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How Solar Heating Works

With many people now focused on reducing their carbon footprint, there has been
increasing interest in renewable energy.

Arguably the best and most cost-effective way to do this is to install a solar-thermal
water heating system.

Solar-thermal means using the heat of the sun directly, rather than turning the sun's
energy into electricity then using the electricity to do work.

Most people in the developed world use lots of hot water for washing and cleaning,
so this is an excellent place to start reducing carbon emissions.
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Let's look at a diagram showing how a typical solar-thermal water heating system works. This is the type of system that would commonly be used in Northern Europe or the Northern parts of North America. It relies on pumping pressurized water through a closed loop between a solar collector and a hot water tank.

From the diagram we can see that a solar water heating system is really very simple. On the roof of the house there is a solar collector. This is usually a Solar Collector, with a network of pipes. The collector absorbs the sun's heat, which is then absorbed by the water. The Colector allows the sun's rays through glass tubes with metal pipes inside. Air inside the tubes acts llike insulation from the atmosphere outside.

This means that the collector can produce hot water even in cold air temperatures, so long as the sun is shining.

Good quality solar collector will last at least 25 years without maintenance.

The water in the collector is moved through a closed loop of pipe work by a water
pump. The pump uses very little power, generally around 25 to 50 Watts of electricity.
This type of system therefore does consume a little electrical power in order to harness
a much larger amount of power from the sun.
As the water in the system heats up and cools down, it expands and contracts. To
keep the pressure in the system fairly constant, somewhere in the loop there will be
an expansion vessel which compensates for changes in volume due to temperature.
The pressure used is only around 2 atmospheres, which is not high enough to worry
about.

Finally, the hot water generated by the solar collector must be transferred to the hot
water tank. This is done using a hot water tank with a special heat transfer coil. This
usually takes the form of a coil in the bottom middle of the tank. This is the coldest part
of the tank, so the system can transfer heat into the tank even if the sunshine is not
very strong. On days with only a little sunshine, your electric/gas/oil powered water
heating will still be needed, but they will have less work to do as the water will have
been pre-heated somewhat by the solar heating system. Modern hot water tanks with
these special solar heating coils are very efficient at transferring heat into the water,
and only a little more expensive than a standard tank.

The water that comes out of your hot water tap has not been through the solar
collector, it remains completely separate. This is partly because a pressurized, closed
system is more efficient at transferring heat, and partly because the closed system
must contain antifreeze to protect the collector from damage in cold temperatures. You
might be worried about the coil becoming damaged and leaking antifreeze into the hot
water tank.

Fortunately, this is not as big a concern as you might think. Solar water heating
systems use a special kind of antifreeze called Propylene Glycol, which is a common
non-toxic food additive.

The whole system will be run by an electronic controller. This uses temperature
sensors to work out when the collector is hotter than the water in the tank, so it
knows when to switch the pump on and of
f.

 

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