PV Surplus Charging: Charge Your EV with Solar Power and Cut Costs

If you have solar panels and an EV, you should maximize this combination. Most PV systems export excess electricity to the grid at around 7–8 ct/kWh. At the same time, grid electricity costs 20–35 ct/kWh. Every kWh of solar surplus that flows into your EV battery instead of the grid saves you 12–27 ct per kWh.

PV surplus charging (also: solar surplus charging, excess-controlled charging) means: the wallbox charges the EV only as much as the PV system currently produces above household consumption.

A control unit (ioBroker, EVCC, Home Assistant) continuously measures:

• PV production (inverter data point)
• Household consumption (smart meter at the meter point)
• Grid import/export (smart meter)

From this it calculates the available surplus and dynamically controls wallbox charging power — from 0 to 100%.

OCPP or Modbus Wallbox

The wallbox must be dynamically controllable:

• OCPP 1.6J: Industry standard, supported by EVCC and most control units
• Modbus TCP: Direct connection, low latency, supported by go-e, KEBA, and Fronius Wattpilot
• Proprietary API: Some manufacturers (e.g., go-e) offer local HTTP APIs

Smart Meter at the Grid Connection Point

For real-time measurement of grid import/export:

• Austria: Intelligent metering system (iMSys) with M-Bus or customer interface (P1 port)
• Alternative: Energy meter with Modbus (e.g., Eastron SDM630, Shelly Pro 3EM)

Important: Austrian grid smart meters have a mandatory customer interface since 2022. It sends current consumption data every 5 seconds — sufficient for surplus control.

PV Inverter with Data Interface

The inverter must provide real-time production data:

• Fronius: Fronius Solar API (HTTP/JSON)
• SMA: Modbus TCP or SMA Energy Meter
• Huawei: Modbus TCP
• Victron: MQTT via Venus OS

EVCC (Open Source)

EVCC is the most popular open-source tool for PV surplus charging in Austria and Germany. It runs on a Raspberry Pi or NAS, supports over 100 wallbox and inverter models, and has a clean web interface.

Strengths:

• Simple configuration (YAML file)
• Large ecosystem: 100+ supported devices
• Free, active community
• Load management for multiple wallboxes

Limitations:

• Pure charging focus — no automation of other loads
• No integrated dashboard for total household consumption

ioBroker with EnergyOptimizer

ioBroker is a universal home automation platform communicating with virtually any device via adapters. The EnergyOptimizer extends ioBroker with specialized logic for Austrian energy optimization:

Strengths:

• Wallbox surplus charging AND dynamic tariff (awattar/Tibber) combined
• Also controls heat pump, boiler, washing machine based on surplus/tariff price
• Integration with green electricity notifications (market price alerts)
• One dashboard for everything: PV, wallbox, heat pump, battery

Limitations:

• More complex initial setup
• Paid (EnergyOptimizer configuration package)

Setup: 10 kWp PV | 4,000 kWh/year surplus | EV 15,000 km/year | Consumption 18 kWh/100km

With a dynamic tariff (awattar) and smart combination: grid charging only when price < 8 ct/kWh (overnight valley) + PV surplus during the day → effective total cost under 3 ct/kWh.

What minimum power does EV charging require?

Single-phase: at least 1.4 kW (6A × 230V). PV surplus charging only works above ~1.4 kW of surplus. On cloudy days or with small systems this can be limiting. Three-phase: from 4.1 kW.

Tip: Some control units (EVCC, ioBroker) supplement small PV surplus with cheap grid power (hybrid mode) to stay above the minimum threshold.

Do I need a battery storage system?

No — surplus charging works without storage. A battery increases flexibility (charging after sunset) but only pays off if the difference between feed-in and grid prices is large enough.

How precise is the regulation?

With smart meter (5s update interval) and OCPP wallbox: regulation accuracy ±100–300W. With Modbus wallboxes: ±50W possible. In practice: you export at most 300W to the grid, minimal losses.

Does this work in a multi-unit building?

Yes, with limitations. If the PV system is communal (energy community), you need access to the generation data points. Individual apartment meters as smart meters + communal PV via API is technically possible, but requires coordination with building management.

The EnergyOptimizer automatically connects your PV system, smart meter, and wallbox, optimizing charging strategy daily — including dynamic tariff integration. Free initial consultation, no risk.