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.
I mean it’s a complicated question, largely due to factors that are outside of your control (weather). You just make your best guess.
We have a 15kWh system in a temperate area, and in the winter some days we only make 4kWh the whole day, and others we make 90kWh or more (so long as we can find things to use that power - it only generates power that has somewhere to go, and we are capped at 5kW to the grid at a time). As far as I’m aware, 15kWh is a large residential system, to the point it may be at or over a legal cap depending on your area.
One thing we noticed is that a battery doesn’t actually hold that much power. We will easily chew through double the battery if the heating is on overnight (a heat pump system, so it’s also reasonably efficient). Our hot water is also heated electrically.
Do you not have the ability to sell to the grid or have net metering? When I was looking at it, the calculation was easy. If you can sell to the grid forban ok amount compared to what it costa to buy, if you have enough generation capacity to be off grid, then it’s always worth being connected to the grid because excess power in the summer will easily cover the cost of being connected. I live somewhere with a lot of competition for power companies, with some specialising in solar, so YMMV.
As mentioned, the battery doesn’t help that much. I calculated a 40 year+ payoff time for the battery (the battery won’t last 40 years). To have enough battery capacity to cover the worst winter periods it may just be cheaper to save your money, not get a battery, and use the money you saved to pay for grid connection 😆
If your worst case scenario is in the winter (heating), that level of power generation may not be achievable on a residential system. If it’s the summer (AC), you have a shot.
Our system also lets us disconnect from the grid (and connect again) at the push of a button. You can always do your best, then use a setting like this (if yours has it) to test your ability before actually dropping your grid connection.
Sorry not sure if this answers your questions, seems more like a ramble, but I’m happy to answer any questions you have about my experience getting solar.
(I also did not DIY it, but did work with an installer to work out what we wanted)
Do you not have the ability to sell to the grid or have net metering?
Really not an ideal solution…
A) That requires permits and inspections and other red tape that will be very difficult and expensive for someone DIYing the whole project. The biggest problem is that it requires a complete electrical inspection before connecting and … there’s no fucking way my house is passing an electrical inspection. It was built in 1910 and has been modified by several half-baked homeowners before me. Nothing is really up to modern code, and it’s all an overly complex patchwork of upgrades and additions that barely works as-is. (Seriously, not a single one of my breakers is labeled. On any of the 4 separate service panels. It’s a nightmare.) To even be allowed to do net metering would likely require a huge gutting and revamp of the entire house’s electrical systems.
B) Even if I did all that, there’s no guarantee the power company would go through with it. Apparently, they have a cap on the number of houses that can do net metering, and if there isn’t any openings, you’re just shit out of luck. (And they keep the $100 application fee, thanks.)
C) My power company’s net metering policy is kind of crap. You never get cash for selling power back to the power company – you get energy credit, which can be banked up and then redeemed for free electricity later. That wouldn’t be horrible, except that they also arbitrarily reset your balance to 0 on March 31st every year, no matter what your balance is at that time, and you get nothing for it. (And they still charge a ~$40/mo ‘basic service’ fee that you have to pay even if you used 0kwh. Those service fees alone could pay for a lot of batteries over time…)
All that combined has me leaning more toward cutting the cord entirely and going off-grid with battery storage … even if it means I have to buy a shitton of batteries and/or have a backup generator available for those few exceptionally cold winter nights.
(And besides, a few long outages recently have really made me want to be fully independent. And wouldn’t it be great to tell the power company to fuck off and never get another power bill ever again?)
A) Ah ok, well good that you’ve thought it through. I had disconnecting from the grid in mind when we fist did ours, and it turned out to be the wrong approach, but our situation was quite different.
B) That seems weird but ok, some power companies here don’t offer anything related to solar but we have a national spot price buy/sell system so almost anyone can start a power company selling the grid power, and you can use almost any power company from almost anywhere, but I know that we’re lucky with that. We are limited (everyone is limited) at how much we can sell at a time in order to keep the power line voltage within tolerance, which I guess your power company handles in another way.
C) Ah that sucks. We get paid 2/3 of the value of buying when selling to the grid - though it is in credit. I haven’t worked out what happens when we never use the credit but it doesn’t seem to get arbitrarily reset!
