Help with the figures, please

DdraigGoch

I am in the fortunate position, courtesy of two bereavements, of being able to consider the following:

Solar Thermal - for preheating point of use electric water heaters

Solar PV - for supplying electricity [and FITs] for aforementioned water heaters

Wood fired Domestic Hot Water - for preheating point of use electric water heaters

I cannot install Oil Domestic Hot Water heating.

I cannot install large scale Gas DHW.



I already have "central" heating courtesy of two woodfired stoves and a woodfired range, plus an awful lot of currently being installed insulation, so do not need any more central heating input. If the fires are insufficient, I shall use spot heating.


I have a huge South south west facing roof. I also already own a Wamsler wood fired boiler [11.5Kw] but the cost of installing the thing is where I am wondering which system would be most economical.

I'm making the following presumptions:

Going with the Wamsler boiler, I need to purchase a suitable tank, sufficient fluing, get it installed and certificated and will then be spending about £30/cold month on heating the water.

I have used 1746KwH over the past 12 months. This includes spot heating during the very cold weather, and without any insulation.

I am now at a loss as to which system to go for. Salesmen for each option tell me their's is best [no surprise there, then! But, to be fair, they do only know their own system...] but I cannot seem to get a level playing field view of the options. I've spent months on this but have rather ground to a halt. Please could someone help me out.

Many thanks in anticipation.

Cardew

There are several threads running in this section that discuss both solar thermal and solar PV.

My opinion is:

Solar thermal in money saving terms is a complete and utter waste of time!

Firstly the output you get in hot water is worth very little, usually around 1,000kWh a year with nearly all of that in Summer, and virtually nothing in winter. That is worth from £30 a year if you have a modern gas boiler, to perhaps £100 a year if you heat with daytime electricity.(why not use Economy 7?) WHICH magazine suggests savings are £55 a year.

Anyone who 'invests' £4,000 or so for those derisory returns, ain't interested in money saving - you lose around £150 in interest on your £4,000 for a start.

Next year if the renewable heat initiatives are adopted, this picture will improve; but I doubt if it will be viable.

Solar PV is a much better bet purely because there is a huge subsidy(the Feed in Tariff -FIT). Even so with the large capital investment(and loss of interest from that investment) payback times are very long - I don't think anyone has come up with less than 12 years.

I suggest you read those threads as the arguments are well rehearsed.

DdraigGoch

Thanks, Cardew. I have now taken your advice, read the threads and come to the conclusion that I would probably be better off installing the wood burning boiler, but only on an "insurance policy" basis, ie the money's gone and this time, instead of nothing at least if the worst scenario - no electricity - happens I can still have hot water at a reasonable cost, discounting the intial cost of the install.

I can see no way around this, other than the twisted thinking you see above! If I put the remainder of my money on deposit for 10 years at the best lock in I [you guys and Martin included, of course ] can find then the cost of electricity will be covered.

Thanks for your advice and thread pointing.

Mankysteve

In the event of power cut you lose your solar electi anyway. G38 standard prevent islanding of solar systems.

Scott_McLean

DdraigGoch, do be advised that Wamsler boiler is not listed as MCS certified and as it is sub 45kW it needs to be if you are going to be eligible for the Renewable Heat Incentive. You would be wise to investigate this further as you would be missing out on the fairly generous RHI payments involved.

Ben84

DdraigGoch wrote: »

Thanks, Cardew. I have now taken your advice, read the threads and come to the conclusion that I would probably be better off installing the wood burning boiler, but only on an "insurance policy" basis, ie the money's gone and this time, instead of nothing at least if the worst scenario - no electricity - happens I can still have hot water at a reasonable cost, discounting the intial cost of the install.

Do you often have such severe electric outages that you're considering installing alternative heating sources? Sounds quite bad, even compared to the number of times the electric goes out each winter here. I have a radiant gas fire that operates without electric if needed, but you can always keep a paraffin or calor gas fire in storage.

DdraigGoch

Thank you everyone for the points you have raised. I'm not looking to use the Wamsler 500 series boiler for anything other than hot water for a bathroom and the kitchen needs. I already have sufficient "central" heating. I use wood as my base fuel, with electricity as back up.

If we had very bad [rolling blackouts sort of thing] cuts then I'd be very concerned about my frozen food!

My concern is that, over 4 years ago, I bought a Wamsler wood boiler, having been assured that it would be large enough to give suitable background heat for the entire building I then discovered that it wouldn't - by any means! So, the point of my query is mostly, since I have come into enough money to install ONE of the systems above, which should I install?

The other question is, of course, should I install any of them?

Given that if I install, for example, my preferred option the wood burning boiler, I will invest about £2,000 and then each month expend about £30 plus associated work chopping/stacking/hauling wood and cleaning up the inevitable dust/grit/soot and so on; would it be more sensible to put that same £2,000 on deposit and use any interest to pay for the electricity/gas I would use instead?

That way, over 10 years, I would still have my initial £2,000, about £120 per annum x 10 = £1,200 in interest, whereas after 10 years with the boiler I would have spent the £2,000, not had the interest and spent approximately ((£30 x 7)x10)=£2100 on wood. The electricity at the current rate [pun not intended!] is 12p/KwH. To have enough DHW for the kitchen/bathroom would have cost approximately [including an annual rise of 5% in the cost of electricity] (((0.12 x 4)x365)x10)=£2203.

So, it seems to me that if I spend the £2000 now on the wood burner then I shall not have to spend £2203 on electricity, but shall have spent a total of £4100 for £2203-worth of electricity..... the cost of which would have been offset by £1200 = £1003 cost/10 years.

It ain't easy being green... nor, apparently, cost efficient. I would like to be as deep green as I can be, but don't know if I can afford it.

Hence my query.

Hoping my maths bear up under scrutiny... and I would really appreciate your points of view.