Inverter Work Modes
Fox inverters can be set to a number of different work modes. These are:
In this mode, the inverter prioritises power allocation as follows:
- House Load
- Battery Charging
- Export
The inverter determines the house load using the CT clamp or meter that measures the incoming grid supply current. The primary goal is to keep the supply current at or around 0A by pushing enough power into the house to stop the current draw from the grid. It does this using power generated from PV or at night, by drawing power from the batteries.
If the house load is being supplied from PV and there is power remaining, the inverter will use excess PV power to charge the batteries.
When the batteries are full, the inverter will send excess PV power into the house. If this exceeds the house load, power flows back out into the grid as export. The inverter monitors the power being exported via the CT clamp or meter on the incoming supply.
If there is an export limit set and this is achieved, or if the inverter reaches it maxiumum output, and the batteries are full, it will back off the power being generated from PV (known as clipping).
In this mode, the inverter prioritises power allocation as follows:
- House Load
- Export
- Battery Charging
The house load is still met first in feed in first mode because the load is a shunted across the grid supply, so the inverter cannot export without first satisfying the house load. Where there is no PV power e.g. at night, the inverter will supply the house load from the batteries and there will be no export.
If there is an export limit set on the inverter, and there is still excess PV power, the inverter will use the excess to charge the batteries. Once the batteries are fully charged, the inverter will clip the PV power to match the house load and export limit.
When you are export limited and operating in Feed In First work mode, it appears to be benfecial to have space in your batteries. The inverter stores excess solar generation in the battery and recovers this during breaks (e.g. clouds pass over), maintaining your export. This maximises your energy export and reduces the clipping that happens when your batteries are full.
In this mode, the inverter prioritises power allocation as follows:
- Battery Charging
- House Load
- Export
The main goal of this mode is to keep the batteries charged so they can be used as EPS in the event of a grid supply failure. PV power generated is first used to charge the batteries. When the batteries reach 100% or the limit set for charge current, excess PV power will be used to supply the house load and where the power available exceeds the house load, power will be exported.
If the batteries are charged (or charge limited), the house load is met and the export limit is met, then the inverter will clip the PV power.
The term weak grid is commonly used in the industry to refer to a grid supply with a relatively high source impedance. As such, it may be subject to significant grid voltage and frequency variations that can cause stability problems for grid tied inverters.
This appears as a fourth work mode in the H1 inverter front panel menu. There does not appear to be any current information on what this mode does.
This mode appears on Fox ESS Cloud but is not available on any inverters at this time, so far as I know. Fox describe this as follows: "The energy of the battery is used to suppress the output power instability cause by the unstable output of the photovoltaic panels, so the power output of the inverter reaches the ideal power curve".
In other words, the battery is discharged to maintain a given level of output power - it's not yet clear how this might be used. Not to be confused with Force Discharge work mode (described below).
Peak Shaving relates to an alternative tariff that may be applied to industrial rather than domestic grid users. These tariffs are not based on kWh usage but apply banded charges based on the maximum power demand in a given period (the point being that additional grid generation has to be started up as demand increases, so there is benefit in maintaining a steady demand).
This mode appears on Fox ESS Cloud but is not available on any inverters at this time, so far as I know. Fox describe this as follows: "A peak shaving limit must be set by adjusting 'import limit' to the desired value. We can increase the peak shaving support uptime by setting 'threshold SoC'. When the battery is above the 'threshold SoC', the system will work in self-use mode. When the battery is below the 'threshold SoC' the peak shaving function will be the priority and the system will only provide power from the battery when the 'import limit' is exceeded. When below the 'threshold SoC', the system will charge from the grid when there is available power without exceeding the 'import limit' to ensure peak shaving for extended periods. If the 'import limit' is exceeded constantly for an extended period of time, the peak shaving function can only guarantee successful operation while energy remains in the battery. If the battery designated 'low level' is reached, the peak shaving function will cease".
