Do Solar Water Heaters Work In Winter: Pro efficiency tips

Climate change is a real threat. So it’s prime time to take action as soon as possible. Planting trees is helpful and has a positive impact no matter what, but it can’t save us! Right now, our top priority should be replacing fossil fuels with renewable energy sources as soon as possible. And to achieve that goal, nothing can beat the effectiveness of solar appliances.

Solar energy is renewable and causes little to no pollution when we make practical use of the Sun’s energy using various devices like solar panels and collectors. And no doubt, solar water heaters are one of the most popular applications of solar collectors. Although solar water heaters are eco-friendly, one question will always be in mind when we discuss their usability! Does a solar water heater work in winter or cold climates? Ultimately, we have to see if solar appliances are meeting our expectations or not. Otherwise, we can not popularise these devices on a large scale.

In this article, we’ll dive deep into understanding if a solar water heater can work in winter or not! Later in this article, I’ll also explain its efficiency in cold climates. If you are considering buying a solar water heater for your cold weather, this is the only guide you need. Let’s start with your primary question first.

Do solar water heaters work in winter and cold climates?

A solar water heater can work in winter and cold climates as long as it’s daytime when solar collectors in the solar water heater can absorb the heat energy from the solar radiation. However, the efficiency of Solar heaters in winter is lower than in Summer.

Cold temperatures can not stop the collectors from absorbing the heat energy; that’s why solar water can work at any temperature. However, at night there is a possibility that the water will freeze inside the tank. For that, solar water heaters are insulated to stop heat loss. Also, a pressurized antifreeze water heater system can work well in freezing temperatures, where we use an antifreeze solution as the heat transfer fluid. 

Next, we’ll try to understand in detail why and how solar water heaters can work in winter!

Reasons behind Solar water heater working in winter

There are three main reasons solar water heaters work even in winter. And the most important thing to understand is the Solar heater’s working principle, and we’ll talk about it first.

Working Principle

A solar water heater works differently than a PV system. A PV system works on the Photoelectric effect, while Solar water heaters work on heat transferring with the basic principle of Solar collectors. Solar collectors are anything that can absorb heat energy from solar heat efficiently, and even your body can act as a solar collector.

Here, understanding a solar heater’s principle is way simpler than a PV system. First, we use the principle of solar collectors to absorb the heat energy, and then we transfer the heat energy from the hotter part to the colder part of the liquid. It’s as simple as that!

Now, even in winter, as long as the Sun is up, we can get a fair amount of heat energy for the solar heater to work. But we need to accept the fact that the efficiency can be pretty low compared to Summer.

Solar water heater insulation

Solar water heater insulation is another big reason you can use it in winter. Almost all the parts of the system are insulated. First, all the pipes and the heat collector are insulated with a layer of wood to avoid any heat loss. Also, generally use an additional rigid layer of polyisocyanurate (popularly known as Polyiso) to retain heat. Polyiso is one of the best heat-insulating materials in the industry, with an R-value of around 6.0 per inch. If the layer is thicker, it will retain more heat.

If you are constructing your Solar heater on your own, you need to make sure the insulation is good enough and use a thick layer of Polyiso.

Basically, good insulation ensures the outside temperature does not affect the internal heat transfer much during winter. But as we know, insulation can not be perfect, and we can expect some noticeable heat losses in winter compared to summer.

Pressurized Antifreeze Solar heating system

A pressurized antifreeze solar water heating system is a perfect solution for freezing climates where you may get snowfall very often. This pressurized antifreeze system is a closed-loop system, where we use a heat transfer fluid to absorb solar heat using collectors and then transfer the heat to a heat exchanger tank filled with normal water. We don’t use regular water directly to absorb solar heat here. Commonly, we use Propylene glycol-water mixture as solar fluid/ heat transfer fluid in the system.

You can mix the glycol at a certain percentage to achieve a lower freezing point than your surrounding temperature. You can use the last five years’ data on the surrounding temperature in your region to get the reference temperature to avoid freezing. And thus, your antifreeze solution/heat transfer fluid is ready.

You should note that you need a pump to circulate the fluid in the entire system. And for that, you may require external power. You can use a solar panel to generate that power if you want to keep the whole thing off the grid. But, that would increase the cost and maintenance of the system.

The efficiency of Solar water heaters in winter

According to a recent report on the efficiency study of a solar water heater, some researchers found the exact efficiency numbers that we can expect in tropical regions. In summer, solar water heaters are 1.98 times more efficient than in winter. And in the rainy season, solar water heaters are 1.05 times more efficient than in winter.

We should remember that efficiency dramatically depends on the climate of a particular region, and these numbers may vary drastically. Primarily you may see much more variation in efficiency if you experiment in higher altitude regions.

5 Tips to make solar water heater more efficient in winter

• Make sure you insulate the system well.
• Use a perfect proportion of glycol in the antifreeze solution to achieve a lower freezing point than the outside temperature. 
• Connect it with a solar panel (or arrays) to induce external power to cope with freezing temperatures.
• Channel out the hot water from storage to a warm indoor space after the evening.
• From December to February, the northern hemisphere is tilted away from direct Sunlight. So try mounting the collector arrays at an angle that they get the Sunlight at around 90° most of the time.

Conclusion

You can definitely use solar water heaters in winter, but you must deal with low efficiency. However, as you know how to enhance the efficiency even in winter, I am sure you can now expect a better result!