What Is Solar Energy? Definition, How It Works, and Pros and Cons

Blue solar panels
Harnessing solar energy is an increasingly affordable and environmentally-beneficial way to produce electricity. VioNettaStock / Getty Images

Solar energy is electromagnetic radiation that is given off by the sun and captured to be turned into useful energy. Plants absorb solar energy to turn sunlight into food through the process of photosynthesis, while humans capture sunlight to turn it into useful electricity using processes like the photovoltaic effect.

The electricity produced by solar energy can be used in power grids or stored in batteries. Energy from the sun is abundant and free, and the costs of converting solar energy into electricity continue to fall as solar technology becomes more advanced and efficient. Solar energy is the most accessible and plentiful source of energy on Earth. It also has the advantage of producing a lower carbon footprint than fossil fuels, which reduces its overall environmental impact. 

Solar Energy Definition

Our sun is a star made mostly of hydrogen and helium. It produces energy inside its core through a process called nuclear fusion, where hydrogen fuses together to make a lighter atom of helium. The energy that’s lost in this process radiates into space as energy. A small amount of this energy reaches the Earth. Every day, the solar energy that reaches the U.S. alone is enough to meet a year and a half of our energy needs.

Currently, the U.S has a solar power capacity of around 97.2 gigawatts. Only about 3% of the electricity generated in the U.S. comes from solar energy. The rest comes overwhelmingly from conventional fossil fuels like coal and natural gas. The Department of Energy predicts that by 2030, one in seven homes in the U.S. will have rooftop solar panels thanks to government incentives and cost reductions through more efficient technology.  

Solar power supply for the farm
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Electricity Generation

Solar technology can take sunlight and change it into energy using photovoltaic (PV) solar panels or by concentrating the solar radiation using special mirrors. Individual particles of light are called photons. These are tiny packets of electromagnetic radiation that have different amounts of energy depending on how quickly they move. Photons are released by the sun during the process of nuclear fusion when hydrogen is converted to helium. If photons have enough energy, they can be harnessed to generate electricity.

PV panels are made from individual PV cells. These cells contain materials called semiconductors which allow electrons to flow through them. The most common type of semiconductor used in PV cells is crystalline silicon. It is relatively inexpensive, abundant, and lasts a long time. Out of all of the semiconductor materials, silicon is also one of the most efficient conductors of electricity.

When photons with a lot of energy come in contact with semiconductors, they can knock electrons loose. These electrons produce an electrical current that can be used for power or stored in a battery.

Most energy produced by solar panels is sent into the electrical grid to be distributed to places that need electricity. Even private rooftop solar panels send extra electricity back into the power grid. Battery storage tends to be expensive, and selling excess electricity back to electric companies is the most cost-effective way to produce solar electricity at the moment. 

Solar Thermal Energy

Solar thermal collector
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Solar thermal energy (STE) technology captures solar energy and uses it for heat. There are three different categories of STE collectors: low, medium, and high temperature.

Low-temperature collectors use either air or water to transfer heat energy collected by the sun to the location that needs to be heated. They may come in the form of glazed solar collectors that heat air to be transferred through a building, metal walls, or roof-mounted water bladders that are warmed by sunlight. They are most commonly used for small spaces or to heat swimming pools.

Medium-temperature collectors work by moving a non-freezing chemical through a series of pipes that collect sunlight to heat water and air in residential and commercial buildings.

High-temperature collectors use a series of parabolic mirrors to efficiently convert solar energy into high-temperature heat that can then generate electricity. The mirrors capture the sunlight and focus it into what’s called the receiver. This system then heats contained fluids and circulates them to produce steam. Much like conventional electrical generation, the steam then turns a turbine, which creates power for a generator to produce the desired electricity.

The mirrors that collect the sunlight must be able to follow the path of the sun throughout the day in order to maximize efficiency. These large systems are mostly used by utilities to create electricity to send through the power grid. 

Solar Energy Today

Solar power plant
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Solar technology has made incredible strides over the past few decades, and it’s expected to grow even faster in the coming years. In almost all parts of the world, solar energy is the least expensive energy to produce. And the costs continue to drop as technology improves. Cost projections for one kilowatt-hour of electricity produced by solar are projected to be half a cent by the year 2050. That’s compared to the current commercial utility-scale rate of about 6 cents per kWh

In 2016, the U.S. Department of Energy released its goals for SunShot 2030, which include reducing the costs of solar energy production and drastically increasing the amount of solar electricity generation. Expanding access to solar energy and reducing the amount of time it takes to create solar infrastructure are among the ways the Department of Energy plans to meet these goals. 

Pros and Cons

Solar energy is increasingly affordable, and may even become cheaper than conventional energy produced by fossil fuels as the technology becomes more efficient. Government incentives for homeowners and businesses alike make it an attractive technology to invest in.

While there are plenty of pros to solar energy, the cons continue to keep it from being accessible to everyone. Unfortunately, not all consumers of electricity are able to install their own photovoltaic system. Some people do not own the place where they live, or their homes do not get enough sunlight to make solar panels efficient. And while the price of solar panels has decreased dramatically over the past decade, the upfront costs of installing rooftop solar are still cost-prohibitive for many. 

On a commercial scale, solar energy production continues to be a way for companies to produce electricity without contributing to the increasing levels of greenhouse gasses in the atmosphere. Solar panels may be co-located with commercial crops in order to reduce the amount of arable land they render unusable for farming. 

Solar electricity generation itself does not emit pollutants, however, the production of solar panels, unless run on solar energy, continues to produce emissions. Solar panels are also not recyclable in most parts of the world. At the end of their useful lives, most solar panels are disposed of in landfills. This process has the potential to release toxic chemicals into the environment.

Some facilities in Europe are leading the way in solar panel recycling and finding ways to reuse many of the original materials for new solar panels. This also reduces environmental impacts by decreasing the number of new semiconductor materials that need to be mined and processed. As solar energy increases in popularity and affordability, the demand for solar panel recycling will most likely increase.