The off-grid solar house – a model for the Solar Age?

In 1992, the Fraunhofer Institute for Solar Energy Systems opened its Energy- Autonomous Solar House in Freiburg, Germany, as a research and demonstration project.21 With 145m2 of floor space on two stories, it has five rooms, a kitchen and ancil­lary rooms. This house proved that a single-family home could make do with the solar energy from its roof and walls the whole year even in the German climate. The ‘autonomy’ here thus concerns not only space heating, but also hot water, gas for cooking, and electricity. Several years of operation demonstrated that this independ­ence is possible without any loss of comfort for residents.22 Like a passive house, this house has:

• Extremely good insulation.

• Large southern windows to exploit solar energy passively.

• Regulated ventilation with heat recovery. The following technologies were also used:

• Highly efficient solar thermal collectors (14m2 with a 1000 litre storage tank) provide enough hot water almost all year round.

• Large areas of transparent insulation (some 70m2) reduce heating demand down to 0.5kWhm2 over a year – only around 1 per cent of the energy needed in a low-energy house and around 4 per cent of what a passive house needs.

• A photovoltaic array (4.2 kilowatts-peak) generates some 3200kWh of electricity per year, more than the efficient appli­ances used in the household (60 per cent less energy consumption than with conventional appliances) need. Excess electricity is used to convert water into
oxygen and hydrogen, with the latter being stored in tanks. The hydrogen is used for cooking and auxiliary heat a few days a year. When the photovoltaic panels have not been receiving enough sunlight, the hydrogen can also be used to power a fuel cell, which generates electricity. The waste heat created in the process is used to heat service water.

Is the off-grid solar house a model for the Solar Age?

The Energy-Autonomous Solar House does not have a grid connection, nor is it connected to a district heating network. As such, crucial solar options – district heating with solar energy or biomass and the use of other renewable energy sources, for instance, are not possible here. As a result, this project required a large amount of seasonal storage that would not have been necessary if the house had been connected to public heat and power sources. The Solar House therefore did not show what houses would look like in the Solar Age, rather, it showed that a house in Germany can do without fossil fuel even in the 1990s

Finally, the Energy-Autonomous Solar House also showed that solar architecture is not a single technology, but rather a cornucopia of technologies that have to be closely coordi­nated to produce optimal results.

Photovoltaic array (4.2kW)


Solar collectors (14m2)





Large, south-facing glazing for passive solar energy


Transparent insulation (roughly 70m2)


Extremely good



Figure 4.7 The Energy-Autonomous Solar House, Freiburg, Germany

Source: Fraunhofer Institute for Solar Energy Systems


Leave a reply

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>