Arnaud's Plug-in Battery Adventure:

Gemini+ generated image on Power Transition

In 2026, energy is an issue. Energy Transition, Solar Energy, The end of the Dutch "Salderingsregel", (plug-in) home batteries, etc... All items that can be found in the (Dutch) news on a very regular basis.
We have already been living in an All-Electric house since 2006 and have 22 Solar Panels on our roof, so the end of the salderingsregeling (essentially a very nice solar-energy grant) has quite some impact on our energy bill. But, since the salderingsregeling has served its purpose, I understand completely why they are ending it.
Anyway, we decided to buy Plug-in batteries and this is more or less our starting point:
* Fully electric house (since 2006), Yearly Power Consumption: 12700 kWh
* Heat pump with ground thermal energy storage
* Underfloor heating / cooling
* 5,500 WP of solar panels
* EV (25,000 - 30,000 km per year)
* Air conditioning (purely for extra cooling)

My Plug-in Batteries:

First choice to be made: How much battery storage do I need? Since our plan is to go get as close to net-zero (essentially try to use as little from the power grid as possible) is to have a look at our Power Consumption during the night in the period April - October. This gives us a number of around 10 kWh. People tend to overestimate the capacity they need. For a normal non-full-electric house, usually up to 5 kWh should suffice.
After a few days of reading up I decided on 2 units of Marstek Venus E 3.0, each with a 5.12 kWh capacity. One has its own direct connection to the breaker panel, so it can output 2500 Watt. The other one is sharing a power socket and is limited to 800 Watt.
Total costs? 2345 Euros for the 2 units and a P1 meter. 150 Euros for the electrician to add an extra circuit breaker into the breaker panel. So for 2495 Euros I have added 10.24 kWh of battery storage with a 3300 Watt output.
Maybe a 3rd unit will be added at a later stage. First I will analyze the actual need in the next few months. But even if it is not "needed", I might still do it. Just for the fun of it :)

Home Assistant Integration:

You are a nerd, or you are not. As I like to think I am, so now I of course needed to add these 2 units into my Home Assistant so I could get all kinds of nice stats, graphs, history, etc. But. I am also a lazy nerd and as tech-savvy as I am, I decided to put my Google One subscription to good use and put Gemini to work to create some nice dashboards. First I hooked up both batteries to my network using MODBUS over TCP, which in essence is a serial connection over your internal LAN network.
After this was done, entering a few prompts into Gemini+, with some links to the Home Assistant (HA) plugin on the Web and copy/paste actions from a few HA screens within 20 minutes, I ended up with my first dashboard. With some extra prompts I made a second one for the 2nd battery and a 3rd one that combines the information. That went a lot easier & quicker than anticipated!

Now Let's Compare:

Even though this is just the data from 27 days and the 2nd battery has only been online a bit over 2 weeks, you can already see a nice trend: Our own self-consumption of solar energy has increased from 29% to 65% already. In kWh, this means we have relocated around 250 kWh this month. We normally would have "donated" this to the energy company, but now we have used it ourselves!

Final thoughts:

We will not get rich using these batteries, but thanks to these batteries we will not have to think too much about when we will use what household appliance. We can just use them when we want to without impact on our electricity bill (Although I can't complain with 0.21 Euro/kWh in 2026/2027/2028). It also means we will be "donating" quite a bit less power to the electricity company. Yes, there will be a ROI on these batteries, but making real money on it? I dunno. But I've had quite some fun sorting things out, making the integration, you know: nerd stuff. And that also counts for something :)

Marstek Round Trip Efficiency in Home Assistant