The Free Press, Mankato, MN

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June 22, 2011

MSU study sees savings in solar technology

By Tanner Kent The Free Press

MANKATO — A Minnesota State University study has concluded that a relatively inexpensive solar technology can reduce energy consumption in large buildings by up to 20 percent.

“We’re pretty excited about the results,” said Louis Schwartzkopf, an MSU professor emeritus in physics and one of the study’s three authors.

“We’re eager to get this out the community so companies and schools can understand this is a good way to save energy with buildings that have large ventilation needs.”

The study was undertaken three years ago by a trio of MSU faculty: Patrick Tebbe, research director and professor of mechanical engineering; Saeed Moaveni, a former professor of mechanical engineering who is now a dean at Norwich University in Vermont; and Schwartzkopf.

The study collected three years of data at three sites in the Twin Cities that had installed so-called “unglazed transpired solar collector” systems — which are also called solar walls and consist of large plates of dark-colored steel or aluminum that are perforated with tiny pin holes. The plates are mounted on a wall and heated by the sun. A ventilation system then pulls the heated air through the perforations and distributes it throughout a building.

Naturally, the preheated ventilation air reduces the demand on a building’s heating system. The net impact, according to the study, is a 10-20 percent decrease in energy consumption.

For a building as large as Breck High School’s fieldhouse — the Golden Valley private school’s fieldhouse was one of three test sites with a solar wall of about 14,000 square feet — that reduction amounts to a $2,400 savings in annual heating costs.

When that rate of return is combined with the relatively low costs of installation and maintenance — installation costs about $10 per square foot (retrofitting is a bit more) and the solar wall has a lifetime of up to 40 years — the payback periods are between one and eight years.

The benefits are most amplified when the solar wall is mounted on a south-facing wall with no windows and a size of at least 1,000 square feet.

The results of the study should help building operators estimate the savings from installing such systems.

There are no buildings in Mankato outfitted with solar walls and only a handful in the state. The study also looked at solar walls installed on the Minneapolis Police Precinct No. 3 building and the AVEDA Corporation Headquarters in Blaine.

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