Battery discharge over night

I think I'm going to answer my own question on this, but here goes...

Last night I moved the battery charging from, 12:00 - 03:00 up to 60% to capitalise on the cheaper rate, eco mode is on, and the inverter is set to load 1st.

Unfortunately upon checking the app this am, the battery was at 6%, I'm assuming because the battery reservation at 60% charge expired at 03:00 and so heating the water zapped my battery, due to the load 1st configuration?

Resultingly today I've had a big pull on the grid to charge the battery at peak hours, so today was far from economical

Weather this week is generally quite poor, so I've elected to charge my battery to 100% overnight, and to top up again in the day using hopefully any surplus solar, but in reality I think the chance of this is quite slim

Anything I could / should do differently on lower solar days, to stop big battery charging loads in the day? I don't have any automation so there is a bit of back and forth, watching the weather forecast and adjusting battery charging schedules 1 & 2 accordingly

Midlands_Solar IIRC you're on Eon Drive tariff, with cheap-rate 0000 to 0700 and export of 16.5p, though not yet configured for export ?

You want to set the battery charging period to be the entire duration of the cheap rate, and use the target-percent to control how much it charges. Once it reaches that, it will hold that level until the end of the timed window. And then I guess you just adjust how much to charge overnight based on how much solar there is. (I tend to reduce charging power so that it takes the entire cheap-rate period to reach my target, since I think that might be kinder to the battery.)

Once you get your export tariff set up, you may as well charge to 100% every night, and just export any solar, since your daytime export rate will be quite generous.

There doesn't seem any point ever charging the battery from the grid at the daytime rate - may as well just run any loads from the grid directly, rather than putting anything into the battery first and suffering round-trip losses. (Doesn't apply to those with an even-higher peak-rate period, such as Agile, Flux, Cosy.)

Many thanks

Yes EON Drive and no SEG at the moment

In the summer months when the weather’s a little more dependable, I’d have thought charging in the day for battery evening running would still be advantageous from a grid independence / cost perspective?

Midlands_Solar I’d have thought charging in the day for battery evening running would still be advantageous from a grid independence / cost perspective?

No, I don't think so... suppose there are 10% round-trip losses, so for each kWh you charge the battery, you get 0.9kWh out. And suppose daytime price is 30p/kWh.

If you put 5kWh into the battery at daytime rate, that costs 5*30 = £1.50. Then you consume that in the evening. So you've paid £1.50 for 4.5kWh of energy, giving an average unit price of 33.3p/unit.

If instead, you run from the grid directly in the evening, those 4.5kWh of energy cost 4.5*30 = £1.35

So it's costing you 15p, plus some wear&tear on your battery, to charge during the day for use in the evening.

And if you don't use all the energy you added to the battery at the daytime rate, that means there's less room to import overnight at the cheap rate. You could export it to the grid - while you paid 33.3p/unit for it, you'll be replacing it for 8p/unit, so it's still a net win. (Beware of the sunk-cost fallacy - just because you paid 33.3p/kWh for it, that doesn't make it "worth" 33.3p/kWh. Selling it for 16.5p and buying it back for 8p is still a win. But just not as good as if you hadn't bothered at all.)

(If you think there might be a power-cut in the evening, then use, you might view the price as worth paying. But even then, it's probably better to pause the battery during the day, and run from grid, rather than discharging it then refilling it.)

Many thanks

My thinking was to use the excess solar generated in the day to charge the battery up over a 2-3 hour period, to then run the house in the evening, and then export the excess energy at the 16.5p SEG rate

Today has probably been the most inefficient since I had the solar system installed, this is just from my own misunderstand on the battery charging, and how the battery is consumed in the early morning.

Charging the battery I had hoped would have given enough charge to see us through the rest of the evening, but at 13% it will run out so again needing to pull from the grid

Today has probably cost me twice as much if not more than I was paying due to my own error 🫣🤐

Just one day in the wider scheme of things of the wider savings isn’t bad, but I’m still a little annoyed at myself

Midlands_Solar Charging from solar is a bit different... you were showing us images of daytime charging from grid above.

But even then, it's not clear-cut. The way I look at it, you need to value your generated solar at 16.5p/kWh. That's more expensive than your overnight rate, so if charging overnight to 100% is enough to cover the whole daytime consumption, then it makes more sense to export all the solar directly, rather than putting it in the battery. But if your battery is not enough to cover daytime usage, then it's better to use the solar to top up the battery. Both those are preferable to importing from the grid at any time during the day, but you never want to charge the battery from the grid during the day. ie always be using the cheapest power you can.

I'm on IOG, which has similar rates. My battery is enough to cover daytime usage, so I just export daytime solar. (Well, it's a bit more complicated than that: my hybrid inverter would start clipping if generation exceeds 5kW, so I do divert a little power into the battery around noon, to avoid that. Then export it to the grid later.)

DD yes thank you, that’s how I view it on the charging and export approach, in our case if the battery is say at 60% by 5pm then that will see us through the evening of typical usage (tv, lights and evening meal cooking)

It’s good to get a bit of a steer / insight just to sanity check my logic.

It would be good if a “how to” beginners guide could be put together on here at or would help a lot of new solar owners like myself get started and a few pitfalls to watch out for

I appreciate that this is subjective based on type of system, and other heating systems used (i.e. oil, gas, and heat pumps) but starting with the basics if a solar array and battery and few pointers would certainly go along way

Midlands_Solar It would be good if a “how to” beginners guide could be put together on here at or would help a lot of new solar owners like myself get started and a few pitfalls to watch out for

It's not really specific to GivEnergy, so this probably isn't the best place for it. There's a youtube channel 'Gary does Solar' which has a lot of useful info, comparing tariffs, etc. 'EVM' is another - though primarily cars, also talks about solar; he's now a GivEnergy spokesperson too. Another is 'DanEVSolar'