Fox ESS H1-5.0-E-G2 inverter
Fox ECS2900-H4 battery 11.52KW
If I set a charging schedule from 0400 to 0700 (with mode scheduler) , and the battery reaches 100% at 0600, then from 0600 to 0700 the system prevents the battery from discharging, so that any load on the house has to be powered from the grid. Am I right that this is how the system currently works?
If so, then if my heat pump is operating between 0400 and 0700, I will be both charging the battery and running the heat pump from the grid. If the battery reaches 100% at 0600, then between 0600 and 0700 the battery will not discharge, and the heat pump will still be powered from the grid. But I could be running the heat pump from the battery between 0600 and 0700, so I am paying an unnecessary amount for grid use in the that hour.
Am I right with that reasoning? If yes, then is there any way of switching off the remainder of the charge period when the battery reaches 100%? In the example, this would mean allowing the battery to discharge from 0600.
If 0400-0700 is a cheap period of electricity, I would NOT want the battery to discharge any energy.
The idea is to start the higher price time with 100% to ride out the period until the next cheap energy session.
Are you on Octopus Cosy?
Three cosy periods of super cheap rates between 04:00 - 07:00, 13:00 - 16:00 and 22:00 - 00:00 every day
Perhaps if you can let us know what Country/Company/Tariff you are on, then the question can be answered easier.
There exists Home Automation systems, that could probable be set to swap the system mode when it reaches 100% to allow the battery energy to be used.
The idea is to start the higher price time with 100% to ride out the period until the next cheap energy session.
Are you on Octopus Cosy?
Three cosy periods of super cheap rates between 04:00 - 07:00, 13:00 - 16:00 and 22:00 - 00:00 every day
Perhaps if you can let us know what Country/Company/Tariff you are on, then the question can be answered easier.
There exists Home Automation systems, that could probable be set to swap the system mode when it reaches 100% to allow the battery energy to be used.
I am with Octopus in the uk on the cosy tariff with cheap periods 0400-0700, 1300-1600, and 2200-0000
Yes - I don't want to discharge the battery during a cheap period, only to have to pay for grid power in an expensive period.
However, in the example I gave, when the battery is full at 0600, the next cheap period is at 1300. If I know that the battery is capable of powering the house until 1300, I won't be using grid power. It's only an extra hour anyway if I charged it until 0700, so the battery needs to power the house for either 6 or 7 hours, depending on whether charging stops at 0600 or 0700.
So, if I don't charge between 0600 and 0700, the heat pump can run off the battery from 0600. If I do charge until 0700, then the battery will not discharge, and I have to pay for running the heat pump off the grid for that hour.
Yes - I don't want to discharge the battery during a cheap period, only to have to pay for grid power in an expensive period.
However, in the example I gave, when the battery is full at 0600, the next cheap period is at 1300. If I know that the battery is capable of powering the house until 1300, I won't be using grid power. It's only an extra hour anyway if I charged it until 0700, so the battery needs to power the house for either 6 or 7 hours, depending on whether charging stops at 0600 or 0700.
So, if I don't charge between 0600 and 0700, the heat pump can run off the battery from 0600. If I do charge until 0700, then the battery will not discharge, and I have to pay for running the heat pump off the grid for that hour.
Imagine it during the cheap rate it's 10p/kW.
Also assume that the battery is 95% efficient. To add 1kW of power it requires ~1.05kW of power.
You fill the battery up. Size doesn't matter. It's now 6am and the cheap rate stays on until 7am.
Scenario 1. The battery isn't doing anything, you consume 2kW from the grid (20p) for the hour.
Scenario 2. You use 100% battery. Since there is loss for power going into the battery, it costs ~21p. And 2kW of wear into the battery.
In the perfect world you want no battery use at all during the cheapest time, and 100% battery during the peak time. There is no benefit to running off battery during off-peak.
Also assume that the battery is 95% efficient. To add 1kW of power it requires ~1.05kW of power.
You fill the battery up. Size doesn't matter. It's now 6am and the cheap rate stays on until 7am.
