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The First U.S. House to Go Solar

The birth of a pioneering solar research program at MIT.

If you walked down Vassar Street in 1940, it would have been easy to overlook the small, one-story house nestled between the squash courts and the local carpenter’s shop. But if you looked closely, you might have noticed the odd sheen of its steeply sloped roof. And had you peered through the windows, you would have seen not a cozy living room but a laboratory packed with equipment. The biggest clue that this was no ordinary dwelling, however, was hidden in the house’s basement: a massive hot water tank nearly the size of the building on top of it.

The 17,400-gallon tank was heated solely by the sun, its energy collected by 14 glass-covered devices on the roof. Water flowed continuously through copper tubes inside these collectors, where it was heated by solar rays and then fed down to the tank. Fans transferred air from the house’s two rooms to the basement, blew it over the tank’s hot exterior, and then returned it to the ground floor to keep the house at 72 °F throughout the winter.

The structure, known as Solar I, was the first U.S. house to be heated with stored solar energy and the first of six “solar houses” designed and constructed by MIT faculty between 1939 and 1978. Several years before it was built, Vannevar Bush, EGD 1916, MIT’s vice president and dean of the School of Engineering, began contemplating the best way to harness solar energy. “All our power comes from the sun; fuel in the form of wood, oil, or coal; waterpower; windpower,” he wrote in 1936 to MIT president Karl Taylor Compton. Unfortunately, he observed, little was known about how to utilize this power source directly.

It just so happened that Godfrey Lowell Cabot, a wealthy industrialist, was having similar thoughts. He’d founded a company that used large quantities of natural gas and oil to produce carbon black, a substance used in printing-press ink and rubber products such as tires, so he recognized the dangers of relying on a limited supply of fossil fuels for energy. He thought solar power was the answer, and he was willing to back up his words with his wallet. “I have made money from this,” he said, “and it seems to me I should put some of my money to work so that men may learn to live on … solar energy.”

In 1937, Cabot donated 100 shares of his company, then worth over $600,000, to Harvard to fund research into harnessing solar energy by burning cultivated plants for fuel. A slightly jealous Compton proposed that Cabot fund research into “the chemical, chemical engineering, and mechanical engineering aspects” of solar energy at MIT. By September 1937, Bush had prepared a research proposal and Compton had appointed a committee to oversee the endeavor, led by Hoyt C. Hottel, an associate professor of chemical engineering. In April 1938, Cabot donated another 100 shares of his company to MIT to establish the Godfrey Cabot Fund for Research on Solar Energy Conversion. The gift would support solar research for 50 years, after which MIT could use the funds as it saw fit. One of the program’s first projects was the construction of Solar I, completed in September 1939.

But Cabot didn’t just fund the research. “I will wager that never has an endowment to a university been followed with such continuous and intense interest on the part of the donor as that displayed by Dr. Cabot,” Hottel reflected in 1989. Cabot’s feedback and many visits to MIT labs provided an important perspective. “He frequently emphasized the point that cost of the product—heat or power—and not the efficiency of producing it was the basis for judging the performance of a solar device,” Hottel wrote.

Indeed, by the time Solar I was torn down in 1941 to make room for buildings needed for war research, it had become clear that its heating system was effective but impractically expensive. Its five successors experienced their own problems: the second solar house hemorrhaged heat at night, the third’s heat storage bins failed during its third winter, the fourth’s heating system caught fire in December 1955, and only MIT faculty knew how to maintain or repair the system in the fifth, so it had to be removed before the house was re-sold. The sixth house fared little better.

Although Solar I proved too costly, the small wooden house on Vassar Street launched five decades of research that provided invaluable insights for the many scientists still toiling in electrically heated labs, looking for ways to economically harness the power of the sun.

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