In my case the battery is relatively small (5.12 kWh), so the 30% discharge floor is a deliberate winter compromise rather than “never use the battery.” I’m on a single-phase 60A supply (in the process of being upgraded to 100A) with ASHP + EV in the mix, and earlier on I found the inverter modes could cause the battery to be “spent” at the wrong time (especially around EV charging), leaving me importing later anyway. With the current setup (Battery First overnight, Load First daytime), the battery reliably recharges in the cheap window and then supports self-consumption during the day. The 30% reserve mainly stops the battery being completely flattened before it can actually do useful work when tariffs are higher and PV is weak.

You’re absolutely right that if I hit 30% early in the evening, I’ll import at peak rates. In my own case, the trade-off has been acceptable because: (a) the battery is small, so it wouldn’t cover the full evening peak anyway, and (b) keeping a reserve has improved predictability and stopped the system “misbehaving” on EV nights. When PV improves (and once heat demand drops), I’ll likely trial 20% again, because at that point the risk of ending up at 30% too early is lower and the opportunity cost is higher.

Also, totally agree with your seasonal pattern: once you’re in April onwards and PV is routinely in surplus, the floor becomes much less relevant because SOC rarely gets anywhere near it.

On the Solar Optimiser idea: good shout. I’ll give it a proper look. I’ve been doing something similar with Octopus downloads + my own tracking, so it’ll be interesting to see how closely it matches month by month.

Thanks!!!

Does anyone lse have this issue with E.on Next?

Yes.  

I used data from Home Assistant and a Shelley to capture data last year and this year Im back with Octopus (not because of the data download, although it was certainly an irritant!).

If you haven't already, have a look at the Solar Optimiser tool on Tim and Kat's green walk website. You can try out different strategies such as self consumption, charge batteries with excess solar or with off-peak electricity, and then it tells you the best tariff by month. I found it fairly accurate and very close to my bespoke analysis using Octopus data downloads.

This is currently my winter-optimised set-up. I find that by stopping battery discharge at 300% end up recharging well overnight and having enough for self-consumption the day after without exporting when I need it. But perhaps may be improved?

@toodles hopefully Sun will cheer you up soon...

On the IOF rumour, I haven’t seen official confirmation that Octopus is fully withholding Intelligent Octopus Flux from new sign-ups, but availability does seem tighter lately (some reports of it being temporarily paused or harder to join amid volatile markets and recent global price spikes from the Middle East stuff).

Standard Flux, I believe, is still open, and it offers decent time-of-use export peaks (around 29p in the 4-7pm window in some regions), so that might be worth a look if your battery can play nicely with it.

In the meantime, leaking as little as possible to the grid is smart household economics… interesting year ahead.

Later, OE increased the Cosy tariff and it became ‘marginal’ as to whether with the ~ 10% losses through the battery it was worth selling my solar and buying grid to fill the battery. I thought long and hard about the practicalities and the morals of this ‘arbitrage’ on a daily basis.

With the export rate having dropped below the buy price now, I have been re-configuring my Tesla app to ensure I leak as little solar energy into the grid as possible! Morally, I feel this is a very good thing to be doing and, as such, my grid consumption will drop a little. The amount gleaned from the Sun is not that great at present, and of course, the ASHP gobbles up what little there is from those 21 panels.

One can but hope that some sunnier weather is on the horizon and that a rise in temperature will allow the heat pump to snooze some of the time. We might then be able to spare some energy for export whenever the battery is fully charged.

I have heard rumours that OE are withholding IOF tariff from new contracts at the moment (this does not augur well does it!?). It is rather likely that this coming summer’s solar energy is going to pay less well than previous years have. Regrets, Toodles.