Bedichek Pool and Solar Panel Temperatures |
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We have a pool which is warm enough to swim in from late June to early September. We use a pool cover, which keeps the pool much warmer than it would be otherwise, and it saves water. However, we would like the pool to be warm enough, which means above 82F, more of the year. It would be nice to be able to use the pool as early as late April and as late as late September. One option that pool owners sometimes use is to install a gas-fired pool heater. However, using natural gas to heat a pool seems like a waste. Also, one must remember to turn on the heater long enough in advance to get the pool warm. Solar power is a more attractive option. However, a professionally installed system would cost around $8,000. That's a lot of money to not have the guilt of burning natural gas and to not have to plan in advance.
I have cobbled together a solar heating system for my pool for about $600. It consists of four 4'x20' solar hot water panels, flexible hoses, a pump, and some control electronics. I bought the panels used from a neighbor for $200 total. The pump is a $40 sump pump that I put in the shallow end of the pool. The hose is mostly 7/8" ID black dishwasher output hose. I use a Labjack U12 connected to a small Linux system to measure the temperatures. I've had fun putting this all together and watching the pool get warmer.
The temperature sensors are based on a National Instruments part which generates a voltage that is linear with temperature. This makes it easy to convert the sensor's output voltage into temperature. There are three sensors. One is in the pool, one is in one of the panels on the roof, and one measures the hot water coming from the panels, just before it goes into the pool.
I also have a small photovoltaic panel on the roof, next to the four hot water panels, which charges a pair of sealed lead acid batteries. This PV system is completely separate from the hot water system. However, the charging current is a measure of the sunight hitting the roof with the hot water panels. The PV panel I bought at a flea market years ago. The batteries it charges are surplus from the alarm system that our house had when we moved in. In the event of a power failure, we could use them to power some small appiances for a short time, using a power inverter that we also had surplus from an earlier effort.
gnuplot script for generating the graphs
C Source code for the program that reads the temperatures
Crontab(1) for my system, which shows how 'solar' is invoked
In November, I added a pressure sensor to the pool filter. I also removed the Polaris pump timer and replaced it with a relay. In doing this, I also rewired the junction box near the pool pump. Here are the new wire connections: