Arnaud's Plug-in Battery Adventure - Part II:

Last month I published a blog post about our first steps with a home battery. Since July was the first full month with our battery system, I thought it would be a nice idea to compare May & July to see what the actual impact is.
Since July 1st also meant a new energy contract, I now have to pay for my unused solar energy which flows back to the energy grid. This results in a change in behaviour: instead of charging my EV after 21:00 (off-peak tariff), I now charge my car with solar power as much as I can. These are two changes with a significant impact on our energy usage, as the stats below confirm.

Additional tariff details:
New peak tariff: €0.20/kWh
Off-peak tariff: €0.21/kWh
Net solar tariff: €0.05/kWh (This will become €0.01/kWh starting 01-01-2027)

And yes, you are seeing this correctly: my peak tariff is actually lower compared to the off-peak tariff, as Greenchoice (my energy supplier) wants to encourage energy use when the sun shines.

And now the stats:

As you can see, there has been a huge jump in self-consumed solar energy: from 33% to 80%. Both the battery system and charging the EV directly with solar power are responsible for this. This means we are using far more of our own generated energy, which greatly helps the energy transition.
The data under "battery" is about 30 kWh too low due to a statistics reset when I updated the Marsteks with new firmware and performed a factory reset. Starting next week, I will monitor both units externally so I am no longer dependent on their internal logging. Anyway, I have moved about 240 kWh of solar energy (which required consuming almost 300 kWh of solar energy).

Costs: 300 * €0.05 = €15.00
Revenue: 240 * €0.21 = €50.40
Profit -> €35.40

In 2027, the profit will come even closer to a full €50, as the value of the solar energy I return to the grid will drop to just over €0.01.

Will this make us rich? No... But it gives us more freedom to use our own energy when we want to. And if you are careful with how much you spend on your battery system (we spent under €2,500 for 10 kWh), you will be able to get a return on your investment in about 6 to 7 years.

Final thoughts:

Not such a long story this time. With only one full month of working with the batteries, I can say I am quite happy with the results, but I am even more curious about the stats after a full year. Keep your eyes on this blog!