EV charging and DESS: viable strategies?

Q&A and troubleshooting
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I’m new to Victron and I’m struggling to find a good strategy for charging my EV in combination with DESS.

Before I had a home battery system, I maximally charged when I had solar surplus. If that wasn’t enough, I manually set a target soc for the car to additionally charge from the grid.

I can potentially keep charging on solar surplus and set up some scripts to do the extra charging during cheap hours, but that would be suboptimal for DESS which heavily relies on correctly predicting load patterns and this strategy is very unpredictable.

What I settled on for now is:

  • setting a fixed charging window between midnight and 4 AM at a slow speed (capacity tariff in Belgium). This helps with predictability.
  • increase the minimal SOC from 20 to 30% at midnight and lower it again at 5 AM to be sure to get through the expensive morning peak without grid consumption.
  • use DESS green mode and disable battery to grid. At least in the dark months, it doesn’t make sense for me to sell to grid from battery since I can’t fill my battery using PV in a single day and buying back the sold energy will almost always be more expensive.

While this helps with DESS predictability, there’s an inefficiency in the system: if my car is on the driveway, I’m charging my home battery to move that energy to the car at night. I’m not sure if the improved DESS predictability is worth this inefficiency.

What strategies are other people using? Is there a recommended way to do this?

Context:

  • new 20kWh battery with a single MultiPlus-II 5000
  • 5kW existing PV inverters
  • heating with heat pump
  • car charges 200-300kWh/month
  • dynamic energy tariff
  • in Belgium, so a big gap between buy and sell price due to high tariffs and additional taxes based on highest peak load of the month
  • I’m an IT-professional and am using Home Assistant
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There is EVCC.io which greatly extends the capabilities of a Victron charging station (planned charges and such). Although your consumption forecast will still get poisoned by the irregular consumption.

The problems you are describing are widely voiced on the forum. There is a DESS node red implementation that would allow you to steer the behavior of the battery, but it will be phased out. I have found a custom integration by ikke050, but I have not used it. My wish for a more flexible system pushed me to develop my own DESS. But that is still far from finished. I wish I could give a better answer, but the current state of DESS just does not allow you to bring your own consumption forecasts.

EDIT: I also found that Victron is using different models for ev forecasting

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Thank you for pointing me towards EVCC. This gave me some inspiration of what I could build myself in Home Assistant :slight_smile: Too bad EVCC isn’t compatible with DESS: it sets the min soc to 100% to force charging which then gets picked up by the DESS planner which in turn want to keep your battery at 100% for hours after EVCC stopped charging.

I’ll also look into the different model for EV forecasting. It would be nice if I could add my shelly wallbox measurements to the Victron system.

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I do not know exactly what you are talking about? But EVCC does not control my battery, that is handled by DESS it only does charge planning. DESS works fine parallel to EVCC, except for the grid limits when both systems want to charge. But that said a home assistant automation could work even better.

About the EV forecasting model: That’s is why EVCC is so nice, it turns the need for a forecast into a predictable and deterministic planning. But some smarts in home assistant can also get you there. So do what fits your needs best.

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Recent versions of EVCC also have the possibility to add your home battery and force charge the battery if prices are low. For example, I used this yesterday when I saw that the predicted load in DESS was too low for the cooking session I had planned and to avoid using the grid during expensive hours.