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What is Solar Energy – Definition, Examples and Uses

Photovoltaic solar power plant

The power of the Sun is the main source of renewable energy on our planet that can replace the energy produced by fossil fuels due to its many uses.

The Sun is the main source of energy for all living processes on the planet, and is also a source of free heat and clean electricity for a large number of homeowners and businesses.

Solar Energy Definition

Solar energy reaches planet Earth under the form of radiant light and heat that is used actively to generate clean electricity and heat water, and passively to illuminate and heat passive homes during the winter.

Besides of being renewable, solar energy is also a free and non-polluting source of power that can create energy freedom for a large number of households and companies in the United States and in many other countries.

Today, we are using the power of the Sun in two different ways: active solar and passive solar.

1. Active Solar Energy

Active solar refers to the use of sunlight to generate clean electricity using solar photovoltaic cells (these cells are usually made of silicon and are able to convert a good portion of the sunlight into electricity due to the photovoltaic effect).

Another form of active solar energy uses large mirrors (or smaller concave mirrors) that are concentrating the sunlight into a point located at the top of a tower (concave mirrors are concentrating the sunlight into the focal point of the mirror), where an agent such as molten salt (or oil) is heated at high temperatures to produce steam, which is then used to spin a turbine and generate electricity using a generator.

Active solar also refers to the production of hot water for domestic use (boilers with hot water radiators) and also for radiant floor heating systems (solar liquid collectors) using only the sunlight.

When the Sun is not available, a back-up system provides the additional heat required for domestic hot water production and for the radiant floor heating system.

This way, active solar refers to the direct use of the sunlight to generate electricity and heat.

2. Passive Solar Energy

Passive solar is used by passive homes to lower the energy consumption from the grid.

A passive home is built using materials that store heat, and is placed on the north end of the lot to ensure an unobstructed access to the Sun because the sunlight is used to illuminate the rooms and heat the house during the winter.

To ensure that the energy provided by the Sun is used during the winter, the passive house will collect the sunlight using south-facing windows, and will store the heat (thermal mass) in heat retaining materials.

That heat is distributed in every room of the house and because the home is well insulated, the house will be kept warm during the winter and will have an extremely low energy bill to pay.

During the spring and summer, the south-facing windows are closed to block the sunlight from overheating the house, and a ventilation system is used to keep the home at a comfortable temperature during the summer.

Solar Energy Examples and Uses

Today the sunlight is used by a variety of devices to produce free and clean energy (solar electricity) and heat (thermal energy).

To produce electricity, we are using solar photovoltaic cells installed on solar (PV) panels and concentrated solar power (mirrors).

For thermal energy we are using the sunlight for water heating, space heating, cooking, cooling and ventilation, process heating and water treatment.

Electricity production

The power of the Sun is used to produce free and clean energy by converting the sunlight into electricity using solar photovoltaic (PV) cells and concentrated solar power (CSP), which uses mirrors or lenses and a tracking system that follows the Sun in the sky to maximize the amount of energy and heat production.

1. Solar Cells

Today, we are using a very wide variety of solar cells that are converting the sunlight into clean electricity using the photovoltaic effect.

We have this way the following types of solar cells:

  • Monocrystalline solar cell (mono-Si);
  • Polycrystalline solar cell (multi-Si);
  • Amorphous Silicon solar cell (a-Si);
  • Biohybrid solar cell;
  • Cadmium telluride solar cell (CdTe);
  • Concentrated PV cell (CVP and HCVP);
  • Copper indium gallium selenide solar cells (CIGS);
  • Crystalline silicon solar cell (c-Si);
  • Dye-sensitized solar cell (DSSC);
  • Gallium arsenide germanium solar cell (GaAs);
  • Hybrid solar cell;
  • Luminescent solar concentrator cell (LSC);
  • Micromorph (uses a tandem-cell a-Si/μc-Si);
  • Multi-junction solar cell (MJ);
  • Nanocrystal solar cell;
  • Organic solar cell (OPV);
  • Perovskite solar cell;
  • Photoelectrochemical cell (PEC);
  • Plasmonic solar cell;
  • Quantum dot solar cell;
  • Solid-state solar cell;
  • Thin-film solar cell (TFSC);
  • Wafer solar cell.

Solar cells are installed on solar panels to increase the power generation capacity of the solar module.

To make a solar array, solar panels are connected in series or parallel.

To produce solar energy on a large scale, we are using solar power plants consisting of thousands or even millions of solar panels installed in areas receiving a good amount of sunlight all year long.

2. Concentrated Solar Power

CSP technology is used by solar thermal power plants that are concentrating the sunlight into a point located at the top of a tower using large mirrors.

The temperature generated this way is very high and is used to heat an agent (usually molten salt) that will produce steam, which is used to spin a turbine and produce electricity using a large generator.

Because the molten salt can hold heat for a longer period of time, a solar thermal power plant can generate energy even during the night or during cloudy days when there is no Sun to be reflected by the mirrors.

Thermal energy production

1. Water heating

A solar water heating system uses the sunlight to heat water directly (active solar).

These devices usually have only two parts, a solar collector and a water storage tank.

The solar collector absorbs the heat from solar radiation on a surface called absorber, and transfers that heat to the water tubes that run through the collector box.

The storage tank is pretty large and is well insulated to keep the water hot for a longer period of time.

2. Space Heating

A passive home is built in a certain position towards the Sun to use the sunlight, mainly for residential heating and keep the energy bills as low as possible.

A house that uses the sunlight in an active mode will collect solar energy by water or air.

The energy collected is stored in water tanks (thermal energy) and batteries (electrical energy).

The collected energy is then distributed into the house using heat pumps and fans.

3. Cooking

Solar cookers are using the sunlight for cooking, drying and pasteurization.

There are solar cookers using a box, a panel or a reflector.

A box cooker consists of an insulated container covered by a transparent lid.

It works well even if there are a few clouds in the sky, and can reach a temperature between 195°F and 302°F (90°C and 150°C).

A panel cooker uses a reflective panel to direct the sunlight onto an insulated container and reaches a similar temperature like the box cooker.

A reflector cooker uses a concave or other geometric form to concentrate the sunlight on the cooking container.

To work properly, the solar reflector cooker requires direct sunlight and can reach a temperature of 600°F or 315°C, which is much higher than the temperature reached by a box cooker or a panel cooker.

4. Cooling and Ventilation

Solar chimneys are used to ensure a natural system of cooling and ventilation for the home.

A vertical shaft is built to connect the interior of the house with the exterior of the building.

As the chimney warms due to the action of sunlight, the inside air is heated, causing an updraft that starts pulling the air through the building.

This way, the house is cooled and ventilated in a natural and free way using passive solar.

5. Process heating

Parabolic reflectors are used to concentrate the sunlight into a point where an agent such as oil is heated at high temperatures and provides heat for several commercial and industrial applications.

6. Water treatment

Solar distillation is used to turn saline water (seawater) into drinkable water.


As time passes, solar energy becomes more affordable, and this is the main reason why this type of renewable energy is more popular today than ever.

The Sun is here to sustain all life processes on the planet, but also to produce free and clean electricity and heat.

It would be great if a larger number of people would rely on solar power at least to lower their energy bills because every kilowatt of solar or other form of renewable energy produced on the planet replaces a kilowatt of energy produced by burning fossil fuels.

Solar means free energy and a clean environment, while fossil fuels mean limited resources and a slow destruction of the environment.

Article written by:

I am a writer and reporter for the clean energy sector, I cover climate change issues, new clean technologies, sustainability and green cars. Danny Ovy

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