We get asked from time to time what is the best way to install a thermocouple on a solar collector during installation. While certain manufacturers include a thermal well in their collector this both solves a problem and causes a problem. The same manufactures that supply thermal wells advocate only installing glycol based systems. The thermal well is installed in or near the top header on one side of the collector. Since the well is only on one side of the collector this can lead to extra line runs on the roof to cross from one side of the array where the solar fluid is exiting the collectors to the other side of the array where the thermal well is located. This is not ideal. Additionally, some manufacturers will install wells that are required to be immersed in the solar fluid. Not bad for a glycol based system that is always wet but on a drainback system this doesn’t work particularly well.
Several of the domestic manufactures have taken the approach of not supplying any wells with the installer then simply using a strap clamp to strap the sensor to the manifold. This has the advantage of allowing you to install the sensor on either side of the collector so no extra wire run. The disadvantage of this approach is that the sensor is then farther away from the collector thus making timely temperature detection more difficult.
One solution to this problem is to simply take advantage of the rubber grommet as the clamp for holding the sensor (see picture).

With this scenario you then are able to install the sensor on either side of the collector as well as get a close temperature indication of what is going on inside the collector.
Another solution is to cut a hole in the back of the collector and through the insulation and then affix the thermocouple to the back side of one of the fins. This has the advantage of getting the temperature reading in the middle of the collector but the disadvantage of voiding most manufacturers warranties.

Solar pool heating systems are one of the most cost efficient uses of solar thermal technology. The cost of heating the average residential pool using a gas or electric heater is approximately $2,000 per year, according to the US Department of Energy. The cost of the average solar pool heating system is between $2,000 and $4,000. Although solar pool heating systems are exempt from federal and most state incentives and rebates, the payback period is usually between one to two years. After the payback period, owners of solar pool heating systems can enjoy their solar heated pool for free!

Solar pool heating systems work much the same way as drainback solar domestic hot water systems. In the collector loop, the pool water is heated in the solar collectors. The pool pump will be turned on and the flow of the pool water will go through the panels when the collector temperature is greater than the measured pool temperature. A pool heating system generally doesn’t include a heat exchanger. When the pool panels are no longer hotter than the pool (or the maximum desired temperature is reached) the flow is no longer directed through the panels. The panels (with the assistance of a vacuum breaker) would then drain the fluid back into the pool. If a certain temperature is required then a back-up heater would be installed after the pool panels prior to the heated water reentering the pool.
If your home already is already utilizing a closed loop solar domestic hot water system, you may be able to integrate a solar pool heating system. A valve would be installed on the glycol mixture’s return line. This valve would be able to divert the heated glycol mixture to a second heat exchanger to heat pool water. A sensor and controller would be required to prioritize the two loads. The domestic hot water system would receive first priority. The heated glycol mixture would be diverted to the pool heating system, the second priority, only after the required temperature of the domestic hot water system had been met.
The above integration of a solar pool heating system into an existing http://www.solarhotusa.com/index.html may not be employed in an open loop system.