Roof renovation as the starting point for 22 SOL•THOR units
Dairy company opts for off-grid heat supply using PV energy
A commercial building in Regensburg took advantage of a roof renovation to install a photovoltaic system.
Facts about the project
- Owner
- Contractors involved
- Location
- Photovoltaic capacity
- Thermal storage capacity
- Building type
- Year of construction and floor area
- my-PV product used
- Other heat generator
- Special feature
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A commercial building in Regensburg took advantage of a roof renovation to install a photovoltaic system. However, instead of feeding the solar power generated into the public grid, the dairy uses the PV electricity independently of the grid and directly on site for its own heat supply.
This is a commercial building owned by Bayernland eG, a cooperatively organised dairy group headquartered in Nuremberg. Each year, the company processes more than 900 million kilograms of GMO-free milk and organic milk into high-quality dairy and cheese products. Founded in 1930, the company is one of the leading marketers of dairy products in Germany and abroad.
Personal customer opinion and resumee
"The system has been in regular operation since it was commissioned at the end of April 2026. Our experience so far has been positive; the 22 SOL•THOR units are operating reliably and without faults," says Stephan Schmid, Head of the Electrical Department in Regensburg, pleased with the results.
Turning an obligation into an opportunity
When the roof of the commercial building in Regensburg needed renovation, this also triggered the legal obligation to install a photovoltaic system. This requirement became the starting point for a well-conceived and economically compelling overall solution.
Why not a grid-connected PV system?
The obvious option of a conventional grid-connected PV system was quickly ruled out: the existing transformer would have required extensive and costly modification to feed electricity into the public grid. Instead, the idea emerged to use all of the PV energy entirely off-grid and feed it directly into the company's own heating network.
The heating network at the heart of the system
The central element of the system is the heating network at the commercial building, which is supplied by a combined heat and power (CHP) unit rated at 600 kW electrical and 1,300 kW thermal as the base-load generator. An additional 22 units of my-PV's off-grid DC power manager, the SOL•THOR, now feed into this network, with a total PV capacity of 78.8 kWp. The solar energy used is converted directly into heat by the DC power managers without a single inverter - with continuously variable control according to the yield from the assigned photovoltaic modules.
This means the solar power is used directly for heat generation without being fed into the grid, eliminating the need for the costly transformer conversion entirely. All of the solar energy remains within the plant and reduces the load on the CHP unit throughout the year.
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Buffer storage tanks and temperature levels
The off-grid PV heat is generated from the PV yield, which each of the 22 SOL•THOR units converts into heat via its assigned heating element. Each of the 22 DC power managers is assigned 880 modules. With a maximum heating output of 3.6 kW, the SOL•THOR can therefore support heat generation. The heating elements are integrated into three 1,000-litre buffer storage tanks, where they use PV electricity to heat the water. The solar modules heat the storage water to as much as 90 °C - well above the heating network flow temperature of 65 °C. As a result, the elevated storage temperature allows the system to continue benefiting from the solar yield even on days with insufficient solar irradiation.
This temperature differential enables particularly efficient energy storage: the amount of heat retained in the tanks is sufficient to supply the heating network reliably even when solar irradiation varies.
Professional installation by regional contractors
The project was implemented by two experienced regional specialist contractors, who carried out the work neatly and in compliance with the applicable standards.
The electrical contractor Wolfseher & Schmid was responsible for all electrical installation work - from routing the PV system cabling and integrating the 22 SOL•THOR units to connecting the system to the company's electrical network.
The plumbing contractor Stemmle carried out all hydraulic work: integrating the three 1,000-litre buffer storage tanks with heating elements, connecting them to the heating network, and completing all pipework at the interfaces between the CHP unit, SOL•THOR and the heating network.
System design based on the operator's own prior experience
No detailed calculations of savings or the solar coverage ratio were carried out before installation for the Bayernland eG commercial building and the associated generation of heat from photovoltaic electricity. The decision was based on the operator's many years of practical experience. For years, the operator has used a self-developed solution in a private setting to utilise surplus PV electricity for heat generation - and is so convinced by it that he trusts the future yield data. In this project, moreover, not only the surplus but the entire yield from the off-grid photovoltaic system on the roof of the commercial building is used.
Whenever the sun shines, electricity is continuously converted into heat
Describing a PV system as operating 24/7 is misleading because it does not generate energy around the clock. However, unlike private systems, where the heat demand is met after a few hours, this situation cannot occur in the dairy's heating network. The dairy's heating network operates around the clock and continuously draws heat. Buffer storage tanks with a total volume of around 120 m³ are available throughout the hot-water network. This storage capacity, combined with the continuous heat demand, ensures that the 22 SOL•THOR units can operate without shutting down because storage limits have been reached. All of the solar-electric heat generated is used within the plant - down to the last watt from the roof.
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Personal customer feedback
"It is all still very new. So far, it is working well," says the operator of Bayernland eG, summarising the system's early operating performance. The results over the summer will show how efficiently photovoltaic heat can also be used in an industrial environment.
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SOL•THOR
in use
The DC Power Manager converts solar power directly into heat – efficiently and with minimal loss by using direct current from PV modules to power a heating element.
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