Should I charge my batteries overnight in Summer?

daksolaruser

Hi there, 
Apologies if this has been covered but I couldn't find anything that sounded exactly like what I'm asking.
I have solar panels and batteries. Last winter I started charging the batteries overnight from the grid at the cheaper rate, using the batteries during the day. No brainer I think?
In late February/early March I was about to switch overnight charging off and use the daytime sun to charge my batteries via the panels 'as intended'. Then I thought - 10p per kwhr overnight versus 38p during the day plus I sell surplus back to the grid at say 15p. It seemed cost-effective to continue charging overnight, topping up during the day with solar and sending more to the grid as a result. 
On the one hand this seems like an obviously beneficial thing to do but I can't help thinking I must have missed something. Is it sensible, from a financial pov? I understand my batteries could suffer from the extra charging/discharging although I'm not convinced this is the case either.
Any advice would be appreciated as my brain is starting to hurt through thinking about it!

Screwdriva

Hi there! This forum is great at solving those headache inducing questions! 

Can I ask which batteries you have and what tariff you're on? 

paradigital

Theres also another angle to consider.  Battery SoH which is usually directly linked to charge cycles.

During the summer months I tend to keep my batteries charged via overnight cheap rate with a max SoC of 90%, I never see lower than around 40-50% at the end of the peak rate (23:30) even on overcast days. This keeps charge cycles low. And my average unit rate for April was 7.06p/kWh.

During the winter I tend to allow discharging down to 20%, and schedule 100% SoC for 05:30.

I’m hoping this use cycle will allow the batteries to outlive their suggested lifetime, thus increasing the ROI.

Exiled_Tyke

I charge during the night all year round.  During the summer I could get away with not doing this, save a few pennies and trus the sun to do the charging for me the next morning. However I only need one cloudy day to mean I'm importing from the grid at peak rate to wipe out whole load of benefit.  At least during the summer I don't tend to need all the battery capacity before bedtime so the night time recharge is slight. 

daksolaruser

Screwdriva said:

Hi there! This forum is great at solving those headache inducing questions! 

Can I ask which batteries you have and what tariff you're on? 

Thanks for replying but I don't need anything specific calculating - just a general sense as to whether I should charge off the grid overnight or not.

charles_b_2

I'm charging overnight at 8p.  If i take a chance on the weather it would be charged via solar by mid morning, but on days like today, sadly its not. But the upside is I i export at 15p. So, subtract the import cost and i still make around 6p (more or less if you take account of conversion losses)

QrizB

daksolaruser said:

Screwdriva said:

Hi there! This forum is great at solving those headache inducing questions! 

Can I ask which batteries you have and what tariff you're on? 

Thanks for replying but I don't need anything specific calculating - just a general sense as to whether I should charge off the grid overnight or not.

The question was probably because there are advantageous tariffs for certain brands of battery.

On your current tariff, there's a small advantage in charging overnight even when there's plenty of sunshine.

EcoScruples

I’m still on the Flux experiment and spent all of 2024 charging overnight.
i have now changed to not charging when the clocks changed in March and will swap back again in October.

Data gathering in process

Alnat1

My system can cap for several hours during the middle of the day so I don't want a full battery in the morning, I want to be filling it when generation goes over 3.6 kW. Because of this I set the battery to top up only to 30% full from grid charge overnight in summer (usually doesn't drop that low anyway) My inverter has options to set different battery limits on grid charge to system charge, not all do.

The Lux inverter has a handy setting "Charge last" which will send any generation under 3.6kWh direct to the grid, then auto fill the battery when generation exceeds this. I set that on days I know it will be sunny. If it's likely to be cloudy most of the day I'll fill the battery with whatever comes off the roof. Again the Lux has settings I can tweak depending how dull it is, I'm able to restrict the speed of battery charge on brighter cloudy days, so some production is exported and the battery fills more slowly.

My cheapest rate is 12.55p on Cosy though, so with losses I'm not gaining much by charging up overnight and selling at 15p.

Qyburn

daksolaruser said:

I understand my batteries could suffer from the extra charging/discharging although I'm not convinced this is the case either.

I don't think charging overnight adds any more battery cycles, it's just doing what the sun would otherwise be doing.

If you take it further, discharge the battery to the grid, then charge back up at cheap rate, then that is adding extra cycles.

Officer_Dibble

Well ditch Flux for starters, I can't believe it's the best tariff for anyone at current prices. Charge overnight at 6.7p/kWh and export at 16.5p/kWh with EON and the decision to charge at night is clear-cut.