PV vs solar thermal energy: differences and areas of application

The use of solar energy is a significant step towards sustainability and energy independence. But before you decide on a solar system, there is a key question: Photovoltaic or solar thermal energy? Both technologies use the power of the sun to generate energy, but differ fundamentally in their functionality, purpose and costs.

photovoltaic systems Using solar cells, sunlight is converted into electricity, which can either be used directly, stored in batteries or fed into the power grid. solar thermal systems On the other hand, use solar energy to generate heat, which is primarily used for water heating and heating backup. The decision between these two technologies depends on individual factors such as energy consumption, available roof space and planned uses.

This article gives you a comprehensive overview of Photovoltaic and solar thermal energy. We look at their advantages and disadvantages, typical areas of application and the costs involved. In addition, we take a look at the legal framework and current developments that influence the use of these technologies.

The aim of this article is to provide you, as a heating engineer, with a sound basis for advising your customers and to select the appropriate solar technology for their individual needs and circumstances.

Knowledge at a glance

• Photovoltaic (PV) converts sunlight into electricity that can be used for household appliances, lighting or electric cars. Surplus electricity can be fed into the grid or stored temporarily in battery storage systems.
• solar thermal uses solar energy to generate heat, which is primarily used for hot water heating and heating backup. Solar thermal systems are particularly efficient as they can convert up to 80% of incoming solar energy into usable heat.
• expenses (vary by region and current price developments):
  • Photovoltaic systems cost on average 12,000 to 16,000 euros (for 8 kWp) and pay for themselves in approx. 10 to 12 years.
  • Solar thermal systems are included 6,000 to 8,000 euros and pay for themselves in approx. 12 to 14 years. Funding programs such as BAFA subsidies and feed-in tariffs reduce costs.
• Combination options: Both technologies can be combined to generate electricity and heat at the same time. This maximizes energy yield and enables an almost self-sufficient supply.
• Areas of use:
  • PV is suitable for households, commercial enterprises and agricultural businesses, for example for electricity production or e-mobility.
  • Solar thermal energy is ideal for hot water, heating backup and industrial processes.
• Location dependency:
  • PV is particularly suitable for regions with diffuse solar radiation, such as Central Europe.
  • Solar thermal energy shows its strengths in sunny areas, such as southern Europe.

What is photovoltaic and why is it so important?

Photovoltaic systems use solar cells to convert sunlight directly into electrical energy, which can be used for self-consumption or fed into the grid. By using solar energy, photovoltaic systems offer an environmentally friendly alternative to traditional fossil power generation. They are particularly beneficial as they reduce dependence on fossil fuels and help reduce CO2 emissions. But how exactly does this technology work and what benefits does it offer in everyday life?

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How does a photovoltaic system work?

Solar cells are the core component of every photovoltaic system. These usually consist of silicon, a semiconductor material that converts sunlight into electrical energy. When light falls on the solar cells, it sets electrons in motion and produces direct current. This is converted into alternating current by an inverter so that it can be used by household appliances or fed into the public power grid.

Recent developments in photovoltaics go beyond traditional roof installation. For example, there are building-integrated photovoltaic modules that use facades or window surfaces to generate solar power. These innovations not only make photovoltaics more efficient, but also more versatile in use.

The use of photovoltaic systems with heat pumps offers a particularly interesting combination. The solar power generated can be used directly to operate the heat pump, allowing households to further reduce their energy costs and improve their environmental balance. This combination of technologies enables an almost autonomous energy supply for electricity and heat.

Where are photovoltaics used?

How versatile is photovoltaics actually? Photovoltaic systems are used in a wide range of applications. In the private sector, they cover the electricity requirements of single-family homes, while larger systems supply industrial plants or office buildings. Even in remote regions without a grid connection, portable PV systems are a valuable solution for the power supply.

One growing area is use in agriculture, for example as so-called Agri-PV systems, in which arable land is used both to grow food and to produce electricity. These systems enable efficient dual use of land and increase the profitability of agriculture.

