How does solar energy work and how clean is it?

Call me a solar enthusiast, if you will. Solar is one of the easiest to perceive as an energy source; just go outside and feel it. Feel it in your skin, feel the heat, feel its power on your eyes. But, what is it and how does it work?

It all starts with the Sun, which emits an electromagnetic radiation that is filtered by our atmosphere before reaching the Earth. The sunlight that we receive is part of that radiation; and is what we convert into electricity. Solar power is an abundant renewable energy source and the technology to harness it keeps evolving. There are three main ways to harness solar energy: photovoltaics, concentrating solar power, and solar heating.

Photovoltaics (PV) use semiconducting materials to convert the energy contained in photons of light into electrical voltage and current. The semiconducting material is used to construct solar cells, which are the main component of solar panels. When photons hit the solar cells, electrons are freed; but then, they need to be herd into an electric current, which is made possible thanks to the semiconducting material. Currently, there are two types of PV solar panels used: silicon-based and thin film.

Concentrating solar power (CSP) collects and concentrates sunlight to transform it into thermal energy. This system needs a concentrator, which is the optical system that directs the beam radiation onto a receiver; and the receiver, where the radiation is absorbed and converted into some other energy form. Some CSP technologies include parabolic troughs, power towers, and solar dishes.

Solar heating systems are mainly used for water heating. Sunlight heats water or a heat-transfer fluid into a solar collector. There are active heating systems, which rely on pumps to circulate water; or passive systems, which rely on gravity.

Going forward, I am concentrating on photovoltaics because it is the one people think the most about when it comes to solar. It is the one use of solar power that produces electricity, which is used by everybody. You are using it right now to read this. You probably have been thinking about going solar on your home, using solar panels on the roof, on your car, on toys, etc.; and that is fantastic if you are thinking on reducing carbon emissions.

Photovoltaic systems use solar panels, either silicon-based or thin film, to convert sunlight into electricity. A home installation, depending on the available roof area, can use an average of 13 panels. If the power output of each panel is 300 W, then the home has a system of about 4 kW. Utility scale solar, on the other hand, is meant to generate enormous amounts of electricity; and it does so, using either photovoltaics or concentrated solar. Longyangxia Dam Solar Park in China has an impressive 850 MW capacity and consists of 4 million solar panels spread over 25 km². By February 2017, it was the largest solar farm in the world; however, with many utility scale projects on development, it will not keep its throne as the largest. India is building a 2,000 MW solar park, which will span across 52.5 km². Nevertheless, China is the world’s largest producer of solar power, as well as the world’s largest solar panel manufacturer.

No carbon emissions are associated with the generation of energy from solar panels once they are installed, but there are other factors to think about. From the material extraction for the cells to the disposal methods at the manufacturing plants, production of solar cells and solar panels can be dirty. It also depends on where the cells and panels are manufactured as some countries have more stringent regulations about hazardous materials disposal, extraction/mining techniques, greenhouse gas emissions, and labor laws than others. Additionally, as noted before, solar energy is land-intensive. Another problem with solar is that it is intermittent. It works while the sun is shining; but other energy source is required for when it is not. Although storage systems such as batteries exist to alleviate this issue, they are expensive.

Despite the energy cost of producing the panels, the clean energy produced by them far outweighs the energy required and emissions produced during manufacturing. Having worked in the solar industry, my advice is that if you want and can go solar, go solar. Depending on where you live, you can take advantage of tax incentives to mitigate the investment cost as a residential solar consumer. Also, radiation may be sufficient to produce enough electricity to partially power a house reducing your electric bill. The payout time will depend on the existing incentives where you live; but solar panels do help mitigate carbon emissions. Just remember to research the company where the panels are manufactured, where their parts come from and their procedures if possible.

Sources:

Sustainable Energy Options for Austin Energy Summary Report, March 2009, SEIA, Euractive (www.euractiv.com), Pickmysolar (blog.pickmysolar.com), Origin (www.originenergy.com.au), Renewable Energy World.