FoxESS Community - Owners & Installers Forum

Hi,

I have a KH10 hybrid inverter which is working perfectly apart from a minor issue. I am charging the battery between 00:30 and 05:30 on cheap electricity and running off the battery / solar during the day.

The issue is that over the course of a day I am importing about 0.7 to 1 Kwh at a much higher tariff which accounts for nearly 10% of my overall bill.

Is there a setting that can be adjusted to better balance import / export?

Thanks

Matt

NoSignal wrote: Sat Dec 21, 2024 2:02 pm Hi,

I have a KH10 hybrid inverter which is working perfectly apart from a minor issue. I am charging the battery between 00:30 and 05:30 on cheap electricity and running off the battery / solar during the day.

The issue is that over the course of a day I am importing about 0.7 to 1 Kwh at a much higher tariff which accounts for nearly 10% of my overall bill.

Is there a setting that can be adjusted to better balance import / export?

Thanks

Matt

Hi, i'm afraid that is fairly normal usage - when you are running in Self Use mode the inverter is biased every so slightly from the grid, so a very small amount of power will be taken - and over the period of a day it adds up.

It's typically something you see at this time of year as in the warmer months and you are generating solar the export sets the bias towards the grid and consequently you only see a fraction of that energy being taken from the grid in summer.

I'm have a question that I think is sufficiently similar here, so I'm posting as a reply.

Just had a new solar+battery system installed. I am noticing that we seem to be "losing" around 1kWh per day (around 10-15% of total usage). That is, the battery begins and ends each day essentially discharged (well, at 20%, which is the min setting). But Grid Purchase+Solar Yield is ~1kWh greater than Consumption. Slightly frustrating, because we're not generating much more solar than that in mid-winter on average, so self-sufficiency is often being reported as very low or even zero.

Now I understand there will be some losses in the system. The battery isn't perfectly efficient. But that accounts for about 0.1 kWh per day at most. The inverter presumably draws some power to run (is that included in consumption or not?). But it's rated at around 15W, which is only ~0.3 kWh per day. I also wonder if there's some imprecision in some of the numbers reported which is contributing.

My guess is that this is probably normal and nothing to be concerned about, but I'd appreciate some thoughts from better-informed people than me. I note, curiously that:
* On one day, there was no overall loss. This was also our best solar generation day.
* Almost all the loss occurs over night. Typically the day starts with Grid Purchase being ~0.5 kWh over consumption, stays like that over the day, but then by the following morning the overall total for the day is around 1 kWh off.

But that accounts for about 0.1 kWh per day at most.

How are you calculating that 0.1kWh?


There are losses in every step here:

* conversion of grid A/C to D/C
* storing it in the battery
* discharging the battery
* converting D/C back to A/C

How much cheap-rate power are you importing from the grid overnight to store in the battery, and how much PV is being stored (presumably not much)?

I also wonder if there's some imprecision in some of the numbers reported which is contributing.

CT clamps can be off by a few %

AndrewClarke wrote: Sat Dec 21, 2024 3:49 pm Now I understand there will be some losses in the system. The battery isn't perfectly efficient. But that accounts for about 0.1 kWh per day at most. The inverter presumably draws some power to run (is that included in consumption or not?). But it's rated at around 15W, which is only ~0.3 kWh per day. I also wonder if there's some imprecision in some of the numbers reported which is contributing.

My guess is that this is probably normal and nothing to be concerned about, but I'd appreciate some thoughts from better-informed people than me. I note, curiously that:
* On one day, there was no overall loss. This was also our best solar generation day.
* Almost all the loss occurs over night. Typically the day starts with Grid Purchase being ~0.5 kWh over consumption, stays like that over the day, but then by the following morning the overall total for the day is around 1 kWh off.

I think I covered this in my previous post about how a grid tied system sets it's bias when in self use mode and takes a very small continuous draw from grid, when solar is being exported that changes the bias to the grid and you won't have any import.
At night obviously there is no solar so the bias is always to take a small amount of power from the grid.

If at night you switch to feed-in mode as bizarre as it seems the bias is forced the other way and you probably would be able to half the power you are importing - and then set the work mode back to self-use at dawn.

On your battery losses, there are many points of loss in the system i.e. you have an ac to dc conversion for the charger, then you have chemical losses in the battery involved in storing and recovering energy and then finally you have to convert it back from dc to ac to use it. Overall you should consider a system loss of approx 10% of the energy you use to what you get out of the batteries.

On the standby power the inverter, BMS and batteries consume it depends on the inverter and the size of your battery stack, typically this can be anywhere between 35 and 150 watts on the biggest of systems - although for a typical 5kw system you will likely be around 50 watt hours.

My colleague Tony has encapsulated the majority of these losses and explains how a hybrid grid tied system works here https://github.com/TonyM1958/HA-FoxESS- ... it-work%3F

At this time of year you see these losses the most as the solar generation is so poor, but don't be disheartened by losses - once we get towards the end of February and the suns elevation increases the losses will be dwarfed by the solar generated.

Many thanks for that, Dave; very helpful and comprehensive.

For the record, we're not charging the battery at night (currently I'm on a flat tarrif, though I am going to change that). So in total we'd charged about 1 kWh to the battery over the whole 4-5 days (since we actually use most of the solar we generate directly). Even if the system were only 80% efficient (and it should be a bit better than that), we'd be losing ~0.2 kWh at most. So it's not primarily battery inefficiency.

But yes, it sounds like it's probably resting power draw from the kit. I will try setting to feed-in overnight and see if it helps.

Sorry I missed the alert regarding your reply. I understand the biasing but wanted to see if it can be adjusted. Looking at a family members Solax system they have roughly half the level of import over the same period to the Fox system.

NoSignal wrote: Wed Jan 01, 2025 7:24 pm Sorry I missed the alert regarding your reply. I understand the biasing but wanted to see if it can be adjusted. Looking at a family members Solax system they have roughly half the level of import over the same period to the Fox system.

No there is no setting to change the level of bias, but you can switch the inverter into feed-in work mode when there is no solar generation as that will change the direction of bias, I automate that process at night and switch back in the morning - you may be able to half the daily grid import using this.