, can help offset the upfront cost. PV panel rentals are also becoming an option in some areas.

Passive solar is a simpler way to use the sun's abundant energy - instead of creating electricity, passive solar reduces the need for electricity. Buildings can be designed to maximize the sun's ability to light and heat, limiting a reliance on electric lighting and heating and cooling systems. Solar energy can also directly heat water in a solar collector and store it in a tank for use when needed. Gravity or a pump can direct the heated water through a home's pipes.

Only about one percent of the world's electrical needs are currently provided by solar power. With the sun providing as much energy to the Earth each hour as humans consume in a day, the potential of solar power has barely begun to be tapped. Advances in technology, concern for the environment, and rising oil prices however are driving the growth of solar power. The declining cost of PV panels is making solar power more and more affordable for homeowners, and utility companies are banking on profitability from the addition of solar power options for customers. Government initiatives, such as California's Million Solar Roofs law, are also making solar power more attractive for homeowners and businesses.

Solar power is a clean, renewable resource, and once the initial investment is made, it's free. When the energy-savings and tax incentives are tallied, PV systems generally pay for themselves within about 10 years.

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