Solar PV to power electric rads / underfloor

Dave-o

Hi All,
Just getting started on looking at solar PV and thanks all for the useful information in the forums.
I am struggling to understand why people don't use solar PV to power electric radiators / electric underfloor heating. If you are generating the electricity, then isn't it better to use it to heat your home than have, say, solar PV alongside an air / ground source heat pump.
Going round in circles with my research!
Cheers.

FrankRizzo

No solar power at night to heat the house

Dave-o

Cheers for that.

Can't you use a battery or one of those Immersun things to store up the electricity you generate?

Or maybe heat the house during the day using the power and then let it cool down overnight?

Martyn1981

Dave-o wrote: »

Hi All,
Just getting started on looking at solar PV and thanks all for the useful information in the forums.
I am struggling to understand why people don't use solar PV to power electric radiators / electric underfloor heating. If you are generating the electricity, then isn't it better to use it to heat your home than have, say, solar PV alongside an air / ground source heat pump.
Going round in circles with my research!
Cheers.

You could use a diversionary switch to store excess leccy in a hot water tank, or to power some sort of heater such as an oil filled rad.

I use the more basic system of just switching an oil rad on when there's enough excess, but that does run the risk of forgetting, and importing leccy.

Generally in the heating season, PV generates less, so there's not as much excess to use. Winter is when wind and hydro work best, but unfortunately these struggle to be economic on the small scale, and are more complicated.

Battery storage is on its way, and starting to gather momentum in some sun rich, high price leccy areas around the world. But don't expect much in the UK for perhaps 5yrs or more, as costs need to fall quite a lot.

Mart.

Dave-o

To add a bit of context, we are renovating and adding a two-storey extension. So we've got the chance to insulate as much as poss.
To me, it doesn't seem to make sense to add solar PV and a heat pump. Let's say the PV costs 5k or so and the heat pump 10k, you then need to add pipes, rads, boiler etc. on top of that. If you just have PV and electric rads in 8 rooms (£300 each), it seems like it would be a very long time before the heat pump and plumbing work etc. paid for itself (if ever).
If you go electric, you can also then make use of battery tech when it arrives and becomes accessible.
That's my thinking - please pick holes as I am sure there must be good reason why this doesn't work!

Dave-o

And thank you by the way!

EricMears

Dave-o wrote: »

To add a bit of context, we are renovating and adding a two-storey extension. So we've got the chance to insulate as much as poss.
To me, it doesn't seem to make sense to add solar PV and a heat pump. Let's say the PV costs 5k or so and the heat pump 10k, you then need to add pipes, rads, boiler etc. on top of that. If you just have PV and electric rads in 8 rooms (£300 each), it seems like it would be a very long time before the heat pump and plumbing work etc. paid for itself (if ever).
If you go electric, you can also then make use of battery tech when it arrives and becomes accessible.
That's my thinking - please pick holes as I am sure there must be good reason why this doesn't work!

The basic problem is that you've got an ample supply of free energy between May & October when you don't need any heating but hardly any generation when you start needing to heat the house. It's unlikely that 'battery tech' would ever be able to store enough energy over the Summer months to warm the house during winter.

Martyn1981

Dave-o wrote: »

To add a bit of context, we are renovating and adding a two-storey extension. So we've got the chance to insulate as much as poss.
To me, it doesn't seem to make sense to add solar PV and a heat pump. Let's say the PV costs 5k or so and the heat pump 10k, you then need to add pipes, rads, boiler etc. on top of that. If you just have PV and electric rads in 8 rooms (£300 each), it seems like it would be a very long time before the heat pump and plumbing work etc. paid for itself (if ever).
If you go electric, you can also then make use of battery tech when it arrives and becomes accessible.
That's my thinking - please pick holes as I am sure there must be good reason why this doesn't work!

Actually I've chatted with a guy who has PV and batts, and uses them to heat the house, but:-

1. He runs a heat pump off them to increase the returns.
2. He lives in Spain.
3. Spanish gen is not only better than UK gen, but more importantly (for heating) has a June to Dec ratio of about 2:1, whereas in the UK even for a very steep (50d) south facing roof it'll be 3:1.
4. I don't think he does this during the very bottom months.

I suppose if you make your house super efficient, and include the savings from not having a gas supply (standing charge) then leccy only heating may work out. But it'll have to be incredibly well insulated, and I still think you'd want to include some sort of heat pump (if only an A/C unit) to bump up your leccy v's heat ratio.

Then treat the PV as a separate investment, which would help a little bit.

Lastly consider batts (and a larger PV system) but this is probably something just to research and maybe come back to in a few years. Even then, doubtful it'll be able to compete with E7 leccy.

Mart.

ed110220

As others have said, unless your house is very well insulated, PV isn't going to make much of a dent in your heating demand. For example just taking where I live, 4 kWp of PV facing due south at 35 degrees will generate an estimated 27 kWh in Dec and 34 kWh in Jan. I pay 3.3p/kWh for gas so I'd save 89p of gas in Dec and £1.12 in Jan if I substituted PV electricity for gas directly (it wouldn't be exactly 1:1, but I think the small values show we're talking about pence here). There are also good environmental reasons for not replacing gas with PV electricity but instead exporting it for others to use (basically because the CO2 emitted in generating one kWh of electricity for the grid is a lot more than that emitted by burning one kWh of gas).

As for heat pumps, have you investigated air to air heat pumps? I'm no expert, but they are a lot cheaper than air to water. Though the general opinion is that they still only make sense if you don't have mains gas.

Ed

Martyn1981

ed110220 wrote: »

For example just taking where I live, 4 kWp of PV facing due south at 35 degrees will generate an estimated 27 kWh in Dec and 34 kWh in Jan.
Ed

Apologies for the pedancy, but aren't those figures per kWp, so would need to be multiplied by 4?

At least it proves I'm paying attention. I'll get my coat (anorak).

Mart.

tunnel

ed110220 wrote: »

For example just taking where I live, 4 kWp of PV facing due south at 35 degrees will generate an estimated 27 kWh in Dec and 34 kWh in Jan.
Ed

Ed, Is that a month or day?, either you're on the equator or the north pole but that don't sound right!!....I've pinned nearly all the 4 corners of the UK into PVGIS and can't get anywhere near them figures