Swedish Property Developer Pioneers Renewable Energy

by J O Dalenbäck, Chalmers University of Technology, Sweden



A Swedish municipal property developer has won an environmental award from the Swedish Association of Municipal Housing Companies (SABO) for its pioneering use of biofuels and solar energy. EKSTA Bostads AB has bought and built 100,000 m2 of housing developments and service premises in the urban districts of Kungsbacka, of which 84,000 m2 are heated by EKSTA.

At present about 85% of the heat supply comes from renewable energy; ie ~70% from processed wood, ~15% from solar collectors, and ~15% from oil and electricity. The aim is to achieve 100% heat supply from renewables and to generate 100% of the electricity used from wind power.

All the major building areas have central heating plants with roof-integrated collectors and buffer storage for the supply of domestic hot water to connected buildings during the summer period. In winter (October-March) supplementary heat for space heating and domestic hot water is supplied to the buffer stores by modern wood-fuel boilers placed in the central heating plant or in a larger neighbouring heating plant. Oil-fired boilers are used in winter peak conditions and to support the solar collectors during periods with insufficient solar radiation.

A prerequisite for achieving a high solar fraction at competitive costs is to have well-insulated buildings. All the older existing buildings were fitted with a third window pane and all accessible attics were supplied with additional insulation in the late 1970s. Most of the buildings were built between 1983 and 1994 to high thermal insulation standards. The typical annual heat demand in these newer areas is around 50 kWh/m2 heated floor area.


Solar heated residential area in Saro, 1989



EKSTA's solar systems were developed in stages over more than 15 years. The first solar collectors were installed in Fjärås in 1979. The plant, 380 m2 of roof-mounted collectors (AGA air modules) combined with a heat pump, was rather complicated and expensive. This experience showed that the investment cost had to be reduced and that the design and mounting of the collectors had to be better adapted to the ordinary building process in order to bring about competitive heat costs. In this first plant the extra cost for the solar system was covered by an experimental building loan from the Swedish Council for Building Research (BFR).

A new line of development was then initiated and the result was a pilot plant with 150 m2 of site-built and roof-integrated collectors mounted on a children's day-care centre in Vallda in 1981. This development resulted in a much cheaper and better adapted collector system compared to Fjärås, but other parts of the system, such as a pressurised buffer tank, were still too expensive.

A small system with 150 m2 of further developed roof-integrated collectors, combined with a non-pressurised buffer storage with immersed heat exchangers, was then introduced in Åsa in 1984. A major design philosophy here was to have the buffer storage shared by the boiler and the solar system, as well as the domestic hot water and the space heating system, resulting in further cost reductions.

The next step was a similar but larger system in Kullavik in 1987: 700 m2 of collectors combined with 50 m3 buffer storage and a wood pellet boiler. To increase knowledge about the direct extra cost for the solar system, EKSTA asked for parallel tenders both in Åsa and Kullavik (conventional heating plant versus solar heating plant). This documented extra cost was then used to calculate the capital cost for the solar system.

Solar systems totalling 4,200 m2 of site-built roof-integrated collectors (TeknoTerm IT) were installed from 1985 to 1992.

The latest development, a 220 m2 roof module collector, has now been applied in a new residential area in Onsala. Prefabricated roof modules with integrated collectors (A-Hus AB), mounted on the heating plant and a carport, are designed to cover 25% of the annual heat demand in nine buildings with 36 residential units (2 500 m2 heated area). This development has resulted in even better integration in the building process, and has reduced investment
cost further and improved thermal performance.

EKSTA has also built two experimental solar heating plants with seasonal storage; one using pipes in clay in Kullavik in 1983 and one with a folded steel tank in Särö in 1989, with the aim of achieving a larger solar coverage. However, at present these technologies cannot compete with stored solar heat in the form of processed wood.

At present EKSTA owns and operates 6,000 m2 of collectors (generating heat equivalent to
250 m3 of oil per year). All plants are still in operation with very low operation and maintenance costs. Main partners in the development of the solar systems are Andersson & Hultmark Projektering AB (engineering consultant), TeknoTerm Energi AB and the Department of Building Services Engineering and the Monitoring Centre, Chalmers University of Technology.


EKSTA's development of building and solar collector area, 1968-1995.



Along with the development of the solar heating plants, most of the existing oil-fired boilers have been replaced by wood-fired boilers. All buildings were heated by oil until 1979 when the first heating plant was converted to wood chips. During 1984 to 1994, four new fully-automatic boilers burning processed wood have been put into operation. The largest one (1 MW) is equipped with exhaust gas heat recovery. The wood briquettes come from a local saw mill and EKSTA has developed a special container system for efficient handling. The present heat supply from wood boilers is equivalent to 1,000 m3 of oil per year.


These projects have shown that it is possible to combine high building standards and renewable heat supply at competitive costs. The average total investment costs (building area including heating plant) amount to less than SEK 10,000/m2 heated floor area (where SEK is the Swedish krona). Tenants pay an average annual rent of SEK 700/m2 heated floor area (including heating and domestic hot water) of which less than SEK 30 covers the annual fuel costs. In comparison, SABO's average fuel costs amount to SEK 85/m2 heated floor area.

The net investment cost for the collector roofs has come down to SEK 1,100/m2 of collector area (excluding VAT). Based on real contracts (November 1995) the investment cost for the solar system in Onsala amounts to SEK 194/m2 heated floor area, or 2% of the total investment cost, resulting in 25% solar coverage. EKSTA's average solar cost is SEK 0.50/kWh, partly due to favourable financing conditions (subsidised rate of interest, investment subsidies). The equivalent prices for other summer heating alternatives are: electricity SEK 0.65/kWh and oil SEK 0.45/kWh. The price for wood briquettes is 0.20 SEK/kWh.

For more information contact the CADDET Swedish National Team in Stockholm.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.