Scenario 1. The battery isn't doing anything, you consume 2kW from the grid (20p) for the hour.
Scenario 2. You use 100% battery. Since there is loss for power going into the battery, it costs ~21p. And 2kW of wear into the battery.
In the perfect world you want no battery use at all during the cheapest time, and 100% battery during the peak time. There is no benefit to running off battery during off-peak.
So let's say you decide to let the battery run from 06:00... when the cheap period actually ends at 07:00
What if the weather is really cold?
The could deplete your battery say by 11:30, and your next cheap period begins at 13:00
Now, what happens when your battery is depleted before the cheap period?
You are now paying to run your heat pump in a peak period, from 11:30 until 13:00
What happens, if you actually charge your battery at 04:00, and keep it held at 100% until 07:00?
In the same in cold weather day, your battery will run out at 12:30, leaving you only purchasing 30 mins of peak energy pricing
Now, the real hard question to answer
The hardest issue you face is knowing for 100% that your battery will cover your heat pump/house load, only once you know this for sure, then you could start to adjust the charge end time to let the battery start being used earlier.
Get this wrong, and it costs your pocket.
I think the only good way, is to have setup some home automation that can forecast your demand?
There are several members with HA systems, that could hopefully advise better than me.
What if the weather is really cold?
The could deplete your battery say by 11:30, and your next cheap period begins at 13:00
Now, what happens when your battery is depleted before the cheap period?
You are now paying to run your heat pump in a peak period, from 11:30 until 13:00
What happens, if you actually charge your battery at 04:00, and keep it held at 100% until 07:00?
In the same in cold weather day, your battery will run out at 12:30, leaving you only purchasing 30 mins of peak energy pricing
Now, the real hard question to answer
The hardest issue you face is knowing for 100% that your battery will cover your heat pump/house load, only once you know this for sure, then you could start to adjust the charge end time to let the battery start being used earlier.
Get this wrong, and it costs your pocket.
I think the only good way, is to have setup some home automation that can forecast your demand?
There are several members with HA systems, that could hopefully advise better than me.
During a charge period (low unit cost period) the most cost efficient way to run the heat pump is from the grid. If you are running the heat pump from batteries during this period then you are losing about 5-10% due to conversion losses - mains volts -> battery charge -> battery discharge -> convert back to ac mains.
If the battery still has useable charge at the start of the next charge period then it just doesn't need to be charged as much and you are then still using low rate electricity to run the heat pump.
If the battery still has useable charge at the start of the next charge period then it just doesn't need to be charged as much and you are then still using low rate electricity to run the heat pump.
H1-3.7-E-G2, 2xEP11-H and 6Kw solar
Manager:1.64
Master:1.47
BMS:1.009
Manager:1.64
Master:1.47
BMS:1.009
Any pointers to ha systems much appreciated.
I agree that for my argument to hold, the battery must be capable of powering the house until the next charge/cheap period starts. But if this the case then I will have unnecessarily paid for an hour of house electricity use, albeit at a cheap rate.
So far this year, apart from a cold snap in November, I have been able to set the charge periods to be 2 or even one hour, and the battery makes it through to the start of the next cheap charging period. I don't expect this to be the case with really cold weather.
But this does mean making a daily assessment of power use in advance by checking the weather/temperature forecasts.
But, whether it's a good idea or not, my original question remains unanswered - is it possible to end the charging period early if the battery has reached 100%?
I agree that for my argument to hold, the battery must be capable of powering the house until the next charge/cheap period starts. But if this the case then I will have unnecessarily paid for an hour of house electricity use, albeit at a cheap rate.
So far this year, apart from a cold snap in November, I have been able to set the charge periods to be 2 or even one hour, and the battery makes it through to the start of the next cheap charging period. I don't expect this to be the case with really cold weather.
But this does mean making a daily assessment of power use in advance by checking the weather/temperature forecasts.
But, whether it's a good idea or not, my original question remains unanswered - is it possible to end the charging period early if the battery has reached 100%?
AFAIK, Home Assistant is your only choice.
I myself don't have it setup, but I suspect that it could take several hundred pounds to get it in place.
