Living without a “second rent”

First the storage, then the house. Constructing a solar house, as here in Weißenburg, Germany, involves a few peculiarities along the way. (Photo: Haag & Ortner GmbH)
First the storage, then the house. Constructing a solar house, as here in Weißenburg, Germany, involves a few peculiarities along the way. (Photo: Haag & Ortner GmbH)

More and more multi-family buildings in Germany are being designed as solar homes. Solar storage then takes centre stage.

Like the funnels of an ocean liner the two metal giants rise into the sky. But here in Middle-Franconian Weißenburg, Germany, there are no ocean liners and the metal giants won’t be visible for much longer either. They are to become the heat storage of a solar housing block with 19 flats, which the housing association Wohnungsgenossenschaft Eigenheim eG is currently building. The two solar storages will each have a volume of 74 m3 and will soon disappear behind the walls of the new building.

Solar homes which are heated almost exclusively with solar heat have not been anything exotic for years now. The solar homes institute Sonnenhaus-Institut e.V. estimates that there are already approx. 1,800 buildings of this type. Multi-family solar buildings are still rare, however. The new build in Weißenburg is thus also the biggest solar housing which the solar heating specialist Haag & Ortner has implemented to date.

260 m2 of collector area – spread over facades and roof area – make sure that there is always enough heat available for heating and hot water. There are virtually no heating costs for the occupants. The Wohnungsgenossenschaft Eigenheim eG will be using excess summer heat for heating tap water in a neighbouring housing complex. Should the solar heat not quite be enough in the winter, then the central heating system of the neighbouring building will provide the remaining heat via a small district heating grid.

The two large storage systems come from the Swiss solar home pioneer Jenni. The company makes about 80 % of its large storage systems for solar homes projects. 15 % are incorporated into smaller or larger district heating grids. Systems which store industrial or business-generated process heat only make up a small share, at just over 5 %. “Because autonomous energy supplies in the heating sector are of central importance to the energy transition,” Tabea Bossard-Jenni from Marketing at Jenni expects the best sales prospects for Jenni storage systems to continue to be in the solar housing sector in the future. Large heat storage will also be required in power-to-heat projects, however. So far Jenni has only had a few individual projects, but there will be more as wind and solar power on the grid generates more temporary excesses.

Power-to-heat will also play an ever-more important role at small scales, as own consumption using PV continues to grow in importance too. The solar homes institute decided to take a new direction at the end of last year. Solar electricity systems, also in combination with heat pumps and battery storage systems, should play a larger role in the solar house concept in the future. The first solar houses with large photovoltaics systems and heat pumps have already been built. It is not yet clear to what extent large heat storage will play a role here, however.

Vacuum storage for indoors and outside

The vacuum buffer storage by Hummelsberger Schlosserei GmbH from Mühldorf in Bavaria has also mostly been used in solar houses so far. “Up to now we have installed 12 vacuum storage systems ranging in size from 7,000 to 37,000 litres,” reports company head Jürgen Melzer, “of which 6 are inside the building and 6 are outside.” The company has implemented an unusual project in Switzerland; an 11 m³ storage was installed at a facility with workshops for disabled people. The storage there stands in one of the barns belonging to the facility.

Something which made it beneficial to use a solar heating system was that there is an integrated laundry on site. The facility thus requires large amounts of hot water even in the summer. “Everything used to be heated all year round using wood. Several people were permanently occupied with keeping the supplies up,” says Melzer. Now an approx. 80 m² vacuum tube collector system ensures that no fuel is required between March and October, which saves 25 m³ of wood a year.

The vacuum storage stands out thanks to its unsurpassably good insulating properties. But you can also insulate well using conventional foam or mineral wool insulation if you make it thicker. Jenni notes, however, that insulation is not everything. They refer to the Swiss solar research institute SPF Rapperswil, which has recently discovered that the coating is more important for energy efficiency than the insulation. “We have already been working with this effect for decades,” stresses Tabea Bossard-Jenni.

Jens-Peter Meyer

This article was originally published in issue 1/2016 of Sun & Wind Energy - The Solar Edition.

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