In the era of photovoltaics, solar collectors might seem to have become slightly less popular—however, this impression is misleading. With the shift in state policies toward less favorable PV settlement systems and emerging concerns about the disposal of PV panels at the end of their lifespan (typically estimated at 25-30 years), solar collectors are gaining renewed popularity.
Harnessing free and eco-friendly solar energy is a strong argument for choosing a cost-effective and environmentally friendly method of heating water. When is a solar installation a profitable solution, and what aspects should be considered during its planning? Let’s dive in.
✅ Do solar collectors work only when it’s sunny? What about cloudy days?
A solar collector operates most efficiently on warm and sunny days but also works on cloudy days. Moreover, it can be effective enough to meet a household's hot water needs, provided the solar system is appropriately sized. This is because the absorbers in solar collectors draw energy not only directly from sunlight but also from diffused light. Even in poor weather, they can function effectively and generally eliminate the need to heat water through alternative means (e.g., using a heating boiler or heat pump).
✅ Solar collector efficiency in winter – does it actually make a difference during the autumn and winter season?
Solar collectors also work in winter, but their efficiency is lower. Although they effectively capture energy from diffused light, during shorter days and low temperatures, they usually play only a supporting role, which can still significantly reduce the load on the heating system, especially on sunny days. Solar collectors require only sunlight to operate, even if the outside temperature is not high. This is possible thanks to properly applied components, such as absorbers, which are responsible for capturing thermal energy.
✅ Can solar collectors freeze? Do they need to be drained for winter?
Additionally, in systems using glycol (an antifreeze fluid), the solar system is protected against freezing, allowing for safe use even at low temperatures. It is worth noting, however, that in winter, solar collectors may require regular snow removal to ensure that the snow does not block light from reaching the panels. This happens rarely, though, as the standard tilt of solar collectors typically prevents snow from settling on them for long. It is also worth mentioning that in our climate, glycol-based solar systems, rather than water-based ones, are the standard. Therefore, the risk of freezing is virtually nonexistent.
In winter, solar systems are safe and still provide some heat output, although less than in summer.
How long will solar collectors work for heating water? When will they need to be replaced?
A solar system based on solar collectors is generally long-lasting. Depending on the manufacturer, it can function effectively for over 20–25 years. After this period, the efficiency of the collectors may decrease, and the heat output for water heating might no longer be satisfactory. However, it will usually be possible to replace only the collectors, as the other components of the system will already be installed.
When estimating the potential lifespan of a solar collector, it is important to refer to the information provided by the manufacturer or distributor of the product. Additionally, it is advisable to schedule periodic inspections and perform maintenance on the solar system to ensure its continued performance.
✅ Does connecting a solar collector to domestic hot water require a boiler with an additional coil, or can it be connected to the existing one?
No, you do not need to replace your boiler, even if it does not have a free coil. If you prefer not to replace your DHW storage tank and lack an available coil, there are solutions for connecting a solar system. Plate heat exchangers for solar collectors can be used. This small device allows integration into the hot water system by transferring heat from the hot glycol inside the solar collectors to the coil circuit, which provides heating for your DHW.
Solar heat exchangers are not complex devices and are therefore not expensive, typically costing 100-150 €. Fortunately, matching the device to a solar collector does not require a large plate heat exchanger (as is often the case with heat pumps), making it a relatively affordable solution.
Using a heat exchanger is definitely more cost-effective and less invasive than replacing the DHW storage tank. Additionally, the heat exchanger, like the solar system itself, is essentially maintenance-free.
✅ Can a solar collector be installed on any roof?
Almost any roof can be used for installing solar collectors; however, exceptions include older roofs that may not have sufficient load capacity or structural integrity. A solar collector typically weighs around 40-50 kg, so the technical condition of the roof must be considered, especially for older buildings. Installation on roofs covered with aged asbestos-cement tiles (eternit) is particularly questionable.
There is also the issue of roof exposure to sunlight, discussed below.
✅ Do solar collectors work effectively only when installed on the south side of the roof?
Maximum sun exposure allows the highest efficiency of a solar system, so the ideal placement for a solar collector is on the south-facing side of the roof. However, in our climate, excellent results can also be achieved by installing the collector on the southeast or southwest side—and, as a last resort, even the west side. These orientations also provide relatively good heat gains for heating domestic hot water.
Of course, compared to systems operating on a south-facing side, these options may result in slightly reduced performance. However, during summer and on warm autumn or spring days, this difference is unlikely to be noticeable. The heat gains will still be sufficient for heating water, provided the solar collectors are appropriately selected and correctly installed. The lower efficiency—or the perceived lack thereof—might be more noticeable in winter, where such a collector would offer little help in heating water. In practice, however, this is often not an issue, as other heat sources are typically required for heating during this time anyway.
At what angle should solar collectors be installed for optimal performance?
The tilt angle of solar collectors on a roof plays a significant role, just like with photovoltaic panels. Opinions on this vary, and the challenge lies in the fact that much of the literature suggests different angles for summer and winter, which makes sense given the sun's position in the sky during different seasons.
Some might ask why not 45 degrees, as it would seem to be the average between 30 and 60 degrees. The answer is simple. Solar collectors are designed to heat water during the summer, and ideally also in spring and autumn. In winter, domestic hot water heating is typically supplemented by a boiler, heat pump, fireplace, or another heating device. Therefore, the tilt angle is optimized for summer performance, with some consideration given to winter needs.
✅ Can a heatwave damage the solar system?
No, this is highly unlikely. Solar collectors are equipped to handle the pressure generated within the system even at high temperatures. Even if no one uses hot water, the risk of overheating is practically non-existent. This is partly because solar systems in our climate use glycol, which has a boiling point of 180–200°C depending on the type of glycol. There is no need to cover the solar collectors to protect them on hot days if household members are using hot water as usual.
However, during an extreme summer heatwave, if you plan to be away, for example, on vacation, you can cover the solar installation with a tarp or specialized cover. These covers for solar collectors can be purchased from various online stores. This precaution can extend the lifespan of solar collectors. It is always advisable to follow the recommendations of the manufacturer and the company that installed the solar system.
This depends on the specific situation, as each installation has its own requirements based on the building. For most buildings, installing a solar collector system takes a few hours, but in more complex cases, it can take an entire day. The installation process involves not just placing the collectors on the roof but also connecting and integrating the system with the existing domestic hot water setup.
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