Home energy ecosystem

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.