How do solar collectors work? DHW Solar system principle

✅ What is a solar collector and how does it work? How do solar collectors work?

Solar collectors are devices used to harness thermal energy from the sun. It seems they have had their peak in popularity, with people's interest shifting more towards photovoltaic panels. However, it turns out that nowadays, photovoltaics are slower to pay off due to the new system of accounting for the electricity introduced into the grid. As a result, solar collectors have regained interest. It is worth noting that having solar collectors is not an alternative to photovoltaic panels; both systems can complement each other well. In this article, we will discuss these and other aspects of solar collectors, their operation, and cost-effectiveness.

Solar Collectors vs. Photovoltaic (PV) Panels

First, it is essential to clarify that many laypeople confuse solar collectors with photovoltaic (PV) panels. While both devices harness solar energy, their construction, operating principles, and installation purposes are entirely different.

A solar collector is installed to capture solar energy and transfer it to water, heating it. Therefore, solar collectors are used to heat domestic hot water (DHW). Occasionally, they are also used to support heating systems (central heating), but this is more of an auxiliary use.

In contrast, photovoltaic panels are electrical devices. These panels contain photovoltaic cells that generate electricity when exposed to sunlight. This electrical energy is then adjusted to the home's voltage (220-240V) by devices called inverters. This electricity can then be used for any purpose.

✅ In summary, solar collectors are used for heating water, while photovoltaic panels generate electricity.

Construction of a Solar Collector - How Is a Solar Collector Built?

The construction of a solar collector can vary depending on the model, but all share the same operating principle, so their basic structure must be similar. The main components of any solar collector include the absorber and pipes.

What is an Absorber in Solar Collectors?

The absorber is essentially the primary component of solar collectors responsible for collecting solar heat. Absorbers are typically made of copper or aluminum.

The absorber is a surface coated with a special layer that enhances its ability to absorb heat. When sunlight hits the absorber, it heats up, and this heat is transferred to the liquid flowing through the solar collector. This liquid is usually water, which heats up this way. However, it's important to note that it is not just water; it's often a mixture of water and antifreeze (glycol) to prevent the collector from freezing in winter. This liquid then transfers the heat to the domestic hot water system.

Pipes of the Solar Collector

The pipes in solar collectors transfer heat from the absorber to the system, usually to a domestic hot water tank for heating.

Housing of the Collectors

Besides these two elements, solar collectors also have several other less distinctive components. Of course, every solar collector has a housing that protects it from heat loss, thus ensuring more heat reaches the DHW. This housing is typically insulated.

The entire unit is covered with tempered glass, chosen for its durability against weather conditions, including extreme ones like hail, while still allowing efficient heat absorption.

How does a solar collector work? Principle of operation

✅ What is the principle of operation of a solar collector?

Knowing the structure of a solar collector essentially means understanding its principle of operation. The working principle of solar collectors is quite simple. The fluid inside the pipes, heated by sun exposure, reaches very high temperatures. This heated fluid then flows to a domestic hot water (DHW) storage tank, where the heat is transferred to the water used by household members.

Since the pipes contain a mixture of water and antifreeze, this solution cannot directly enter the DHW tank. Instead, it flows through a coil inside the tank, heating the water without mixing with it. The entire process operates cyclically, and the circulation of hot fluid from the solar collectors is driven by a circulation pump.

What if the DHW tank doesn't have a coil? Plate heat exchanger for solar collectors

Sometimes, the DHW tank does not have an available coil for connecting the solar circuit. Older tanks often have only one coil, usually already used for the primary heat source (for example, a central heating boiler). What should be done in this case? Should the tank be replaced?

The solution could be to replace the tank with a new one that has two coils. However, this is only cost-effective if the existing tank is nearing the end of its life and is due for replacement. If the current DHW tank is still in good condition, it may not be worth removing it. Instead of spending a large sum on a new tank, it may be more economical to purchase a plate heat exchanger for solar collectors, which typically costs no more than a few hundred zlotys. This addition can effectively "extend" the DHW circuit from the heating boiler.

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Placement on the Roof - Where Are Solar Collectors Installed?

Similar to photovoltaic panels, the proper positioning of solar collectors with the correct angle of inclination plays a crucial role. The key is to place them in a location with ample sunlight, so it is recommended to install them on the south-facing side of the roof. If the roof layout does not allow for a strictly south-facing position, a southwest or southeast orientation can also be effective in our climate conditions.

Angle of Solar Collector Installation on the Roof

Like PV panels, the angle of inclination for solar collectors affects their efficiency in absorbing heat. The situation can be complex because many experts recommend different angles for summer and winter. As a point of interest, there are systems worldwide that automatically and seamlessly adjust the angle depending on the season. However, for a residential solar system, this would not be cost-effective.

☑️ In summer, the optimal angle for setting the solar collector is around 30°.

☑️ In winter, the optimal angle is around 60°. This also helps with snow clearance in snowy winters.

✅ Aiming for an angle of around 40° seems optimal in most cases. Generally, it is not advisable to position the solar collector for winter conditions since domestic hot water (DHW) will still be heated by the primary heat source (boiler, heat pump, etc.) during winter. Depending on specific conditions, other average angles, such as 45°, may also work well.

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