I’ve been thinking a lot about monitoring solar performance in solar hot water systems. This is after the past few days of being contacted about systems that aren’t performing or, because of their design, don’t have a chance of working.
For instance:
- A firehouse in Wisconsin. The government agency in charge found that a year after the solar system was installed, the utility bills hadn’t budged. A monitoring system is currently being installed.
- A commercial building in North Carolina, in the engineering stage. A small load of 190 gallons per day is expected. But the engineers’ drawing calls for two 120-gallon storage tanks and a boiler large enough to heat half a hotel. Oh, and two 4’x10’ flat-plate solar collectors.
- A Texas firehouse. The firemen are happy with all the hot water, but it’s all provided by a Solar Phoenix, not the solar atop the building’s roof. Here’s the reason: The Phoenix is set to 140F, but the solar controller is set to shut off at 140F. The Phoenix and the 119-gallon tank were piped incorrectly with the pump circulating both of them. The solar controller indicated the solar had never made an ounce of energy. At 12 noon on a sunny day, the controller was reading the stagnating temperature at the panels at 105F. That can’t be right; it should be close to 300. Where’s the sensor located?
- A municipal building in Washington State, now being engineered. The system has six collectors, feeding hot water to three 120-gallon storage tanks and an 80-gallon drainback tank. The 80-gallon drainback tank is way oversized: the six panels hold only 6 gallons plus the pipe volume. In this case, incorrectly sized equipment will lead to poor performance. Are the design engineers just guessing?
Data logging helps clients see how well their solar thermal system performs.
Too many wonderful solar thermal projects simply won’t work because of improper installation or design. The solution? Data logging for monitoring the system’s operation and performance to catch the problem right away. One solar location may be generating an average of 1,000 Btu per square foot; another 1,200 Btu. I would suggest measuring energy collection per square foot, accumulating it, and then converting that information into the amount of fuel replaced.
Why is this important? To hold contractors and designers responsible for their design and installation. If the system is not performing within acceptable parameters, the problem may be easily determined by analyzing the real-time data.
I monitor my own solar thermal system using the Resol controllers sold by HTP. The data is always on my smart phone and I can check it no matter where I am. I admit to a certain kind of thrill when I see the
tank’s full of solar-heated hot water even if I’m in, say, Texas and can’t use it to take a hot shower.
I can better design future systems by understanding how solar reacts. For instance, I was monitoring historical info on a solar system and noticed an unusual pattern that let me to realize the collector sensor was in the wrong end of the collector. This is just one of many of the simple issues that can be diagnozed through data logging.
HTP’s superior solar water heaters, the Versa Hydro and the Solar Phoenix, will soon have their own internal data-logging equipment – look for the introduction at ASHRAE in January.
Unirac’s senior director of engineering and program management, Juan Suarez, offered an interesting idea recently in Renewable Energy World. As we all work toward lowering cost to expand the solar market, he suggests, perhaps we need warranties that cover performance, rather than defects. This would, in turn, “lower the cost of replacing parts or system failure.”
He continues, “Lowering the total cost of ownership (TCO) over the lifetime of an array and expediting ROI will spur the expansion of the solar market.”
Customers who care enough about solar and the benefits it brings should be entitled to an optimally performing system.
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