Solar Energy System of the Month:

New: Research Information from BINE in the Solar Magazine

The System of the Month for January 2001 is a prelude to the cooperation between the Solarserver and BINE, the information service for new energy techniques and their uses. The goal of the cooperation is to introduce research results to the general public.


Product of the Month/ January 2001

Local Solar Heating Systems for the Eco-City

Concepts in city planning are being increasingly developed, in which the provision of renewable energy in housing developments is playing a main role. However, in comparison to the design of individual one-family houses, solar collectors for entire villages are still rarely planned.

pilot system in Steinfurt-Borghorst

Research and trials of systems that combine collector surfaces of over 100 square meters with large-dimensioned long-term storage have been in use for about a decade: the Federal German Government gave the starting shot for 7 pilot programs with the Sponsorship program " Solar Heat 2000". BINE Info 8/99 drew the balance and allowed a glance into the future.

Photo: pilot system in Steinfurt-Borghorst
Source: BINE Information Service

Solar Coverage Rate-40-60%

Coordinated total concepts that largely encompass heat protection and efficient energy production, were standing by at the beginning of the pilot project. Systems with long-term heat storage were brought into operation in 1996 in Hamburg and Friedrichshafen, and in 1999 in Neckarsulm. All three systems were constructed, for economical purposes, to contribute almost two thirds of the entire heat consumption for household heating and hot water through solar rays. A comparison of solar heating costs shows, that local heating systems work more efficiently than the solar heating systems in one- and multi-family houses: a kilowatt hour produced with a typical small solar heating system (one to two square meters of collector surface per person) costs 30 to 60 pfennigs. Local heating systems with short-term storage supply, according to the calculations of the researchers, the same heat for 15 to 30 pfennigs. A kilowatt hour of solar heat from a system with long-term storage could cost between 33 and 55 pfennigs. In any case, the less expensive system-costs of the larger systems make local heating systems more attractive.

Scheme for solar supported local heating system with seasonal heat storage

Scheme for solar supported local heating system with seasonal heat storage
and direct or indirect heating system connection.

Graphic: BINE Information Service

Four types of storage are in operation, that are being used in reference to the particular geological conditions. Hot water storage tanks were preferred in Hamburg, Hannover and Friedrichshafen; in Neckarsulm subterranean tube storage; and solar heat is stored in gravel and water in Steinfurt and Chemnitz. The system with the most modern solar roof is in Rostock. Windows and blind elements are integrated in the solar roof of the "Helios" building. All collector backs are ventilated: the humidity that comes out of the building and under the collector can be siphoned off. Since the end of 1999, a ground water heat storage tank (Aquifer tank) has been in operation in Rostock. The system supplies 108 apartments with hot water and supports the heating . The production from the collector with a surface of 1,000 square meters is fed into the 20,000 cubic meter storage tank. A low temperature heating system with radiators lowers the return temperature and creates more economical operating conditions for the solar heating system. The Technical University of Chemnitz calculated a solar heating price of 47 pfennigs per kilowatt hour.

Experience and Outlook

The heating system layout and the type of domestic water heating determine the return temperature of the local solar heating network and thus the solar heat yield . A higher available solar heat capacity is reachable with low temperature heating systems than compared to a conventional heating system. Indeed, these systems generate additional costs, and it depends on the commitment of the builder and the planner, if they will be realized. The "Helios" Project is valued as proof, that low-temperature heating systems are possible even in apartment buildings. The percentage of solar coverage of the local heating supply can be increased through direct connection to the heating system: not using a heat exchanger sinks the return temperature to approximately 40 degrees Celsius. This means a solar gain of 7%.

Frequent flaws were ascertained in conventional house technology during the pilot tests. Hydraulically irregular water and room heating systems, plate-heat exchangers with too little transfer power and regulation problems in outdoor temperature controlled heating systems are restricting efficient energy use. The operator of the local solar heating system can have little influence here--the local solar heating system stops at the house switch. In order for the solar heat production to be efficiently used, all participants, especially the implementing companies, have to be included and motivated.

The testing and development phase is not yet concluded. In the past years, the basic concepts were endorsed, weak points were analysed and ways to increase efficiency were presented. High investment costs remain an obstacle for operators and the housing market. New financing concepts could help with this.

1000 square meter solar roof: multi-family house "Helios"
1000 square meter solar roof: multi-family house "Helios" in Rostock

Without state sponsorship, only local solar heating systems with short term storage could, in the foreseeable future, come into efficient operation . The goal of the long-term storage system is to reach prices that, without sponsorship, would be at the most twice as high as those for heat from natural gas or oil.
Photo: BINE Information Service

Materials and Illustrations: BINE Information Service FIZ Karlsruhe
Solar Server Editorial Staff: Rolf Hug
Translation: Mary Meier

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