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The Largest Solar Water Heater Plant is in ... Denmark?

A windswept Danish island shows that solar power needn't be the sole province of sunnier climes.
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The cobblestone streets and historic houses and shops create the impression that nothing on the Danish island of Ærø (aka Aero) has changed for centuries, and its biggest tourist attraction traditionally was its ship-in-a-bottle museum. But a trek just outside its largest towns will bring a 20th-century surprise — giant solar water heating plants.

Interest in the solar alternative began on the island in the 1970s with Denmark's "No to Nuclear" movement. The two oil shocks of that decade when petroleum prices leapt and availability plummeted added to solar's attraction.

"Ordinary people" — a smith, some teachers, a farmer, also a bank manager — established the Aero Energy Office, which became the focal point for information on renewable energy resources. Those clever with their hands built homemade solar hot water collectors. Then came Energy Plan '81 promulgated by the Danish government. The policy designated Aero Island and some other remote spots for renewable since planned natural gas pipelines would bypass them.
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To kick off the renewable program the Danish government began an educational initiative to gain public support. Renewables needed community backing to succeed as each town on the island ran its own energy plant. The islanders learned, for example, that their Swedish neighbors had great success in the 1980s with large fields of solar hot water collectors providing most of the summer heating load, including hot water, for several housing complexes. Like houses in the towns of Aero, the flats in Sweden got their heat from hot water flowing through pipes connected to a shared boiler.

The Swedish experience motivated those living in Marstal, the largest town on the island, to put up what has become the world's largest solar water heating collector farm. It takes up a space of almost 200,000 square feet. The collectors generate the thermal equivalent of 8.2 billion watt hours per year for the Marstal District Heating, helping to supply heat for 1,400 households. The solar unit provides all their heat from June through August, including hot water. Boilers take over the rest of the time.

Throughout the year, solar energy satisfies 30 percent of the town's annual heating needs, and work is under way to raise that to 50 percent. The Marstal District Heating had earlier relied solely on highly polluting heavy oil for fueling its boilers, which made the solar choice an easy one.

Other district heating complexes on the island followed Marstal's example. In 1998 Aereoskoebing District Heating installed 52,743 square feet of solar collectors; in 2001 the Rise District Heating built a 43,000-square-foot solar plant; and most recently, the Soeby District Heating went solar with a farm taking up 24,000 square feet. Totaled, the island boasts 46 square feet of collector area per person, the highest per capita in the world, far exceeding places like Southern California or Arizona that receive at least twice the solar radiation than does Aero Island.

Aero's renewable outlook isn't totally solar — an estimated 50 percent of its electricity comes from three massive windmills, and all renewable sources combined provide 80 percent of the island's energy.

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