There is a learning curve in using it, as you need to be able to program in the logic to it... when battery SoC = 100% swap mode scheduler from Charge to Self-Use.
So let's say you are not good with wiring up things, so you need the solar team in to do this (or sparky?)
Pay £xxx
The kit, pay £xxx
Let's for argument sake, say this costs you £500 to setup...
Will you save this amount by allowing the battery to discharge, and as mentioned above by others, you will be loosing a bit of £ by AC->DC->AC conversion, and extra wear and tear on the battery.
Ideally we need someone who has setup HA to let you know the costs involved, and if it can actually work as intended.
I myself don't have it setup, but I suspect that it could take several hundred pounds to get it in place.
There is a learning curve in using it, as you need to be able to program in the logic to it... when battery SoC = 100% swap mode scheduler from Charge to Self-Use.
So let's say you are not good with wiring up things, so you need the solar team in to do this (or sparky?)
Pay £xxx
The kit, pay £xxx
Let's for argument sake, say this costs you £500 to setup...
Will you save this amount by allowing the battery to discharge, and as mentioned above by others, you will be loosing a bit of £ by AC->DC->AC conversion, and extra wear and tear on the battery.
Ideally we need someone who has setup HA to let you know the costs involved, and if it can actually work as intended.
Storing 1kWh in your battery and then recovering it takes approx 1.1kWh of power (the battery has an RTE of 95% plus AC>DC and DC<AC losses) - so if you take the power from the battery instead of the grid, it would actually cost you 10% more to do that.tonyl wrote: ↑Thu Dec 04, 2025 11:04 pm So far this year, apart from a cold snap in November, I have been able to set the charge periods to be 2 or even one hour, and the battery makes it through to the start of the next cheap charging period. I don't expect this to be the case with really cold weather.
Also the batteries have a finite life (in battery cycles / throughput) and for each 1kWh you rotate through them, fully costed that would be around 8p to pay for them (depending on your batteries and what you paid for the install it might be as low as 5p or as high as 10p) - you can ignore that cost as you've bought the batteries already but you should consider it as real.
So all of that said using the battery rather than the grid is more costly unless the amount you pay to charge the battery is considerably smaller (or you use PV generation) - the final thing to say and something i've learnt from experience a couple of times, if you get the power calculations wrong and end up running the batteries out, you'll pay peak rate which is painful... i've done it a few times and i've made sure that my home assistant works overtime so I don't do that again.
Will has done a good video that guides you through it, and he has plenty of other good content on his channel that is worth a look at if https://youtu.be/kE_6HtzcyXg?si=LLGTEeaXl3nOv2De
No it isn't, at least not yet - Fox are making some changes in the background to enhance Force Charge/Discharge but until they are available it's a definite no - home assistant is the only answer.
My aim is to have the battery at 100% as close as possible to the end of the off-peak tariff period, which is 05:30.
Now that winter conditions have settled in, I can almost guarantee that the battery will be down to minimum SoC of 10% before the off-peak tariff comes in again (maybe I should install more battery capacity, but that's another topic) and I have found over time that mains charging runs at almost exactly 1% per minute in my modest system.
I need 90% charge to get from min SoC to max SoC, which requires 90 minutes' charge time, so I set the scheduler to Force Charge starting at 04:00 and that gives me a full battery exactly when I want it for maximum charge going into the day while using minimum mains power.
I do allow a couple of extra minutes for variations but the principal is there and it works perfectly for me and may be helpful for others.
Cheers,
John
Now that winter conditions have settled in, I can almost guarantee that the battery will be down to minimum SoC of 10% before the off-peak tariff comes in again (maybe I should install more battery capacity, but that's another topic) and I have found over time that mains charging runs at almost exactly 1% per minute in my modest system.
I need 90% charge to get from min SoC to max SoC, which requires 90 minutes' charge time, so I set the scheduler to Force Charge starting at 04:00 and that gives me a full battery exactly when I want it for maximum charge going into the day while using minimum mains power.
I do allow a couple of extra minutes for variations but the principal is there and it works perfectly for me and may be helpful for others.
Cheers,
John