All that combined has me leaning more toward cutting the cord entirely and going off-grid with battery storage … even if it means I have to buy a shitton of batteries and/or have a backup generator available for those few exceptionally cold winter nights.
Yeah it sounds like you’ve got some strong arguments for it!
And wouldn’t it be great to tell the power company to fuck off and never get another power bill ever again?
Well, I like my power bills because most of the year they are credits 😆
It seems like most of my experience might not be helpful to you. I’m willing to send you a year of power generation data from Home Assistant if you think it would be helpful? It would show you the variation day to day and might help you see what kind of impact there is with poor weather.
At a guess I’d say I don’t think one 10kWh+ battery would be enough to go off grid. Two might cover most situations if you have enough panels, don’t live in a super cold area (or have non-electric heating), and do power hungry things only in the daytime (charge car, run dishwasher, run clothes dryer, etc). Also an electric stove can use more power than you might think, cooking a roast dinner can chew through half our battery no trouble. Plus it will work out better if you shower in the morning (so heating mostly happens when the sun is shining). Three batteries still won’t cover every day but I think if you have a generator available and are careful about timing during the winter period then it should get you through most of the time.
Solar panels are pretty cheap now, so don’t under do it. Load up on your daytime capacity and use the power then, to reduce your reliance on the still expensive batteries.
Maybe make the call based on the lead time to order the components. If you find you didn’t get enough capacity, it’s easier to solve if you have a 2 week wait to get some more panels and an extra battery vs if you have to wait 6 months.
Sorry, not sure if I’m helping 😅
Nah, don’t worry – that’s helpful! And sure, I wouldn’t mind seeing that data. Though our situations are pretty different, more data couldn’t hurt, right?
At a guess I’d say I don’t think one 10kWh+ battery would be enough to go off grid. Two might cover most situations if you have enough panels, don’t live in a super cold area (or have non-electric heating), and do power hungry things only in the daytime (charge car, run dishwasher, run clothes dryer, etc).
Heh, yeah. I think 20kwh battery would be the absolute bare minimum for us, and I’m leaning toward at least 40kwh. (Especially when you factor in other things – the conversion from battery power to 120v/240v is only ~80% efficient, depending on inverter.* And the batteries will lose capacity over time, so it’s better to overbuild and not need to replace them as soon.)
*Another upgrade path for the future is to run a DC power circuit through the house, at least for some lights and little stuff like phone/tablet chargers. DC power will be significantly more efficient because you don’t have to go through that 80% efficient inverter to get it out of the batteries. Maybe I can even manage to find a heat pump that runs directly on DC.
We’re on pure electric everything here, after all. No gas of any kind.
Plus it will work out better if you shower in the morning (so heating mostly happens when the sun is shining)
For the water heater in particular, I’ve already got a plan: going to put that sucker on a timer, so it can only run during the daytime. Actually already got a $1 thrift store timer, big old electro-mechanical thing, that should be able to do that job. A decent hot water heater will stay hot for days without power, and it’s just two of us here, so it won’t run out too quickly. Let it heat up during the day and then disconnect at night, and the water heater won’t be a drain on the batteries at all. (That works well with our existing routine of showering in the evening, too. It should be nice and hot after running all day, and if it stays cold most of the night, no big deal. In fact, after some experimenting to see how quickly it heats up from dead cold, I might not even have it run during all daylight hours, just start it up a few hours before we usually shower.)
To some degree, I might try to do the same thing with heat, using programmable thermostats to raise the temperature during the day and then reduce heating demand during the night. Thermal storage is a lot cheaper than battery storage, after all. Who knows, might even go super crazy and actually build in some water tanks that can be heated during the day and then release that heat at night. Got a bunch of old 55 gallon drums sitting around I’m not using for anything else … just need some heating elements and timers… (But, yeah, that part would definitely be a project for later. And still not sure I want big drums of water sitting around in our living space, especially because they’ll be nearly useless in the summer.)
If it gets really desperate, I might even put the refrigerators on timers. They should be able to stay cold overnight okay, and then they can run all they want during the day.
I had an electric water tank for some years, it did only heat during 4h a day splitted in 2 morning and 2 afternoon, thats more than enough. Just install a temperature logger so you keep track of the temperature. In terms of batteries, they are too expensive for a normal use, invest on a few more panels and try to reshape your consumption.