The settings referred to here do not appear in the current inverter settings. The 'import limit' applies to the grid consumption power. The 'threshold SoC' appears to be a new setting. When the battery is above this, self use mode will aim to reduce grid consumption to zero using the battery to supply the house load. If the battery drops below the threshold, peak shaving is activated and the grid 'import limit' is applied and the inverter outputs power to maintain the import limit (similar to self use, but with a higher standing grid usage). If there is spare power (i.e. the house load is less than the import limit) and the battery is below the threshold, the inverter draws the remaining power from the grid to charge the battery back up to threshold. The designated 'low level' appears to refer to the current Min SoC On Grid setting.
There is one significant assumption here - that the inverter is capable of supplying the peak house load - however, this might not be the case and if the inverter output power is exceeded, power will be drawn from the grid regardless. Nevertheless, it would be beneficial for the grid if peak power demands were removed and replaced with a lower, more consistent, power demand. The problem is, today, electricity tariffs do not encourage this - although there is discussion of peak shaving as part of the demand flexibility service.
This work mode can only be set as part of a strategy period (see below) and charges the battery from the grid using your max inverter power or max charge current, charging up to your Max SoC setting. Force Charge work mode differs from the 'Charge from Grid' battery setting in that, PV generation remains available when charging from grid (reducing the power drawn from the grid), but it is disabled in Force Charge Work Mode so all charge power is drawn from the grid.
There is no way to set 'Force Charge' (where the batteries do not discharge) using strategy periods. Instead, set a period where the work mode is Backup if you need to preserve the battery charge.
Force Charge work mode is available on H1/AC1 inverters from Master firmware v1.68. When setting this mode, you also need to set values for fdPwr and FdSoC, even those these values do not appear to do anything. The default values are fdPwr=0 and fdSoC=10.
This work mode can only be set as part of a strategy period (see below). This mode discharges the battery to the inverter output, delivering power to your house load and grid export. There are 2 additional settings for this mode:
- FDSoc: is the minimum battery state of charge for Force Discharge. When the battery reaches this level, discharging will stop and the inverter will resume normal operation delivering sufficient power for your house load. If the battery discharges to your Minimum On Grid SoC, the inverter will stop delivering power and your house load will draw from the grid.
- FDPwr: is the output power level to be delivered, including your house load and grid export.
Force Discharge work mode is available on H1/AC1 inverters from Master firmware v1.70.
Before using Force Discharge, assuming you want to export to the grid, make sure you disable any solar diverters, such as water heaters or EV chargers that consume excess solar. If you don't, they will draw power to consume your power and reduced your export to zero.
You can also offset your house consumption during Force Discharge by manually setting an export limit. With this, the lower of FDPwr and your export limit will apply so, for example, if you set FDPwr to 6000 (6kW) and your export limit to 3680 (3.68kW), your inverter will adjust its output power to maintain 3.68kW export power, leaving up to 2.3kW head room for house consumption.
Strategy periods and schedules are supported on H1/AC1 inverters from Master firmware 1.68. These allow you to set up to 8 time periods where a specific work mode will be active. The work modes include: Self Use, Feed In First, Backup, Force Charge and Force Discharge. Each strategy period includes an asociated Minimim On Grid SoC setting that over-rides any battery settings.
Strategy periods can be enabled / disabled as a block. They cannot be enabled / disabled individually. In fact, when strategy periods are enabled on the inverter, changes to work mode through the Fox app or the inverter front panel are disabled and battery charge settings are cleared.
To build strategy periods using foxesscloud.com, add the periods you require and then Enable them so they are saved to your inverter. If you navigate away from the page without enabling, the periods will be lost. When you disable the strategy periods, they are removed.
For all times / periods, you must set a value for FDSoc and FDPwr, even though these are not used. Use FDSoc = 10 and FDPwr = 0 as defaults.
If you want to be able to set or edit the times, go to the tab 'Template Preset' and click '+ newly added', give your template a name and comment that describes what it does. You can then add strategy periods and electricity price periods
Note that start and end times are inclusive: if you set an end time of 19:00, the period will end at 19:00:59. If you want the period to end at exactly 19:00, set the end time to 18:59.
When setting times, the end time must come after the start time, so you cannot set a 'wrap-around' period such as 23:30 - 04:59. Instead, use 2 time periods 23:30 - 25:59 and 00:00 to 04:59. If you find you can't change the start time, set the end time and then go back and do the start time.
