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This small box supposedly optimises solar power usage

18/5/2024

Translation: Megan Cornish

Thanks to an app, I now know that our household uses a good third of the solar power from the PV system on our roof. More would be better. A small grey box will apparently help with this.

This is part 2 of a series of articles on how photovoltaics and smart controls can reduce your electricity usage at home. You can find the other articles in the series below.

With solar modules on the roof of our house, we generate about as much electricity per year as we use. The only problem is that it’s not always when we need it. If the sun shines for days on end in May, intelligent controls initially direct the electricity we generate to charge the battery of our electric car. If that battery’s full, the only option is to sell power to the local electricity company – at a ridiculously low price. The electricity providers are usually stingy.

Isn’t there a way to increase how much energy we use from our photovoltaic system? In 2022 it was 37 per cent, and in 2023 it was at least 40 per cent. But I want more. Someone who must know how I could do this is Hans Fischer. He’s one of the minds behind the Solar Manager, a black box that’s placed in the power distribution box, measuring – and most importantly – controlling the flow of electricity. This is done via sophisticated software. As the Solar Manager is compatible with wallboxes, solar inverters, battery storage, heat pumps and many other devices (here’s an overview in German), you can use the device and its controls without being dependent on software solutions from a device manufacturer.

Where is there still potential?

In my house, the Solar Manager has so far «only» been controlling the inverter and the Easee wallbox. I don’t have a power storage unit (yet). All in all, it’s a pretty simple system. If electricity comes from the roof, we use it in the house. If you need more than what you generate, you’ll also buy it from an external source. If the sun produces more electricity than we need in the house and the electric car is connected to the wallbox, it gets the excess electricity.

This is what the electricity flow looks like on a cloudy, rainy morning when the electric car’s charging.
Source: Martin Jungfer

Using two Mystrom plugs, I found out how much electricity other devices in the house use, for example the office Mac. Mystrom plugs can be connected to the Solar Manager. So, I could activate a rule that only lets the Mac run when there’s enough sun. My boss would almost certainly not think it was cool if I missed a team call because of cloudy skies. So, there’s little potential here to optimise how we use our own power.

In any case – as Hans Fischer knows – heat pumps and boilers are devices that require a lot of electricity. Although both of ours are just six years old, they’re «dumb». They have no interface to communicate with other devices.

This is where the Internet Service Gateway (ISG) comes into play. A grey box – only as big as a box of chocolates – turns the dumb heat pump into a smart one.

Stiebel Eltron Internet Service Gateway ISG web

Ventilation technology

EUR828,15

Stiebel Eltron Internet Service Gateway ISG web

A Stiebel Eltron technician installs it in the basement, connects it to the internet and installs a Shelly switch for measurement, ensuring that the Solar Manager can recognise and control the heat pump.

A Shelly Pro 3 EM measures the energy flows and can optimise them working alongside the Solar Manager. (And yes, the electrician installed it upside down. Because it’s a bit tight in the control cabinet, that was the only way it would work.)
Source: Martin Jungfer

After a few months, Hans Fischer paid me a visit to assess the situation in situ – and takes a look at the data that the Solar Manager is constantly collecting. The new ISG hasn’t been in operation long enough to see whether and how much it will save me on electricity costs. Hans explains that the comparative data from the previous year is only of limited use. Solar output is not a fixed value, nor is usage in the house. The data can quickly differ, for example if a month had a few more sunny days than the previous year. Or when the electric car has been fully charged for a weekend trip.

Data analysis: Hans Fischer can see in the curves for electricity production, electricity usage and water temperature in the boiler that everything’s going as planned.
Source: Martin Jungfer

Nevertheless, the ISG is already having an impact. It makes it possible to heat the water in the boiler to the desired temperature when the sun is shining. In addition, slightly warmer water runs through the underfloor heating pipes when the sun supplies electricity. The water retains heat, meaning less electricity is needed at night.

This graphic shows 1 May: the yellow area represents solar power production, while blue shows electricity usage. The red line shows the water temperature in the boiler. The yellow line shows the electricity that was charged into the electric car via the wallbox. For example, here you can see that the Solar Manager settings ensure optimal use of the electricity generated. On 1 May, I was able to use over 80 per cent of the solar-produced electricity myself.
Source: Solar Manager

Small-scale optimisation is also possible

In the first few months, the ISG – which turns the heat pump into an «intelligent» consumer – hasn’t yet proven that it’s worth the money. To get a fair picture, I’ll give it a few more months until fluctuations in sunshine duration and our consumption average out.

Until then, I’ll optimise on a small scale. The dehumidifier in the basement is now controlled by the Solar Manager, and the e-bike battery charges when the sun shines. Every kilowatt-hour counts. And I also enjoy tracking the values on the Solar Manager app and optimising how we use our own energy.

If you missed the first instalment in this series, here’s my article on the basic principle behind the Solar Manager and my experiences with it.

Header image: Martin Jungfer

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Martin Jungfer

Head of Content

Martin.Jungfer@digitecgalaxus.ch

Journalist since 1997. Stopovers in Franconia (or the Franken region), Lake Constance, Obwalden, Nidwalden and Zurich. Father since 2014. Expert in editorial organisation and motivation. Focus on sustainability, home office tools, beautiful things for the home, creative toys and sports equipment.

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