One innovative area of application is motorway canopies with solar modules, which not only generate energy but also provide weather protection. The integration of photovoltaics into urban infrastructures, for example in charging stations for electric vehicles powered by PV systems, is just as interesting. Another growing segment is the use of PV systems in agriculture. Here, they support, among other things, the operation of irrigation systems or the supply of electricity to cold stores for crop yields.

Costs and profitability of photovoltaic systems

The investment costs for photovoltaic systems can vary depending on system size, output and location. In Germany, the average cost of a PV system on a single-family home is around 1,200 to 1,800 euros per kilowatt peak (kWp), including installation and inverter. For a typical 10 kWp system, the total costs amount to around 12,000 to 18,000 euros.

While the initial investment appears high, photovoltaic systems often pay off within 8 to 12 years, depending on self-consumption rates, electricity prices and funding opportunities. In the long term, they not only reduce electricity costs, but also contribute to increasing the value of the property. Although battery storage systems increase purchase costs by around 5,000 to 10,000 euros, they increase independence from external energy sources and increase the use of the electricity generated.

Heat pumps can also sustainably increase the value of your property — if you are interested, feel free to read this item.

Why is an investment in photovoltaics worthwhile

The efficiency of photovoltaic systems has developed rapidly in recent years. But why are they so attractive? One main reason is the opportunity to reduce electricity costs in the long term and benefit from government funding programs such as the feed-in tariff. Today, modern PV systems operate efficiently even under adverse lighting conditions, making them attractive even for areas with less sunlight.

For private households, a photovoltaic system not only offers financial benefits, but also the opportunity to become more independent of rising electricity prices. Companies, on the other hand, can reduce their operating costs and improve their environmental balance with PV systems. Another advantage is the combination of photovoltaics with battery storage systems, which means that the generated electricity can be used at any time of day.

Basics of solar thermal energy: Using heat from solar energy efficiently

Solar thermal systems use solar energy to generate heat, which is then used to heat buildings or water heating. These systems typically consist of solar collectors, which are installed on roofs or open spaces, as well as a heat storage system, which makes the energy obtained available when needed. But how exactly does this technology work and what advantages does it offer?

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How does a solar thermal system work?

Solar thermal systems convert sunlight directly into heat using special solar collectors. These collectors, often in the form of flat or tube collectors, absorb the sun's rays and transfer the generated heat to a carrier medium, usually water or a frost-proof liquid. This medium flows through a closed pipe system into a heat storage tank. When required, the heat storage unit transfers the energy to heating or hot water systems, which saves fossil fuels.

Technological advances have recently been made that further increase the efficiency of solar thermal systems. For example, vacuum-insulated tube collectors enable significantly better heat absorption, even in diffuse lighting conditions or in colder climates. In addition, solar thermal systems are increasingly being integrated into hybrid systems, which combine them with heat pumps to enable even more flexible use of the heat generated.

What are the benefits of solar thermal energy

Solar thermal systems score points for their high efficiency and environmental friendliness. They can convert up to 80% of solar radiation into usable heat, making them particularly effective. This results in significant savings in heating costs and reduces dependence on fossil fuels. Another advantage is the reduction of CO2 emissions, making it an ideal choice for environmentally conscious households.

Especially in summer, when solar radiation is highest, solar thermal systems can cover almost all of a household's hot water requirements. This not only protects the environment, but also reduces the burden on the budget. Recent developments such as vacuum tube collectors, intelligent control systems and integration into hybrid energy systems also make it possible to further increase efficiency and flexibly combine solar thermal energy with other technologies such as heat pumps or photovoltaic systems. In addition, solar thermal energy is being used more and more frequently in industry to generate process heat, which significantly expands the range of application of this technology.

Where is solar thermal energy used?

Solar thermal systems are used in a wide range of applications. They are used primarily in residential buildings for water heating and heating backup. Swimming pools also benefit from solar thermal energy, as they constantly require large amounts of hot water. They are also used in industrial processes, such as to preheat process water.