To activate a template, go to the tab 'Template', select your template and Enable it:
Demand Flexibility encourages load shifting to help with peak shaving during periods of high demand. This example template (SavingSession) can be used to achieve this:
This charges the battery at standard rate between 2pm and 4pm to 100% SoC. Then between 4.30pm and 6pm, the battery discharges back to the grid at 6kW. I have set my export limit to 3.68kW, so the inverter will automatically adjust it's output to meet my house load (up to 2.3kW) while maintaining an export rate of 3.68kW for 90 minutes - so I discharge around 5.5kWh to the grid.
Given Force Discharge and the ability to set strategy periods - can I use this to exploit Octopus Flux?
My battery capacity is 14.2kWh and my daily use is around 14kWh, with 7.6kWh of this being consumed between 4pm and 2am each day. Solar yield will vary, but for the winter, I'm assuming an average of around 7kWh per day.
Let assume I charge my battery from the grid each night between 2am and 5am and that I've used all the energy by 2am. So, I add 90% to my battery less the inverter and battery losses at around 95% efficiency. This consumes 13.5 kWh from the grid plus around 1kWh for my house running, at 16.51p/kWh, costing me £2.40 inc VAT (ignoring the standing charge as I have to pay that anyway).
I consume energy from the battery through the day, topping up with solar if it's available - hopefully leaving me with 100% or 14.2kWh in the battery at 4pm. I need to keep 7.6kWh plus min soc of 10% to get through the night - that equates to a fdSoc of 64% - so with 100% at 4pm, I can send 36% or 5.1kWh back to the grid between 4pm and 7pm at 27.51p/kWh. So, I get £1.40 back, reducing my bill from £2.40 to £1 per day.
With greater solar yield in the summer, I'd make more as any excess, once the battery is full would be exported at 16.51p/kwh, potentially offsetting my complete bill and putting me in profit for the year.
There are other changes I could make, with experience, to optimise the setup: first one is to reduce Max Soc on the inverter so I don't fill the battery from the grid but leave space for solar to top this up - this would be a benefit when I thought my solar yield was going to be more than 7kWh.
The second, more contentious one, would be to set an export limit on the inverter. If I want to export 5kWh over 4 hours, I could set an export limit of 1500W with fdPwr set around 4000W. This means I would export 1.5kW consistently and variations in my house load would mostly be made up by the inveter. The lower power drain on the battery reduces the thermal losses. While this would probably work OK for winter, I'd increase the export limit with higher solar yields in the summer so I can take better advantage of over production when my battery is full earlier in the day. Might be nice if I could change the export limit as part of a strategy period...
Thirdly, I can limit the charge rate to reduce the inverter and battery losses during charging. My battery gives me 320v and I want to add 12.7kWh over 3 hours. 4.3kW at 320v gives me a max charge current of around 14A. Better still if I could set fcPwr when charging from the grid to control the charge power and set fcSoc to control Max Soc , like I can control the discharge power and Soc...
If you are using this Home Assistant integration, you can automate changing the work mode using the example yaml code below.
If you are using a different integration, the setup will be different - always check for information specific to your integration.
- Go to Settings, Automations and click on CREATE AUTOMATION and select 'Create new automation'
- Click the 3 dots in the top right hand corner and select 'Edit in YAML'
- Delete the default YAML code and then copy and paste the following code. This changes Self Use to Feed In First, triggered at 11am:
alias: Set Feed In First at 11am
description: Change inverter work mode to Feed In First
trigger:
- platform: time
at: "11:00:00"
action:
- service: modbus.write_register
data:
hub: FoxESSInverterModbus
address: 41000
slave: 247
value: 1
mode: single
-
Click Save
-
Click RENAME to set the name of the automation
-
Click the arrow at the top left hand corner to return to Automations
-
Repeat this process, using the following code to create an automation that changes Feed In First to Self Use, triggered at 7pm:
alias: Set Self Use at 7pm
description: Change inverter work mode to Self Use at 7pm
trigger:
- platform: time
at: "19:00:00"
action:
- service: modbus.write_register
data:
hub: FoxESSInverterModbus
address: 41000
slave: 247
value: 0
mode: single
Click on an automation to change the time or add further conditions etc.
If you want to manually change work mode outside the set times, just go to Settings, Automations and click on the 3 dots and select Run.