Should I get more battery capacity? - Is it worth the cost?

Before adding a comment I'd recommend reading this community post where I've added a bit of extra detail to better illustrate how I view the payback of the extra battery: youtube.com/post/Ugkx3IwGg11F0Q8f0WOVl_RVqag2jGQS2…

Great analysis Tim, thanks.

Top video Tim. Thanks. Best regards Martin

Thanks Tim, I did find it useful to watch you work through these numbers. Wow, you use a lot of power. If we ever meet up we must do some U-Value calculations something seems wrong somewhere!? I agree with your conclusions, when you think we don't get 100% sunshine and installation costs. Expensive for benefit as there are other items you didn't take into account as I am sure you will know. Shame really, I was hoping I could buy that 5.2 Kwh battery from you AS I am doing similar calculations for my system..🙂

Wow, thanks for this incredible analysis! -- and very clear thought process! In the U.S., the 5.12 kWh EG4 costs $1,149 from EG4, or $1,260 from Amazon. I guess it's time to chase down local rates for a similar analysis...

Great work and very clear. I am about to order 19 panels and 9.5kwh battery via EON and this comes with a tarriff of 6.9p off peak and 40p export rate. Adding additional battery's is therefore a no brainer to exceed the break even position achieved via octopus

Great analysis. 14kwh is ample - my analysis of my heat pump house’s usage was that 9.5kwh battery would give me 80% of the financial value of a 44kwh battery (which would cover all import). Still deciding whether to get an AIO though.

Nice video Tim - thanks. The interesting bit that I picked up in all this was your understandable reluctance to manually insert into your lifestyle any daily force discharging to the grid. We installed 2 x Powerwall2 late last year and one of the beauties of that system is that if you put it in “reduce cost” mode, it does all of those calcs itself and effectively ensures that by the start of the cheap/recharge period, you have dumped any extraneous power to the grid to pickup the arbitrage. Even better, even though we are on Outgoing Octopus Fixed, so exporting is always 15p, I’ve configured the Tesla gateway to think that we make more money by exporting between 5pm and 7pm, so it keeps the battery as full as it can up until 5pm, and then throws everything it’s got at the grid just at the peak usage period. And all of this with no manual input by me. It occasionally misjudges and we run out of the battery before the cheap period starts, but not often and not by much. So there are some advantages to the Powerwall setup.

Thanks for this! It saves me working it out.

Just had a second Powerwall fitted and have been surprised by how much more flexibility it gives us which means we run the dishwasher and washing machine when we want, its much easier to use all the electricity we generate and the ability to charge the car directly from the battery is very useful (charge and discharge is now 10kWh), when we get a second Air-Air heat pump we can run it on cheep electricity. As I don't sell back to the grid (I'm on the last of the FIT) I don't have to worry about excessive cycling. I have found focusing just on the financials can blind you to other benefits.

Interesting analysis and video. I’ve done exactly the same thing as you’ve described but with Tesla powerwalls and solar panels. However we have a heat pump and 2 x EVs to charge. In my case my calculations worked out in favour of getting the additional storage , but it is very much a case by case on your personal usage and circumstances. The one thing you didn’t touch on though that’s probably worth thinking about is the potential future rise in grid import costs per kWh in the future. You might find in years 8 onwards for example the cost is much higher which means your payback is quicker than originally estimated.

Did I miss the calculations for conversion losses? What about leaving an extra buffer? You won't want to force discharge all of the battery every day. A higher power inverter such as a Sunsynk could discharge at a much quicker rate than the GivEnergy does. This video reinforces my view that home storage batteries are not a no brainer. Calculations are always needed.

We have 4kw solar array running a 10kw system with 31.5kWh of storage cost us about £10k 2 years ago. I plan to run the batteries at 80% of thier capacity durring good solar production, and 100% durring the winter months to help prolong the life of the batteries.

That automation is really not difficult. Happy to help you, show you my automations which work with IO

This is great, thank you. I've been going through the same process recently; we have 9.5kwh and over winter it pretty much always runs out at some point between lunchtime on the coldest days or mid evening most days. I concluded that even though an evening of peak rate electricity is often several times more than the rest of the day's offpeak, it's still cheaper than investing in a new battery. Buuuuuut... I'm still leaning towards getting another 9.5kwh (or maybe just a 5.2) before next winter anyway, because it's not just the financial value, there is value in the satisfaction of being able to make better use of our soar generation all year round, and avoiding using peak time grid electricity when it's at its dirtiest. This time of year annoys me because we export lots during the day when the battery is full, but it still runs out before the sun comes up the day after if we leave the heating on. Plus maybe sharing the load between two batteries will make them last a bit longer...?

Hi Tim, So many variables to consider. Presumably the changes in the overall cost of electricity over time is less important than the difference between import and export? Not only a second hand battery market to consider but improvements in battery technology to keep an eye on. Also vehicle to grid technology can be an option in the future.

Worth pointing out that force discharging your GE battery at the end of the day is straightforward. I've got it set up in the app to export anything left in the battery at the start of the off peak period. So I make a little bit of money with whatever I didn't use. All automated so no hassle or manual input required

Another consideration would be to look into the practicality of whether additional battery can actually be charged during the cheap tariff period based on inverter and battery max charging rates

Thank you! The conclusion has not changed, feels like battery costs need to come down to make this viable……

I did consider however, the route I now think is using my cars massive 65 kWh battery to backfeed back in to the house, it can already feed a 13 Amp socket from the charge socket so a suitable EV charger and car and we are looking at 7Kw to the consumers unit