question

Why would you need power assist in self-consumption? By default all loads will come from battery until the inverter runs out of grunt and needs to supplement with grid. It is somewhat the opposite use case.

Power assist is for cases where you want to power loads from mains and have the inverter cover the shortfall.

ESS will go to grid when minimum SOC is reached as it is about preserving the battery charge, discharge is blocked so the inverter can't supplement the supply as it would further lower the SOC which is not desirable. Charging is also prevented until solar is available or the SOC drops below minimums (grid failure). ESS is about efficiency and minimising grid usage, allowing a battery to continuously charge/discharge at minimum SOC would invalidate that purpose.

Rather set a much lower minimum SOC, or look at limiting the inverter power in ESS.

Using power assist allows me to replace two grid connections with a single connection as the only reason I had two connections was to accommodate occasional spikes in demand. The need for power assist is brief and will not significantly deplete the battery. ESS does everything I need, except it prevents power assist from allowing me to combine two grid connections into one.

In the broader South African context Eskom have indicated that they intend changing the tariff structure to include a significant grid connection fee based on connection size. Many existing systems using ESS to optimize self consumption will then also be looking to reduce connections size via power assist.

I experimented setting the current limit lower once the minimum SOC had been reached, but the system continued to draw everything it needed from the grid.

Via the tab on the dashboard that takes me to “controls, then I scroll down to “grid current limit”

ESS ignores the grid limit at any SOC, unless I choose “keep battery charged”. My battery is too small to support all the loads all night so it always reaches the set minimum SOC. It is a three phase system supplying unbalanced loads so most of the time peak shaving on one phase can be achieved via the DC bus without even drawing from the battery. My ideal system would be ESS that allows peak shaving at the set minimum SOC (65% in my case).