First multi-generation house capable of self-sufficiency in Switzerland

Massive dimensions in multi-generation house

In a Swiss multi-generation house, the photovoltaic yield of summer is taken into winter – with a 100,000 litre hot water storage tank. 



Project management: Barbara and Markus Ursprung,  
Net-plus GmbH
Oldani Architektur & Bauberatung GmbH

Construction type: New building and renovation: 50 % demolition and new construction, 50 % renovation and external insulation
Construction year: 1985 (Existing building) und 2021 (Expansion)
Living area 921 m²

PV-power and orientation: 144 kWp, divided into 8 directions = 4 roof surfaces and 4 facade areas
Facade (North-East, North-West, South-West, South-East)
Roof (30° North, 30° South, 41° North-East, 41° South-West)

Heat storage size: 100.000 litre heat storage tank with 4 meter diameter, 12 meter height and a 25 cm thick isolation
Additionally a 500 litre and a 400 litre boiler with heat pump

my-PV product in use: 5 x AC•THOR 9s
Plant control by/with: Loxone and KNX


Customer declaration

How did you come to my-PV?

For a large renovation project with partial new construction of a residential complex in a village in the south-east of the canton of Aargau in Switzerland, very special requirements were applied. The key data of the multi-party house with several flats and rooms, that cover special requirements for communal use of the common areas, are definitely very impressive with more than 900 m². Even more impressive is the heat storage tank built into the heart of the house, with the incredible capacity of 100,000 litres, which extends over several floors. This extremely large hot water tank with a diameter of four metres and a height of 12 metres supplies the multi-party and communal house with hot water and heat. The goal: to realise the first multi-generation house in Switzerland, with the given basic conditions, that is capable of self-sufficiency.

To prevent the house's grid connection from being overloaded with its own feed-in from the 144 kWp photovoltaic system, the client, Markus Ursprung, wanted a power limit on the grid feed-in. Of course, a stronger feed-in would have led to additional costs - another argument for higher self-consumption of photovoltaic power. Due to the higher self-consumption achieved by the 5 AC•THOR 9s, the feed-in has also been greatly reduced, which means that the energy is now stored or reused directly at the "production site".

A special aim by the owner was to produce boiling water (95 °C). A heat pump cannot do this, because the temperature range cannot be achieved here at higher water temperatures. The AC•THOR 9s, on the other hand, doesn't care at all: if there is enough surplus electricity, it can simply use it to heat the hot water tank until the desired temperature is reached - even the 95 °C is no problem there.


Obstacles/pecularities regarding the set-up?

It requires a well thought-out coordination with regard to the technical design to supply a multi-generation house with, for example 250m² of shared living space, two kitchen areas and the various private rooms with sufficient heat. There was a high degree of complexity and therefore the right support was very important! The manufacturer has to be able to provide exact specifications. This proved to be the biggest but manageable challenge with my-PV.

Brief explanation of the system – what should be mentioned?

"We store the energy for winter in summer because this way we don't need more energy in winter than in summer," Markus Ursprung explains the idea behind the system. Hence the seemingly oversized hot water tank design – with 100,000 litres, probably the largest hot water tank currently in use with my-PV products.

A total of 5 AC-THOR 9s control the photovoltaic power coming from the façade and the roof, which is generated from the power of the sun from all 8 sides (four side surfaces and four roof surfaces) of the building envelope and the roof surfaces. The excess power is then used during the day to heat the hot water, which would allow the large storage tank to bridge even weeks-long "lulls in the sun". In winter, there is still some of the residual heat left over from the 25 cm thick insulated storage tank, creating a self-sufficient environment.


Persons in the household – Hot water requirement etc.?

The 12 people who live in the barrier-free and age-appropriate multi-generation house, manage the garden together, use many areas together and are also very different in age. With the large hot water storage tank and the power of the sun, which is fed into the storage tank via AC•THOR 9s, the 12 residents of the house in the canton of Aargau always have enough hot water available.

After more than a year of operating experience, the client Markus Ursprung summarizes the project with the following quote: " I measure the temperature at every height so that I can calculate the exact energy content of the water tank. I connected 4 temperature sensors to each AC•THOR 9s. The PV power often fluctuates between 20 kW and 60 kW; and it is precisely these fluctuations that AC•THOR 9s can take over. What other consumer could handle such fluctuations in performance?”

An example of these fluctuations can be seen here:


Is hot water backup being used with mains power?

The potentially available hot water backup, which can always be activated with the my-PV units on days with low solar radiation, was not activated in this case.

In contrast to a heat pump, which should also have a long or preferably continuous running time for a long service life, AC•THOR 9s can be activated quickly, depending on the surplus power. This means that even short-term yields caused by different cloud formations or sunshine duration can be precisely reproduced in the hot water by the AC•THOR 9s at any time, i.e. they are available for heating water. The large fluctuation peaks are efficiently used in the house itself and not fed into the grid. This way, the feed-in peaks of the public grid are decreased because the surplus is used in the house.

Or, as the building owner sums it up: “I can use the surplus sensibly!”

Personal customer opinion and resume:

“If you have enough space available, then larger photovoltaics systems with the solutions from my-PV are cheaper and easier to implement than a heat pump," sums up the building owner Markus Ursprung.

This is because even the surpluses of the yields in summer can be transferred to winter with a large heat storage tank. This saves energy, relieves the strain on the grids and also paves the way for using renewable energies for the entire annual demand in the future.


my-PV GmbH
Betriebsstraße 12
A-4523 Neuzeug

+43 7259 39328

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About us


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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