if your hot water usage is low (and it looks like for the OP it is) then the cost of a heatpump system might not be justified. You may be able to get that same result cheaper with an electric storage system and enough extra pv to cover the usage.*
Its been a couple of years since i checked the maths and it depends on FiTs and if you can get the heating cycle to run when the solar panels are producing etc etc.
- I would work out my hot water usage in KWh (include tank losses)
- work out how many KWh that would be if a sanden unit was used.
then look at these 3 options:
option 1 - get a price on a sanden system supply and install and on the solar pv your thinking of putting in (sized to cover your sanden and anything else you want)
or
option 2 - get a price on a resistive storage HWS supply and install of the same size AND solar PV upsized to cover the additional KWh needed by the HWS (probably work with winter PV generation estimate for this).
or
option 3 - get a price on a resistive storage HWS supply and install of the same size AND solar PV upsized to make the same total price as option 1.
for each option
- make some adjustment for the extra grid power each HWS will use on overcast days
- make some adjustment for the excess solar PV available for use in your house or sold to the grid. Extra allowance if the house is left empty for long periods and all pv power can be sold.
- consider the lifetime/maintenance/warranty of components
- dont forget install costs - trades are expensive
At relatively low hot water usage options 2 and 3 come out ahead. At high usage option 1 comes out ahead. Where the switch over point is depends.
hope that helps
*you obviously need to have the roof space to install the extra pv
Posted Sunday 12 Jul 2015 @ 3:19:12 am from IP
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