Just over two years ago, I took the plunge and added a lithium-ion storage battery to my home. It went in the cellar. Its been doing its job faithfully ever since, and has been pretty cool. I reckon 85% of our energy usage has been either free or off-peak electricity since we got it installed. Here is a pic:
The original blog post is all the way back here. Anyway, today we had someone come to the house to talk about doubling it, and having not 9.5kwh of storage, but 19kwh, by sticking another one right next to it. Cunningly I had forward-planned this, by asking them to make that big wooden backboard big enough for two batteries during the initial install.
At the time, I was not sure what the right size of battery would be. We nearly got a Tesla powerwall, but they were hard to get hold of. They had a 13kwh capacity at the time, so we ended up with slightly less at 9.5kw. It also has a separate inverter (some modern batteries have the inverter in the same box now) and the inverter is limited to just 3kw input/output. So that means if at any point we draw more than 3kw by cooking/heating/whatever, then we pull power from the grid EVEN IF the battery has tons of charge in it. Now with our solar panels, its a bit different because if they are producing at their peak (about 4kw), we can in theory use 7kw of power and still not touch the grid, but that involves being very organised :D.
I mention the 3kw limit because that is not changing. We could in theory get another inverter but thats a lot more hassle. With a second identical battery its just attached to the wall and then connected with a phat cable and thats it. So we will then have 19kwh of storage, that we can use 3kw per hour. This is not ideal, but we are doing it anyway. Why?
We are likely going to get a heat pump soon, probably this year. Heat pumps are very environmentally friendly, but they do increase the amount of electricity you use. In our case it will mean getting rid of an expensive and emissions-heavy oil boiler and oil tank, so its definitely a win, but our actual electricity usage will rise a fair bit. Right now, we have everything balanced perfectly. In a dark cold winter, we get almost nothing from solar (0.67kwh today), and we use about 11kw. So we can buy 10kw overnight at cheap rates, and combined with some solar, we can still just about get through the day without using peak electricity.
The heat pump will change this. We will have a higher average daily electricity consumption, so in order to have the same fully off-peak strategy, we need more storage, and its cheap enough (£3,900 supply+fit) that we may as well double it. I think we don’t NEED double, but I’d rather have 2 identical batteries for compatibility reasons and would rather be too big than too small. We should get the battery fitted soon, way before we get the heat pump. If you wonder about charging the EV… thats done entirely during off-peak times, so its never a problem.
In an ideal world, we would also have re-wired the entire house to survive a power-cut and run off the battery. In practice this is REALLY hard to do. Its not the kwh that is the problem, but the kw and the amps. Houses can draw up to 100amps in the UK, and no, no home battery is going to provide that. What SOME home battery installs do is wire ‘some circuits’ so they work in a power-cut. So basically you can have all the sockets in one room, or all the lighting. Thats likely low amps and low power. However it does involve running extra cables and a new fusebox in the cellar, and when we looked at what fuses were behind what sockets… it all turned into a bit of a nightmare. So we went for a bit of a bodge…
We are going to (pending the quote) have 2 sockets fitted next to the battery in the cellar on a separate battery circuit. In a power-cut, they will still work. So we can charge up a laptop or phone quite happily down there, although its a cold 1650s brick cellar with a well in it, more suited to a lord-of-the-rings re-enactment than leisure time, so no, we won’t be living down there. On the plus side, thats still better than having NO power in a power cut. We had power out for 6 hours a few months ago, so its a thing here. I also think that given climate change and extreme weather, this will be more likely. All our power cables here are overground on poles, so vulnerable…
It might sound ‘not very resilient’ but we have two log-burning stoves here, so not short of heat, and actually we can always charge phones in the car anyway (even watch netflix and disney and apple tv in the car), so we are not totally bereft :D.
BTW if you follow me on X and saw THAT POST about the solar farm, I have not forgotten to blog about it…I just need more information…