AC ELWA 2 and SOL•THOR in a Single-Family Home
Photovoltaic Heat in Two Versions for Hot Water & Heating
A grid-connected and an off-grid PV system in the Black Forest generate hot water and support the heating system.
Facts about the project
- Owner
- Photovoltaic output and orientation
- Number of modules and type
- Heat storage size
- Building type
- Year of construction
- my-PV product
- Heating element
- Inverters and battery storage
- System control
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A Special Single-Family Home
The soon-to-be 180 m² home of Mr. Schneider in the Black Forest has several unique features. Different stages of expansion are now common in many single-family homes, but here the PV system has been expanded multiple times, and the heating system is designed to remain off for many months while the photovoltaic system provides the heat. Two different PV systems were installed: a grid-connected photovoltaic system of nearly 27 kWp, complemented by a 22 kWh battery (from sonnen). This PV system is mounted south-facing and east-west on roofs with varying inclinations. In addition, a second, off-grid photovoltaic system was installed, which feeds nothing into the public electricity grid and converts all PV output directly into heat. This second off-grid PV system is much smaller at 3.4 kWp, as it is only intended to handle hot water and supplementary heating.
But how did the resourceful owner come up with this solution?
Personal customer opinion and resumee
“My highlight in using the products for solar-electric heating is the seamless monitoring via the my-PV Cloud. You can clearly see how the devices operate and how the energy is used optimally. Even on cloudy days, the water gets warm, and no stove is needed for heating. This saves a lot of money—I am very satisfied with the my-PV products,” summarizes Mr. Schneider from the Black Forest.
Mr. Schneider is an electrician himself and, through his company, installs many products from the Austrian manufacturer of PV heating solutions, my-PV. He has received positive feedback from various customers regarding their functionality and gained personal experience with installation and commissioning, which made him naturally curious whenever news came out of Upper Austria.
In 2004, the heating system in the existing building—a 90 m² single-family home from 1997—was renovated and switched to a pellet heating system. A 750-liter buffer tank was installed in the basement to store heat efficiently and reduce the frequency of pellet heating operation. The large buffer tank also created ideal conditions for using excess photovoltaic electricity, as it provides perfect storage volume for that purpose.
The first integration of a my-PV product for the grid-connected system happened in 2023. At that time, the system had 15 kWp available and could easily supply the house with its own PV electricity, but a lot of surplus energy was fed into the public grid. To make better use of this increasingly poorly compensated surplus PV power within the home, the solution was an Austrian PV heating element called the AC ELWA 2. This steplessly controlled heating rod receives real-time information about surplus electricity from the installed battery, the sonnenBatterie, ensuring that only electricity not already used in the house is converted into heat.
The AC ELWA 2 now continuously modulates according to PV surplus, using the excess energy to heat water via its heating rod. In this way, the buffer tank—which also heats domestic hot water via internal smooth-tube heat exchangers—is gradually warmed. The exact amount of energy required for heating can be found here.
Solar-Electric Heat from an Off-Grid PV System
When my-PV introduced another device, the SOL•THOR, in June 2024, the electrician was thrilled and ordered one for his growing single-family home. The direct current power manager, which transfers PV electricity directly—without an inverter—to a heating rod in a stepless manner, has been available on the market since spring 2025. This allows even more PV energy to be used for heating in the Schneider household through a separate heat input. Although this is not strictly necessary due to the large grid-connected PV system, the electrician sees the experience with the device as a personal advantage and a benefit for future customers.
Every watt generated by the PV modules is used by the SOL•THOR via a conventional heating rod—in this case, a my-PV 3 kW screw-in heater—to heat the water in the buffer tank, until the target temperature in the tank is reached. Then the SOL•THOR switches off. Unlike a solar thermal system, switching off does not create any problems (e.g., stagnation issues); the owner loses at most a few kilowatt-hours. Proper system sizing is important here—or one may intentionally oversize the system to achieve high yields from the PV modules during transitional seasons or winter, since PV modules do not create a major cost burden.
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Were there any obstacles in implementing the products?
“Since I have already installed the AC ELWA 2 for many customers in my work as an electrician, it was a piece of cake. But even the implementation of the SOL•THOR, including the my-PV screw-in heater, went smoothly,” summarizes Mr. Schneider his experience with the solar-electric solutions.
Is hot water supply backup used?
Currently, two people live in the single-family home. The exact hot water demand is not known. Since heat is supplied to the buffer tank via two PV-based solutions, no hot water backup is used. For many months in summer—specifically from mid-March to the end of October—the pellet heating system remains off, and hot water is provided solely by solar power and surplus PV electricity, or via the direct current from the off-grid PV system.
If solar output is no longer sufficient for heating, the pellet heating system can start—but due to the large buffer tank, this is only necessary from the end of October.
What are the advantages of adding off-grid PV heating?
“My PV system already provided enough surplus PV electricity for heating applications using my-PV solutions. But the off-grid solution is super easy to install and requires virtually no maintenance,” says the trained electrician.
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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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