How in the world do solar panels work?
There is a lot of science going on behind the scenes here.
Stephen Shankland / CNET
It sounds like magic: catching solar energy and converting it into electricity to power your toaster. However, it is science, not magic. Solar panels use a strange science, the photovoltaic effect, to convert one form of energy into another. This is how solar panels harvest light and convert it into electricity.
The sun is an intense powerhouse that emits in the range of 10 decillion (that’s a 1 followed by 34 zeros) joules of energy per year. That is much. The whole planet is bathed in this flood of energy, and it’s one of the things that makes this such a pleasant place to live. It drives the weather, warms the atmosphere and makes life possible. So wouldn’t it be useful to be able to convert some of that energy into a form that we could use?
Plants do this through photosynthesis, using light to combine carbon from the atmosphere into sugar, which they metabolize to grow. And the solar panels that can be seen on more and more roofs do something similar: they convert light into electricity. You can do this because of what is known as the photovoltaic effect, which converts solar energy into electrical energy.
See how solar panels use the sun’s energy to power the appliances and other electronic devices in your home.
Colin McDonald / CNET
It works like this: when light hits an atom, it is sometimes absorbed by one of the electrons around the atom, increasing the energy of the electron. With some materials (like some metals and silicon) this extra energy is enough to loosen the electron from the atom and move it within the material’s crystal structure. If you create two layers of crystals, you can take advantage of this.
A layer called an N-type material is contaminated with a chemical (scientists call this doping), which means that it contains a lot of electrons, so it has electrons left over. The other layer is contaminated with a different material that makes it want to accept more electrons, called a P-type material. These electrons cannot jump over the junction of these two materials (called the NP junction) so easily, so there is a voltage difference between the two layers. If you then connect a circuit on each side of this panel, that voltage can be used to power a device or charge a battery.
Each solar cell generates only a small voltage, typically around 0.5 V. The amount of current generated depends on the size of the cell. If you connect several cells together, this voltage can be increased. So if you cover your roof with solar panels wired together, you can harvest enough electricity to power most of the house.
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Solar panels also produce direct current (DC) instead of the alternating (AC) current that your utility company supplies. This means that the energy from a solar panel has to be converted before it can power the toaster. It also needs to be stored often: you might want to toast when the sun isn’t rising and the solar panels aren’t generating electricity in the dark.
This of course depends on how much light needs to be converted and there are other constraints on the process. The amount of energy they capture depends on the properties of the light absorbing material and the connection between the two materials. This combination only absorbs certain frequencies of light. Some modern solar panels get around this by including multiple materials and connections between them (called multijunction cells) that can absorb different frequencies of light to capture more of the available energy.
Solar panels are expensive, but prices are slowly falling
And there is the cost. Solar cells are not cheap to manufacture because they require precise growth of large crystals with very precise chemical compositions. The other parts of the system (like the controller) are also expensive because they have to handle large amounts of energy. When I put the details of my home near Boston on Google’s Project Sunroof site (which calculates the costs and benefits of installing solar panels on your roof), I estimated that I could produce about 7 kilowatts of energy by just under 490 square feet of solar panels on my roof. That, she estimated, could save me over $ 900 a year, or $ 18,000 over the 20-year life of the system.
However, the initial cost would be high: this system would cost over $ 30,000 to install. But you don’t have to buy a solar system straight away, because there are companies that, so you pay over time. In America, federal agencies are stepping in to help too – installing a solar system can get you one up to 26 percent of the cost.
However, this price is constantly falling as new ways of making solar cells are developed and new factories are being created to make solar cells. While solar power is unlikely to completely replace other types of electricity generation, we will see solar power as an increasingly important source of electricity. And all because of the strange nature of some materials that convert light into electricity.
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