Warming up to Solar Water Heating
"From April to September, solar power will cover 90 per cent of your (water) heating," says Michael McGahern, whose company, Ottawa Solar Power, sells, installs and services solar hot water systems as quoted in an Edmonton Journal article*. "From June to September, it'll be 100 per cent."
Throughout the rest of the year, when sunlight is less intense, McGahern estimates that solar energy provides 50 to 60 per cent of a home’s hot water needs. The systems that he installs switch over to traditional electrical power sources when solar power is not adequate.
The cost of a solar water heating system is approximately $6,500. Although the federal government ended grants for solar heating retrofits in March 2010, these systems are still affordable. With very few moving parts, a solar water heater can last 25 years or more. Homeowners recoup their costs within several years then enjoy many years of free hot water heating.
From a humble beginning more than a hundred years ago as a water tank painted black, solar water heater technology has come a long way. The oil crisis in the 1970s provided an economic incentive for research into harnessing the sun’s renewable energy. As a result, these devices have become very affordable, efficient and popular in Australia, Japan, China and many European countries. It is estimated that 30 million homes in China use these heaters and the price there is just $190 (as of 2011). Germany has the largest number of solar heating installations in Europe. Interestingly, many German cities are as far north or more northerly than Canada’s major cities.
How does a solar water heating system work? The basics:
There are two main types of solar heaters: those that pump water directly through a heat collector and those that pump a fluid (such as glycol) through a heat collector then pass that heat to the water through an exchange system (usually coiled tubes immersed in water). The collector itself can be mounted on a south-facing roof or wall and consists of rows glass or copper tubes within a protective panel. Systems designed for large commercial properties sometimes concentrate the rays of the sun with a parabolic mirror to maximize the potential heat absorption. This technology is expected to make its way to the residential level at some point.
Another key distinction between systems is backup power. Purely solar-powered systems rely only on the sun while others have backup electrical or gas power when sunlight is not sufficient. Most Canadian homeowners will need to purchase a system with backup power since the angle of the sun during the cooler months cannot meet the water-heating needs of most households.
Since hot water heaters are located on the main floor or basement of most homes, the water must travel up against gravity to reach the solar collector. Moving the water through the tubes is accomplished with a pump (an active system) or by natural convection (a passive system), in which heat rises and cold descends.
What about freezing winter weather in Canada? Any company that sells solar water heaters in Canada will (or certainly should) be offering products that are built to withstand freezing temperatures. When water freezes it expands and can burst tubes. Some products are designed with flexible tubing such as silicone rubber to avoid breakage but that is fairly uncommon. Typically, solar water heaters use fluid that contains a type of anti-freeze or it has a drain-back system. The latter allows water to drain out of the tubes when the temperature falls to a near freezing level.
Overheating can also be an issue, especially when homeowners are vacation and hot water is not being used for showering, laundry, etc. Heaters that incorporate the drain back system are designed to avoid producing overly hot water. When the temperature in the storage tank reaches a desired temperature, the pumps are shut off, which puts an end to the heating process.
Although heating water is a basic need, harnessing the heat of the sun and delivering it to taps can be somewhat complex. With these solar water heating basics in mind, homeowners will have a good starting point to research local companies. Just as with any home improvement project, it is a good idea to obtain multiple quotes, ask for references and get the price and details in writing. A reputable solar water heating company will ensure that the homeowner has a system that meets their hot water needs while providing an earth-friendly alternative that is very economical in the long-term.
*Solar Powered Homes, Edmonton Journal, March 3, 2008