Common House Solar Hot Water Heating system
The Common House has a Solar Hot Water system that augments the natural gas powered hot water heater. The system was manufactured and installed by Backwards to the Future Ltd., in September 2005, during a state of Michigan program that offered a cash rebate on such installations. The system provides an environmentally friendly energy option and reduces our carbon footprint.
The system as installed cost $6540 for two sets of collectors and the state of Michigan rebate of $1400 per collector saved us a total of $2800. We estimated that the system would produce energy equivalent to 144 ccF of natural gas annually, which would make a payback period of approximately 26 years if the price of natural stayed at around $1 per ccF. Of course, the emissions and carbon offset savings would be substantial but were not part of the calculatd payback since there is no standard market for that yet in the US or Michigan.
The installation was financed by a number of households as "investors" in the system who would be paid back as the system produced energy -- at the same rate as was paid to DTE. Once the system was paid off, the community would own it outright.
The system works best on dry, bright days, with late January producing the best heat gain so far! A member investor notes the readings on the meter monthly, and updates the spreadsheet below and bills the Common House for energy produced! Annual reports are posted to the News page.
- SDHW - solar domestic hot water
- The DTE meter readings and associated cost for Natural gas are taken from the monthly CH utilities bill, but only to calculate the DTE cost per ccF in effect for that month since that is what we price the equivalent energy produced by the SDHW at.
- The meter on the CH SDHW measures energy produced in kilowatt
hours (kwh) where as DTE charges us in ccF (hundreds of cubic feet)
of natural gas used.
Based on the amount of energy that can be extracted from 1 ccF of
Natural gas, we convert from kwh to ccF using the following formula:
x kwh * 3.6e6 J/1kwh * 1Btu/1055J * 1McF/1.027e6Btu * 1000cF/1McF * 1ccF/100cF = y ccF x kwh * .03322611757430882753 = y ccFThis formula favors natural gas as not all the volume of natural gas produced yields useful energy (it is about 85% efficient) whereas the SDHW meter is much more accurate in measuring how much useful energy is produced.