Hello Blue Team
I have a challenge I can’t get to the bottom of for a while: the solar forecast is consistently under-reporting; as a consequence, DESS is targeting a higher SOC level, but because the PV generation power is far higher than what we can export, the energy is being lost. At the design stage we planned on using the battery as a buffer and have the installation constantly exporting 24/7,
Since DESS targets higher SOC, in the morning there’s no “room” in the battery to absorb the energy generated, and by midday (or earlier) the battery is full, shutting down the MPPT’s
At the moment I have to manually intervene to disable DESS and set a negative setpoint to export the energy. (I’m aware of Node-RED but would love to see DESS capable of working out a wider range of scenarios)
Export agreed with DNO is 5kW but at times we can’t achieve that as the voltage rises unpredictably found that 3.6kW works almost all the time, giving us the capability of exporting all the surplus spread across a 24h period
To try and resolve the high grid voltage, we experimented configuring the Multiplus to absorb/export reactive power based on input voltage, but this made the Multiplus unstable, adjustments were made to fine-tune, and then grid conditions would change making it unstable again, so we gave up for now, i suspect the grid impedance is too high, regardless,
our main goal is to have the DESS working autonomously in an efficient way; we tried resetting the forecast a couple of times, but it settles to the same wrong prediction
Installation device list:
- MultiPlus-II 48/5000/70-50 GX
- Grid meter CG ET112
- DIY EVE cells 3 x banks 16S total 940Ah ≈49kWh JK-BMS
- SmartShunt 500A the shunt is used as main SOC for better precision
- MPPT 250/70 8x Longi 620W = 4960Wp PV (south facing 45°tilt)
- MPPT 250/70 8x Longi 620W = 4960Wp PV (south facing 45°tilt) both MPPT’s are on the same table
- AC Solax 3.6kVA 16x Longi 620W = 9920Wp PV (8x east and 8x west 45°tilt) (CG EM111 used to feed the data into the GX device)
- Victron EVCS (not so relevant in this case)
Installation ID: 814839 link
Screenshots
this is what we desire:
Under-reporting of generation is about 25-30%
this is predicted for tomorrow with DESS off (ESS setpoint -3600W)
and this is predicted for tomorrow with DESS on
If anyone has any inputs/comments it would be very much appreciated
Thank you, George