Include battery (storage) control mode as part of the optimisation data frame

[fredriklj]

Many inverters connected to a storage (battery) can be controlled according to Sunspec (true for at least fronius and solaredge). There is a quite good explanation of how it works here:

https://loxwiki.atlassian.net/wiki/spaces/LOXEN/pages/1316061809/Fronius+Hybrid+with+Modbus+TCP#[hardBreak]2.-Control-the-battery-charge-rate-and-discharge-rate.

This can, somewhat simplified, be translated into six useful modes of operation for your battery storage. These are:

1. Self sufficient mode: the inverter will (based on readings from a meter) balance the charging and discharging of the battery as to minimise transmission to/from the grid based on consumption and PV production. This could be regarded as a default mode,

2. Prevent discharging: the inverter will charge the storage until full and export surplus from PV, but not draw any current from the storage. This is useful during times when the energy prices are low (it is not worth the wear of the battery to use it). Effectively this is a type of idle state, where only surplus energy is used for charging.

3. Prevent charging: the inverter will draw current from the storage to minimise transmission from the grid, but will export any/all surplus generated from PV. This mode is useful when energy prices are high to maximise export of surplus from PV.

4. Charging: the inverter will charge the battery with the specified current (up to what the inverter and battery is capable of), irrespectively of consumption or PV production. This mode is useful when energy prices are low, to charge the battery to a certain SoC for later use of the energy.

5. Discharging: the inverter will discharge the battery with the specified current (up to what the inverter and battery is capable of), irrespectively of consumption or PV production. This mode is useful when energy prices are very high, to maximise export of energy to the grid.

6. Idle: the inverter will neither charge nor discharge the battery, irrespectively of consumption or PV production. This mode is mostly useful for long periods of low energy prices, to minimise wear and depletion of the storage.

I have been trying to sort out from MPC optimisation when to switch between the modes. It is not too hard, but there is a slight room for errors when predictions are off and it feels like much of this is already available from the optimisation model.

It should, I think, be fairly easy to provide an additional column in the data frame to identify mode 4 (charging from the grid to the battery), and mode 5 (when to discharge from the battery to the grid). It would also be useful to know if charging/discharging should be 100% of what the system is capable of or less. This could be expressed as percentage or power of maximal capacity.

Mode 3 (prevent charging) could be selected when the current export price is higher than the import price later. Could be more optimal to export PV production when the sun shines and then charge the battery from the grid later.

When the import energy price falls below "weight_battery_discharge", then mode 2 can be selected. No reason to discharge the battery when it is cheaper to import from the grid.

I think there is no use for the idle mode in the optimisation, so it can be disregarded.

It would have been extremely nice to get these modes out from the optimisation directly, instead of trying to reverse the battery power column into this.

Any thoughts?