Solar, solar thermal, photovoltaics: what's the difference? - SHIELDEN

Solar, solar thermal, photovoltaics: what's the difference?

The difference between solar and photovoltaics is that photovoltaics is a type of solar energy generation. Solar, on the other hand, is the generic term for photovoltaic and solar thermal systems, as both use the power of the sun to generate energy. Photovoltaic systems generate electricity and solar thermal systems generate heat.

Comparison: solar thermal energy or photovoltaics

When it comes to the question of "solar thermal energy or photovoltaics", a decision must be made as to which type of energy is to be generated. Solar thermal energy uses the sun's energy and converts it into heat. The heat can be used for heating or hot water. Photovoltaics, on the other hand, use sunlight to generate electricity.

Let's take a closer look at the other differences.

Different uses

Both solar thermal and photovoltaic systems are installed on the roof of the house and have their respective advantages and disadvantages. A photovoltaic system requires more roof space, while solar thermal collectors are more expensive. Your decision should be based on your individual requirements.

If you have sufficient roof space available, you can also consider a combination of both systems. Combined installation and use are possible without any problems.

Use of photovoltaics

Photovoltaics can be used to generate electrical energy that can either be used in your own household or sold. The electricity is sold by feeding it into the public grid. You receive a feed-in tariff for this from your grid provider. However, this has fallen sharply in recent years and the price of electricity has risen. Most owners of a PV system therefore opt for self-consumption of the electricity, as this is more economical and saves a lot on electricity costs in the long term.

You can use the electricity from your photovoltaic system not only for electrical appliances, but also for heating or to heat your domestic water. This is possible, for example, with an electric heating rod or in combination with a heat pump. This combination also increases your self-consumption, as you use more of your solar power yourself. An additional electricity storage unit even provides you with your own solar power at night.

Use of solar thermal energy

With solar thermal energy, the heat from the sun is used to support the heating system or to heat domestic hot water. Solar thermal systems cannot produce heat for sale and are only intended for personal use. Solar thermal systems can provide a large proportion of the heat required for hot water preparation, but are usually not sufficient for the entire heating requirement.

However, this also depends on the type of building. New buildings generally have a lower heating requirement than old buildings. This is partly due to better thermal insulation and newer heating systems.

Different modes of operation

Both photovoltaic modules and solar thermal modules consist of several layers. In photovoltaic modules, solar cells are responsible for electricity production. Solar thermal collectors, on the other hand, consist of tubes that have a special fluid for heat transport.

Photovoltaic function

Photovoltaics works by shining sunlight onto the PV cells. The light sets the electrons in motion and direct current is generated. The direct current is then converted into usable alternating current in the inverter. From there, the electricity runs to the electricity meter and finally to the domestic electricity grid or electricity storage system for consumption.

Solar thermal function

Solar thermal energy works using the infrared light spectrum of the sun. The tubes of the collectors absorb the radiation and heat a special liquid inside. The warm liquid is drained off and fed to a storage tank containing water. In the storage tank, the heat is transferred to the water and then pumped into the heating circuit.

Required roof area

The roof area required for solar thermal and photovoltaic systems differs greatly. Photovoltaics require considerably more solar modules as they are less efficient. Solar thermal systems, on the other hand, get by with just a few square meters. In addition, it is often worthwhile to cover the entire roof area with photovoltaics, as the costs fall in relation to the increasing number of PV modules.

This is how much roof area is required for photovoltaics

With photovoltaics, a roof area of around 50 m² is required to cover an annual electricity consumption of 4,000 kWh. This corresponds to the average consumption of a single-family home. On average, you can assume an output of 1 kWp per 5 m² area with photovoltaic modules. Added to this are the required clearance areas.

This is how much roof area solar thermal requires

In the case of solar thermal energy, the size of the roof area depends on the type and use of the collector. A flat-plate collector requires 4.5 to 7.5 m² to cover the hot water needs of 3 to 5 people. A tube collector requires only 4 to 6 m². For heating support, 7 to 11 m² are required for a flat-plate collector and 5 to 9 m² roof area for a tube collector.

