Photovoltaic heat for holidays at the farm

Reference project Attwengerhof

Photovoltaic surplus for heat preparation at a scenic family-owned farm in Salzkammergut.



Client/owner/planner: Family Wolfsgruber

Location: Salzkammergut, Upper Austria
Construction type: Agricultural building with residential tract, heated outer buildings 
Construction year: Existing building 
PV-power and orientation: Several module fields with different orientations (South, West and East). In total 40 kWp

Heat storage size: 4,000 liter buffer tank for woodchip heating

my-PV product in use: AC•THOR 9s in operating mode M3 for 18 kW application with two 9 kW immersion heaters
System control by/with: Compatible inverter


Customer declaration

How did you come to my-PV?

Family Wolfsgruber was looking for a way not to feed excess photovoltaic energy into the grid, but to use it directly for the operation of the farm instead, including residential buildings. “Full feed-in was never the goal,” explains Stefan Wolfsgruber, pointing out the greatest possible self-sufficiency for operating his farm. At the same time, the existing biomass heating should be relieved as much as possible in order to protect the life of the boiler. Precisely these needs can be perfectly met with the solutions from my-PV.

Obstacles/specialities during the installation

AC•THOR is really easy to install and configure with the immersion heater. An existing pellet heating system from ÖkoFEN has the option of integrating a third-party system – in this case with AC•THOR. AC•THOR was the chosen product because it has a hot water backup function that maintains the desired minimum temperature overnight. This is important for operation at night, where sufficient hot water must be available as well for comfort purposes.

Brief explanation of the system – what should be mentioned?

The pellet boiler is switched off from mid-March to September, which means that it is not used for heating in spring, summer and early autumn. The surplus PV energy is optimally used with the electric heating by AC•THOR. The required temperature is set to 85° C to get the maximum out of the photovoltaic system. In order to draw as little power as possible from the grid, the hot water backup is set to 40 °C; this means that if the temperature drops below this, AC•THOR uses grid power to heat water. In winter, however, AC•THOR and the pellet boiler work together and only when the water temperature drops below 60 °C, the pellet boiler switches on during the winter months.

What is family Wolfsgruber's opinion on the project and what possibilities of expansion do they consider? They share their experiences in the interview. 



Obstacles/specialities during the installation

A photovoltaic thermal solution does not require any permits. For heating technology, the installation of heating rods in a heat accumulator is a completely normal standard application. Even the linear power modulation by my-PV, with which these electric heaters are finally suitable for photovoltaics, does not change anything. This means that there are no expenses for administrative procedures or permits.

Brief explanation of the system – what should be mentioned?

A 4,000 liter heating tank was already part of the existing wood chip heating system. An ideal storage capacity for my-PV, in order to accommodate surplus PV from the new, high-performance photovoltaic system. The two 9 kW immersion heaters were easy to install as the required 1.5” connection sockets on the buffer were already available.
In addition, an extra electricity meter from my-PV was not even required to detect the surplus at the grid connection point. Thanks to the system openness of our company for control by third-party providers, the measurement signal from the inverter manufacturer could be used. Thus, family Wolfsgruber saved another essential component and there was no additional space requirement in the house junction box.

Persons in the household – hot water needs etc.?

Stephan and Nina Wolfsgruber live at the farm together with their three children and Stephan's parents. In addition, there is a heat requirement for hot water and heating for five holiday apartments and two further residential units, which are connected to the buffer storage tank via a small local heating network. Overall, the heat requirement is immense. Unfortunately, even with a 40 kWp PV system and an 18 kW heating solution from my-PV, it is not possible to switch off the heating in summer, as it could easily be done in a one- or two-family house, for example. The benefit at the Attwengerhof in Traunkirchen lies in the relief and protection of the wood chip boiler, as well as in increased self-sufficiency and higher self-consumption.

Is a hot water backup with mains power used?

The biomass heating is in operation all year round. During the summer months, however, the boiler is only fired up in the late afternoon to give the system the opportunity to load the storage tank with photovoltaic heat during the day and not to block any storage reserves.


Personal customer opinion and resume:

Due to the advanced age and the many full-load hours of the wood chip system in winter, the operators are now happy about the possibility to relieve their boiler and to extend the service life of the heating system. Stephan Wolfsgruber's advice is: "Anyone who has the opportunity to install a photovoltaic system on their roof should do so." In his opinion, today's farmer is also an energy farmer and it is important to use what nature gives us in order to do something good for nature in turn!


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We at my-PV get more out of photovoltaics than just electricity, we move your building technology into the future. Use your solar power yourself instead of feeding it into the public grid: Electricity, hot water, heating and charging options for your e-car. With our products, you can use your self-generated photovoltaic electricity for your own needs without any detours. This way, you save costs in the long term and act environmentally friendly!



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