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Fuel Cells for Distributed Power Supply at the. "Rappenecker Hof"
Rudi Kaiser, Felix Kosack, Nils Reich, Andreas Steinhuser
Peter Adelmann1
Fraunhofer Institute for Solar Energy Systems ISE
Heidenhofstrasse 2, 79110 Freiburg, Germany
Tel.: +49 (0) 761/4588-5225, Fax + (0) 761/4588-9225
Andreas. Steinhueser@ise. fraunhofer. de
1Phocos AG Deutschland, Bergstrasse 2, 89171 Illerkirchberg, Germany
The "Rappenecker Hof", a hikers’ inn on the Schauinsland mountain near Freiburg, Germany, was the first solar-powered inn in Europe. A hybrid system consisting of photovoltaics, a wind turbine and a diesel generator has supplied electricity since 1987. In addition, thermal solar collectors provide domestic hot water. Up to now, the system concept has been based on a battery with a rated voltage of 162 V. The solar generator, the wind turbine and the rectifier from the diesel generator have fed electricity directly to the DC circuit. The basic power supply concept is about 15 years old. Technical progress in systems technology and an increased energy demand resulting from changes in the inn’s catering concept forced to modernise the system.
2. Design of the new power supply system
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Fig. 1: The "Rappenecker Hof with the solar generator (centre) and next to it the storage room to house the gas cylinders for the fuel cell (on the left). |
The starting point in planning the new power supply concept was the decision to continue and reinforce the "Rappenecker Hof’s" character as a pioneering system for stand-alone power supplies. For this reason, a fuel cell was chosen as the auxiliary power supply for the "Rappenecker Hof". The photovoltaic generator and the wind turbine will continue to supply around 70 % of the annual energy consumption. A 48 V battery compensates for fluctuations in supply and demand.
The fuel cell guarantees a reliable power supply during periods when the contribution from the renewable energy sources is too low. To ensure that the system can supply electricity reliably at all times, particularly during the initial test phase, the existing diesel generator has been integrated into the power supply concept. If insufficient power was available or the fuel cell broke down, the diesel generator would ensure that the battery can be recharged.
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Fig. 2: Block circuit diagram of the energy supply concept for the "Rappenecker Hof’. Usage of waste heat from the fuel cell and the diesel generator has already been planned, but not yet implemented. Two inverters with different power ratings are integrated into the power supply system that has been implemented at the "Rappenecker Hof". A 5 kW inverter supplies the entire domestic circuit, with the exception of the two dishwashers. Since these are operated sporadically only, they are connected to a separate 3.5 kW inverter. These inverters are usually in the energy-saving stand-by mode. The presence of two inverters provides automatically a back-up if one inverter should fail. In this case, the other circuit branch can be supplied with slight restrictions. For transparency, only one inverter is shown in the block circuit diagram in fig. 2. |
The charge controller is responsible for the management of operation of the complete system. Depending on the prevailing state of charge of the batteries, the fuel cell and the diesel generator are automatically activated and then switched off again once a specified state of charge is reached. If the system should be not available due to maintenance work or a system breakdown, the system operator can still start the diesel generator manually and connect it directly to the domestic circuit, as indicated in the block circuit diagram. The information on the state of charge needed for operation management is determined by the battery management system described in section 4 and sent to the charge controller.
With the former power supply concept, where the inverter was dimensioned to be relatively small, the diesel generator had to be connected manually and the domestic circuit connected directly to the diesel generator whenever there was a high power demand, e. g.
when the dishwashers were operated. Now the complete energy demand can be met with the inverter and the battery. By this, optimal use of the regenerative energy sources, sun and wind, has been made feasible.