Incoming geek post:
Going back to a previous point here's some food for thought about the financial viability of solar and batteries:
I spend £360 per year on my electric bill and zero on gas because I don't have it.
Let's say most people spend £1200 per year on their bills then I'm £840 better off which seems nice.
The battery and solar package together cost about £13000. However the saving I make wouldn't be realised if I hadn't also spent £7000 on a air source heat pump. This means I'm in for £20k to achieve a saving of £840 over what I would've paid had I just gone gas/electric. Let's say a gas boiler would've cost £2000 anyway so it's actually cost £18k on day one
You don't need a calculator to see that the payback period is one hell of a long time if we just leave it at that.
Now let's bring in our friendly Government and their various eco incentives. I get £282 per quarter for 7 years on the heat pump which is about £7900. Heat pumps are incredibly efficient so you get an incentive due to the reduced carbon emissions they produce. For every kWh of energy that goes in to a heat pump you get about 3kWh of heat out meaning they're 300% efficient compared to the best gas boilers at about 85 to 90% efficient. You can also power a heat pump using renewable energy which then makes them 100% carbon free. How nice is that
I also get £240 per year for 20 years on the solar panels
So now the saving over the first 7 years is £7900 + (240 x 7) + (840 x 7) = ££15460
So we're nearly there right..... Still saving £840 per year and getting £240 for the panels so let's call it 9 years to break even woohoo!!
But now I'm going to throw a huge spanner in the works.... My house is ridiculously efficient. This means that my bills wouldn't be anywhere near average if I was on standard gas/electric. They'd actually be closer to £800 per year. My saving is now down to £440 from the previous £840
So the new saving over the first 7 years is £7900 + (240 x 7) + (440 x 7) = £12660
The savings in year 8 through to 20 is £680 so to get to our magic break even figure of £18k you've got another 8 years making a total of 15 years.
There's myriad assumptions in here of course so the true figure would be probably be different although your guess is as good as mine if it would be better or worse.
What the above quick calc illustrates I think is that you can't look at any one item in isolation. Each eco thing you do has an effect on the payback time of the others. For me the starting point was solar on it's own. Adding a battery increased the payback time. Adding the heat pump reduced the payback time. Making the house more efficient which we obviously all should (must) do increases the payback time.
House insulation is one of the most counter intuitive things when it comes to calculations. You have to have a well insulated house for a heat pump to be effective. If you have a well insulated house your bills without a heat pump would be reduced anyway so your payback on buying solar/battery/heat pump gets much longer. So what do you do?
Lot's of people will tell you that they save this on their panels and that on their batteries but they're in cloud cuckoo land. They live in a dream world and haven't actually calculated out the true cost taking in to account the opportunity cost of everything they've done. One thing they never take in to account is what the £18k up front would've made over the 15 year payback if they invested it at 5% ROI. That makes quite a difference doesn't it. I could've just insulated my house to the same standard, stuck £18k in an investment of some kind and paid my £800 per year bills using the returns.
I think I best stop. I'm a complete geek with all this, I did all the above calculations prior to buying anything 'eco' but still went ahead happy in the knowledge that it wasn't that great a financial move. You can't really put a price on the 'feel good' factor and that's what it came down to for me.
Cliffs: I'm a geek.