Solar energy, solar thermal, photovoltaics: what’s the difference?

The difference between solar power and photovoltaics is that photovoltaics is a type of solar power. On the other hand, solar power is a general term for photovoltaic and solar thermal systems because both use the energy of the sun to produce energy. Photovoltaic systems produce electricity, and solar thermal systems produce heat.

Comparison: Solar thermal or photovoltaics

When it comes to the question of “solar thermal or photovoltaics,” you have to decide which type of energy you want to generate. Solar thermal uses the sun’s energy and converts it into heat. The heat can be used for heating or providing hot water. Photovoltaics, on the other hand, uses sunlight to generate electricity.

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

Different uses

Solar thermal systems and photovoltaic systems are both installed on the roof of a house and each has its own advantages and disadvantages. Photovoltaic systems require more roof space, while solar thermal collectors are more expensive. Your decision should be based on your personal requirements.

If you have enough roof space, you can also consider a combination of both systems. They can be installed and used in combination without any problems.

Utilization of Photovoltaic Power Generation

Photovoltaic power can be used to generate electrical energy, which can be used for your own home or sold. Electricity is sold by feeding it into the public grid. You receive a feed-in tariff from the grid provider. However, this has dropped significantly in recent years and electricity prices have risen. Most PV system owners therefore choose to self-consume their electricity, as this is more economical in the long run and can save a lot of money on electricity bills.

You can use the electricity generated by your photovoltaic system not only for electrical appliances, but also for heating or domestic water. This can be achieved, for example, via electric heating rods or in combination with a heat pump. This combination also increases your self-consumption, since you use more solar energy yourself. Additional electricity storage can even provide you with your own solar energy at night.

Utilization of solar thermal energy

With solar thermal, heat from the sun is used to support heating systems or to heat domestic hot water. Solar thermal systems do not produce heat for sale, only for personal use. Solar thermal systems can provide most of the heat needed to prepare hot water, but are usually not enough to meet the entire heating demand.

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

Different operating modes

Both photovoltaic modules and solar thermal modules consist of multiple layers. In photovoltaic modules, solar cells are responsible for generating electricity. On the other hand, solar thermal collectors consist of tubes with a special heat transfer fluid.

Photovoltaic function

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

Solar thermal function

Solar thermal energy works using the infrared spectrum of the sun. The tubes of the collector absorb the radiation and heat a special liquid inside. The warm liquid is discharged and transported to a storage tank filled with water. In the storage tank, the heat is transferred to the water, which is then pumped into the heating circuit.

Required roof area

The required roof area for solar thermal and photovoltaic systems differs greatly. Photovoltaics require more solar modules because they are less efficient. On the other hand, solar thermal systems only need a few square meters. In addition, it is usually worthwhile to cover the entire roof area with photovoltaics, because the costs fall as the number of photovoltaic modules increases.

This is how much roof area is needed for photovoltaic power generation

If photovoltaic power is used, a roof area of ​​about 50 m2 is required to cover an annual electricity consumption of 4,000 kWh. This corresponds to the average consumption of a single-family house. On average, you can assume that the photovoltaic module has an output of 5 kWp per 1 m2 of area. In addition to this there is the required clearance area.

This is how much roof area you need for solar thermal

In the case of solar thermal, the size of the roof area depends on the type of collector and its purpose. Flat plate collectors require 4.5 to 7.5 m2 of area to meet the hot water needs of 3 to 5 people. Tubular collectors require only 4 to 6 m2. For heating support, flat plate collectors require 7 to 11 m2 and tubular collectors require 5 to 9 m2 of roof area.

Different levels of efficiency

Solar thermal systems have a higher efficiency than photovoltaic systems, at 60% – 90%. The latter have an efficiency of 15-20%. Photovoltaics also have more complex technology, but are easier to install since prefabricated modules can be used. Solar thermal systems, on the other hand, require laying pipes and installing boilers and pumps.

Photovoltaic efficiency

Photovoltaic power generation has an efficiency of 10-25%, depending on the type of module. Monocrystalline solar modules have an efficiency of up to 25%. They are also the most expensive photovoltaic modules. Polycrystalline modules have an efficiency of about 16% and are slightly cheaper. Thin-film modules have an efficiency of between 10% and 13%.

Solar thermal efficiency

The efficiency of solar thermal energy depends on the type of collector and its inclination to the sun. Flat-plate collectors have an efficiency of between 60 and 85%. With tubular collectors, the efficiency can even reach 90%. Tubular collectors are correspondingly more expensive.

Comparison of photovoltaic power generation and solar thermal power generation costs

For a single-family house, photovoltaic power generation costs between €5,000 and €15,000, depending on the size of the system. This includes assembly, installation and commissioning. Solar thermal production of hot water costs around €5,000. Heating and hot water costs are around €10,000.

Photovoltaic costs

A smaller 5 kWp system can cover the average annual electricity consumption of a single-family home. The cost of each kilowatt-peak photovoltaic power generation is between 1,000 and 1,800 euros. Therefore, a 5 kWp photovoltaic system costs about 7,000 euros. An additional storage unit costs just under 5,000 euros. Subsidies can be used to reduce the cost.

Solar thermal costs

The costs of solar thermal energy depend on whether the system is used only for hot water or whether it also supports heating. Hot water preparation for a detached house costs around 5,000 euros. For hot water and heating support, the costs are around 10,000 euros.

Hybrid modules: combining solar thermal and photovoltaic power generation

Solar thermal and photovoltaic power generation can be easily combined. This can be achieved with two separate systems or with so-called hybrid modules (also called PVT modules). A hybrid module consists of a photovoltaic module on top, which collects the sunlight, and a solar thermal collector on the bottom, which absorbs the heat. In this way, electricity and heat are generated simultaneously.

Hybrid modules are particularly suitable for situations where a large amount of heat is required throughout the year, especially in the summer. In private households, this is less likely to occur, as hot water consumption is limited and heating is usually only required in the 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 may be more worthwhile. However, the decisive factor is your individual demand for electricity and heat.

Conclusion: Solar energy, solar thermal, photovoltaics?

The difference between solar power and photovoltaic power is that solar power is an umbrella term for types of solar power generation. The different types include photovoltaic power and solar thermal power. Photovoltaic power uses the sun to generate electricity. On the other hand, solar power systems that use solar thermal power produce usable heat.

technology	Photovoltaic panels	Solar Collectors
use	Electricity, hot water, heating	Hot water, heating
On-grid electricity price	accept	No
subsidy	accept	accept
Required area	L Large	S Small
Operating costs	Very low	Relatively low
Payback period	10-20 years	15-20 years
life	25 – 40 years	20-30 years
Initial Cost (Single-Family Home)	€5,000 – €15,000	Hot water €5,000, heating and hot water €10,000

Photovoltaic systems are especially valuable for households with high electricity consumption. All that is needed is a sufficiently large roof area. As electricity costs are rising, the highest possible self-consumption of solar energy is the most economical. To increase self-consumption, an additional heat pump or electrical storage can be installed. With a heat pump, you can reduce both heating costs and electricity costs.

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

A kilowatt-hour of heat costs less than a kilowatt-hour of electricity, which is why photovoltaics often save more money. The electricity is also more versatile, as it can also be used for heating or heating domestic hot water. However, ultimately this depends on your personal consumption and the conditions of the building.