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How do solar cells work?

Francisco CastroMay 13, 20193050

You’ve seen them on top of homes, calculators, and even in space, on the side of satellites and on the International Space Station. 

The basic unit of any solar power installation is the photovoltaic (PV) cell. These cells convert sunlight into electricity at the atomic level through a process called the photovoltaic effect. 

According to NASA, it was French physicist Edmun Bequerel who in 1839 first noted the photoelectric effect when he found that certain materials produced small amounts of electric current when exposed to light. But over 100 years, scientists only managed to get 1% of energy from these cells while they used different materials - selenium, copper, gold. It wasn’t until 1941 that Russell Ohl used silicon. 

The first actual solar cell was built by Bell Laboratories in 1954, a mere curiosity given its expensive cost that made it prohibitive for widespread use. Still, their efficiency was a mere 4%. 

Composition

A photovoltaic cell is fabricated out of silicon, which acts as a semi-conductor, meaning that it shares some of the properties of metals and some of those of an electrical insulation. 

Sunlight is composed of minuscule particles called photons, which radiate from the sun.

When photons hit the silicon atoms of the solar cell, they loosen up electrons, which are trapped on the front by an anti-reflective coating, which prevents the loss of light. 

On the back of the cells is also a thin semi-conductor layer specially treated to form an electric field, positive on one side and negative on the other. The light trapped on top is transmitted to the energy-conversion layers below. When sunlight falls on the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can generate electricity.

Each solar cell is only a few square inches in size and protected from the environment by a thin coating of glass or transparent plastic. Given its size, each cell is only able to generate about two watts of electric power. To boost their output, solar cells can be arranged into groupings connected to each other and mounted in a support structure or frame to form the solar panels. These modules are designed to supply electricity at a certain voltage. 

For residential solar installations, panels are usually 60 or 72-cell panels.

The panels themselves are also arranged into groups to form a solar array - the layout of modules that go atop a home roof or on ground-mounted structures. The more modules in the array, the higher quantity of electricity they produce. However, this power is in Direct Current (DC) and must be converted into Alternating Current (AC) before your appliances can use it. That conversion is performed by an inverter.

Even with the most purity, solar cells stand to lose some of their efficiency, in part because 1/4 of the solar energy to the Earth cannot be converted into electricity by a silicon semiconductor. Some of the energy also evaporates as heat. 

Degradation is also another issue affecting solar cells. As time passes, they will generate less and less energy, partly because of UV exposure and weather. A report from the National Renewable Energy Laboratory (NREL) states that the median degradation rate is 0.5% per year. This loss is minuscule and allow for solar panels to have lifespans of between 25-30 years, and even more.

Usefulness

As the U.S. space program took off in the 1960s, so did the use of solar cells, which began to provide power aboard spacecraft. In the 1970s, photovoltaic technology gained recognition as a source of power for non-space applications as the country was gripped by an energy crisis.

By the 80s, the efficiency of solar cells was reaching 20%. The technology kept progressing through the decades and in 2000, at the International Space Station, astronauts began installing solar panels on its wings. Each wing consists of 32,800 solar cells.

Helped by lower costs and more efficient solar cells, the solar industry has grown since then. There are now over 2 million solar installations in the U.S. Costs have gone down dramatically in the past decade. In 1956, solar panels cost an average of $300 per watt. Today, the average is between $2.67-$3.43. Most residential solar power system range in price from $11,214 - $14,406, making them affordable for most property owners. 

To find out the correct size of a solar power system for your home and what it will cost, you can input your home address and monthly electricity bill in the Hahasmart price checker. In just a few seconds, you’ll get a detailed quote that shows how much you can expect to save on your energy bill throughout the life of the solar power system. The price checker will even help you contact a reliable solar installer in your area. 

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