I'm curious: Do you guys ever allow your battery to discharge during off-peak?

psiloc

Hope it's OK that I would still post here...!

I know we're approaching (or are we already in?) the time of the year where this is just academic. But I'm wondering how many of you would ever allow your battery to discharge as normal to power your home, despite it being the off-peak period?

I always had this option enabled for whenever there was enough solar forecast and battery power stored where the battery would make it through the night, which it would regularly do throughout the summer. But it turns out this has been saving me about just about 9-15p each day based on the baseload of the house overnight.

I mean, I guess that adds up, but is it worth the wear and tear on the battery? What's the consensus here at WW?

admin

psiloc We have certainly done the same for some of the summer.

One could argue, you can fill up in off-peak and then start exporting sooner in the day, at a profit.

But I guess that potentially has more impact on battery degradation than merely supplying house load. Another argument for using it in the way you have is that it's 'more green'. You may not want to buy more leccy than you need.

miffy

We are on Octopus Flux. We have a 5kW GivEnergy Gen 2 hybrid inverter, with 2x 9.5kWh batteries, and two solar arrays, 5.2kW facing SE, and 3.8kW facing NW on a 30' angle roof.
In winter, or really poor weather like recently, we Pause Discharge the battery between 05:10-15:50. This is to ensure we have enough power in the batteries to avoid drawing power from the grid at peak rate. It also means that we are on mains and solar power, no battery power, during the day.
[NB the reason we use 05:10-15:50 instead of 05:00-16:00 is to avoid any rule clashes with WW.]
From 15:50 to 02:00 the batteries power the house. They might go flat before the 02:00 charge period though, but at least the peak rate time is easily covered.

The GE batteries are supposed to last 15-20 years, and installations since Sept 2023 have a warranty of 12 years. Ours were fitted March 2023, so it's much shorter. There have been a number of discussions on battery wear and tear on the various GE facebook groups, and various GE employees and other expert people have commented on the debate. I'm uncertain if a WW discussion board is the best place to get more info on this topic.

psiloc

Well I've done all that sort of research already and concluded that I don't think there is a definitive right or wrong answer. I think there are too many variables over too long a length of time.

I'm specifically interested in what a group of well informed people like WW users are actually doing in practice.

WindyMiller

psiloc Over the summer my goal was always to use the cheap overnight energy available to ensure the battery was fully charged and the system could then export the solar as soon as possible. I used the battery primarily to take advantage of plunge pricing and could get in 3 charge/discharge cycles a day when these occurred. I figured that I wanted to get the most from the battery having already made the outlay for it. I expected 10 years from it on a 1 cycle per day. If I used that up a bit more quickly I wasn't bothered as by then, even better battery technology would be available.

Now winter is approaching and many days will not have enough solar to fill the battery I have changed strategy to import just enough to get us over the evening peak (and smaller morning peak on Agile). This involves 2 much smaller and gentler charge/discharge cycles per day helping to compensate for the hammering the battery gets on plunge pricing days. I still hope for 10 years battery life but, as long as it doesn't feel like an early life failure, I will not be too concerned if gives up a few years early if I think I've got the most out of it.

So, to hopefully answer your question, effectively during the winter months the battery will power the house during the highest priced period of the day and the grid will power the house and recharge the batteries during the lowest priced periods of the day. (Any solar I treat as a bonus but the smart charging algorithm is compensating a bit for this and importing less from the grid.)

I have another thread going as I try to fine tune the smart charging algorithm to achieve this.

PS The very useful Android 'Inverter' app displays battery cycles. My system was installed in May 23 and the app says my 2 batteries have used 400 and 404 cycles. This is just under 1 a day so I think I will still get 10 years from the batteries. I haven't noticed too much loss of capacity and as long as they don't get worse than 80% of the when new capacity they will still be quite serviceable.

JayC

psiloc I have a 13.5 Giv AIO on IOG. Every night I charge for two hours, then export all of that, then charge again (buy _12kWH at 84p, sell that for £1.80, buy 12 more at 84p = a near battery fill to start my day for around 18p)
With a 12 year guarantee and unlimited cycles I am not concerned with battery degradation. With PV on top I frequently export excess at the end of each day.

MrMessy

@psiloc I'm doing pretty similar to @JayC
I've got 2x9.5 batteries and a Gen2 hybrid, so it takes all of the 6hrs on IOG to fully charge them. I'm using the batteries to run the house, exporting all solar and then dumping any excess at the end of the day, although with an ASHP that's not likely to be much over winter. It's all laid bare in the IOG thread for anyone who's interested.
As the batteries and inverter have an unlimited milage 10yr warranty, I figure I may as well use them. Even on the older warranties I think the batteries were 6000 cycles and I'm doing 1 per day max, so 3650 over 10 years.
There was a thread recently on one of the Giv FB groups where someone had recorded minimal degradation over 3 years, so I think the 70% or whatever it is at the end of the warranty period is not going to be an issue.