Solar Energy

 


Synopsis of Solar Energy

The Sun is about 900,000 miles across and is at least 10 million degrees at its center. The surface of the sun is roughly 6,000°C and its hot gases emit light that has a spectrum ranging from the ultraviolet, through the visible, into the infrared. Photovoltaic or solar cells convert solar power directly into electrical power. Light consists of discrete particle-like packets of energy called photons. Sunlight contains photons with energies that reflect the sun’s surface temperature; in energy units of electron volts. The energy density packed into the photons varies, but the visible region of the light spectrum tends to contain among the highest concentrations of energy that hits the planet.

In the past decade, solar energy has attracted significant attention from investors, policy-makers and the public generally because it is widely available, geopolitically secure and environmentally sustainable. Indeed, solar energy does not create greenhouse gases as a byproduct of generating electricity. Not surprisingly, it is widely considered among the most compelling solutions available for the world's need for clean, abundant sources of energy.

Skeptics need only consider the $7.5 billion solar-energy industry still growing at a rate of more than 30% every year to appreciate the growing popularity of solar energy in mainstream electricity markets. Still, in 2001, solar electricity provided less than 0.1% of the world's electricity. 

Several technologies have been developed to harness that energy, including concentrated solar-power systems; passive solar heating and day lighting, photovoltaic systems, solar hot water, and solar process heat and space heating and cooling. To understand the mechanics of these technologies, the best place to begin is the beginning of solar-energy technologies - photovoltaics.

Photovoltaic solar cells convert solar radiation, or sunlight, directly into electrical power. Solar cells are the basic building blocks of photovoltaic systems. PV-based solar energy has become one of the most successful energy technologies the world has ever seen, achieving cost-reductions similar to those achieved by Ford during the era of the Model-T.

There are two types of photovoltaic solar cells: crystalline silicon cells and thin-film solar cells. Crystalline silicon solar cells typically use silicon or polysilicon substrates.  Individual cells vary in size from about 1/2 inch to about 4 inches across and include additional layers placed on top of the silicon to enhance light capture.  In "thin-film" solar cells, the substrate is made of glass, metal or polymer substrates and has small deposits of gallium or semiconductor materials placed on top. The substrate may be just a few micrometers thick.  Thin film solar cells are typically less efficient than crystalline silicon solar cells.

PV Solar Panel

When sunlight strikes a solar panel, electricity is produced because sunlight releases electrons. Solar cells are frequently combined to produce a large amount of electrical energy in solar-modules and ultimately solar arrays. Solar cells with conversion efficiencies in the neighborhood of 20% were readily available at the beginning of the 21st century, with efficiencies twice as high or more achieved with experimental cells.