Solar Energy System of the Month:

Research in a New, Solar-Optimized Building: Fraunhofer Institute for Solar Energy Systems (Fraunhofer Institut für Solare Energiesysteme (ISE)) in New Quarters

For some weeks now, the approximately 300 employees of the Freiburg, Germany Institute for Solar Energy Systems (Freiburger Instituts für Solare Energiesysteme (ISE)) have been working under one roof. In light of the field of activity of the institute, it is then understandable that solar collectors are on the roof and photovoltaic modules are mounted on the façade.

The new Fraunhofer ISE Institute for Solar Energy Systems

In all, the 20 kW nominal output PV modules and the 20 square meters of collectors serve to actively use solar energy. That the building complex counts as one of the outstanding solar office and industry buildings can first be seen when one looks closer at transformed energy concept.

Photo: The new Fraunhofer Institute for Solar Energy Systems


Work Place Quality, Functionality and Energy Efficiency - the Central Components of the Building's Concept

Whereas before they were divided among eight different properties, offices and laboratories are located under the single roof of the 13,000 square meter building designed by the Copenhagen architectural firm Dissing + Weitling. Immediately, the ISE begins saving over half a million dollars in rent for one year. Architecture and (solar) technology entered a forward-looking partnership - according to the motto of the planning team: "Exemplary Building with the Sun". The guidelines were clear: efficient energy use, high quality within the work place and a corresponding design. So the ISE Building is by no means one of the spectacular solar buildings, like, for example, the admirable "Heliotrop" building in Freiburg by architect Rolf Disch. On the viewer, the new ISE impresses a sense of objectivity and functionality.

Because of the north/south orientation of the land next to Heidenhofstrasse northwest of down town, the planners decided for a longitudinal building" with an associated opening axis (Traffic Line) as well as three east/west oriented wings. An atrium with a shed roof and photovoltaic modules receives visitors who enter through the south-facing head of the building. Here the aesthetic aspects of the building come into their own: It comes across as open, communicative, and functionally elegant. The administration and central services are housed in this part of the new building.

On the west side parallel to the building´s opening axis the plant room, cleaning room and workshops are attached to each other. The three story wings house in part the climate-controlled laboratories on the north side and on the south side are offices, which don't require an active climate control. The wings' flat roofs take over the function of surfaces for open air experiments.

Graphic: The wings are oriented east/west, respectively, their separation purposefully large with use of daylight taken into consideration. Both the wings' structure and zoning combine passive solar energy use in winter with low heat gain in summer.

Source: Fraunhofer ISE


Climate Control and Ventilation

Through integral planning, the numerous possibilities of passive climate control for the offices should be completely exhausted. By means of a dynamic building simulation the planning team determined the necessary measures: Glass surfaces and specific types of glass in the façade were matched; an effective, outside sun glare shield on the outside is automatically controlled; the ventilation is optimized.

In summer an air exhaust system working with the steel accent-ceilings (they cool off faster than ceilings that are hung up) take care of the building's cooling. The air is replaced up to five times per night. Additionally, the skylights are opened by hand in order to minimize any pressure loss, which could result considering the high rate of airflow. Even long periods of hot weather don't represent a problem; the concept assumes few days with room temperatures above 26 ºC.

An air/ground register for the cooling and preheating of intake air is an additional component of the main building's ventilation system: Seven 100-meter long pipes with widths of 25 centimeters lie six meters deep in the work room of the excavated second level basement of the building´s opening axis.To provide enough fresh air for the offices in cold times of year there is an air exhaust system: The ground air exchange averages 30 cubic meters per person per hour.

The outside air flows through slit vents in the window frames into the offices and through ventilation plate fins over the doors into the floor. From there the exhaust air is centrally removed, its heat recovered, which is then led to the laboratories.

Graphic: The ventilation concept of the main building.

Source: Fraunhofer ISE

ventilation concept of the main building

Light and Lighting

Both doing without an air conditioning system for the offices and the lighting control system, which provides agreeable daylight for the workstations, save electricity. The roof- and façade-integrated solar power system is able to precisely calculate the electricity needed for the entire electric lighting system, and with its roughly 200 square meters it can provide for this need.

The wing structure of the building was chosen in order that the employees of ISE not only receive light powered by solar energy, but also receive enough sunlight-such a design increases incoming sunlight. The orientation of the office space minimizes disadvantageous east and west facades. For example, architectures confront the blinding low sun throughout the year from these directions. The façade layout and design as well as the lighting were first chosen after a light simulation. Architectures and engineers design a façade with four functioning segments: balustrade, windows, blinds, and skylights.

