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A well-designed solar system will typically provide up to 75% of your hot water requirements and up to 20% tax-free return on your investment.
The sun gives out an almost unlimited amount of energy and when the sun shines there are about 1000 watts of free energy available for every square metre of land. This energy is ideal for heating water and harnessing this power can make large savings.
Solar water heating converts the energy of both the visible and the infrared sun rays into heat whenever there is daylight, although more heat will be delivered on a clear day than when it is overcast.
Although a solar water heating system could be designed to fully meet your winter demand, it would generate excessive hot water in summer and be at an unacceptable cost relative to the financial return.
The main component of a solar water heating system is the collector. The function of the collector is to capture as much solar energy as possible and transfer it in the form of heat to the fluid in the collector, either the storage water or a glycol based mix.
The heated fluid is transferred by pump, or thermo-siphoning, either directly into the hot water cylinder or into the storage water through a heat exchanger.
The amount of collector area needed depends on the efficiency of the collectors, your daily water usage, the geographical location of the house/site, the orientation and slope of your roof, and the type of heat transfer system employed, thermo-siphon or forced.
Your return on investment is dictated by the performance of the system.
The Benefits Of Solar Water Heating
Being cushioned from inevitable energy price increases or future fuel shortages.
Free hot water well after the system has paid for itself.
At today's energy prices you can expect a tax-free rate of return of 12-16% on a solar hot water system installed in an existing home and over 20% return in a new home. Energy prices are sure to increase in the future.
Reducing this country's dependence on foreign oil.
Avoiding air pollution and wastes created when your supply company generates power.
Over 20 years a Solar Hot Water System avoids more than 50 tons of carbon dioxide emissions - equivalent to the volume of 50 large houses. Carbon dioxide traps heat in the atmosphere, thus contributing to the "greenhouse effect."
Types of Solar Water Heaters
Solar water heaters can be either Passive or Active.
A passive solar system (also known as thermosiphon system) has no control or pumps and relies, for its heat transfer, on thermosiphoning. As the fluid or water in the panel heats it uses the natural tendency of water to rise as its temperature increases to push fluid or water from the collectors to the storage tank, which must be located higher than the collectors.
There are two significant drawbacks with thermosiphon systems:
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The hot water tank must be located higher than the collectors - usually on the roof itself.
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There must be a significant temperature differential between the tank and the panels before water will circulate. In temperate climates, such as New Zealand's, where cloud cover may come and go, thermosiphon systems are frequently inactive even though the panels have collected solar radiation.
An active solar system (also known as forced circulation) utilizes an electronic controller and an electric pump to circulate the fluid or the storage water. Active systems are more efficient and usually easier to retrofit than passive systems because their storage tanks do not need to be installed above or close to the collectors. Tanks can go into attics, basements or even outside the home at ground level.
Advantages of forced-circulation systems:
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Higher efficiency ratings than thermosiphon systems. This is because forced circulation systems do not require consistently high daytime temperatures, as is the case with thermosiphon systems.
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The tank does not have to be located above or even next to the solar panel.
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The tank can be located vertically or horizontally anywhere on your site. This is a special advantage if you have internal space restrictions or want to free up that hot water cupboard for more storage. Examples of places to put a cylinder: inside the roof space or at ground level, inside or outside.
Negawatt's Chromagen System uses the active type. More...
Within those two types you have Open Loop or Closed Loop system.
An Open-Loop solar system circulates your storage water directly through the collector and stores it in the tank. This works fine with water that is not hard or acidic. Hard or acidic water corrodes copper pipes in the collector, causes scale deposition, lowers efficiency and reduces the life span of the system. Open Loop systems are not suitable where frost or freezing temperatures are expected unless some type of freeze protection device is fitted.
A Closed-Loop solar system circulates a heat transfer fluid through the collector. This fluid is generally a solution of glycol mixed with a metal inhibiter to protect the fluid circuit from freezing and preserve the life of the system. It picks up heat in the collector and transfers it through a heat exchanger into the storage water.
Key advantages of a closed loop system are:
The Closed-Loop system has been recommended to be the most ideal and efficient for New Zealand conditions by EcoLiving magazine Issue No 10.
Negawatt's Chromagen System utilises the Closed-Loop heating circuit. More...
Contact Negawatt for a quote and more information.
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