PV Surplus Charging: Charging Your EV with Solar Power - Here's How
Summary (TL;DR)
With PV surplus charging, your EV is automatically charged with solar power not currently being consumed in the household. Instead of feeding the surplus for 5-10 ct/kWh, you use it yourself and save 20-25 ct/kWh. Prerequisites: A PV-capable wallbox (from €700) and at least 1.4 kW surplus. With phase switching, it works from this minimum power; without it, you need 4.2 kW.
What is PV Surplus Charging?
With PV surplus charging, solar power not currently being consumed in the household is charged directly into your electric vehicle. Instead of feeding the surplus into the grid for only 5-10 cents/kWh, you use it yourself - and save the full purchase price of 20-25 cents/kWh.
The Economic Advantage
| Scenario | Compensation/Costs | At 2,000 kWh/year |
|---|---|---|
| Feed surplus | +8 ct/kWh (OeMAG) | +€160 |
| Use surplus yourself | -22 ct/kWh saved | -€440 savings |
| Difference | €280 more in pocket |
Technical Requirements
Understanding Minimum Power
EVs have a minimum charging power - they don't charge arbitrarily slowly. Most vehicles require at least 6 amps per phase, which corresponds to:
- Single-phase: 1.4 kW minimum power
- Three-phase: 4.2 kW minimum power (3 x 1.4 kW)
Without special technology, charging only starts from 4.2 kW surplus. On cloudy days or with smaller PV systems, this value is often not reached.
The Solution: Phase Switching
Modern PV-capable wallboxes can automatically switch between single and three-phase charging. With low surplus, they charge single-phase (from 1.4 kW); with lots of sun, three-phase (up to 11 kW). This way you use every available surplus even on cloudy days.
Suitable Wallboxes for PV Surplus Charging
| Wallbox | Phase Switching | Price | Special Feature |
|---|---|---|---|
| Fronius Wattpilot | Yes (automatic) | €700-900 | Integrated aWATTar connection |
| myenergi zappi | Yes (automatic) | €900-1,100 | Own CT clamps, no ext. system needed |
| go-e Charger + Controller | Yes (with Controller) | €800-1,000 | Very good app, Austrian manufacturer |
| openWB | Yes (automatic) | €1,200-1,800 | Open source, maximum flexibility |
| KEBA KeContact P30 | No | €800-1,000 | Only with ext. energy manager |
Setup Step by Step
- Have PV-capable wallbox installed (electrician)
- Set up energy measurement: CT clamps at house connection or smart meter connection
- Connect wallbox with inverter/energy manager (Modbus, SunSpec, API)
- Activate surplus charging in the app
- Define minimum charge level (e.g., 'Always charge at least 20%')
- Optional: Combine with dynamic tariff for night charging
Typical Yields in Austria
A 10 kWp PV system in Austria produces about 10,000 kWh/year. Of this, you can realistically use 2,000-3,000 kWh for the EV - depending on your driving profile and when the car is at home.
| PV System Size | Surplus for EV | Savings/Year |
|---|---|---|
| 5 kWp | 1,000-1,500 kWh | €200-300 |
| 10 kWp | 2,000-3,000 kWh | €400-600 |
| 15 kWp | 3,000-4,500 kWh | €600-900 |
Combining with Dynamic Electricity Tariff
The optimal strategy combines PV surplus charging with a dynamic electricity tariff: During the day you charge with solar power, at night with cheap spot market electricity. This way you achieve the lowest total costs.
Frequently Asked Questions About PV Surplus Charging
FAQ
Does PV surplus charging work without battery storage?
What happens on cloudy days?
Can I still guarantee a minimum charge level?
Conclusion: PV Surplus Charging Maximizes Your Savings
With PV surplus charging, you use your solar power optimally and drive practically for free. The investment in a PV-capable wallbox pays off quickly through higher self-consumption. Combined with a dynamic tariff for the night, you have the perfect charging strategy.
About the Author
Christian Werner is an IT consultant and founder of Werner.Solutions in Graz, Austria. He helps Austrian households and SMEs optimise their energy costs through dynamic electricity tariffs and smart automation — combining IT expertise with practical energy consulting.
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