Articles on Jasper Grahl

Running a Raspberry Pi 24/7: what a short power cut revealed about my system

Tue, 10 Nov 2026 21:00:00 +0100

My energy management system JG Energy runs around the clock on a Raspberry Pi 5 with an SSD. It controls the wallbox, the home battery and charge plans for two EVs. If the Pi fails, you notice in everyday life – at the latest when the car isn’t charged in the morning.

In early November there was a short power cut one morning. The Pi restarted on its own afterwards, and everything kept running. Still, the incident exposed four weak spots I hadn’t known about.

Controlling a Marstek Venus E locally: Modbus TCP, the UDP API and why you should verify every write

Tue, 10 Nov 2026 20:30:00 +0100

The Marstek Venus E is an affordable plug-in home battery with 5.12 kWh. It regulates itself: a smart meter at the grid connection – a Shelly Pro 3EM in my case – tells it whether power is currently being imported or exported. The battery then charges or discharges so that the meter reads as close to zero as possible.

That works well as long as the battery is the only “smart” consumer. As soon as a wallbox enters the picture, things get complicated. So my energy management system JG Energy steps into the control loop locally – not with its own power control, but with two simple limits.

Is a second home battery worth it? A simulation with eight months of minute data

Tue, 10 Nov 2026 20:00:00 +0100

My home battery – a Marstek Venus E with 5.12 kWh – is full by midday on sunny days. After that, the surplus goes to the grid for a few cents. The obvious idea: a second battery of the same kind. Cost: around €850, including the additional smart meter it needs.

Before spending the money, I wanted to know for sure. My energy management system JG Energy stores a daily log with one value per minute: grid import or export, PV power, battery and wallbox. That’s enough to simulate a second battery quite realistically.

Growatt Thor with your own OCPP server: solar surplus charging, a 0 A lock and the firmware's pitfalls

Tue, 10 Nov 2026 19:30:00 +0100

The Growatt Thor is a solid 11 kW wallbox with a built-in solar mode. That mode wasn’t enough for me, though: it kept dropping charging sessions with SuspendedEVSE, and it knew nothing about my home battery or the exact readings of my grid meter. So since early 2026 my energy management system JG Energy controls the box entirely on its own – through a self-written OCPP server on a Raspberry Pi.

Hyundai Bluelink blocked (error 9035)? Getting your EV's state of charge from the official Pleos API

Tue, 10 Nov 2026 19:00:00 +0100

If you have your Hyundai, Kia or Genesis connected to Home Assistant, evcc or a script of your own, you have probably seen this since mid-October 2026: error 9035. From one day to the next, no state of charge came through. For me a whole system depended on it – my energy management JG Energy needs the Ioniq 5’s state of charge to run surplus charging and charge plans.

Here’s what happened, how I solved it with the official Pleos Vehicle Data API, and what to watch out for.