Solar Water Heaters

The Efficiency of Solar Hot Water

Fossil Fuels In Canadian households, hot water represents the second largest energy consumer after space heating, and such, the most viable and most widely used application for solar panels is for heating water. Solar water heating is popular because it requires quite simple technology and because solar heated water can be stored much more easily compared to solar space heaters. In contrast with solar electricity production using photovoltaic cells (PVs), solar hot water (SHW) collectors are typically more than three times as efficient at generating energy using the sun's rays.

Everybody loves to shower in the hot water - especially if it was free to heat it with solar!

- Steveo

Solar Hot Water System Types:

There are five basic types of solar water heating systems used in North America today. They are:

  • Batch
  • Thermosyphon
  • Open-loop direct
  • Pressurized glycol
  • Closed-loop drainback

Although all of the above systems may be available in Canada, only two are really practical for use in households in the cold Canadian climate. They are the pressurized glycol and the closed-loop drainback styles of solar collectors.

In addition to the basic styles, all solar hot water heaters for domestic water fall within two classes of systems. There are "open loop" (the domestic water itself is directly heated) systems and "closed loop" (a heat-transfer fluid is heated by the collector and the heat is passed on to the domestic hot water by means of a heat exchanger) hot water systems. Additionally, like solar heating systems in general, some are "active," using moving parts such as pumps and valves, and others are "passive," using no moving parts.

Pressurized Glycol Solar Hot Water Systems

In this active type of, closed-loop solar hot water system, potable water flows into a solar storage tank, but it never enters the solar panels nor does it come into contact with the fluid that circulates in the solar panels. The fluid that does circulate within the solar collectors, a water and antifreeze mixture, stays in a separate pressurized system away from the potable water. The fluid is pumped in a loop starting in the solar collector into a heat exchanger within the solar storage tank. the fluid then releases it's heat into the potable water that surrounds the heat exchanger. Since the fluid within the collectors is an antifreeze mixture, it can remain in the solar panels during the night without fear of freezing.

Closed-loop drainback Hot Water Systems

The closed-loop drainback system is another active system that employs a heat exchanger coil within a solar water storage tank. In fact is type of solar hot water system works quite similarly to the pressurized glycol system in that it maintains two separate water systems so that the potable water never enters the solar collectors.

The significant difference between the drainback system and the pressurized glycol solar water systems is that instead of using antifreeze mixed water in the collectors and the heat exchanger, the system uses distilled water. And, to keep the distilled water from freezing once the sun's rays become too weak to heat the water, the system automatically drains the water out of the solar panels into a secondary storage tank. When the temperature within the solar collector becomes high enough the fluid is then pumped back into the collectors and throughout the system.

Parabolic Mirror Based Hot Water Heaters

I just read about SOLARTRON Energy Systems Inc., a Canadian company that has developed the "SolarBeam Concentrator" which provides more solar heat energy than conventional hot water systems. The interesting thing is that since it is more efficient, the payback period is as little as six years, compared with 20 or more years for conventional flat panel solar panels or 15 years for evacuated tube solar panels.

The SolarBeam Concentrator system may be the most efficient solar hot water heating systems available in Canada. Since they are not panels but dish like heaters that concentrate energy using a focal point as when using a parabolic mirror, the SolarBeam is more efficient that simple hot water solar panels. Also, the SolarBeam concentrator is often installed with a computer-controlled tracking system for the solar panels that maximizes solar concentration throughout the day.

The above is based on this press release.


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