Different levels of efficiency

At 60% - 90%, solar thermal systems have a higher efficiency than photovoltaic systems. The efficiency of the latter is 15 - 20%. Photovoltaics also have a more sophisticated technology, but they are easier to install as prefabricated modules are available. Solar thermal systems, on the other hand, require pipes to be laid and a boiler and pump to be installed.

Photovoltaic efficiency

The efficiency of photovoltaics is 10-25%, depending on the type of module. Monocrystalline solar modules have the highest efficiency of up to 25%. They are also the most expensive PV modules. Polycrystalline modules have an efficiency of around 16% and are slightly cheaper. The efficiency of thin-film modules is between 10 and 13%.

Solar thermal efficiency

The efficiency of solar thermal energy depends on the type of collector and the inclination to the sun. The efficiency of flat-plate collectors is between 60% and 85%. With tube collectors, an efficiency of 90% can even be achieved. Tube collectors are correspondingly more expensive.

Cost comparison of photovoltaics and solar thermal energy

For single-family homes, the cost of photovoltaics is between €5,000 and €15,000, depending on the size of the system. This includes assembly, installation and commissioning. The costs for solar thermal energy for hot water are around €5,000. For heating and hot water it is around €10,000.

Photovoltaic costs

A smaller 5 kWp system can cover the average annual consumption of a single-family home. The costs per kilowatt peak of photovoltaic output are between €1,000 and €1,800. A 5 kWp photovoltaic system therefore costs around €7,000. An additional electricity storage unit costs just under €5,000 extra. The costs can be reduced with subsidies.

Solar thermal costs

The costs for solar thermal energy depend on whether the system is only intended for hot water or whether heating is also to be supported. Costs of around €5,000 are incurred for the preparation of hot water in a detached house. For hot water and heating support, the costs are around €10,000.

Hybrid modules: Combining solar thermal energy and photovoltaics

Solar thermal energy and photovoltaics can be easily combined. This is possible with two separate systems or with so-called hybrid modules (also known as PVT modules). A hybrid module consists of photovoltaic modules on top, which collect the sunlight, and solar collectors underneath, which absorb the heat. In this way, electricity and heat are produced simultaneously.

Hybrid modules are particularly suitable when a lot of heat is needed all year round, especially in summer. This is unlikely to be the case in a private household, as hot water consumption is limited and heat is usually only required in winter. Hybrid modules are therefore more suitable for facilities such as public swimming pools, hospitals or hotels.

For detached houses and apartment buildings, a combination of hybrid modules with additional photovoltaic modules is more likely to be worthwhile. However, the decisive factor is your individual need for electricity and heat.

Conclusion: solar, solar thermal, photovoltaic?

The difference between solar and photovoltaics is that solar is an umbrella term for types of solar energy generation. The different types include photovoltaics and solar thermal energy. Photovoltaics uses the sun to generate electricity. Solar systems that use solar thermal energy, on the other hand, produce usable heat.

Photovoltaics Solar Thermal
Technology Photovoltaic modules Solar collectors
Use Electricity, hot water, heating Hot water, heating
Feed-in Tariff Yes No
Subsidies Yes Yes
Required Area Large Small
Operating Costs Very low Relatively low
Payback Period 10 - 20 years 15 - 20 years
Lifespan 25 - 40 years 20 - 30 years
Initial Costs (Single-family house) €5,000 - €15,000 €5,000 for hot water, €10,000 for heating and hot water

PV systems are particularly worthwhile for households with high electricity consumption. All that is required is a sufficiently large roof area. Due to rising electricity costs, the highest possible self-consumption of solar power is the most economical. To increase self-consumption, an additional heat pump or electricity storage unit can be installed. With the heat pump, you can reduce your heating costs as well as your electricity costs.

Solar thermal systems only require a small roof area. In existing buildings, solar thermal systems are generally only used to heat water, as the building envelope is often poorly insulated. In new buildings, solar thermal energy is also used to support the heating system.

One kilowatt hour of heat costs less than one kilowatt hour of electricity, which is why photovoltaics can often save a lot more money. Electricity is also much more versatile, as it can also be used for heating or for heating domestic hot water. Ultimately, however, it depends on your individual consumption and the conditions of the building.

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