Umbra on solar hot-water systems
I would like to change to solar heating for providing some of our electricity requirements, particularly for hot water. Can you advise me how to go about it?
Grahamstown, South Africa
I notice you’re in South Africa. I can talk about solar equipment as found in the U.S., and perhaps these general thoughts will be useful to you. Since the web is worldwide, I was able to see at least the signs of government support for a solar water-heater campaign in South Africa. Certainly we have all reason to believe that it is sunny enough there to do all sorts of solar energy production.
Here in the U.S., solar hot-water systems are considered a good first step in installing renewable-energy systems on your home. Unlike photovoltaic solar cells, which use the sun’s energy to create an electrical charge that runs our electrical appliances, solar hot-water systems serve as a replacement for a lot of the electricity (or gas) normally used to run a water heater. They use the sun’s energy to warm liquids, through methods familiar to anyone who has left a hose lying in the sun all day. The two systems look a little similar, because both involve large, flat, shiny panels on the rooftop. Basic solar water-heater panels will be maybe four feet by 10 feet, and you might have two of them, while PV panels might be smaller and more numerous.
In solar water-heating systems, the water can be heated in two rudimentary ways. In the first, the sun shines onto tubes or other containers into which cold water flows; it departs as hot water, then is stored, awaiting your pleasure. In the second method, a nontoxic glycol heats in the sun, then flows into a heat exchanger to give its heat to the water you will use. Some systems use a small electric motor (powered by your utility or generator) to circulate the water — these are “active” systems — and others rely on warm water rising and cool water sinking to circulate the water — “passive” systems. Other permutations include insulated tanks, conventional backup tanks, various reflective collecting plates, tanks on the roof, tanks in the house — you can get the details you’ll need on our government website or on one of these actual solar contractor sites. You probably also should look at the many South African solar businesses plying their wares on the web, some of which are listed on this Central Energy Fund site.
Although at first glance it seems like there may be lots of complicated choices to make between slightly different systems, I think you can easily eliminate a few. For instance, if you live in a climate where temperatures go below freezing (OK, this probably isn’t South Africa), systems with outdoor piping aren’t appropriate. Some systems require the water to be stored on the roof, and if your roof can’t hold the weight and you don’t want to structurally upgrade your home, that would eliminate that choice. Some systems will be more expensive, some will require more maintenance, some will be more efficient. A contractor where you live will be the truly useful adviser to you in this project. You will need the contractor to evaluate your site and tell you how much sun you receive, how and where a solar hot-water system would be installed, and how efficient various systems would be in your location.
To encourage you, let me add that here, at least, installing a solar hot-water system can be a financial benefit fairly soon. Our same old thorough government site can help you work out the economics for your home.
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