My Experiences with Solar Electric and Solar Hot Water Systems
An energy management consultant since 1974, Andrew Rudin shares his personal accounts, the good and the bad, with using solar panels to generate electricity and to heat water.
What about the pure economics of the system? Was it worth the investment purely from an energy point of view? The late ecologist Howard Odum was interested in what he called the emergy of a PV system—its embodied energy. I sent him all the data he requested about the copper, aluminum, silicon, and plastic in my system. He determined that the electric production was borderline worth the energy it took to manufacture the panels, inverter, wire, and so on. That was in 2002. The system is producing less energy now, so it might not meet Odum's criteria today.
So while everyone has a roof, I have one that pays me back, albeit very slowly to date. The inverter seems to be the most crucial part of the system. If it breaks, I will have to pay thousands of dollars for a new one.
I was optimistic when I began this project 12 years ago that solar energy would achieve wide acceptance. But I then heard the coordinator of the solar-PV grant program describe solar electricity as "Gucci power." I felt terrible about that. More important, all I hear and read about solar PV does not acknowledge some basic truths that I have learned.
When they are covered with snow, the panels don't work. We carry on because our system is net metered, and electricity is not interrupted. This means, however, that while we displace PECO's kWh with sun-derived kWh, PECO has to maintain sufficient generation capacity to serve all of the now more than 1,000 PV systems in its territory. The kWh the PV systems do displace are likely to be produced on sunny days in the summer. This may offset the high cost of operating some of PECO's natural-gas peaking generators.
PV systems have improved. They operate more efficiently than my system did, even when it was first installed. And the annual degradation of the solar cells isn't as high for PV modules manufactured today as it is for the older ones that I have. My system cost about $9.70 per watt to install (excluding tax benefits), but now, according to Ron Celentano, the median installation cost for a residential system is about $6.10 per watt, and could be under $5 per watt excluding rebates and tax benefits. The federal tax credit for PV is now 30% of installation costs compared the 10% that I received 12 years ago. And I could have gotten as much as 36¢/kWh for my SREC for part of the life of my system, compared to the 13¢/kWh that I currently receive. Finally, electric rates are higher today than they were 12 years ago, and will probably increase as time goes on.
I don't know if the system increases the resale value of this home. My guess is that it doesn't, although EPA says that it should.
My Solar Hot-Water System
I use our local library a lot, saving money by borrowing instead of purchasing books. One librarian asked me to look at the library's electric and gas consumption, and suggest how the library might reduce energy costs. When I examined the building, I discovered an abandoned solar hot-water system on the roof, probably installed when the library was built in 1982.
Eventually, the library wanted to replace the roof and the rooftop HVAC equipment. The panels were in the way, so I asked for two panels in trade for my energy-consulting services. I installed them on the roof of my sunroom, below the main roof on which the solar-electric system is installed. In December 1998, I hired a contractor to do the installation. Cost to install the system was $2,450, not including the two free panels. The 10% federal tax credit was $245.
The system uses a 65-gallon storage tank to preheat water. When there is adequate sunlight, a small (10W) PV panel generates enough DC current to heat a 3-inch cylinder of liquid. This liquid expands to push a brass shaft to open a valve. The open valve allows pressurized water from the local water utility to fill the panels until an air vent at the top of the system closes.
The shaft continues to open until it presses a switch that operates a variable-volume DC pump. The pump circulates water through the storage tank and the two solar panels, where the water is heated. When there is insufficient sun, the process reverses. As the shaft retracts, the pump turns off. Then the valve opens up to drain about 2 gallons of water either into an interior drain during the winter, or into the garden at other times of the year. A vacuum breaker allows air into the panels. Late one fall, I forgot to pull the drain tube out of the garden. Water in the tube froze, preventing the drain-down. The next morning, water was blowing off the roof into our garden. A copper pipe had burst, costing me $100 for a plumber to replace the broken section. I could have lost the whole system that night.
The solar system preheats the water from the local water utility in the 65-gallon tank on its way to our backup DHW system. Originally, the backup system was a stand-alone gas water heater vented through the wall. After the experiment described below, I replaced it with an indirect-fired tank that is heated by our high-efficiency natural-gas water heater.
To estimate the savings from the solar DHW system, I bought and installed a natural-gas submeter, just to measure gas for our vented domestic water heater. For the year ending in May 1999, the submeter measured 99 hundred cubic feet (ccf) of gas. Then I turned the solar system off but kept reading the meter. For the next 12 months, the water heater used 145 ccf without the solar system. Then I turned the solar system on. For the next 12 months, the water heater used 86 ccf with the solar system operating. My wife and I were away on vacation for about the same number of days during each of the three summers.
The solar DHW system saved me 52.5 ccf per year. The October 2010 PECO invoice shows a gas commodity price (excluding the monthly meter charge) of $1.03/ccf, so the 52.5 ccf has a current value of $54.
Gradually, the air vent/vacuum breaker stopped working, allowing water to slowly spray out. Then, in the spring of 2008, the variable-speed DC pump stopped working. I decided to replace these things myself, because the materials alone cost a steep $344.50. The system has been working flawlessly ever since.
Andrew Rudin can be reached at firstname.lastname@example.org.
So, the total cost of owning this solar DHW system has been about $2,650, including the repairs but excluding the cost of the free solar panels. If the system had operated continuously since January 1999, I would have saved the current value of the system, which is about $600. The payback on my system is about 49 years, if nothing else breaks down, which is unlikely.
Being an Early Adopter
I showed this article to Ron Celentano. He e-mailed back: "You don't give yourself enough credit for being a pioneer with this technology -- or at least you don't convey that in your article. Unfortunately, it's the pioneers that get burned the worst, but they also have the first thrill of surfing the wave, before the boring mainstream sets in."
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