There are 2 types of solar water heating systems, passive and active. Active systems are more commonly used in cold climates like ours.
- Active systems have solar collectors mounted on a roof or south facing wall. These collectors absorb the sun’s radiation through a heat transfer liquid.
- The radiation is converted into useable heat energy by pumping the heat transfer liquid through a heat exchanger that transfers the energy to the water heater system.
- This heat exchanger pre-heats the water entering the conventional water heater system, reducing the amount of energy needed to heat up water to the desired temperature.
Only active systems qualify for the Home Energy Efficiency Loan.
Common active systems
The most common active systems used in Manitoba are drainback and glycol.
Drainback systems use pumps to circulate household water between the collectors and a water heater inside your home. When the collectors get cold and the pumps are turned off, water automatically drains from the collectors into a reservoir tank inside the home.
Glycol systems capture and store heat in a closed loop filled with a propylene glycol (anti-freeze) solution. The heat is transferred to the water supply by a heat exchanger.
Compare the performance, cost, installation, and maintenance of both systems.
- Drainback system:
- water is a more efficient heat transfer liquid than glycol;
- may be more expensive, as it requires a drainback tank;
- careful installation is required to ensure that water drains automatically when necessary;
- minimal annual maintenance.
- Glycol system:
- glycol heat transfer efficiency diminishes over time;
- may be less expensive, but requires periodic glycol replacement;
- may be easier to install as placement of collectors and pipes is not critical for freeze protection;
- glycol should be replaced every 2 to 5 years.
Solar collectors
Several types of solar collectors are available with the most common being flat-plate (glazed or unglazed) and evacuated tube.
A glazed flat-plate collector system consists of solar heat-absorber plates fitted with a network of copper tubes. The tubes are in a glass-covered (glazed) insulator box. The sun passes through the glass and heats up the fluid in the copper tubes. The glazing reduces the amount of heat that escapes and protects the panels from moisture and other contaminants. Most household systems consist of 1 or 2 collectors. Unglazed flat-plate collectors can absorb more of the sun’s energy but loses more heat to the air in colder weather. Unglazed collectors work well in seasonal applications like summer outdoor pool heating.
An evacuated tube collector system consists of a series of insulated glass tubes that are arranged in parallel rows, each containing a small absorber pipe. The inner pipe absorbs solar energy and transfers it to a water or glycol solution. The air between the pipe and the glass is evacuated to trap heat in (like a thermos), maximizing the amount of heat energy transferred to the fluid. These evacuated tube collector systems tend to take up less space than equivalent flat-plate collector systems.
Compare the performance, cost, installation, and maintenance of both collectors.
- Glazed flat-plate collectors:
- typically performs better on warm, clear days;
- may be less expensive;
- direction and angle is less critical, providing more installation options;
- the whole collector may need to be replaced if a portion of it fails.
- Evacuated tube collectors:
- can produce higher output temperatures at very cold temperatures;
- may be more expensive;
- direction and angle is more critical, providing fewer installation options;
- individual tubes can be easily replaced with little effect on the whole system.