Reducing the Grid in your Home

Good discussion on moneysavingexpert.com – lets get into the same subject on our own technical forum please

It started with someone called Bricken saying:

I have looked at a few websites. some offer diy systems around £7000 others offer to supply and install but when it comes to details and price they want to send a rep. I hate reps they really dont understand terms like leave now or conman so if you live in the north west and have a hybrid system that you are happy with. I have ssw pitched slope with no shaded areas i am looking at a 12 panel system how much did it cost you. So i have an idea before i get into it with the reps.


12 panels used to mean 3kWp but understand you can now get panels bigger than 250Wp. Even so, basic system (without island function) unlikely to cost more than a 16 x 250Wp one which I understand is coming in at around £6k.

To convert that to an ‘island’ system you’d need to add one (maybe two) of the Sunny Island units I mentioned earlier giving a potential total of £7k or £8k. You might be able to negotiate a better price than that but laugh at any offers above it.

But don’t go down the DIY route ! You’d have to pay 20% vat rather than the 5% that a MCS registered installer could charge and you wouldn’t be able to claim FIT payments (the generation payments do still apply for self-contained systems but obviously you won’t get the export payments).
N Derbyshire.
4kwp S Facing 17.5deg slope (dormer roof).
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# 3 rogerblack Old 13-11-2013, 4:20 PM
Fantastically Fervent MoneySaving Super Fan


Do you mean an actual disconnected from the grid system that is never connected at all?

This is hugely expensive, in general, and only sensible if your alternative is running a generator.
You will also not get much power at some times of year.

If you mean Liverpool, then the average output for december pointing south with a 3kW array is about 90kWh. If you mean Fort William – it’s 45kWh.

That is – 3kWh/day – or 1.5kWh/day. And you then need to knock off 50% or so typically at best for battery charge/discharge efficiencies.

1.2kWh/day will run an efficient fridge/freezer, one very small energy saving light bulb for a few hours a day, and a laptop for a couple of hours.


Hiya Bricken. Firstly, Eric beat me (on both threads) to the mention of Islanding. If you haven’t already, have a read of the SMA ‘stuff’, other companies offer similar kit.

Regarding going off-grid, or ‘reduced grid’, I’ve been watching and waiting and reading with interest. Also been chatting with off-griders. Generally the rule seems to be, if you have grid available, stick with it. Reduced grid is very possible, but off-grid is a big jump. Why?

Well, for reduced grid, you can cherry pick, start with PV (grid tied), then maybe move on to some battery back-up for night time lights, and expand from there, but batts are expensive, and don’t last too long yet.

As you go further off-grid you’ll need to provide for longer, poorer periods of generation, but these will happen less and less often, so you have to spend loads on batts or additional generation, for 4 bad days, then 5 bad days etc, despite those representing a smaller and smaller part of your consumption.

In fact for off-gridders, most I chat with seem to give up at a certain point and have generators for those infrequent times. The challenge of course then becomes how little fuel they can use, by installing ‘just a few more’ PV panels.

For reduced grid, just replace ‘the generator’ with ‘The Grid’.

There are also more and more systems being offered with integrated battery systems. But these cost mega bucks still, but are heading the right way.


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