In comparison, photovoltaic systems focus on power generation and are used in a wide variety of areas, from power supply for households and businesses to integration into e-mobility solutions or agri-PV systems. While photovoltaics flexibly provide electricity for various applications, solar thermal energy offers direct heat generation, which is particularly effective in areas with constant heat demand.

One innovative area of application of solar thermal energy is integration into building concepts that rely on high energy self-sufficiency. For example, solar thermal systems are increasingly being combined with floor heating systems, which work particularly efficiently at lower temperatures. In contrast, photovoltaics are more suitable for applications where electricity is to be generated and stored, for example to supply electrical devices or to feed it into the power grid. The combination with other technologies, such as photovoltaic systems or heat pumps, also opens up completely new opportunities to supply buildings with almost zero emissions and to cover both electricity and heat requirements sustainably.

Photovoltaic or solar thermal energy: Which technology is better?

The choice between photovoltaic (PV) and solar thermal energy depends on several factors: How efficient are the systems, what costs are involved, and what role do geographical conditions play? Each technology has its strengths, which make it more attractive depending on the application and location.

How efficient are PV and solar thermal energy?

Photovoltaic systems efficiently convert sunlight into electricity and work reliably even in diffuse solar radiation. This makes them ideal for regions with changeable weather conditions or limited sunlight. However, their efficiency depends heavily on the quality of the modules and inverters.

Solar thermal energy, on the other hand, achieves an efficiency of up to 80% when converting sunlight into usable heat, which makes it particularly efficient for applications such as water heating and space heating. This uses solar energy to heat water in a buffer tank. This hot water can either be used directly to supply households with hot water or used in heating circuits, similar to a heat pump. Solar thermal systems can often generate more energy in the form of heat per square meter of collector area than PV systems in the form of electricity, provided that sufficient direct solar radiation is available.

What are the costs of installation and operation?

The costs for both technologies vary greatly and depend on the size of the system, the structural conditions and the energy requirement.

photovoltaics

Photovoltaic systems often require higher initial investments, but benefit from lower module prices and government subsidies such as the feed-in tariff. A typical 8 kWp system could be installed for a single-family house with an average electricity requirement of 4,000 kWh per year. The costs for this are around 12,000 to 16,000 euros, including inverter and installation.

Example calculation for PV system*:

• Acquisition costs: 14,000 euros
• Government funding: Feed-in tariff of approx. 8 cents/kWh for excess electricity
• Power savings per year: 1,200 euros with self-consumption of 70% and an electricity price of 40 cents/kWh
• Payback: Ca. 10 to 12 years, depending on funding and self-consumption

In addition, a battery storage system can be installed to increase self-consumption and to use the generated electricity even at night or when there is little sunlight. These storages cost around 5,000 to 10,000 euros, however, increase independence from external energy sources and the use of generated electricity, which increases the overall efficiency of the plant.

solar thermal

Solar thermal systems are often cheaper to buy than PV systems, but there may be additional costs for integration into existing heating systems or the installation of heat storage systems. For a typical single-family house with an annual hot water requirement of around 2,000 kWh, a solar thermal system for hot water heating costs around 6,000 to 8,000 euros, including installation and storage.

Sample solar thermal calculation*:

• Acquisition costs: 7,000 euros
• Funding through BAFA subsidy: 30% of costs, approx. 2,100 euros
• Savings per year: 400 euros with reduced heating costs due to less gas consumption (price: 10 cents/kWh)
• Payback: Ca. 12 to 14 years, depending on production and energy saving

*These are sample calculations that represent typical costs, subsidies and savings; the actual values may vary depending on individual circumstances such as plant size, location and energy consumption.

What role does location play?

The geographical location and climate are decisive for the choice between PV and solar thermal energy.

• Photovoltaic: In regions with frequently cloudy skies or lower solar radiation, such as Germany, the Netherlands and Great Britain, PV offers the advantage of generating energy even in diffuse lighting conditions. This makes photovoltaic particularly popular in Central Europe, where it is a widespread choice due to its versatility.
• solar thermal energy: This technology is particularly suitable for areas with high annual hours of sunshine, such as southern Europe — such as Spain, Italy or Greece. In these countries, where solar radiation is high all year round, solar thermal energy is often used to heat water and to support heating systems. In mild winter regions, it can be used all year round and shows particularly high efficiency.