Set flush with the roof, the skylight allows as much light to enter as possible; a continuous outside sunblind with two-part service guarantees protection against the sun yet still allows enough daylight in.

Graphic: The interaction of daylight and artificial light.

Source: Fraunhofer ISE

interaction of daylight and artificial light

When it is completely shut the blinds close in front of the windows while they stay in a level position in front of the skylight. Energy efficiency also means reasonable saving: The ISE engineers decided for an electronic lighting system without "standby" use. The floor lighting of 75 lux (unit of illumination) takes over an indirectly incandescent lighting system in each office whose electric circuit is automatically switched off when enough natural light is present. The individual workstations have desk lamps with 500 lux. Together, only ten watts per square meter of light output have been installed in office areas, and in the halls just 6 W/m². The yearly demand for artificial light is about 10 kilowatt-hours per square meter.

Solar Energy Supply and Effective Energy Conversion

Despite all of the energy-saving measures and the heat recovery from the exhaust air, the building's PV system and the solar thermal system can only cover a fraction of the entire ISE demand: a gas-powered block-type thermal power station (BTTP) combined with an absorption refrigeration machine covers the high year-round energy demands of clean-rooms, laboratories and production sites (i.e. electric diffusion ovens with 300 kilowatt connected loads).

The waste heat, which can be used for heating in winter, can be converted to cold air in the summer. This power/heat/cold combination is only economical if the highly significant, failsafe electricity supply is included in the calculation. This is guaranteed by the BTTP, which also reduces the investment costs with which such a system is normally associated.

Photo: View of one of the two modules of the block-type thermal power station, model MDE.

Source: Fraunhofer ISE

one of the two modules of the block-type thermal power station

After eight years the station should pay for itself, then it should cost about 15 % less when compared to a conventional energy supply that requires almost double the initial investment. Future considerations are possible: If required or wanted, the BTTP can be replaced with a fuel cell aggregate using natural gas.

The Characteristics (Data) Of Energy Supply
Table: Fraunhofer ISE


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The solar components of the energy supply are noticeable - even if they are hardly noticeable to the eye due to their clever integration into the building's façade. The solar power system delivers a total of 20 kilowatts, of which 10 kilowatts peak output (kWp) are modules hung onto the wing facades, another 7 kWp is delivered by solar cells in the insulation glass at the southern part of the shed roof construction of the atrium and 3 kWp are integrated into the south end Façade of the the building´s opening axis. With a g-value of 24 % (energy transmittance based on solar radiation), the modules take on both functions of heat and sun protection. Collectors with an entire surface area of 20 square meters contribute three-fourths of the warm water demand of the lunchroom.

Through measures taken to save energy and because of efficient energy supply, the heating needs of the institute should be around 40 % below the level set by the Heat Conservation Provision (Wärmeschutzverordnung), and they should not rise due to future equipment or functionality upgrades. If the BTTP were also operated nights, then the primary energy needs would sink further. If this makes sense, however, should be checked - up until now the costs of producing energy onsite during nighttime hours exceed the supply price for electricity supplied by conventional, mostly fossil sources.

Fraunhofer ISE

Three kilowatts of photovoltaic output are integrated into the south side façade of the new building's opening axis. The modules provide both heat insulation and sun protection functions.

Source: Fraunhofer ISE

After all employees have successfully moved in and after the inauguration takes place on November 23, the team that has worked on the building will continue to do so: Continuous monitoring and evaluation of the building is to take place in accordance with the research project "Solar Building: Monitor (SolarBAU: Monitor)", sponsored by the Federal Ministry for the Economy and Technology (Bundesministerium für Wirtschaft und Technologie (BMWi)).

The ISE will give architectures, engineers, building planners, building owners and building specialists, as well as other interested parties, the opportunity of expert tours through the new building (Architecture: Dissing + Weitling, Copenhagen). Points of emphasis: daytime light use, passive cooling for a high quality work place in a low energy-use environment as well as the integration of solar energy systems for energy supply.

The new Fraunhofer ISE Institute for Solar Energy Systems

Tours through the building take place during the following dates
(15 - 16.30, Price: 15 DM (about $ 7) / person): Friday, October 12, 2001;
Friday, December 14, 2001;
Friday, February 8, 2002;
Friday, April 19, 2002.
Source: Fraunhofer ISE

You can also find information on the Internet at

Also read the Solar-Report over the ISE Creativity and Continuity - Solar Research in Theory and in Practice

Material and Pictures: Fraunhofer Institute for Solar Energy Systems (Fraunhofer Institut für Solare Energiesysteme ISE), 79100 Freiburg, Germany.
Solarserver Chief Editor: Rolf Hug.

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