Sunshine on tap in Sweden's dark winter

Technology with possible uses in Gulf as Swedish town stores solar heat in sunny months and uses it when cold weather strikes

The Arlanda Airport in Stockholm uses a natural, below-ground reservoir to store hot water for use in winter and cold water for summer air conditioning.

ANNEBERG, SWEDEN // It is a country better known for cold winters than for hot summers, but solar technology being developed to keep homes in Sweden warm could help to keep Gulf homes cool.

Stig Ram, a former Ericsson employee, is conducting a unique experiment in solar heat storage for the municipality of Danderyd, 10km north of Stockholm.

Anneberg, a community of 50 families, has an unusual district heating system that draws on the sun's energy, even in the depth of the dark, cold Scandinavian winter. The trick is to use the community's bedrock - a pink granite - as an underground heat reservoir.

"Seasonal uneven distribution of solar radiation makes storage of solar power necessary for winter use," says Mr Ram, a Sunbeam sports-car enthusiast whose Anneberg apartment features Persian, Iraqi and Turkmen rugs and carpets. Beneath the wooden floor runs an intricate system of pipes carrying solar-heated water.

A morning snow flurry in early May makes the cosy warmth exceptionally welcome.

Normally at this time of year, Anneberg's 2,400 square metres of rooftop solar heat collectors produce copious supplies of hot water, much of which is pumped down about 100 boreholes into the 60,000 cubic metres of bedrock used to store heat for winter.

The typical "charging period" for the reservoir is March to November, when there is no snow cover on rooftops and the solar panels collect more energy than is immediately needed for heating water and homes. During the rest of the year, the flow is reversed, bringing warm water up.

The district heating system dramatically reduces the amount of power that residents of Anneberg need to purchase from Sweden's national grid. Only on the coldest days in winter is electricity needed for supplemental water-heating.

Developing environmental technology at the municipal scale for export is a Swedish speciality, says Andreas Carlgren, the environment minister. He is counting on the technology to help the country retain a competitive edge in a global market for renewable energy products that could otherwise soon be dominated by China.

Mr Carlgren says Sweden is also interested in exporting district cooling systems being developed in the country and has Gulf states in mind as a future market.

One such system developed recently for Stockholm's Arlanda Airport uses a natural, below-ground reservoir to store hot water at one end for use in winter and cold water at the other for summer air conditioning. That system is powered by biogas collected from decomposing wood waste, but in other locations it could run on natural gas or solar power.

Sweden's national grid already supplies some of Europe's cheapest and lowest-carbon electricity, generated mainly from hydropower and nuclear plants. It means Anneberg's solar system does not really save money here. Nor does it have a major effect on carbon emissions.

"People have the idea that energy from the sun is free, but I am here to tell you that it is not," says Mr Ram.

Operating costs include the maintenance of pumps, which can cause big problems if they fail. One effect of pump failure is that water inside plastic pipes can boil, damaging materials designed for contact with fluids no hotter than 70°C.

A reliable supply of back-up electricity is essential for avoiding such problems.

The whole system is controlled by custom-designed microprocessors, which do not come cheap. Mr Ram would like to see a simpler design, with less potential for a lack of spare parts to become problematic.

Yet if Anneberg's district solar system were installed in any of a number of countries with equally cold winters and which currently burn coal for power and heating, the estimated 60 per cent electricity saving would significantly lower energy costs. Moreover, emissions of carbon dioxide would be reduced by 400 to 450 tonnes a year.

The Swedish project is effectively a pilot for technology that the country might some day export.

Already, a second project has been developed in western Canada to test the concept. The project is in Alberta, a province that generates most of its electricity from coal-fired plants and burns natural gas for heat.