Hello @Lpopescu and Victron team!
Half a year ago I started to using DESS, because of spot prices - previously I used simple ESS in combination with EVCS supplemented by some extra features in Node-RED. For about three months I am running DESS in trade mode (instead of green mode) with battery to grid restriction activated.
I made some conclusions based on half a year experiences with EVCS and DESS. Please take this as an unbiased opinion based on experience, whether some improvements could be made.
1. EVCS and overload protection
When I switched to DESS I must decrease input current limit setting in Multis to 25 A (3 phase system with Multis 48/3000/35-32) and activate overload protection in EVCS, because if DESS charging the battery from the grid this can leads (in combination with manual/scheduled EV charging and house consumption) to overloading main circuit breaker. For EV charging I am using max. 16 A and in case of manual/scheduled charging everytime 3p charging. I also had feature in Node-RED to set min. battery SOC to nearest lower multiple of 5 of the actual battery SOC for blocking EV charging from battery instead of grid.
But with overload protection activated I was struggling with fake activations of protection when EV was charged partially from the battery and partially from the grid until new min. SOC value was reached. So I changed function in Node-RED for set nearest higher multiple of 5 of the actual battery SOC with 100 % as max. limit. After that the behavior of the system is better, but sometimes protection is still fake activated, usually a while after manual/scheduled charging starts, even if house consumption is on “idle” (approx. 400 W). There is usually no problem after second or third attempt to start charging…
2. EVCS in auto mode with DESS
Auto mode is absolutely not usable if DESS is active. When there is no feed-in to grid, EVCS waits for sun basically for infinite time, even if low excess power setting is active. It’s expected behavior, but it’s nothing that can’t be addressed.
When I deactivate DESS for a while for start feed-in to grid and also start charging and then activate DESS again, another bad behavior is then observed - EVCS stucks at minimal charging current (6 A in my case) without attempting to increase the charging current. Also this situation often leads to charging EVCS from grid while battery is charging from MPPTs, so EVCS is charged in auto mode from the grid without time limit based on EVCS setting, because the battery is being charged and time counter is not activated. I think that better solution was implemented in previous SW versions, where min. SOC for start charging in auto mode was also min. SOC for stop charging.
3. DESS (and EVCS) and negative grid prices
This is something, which is intended to DESS rather than EVCS, but in case of charging EV battery with higher capacity than the house battery, it makes more sense and importance.
I think, that behavior of trade mode in case of negative prices is not correct, because if price became negative, the goal should be cover consumption and also charge the battery from grid, not from PV (I can imagine this in Green mode, but not in Trade mode). DESS should use as much energy as possible from the grid and automatically limit power from MPPTs (if the consumption is over the set input current limit, PV could be for example also used to charge the batteries).
I am using DESS in trade mode, because I want to feed-in PV energy directly to grid in case of higher positive price (especially in the morning) and after that when price drops use PV to charge the batteries. Second benefit should be to use as much energy from grid as possible in case of negative price to get better final energy bill (obviously :–) ), to help stabilize the grid (when there is a lot of excess energy) and to not use PV (extend the life of solar panels and MPPTs).
4. (Not) charging EV from house battery and during grid lost in manual/scheduled mode
It will be great to implement feature for possible blocking of using house battery for EV charging, because charging EV battery with higher capacity from house battery (usually with lower capacity) due to energy losses is totally inefficient.
Also will be great to add feature for stop charging in manual/scheduled mode in case of grid lost situation for prevent overloading of Multis.
I have both features made in Node-RED, but for any other people who are not familiar with programming, this would be very useful features.
