Hi everyone,
I’d like to share some insights and observations regarding DESS mode optimization, particularly relevant for those of us in Ukraine navigating the complexities of grid feed-in limitations, battery SOC management, and the need for grid resilience. Many of us are grappling with the trade-offs between “Green” and “Trade” modes, and how to effectively manage battery discharge to maximize solar utilization.
Our specific challenges include:
- Green Mode Limitations: While Green mode prioritizes higher battery SOC, it often leads to PV throttling when the battery reaches 100% SOC and grid feed-in is limited.
- Trade Mode Drawbacks: Trade mode maximizes grid feed-in but can deplete the battery too quickly, even during off-peak hours.
- Time-of-Use Tariffs: Day/night tariffs offer opportunities for strategic battery charging, especially during winter months.
- Grid Outage Risk: The ongoing threat of grid outages due to russian attacks on energy infrastructure necessitates maintaining a higher battery SOC, particularly in the mornings.
My test setup comprises:
- 23.09 kW of PV solar arrays (facade and roof mounted)
- 6 kW grid feed-in limit
- Two Multi RS inverters (combined ~11 kW grid/load capacity)
- 58.5 kWh battery bank
- Daily consumption ranging from 30-60 kWh (28 kWh in summer, 64 kWh in winter)
Through VRM data analysis, I’ve found that a hybrid approach works best:
- Cloudy Days/Winter: Green DESS mode combined with scheduled “Keep charged” mode at night is ideal. DESS alone is often too slow to adequately charge the battery overnight for morning readiness.
- Sunny Days (including Winter): Trade DESS mode is preferable, but only when coupled with a dynamically adjusted
batteryDischargeRestrictionSchedule
. This schedule should allow battery discharge (restrict: false
) during daylight hours and restrict it (restrict: true
) at other times. This prevents premature battery depletion before the cheaper night tariff kicks in and allows Trade mode to effectively spread grid feed-in across unrestricted hours, minimizing PV throttling at 100% SOC.
A significant issue is that the batteryDischargeRestrictionSchedule
doesn’t automatically follow sunrise/sunset times, requiring manual VRM adjustments.
To automate this process, I’ve developed Node-RED flows:
- Dynamic Battery Discharge Schedule: This flow calculates sunrise/sunset and sets the
batteryDischargeRestrictionSchedule
accordingly. https://flows.nodered.org/flow/d898c109109db493d6c271e25ffdafc0 - Night Pre-charge: This flow switches the Multi RS to “Keep Charged” mode during off-peak hours to ensure a high SOC in the morning. https://flows.nodered.org/flow/e6db15a0f410e891b9f3588620091674
I welcome your feedback, suggestions, and questions. Let’s discuss how we can further optimize DESS performance in these challenging conditions.