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Best practice case study: Cutting the cord

multi-family dwelling without grid connection

The solar façade generates 27 MWh of clean electricity every year. This is 29 % of the total electricity consumed in the building. (Copyright: Umwelt Arena Schweiz)

Cutting the cord

Self-sufficient multi-family dwelling gets by without grid connection

A multi-family dwelling in Switzerland with an innovative building concept gets its energy entirely from solar radiation. Complemented by a sophisticated storage system for electrical energy and heat, it is well supplied even when the sun isn’t shining. The result is a self-sufficient building completely independent of electric and gas grids.

An apartment building completely without any connection to the electricity or gas grid: this vision has made Walter Schmid, founder and Chairman of the Board of Directors of the Environmental Arena in Spreitenbach, Switzerland, a reality. He bought a site in Brütten, a small town on the way between Zurich and Winterthur, demolished the restaurant on it completely and started to build the first completely energy self-sufficient apartment building in Switzerland.

The house, which was built in 2016, produces all the energy that the residents consume, both in the form of electricity and heat, without a grid connection and without any external energy source. Even mobility has been taken into account. For example, the nine families who live in the house have an electric and a biogas vehicle for shared use.

The energy for the building and vehicles is generated on the one hand by the solar modules, which constitute the complete building envelope of the apartment building in Brütten. To achieve this, the installers mounted thin-film modules on the cold façade on all sides of the three-storey building. The manufacturer Meyer Burger from Thun has produced a total of 470 m² of module area. In order to cover the entire façade area, the panels had to be manufactured in very different sizes.

Don't dazzle your neighbors

In order to meet the optical requirements of the architect, Meyer Burger fitted the modules with a matt surface. This was also necessary to get permission to install a solar façade in the Brütten residential area. A different module surface would have reflected part of the sunlight and dazzled the neighbouring buildings.

A second generator covers the entire roof and at the same time acts as cladding. The installers covered all 14 sections of the complex roof with the integrated system. In this case high-efficiency monocrystalline solar modules were used, which were also manufactured by Meyer Burger. The Thun-based company also supplied the complete substructure.

The solar roof has a total power output of 79.54 kW. The solar façade has a nominal power of 46.95 kW. However, this is hardly ever achieved due to the unfavourable orientation towards the sun. The vertical installation, however, has a decisive advantage compared to a roof system. This is because the roof system is primarily oriented to the sun's position in summer. The solar façades, on the other hand, are better oriented towards the lower sun in winter. In addition, the planners have calculated that the solar skin of the building can cover the residents' entire energy requirements for one day with just one hour of sunshine in summer.

This means that, especially on sunny days, much more energy is generated than the residents consume. For this reason, the planners have developed a comprehensive storage concept. First, the surplus solar power is fed into a lithium iron phosphate storage unit from Helion Solar in the basement. This consists of two blocks, each with an power output of 55 kW, which are connected in parallel and integrated into the building system. Together they can store 192 kWh of electricity, with a usable capacity of 153 kWh. However, this is sufficient to cover the energy requirements of the entire building completely for two or three days

Batteries become energy suppliers

The two battery inverters set up the grid inside the building and keep it stable. Even in an apartment building without a connection to the general distribution network, the frequency in the house network needs to be stable at 50 Hertz so that residents can operate their normal electrical devices. This is also valid for the heat generators, which are operated with solar power from the façade and the roof. These battery inverters are also used to control the solar systems. Their own solar inverters wait for the battery inverters to set a frequency. Just after that, they switch themselves on. If the solar systems deliver too much power, the battery inverters increase the frequency and the inverters of the solar systems adjust themselves.

When the lithium-ion storage is full and the load in the building is less than the yield from the solar systems, a long-term storage is fed with the solar power. This is an electrolyser that uses the excess solar power to split water into its components. After all, it can absorb an power output of 14.5 kW and thus produces 2 m³ of hydrogen per hour and stores it in two hydrogen tanks at a pressure of 27.5 bar. These two tanks are located outside the building and have different sizes. The larger of the two hydrogen storage tanks has a capacity of 72,000 l of hydrogen. The smaller tank has a volume of 48,000 l.

Fuel cell provides winter power supply

With the hydrogen stored in these tanks, a combined heat and power unit (CHP) with a fuel cell can be operated if necessary. This can produce electricity with an power output of 6.2 kW and feed it into the battery storage tank. On cloudy days, this can guarantee the power supply for the building. The CHP also uses the surplus heat generated during electricity production. It feeds this into the heat accumulators of the building with a pre-flow temperature of 60 degrees and a heat output of 5.5 kW.

Two giant steel enamel tanks were installed to ensure sufficient heat even on dark autumn and winter days. Together, these can store 250 m³ of hot water. If the storage tank is full, the water temperature amounts to 65 degrees Celsius. This hot water is mixed with cold water and sent into the heating system at a temperature of 28 degrees. This temperature is enough because underfloor heating is installed throughout the building. In contrast to conventional radiator heating systems, they operate at such a low temperature.

Heat pump uses three sources

If the two storage tanks are completely charged and there is still heat surplus, a thermal long-term storage tank is fed with it. This also acts as one of the heat sources for the water-water heat pump. This starts up when there is either enough solar power left that neither the battery nor the hydrogen storage tank can hold, or when the temperature in the thermal short-term storage tank drops below six degrees Celsius.
However, the heat pump only uses the long-term thermal storage if it is extremely cold and the solar systems supply very little electricity. At higher temperatures, it uses the outside air as a heat source. When the temperature in the long-term thermal storage tank drops below eleven degrees Celsius, two geothermal boreholes at a depth of 338 m feed the heat pump.

In this way, it achieves maximum efficiency. In addition, the heat from the hydrogen electrolysis and from the battery room is also used and temporarily buffered in a lowtemperature storage tank. This reaches a temperature of 35 degrees Celsius, which is sufficient to supply the heating systems in the building with energy.

The heat is distributed either directly by the heat generators feeding it directly into the heating and hot water circulation systems. Or it is distributed indirectly. Then the heat generators first provide their energy to the thermal storage tanks, which then distribute the heat in the building.

Strictly insulated

With this ingenious cascading system of generators and storages, the generation of solar power time-shifted with consumption can be optimally captured. Even longer periods without solar power can cover the building due to the fuel cell CHP. But even with this it would hardly be possible to power an energy polluter. That' s why the planners have also reduced consumption drastically. In addition to the consistent use of energy-efficient equipment, they have also insulated the building at a high level.

The triple-glazed windows also contribute to the fact that the heat requirement is modest at 14.7 kWh per m² per year. This means that the building only needs 19.5 MWh of heating energy per year. In addition, there are used 23 MWh for hot water supply. This heat requirement can easily be met with the heat pump, the waste heat from electrolysis, the fuel cell and the battery room.

After all, 92 MWh of solar power per year are available for operating the heat pump and supplying the residents with electricity. Of this, 71 % comes from the roof of the building - after all, 65 MWh per year. The remaining 29 % is supplied by the solar façade. This generates around 27 MWh per year. This means that the building has a comprehensive system of generators and storages that is perfectly harmonized in detail. But this system is suitable for covering the energy consumption of the residents for the entire year.

This best practice case study initially appeared on www.solarage.eu.

Solar Age is an exhibitor at EM-Power 2019, booth C4.171.