What the Solar?
Solar Energy can be classified into two categories, Thermal
and Light. Photo-voltaic cells (PV) can provide a clean, renewable
energy source which can supplement and thus minimize the use
of mains electricity supply.Thermal energy obtained from the
sun can be used for a number of applications including producing
hot water, space heating and even cooling via use of absorption
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What is an Evacuatded
Evacuated tubes are the absorber of the solar water heater,
This type of tube is chosen for its reliability, performance
and low manufacturing cost.
Each evacuated tube consists of two glass tubes made from extremely
strong borosilicate glass. The outer tube is transparent allowing
light rays to pass through with minimal reflection. The inner
tube is coated with a special selective coating (Al-N/Al) which
features excellent solar radiation absorption and minimal reflection
properties. The top of the two tubes are fused together and
the air contained in the space between the two layers of glass
is pumped out while exposing the tube to high temperatures.
This "evacuation" of the gasses forms a vacuum, which
is an important factor in the performance of the evacuated tubes.
In order to maintain the vacuum between the two glass layers,
a barium getter is used (the same as in television tubes). During
manufacture of the |
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evacuated tube this
getter is exposed to high temperatures which causes the bottom
of the evacuated tube to be coated with a pure layer of barium.
This barium layer actively absorbs any CO, CO2, N2, O2, H2O
and H2 out-gassed from the evacuated tube during storage and
operation, thus helping to maintaining the vacuum. The barium
layer also provides a clear visual indicator of the vacuum status.
The silver coloured barium layer will turn white if the vacuum
is ever lost. This makes it easy to determine whether or not
a tube is in good condition.
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What is heat pipe?
The principle behind heat pipe's operation is actually very
simple.
At sea level water boils at 100oC (212oF), but if you climb
to the top of a mountain the boiling temperature will be less
that 100oC (212oF). This is due to the difference in air pressure.
Based on this principle of water boiling at a lower temperature
with decreased air pressure, by evacuating the heat pipe, we
can achieve the same result. The heat pipes used in solar collectors
have a boiling point of only 30oC (86oF). So when the heat pipe
is heated above 30oC (86oF) the water vaporizes. This va pour
rapidly rises to the top of the heat pipe transferring heat.
As the heat is lost at the condenser (top), the va pour condenses
to form a liquid (water) and returns to the bottom of the heat
pipe to once again repeat the process. |
When the heat pipe is shaken,
the ball of water can be heard rattling inside. Although it
is just water, it sounds like a piece of metal rattling inside.
Even though the heat pipe is a vacuum and the boiling point
has been reduced to only 25-30oC (86oF), the freezing point
is still the same as water at sea level, 0oC (32oF). Because
the heat pipe is located within the evacuated glass tube,
brief overnight temperatures as low as -20oC (14oF) will not
cause the heat pipe to freeze. Plain water heat pipes will
be damaged by repeated freezing. The water used in the heat
pipes still freezes in cold conditions, but it freezes in
a controlled way that does not cause swelling of the copper
pipe.
What units are used to express Insolation levels?
The values are generally expressed in kWh/m2/day. This is
the amount of solar energy that strikes a square metre of
the earth's surface in a single day. Of course this value
is averaged to account for differences in the days' length.
There are several units that are used throughout the world
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Is my region's
insolation level low, moderate or high?
The following scale is a basic guide for insolation levels.
Although a value of 5 is not considered very high during the
summer months, as an average annual value this is very high.
You will see that in central Australia, which is a hot, sunny
place, the annual average insolation is 5.89.
You may compare you location to the following two extreme
locations.
Average annual insolation levels:
Central Australia = 5.89 kWh/m2/day - Very High
Helsinki, Finland = 2.41 kWh/m2/day - Very Low
What size collector do I need?
When determining what size collector you need, you must consider
two key factors: insolation level and energy requirements
The calculator below can help to determine how many evacuated
tubes you require given your energy requirements. Solar collectors
come in a set of standard sizing of 10, 20, 24 or 30, depending
on your region
For more solar technology,Please contact us with solarsking@hotmail.com
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