Re: Automating immersion heater from Solar Voltaic ?

[Simon Haslam <simon_haslam@xxxxxxxxxxx>]

It sounds a good idea but I suggest your friend checks his sums and
looks a=
t his hot water usage carefully before going too far down this route.

For example, a 150l cylinder takes about 7kWh* to heat from 19C to 60C
(tha=
t's just a figure I had to hand) and loses about 1-2kWh (IIRC) a day.
Above=
that the immersion thermostat will cut off the supply. So if your friend u=
ses that much hot water a day in summer then it will easily absorb 2-3 kWh
=
from his panels. However with a modern gas boiler say that's 8kWh gas
which=
on my tariff is 6.7 (first 125 pqtr) or 2.7p/kWh =3D about =A316 a month i=
n the summer which needs to be compared to what he'd get for exporting the
=
electricity. (I'm not sure on this - the FIT distorts things somewhat).

Home PV is a bit like Solar Thermal where you get the most energy when you
=
least need it. I'm not certainly not saying using PV for DHW is a bad
idea,=
just to make sure it's worth the effort... and if you do the calcs please =
post them on here so that others can see your conclusions :)

* kWh energy stored in DHW ~=3D <volume(l)> * 4.18 * <temp
diff> / 3600
=20



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