What is the difference between solar thermal and photovoltaic energy?

More and more, we are moving towards a sustainable energy transition, so it is quite normal to hear these terms and not differentiate between them. Both technologies take advantage of the sun’s radiation, but they do it in very different ways. Therefore, today we are going to delve into the difference between solar thermal and photovoltaic energy, explaining their operation, applications, advantages and disadvantages, so you can better understand which one is more adapted to each need. Keep reading!

The main difference between solar thermal and photovoltaic energy

The difference between solar thermal and photovoltaic energy lies in how they harness the sun’s energy. While solar thermal energy transforms solar radiation into heat, photovoltaic energy converts the same radiation into electricity.

In other words, solar thermal energy is mainly used to heat water or generate steam, and works much better for domestic or industrial use, if it requires heat. Photovoltaics, on the other hand, is used to produce electricity, which can be used instantaneously or stored in batteries. Both technologies fall under the concept of solar energy, but their purpose, design and impact are very different.

Operation of solar thermal energy

Solar thermal energy works through solar thermal collectors, which are devices that capture heat from the sun. The most common systems are flat plate collectors and evacuated tubes. In addition, it is very efficient for some tasks such as water heating, no matter if it is for a house, a swimming pool, a hotel, or a sports center. It is also very present in the food industry, because they require a more constant heat source than the average. Its operation could be separated into 4 parts:

1. Solar heat collection: The collector absorbs solar radiation by means of a dark, selective surface.
2. Heat transfer: The absorbed heat is transferred to a heat transfer fluid, usually water or a mixture with antifreeze.
3. Storage: The hot fluid is stored in an accumulator, which maintains the temperature for later use.
4. Distribution: Hot water can be used in sanitary systems, heating or even industrial processes.

Operation of photovoltaic energy

Photovoltaic solar energy is based on a completely different principle, since it uses solar panels made up of silicon cells that have the capacity to transform sunlight into electricity. This type of energy is ideal for self-consumption of electricity, off-grid installations or large-scale generation projects, such as solar photovoltaic plants, so it has many more uses than thermal energy. This energy works like this:

1. It captures sunlight through photovoltaic cells, which capture photons from the sun.
2. The electric current is generated. The photons hit the atoms of the semiconductor material, releasing electrons and generating a continuous electric current.
3. It is converted to alternating current by an inverter. In this part, the electricity generated is transformed into alternating current, suitable for consumption or for simply injecting it into the electrical grid.
4. Finally, it is distributed or stored. Energy can be consumed directly or stored in batteries for later use.

And what about the plants?

Another difference between solar thermal and photovoltaics is in how they are approached on a large scale. Solar thermal power plants use mirrors that concentrate sunlight at a point where steam is generated to drive turbines. For example, solar towers or parabolic trough systems.

A solar photovoltaic power plant, on the other hand, consists of a large area covered by photovoltaic panels that convert sunlight directly into electricity. These plants are connected to the grid and can supply thousands of homes.

The difference between solar thermal and photovoltaic power plants is therefore structural and functional: one produces electricity from heat (thermal), the other generates it directly from light (photovoltaic).

Solar thermal and photovoltaic applications

Starting with solar thermal energy applications:

1. Domestic hot water (DHW) in single-family houses, residential buildings or public facilities.
2. Space heating through radiant floor systems or low temperature radiators.
3. Swimming pool air conditioning, especially in hotels or sports complexes.
4. Industrial processes requiring heat: pasteurization, drying, washing, sterilization, etc.
5. Desalination of water in coastal areas with shortage of drinking water.
6. Solar thermal power plants, which generate electricity through steam turbines in large installations, using technologies such as parabolic troughs or solar towers.

Regarding photovoltaic solar energy applications:

1. Self-consumption of electricity in homes, offices, companies and communities of neighbors.
2. Rural electrification in isolated areas without access to the power grid.
3. Grid-connected photovoltaic solar plants, which sell the electricity generated.
4. Electric mobility, with solar-powered charging stations.
5. Portable applications, such as solar chargers, mobile devices or emergency kits.
6. Hybrid installations, combined with batteries or generators to guarantee electricity supply.

Summary of advantages and disadvantages of thermal energy and photovoltaic energy

For a better comparison, here is a table with the advantages and disadvantages of these two energies.

Understanding the difference between solar thermal and photovoltaics is not only important for making informed renewable energy decisions, but also for designing the most efficient and sustainable solutions possible. While solar thermal stands out for its efficiency in heat production, solar PV has become a key player in clean electricity generation.

Each one has its space, its utility and its context. Therefore, often the ideal is not to choose between one or the other, but to combine them to make the most of the sun’s energy.