Home energy ecosystem where your EV, solar PV, and stationary home batteries all play together. Let’s break it down step-by-step with the options that exist today (and the caveats around AC vs DC / V2G).
1. The Components
- Solar PV system (inverter + panels)
- Stationary home battery (e.g. BYD, Tesla Powerwall, Polarium, etc.)
- EV + bidirectional charger (Wallbox Quasar 2, Indra, Nuvve, Fermata, etc. — depending on region/car support)
- Smart energy management system (EMS) (Tibber Pulse, Home Assistant, Easee Equalizer, or vendor-specific EMS)
2. Connection Principles
There are two main topologies:
A) AC-Coupled (most common)
- Solar inverter → house AC bus → home battery + bidirectional EVSE all connected on AC side
- The house sees all sources (grid, PV, batteries, EV) as AC.
- The EMS decides: charge EV from PV, discharge EV to house, or backfeed grid.
- Easier retrofit (you don’t have to replace your solar inverter).
B) DC-Coupled (less common, more efficient)
- Solar panels and stationary battery both connect on the DC bus of a hybrid inverter, then convert once to AC.
- An EV DC bidirectional charger could also sit here — but standards for DC V2H/V2G (CHAdeMO, CCS ISO 15118-20) are still rolling out.
- Higher efficiency (fewer conversions), but more restrictive in terms of equipment choice.
3. Usage Scenarios
- Self-consumption max
→ Daytime solar charges house battery & EV. At night, discharge home battery first (higher cycle life, cheaper to replace), then EV as backup. - Grid services / V2G
→ EV (biggest battery) exports when grid prices are high / demand spikes. Needs a certified V2G charger and utility agreement. - Backup power
→ Stationary battery covers short outages. EV kicks in for longer ones. Requires islanding support (e.g. SMA Sunny Island, Fronius GEN24, Tesla Powerwall Gateway).
4. AC Charging + V2G (what to note)
- EVSE must support bidirectional AC (ISO 15118-20) → still rare; most V2G pilots use CHAdeMO DC (e.g. Nissan Leaf). CCS AC V2G is coming in Europe 2025+.
- Control layer matters most: You want Tibber/EMS or Home Assistant automations to say:
- “Charge EV when PV surplus > 3 kW”
- “Discharge EV to house if spot price > 1 SEK/kWh and house battery < 30%”
- Prioritize cycles: Don’t cycle your EV battery daily if you don’t have to — home batteries are cheaper €/kWh over lifetime. Use the EV for peak shaving / emergency power, not as your primary daily buffer.
5. Best Practices
✅ Size your stationary battery so it covers overnight use most days (~10–20 kWh for a Swedish household with heat pump).
✅ Use dynamic load balancing (e.g. Tibber + Easee/Wallbox Pulsar) to avoid tripping fuses when EV + stove + sauna run together.
✅ If possible, choose an inverter/EMS that supports open protocols (Modbus/TCP, MQTT) → gives you flexibility to integrate EVSE and batteries from different vendors.
✅ Check EV support: Today, only a few (Leaf, some Kia/Hyundai, BYD, MG) allow true V2G. Many promise ISO 15118-20 CCS “soon”, but VW ID.7 for example does not yet support V2L/V2G.