So what happens? If I set “Maximum charge power” in my case to 7.5kW the DESS system assumes a full charge duration of 2 hours for a 15kWh battery, if enough solar power is available. At first sight this seems to be correct, but it is not: Since the battery in reality charges much slower, the calculated SOC is never reached, leading the system to use “Strategy 0: Follow the target SOC” (see here) and pull energy from the grid, which is not desired in green mode.
For the end user more intuitiv might be: “average charge power” or “sustained charge power” which both will be significant lower than “Maximum charge power”.
In my example setting “Maximum charge power” to 3.3kW or even lower leads to a almost perfect alligned DESS SOC forecast and prevents pulling energy from the grid at high solar rates, since the forcasted SOC is much lower.
Proposal:
change in VRM → settings → DESS → battery → “Maximum charge power”
to either “average charge power” or “sustained charge power” and update your documentation.
This might also concern “Maximum discharge power” depending on the internal calculation which I’am not aware of.
the naming “Maximum Charge Rate” is correctly, because it describes the maximum that will be assumed for the targetSoc schedule. (That doesn’t necessarily mean that VRM will assume that rate for EVERY charge happening. If solar expectation is 2000W, it will consider only a charge of 2000W during a certain window)
The maximum rate has mostly a meaning, when it comes down to charging from grid during night.
During the day, a “strict charge rate” is very rarely enforced. Usually the system works in a way to charge whatever solar is available. However, if the schedule decides that reaching 45% by noon is a mandatory goal to be able to have a “greenish schedule” for the rest of the day, it may use a fixed rate (not necessarily the maximum possible) and accept that missing energy is pulled from grid.
this for example may happen, if grid prices are lower in the morning than at the evening, but solar wont be enough to reach the 45% soc required to cover all loads for the rest of the day.
You could set a time based “grid2bat” restriction in VRM, saying “I only want solar charging during the day, so from 6-16, restrict grid2bat, please!”
But keep in mind that this may cause unreached target soc levels. So, for the example above:
You then may end up with only 35% soc at noon, causing your system to run into battery minimum early at the evening and then HAVING to pull from grid at maybe higher rates.
