July 6, 2024, 4:59 am | Read time: 5 minutes
More and more often, photovoltaic and solar thermal systems are seen on rooftops. It’s no surprise, as they allow for the generation of electricity or heat from solar energy. This often raises the question of which system is more practical. But why not both at once? PVT collectors make it possible.
PVT collectors are increasingly gaining popularity. This technology combines photovoltaics and solar thermal energy. The roof area can thus be efficiently used to harness solar energy for both electricity and heat generation. myHOMEBOOK has taken a closer look at the technology, explaining the advantages and disadvantages and whether the investment is worthwhile.
Overview
PVT Explained Simply
The acronym PVT stands for “Photo-Voltaic-Thermal” and is essentially self-explanatory. It involves the combination of photovoltaics (PV) and solar thermal energy (ST), which simply means generating electricity and heat. A PVT collector is essentially a solar thermal system with photovoltaic modules. The PV modules are located on the surface of the PVT collector, while the ST modules are underneath. Both systems utilize different parts of sunlight, with wavelength playing a crucial role. Thus, the two types of collectors do not compete with each other.
There are various types of PVT, but the structure can be described as follows: At the top is a frame or cover. Below that is the PV layer, followed by a thermal absorber layer. Next is a solar fluid, and beneath that is a thermal insulator.
How PVT Systems Work
As mentioned earlier, PVT collectors generate electricity and heat through sunlight. In hybrid collectors, the solar cells absorb sunlight, which is converted into “conventional” electricity by an inverter. Beneath or behind the individual PV modules are thermal absorbers. These absorb the heat from the PV modules as well as ambient heat with a fluid.
Energy expert Stephan Herpertz from the Consumer Center NRW further explains: “Some PVT collectors additionally use outside air as a second heat source. They transfer the captured heat to a heat transfer fluid in the so-called solar circuit, through which the heat is transported for further use. This cools the PVT collector.”
Types of PVT Collectors
There is not just one type of PVT collector. Instead, various designs and types are available on the market, selected based on the area of application and requirements. The most commonly used types include:
- Concentrating PVT Collectors: These use mirrors and lenses to increase the intensity of light. Typically, a tracking system is required for this.
- Air-Brine Collector: These collectors use air as the heat transfer medium, combined with a brine heat exchanger.
- Covered PVT Collectors: Covered or glazed PVT collectors have an additional glazing that encloses an insulating air layer between the PV module and the additional glazing. The cover improves thermal insulation and increases the overall efficiency of the collector.
- Uncovered PVT Collectors: These models are also called unglazed or open collectors. They do not have an additional layer of glass or plastic. Therefore, they are cost-effective for generating electricity and heat. However, they are less efficient and more susceptible to environmental influences.
- Liquid-Based PVT Collectors: These collectors are often referred to as hydraulic collectors. They use water or special heat transfer fluid to remove heat. They are efficient and have a higher heat capacity, but installation and maintenance are more complex.
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Advantages
There are indeed countless advantages associated with PVT collectors. The most important point is that this is a combination technology. You don’t have to choose between photovoltaics and solar thermal energy; you can benefit from both technologies simultaneously. This allows for very efficient use of the available space–usually the house roof.
In terms of efficiency, PVT systems are also advantageous. The solar thermal layer removes heat, cooling the solar cells above. This increases the electricity yield, or the efficiency of the PV cells is improved.
Additionally, the combination with a heat pump is a plus. It is possible to operate the heat pump with the PVT collectors, supplying it with electricity and heat. Furthermore, the PVT collectors can be used as heat and electricity generators. The snow melts due to the heat from the ST modules, so the electricity yield is maintained even in cold or snowy months.
Cost savings are also crucial with this system. Hybrid collectors can help reduce energy costs by covering both electricity and heat needs. This can lead to significant cost savings in the long term.
Disadvantages
However, PVT systems also have some disadvantages, though they do not significantly outweigh the benefits. The biggest drawback is the cost. PVT systems or collectors are more expensive to purchase than traditional PV or ST collectors. The selection is also still relatively limited. Maintenance can be more demanding, as both electrical and thermal systems need to be managed and maintained.
Another issue could be the insufficient heat demand of a house. It is well known that less hot water is used in summer, and the demand is simply too low. Therefore, a PVT system is generally worthwhile if there is a high heat demand year-round. In the PV module, the accumulated or unused heat can lead to energy losses.
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Applications of PVT
PVT systems offer many applications. They can be installed on residential buildings to meet both electricity generation and heat needs. They can also be installed on commercial buildings and especially in agriculture. In short, PVT collectors can be used in various areas or sectors. They can contribute to simultaneously meeting electricity and heat needs, reducing energy costs, and promoting sustainability.