Will solar PV power my underfloor heating?
Posted by Paul Hutchens on 20 May 2013 at 9:29 am
Q: We are having a 4kW solar pv system fitted. We are also considering electrical underfloor heating. After reading some very interesting pages on your site I am beginning to wonder if electrical underfloor heating is the best option as this will mainly run when it is dark? Is my thinking flawed as I hoped that the generation payment and export payment would, in effect, subsidise any subsequent energy I have to buy?
We have a gas combi boiler, so would hot water underfloor heating make more sense? and would I have to install an immersion heater, run the central heating pipes through this, fit an Immersun, and also be able to somehow integrate the tank water in the existing combi powered DHW system?
A: This is an interesting and slightly involved question that identifies some of the key principles of renewable energy use in a home. I think that it would be good to cover a few basics and to answer this in stages:
- A 4kW solar PV system can produce enough energy to power an average home – around 3,500kWh per annum. This does not mean that the home will be self-sufficient by any means though as electricity is not used consistently and evenly – and is often needed when it is dark and no energy is being produced.
- There are battery based storage systems available but they are expensive.
- Therefore it is fair to say – as in your question – that the generation payment and export payment would, in effect, subsidise any subsequent energy you have to buy but without any direct link between supply and demand or the exact amounts involved.
- Electrical under floor heating is a “dry” system that cannot run off the combi-boiler; it is powered by electricity which could be boosted by the PV in sunlight.
- The combi-boiler could power a “wet” under floor heating system but there will be no direct contribution from the solar PV.
- To get a solar PV contribution to the hot water or under floor heating you would need to install a cylinder to be heated by the boiler – which would in effect now NOT be a combi-boiler having been converted to heat a cylinder rather than heating water instantaneously. The boiler and the immersion heater (which is electrically heated so can take a PV contribution) will heat the cylinder which will, in turn, provide the hot water for the “wet” under floor heating system. You could use a thermal store – a different type of cylinder but that may get too complicated for the purposes of this answer.
In summary, I think your set up would not make it convenient or cost effective to use PV to power under floor heating – unless you use electric under floor heating. This will be independent of the gas boiler.
More information about solar PV and underfloor heating on YouGen
Photo Credit: kevinthoule via Compfight cc
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