Polar Energy, continued
All Steamed Up
It may be 20 below outdoors, but Whistler, British Columbia, Mayor Ken Melamed is bathed in the heat of the sun—literally. Head of one of the venue cities for the 2010 Winter Olympics (also one of the “greenest” communities in Canada), Melamed recently installed a solar hot water system on the roof of his home. “Generally, we are pleased,” he reports.
Mayor Melamed is far from alone. When it comes to solar energy technologies, domestic water heating is among the most viable for high latitudes. “There’s always a need for hot water, year-round,” says Kurt Koegel, spokesperson for Solar Skies, a Starbuck, Minn.-based solar thermal collector manufacturer. “That’s where you get the most bang for the buck.”
With a thermal efficiency averaging an admirable 35 percent over the course of a year, U of M solar energy researcher Jane Davidson says solar hot water systems can be capable, even in Minnesota’s climate, of meeting a home’s entire needs. These systems are not without challenges in northern latitudes, however. As anyone who has suffered the indignity of burst pipes can tell you, water freezes up in no time if left out in the cold.
As a result, says Minnesota Department of Commerce energy specialist Phil Smith, solar thermal applications in a climate like ours need to use evacuated tube or flat plate systems, which gather the sun’s heat with a second substance, then transfer it to water. The 104 Solar Skies solar thermal collectors installed on the roof of Kalahari Resorts in Wisconsin Dells, for instance, use tubes full of propylene glycol to capture the sun’s heat, and then pass it along to water circulating in separate pipes.
“You have to protect against heat loss and against freezing and use lots of insulation,” says Koegel. But with such safeguards in place, he says, solar can work for “anyone who uses hot water,” no matter the latitude.
Heating indoor spaces demands enormous amounts of energy—and the colder the climate, the greater the demand. In the remote town of Sisimiut, Greenland, 45 miles north of the Arctic Circle, 18 vacuum tube and nine flat plate solar collectors soak up heat from the sun during summer’s 24-hour daylight. The heat is used to warm the classrooms of Knud Rasmussen Folk High School.
Specially designed for top performance in the extreme north, the vertically aligned panels can catch sun on both sides—including light reflected from snow—and withstand temperatures down to minus 58 F. Heat exchangers first transfer solar energy to the hot water system. When that’s fully charged, they switch over to space heating. The system reduces the school’s consumption of costly fuel oil by half during the summer, saving an estimated 40 to 50 tons of greenhouse gas emissions each year.
There is no question the sun can be a great source of space heat. It can be a good choice where other sources of energy are available to supplement—as will be the case with District Energy St. Paul when it adds solar to its downtown building/heating energy mix later this year. It’s also handy in places where conventional sources of fuel are expensive or hard to access.
But there are plenty of opportunities for improvement. One has to do with availability. “The problem is, you have very high loads in the wintertime when it’s the coldest outside and when you have the least sun,” says Davidson, who’s hot on the trail of one big idea for serving up solar energy even when the sun doesn’t shine. As lead faculty member with the U of M’s Solar Energy Laboratory, she’s working on ways to gather sun energy at one time of year and use it another.
Most promising to date is a system consisting of a water-attracting liquid desiccant. In summer, sunlight heats and drives water from the liquid, transforming electromagnetic waves into thermal and potential energy. In winter, the desiccant reabsorbs water and releases heat.
With the help of a 400-gallon prototype now under construction in her lab, Davidson aims to engineer a system that works well enough to meet 100 percent of a northern household’s space heating needs.
“That’s our idea,” she says. “If the storage can be sufficiently large, you can eliminate the cost of a furnace, and it becomes even more economical.”
Solar in a Nutshell
How can northerners best harvest the sun’s bountiful energy? The possibilities seem endless.
The cheapest, lowest-tech and, by far, most common approaches involve passive solar energy. When you read a book by daylight or warm yourself by a window, you are using passive solar. Building technologies and strategies that tap this resource are all about bringing in light and heat in winter and keeping heat out in summer. Specifics include window placement, building siting and materials choices. The benefits of passive solar add up at all latitudes.
A second approach that works well in climates with widely fluctuating heating and cooling needs is solar water heating. Because homes and businesses use hot water year-round, such systems always have a job.
Related—and sometimes connected—to solar hot water is space heating using active solar heat collectors. In places like Minnesota, this capability is far more useful in winter than in summer for obvious reasons. Advances toward making the installations more versatile for northern climates include adapting them to space cooling or electrical generation once winter ends.
Of course, heat and light won’t run your refrigerator or your future solar car. That’s where photovoltaic enters the picture. In northern climates, PV makes the most sense when you can feed excess power into the utility grid in summer—when the solar collectors are cooking—and draw on your credit in darker days.
Nowadays, utility-scale solar facilities are gaining more and more attention. These facilities capture the sun’s energy over large spaces using PV panels, or by concentrating heat and using it to generate electricity. While this approach has a clear advantage in sunny southern climates, it’s being applied in Canada, Germany and Scandinavia as well.
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Last modified on January 23, 2012