Solar Power

The technology that makes solar energy useful to us has taken huge leaps forward, especially in the past twenty years or so. In fact, you may be using solar technology already in pathway lights or other small applications, where a few photovoltaic (PV) cells suck up sunlight during the day and keep the lights on for you after dark.

The technology used to create this power is based on a substance that is able to convert the sun's energy to electricity. When sunlight hits specific materials, most notably silicon, it makes the electrons inside jump around. Once those electrons are herded in the same direction, they create a flow of energy, commonly known as electricity. It's like a cattle drive, only much smaller!

Solar power first came on the commercial scene in the United States on a large scale in the 1970's, when the price of oil skyrocketed-at least, according to the prices of the day. The first type of solar technology to gain popularity was mechanical solar power. In early models, a solar reflector would heat water, creating steam, which would then power a small steam engine of the day.

Engineers discovered that by using curved, or parabolic dishes, they could focus the sun's light more intensely, create more steam, and therefore make the engine work faster. More modern examples employ huge "dishes" of multiple mirrors which track the sun throughout the day. In the center of the dish is a receiver, which transmits the heat to a hydrogen-filled engine.

When the hydrogen is heated it expands and drives pistons, which in turn drives a generator and produces electricity. These types of solar power are considered mechanical solar technology, and these can be around 30% efficient.

The other type of solar technology is photovoltaic. It is only about 12 to 15% efficient, although improvements are being made almost daily. Rather than generating heat, as in the mechanical solar designs, photovoltaic generation produces energy directly.

Some promising designs have come near to or surpassed the 40% efficiency barrier. If these designs were mass produced at a reasonable cost, this level of efficiency could bring photovoltaics to a much broader cross-section of the world.

One of the strengths of solar technology, especially photovoltaics, is that it requires very little maintenance. The solar panels have no moving parts, so there is nothing to break. Many of the units installed in the 1980s and even the late 1970s are still functioning.

A technology in current use is Concentrated Photovoltaic, or CPV. This uses mirrors and curved dishes to concentrate and increase the sun's effect on the PV system. Using a concentrator, efficiencies nearing 40% have already been demonstrated.

Concentrator systems are typically large, and so are not good choices for home installation. But combine large, power-generating CPV installations with smaller rooftop or stand-alone units in homes, and the potential for decades of clean, renewable energy is clear.