With the price of electricity and the attention to sustainable living increasing, renewable energy technology for heating is becoming very popular.
In most South African homes water heating is done by geysers taking electricity and converting it to heat. Solar heating and heat pumps offer a more sustainable and cost effective way to heat water.
How do you decide?
Your roof will help determine how you should heat water. If you have a roof that faces north and gets full sun, flat panels are the most trouble-free option and will provide most of your hot water needs. If your roof gets limited sun, evacuated tubes may be necessary to provide enough hot water. If your roof gets very little or no sun, you may need a heat pump.
Flat panel & evacuated tubes
Heating water via sunlight comes in two basic forms: flat panels and evacuated tubes.
Flat panels have a single large panel of glass over a collector lined with copper pipes to collect the sun’s heat.
Evacuated tube panels are made of rows of long glass tubes. In each glass cylinder, the heat is absorbed by a copper rod filled with a fluid (either water or an anti-freeze mix) which is insulated from the colder outside air by an insulating vacuum. Evacuated tubes generally create more hot water, especially when the sun is weak and the weather is cold, but they have one important disadvantage. Due to their efficiency, the collector risks overheating in summer. This problem could easily be avoided by covering the collector with a UV reducing product (preferably not sunscreen lotion).
Heat pumps, although also using electricity, are a method of heating water more efficiently than an electric geyser. Heat pumps use similar technology as air-conditioners in that they transfer heat from the air outside into the water. This is done using a refrigerant which absorbs heat as it vaporises. The condensed refrigerant releases the heat in order to warm the water. Heat pumps are reported to be three to four times more energy efficient than electric geysers. However, if it’s a greener option you’re looking for, a heat pump may not be suitable as most refrigerants (which are in the process of being phased out) create greenhouse gases which are harmful to the ozone layer.
Direct or Indirect?
Some panels heat water directly, which is called a direct system. But many heat a glycol solution so that panels don’t freeze on cold nights. The glycol solution heated in a flat panel flows through a coiled pipe inside the solar tank to heat the water. (The glycol and water never come in contact.) This is called an indirect system. With indirect evacuated tubes, the fluid is sealed within each tube and heats the water at the top of the tube, where it is inserted into a water pipe or tank.
Direct systems are less expensive and more efficient, so if you live in a frost-free zone, they are a great option. Having a home in an area that gets winter frost regularly, an indirect system is the preferred choice. Based on these facts a house in Cape Town, for example does not require an indirect system as temperatures do not reach below freezing point.
A solar water heater should eliminate not all but most of your electricity use for water heating. An electrical backup element in the tank is standard. A timer is essential for many reasons. First for managing the electrical usage to your element. Secondly the pure convenience of not manually switching the geyser on and off. The third reason is that timers (i.e. Geyserwise) recognize errors within the SWH system making troubleshooting detectable for maintenance. Finally having an intelligent controller system like Geyserwise manages the SWH equipment.
But with cloudy weather or a weak winter sun, extra heat will be needed to bring the warmed water up to a hot enough temperature. The key to saving energy is to avoid heating the water with electricity just before the sun gets to work. Therefore, every solar water heater should have a timer.
If your family is in the habit of showering and bathing at night, you can save the most by keeping the electricity off until the next afternoon. If morning showers require extra hot water, experiment with a short boost at 4 or 5 am, shutting off by 6 am for the rest of the morning. A thermostat timer like the Geyserwise allows the extra control of setting different temperatures for different times of the day.
A Roof Bracket
Your roof may be pitched at too low a slope to take the best advantage of the winter sun. Many people prefer the look of panels flat against the roof, but for maximum efficiency, your installer should be able to tell you the ideal angle for panels at your latitude. (36 degrees to 44 degrees) If your roof has too low a pitch, consider installing a bracket to support the panels to the ideal angle, which will increase winter heat gain by about 10 to 20 percent.
|Heat Pump System||
|Evacuated Tube System||
|Solar Flat Panel System||
For more information regarding solar energy options please contact Kenneth Higgins from Solar Rise on 076 648 0490 or email@example.com
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