Monitoring my Solar Heating Panels

[wayner]

Last year I had evacuated tube solar panels installed to heat my pool. This year I just started using a Raspberry Pi with two DS18B20 temperature sensors to measure the temperature of the pipes that carry the water to and from my panels. These are being logged to a database and I can then run reports from the database. The temperatures aren't exactly the temperature of the water in the pool, but seeing the delta between the two shows how much the water is being heated by the panels.

Here is an example of what the data looks like. My system normally shuts down from about 10pm to 5 am - but I kept in running overnight on May 23/24 to heat it up using the gas heater (the timer did shut it off at 10 but I turned it on an hour later - you can see a notch down in the chart that shows this). But you can clearly see when the pump shuts down for the night on May 22 and 24.

I will post more info regarding this on github if anyone is interested. I am also working on a floating solar/battery powered Raspberry Pi PC that will measure temps in my pool and perhaps pH and ORP (a proxy for chlorine?). But those probes, such as the ones from Atlas Scientific, are around $100 each all-in.

 

[JasonLion]

I really really don't recommend ORP. It has only a lose relationship with FC levels, one that changes over time in unpredictable ways.

 

[wayner]

Ok, that saves me $100 - is there any way to automatically read FC levels?

 

[JasonLion]

There isn't anything reliable and affordable to read FC. There are some over $1000 probes that need to be replaced frequently, but that doesn't seem practical.

 

[Isaac-1]

I am not sure what your goal is here other than gathering statistics, and to get much out of that it would help to know how much sunlight is hitting the panel as well as wind speed and humidity.

 

[wayner]

I am really just trying to get a better handle on how much heat the solar panels are putting into the pool, and optimizing when to run the pump. And it is also a project to play with the hardware and software of my Raspberry Pis. Shouldn't the temperature delta times the hours give me a good idea of how much heat is being put into the pool.

What would the humidity tell me? And even if I could determine how much sunlight is hitting the panel, what would that tell me?

 

[Isaac-1]

What you have now would only provide information on BTU's added to the pool if you also knew actual flow which will change with how dirty your filter is along with other things. Solar input along with wind and humidity and air temperature could be used to calculate wind losses at the panels and evaporative heat loss at the pool.