Domestic batteries revisited

[DrFfybes]

There was a thread a while ago about whether it was worth using batteries charged off peak to time shift use, but as technology changes, batteries become cheaper, and solar improves, I'm wondering how the maths stack up now.

There seems to be a lot of obfuscation on the issue, tying in with solar, and showing how it makes the solar more efficient/economic, but I'm not actually convinced there is much benefit.


Looking at nakedsolar who seem reasonably up to date..
https://nakedsolar.co.uk/storage/
From what I can see, Li batteries last 11 years, or 4000 charge cycles.
Each kWh of storage seems to be about £900 installed with the gubbins, so if you assume you can use it 4000 times that works out at 22.5p per kWh stored and released. There are some cheap batteries out there, but when I looked deeper the discharge rate was quite low so they are a bit more restricted in what you can get from them.

So, in terms of topping up at 7p and discharging during the day, they are pretty much cost neutral at the moment. Of course if the gap between on and off peak leccy widens then that changes.

I then looked at them as a solar add-on. However, Octopus pay 15p per surplus unit on a fixed system, so by that metric they don't make any sense commercially either at the moment.

Am I missing something, or when we go solar later in the year do we just keep it simple and have an option for batteries as they become cost effective?

Paul

[quelquod]

On the same basis we opted recently for solar panels only, no battery. With Octopus paying 15p/unit exported the economics of storing daytime surplus makes little sense so you’re left only with any advantages from time-shifting your grid consumption. Listening to the concerns about paying expensive gas-based electricity costs to cheap wind-powered generators I think it’s as well to wait and see while battery costs fall (with a bit of luck!). With our installation adding a battery later is just a matter of connecting it up.

[GrahamPlatt]

I’d wait until that “million mile” battery comes out. Shouldn’t be long now (indeed, having just researched a link, I see they’re now talking of four million mile batteries in the pipeline). The economics will shift steadily towards affordability (as has been the case with the panels).

[funduffer]

There was a thread a while ago about whether it was worth using batteries charged off peak to time shift use, but as technology changes, batteries become cheaper, and solar improves, I'm wondering how the maths stack up now.

There seems to be a lot of obfuscation on the issue, tying in with solar, and showing how it makes the solar more efficient/economic, but I'm not actually convinced there is much benefit.


Looking at nakedsolar who seem reasonably up to date..
https://nakedsolar.co.uk/storage/
From what I can see, Li batteries last 11 years, or 4000 charge cycles.
Each kWh of storage seems to be about £900 installed with the gubbins, so if you assume you can use it 4000 times that works out at 22.5p per kWh stored and released. There are some cheap batteries out there, but when I looked deeper the discharge rate was quite low so they are a bit more restricted in what you can get from them.

So, in terms of topping up at 7p and discharging during the day, they are pretty much cost neutral at the moment. Of course if the gap between on and off peak leccy widens then that changes.

I then looked at them as a solar add-on. However, Octopus pay 15p per surplus unit on a fixed system, so by that metric they don't make any sense commercially either at the moment.

Am I missing something, or when we go solar later in the year do we just keep it simple and have an option for batteries as they become cost effective?

Paul

The table in the link you provided shows many batteries have a warranty for 10000 cycles, so 4000 seems pessimistic.

FD

[BullDog]

There was a thread a while ago about whether it was worth using batteries charged off peak to time shift use, but as technology changes, batteries become cheaper, and solar improves, I'm wondering how the maths stack up now.

There seems to be a lot of obfuscation on the issue, tying in with solar, and showing how it makes the solar more efficient/economic, but I'm not actually convinced there is much benefit.


Looking at nakedsolar who seem reasonably up to date..
https://nakedsolar.co.uk/storage/
From what I can see, Li batteries last 11 years, or 4000 charge cycles.
Each kWh of storage seems to be about £900 installed with the gubbins, so if you assume you can use it 4000 times that works out at 22.5p per kWh stored and released. There are some cheap batteries out there, but when I looked deeper the discharge rate was quite low so they are a bit more restricted in what you can get from them.

So, in terms of topping up at 7p and discharging during the day, they are pretty much cost neutral at the moment. Of course if the gap between on and off peak leccy widens then that changes.

I then looked at them as a solar add-on. However, Octopus pay 15p per surplus unit on a fixed system, so by that metric they don't make any sense commercially either at the moment.

Am I missing something, or when we go solar later in the year do we just keep it simple and have an option for batteries as they become cost effective?

Paul

The table in the link you provided shows many batteries have a warranty for 10000 cycles, so 4000 seems pessimistic.

FD

Perhaps the domestic battery packs are using batteries removed from end of life hybrid vehicles? I understand Nissan are repurposing battery packs removed from Leaf cars as domestic storage. Obviously, those battery packs have a lot of their charge/discharge cycles already used. Maybe that's one explanation?

[DrFfybes]

The table in the link you provided shows many batteries have a warranty for 10000 cycles, so 4000 seems pessimistic.

