I’m planning to cut my grid connection and go full off-grid. Which raises the question of how much capacity I really need. And what you see here is me trying to answer that question based on ~51,000 5-minute data points of usage data my power company provided to me, complete with custom-made python script to parse all that data and pretty charts! (Yes, I have 6 monitors. And this kind of shows why.)
And what I’m really torn about now is how much battery capacity I need. Should I get enough to cover the absolute worst case scenario (~66kwh) or is something closer to my average overnight usage (~20kwh) acceptable?
Not the absolute end of the world if the batteries run dry and I need to temporarily supplement with generator backup, I suppose. Nobody is life-or-death depending on any electrical appliances here, and even on the coldest days, waiting a few minutes to go start a generator isn’t a huge deal.
But definitely would like a word from the wise about how much battery capacity I really need. And also how much solar panel wattage I need, I suppose.
We live in North Scotland in an old house that has solid walls with no insulation, with about 300mm of roof insulation.
40kwh of batteries.
Heatpump with ufh.
8kwh of solar panels.
What we were told with the batteries is that we can’t use all of them. You have to leave about 10 percent in them at a minimum or you may damage them. So factor that in.
Heating is through a heatpump. And log burners when it’s really cold. In the last winter we had it at -11c at times. It’s quite windy and stormy at times up here.
Solar panels. They don’t really put out any power in December or January. We were lucky if we were getting 1 kWh a day in January…
Though they do power us most of the spring, all summer, and most of autumn. Basically from the middle of November, December, January, February, and the middle of March we need to supplement from the grid because of the heating. Though if I lived alone I wouldn’t need to supplement any power in most of Nov, or Feb. But as I live with people who really feel the cold we need to have the heating on even during the warmer days of March.
If we didn’t have a heatpump then we’d hardly need to supplement at all as our daily electricity usage is about 12kwh. But then we’d need to use heating oil etc etc.
If we were to try to go off grid then we’d need to get rid of the heatpump AND have to at least triple our solar panels.
We were projected by, I think, OpenSolar project to be able to produce 4kwh a day in Dec and Jan with our panels but in reality in the whole of December we produced about 50kwh and in Jan it was less than 30kwh for the month (though it was a really bad in Jan. The worst weather for nearly 20 years.)
Our daily electric usage in December and January with the heatpump was about 50kwh. Which means what we produced in the whole of January and December wouldn’t power and heat us for 2 days…
Over the next year we will be insulating the house and roof etc as much as possible. So, hopefully, next winter we won’t need nearly as much heating. Hopefully. Have you noticed I used the word hopefully a lot…?
I want to go off grid but I don’t know how.
It’s either, get rid of the heatpump and triple the panels, which we don’t have the land for. Or a wind turbine.
If we go the wind turbine route then we’d probably need a 5kwh version to produce about 2kwh. And I think the 5kwh ones are expensive. Though we may get away with a smaller turbine once the house is insulated.
No idea if I’ve helped, but if not then hopefully you’ve got a few ideas to think about.
In the perfect world we would’ve spent the first year here insulating everything as much as possible. Then look at the heating etc. Unfortunately time constraints meant we needed to do the windows and doors then renovate the inside first. Hindsight is a great thing.
Huh… Good to hear that kind of thing, I guess. And here I was thinking that maybe around 6kw of panels would be more than enough for our average usage. But if you’re struggling that much on 8kw, maybe I should go bigger, a lot bigger. (Luckily, I’ve got the land for it, and I could put up an absolute ton of panels if necessary.)
Also definitely thinking of putting up a wind turbine or two, which would hopefully help supplement, especially in those cold, dark times when the gap between production and demand is the highest. Could easily be worth the cost if it means we need fewer batteries.
People will get better results with 6kwh than we do with 8kwh in different countries.
It all depends on location. And panel direction and angles.
If you can wait for the batteries then what about going for sodium ones? They are supposed to last longer than lithium.
If you’ve got the cash, the land, and the know-how I would go bananas with the panels. They are maintenance free, unlike turbines. They usually have 30 year guarantees, unlike turbines.
Just do some good research in to dump loads.
We are going to be adding another 18 or so panels when our barn roof is repaired. Plus a few more on our car port and then completely fill the main house roof next year at some point. There’s no point in doing it until all the insulating is finished and we finally know how much energy we will need in the winter months.
You mentioned you have solid walls, have you looked at insulating them? My house has similar walls, and the various options and trade offs are driving me to distraction and decision paralysis. If you have any thoughts on options, could you share them?
Well we already made up our minds that we were going to externally insulate before we moved in. It may be more expensive but there’s a lot less mess and upheaval when compared to internal insulation.
If we did internal insulation then we’d have to rip out all the plasterboard/lath and plaster etc, rejig the electrics etc, insulate, refit plasterboard and plaster. Whereas with external then all I have to do is clean the render off and reroute the guttering and downpipes.
Plus I’m doing it all myself. Mostly to save money, but also because where we are there’s not many people around who do the things we need doing.
Example: when we moved in we had an oil boiler but no heating yet the quickest a plumber could get out to us was about 2 or 3 weeks, and that was doing a favour for the farmer who we bought the house off.
Now that type of external insulation…?
Like I said, our house is all solid walls but only about 30% of it is the original sandstone that they dug out of the ground to build it. The rest is high density concrete blocks.
On the concrete part of the house I’m probably going to use the standard EPS. I’m unsure whether to use standard adhesive or use the special foam adhesive. Or a mix of both. But I’ll definitely be using plastic fixings to prevent as much thermal bridging as possible.
On the original part then that’s a bit more tricky because the walls have to ‘breathe’. There are a few things I can use such as wood wool or mineral wool. Finished off with lime render of some sort.
We are also going the MVHR route. Which will keep the humidity down etc.
There is another thing called geocell insulation
https://unitylime.co.uk/shop/brand/geocell/geocell-foam-glass/
Apparently that stuff could go in between the plaster and wall, and apparently it doesn’t stop and condensation but it does keep the heat inside. I’ve only just heard of this stuff so I don’t know much about it. I learnt it from a guy who sells it when I was at a Self Built show a free mouths shop. I will do the research on it at some point, and if it does allow the walls to breathe then I’ll also get loads of that and pump it into my walls. Fingers crossed.
What are your thoughts?