In September 2006 Live Green Apartments had a solar thermal system installed at 622 Grand Ave to provide 75% of the hot water needs for the residents. It is estimated 800 therms of natural gas will not be needed because of the solar thermal heat. You would need 482 mature trees to clean the air pollution generated by this amount of gas of 30 years (9,640 pounds of carbon dioxide generated each year, over 144 tons over 30 years). This system also prevents some mercury from polluting our lakes and streams.
The system is made up of three main components: the solar panels (eight 4 foot by 10 foot panels), a heat exchanger, and two water storage tanks. A solution of glycol mixed with water cycles through the solar panels on the roof, down the side of the building, and into one side of the heat exchanger in the boiler room. Glycol is used in Minnesota because it can withstand temperatures of -100 degrees. In the boiler room there are two 120-gallon water tanks that store the water that is cycled through the other end of the heat exchanger where it gets the heat brought down by the glycol from the solar panels. These water tanks are connected to the gas hot water heater. If the sun does not heat the water enough the hot water heater kicks on and heats it the rest of the way.
There is a big advantage to solar thermal heat versus solar electric: solar thermal works well even on cloudy days, where solar electric relies more on direct sunlight. So even on a cloudy day the panels will heat up. The system preheats the water almost everyday, even on the days when it is below 0. In general it has preheated the water 5-10 degrees on cold days and up to 120 degrees on warm days.