FD

They do, but I think trying to claim on it after 15 or 20 years might be a fools errand, even assuming it is insurance backed

Then there's the small print, what is a 'cycle', how many in a day, at what percentage capacity loss is it counted as failed, etc etc.

Paul

[Spet0789]

When manufacturers talk about batteries “lasting” for so many years or charging cycles, they mean retaining X% of their day 1 capacity, where X is usually around 70-80. The capacity degradation is generally pretty linear beyond then so even after 20 years, the battery will still have around 30% capacity.

For an electric car with a strict size and weight budget, this is important.

For home use it’s irrelevant. Buy batteries today. In 10 years, add new batteries with half as much capacity again to regain the total capacity and so on. Batteries are pretty small in a house context.

To put it another way, the true capacity weighted life of your batteries is much longer and you don’t need to discard house batteries even if they only have say 20% of capacity left. They’ll still do a job for you.

[servodude]

When manufacturers talk about batteries “lasting” for so many years or charging cycles, they mean retaining X% of their day 1 capacity, where X is usually around 70-80. The capacity degradation is generally pretty linear beyond then so even after 20 years, the battery will still have around 30% capacity.

For an electric car with a strict size and weight budget, this is important.

For home use it’s irrelevant. Buy batteries today. In 10 years, add new batteries with half as much capacity again to regain the total capacity and so on. Batteries are pretty small in a house context.

To put it another way, the true capacity weighted life of your batteries is much longer and you don’t need to discard house batteries even if they only have say 20% of capacity left. They’ll still do a job for you.

Eventually, once the politics subsides, I'm pretty sure there will be batteries pretty much everywhere doing the job of bucket capacitors so that everything becomes much easier to maintain at a grid level. It makes so much sense.

[JohnB]

If there were clear arbitrage opportunities then commercial concerns would be doing it with shipping containers of batteries. Now maybe they are, and that's keeping the battery price high as demand outstrips supply. You are betting on the generation profile of the country over a 15 year period, and that battery prices won't fall faster than 22p/day/kWh. While I like the idea, early adopters tend to get stung unless there are subsidies, and I don't think there are for home batteries.

Vehicle to grid seems a better bet, you get to drive your storage device.

[Tedx]

Was there a company making home hydrogen manufacturing devices that you could install in your garage and fill up your car overnight?

Last I heard, business was booming.

[BullDog]

If there were clear arbitrage opportunities then commercial concerns would be doing it with shipping containers of batteries. Now maybe they are, and that's keeping the battery price high as demand outstrips supply. You are betting on the generation profile of the country over a 15 year period, and that battery prices won't fall faster than 22p/day/kWh. While I like the idea, early adopters tend to get stung unless there are subsidies, and I don't think there are for home batteries.

Vehicle to grid seems a better bet, you get to drive your storage device.

That's exactly what's happening commercially. To name three that I can think of, Gore Street Energy, Gresham House Energy and Harmony Energy. All three are running commercial battery storage facilities. I am sure there's more besides.

[DrFfybes]

Vehicle to grid seems a better bet, you get to drive your storage device.

It does seem a sensible move, and I know quite a few BEV owners who would like to see it happen with their 70kWh batteries sat idle much of the time.

When manufacturers talk about batteries “lasting” for so many years or charging cycles, they mean retaining X% of their day 1 capacity, where X is usually around 70-80. The capacity degradation is generally pretty linear beyond then so even after 20 years, the battery will still have around 30% capacity.
[...]
In 10 years, add new batteries with half as much capacity again to regain the total capacity and so on. Batteries are pretty small in a house context.

You are probably correct - at the moment small battery systems are price driven as much by installation and control systems as the actual battery itself.

I did some more maths, and it isn't even that simple. AIUI import/export is metered in 30 minute chunks, so with the oven, kettle, and washer going you could still be a net user during the day at certain periods so you need to be smart with timings. In winter a 5kW array only produces 3 or 4 kWh per day, which is going to be used well before the Air heater comes on so no benefit from the battery for 3 months of the year unless we use a variable tariff might with cheap overnight power, but then it all gets very complicated.

And it makes the solar maths a lot easier if I just look at output and consider it at 15p/unit generated

[edit] except for the units we actually use, which are worth 30p to us, but we will use more of the production in winter than summer, and then...... oh dear, my head hurts now
Paul

[scotview]

Vehicle to grid seems a better bet, you get to drive your storage device.

The MG fleet of BEV's have a working V2L (vehicle to load system) delivering about 3kW, continuous.

I've looked into this for back up power purposes to run our central heating electrics. A safe work around could be for the V2L to charge something like a Bluetti power unit. Once fully charged, the Bluetti could safely be connected to the DC input of a home battery inverter to recharge the home battery. The home battery, via a changeover switch could then power the home in an emergency, with an earth rod installation.

