Re: Automating immersion heater from Solar Voltaic ?

[Peter + Jane <pandj.munnoch@xxxxxxxxxxxxxx>]

Interesting one. My PV installation is sceduled=20
for 24th Jan (weather permitting). I have had=20
exactly the same thought. Export electricity is=20
worth 3p / unit. In my case my heat pump on=20
Economy 10 is 6p / unit. COP heating DHW is (say)=20
2, so dhw heating is 3p unit. No benefit.
But we have a hot tub :-) :-) . Not set up  for=20
heat pump so X10'd on Economy 10. I use an=20
appliance module and a contactor. So my thoughts=20
were how to get a switch on / off logic based on=20
over generation. I use an OWL+ usb on consumption=20
monitoring. If the usb were permanently connected=20
data is almost real time,. I thought about a=20
second OWL on solar, then export data to Excel=20
and drive an X10 Powerflash somehow.Or, since the=20
inverter sends Bluetooth data but not sure what, wait and see.
That's as far as I got. Figured installing the panels was a first step.
I thought I would gather my facts and then float=20
it as a business opportunity for a forum member=20
to develop a box and give me an early prototype for coming up with the
idea=
.
Now I feel gazumped!
Interested in the views of the cogniscenti.
Rgds
Peter

At 18:14 17/01/2011, you wrote:
>
>
>It sounds a good idea but I suggest your friend=20
>checks his sums and looks at his hot water usage=20
>carefully before going too far down this route.
>
>For example, a 150l cylinder takes about 7kWh*=20
>to heat from 19C to 60C (that's just a figure I=20
>had to hand) and loses about 1-2kWh (IIRC) a=20
>day. Above that the immersion thermostat will=20
>cut off the supply. So if your friend uses that=20
>much hot water a day in summer then it will=20
>easily absorb 2-3 kWh from his panels. However=20
>with a modern gas boiler say that's 8kWh gas=20
>which on my tariff is 6.7 (first 125 pqtr) or=20
>2.7p/kWh =3D about =A316 a month in the summer which=20
>needs to be compared to what he'd get for=20
>exporting the electricity. (I'm not sure on this=20
>- the FIT distorts things somewhat).
>
>Home PV is a bit like Solar Thermal where you=20
>get the most energy when you least need it. I'm=20
>not certainly not saying using PV for DHW is a=20
>bad idea, just to make sure it's worth the=20
>effort... and if you do the calcs please post=20
>them on here so that others can see your conclusions :)
>
>* kWh energy stored in DHW ~=3D <volume(l)> * 4.18 * <temp
diff> / 3600
>
>
>
>
>


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