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Solar Hot Water vs PV systems - storing surplus electricity

PostPosted: Sun Nov 01, 2015 10:38 pm
by EWesselius
Dear Madam or Sir,

I should possibly talk directly to a solar / heating specialist, but saw this forum and thought this may be a good source for info too.

We are planning to build a 5 bedroom house in the Waikato NZ, North facing, well insulated, walls R2.2 and roof R4.0 or higher, double glazing + argon low E glass and we plan to add solar power to the roof. We are still in the house design planning stage but we would like to know if we could be more or less self-sufficient during the winter time with for example a 5 KW Photovoltaic (PV) solar system.

Would a Solar Hot Water System be more efficient and cost beneficial than the PV system for heating up water?
Solar Hot Water System seem cheaper as initial cost. In the winter it may not heat up so well, while in the summer it would??
Similarly the same for PV system assuming less sun during winter time??

For the PV system we plan to put it on the North side of the rough sloping roughly 20-30 degrees. However, energy usage during the day may be less than during the late afternoon and so we were wondering if a panel set on the West side would be beneficial too. The idea being that more energy may be used in late afternoon. In latter case it would be required to have an inverter per panel set. Maybe we need to have some panels on the east side too, for breakfast time :-) and morning news, before going to work.

How much kWh would we get on average in the winter time from a 5kW PV system.

Heating in the winter is our main concern. We would like to use our own electricity but at night that would not work when we need it the most :D. So instead feeding surplus back to the grid during the day, at least get some return, we were wondering if the PV electricity could not be stored as heat in a dedicated very well insulated hot water tank and then at night or colder days circulate this through pipes in the concrete slab (underfloor heating). Would that work and be more cost effective?
How big would this tank need to be to bridge say at least 80% of the colder days in the winter?

Storing the PV electricity in batteries could be an option too, but this may not be beneficial at the moment?

The slab we intend to insulate at the sides and bottom and would work as heat sink during the day too as we intend to leave the polished concrete at least at the North facing side bare.

Looking very much forward to your reply.

Kind regards,
Erik Wesselius