Oil Boiler or Solar PV

vandici

Hi all, I'm new to this forum so please be gentle!
We have recently finished an extension to a bungalow we bought 3 years ago are now considering the next step - new boiler or solar PV.
As part of the refurb we had a multifuel burner with back boiler, linked to a 300lt themal store, this is providing most of our heating and DHW requiremnts (but a chilly house when the burner has not been lit). Would it be sensible to consider solar PV as a source of top up heat (via its 2 immersion elements) to heat the thermal store during the winter period by way of the reduced electric costs etc gained thro the summer period?
The other option is a new oil boiler which will cost in the region of £3500 + vat. The bungalow is near Norwich has a 14metre long roof which faces south with no overshadowing. Can anyone recommend an installer in the East Norfolk area? Thanks!

Martyn1981

Hiya Vandici, welcome, and I'm sure you're going to get lots of help and advice. Some extra info first.

When you say winter heat from saved summer leccy, just checking, do you mean spending money in winter after saving it in the summer? Or did you mean trying to store summer heat or leccy?

Would you consider throwing the £3,500 for a new oil boiler into the mix for winter electric heat eg £3,500/20 years gives you £175pa to spend?

Roof size, 14m long is really big, and suggests at least one row of approx 13 panels in portrait. How high is the roof, for a second row, it'll need to by about 3.5m to 4m for two rows of panels (approx 1.6m to 1.7m high).

What pitch is the roof? To maximise winter generation for water heating a steep roof is much better, say 40deg or more. Whereas a shallower roof of say 20deg would be more summer orientated. Easy to work out estimates of generation, both annual and monthly, so this can be assessed.

Also I posted a link to this thread on another thread as Energetic will probably be able to offer loads of advice - but I think he's pretty busy at the moment:

https://forums.moneysavingexpert.com/discussion/4326665

Mart.

John_Pierpoint

Presumably you have done everything possible to increase the insulation for the bungalow? An extra £100s of insulation can be as effective as £1000s of heating hardware.
Does the bungalow have a gas supply ?
It would help if you could post a picture - it does not have to be your own bungalow, for obvious privacy reasons, but you might be able to find something very similar on (say) Google and link to it so that the picture appears here.

Like this perhaps:

thenudeone

A single immersion heater usually uses 3kW

Even a large domestic Solar PV system will not be producing that much electricity for most of the day, especially in the winter, so you would end up importing some electricity to heat water most of the time.

There's been plenty of discussion about how to get round the problem. The simplest is to buy a 240V-110V transformer (commonly used by builders for power tools) and wire the immersion heater to the 110V output. My schoolboy physics tells me that the immersion power would then be 700w which is much more likely to be within what your PV is producing, and ok to increase water temperature before it's heated elsewhere.

vandici

Hi Guys,

Thanks for replying!

MART When you say winter heat from saved summer leccy, just checking, do you mean spending money in winter after saving it in the summer? Or did you mean trying to store summer heat or leccy?
Yes thats correct using the cash saved in the summer to spend on electric thro the winter.
I was a bit optomistic with the roof size, it is 14m but probably only 12m could probably be used the depth available would be 2m, the pitch is 30 deg.

JP the old part of the bungalow is now well insulated, cavity walls all filled with polypearl, new extension all done during build process. I do intend to put another layer of loft insulation in the old part of the bungalow at some point.
Unfortunately no gas available in the village.

I have also wondered about solar water heating to top up the thermal store, but i'm not sure how effective they would be during the winter time and during summer it will probably generate a lot more than 2 people could sensibly use and end up dumping the heat.

I have limited funds left, and want to spend it in the most cost effective way! We went for the thermal store because of the multitude of connections it offered and the ability to connect several heat sources. But which heat source is more of an issue!

Energetic_2

Hi Yes flat out with these pesky EU technocrats making another catastrophic change to our industry, would be nice to have a clear 12 month period with some confidence and stability.

To the OP: I agree with john, insulate before considering anything else.

Conventional wisdom dictates that there just isn't enough sun in the winter months for PV to make a meaningful contribution but during the shoulder season, like now, when there is often good sunny days it can really help. We have systems doing 16kWh on good days at the moment as i'm sure some of the guys on here with systems will tell you.

You could go for PV and use the income from the feed in tariff and the money you save on your bill in summer to offset your winter bills, which i think is what you're getting at.

Long story short, too many variables to offer you a proper answer, a decent site survey would be good. I know a very knowlegable PV guy in the norfolk area who might be ablr to help.

grahamc2003

vandici wrote: »

Hi all, I'm new to this forum so please be gentle!
We have recently finished an extension to a bungalow we bought 3 years ago are now considering the next step - new boiler or solar PV.
As part of the refurb we had a multifuel burner with back boiler, linked to a 300lt themal store, this is providing most of our heating and DHW requiremnts (but a chilly house when the burner has not been lit). Would it be sensible to consider solar PV as a source of top up heat (via its 2 immersion elements) to heat the thermal store during the winter period by way of the reduced electric costs etc gained thro the summer period?
The other option is a new oil boiler which will cost in the region of £3500 + vat. The bungalow is near Norwich has a 14metre long roof which faces south with no overshadowing. Can anyone recommend an installer in the East Norfolk area? Thanks!

If you only want to heat water, then you'd be much better advised to go with solar thermal, which is much more efficient at producing heat. There are various types of solar thermal these days, the traditional passive systems, and the powered 'thermodynamic' panel systems, which are basically heat pumps which produce much more heat, even at night. The rhi for solar thermal hasn't been decided yet, and if its low relative to the current fit, it make make more financial sense to go for the lower efficiency pv rather than the nhigher efficiency thermal, in your applictaion. A thermal system is much smaller than a pv system, so even after fitting a thermal system, there may still be room to fit pv if you want. Imv, it's generally a waste to heat water (requiring low quality energy) with high quality electricity - the value to you won't be 15p/kWh, but more like 4p/KWh if you offset gas heating.

Martyn1981

Hiya Vandici, I'm with you now. So you'd keep the multifuel boiler, but rather than spend more on a new oil boiler, you'd 'suffer' extra leccy costs through immersion heating. Is that about right?

Then to save leccy costs you'd use offset savings from the summer, and maybe consider a diversion device (such as an Immersun) to put spare leccy into water heating?

Sounds like a good idea as long as the site is good for PV, since that way the PV should return it's investment cost if it gives a suitable return.

Quick check for the general Norwich location on PVGIS for a south facing 3.6kW system gives guesstimate of 3,430kWh's pa.

At current FIT and export rates that works out at £607 pa, plus leccy savings.

So, if I'm understanding this correctly, PV should pay for itself, whereas oil boiler costs will depreciate and disappear. As to whether leccy savings, and oil savings, will match extra cold weather leccy consumption, I'm afraid I'm not sure.

Mart.

Edit: I see Energetic has arrived, so you are now in more knowledgeable hands.
Also, as you don't have gas, I'm not sure that solar thermal will work for you. Like PV it won't do much in the winter, and summer excess may be wasted, whereas PV leccy can be used for other purposes once your thermal store is full or exported for income. NB at the moment export isn't measured just estimated at 50%, but that might change. M.