Solar pv saving ?

anuvvasaver

I am shortly having solar pv installed but am having difficulty figuring out whether I would be better to turn the gas boiler off during the day and use the immersion to heat the water utilising the 'free' electricity when I'm not using anything else (ie washing machine,kettle etc).
I am fairly certain that this won't work during the winter when we will also need the heating on (and pv output inevitably falls) but if anybody else has already looked at this and has some tips I'd appreciate their views.

KevinG

With solar panels I would consider whether you would be better off an "economy 7" type tariff and heating water overnight on this, which is what I do during the summer. Most of the benefit you get from the panels will reduce your consumption at the higher daytime rate. Don't get hung up about "using" the free electricity - it makes no difference whether you use it or not, the saving is the same, as all power generated, as well as qualifying for the feedback tariff, reduces your consumption anyway (your meter runs backwards).

anuvvasaver

I'm not sure that with 2 kids an economy7 tariff will save us money as most of our consumption is during the day. I work lates and therefore the washing machine et al tend to be used in the mornings and the kids fire up their pcs and the wife the cooker in the afternoon. I was looking at turning on the immersion when I go to work for 3-4 hours till the missus gets home and again in the evening til dusk. wdyt ?

KevinG

Difficult to say - everyone's circumstances are different. Mine are very unusual in that I have solar panels (only fitted last week - I am now a sun-worshipper!) and a Micro CHP boiler that runs on LPG (no mains gas) and also generates electricity. I've had Economy 7 for years and its marginal, we try to run the washing machine and dishwasher on cheap rate as much as possible, other than that its the immersion heater in the summer, for 3 hours in the early morning, which usually gets us through the day, if not we do a quick boost using the boiler, which I think still works out cheaper than using peak rate electricity, taking into account the 1kWh or so of electricity that also gets generated. Unfortunately the feedback tariff for Micro CHP boilers is only about a quarter of that for solar panels. LPG is much more expensive than mains gas; you will have to work out whether it is cheaper for you to use the boiler or the immersion heater on peak rate electricity, but I suspect it might be the boiler, as long as it is fairly efficient. As I said, you will get the same benefit from the solar panels irrespective of which way you choose to heat the water.

Andy_WSM

KevinG wrote: »

- it makes no difference whether you use it or not, the saving is the same, as all power generated, as well as qualifying for the feedback tariff, reduces your consumption anyway (your meter runs backwards).

That's only true if you have an old style meter. My PV system doesn't touch my digital meter, so I tend to do all my washing, drying & water heating on bright sunny days to make the most of the free power.

Was considering going the eco 7 route though as I use virtually no daytime electricity this time of year, only night units.

KevinG

Andy_WSM wrote: »

That's only true if you have an old style meter. My PV system doesn't touch my digital meter, so I tend to do all my washing, drying & water heating on bright sunny days to make the most of the free power.

I wondered about that as it obviously affects the economics of it. The form for registering for the feed-in tariff asks if your meter has started running backwards. I answered yes when I registered the boiler last year and will do so again when I register the solar panels (I haven't got the MCS certificate yet). If this is a problem to the electricity company I assume they will want to replace the meter, but they haven't suggested it yet. With a meter that runs backwards every kWh you generate knocks that amount off your electricity bill as well as qualifying for the feed-in tariff, so it doesn't matter whether or not you use it.

anuvvasaver

Kevin,
Just beware, I read on another thread that a woman had found that her meter was running backwards and had been threatened with theft by her supplier. Also that she had been charged not only for the imported electricity but also the electricity that she had generated and used herself. She found that on a sunny day the more appliances she turned on the slower her meter spun !!
Sounds like an installation error but....see the thread about solar panels and siemens meters for more info.

KevinG

Yes, I've read around a bit more now and clearly meters that run backwards when there is a net export of electricity are supposed to be replaced. I don't see how can be accused of theft when I have declared this fact on the forms! I read the horror story about being charged for generated units as well, mine is behaving perfectly, apart from the backwards issue, which is working to my advantage, but should I be shouting louder about it? I don't see why, the electricity company have all the information. If the meter is replaced we will have to change our usage pattern.

anuvvasaver

I think I would do as you would. If you've done all you should and it's all working right, why fix it ?

anuvvasaver

KevinG thinks that doing this would be marginal with regard to savings made.
I currently pay 11.58p per unit for Electricity and 3.150 per Kwh for Gas, does anyone think that I might make any better saving if I use the pv generated electricity (plus a possible 'top-up' from the mains) instead of the gas boiler during the day ?
Alternatively, is it actually cheaper to turn the boiler off during the day and then reheat from cold later, or leave it topping up the tank with hot water all day ?