In climates where there are freezing temperatures, the water in solar hot water panels is in danger of freezing. No hot water is produced when this happens, and it’s possible that the panels or piping could be damaged when the water expands as it freezes. However, it’s perfectly possible to get solar hot water in a cold climate – even during the winter.
The most common way to prevent the solar hot water panels freezing is to use glycol-based solutions in the panels. This requires a closed loop system where the heat is transferred from the glycol solution into the water you use in your house via a heat exchanger. These systems are more expensive than simpler systems, but they are much more resistant to freezing and can continue to produce heat through the middle of a cold winter. You will probably want a tankless hot water heater as backup because they may not produce enough for your needs when there are long spells of cloudy weather, but they will still produce hot water. Both active and passive heaters can be outfitted with glycol so long as there’s a closed loop system.
Four-Season Solar Thermal Systems
Glycol-based solutions are typically used in active solar thermal systems, but they are also used in some Thermosyphon systems. In order to use glycol in a Thermosyphon system, it must be a closed-loop system in which the solution in the solar thermal panels does not mix with your household water supply. The glycol acts as antifreeze, preventing the pipes from freezing. These solutions are typically 50/50 glycol and water. Active glycol systems tend to be expensive, but they are considered the best choice for very cold climates.
There is one type of water-based system that can be used in frost-prone areas. This is the drainback system, which does not easily freeze so long as the piping is sufficiently inclined so that drainback can occur quickly. However, I suspect that this system is less tolerant of extremely cold temperatures for long periods of time than a system that uses a glycol fluid.
Three Season Solar Hot Water Systems
It is also possible to use a very simple system such as the batch heater during the summer and drain it during the winter. You will get no hot water from it in the winter, but it should still be usable the next summer.
As you can see, there are several choices of thermal hot water systems for homes in a cold climate. Whether active or thermosyphon glycol, drainback or summer-only batch, there is probably something available that will fit your needs and pocketbook.