What do you know about solar panels

A solar system converts the sun's energy into heat, which, for example, heats the drinking water or supports the heating. Many questions often arise when homeowners want to buy new solar collectors. It is usually unclear which type of collector you should buy, how many you need and what they actually cost.

Comparison of collector types

The collectors of a solar thermal system, also called solar collectors, convert the light from the sun into usable heat. How efficiently this works depends on your solar collector structure. Homeowners can purchase flat-plate collectors or vacuum tube solar collectors, for example. There are also swimming pool absorbers and mixed forms of flat and tube collectors.

Buy flat-plate collectors for the solar system

You can quickly recognize flat-plate collectors by their box-like structure. They consist of a sturdy housing that faces the sun and is covered with a pane of glass. The absorber is located inside the components. This is a dark colored plate that warms up in the light of the sun. Pipes, which are usually located on the back of the absorber, absorb the energy and convey it to the heating system via a solar fluid. So that the box itself loses as little heat as possible, it is lined on the inside with a protective insulation layer.

If the roof is pointing in the right direction and the unshaded area is large enough, homeowners can purchase flat solar panels. Because these are comparatively cheap. With the same area, however, they achieve a lower yield than vacuum tube collectors.

Purchase vacuum tube solar collectors

Typical for tube collectors are the many individual glass tubes that are connected to one another via a distributor and collector. Each of these consists of two tubes lying one inside the other, between which there is an approximate vacuum. As with a thermos, the almost airless space minimizes heat loss. Inside the tubes are the collector and a special medium. This evaporates when it absorbs the solar heat and flows through it to the top of the tube. Here it gives off its energy to the solar fluid via a heat exchanger and cools down. It becomes liquid and the cycle begins again.

If the conditions on their own roof are not ideal or if the space is limited, homeowners can purchase vacuum tube solar collectors. Although these are somewhat more expensive than flat-plate collectors, they also achieve higher profits on the same area.

Vacuum flat collectors are an interim solution

Vacuum flat collectors are supposed to combine the advantages of flat and tube collectors. While the absorber is constructed exactly like a flat plate collector, a vacuum replaces the usual insulation. However, due to the rectangular shape, the construction effort is significantly higher here. In addition, the vacuum often cannot be maintained for a long time, which is why it has to be renewed at regular intervals. The solar collectors are comparatively expensive, but also enable a higher energy yield.

Swimming pool absorbers are simple solar panels

Swimming pool absorbers consist of dark colored mats into which a system of pipes is integrated. They have a simple structure and are comparatively inexpensive. The absorbers can be used, for example, to heat the water in a swimming pool. They are installed on roofs, porches or open areas and bath water flows through them directly. Swimming pool absorbers work with low system temperatures and mostly only in summer. Due to the higher outside temperatures, they achieve a good level of efficiency. However, this falls quickly when temperatures drop again.

Acquire the correct area for the solar panels

The right size of the solar system depends not only on the conditions on the roof, but also on the planned use. A distinction can be made between systems for hot water preparation and heating support.

Solar system for water heating

A solar system for hot water preparation uses the energy of the sun to heat drinking water for showering, bathing or washing up. If homeowners want to purchase solar panels, they should be of the following size:

  • 1.0 to 1.2 square meters of flat-plate collectors per person in the household
  • 0.8 to 1.0 square meters of vacuum tube collectors per person in the household
The required area can be larger if the roof has an unfavorable orientation or is shaded. An experienced installer on site, for example, provides a reliable answer.

Collectors to support the heating

The solar heating supports the conventional heating technology with free solar heat. Since more energy is required here, the collectors are usually larger. How large the area should be depends on the individual conditions and the desired solar proportion. If homeowners want to purchase solar collectors, they can roughly calculate with the following value:

  • 1.0 square meter collector surface per 10.0 square meter heated building surface
Since not every house is the same and the requirements for such a system can differ greatly, we recommend individual advice here as well. Because this is the only way to find the optimal collector area.

Cost of collectors in a solar system

Before homeowners buy solar panels, the price is also a decisive criterion. If you compare these with flat and evacuated tube collectors, this mainly reflects the performance of the components. In relation to one square meter, the costs with assembly and accessories are as follows:

  • Flat-plate collectors cost around 300 to 500 euros per square meter
  • Vacuum tube collectors cost around 500 to 600 euros per square meter

Funding for the purchase of solar panels

Since solar systems are particularly environmentally friendly, the state supports both the construction and expansion of existing systems. Grants of 30 percent can be applied for through the Federal Office of Economics and Export Control (BAFA). If the measure is part of an individual renovation plan (iSFP), the funding rate increases by an additional five percent through the so-called iSFP bonus. In addition to the costs for the system itself, the costs for connection to the hot water system and / or the heating system are also eligible, including solar storage tanks and risers. The prerequisite is that more than 50 percent of the solar system serves one of the following purposes:

  • Preparation of hot water
  • Heating of rooms
  • Combination of water heating and space heating
  • Solar cooling
  • Supply of heat and / or cold to a building network

Solar collector systems that have a gross collector area of ​​at least 20 square meters can alternatively be subsidized through a "yield-dependent subsidy".

Systems with collectors without a transparent cover on the front, such as swimming pool absorbers, are not eligible for funding. A current list of collectors and solar systems eligible for funding is available on the BAFA website.

Finance solar systems at low interest rates

If you need financing for a solar system, you can apply for a low-interest loan through program 167 of the KfW Reconstruction Loan Corporation. Homeowners receive up to 50,000 euros per residential unit. Since it is a supplementary loan, it can also be combined with the BAFA grant. Important: The program expires on June 30th, 2021. From July 2021, with the integration into the federal funding for efficient buildings (BEG), there will be a new credit alternative with a repayment subsidy from KfW.

First apply for funding then purchase solar panels

If you want to use the attractive subsidies from BAFA and KfW for your project, you must apply for them before hiring a specialist. Applications for BAFA grants are made electronically via the website. KfW promotional loans can be applied for through a financing partner. This can be a commercial or direct bank, but also an insurance company or a financial service provider. Once they have received confirmation, builders and renovators can purchase the solar collectors and have the measure implemented. If you missed the application period, you often receive subsidies retrospectively via the tax bonus for the renovation.

Conclusion by Alexander Rosenkranz

There are numerous decisions to be made when homeowners want to purchase solar panels. Because when it comes to the price, it depends not only on the type of collectors, but also on the use of the solar system. There is also support from the Federal Office of Economics and Export Control and the Reconstruction Loan Corporation.

Advice from your heating installer on site

Do you need individual advice or an offer for your new heating system?

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