Energy self-sufficiency in existing buildings
A residential building in Hellenthal relies on photovoltaic heat
Thanks to photovoltaic heat, a 50-year-old house uses just 405 kWh of gas and 182 kWh of grid electricity per year.
Facts about the project
- Owner
- Photovoltaic capacity, orientation
- Inverter, battery storage
- Thermal Storage Size
- Building Type
- Year of construction and floor area
- Installed my-PV Product
- Heating Element
- System control
)
Moving away from solar thermal energy
When Hellenthal became Bram Verbeek’s new center of life in 2015, a large-scale solar thermal system (ELCO Auron with 70 tubes) was already installed on the south side of the house roof. This solar thermal system reliably supplied hot water in summer — but in practical operation it also revealed weaknesses: after two leaks in the hard-to-access collectors, it became clear that maintenance and repairs involved considerable effort and cost.
The decision was therefore deliberately made to switch completely to a photovoltaic system installed on the south-facing side of the roof. The goal was not only to simplify the energy supply, but also to operate the building as independently and efficiently as possible using its own energy — an approach that offers significant potential, especially for many existing buildings.
Personal customer opinion and resumee
The key lies in the combination of a dedicated photovoltaic system, the efficient use of surplus energy, and the integration of existing building features.
“Solutions like the AC•THOR from my-PV play a crucial role in maximizing self-consumption and further reducing dependence on the energy supplier,” the owner concludes.
Gradual expansion from 12 to 43 PV modules
The initial setup began with 12 PV modules installed on the garage in an east–west orientation. Step by step, the system was expanded - today, a total of 43 modules are installed facing east, south, and west. Eight modules are mounted vertically on the balcony on the east and south sides. These deliver particularly valuable yields in winter, when the sun is low, and they also remain free of snow.
However, as the system was continuously expanded, a new issue arose: at times, high electricity surpluses - especially between March and October. Feeding large amounts of electricity into the grid is not desirable due to low compensation rates; instead, the goal was to use as much of the energy as possible within the household.
The right solution was found with my-PV, the Austrian expert in generating heat from photovoltaic electricity. With the AC•THOR, surplus PV power is converted directly into heat and used for hot water preparation - continuously regulated. Integration was straightforward via an existing connection in the buffer storage tank. Since then, the self-consumption rate has increased significantly - without feeding electricity into the grid.
)
Individual Energy Concept for an Existing Building
The residential house, constructed in 1977 using solid construction, presents specific challenges: “Heating with a heat pump is not an option, as there is no underfloor heating and the house cannot be heated with a water temperature of 34 degrees. That’s why I decided to heat and cool the house with three air conditioning units and to use the residual heat, which I no longer needed for hot water preparation, as support in the heating circuit,” explains Bram Verbeek, describing his approach.
A key advantage of the solid construction is deliberately utilized: the building itself acts as a thermal storage unit. Doors remain open so that heat and cool air can be distributed evenly. Instead of traditional nighttime temperature reduction, the system deliberately “preheats” when there is excess electricity. The stored energy is then released later - especially during the evening and nighttime hours.
This simple yet highly effective principle reduces energy demand precisely when no photovoltaic generation is available.
Measurable Results: Minimal Energy Consumption
The consistent optimization is impressively reflected in the actual consumption data:
Gas bill (22/10/2024 – 21/10/2025):
405 kWh → €153.33Electricity bill (01/02/2025 – 31/01/2026):
182 kWh → €223.02
The development confirms the chosen path and, with transparent gas and electricity billing, demonstrates real values: “For the calendar year 2025, only 168 kWh of electricity and 33 m³ of gas were consumed - figures that are exceptionally low for a house of this size and age,” says the owner of the now 50-year-old home enthusiastically.
In addition, a Victron Energy inverter and charging system has recently been fully commissioned. As a result, grid consumption is expected to decrease even further in 2026. Initial results are already promising: despite winter conditions in January - with limited solar radiation due to the location - the battery is fully charged, and the large buffer storage tank reaches temperatures of up to 60°C.
A Transferable Concept with a Future
This project clearly demonstrates that even older existing buildings can be elevated to a new energy level through well-thought-out measures and intelligent system integration - and with an excellent cost-benefit ratio.
)
)
)
)
)
)
)
)
)
)
AC•THOR
in use
Simple & efficient: AC•THOR controls electrical heat sources depending on the availability of PV energy and heat demand. And that for both hot water, as well as for space heating.
More infos about AC•THORMore Reference Projects
)
A resourceful Upper Bavarian benefits from the renovation of his house and implements PV heat as blackout precaution.
Read more...)
Belgian family boosts PV self-consumption to 74% with AC•THOR, all without battery storage.
Read more...)
A Belgian homeowner heats up his outdoor-jacuzzi in an environmentally friendly way with the AC•THOR.
Read more...