An interesting development is the combination of both technologies, which allows households to generate both electricity and heat from the sun. Such hybrid systems maximize energy yield and enable holistic use of available roof space.

Who benefits most from photovoltaics and solar thermal energy? Overview of areas of application and target groups

Photovoltaics (PV) and solar thermal energy are designed to meet different energy needs, thus serving specific target groups and areas of application. The choice of suitable technology depends on factors such as energy demand, local conditions and long-term goals.

Photovoltaics: versatility and wide applicability

Typical target groups:

• private households: Single-family and multi-family homes in particular benefit from PV power generation, whether to reduce electricity bills or to feed it into the grid.
• commercial enterprises: Companies use PV systems to reduce operating costs, increase their energy independence and achieve sustainability goals.
• agriculture: Photovoltaics are used on the roofs of barns and stables or as Agri-PV, in which arable land is used simultaneously for agriculture and electricity generation.

Areas of use:

• Self-consumption and feed-in: PV systems provide clean electricity for households and businesses and feed surpluses into the grid.
• E-mobility: More and more households are combining PV systems with wallboxes for electric cars.
• Innovative applications: From building-integrated photovoltaics (BIPV) to solar roofs over parking lots or motorways, PV offers a wide range of uses

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Solar thermal energy: efficient heat supply

Typical target groups:

• private households: Families or households with high hot water requirements benefit in particular from solar thermal systems.
• swimming pools: Solar thermal energy is ideal for heating pools and swimming pools, especially during summer months.
• Industrial companies: Industries with constant demand for process heat, such as the food industry, use solar thermal systems to reduce fossil fuels.

Areas of use:

• water heating: Particularly efficient for households looking for a sustainable alternative to traditional water heating.
• Heating system support: Combined with floor heating systems or heat pumps, solar thermal energy offers a year-round, environmentally friendly heating solution.
• Hybrid solutions: Solar thermal systems are increasingly being combined with PV systems to simultaneously meet electricity and heat requirements

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How can PV and solar thermal energy be optimally used in residential buildings?

In residential buildings, both photovoltaics and solar thermal energy offer specific advantages, which can be combined or used individually, depending on energy requirements and use.

• Photovoltaic: PV systems are ideal for generating electricity for household appliances, lighting and charging stations for electric cars. Surplus electricity can be fed into the public grid, which not only reduces the electricity bill, but also enables an attractive feed-in tariff. Battery storage systems also help to increase self-consumption and further increase energy independence.
• solar thermal energy: Solar thermal systems are particularly efficient when it comes to providing hot water and heating backup. They are ideal for households with high hot water requirements, such as family homes, or for buildings with floor heating systems that operate at lower temperatures.

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Why hybrid solutions could be the future of solar energy

Hybrid solutions that combine photovoltaic and solar thermal components make optimal use of the strengths of both technologies. These systems generate electricity and heat simultaneously, which significantly increases the overall energy efficiency of a house.

• Maximized energy yield: By generating electricity for daily use as well as heat for water and heating, hybrid solutions cover a wide range of energy needs.
• Optimized space requirement: Hybrid systems are particularly advantageous when roof space is limited, as they make effective use of available space.
• Future-proof technology: With rising energy costs and a growing focus on sustainability, hybrid solutions offer a long-term economic and ecological solution.

One example of innovative hybrid technology is the integration of PV thermal modules, which combine both functions in a single system. These modules are particularly suitable for energy-independent buildings or applications with increased heat and power requirements.

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Schedule a demo with autarc

Contact us today to plan a personal demonstration of our software and find out how autarc can support your municipal heating planning. Discover how we can help you achieve your goals of sustainable and efficient energy supply.

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(1) Photo by Los Muertos Crew.

(2) Image source: Pixabay

(3) Image source: Erdgas Südwest

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