This could be extended to power items in the home which would theoretically mean the need for smaller home battery capacity. The problem though, is when you start to heat your home fully with electricity, necessitating a big increase in electrical power requirement in the winter.

[9873210]

Vehicle to grid seems a better bet, you get to drive your storage device.

I expect most grid storage to be dedicated batteries owned and operated by the grid or it's contractors.

Car batteries have size, mass and discharge rate requirements that are not important for the grid. You can also extend their lives by not running unnecessary cycles and optimizing charging -- which means on the batteries schedule and not when the grid suddenly needs to store excess power. You can still charge the car battery off-peak, which helps the grid somewhat, but is far less than the same battery could do if you run it hard and risk damaging it.

There are promising chemistries, such as iron-air and flow batteries that should be a better fit to grid requirements that the lithium-ion designs that are optimized for cell phones. The grid needs enough storage to make it worthwhile to develop these.

For a battery to be of highest benefit to the grid it's operation needs to be tightly coupled to the grid. They need to charge and discharge on demand. Crude peak/off-peak prices really aren't enough. It would be possible to remotely control lots of small batteries, but it's technically hard and probably "politically" harder. Most owners will say "It's my battery I want to use if for my own purposes rather than for the benefit of the grid." Much, much easier to handle a few mega batteries owned by or leased to the grid operator.

I'd expect the niche for car batteries would be back-up power for when the grid fails. This provides a direct benefit to the owner of the car, but does not provide for most of the grids needs. How many of you who own a backup generator turn it on before the lights go out?

[JohnB]

I expect it will come down to charging structures. In the same way that some companies offer spot pricing to smart meter customers, future tariffs will have a range from more expensive consumer-led control, to cheaper ones if you accept that the grid can drain your battery to a certain level on demand. A lot of the complexity will be handled by user agents, where your agent individually, or as part of a co-operative negotiates with grid agents.

This may all sound complicated, but computing power is cheap, and the pricing will adjusted to get the required take-up. So you'll still be able to charge on returning home at 6pm, and never discharge, but it will cost you.

[stevensfo]

I expect it will come down to charging structures. In the same way that some companies offer spot pricing to smart meter customers, future tariffs will have a range from more expensive consumer-led control, to cheaper ones if you accept that the grid can drain your battery to a certain level on demand. A lot of the complexity will be handled by user agents, where your agent individually, or as part of a co-operative negotiates with grid agents.

This may all sound complicated, but computing power is cheap, and the pricing will adjusted to get the required take-up. So you'll still be able to charge on returning home at 6pm, and never discharge, but it will cost you.

But if the cost of batteries and panels come down, why should anyone include 'the grid'? A simple array of DIY solar panels and batteries serving your every need? Completely independent.

I only say this cos we may get an EV car in the future and I'd like to put a few panels and batteries to run it. I certainly wouldn't want funny companies that go bankrupt every two seconds to be in charge. You don't have a contract to charge your rechargeable AA batteries!

Steve

[JohnB]

To be independent of the grid means you have to have expensive over-capacity. You install generators/batteries/panels/turbines to handle the longest cold, calm spell you predict, then hardly ever use that capacity. Better to scale back, let the grid take your excess, and connect you to sunnier/windier/wetter places elsewhere across the continent when you struggle.

[scrumpyjack]

I'd like one of these - a fusion reactor in a container

https://www.bbc.co.uk/news/business-65123116

There's room in the garden for it

[9873210]

But if the cost of batteries and panels come down, why should anyone include 'the grid'? A simple array of DIY solar panels and batteries serving your every need? Completely independent.

Because of the Law of Large Numbers.

For the grid the difference between peak and off-peak demand is perhaps a factor of two and varies over a day or longer. For a household the difference will be a factor of 10 or more and varies over both short and long time-frames. If each household is an island then in total far more storage is needed

The same applies to supply. The grid can have solar, wind, tide, hydro, nuclear, hydrogen peakers and imports. The wind will be some from Dogger Bank and some from the Highlands. Diversity limits the impact of events such as cloudy day. This is not available to a single customer.

The grid can also do things in demand management such as shutting down industrial users such as aluminium refining for a few
hours.

Also the industrial revolution shows that specialization and scale beats household level activity in almost every field. The desire for independence is a desire to be poor.

[stevensfo]

I'd like one of these - a fusion reactor in a container

https://www.bbc.co.uk/news/business-65123116

There's room in the garden for it

Whereas the UK version:

For example, in the UK a government-backed prototype fusion plant is being planned for a site spanning 300 hectares (740 acres) that currently hosts a coal-fired power station.
and
"Of course there have been rare meltdowns in reactors and it's understandable people are worried about that," he says, referring to disasters such as Fukushima and Chernobyl.

It will be great for those living next door. The thrill of sitting in their gardens and watching the fusion plant being built, the glow of pride seeing the future unfold, the laughter in the pubs as they joke about whose house price has dropped furthest and the heart palpitations every time a door slams at night.

Steve