Solar power: Thermal and PV

M

moneymakeover

Registered User
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I was recently considering getting solar thermal: I reckon in warm months it will mean switching off the gas for 6 months.

Our back roof is perfectly south facing with good angle.

So from say May until October we could simply turn off the gas boiler which we currently use for pumped shower.

However looking at the gas bills for these months the savings from above mentioned gas will only be about €250 so re-considering.

The other option is Solar Photo Voltaic
  • Disadvantage is the grid doesn't buy back any units.
  • But another option would be to add batteries which doesn't seem to be very popular
    we are never at home in the day time so I can't see any value in PV without batteries

BTW I suspect the main electricity usage is due to tumble dryer which is on every day in winter.

Wondering if people have advice please

Below is 12 months of electricity and gas bills

Gas
02-Jul €88
01-May €212
27-Feb €257
21-Dec €179
26-Oct €80
24-Aug €72
Total for the year €888

Electricity
06-Jun €166
13-Apr €191
06-Feb €193
01-Dec €147
06-Oct €64
03-Aug €81
Total for the year €842
 
I think you've spotted the flaw yourself. Payback time for solar thermal and PV is very long for most people in Ireland. And don't forget the significant standing charges on your gas and electricity bills which don't go away when your usage drops. Maybe if summers like the current one start being more common, and we all start using air conditioning, there will be a better match between hours of insolation and electricity usage. Until then, PV without storage is problematic.
 
If you had an electric car and live away from free recharging point and car is around in the day time may pay for itself,
 
Yes, if you are an electric taxi driver who only works nights and does low mileage, solar PV could work. For the other 99.9999% of people, your mileage may vary.
 
Last edited:
Laughahalla said:
Payback on Solar PV is now reduced due to grant. Might be worth consudering.
Click to expand...

That all depends on your usage patterns. Despite the current grant levels, many people will never see a payback on the original outlay & maintenance costs.
 
I am in a similar position to you (except with oil heating), and the only thing I would add is that firing up the boiler for 1/2 an hour to an hour a day from May to October might be better for it than leaving it sitting idle for that time. I am only guessing but I think leaving it idle for 6 months might cause more problems, e.g. corrosion etc.

I have run the numbers and cant see the payback for going either solar hot water or solar PV. Maybe when I'm retired and the electric car will sit on the driveway during the day.
 
I presume using a good quality "instant" electric shower is more efficient in terms of energy usage & cost, during summer months rather than heating a hot cylinder only & the associated loses of heating / piping water from boiler to hot press.

Has anyone worked this out by calculation?
 
Battery is the way to go here.
You can also ‘store’ some of the energy created by using an immersion divertor to heat your water while you are in work.

I have a 3kw system that I installed last September while gutting the house. I had the roof off and had the system installed for cost price so it was a no brainier to do it at that time.

My motives were not purely financial though, I wanted to do my small but for the environment and I also drive an EV but I’ve only charged that at home twice in 18 months due to work chargers.

Anyway, I’ve no battery. Too expensive at the time. They have dropped big time and I am actively looking into installing one. Ive barely had the gas boiler on since April, obviously haven’t needed the heating due to the warm weather and I’ve only boosted the water twice since then (1 hour each time).

The system fills my 200L hot water cylinder most days as I have a divertor and surplus powers the base load of the house but the majority goes back to the grid. I could fill a 5kwh battery most days and that’s after filling my water tank. Generation at the moment is about 10-12kwh per day.
 
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