FoxESS Community - Owners & Installers Forum

Hi,
Noobie here so apologies if this has already been covered ...
I'm trying to work out wether or not to exit my fixed rate deal and change to overnight charging at a cheaper rate and battery usage during the day?
First off; I'm not exactly sure if I can (or how to) set the system up to charge the battery overnight and then use solar or battery during the day?

I have a FOX EPS 5.18kwh battery with 4.6 kWh usable capacity.

Secondly; I'm assuming that my savings would be the difference between the fixed rate (26.65p) and the cheap overnight rate (6.5p) i.e. 4.6 x (26.65 - 6.5) = 92.69p / day ?

Cheers in advance.

Chris

Hi, yes you can set the system to charge from a low tariff overnight, in the app you can use either the ‘Grid Charge Setting’ under Quick Settings or use the more advanced Mode Scheduler and set a Force Charge schedule.

Probably easiest for now to use the simpler Grid Charge and leave Schedules until you need more flexibility.

On the savings it all depends how you calculate it, to include everything you have to factor in the losses of converting power from grid and storing in the battery, the chemical losses in the battery and then the conversion from battery to grid again - typically i’d say around 10% losses so approx you’d need to buy 1.1kWh to sell 1kWh so increase your 6.5p to 7.15p to cover that.

Arguably you had to buy the batteries in the first place and they have a specific lifetime which means that eventually you’ll need to replace them so to get the actual cost figure you should really add in the purchase cost - the maths for that are a bit more complex but to save you from that it’s usually around 8p per kWh you should add if you want to break even.

So fully costed you’d be more like 4.6 x (26.65 - 7.15 - 8) =52.9p/day

Or you could just say i’ve sunk the cost of buying the batteries and not include the 8p.

Thankyou! Also for confirming that the battery capacity rating is the limit to what I can save overnight! That wasn't an obvious question!

The deterioration factor helps!

I've also realised that I will have to look into the daytime rate which may be more expensive than my fixed deal.

Cheers

Chris

You can look at inputting numbers into this website.

https://timandkatsgreenwalk.co.uk/
He does state that he doesn't account for AC/DC losses yet, and could add it in a future update.