Solar PV to power electric rads / underfloor

pinnks

I don't think you'll have much luck with trying to use Solar PV for space heating. I use gas for central heating and water top-up in winter and turn the gas off over the summer. 1980s insulated 4 bed detached gobbles about 10,000kWh of gas in the 6 winter months. During the same period I generate about 1,500 kWh. Some of that goes in normal background load, so you can see that at best I would generate about 10% of my space-heating requirements.


Not very scientific but gives an indication of what others have ben saying.


I use an immerSUN and a couple of oil-filled rads to take the chill off the living room in March/April and Sept/Oct when generation is still quite good but over the winter itself they don't add a lot.


Hope this helps.

DREKLY

Hello Dave-o, whereabouts in Kernow are you ?
I am about to have a 4Kw install, with immersun to heat
the immersion water tank - no gas here either, near Penzance.:)

MFW_ASAP

You would have to insulate your home to near Passive House levels to be able to heat it with solar PV. You'd also have to have the house airtight, which means introducing heat recovery air ventilation (you could connect the PV to a pre-heater attached to the air intake).

The issue you'll have is that you'll have no heating at night (which lasts a long time in december) and no heating on rainy/snowy days, which is exactly when you would want it.

If you're not keen on a Heat Pump, then a combination of solar thermal and wood burning boiler stove connected to a thermal store (a wet radiator system) would supply your heating needs in both summer and winter, and you'd be carbon neutral. This would require you to build fires and have a place to store wood.

The most convenient heating method (and one that would not put off potential buyers if you come to sell the house) would be a heat pump. Personally, I'd go for that option - it's no fun sitting in a cold house wrapped in jumpers and blankets, I can assure you!

dontgetcaught

Glad I got in on this
I have Pv solar, (Stage1)if you want to see what you get near you try https://www.generaytor.com, that will give you an idea of the generation you will get by comparing real figures.
The secret is not the savings but the income pays for the system, and you get a nominal payment for your export, but you do not have to export it, you get the same payment use it or not, so it's use it or loose it.
I am now looking at changing my house systems (Stage2), I am in the process or refurbishing the Central heating and Hot water systems, new bathroom etc.
Unless I hear differently I think I will be changing the Hot water Cylinder to a Heat/Thermal Store, heating this with surplus electricity via a controller like SolarImmersion, or similar, still researching this, help needed.
This will provide must of my mains pressure hot water and some heat to the central heating system, then the gas boiler can top up when extra heating is needed in the winter.
I can the upgrade my gas boiler (and it needs it Stage3) with hopefully a smaller boiler having seen the effect of these changes.
Advice welcome

Dave-o

Thanks all.
We are up near Perranporth, on the coast and have a decent S facing roof.
I just can't work this all out. Even if electric heating costs more for the 3 / 4 months per year that you need it, surely it is cheaper to use it than install a boiler, pipework, heat pump or similar over a 20 year period.
Let's say that PV + enough rads costs 8k to install and then you recoup, say, £600 per year on FIT, savings etc. I can't see a heat pump and the massive amount of pipework, elec required to power it ever catching up. The annual savings would pay for the winter heat required from the rads, no?
If not, is anyone clever enough to explain why not as I am struggling a bit! (a lot actually!)
Cheers.

dontgetcaught

Dave
In my case I separate out the pv from the house, that's just a good investment.
I am right you have no gas and dont want an oil boiler.
Have you considered a heat store with back up heat
(heat stores are cylinders where you store hot water not like the traditional cylinder but for heating purposes, you use this water direct in your central heating system or from either
-electric on e7
-wood burner with backboiler
-not insulting you but you have a lot of wind (down there) a wind turbine
most of the year you will get some help from the pv panels, really cold times can get a lot of sun if it comes from a high pressure.
You are right that the cost of a secondary heat source would pay the bills for a few years, but the downside to that is fuel is expected to rise, but with all of us on reducing energy consumption, they may not be able to put the price up as much as the past. (petrol prices have dropped again lack of demand)
using a heat store you could have the required connections in case you find that you want to add the secondary (to solar pv) heat source.
What do you think?

Dave-o

Sounds like a great combination. How would it work on a cold day (doesn't get that cold down here) if I was out (or away for a few days) and wanted the house warm for getting home?
Thanks for the thought. This sounds interesting.

dontgetcaught

the solar heating puts all surplus energy into the hot water
so tops it up, if your away your base load is way down
you get home and the insulation on the cylinder has reduced losses to a minimum, you just pump the hot water into your radiators
http://www.energysavingtrust.org.uk/domestic/thermal-stores
there are lots of diagrams on the net

let me know what you think having done some reading

i know it sound too easy

loskie

Only rely on a woodburner if you have very good access to free or cheap logs. Full price they are expensive to buy. It takes effort and management and you need to be at home to keep it going.
Look at wood pellets or logs with a large thermal store if a new build or major renovation. Remember these fuels will get more costly too as demand rises.
Energy Saving Trust may have info on installations local to you that you can visit and hear the reality from the owners.

Dave-o

Thanks again for all the advice.
What if we went for the system suggested by dontgetcaught, i.e. using a combination of solar PV and a log burner with back boiler, both feeding in to a thermal store.
If the two abovementioned sources don't produce enough heat, an electric immersion kicks in.
We live in Cornwall (warmer in the winter than the rest of the UK - but colder in summer!), the best place for generating electricity from PV and would be insulating the house up to the eyeballs.
However, the most important thing for our family is to make sure the place is warm and that several children can have several baths if needed!
Feedback from people around here on both ASHP and GSHP doesn't seem to be too positive. Does anyone have any practical, first- (or second-) hand experience of any of the above?
Cheers.