Earth Notes: KEHS talk: Home Batteries (2025)

[00:00]

[Damon] Home Batteries --- And just to be clear, this is an electrical battery, so I have two sorts of batteries at home, I have a heat battery and I have electrical batteries.

[00:09]

So, what and why? Why would you have home batteries? Well, you already have storage at home. You store your clothes, you store your food, you know, you wouldn't want to have none.

[00:21]

We have a small house, but storage for all sorts of things you don't want to run out of tomorrow, or have to go somewhere expensive for, is good. You don't have to buy all your stuff in the corner shop because you forgot, so you do a bulk buy.

[00:33]

Batteries can be useful because you can buy electricity when it's cheaper if you're on a variable rate, for example.

[00:39]

So, and if you've got a water tank, for example, at home, hot water tank, you're already storing heat in there. And you have gadgets with batteries, you wouldn't have to want to walk around with this plugged in all the time.

[00:52]

Who remembers having to have your laptop plugged in all the time to do anything? So, you can store electricity directly off-grid or from solar PV.

[01:03]

So, it's possible ... I have solar on the roof and the most obvious reason to get a battery is because, surprisingly enough, I want to do things when the sun isn't up.

[01:13]

So, you want to capture the solar off your roof and then use it even when the sun isn't up.

[01:18]

But there's plenty --- Dan will tell you later about how he's got a huge battery so that he can fill it up during the winter and run his heat pump off it during the day --- whether or not the solar is doing anything.

[01:31]

I have --- this exciting collection at the top --- I have a little off-grid system and these are things a bit like car batteries.

[01:39]

And so, my website, if you ever go to my website, which you might for one of these things, that's entirely run off a Raspberry Pi off these things.

[01:46]

They never touch the grid and I can charge my laptop and stuff off there.

[01:51]

But I also have these AC-coupled batteries, and this is what you would probably be doing if you've got batteries attached. This is one brand Enphase, there are many others,

[02:02]

which will absorb energy, for example, from PV and release it when you use it.

[02:08]

And they try and stop energy flowing in or out of your house at all so you don't end up paying for it.

[02:13]

But here's a heat battery, this is during assembly, under my combi as it then was, so I could fill this up with electricity overnight and our combi doesn't have to run for hot water.

[02:26]

It's three different sorts of battery, but probably the sort we're thinking of when you're in here is this one --- the AC-coupled battery.

[02:33]

So, why do we need batteries? Well, there's this little thing called climate change and renewables coming on and a change of that means that we can't do what we used to with electricity,

[02:47]

which is turn up the generators when we want more electricity.

[02:51]

And in particular, turning it up at peak rate when everyone gets back from school and wants their dinner. This is basically this peak, is people having their dinner in the evening.

[02:59]

And so what we need is storage so we can fill up when the sun is shining or when the wind is blowing and release it later when we want to use it.

[03:08]

And so using your own solar... So, in California they got to this problem where their demand used to be, and the second problem like this, the demand curves throughout the day....

[03:17]

This is midnight, coming through to midday, through to midnight again, used to be quite flat.

[03:23]

But as more and more solar came on, the demand off the grid goes down lower and lower and lower.

[03:29]

And then it has to recover really quickly to make up the evening peak when the sun's gone down, [and] people's air con is still running!

[03:36]

And this is little thing called "ramp rate" is really difficult for the grid to deal with.

[03:40]

You can't do a 0-60 in your coal [generation] plant, right? You need to take it gradually.

[03:47]

So storage again helps "flatten the duck", as it's called, this is a duck shape, right?

[03:53]

It's called flattening the duck.

[03:56]

Will a battery save you money? Well, Dan believes it is saving you money, right?

[04:01]

I think on the whole it's pretty marginal. But the grid is definitely, will need lots and lots and lots more storage and stuff.

[04:10]

We can put behind our own meters so that we get charged less is also good.

[04:16]

And I think, Alan, also you believe you've saved a reasonable amount from your...

[04:20]

[Alan] With a battery? Yes.

[04:21]

[Alan] Yes, because we're using it overnight. So in the winter months we charge the reduced rates.

[04:29]

[Damon] And again, so both Dan and Alan have time of day tariffs, so they get charged a different amount by the hour of the day.

[04:36]

And they both have solar. So I don't have a time of day tariff, but I do have solar.

[04:43]

So sometimes, usually, batteries with solar is a really good combination.

[04:48]

Sometimes just batteries and a time of day tariff also works and may save you money.

[04:54]

So just the point that came up earlier, there are two things about a battery that matter.

[05:01]

One is kilowatts, which is the maximum power it can [supply]. When you flick on your kettle, that's three kilowatts typically.

[05:08]

When you turn on your oven, it's two kilowatts.

[05:11]

My batteries that I've shown you, they are slightly old now and [they're] an older design.

[05:16]

So mine can only do just over a kilowatt of power.

[05:20]

So if I turn on the kettle and the sun isn't shining, it will still bring two thirds of electricity in from the grid.

[05:25]

But these days, you don't need to do that. So you should make sure you have a kilowatt rating, which is at least about three, which will cover an oven or a kettle or something.

[05:33]

But the other thing is how much energy you store, and that's your kilowatt hours.

[05:38]

And ... there isn't a perfect simple answer, but generally you should think about carrying about a day's use.

[05:48]

For example, if you're on solar, you fill it up during the day off your solar and it discharges overnight.

[05:54]

And then you don't need to import overnight.

[05:57]

Now, if someone said to you, oh yes, let's have a big store of energy. Why don't we give you a big can of diesel and put it in your hallway?

[06:04]

You would probably think, that's not such a great idea.

[06:07]

So a battery, a battery actually stores less, much less energy per size and per weight than diesel by the can considerably less.

[06:16]

But you wouldn't want in the can of diesel sitting in your hallway.

[06:20]

So the rules have changed recently to make it clear that you shouldn't put batteries somewhere that might be an escape route like your hallway or somewhere, preferably not in the house at all.

[06:29]

So Alan has a garage, you have a garage. I have a porch, so mine's going to have some of the porch.

[06:35]

Garage. Right. So if you've got a garage, that's the best.

[06:40]

Keeps the rain off them as well. It stops them getting frost.

[06:43]

But otherwise, the porch ... Don't have them in the house on the whole. So I've got a friend who's in an attic apartment and wants to have one.

[06:52]

And I'm suggesting not or at least keep it well away from the fire exits.

[06:59]

So how much? So I'm suggesting with PV, you maybe want to go for a day so that ... this being Britain, we're not guaranteed solid sunshine for the whole of summer.

[07:09]

So sometimes a little bit more so you can coast through some of the next day as well.

[07:13]

Where where storage really helps is in the shoulder months, not the summer, not the winter, where you've got some rainy days and some sunny days.

[07:22]

So something like a summer day's consumption is a good rule of thumb for PV, battery and PV.

[07:29]

But if you want to do what Dan or Alan are doing, you get an off-peak rate.

[07:35]

You fill up the thing overnight on cheap electricity and you run your house off it, unless you know it's going to be sunny, in which case you leave space for the solar to fill it up for you.

[07:45]

You can save quite a useful amount of money. And this is what the grid is going to need to do anyway.

[07:49]

So you're helping save the planet, in which case you should be covering not a summer day's consumption.

[07:55]

You should be covering at least a winter's day consumption. If that's including your heat pump, that's going to be a lot more.

[08:02]

So for us [a] summer day's consumption is about five or six kilowatt hours, excluding any heating stuff.

[08:08]

Winter: I can't actually remember, maybe 15, so three times more for us.