DIY: Custom Solar EV Charging
05/09/2026 · 6 min
I connected the original portable charger of my electric car to Home Assistant, so charging could respond to the electricity my solar panels had available. The project combines local automation with a simple idea: use the equipment I already owned.
Solar electricity leaving the house
My rooftop installation has roughly 3.5 kWp of solar capacity. On sunny afternoons, generation often exceeded household consumption, and the surplus went back to the grid without compensation in my setup.
I considered a home battery, but the upfront investment and expected payback did not make sense for my consumption. Selling the surplus also wasn't attractive to me.
Meanwhile, my electric car already had a 64 kWh battery. I could use more of that solar energy by changing when I charged the car. This is ordinary AC charging: the vehicle does not supply electricity back to the house.
Making my existing charger solar-aware
I wanted automatic charging based on available surplus, while keeping my inverter and the original portable charger. Home Assistant would make the decisions locally and provide manual control from the same dashboard I use for the house.
At my chosen 12 A setting, the charger draws approximately 2.76 kW at 230 V. The challenge was identifying sustained surplus large enough to support that load without constantly switching as clouds passed.
Commercial chargers were a credible alternative. V2C Trydan even integrates directly with Shelly meters. I chose DIY to reuse my hardware and keep the automation in Home Assistant.
Measure, decide, switch
I separated the system into three responsibilities:
| Responsibility | Component | Role |
|---|---|---|
| Measure | Shelly EM | Measures net grid import and export |
| Decide | Home Assistant on Raspberry Pi 4, in Docker | Evaluates the charging conditions |
| Switch | Shelly Plus relay and Schneider contactor | Enables or disables the charger's supply |
The Shelly relay controls the contactor coil; the contactor carries the charging load. The charger connects through a Legrand Green'up socket with dedicated protection.
The Green'up 090470 kit is intended for EV charging. Electrical installation and protection must follow the manufacturers' instructions and applicable local requirements.
Measure what's available, not just what's generated
If the panels generate 3.2 kW and household appliances consume 800 W, only 2.4 kW remains. Starting a 2.76 kW load would then draw approximately 360 W from the grid.
Measuring net grid exchange accounts for the house's consumption automatically.
Starting the charger also changes that reading. With 3 kW of export before charging, switching on the car leaves approximately 240 W of export. That is the intended result: the surplus is now being consumed.
Give the controller time to react
Different start and stop thresholds, time windows, and a cooldown prevent unnecessary switching. These example settings explain the policy:
| Decision | Example condition |
|---|---|
| Start | Export above 2.9 kW for five minutes |
| Stop | Import above 300 W for two minutes |
| Restart | Wait ten minutes after stopping |
The policy tolerates brief imports rather than reacting to every cloud. It maximises surplus use without promising zero grid consumption.
The software setup follows four steps: integrate the Shelly devices locally; verify measurement units and import/export direction; configure the solar-mode toggle and timed rules; expose readings and control on the dashboard. Automation should also handle stale measurements and re-evaluate after startup or cooldown expiry.
Access from my phone
Home Assistant's iOS and Android apps connect to the server running at home. Cloudflare Tunnel provides an HTTPS route for access while away, without opening an inbound router port.
The tunnel provides remote access; charging decisions remain local. Authentication is still required.
An existing charger, integrated into my home
The finished system makes charging respond to solar surplus instead of relying on a fixed schedule or manual switching. I reused the inverter, the original charger, and the Raspberry Pi, while bringing charging into my existing home-automation setup.
The trade-off is clear: my controller switches a fixed 12 A load on or off. Compatible commercial chargers can adjust charging current to follow smaller changes in available power.
What it costs compared with a smart wallbox
An indicative reproduction budget is around €300–€450 for the meter, relay, contactor, Green'up socket/protection kit, and installation materials, reusing the Raspberry Pi and the original charger. This is a parts estimate, not my invoices or an installed quotation.
| Option | Indicative equipment cost |
|---|---|
| My setup, reusing the Pi and the original charger | €300–€450 estimated |
| V2C Trydan 7.4 kW, advertised package with protections | €680 |
| Wallbox Pulsar Plus 7.4 kW | €699 |
| Wallbox Pulsar Plus with a separately purchased meter | About €832 |
Prices checked: V2C Trydan · Wallbox Pulsar Plus · Wallbox meter · Green'up 090470 kit
Retail prices checked on 6 September 2026. Confirm package contents, meter compatibility, shipping and destination VAT; labour and site-specific electrical work are additional.
For my situation, reusing equipment put the estimated parts budget roughly €230–€380 below the listed V2C package and €380–€530 below the Wallbox-and-meter combination. These are equipment-budget differences, not measured electricity savings.
The result is a practical fit for my home: more control over when I use my solar energy, without replacing a working charger. An integrated wallbox offers finer charging control; this project solved my immediate need with a smaller hardware investment.
Technical references
Legrand Green'up 090470 kit · V2C with a Shelly meter · Home Assistant automation triggers · Cloudflare Tunnel