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Your collector seems to warm (130°F), you lose a part of collected energy before it goes back to your pool. A solution could be to augment water flowrate. It is a common mistake to want hot water at the output. Look at this chart: https://coropool.wordpress.com/2016/07/11/understandind-solar-efficiency-and-loses/
We tried different glues and configurations. It take more than one year of work to finally find a solution and without glue (cheaper and last longer). We are writing a tutorial, you will be surprise how it is easy to do. Subscribe to our newsletter to receive updates.
Flow rate of the full circuit (in 2" pipe). Then there is then a formula that give you the power captured into water.We are working on a coroplast based solar heater (simpler, cheaper and more efficiency than tubes). Today we produced more than 600W of power with only one square meter!Subscribe here to get updates: https://coropool.wordpress.com
Could you post flowrate and input/output temperature, so we could calculate power? I doubt this configuration is efficient because the small surface area (sun is 1000 W/m2) and plastic is a poor heat conductor.