Energy from the sun drives nearly all biological processes on the earth. It powers food webs through photosynthetic plants, which can convert solar radiation to food in the form of sugar. We depend on the sun for light, heat, and everything we eat. Can we also use the sun’s enormous power to provide us with a source of renewable electricity?
There are two methods of producing solar power, both of which work to convert sunlight into electricity. The first is an indirect method called concentrated solar power, or CSP. CSP uses mirrors or lenses to concentrate a large area of sun into a smaller beam, which is then converted to heat. In its simplest form, think about using a magnifying glass to focus an intense beam of light on a dried leaf. The glass bends the light and concentrates the beam onto a focal point. Depending on how strong the lens is, the leaf begins to smolder. This is the idea behind CSP; to concentrate and intensify incoming sunlight into a large amount of heat, which can then be used to drive a heat engine connected to an electrical power generator.
The second way to produce electricity from sunlight is through the use of photovoltaics (PV). This is a direct method of electricity generation. You’re probably more familiar with photovoltaics than you think: solar panels are made up of photovoltaic cells (also called solar cells), and solar-powered calculators operate with the help of very small photovoltaic cells. A photovoltaic cell works because of the materials it is made of, most commonly silicon. These special materials are known as semiconductors, and have a property called the photoelectric effect, meaning they are able to absorb photons (tiny packets of light energy) from the sun and release electrons. The free electrons can then be captured in the form of an electric current. Each individual cell produces only a small amount of electricity, so for more power, cells are connected electrically to make a module. Many modules, in turn, can be wired together to produce an array, capable of generating much more electricity than the cells or modules alone.
The possibility of harnessing the sun’s power first began to be explored in the late 1800s, driven by fear that coal stores would soon run out. Growth of solar technology was slow, however, as coal and petroleum continued to dominate the energy market with their availability and low cost. After the oil embargo and energy crisis in the 1970s, interest in solar power was rekindled, and both methods of production (CSP and PV) began to expand. Today, solar power provides approximately 0.5% of the world’s annual electricity, and that number increases every year.
So how do concentrated solar power and photovoltaic systems compare? In the 1980s, CSP was favored over PV systems due to a relatively low cost. In recent years, the economics of solar power have turned around as mass production of PV panels has driven installation prices down. Other factors have also worked in favor of PV systems. Photovoltaics are capable of being deployed almost anywhere, whereas CSP systems require high levels of sunlight (limiting geographical distribution), access to water, and a generally larger scale of production. CSP is technically more complicated, as well, since the increased number of steps to a finished product (concentrating lens, engine, generator) provide multiple challenges. The one major advantage of CSP is the ability to store solar energy for longer periods, enabling more continuous electricity production.
Although solar power technology has come a long way since its origins, some issues remain. Global distribution depends on reliable storage and distribution methods (and price of materials), but if these limitations are overcome, solar power could change the face of energy consumption. Sunlight, like wind, costs nothing, and makes solar power a cheap, clean, and renewable source of power.