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Its the 13th of February and
the weather forecast strongly agrees with what is happening outside. Its
cold, its windy and we have had a series of snow showers. However, every
so often the sun pops out and my solar panels positively welcome the warmth!
 Image
taken from the weather.com website
on the 13th of February.
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During the sunny periods the
panels warm rapidly. The controller is set so that when the panels are 15°C warmer than the base of the hot water cylinder, the system kicks into
action, transferring heat from the panels to the bottom of the cylinder.
As the cylinder warms and the
panels have their heat transferred to the cylinder, the system stops
when there is only a 5°C difference.
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On a day
when the outside temperature is about 1°C and the sun came
out for a maximum of about 10 minutes at a time , the panels were
able to get to a temperature of 46.9°C
The measurement seen to
the left is taken from TKO on the solar panels - see diagram below |
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Over the course of the morning the panels generated about 2KWh
the equivalent of leaving a 2 bar electric fire running for an hour.
When the sun was out, and the system was running, the sun was delivering
at the rate of 2.7kW! |
The solar water heating system raises the temperature of the lower
part of the hot water cylinder by transferring heat from the panels
to the cylinder until there is a point of relative equilibrium. On a cold winters day with little sun like 13th February the day
this study was carried out, the solar system shuts down and allows
the panels to build up heat again before kicking in and transferring
heat to the cylinder. |
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Remembering that like air, hot water rises, the hottest water that
was earlier heated by the boiler will remain at the top of the cylinder
. The area below the cylinder will be substantially cooler and thus
more readily heated by the solar panels. |
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By the end of the day when what little sun there is has gone,
and what with any washing or other use of hot water in the house
having drawn off the upper hot water from the cylinder, the residual
water that now has to be heated by the boiler is at 31° C. Without
the solar heating it would be nearer 0° C thus taking a huge strain
off the boiler and saving money even mid winter!
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The schematic below shows the relationship between the hot water cylinder
and the solar panels. DC is the controller which monitors the differences
between TKO and TBU. When TKO is 15°C higher than TKO, the system runs
until the temperature difference is 5°C when it shuts down.
Hot water leaves the cylinder from the very top while cold water enters
from the very bottom. The hottest water is always at the top of the cylinder
ready for use.
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