Heating the buffer tank with SOL•THOR

With the PV system upgrade and expansion (still without an inverter, since it’s DC operation), more power is now available. The perfect match for autonomous DC-powered heating comes, once again, from Upper Austrian manufacturer my-PV. The DC Power Manager SOL•THOR offers a wider control range. In the 400 m² multi-family home, there’s a significant demand for hot water. Two 1,000-liter buffer tanks are installed in series, ensuring hot water availability. Around 500 liters in the upper (hottest) section are always ready for domestic hot water preparation via an external fresh water module. Below that is the heating circuit connection, where the supply temperature also needs to reach high values.

The PV system — eight Trinasolar 450 W modules, totaling 3.6 kWp — feeds the my-PV 3 kW immersion heater installed just below the heating circuit outlet in the buffer tank. The SOL•THOR powers it directly with DC electricity from the sun. Thanks to the adjustable 31°–55° tilt, the PV system also produces notable winter yields in sunny Mühlviertel, keeping the buffer tanks heated.

A new product with implementation hurdles?

The SOL•THOR entered the market in larger quantities with the ramp-up of series production in spring 2025. Implementation of a new product can sometimes be tricky – but my-PV’s DC solution proved straightforward. Shortly after commissioning, a software update triggered an error message, but after a brief moment of concern, the homeowner now reports that the SOL•THOR operates flawlessly. The 3 kW immersion heater can be continuously modulated by the SOL•THOR based on PV yield, turning every watt into heat.

Multi-family house with high water demand

Three adults live in the renovated (2014) 400 m² multi-family home. Total water consumption (not just hot water) is 116 m³ per year. No grid electricity is used for hot water backup — a feature that SOL•THOR offers for cases where no primary heating system exists. Here in Unterweißenbach, a pellet boiler is available for days with insufficient PV yield. However, since starting SOL•THOR operation in January 2025, PV electricity has been sufficient for hot water production.
“I can go at least six months a year without using my pellet boiler. That saves me a lot — for the nearly 2,000 kWh that the SOL•THOR provided between late January and late July, I saved €120!” says owner Peter Brandstötter.

Advantages of autonomous PV heating

For this innovative Mühlviertel resident, autonomous PV heating offers multiple benefits: operating costs are reduced, as PV electricity directly heats the heating water, replacing pellet consumption. Additionally, because the system operates entirely off-grid (without inverter or grid connection), there’s no need for permits, taxes, or bureaucratic procedures for the heating system installation.

The setup consists simply of module mounts, the PV modules, cables to the SOL•THOR, and a cable from the SOL•THOR to the immersion heater — a very manageable expense and minimal complexity for retrofitting or installation.
“The simplicity of the setup impresses me every time. And I think far too few people around me know about the easy implementation and many benefits,” says the convinced homeowner.

Plans for future expansion?

During the installation, a second my-PV 9 kW immersion heater was installed in the second buffer tank (not yet in operation). “In the future, I’d like to add a grid-connected PV system where an AC•THOR 9s uses surplus electricity for heating. Of course, priority will go to household electrical consumption, but the surplus will go toward heating support,” says Brandstötter, already envisioning further PV heating expansion.

Customer Insights on SOL•THOR: Watch the Video (in German)

We visited this innovative my-PV customer at home to explore our first SOL•THOR reference installation up close. Watch the video for an inside look at the project and hear the owner’s personal insights and experiences.