January 25, 2015
Heating water can account for 25 percent to 30 percent of the average home's energy. Reducing energy consumption also reduces your carbon footprint. Depending on who you talk to, a solar hot water system can save you 50 to 95% of the costs to heat water. After doing some research on solar hot water heaters, I thought it might be feasible to install one on the roof of our townhouse. Florida gets a lot of sun and it doesn't get too cold in the winter. Freezes are rare. The research says we needed 5 to 6 hrs of sun between 10 and 4. If you don’t get enough sun, you need bigger collector panels.
It is hard to pin down exactly how much you will save with a solar hot water system. There are a lot of variables including your geographic location, collector efficiency, location of the collector, how hot you set the temperature, and how much hot water you use. Various estimates say that solar can reduce hot water costs by 50-70% in the Northeast and up to 95% in Florida. Your mileage may vary.
Our electric water heater is in the garage. I thought the garage roof right above the heater would be the ideal spot for a solar panel. Wrong. In January, this area has sunlight from 9:30 to 11:45, shade from 11:45 until 2:30, and sun again from 2:30 until 4:30. There is no sun at the best time of day.
Undeterred, I took a look at the east facing roof at the back of the house. I observed when the sun was hitting the roof and kept a log. The result: In January, there is full sun from 10:30 - 3:30. Not ideal, but good enough. I then spent a few days trying to figure out if there would be enough sun the rest of the year and it looks good. This site has some good information on figuring out the position of the sun throughout the year.
February 4, 2015
After my preliminary research, I spoke to 2 local vendors: Wayne’s Solar and Solar Fit. Wayne’s sales rep was able to explain clearly their direct circulation system, He also climbed into the attic to see if it was feasible to run the pipes through the attic at the back of the house, out through the soffit, and down through the garage roof. He said it was feasible and gave me a quote for $4795. FPL (our local utility) offers a $1000 rebate for solar hot water so the net was $3795. Solar-Fit’s rep gave me a nice overview of their passive system and their direct circulation system. The passive system was less expensive, but if you had a few cloudy days in the middle of the winter, the passive system would produce water colder than the water coming into the house, which isn't very efficient. Solar-Fit’s price was $5950. When I told the rep that I could get a comparable system for around $5000, she dropped the price to $5500 and said that was her best offer.
Both proposed systems use a 4x10 foot flat-plate collector mounted on the roof, an 80-gallon storage tank, a controller to sense the temperatures at various points in the system, and a small pump to move water from the storage tank to the collector when the temperature in the collector is warmer than the temperature in the tank. Both systems had protection against freezing, which doesn't happen very often in this part of Florida, but it happens enough that the systems need freeze protection.
I got into a discussion with the Solar-Fit rep about solar hot water systems’ ROI. A few months ago, FPL did an audit of our electricity use and determined that in a typical month, water heating accounted for 30% of our total electricity cost. Cooling and heating accounted for another 30%, and appliances and lighting made up the remaining 40%. Our bills run around $100 a month, which means that, according to FPL, our hot water costs are about $30 a month or $360 a year for a family of 2. On a brochure the rep gave me, the costs used in their example were twice mine. The brochure assumed an 80% savings. However, during our discussion, she assumed $40 per month and a 95% savings. Needless to say, there are contradictory numbers when it comes to ROI. The system will pay for itself anywhere from 7 to 15 years depending on electricity rate inflation and whose numbers you use.
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