I’ve recently finished installation of solar panels for my pool, in which I’m trying to troubleshoot my flowrate/performance. This was a DIY project that I started last fall, knowing that it will undoubtedly be less efficient than a commercial system (no going back now!).
My collector panels are made up of ½” black poly-tubing coiled on a 4’ x 4’ piece of black painted plywood. I have 12 panels, each with approximately 200 ft of poly-tubing. They are mounted on a 2 story roof (approx. 25’ high). I am running the panels in parallel, two rows of 6 panels. Panels are facing directly east in southern Michigan --unfortunately we don’t have a south facing roof, and I could not convince my wife to let me install them facing the west (towards the road).
Volume of our pool is approx. 23K gallons, with supply/return lines of 1.5” diameter. The mounting location is approximately 60’ from my equipment pad (35’ horizontal, 25’ vertical). I utilized 2” PVC from the 3-way diverter valve up to the panel headers, which reduces to a 1.5” header connecting to the ½” tubing at the panels. I am using the Pentair SolarTouch controller. I’ve attached several pics of my setup for reference.
I took suction-side and discharge-side pressure readings on my pump last year before installing the panels, which allowed me to estimate 50 feet of TDH, and 62GPM from the pump curve. My pump is a Sta-Rite Duraglas 1hp (Model: P2Ra5E-181L). My filter is a Hayward EC-65 (DE). Filter pressure is typically 8 psi when solar is off.
During normal operation, I’ve been diverting 75% of the water to the panels with the other 25% direct return to the pool. I generally see a 10 psi increase in filter pressure with solar on (reading is ~18 psi), which makes sense given the 25’ elevation.
My problem is that I’m having trouble getting adequate flow. Here’s a summary of what I’ve observed:
•Normal Operation - All 12 solar panels open; divert 75% water to solar panels. RESULT: Average combined flow rate from the 12 panels is 21 gpm (i.e. <2gpm per panel). Measured pressure at the supply header on the roof is 3 psi –does a 15 psi pressure drop from filter to roof seem excessive?
•All 12 solar panels open, divert 100% to the panels. RESULT: Average combined flow rate of 23.5 gpm from the panels.
•6 panels closed, 75% diverted to solar. RESULT: Average of 3gpm from each of the 6 open panels.
•11 panels closed, 75% diverted to solar. RESULT: 4 gpm from the 1 open panel.
•All 12 solar panels open; divert <75% water to solar panels. RESULT: Water unable to make it through the panels back to the pool.
At this point, in order to increase flow I assume I need either: A) Larger pump, or B) Booster pump. Any recommendation as to which route is better, or if there is any other trouble-shooting advice? I've seen many other posts indicating that similar sized pumps (0.75hp, 1hp) have been adequate for their solar installations on 2-story houses --not sure if the coil design is the contributing factor for my issue?
Other notes that may or may not be relevant:
•At both of the coil discharge headers, I can feel vacuum being pulled when I disconnect a coil. Gravity must be helping pull water through panels.
•When diverting at least 75% to the panels, I can tell just by feeling return jets at the pool that I’m getting less flow/circulation.
Here are the results on a very small-sample size of panel performance thus far:
We had an 80% sunny day yesterday, outdoor temp in the morning was low-70s with temps peaking at 83F in the afternoon. Pool temp was 68F at 6AM, and 73F at 4PM. Given the warm temps and large quantity of sun, I was hoping for a higher increase by the end of the day. Note: For reference, neighbor who has similar size pool without solar cover had water temp of 72F by the end of yesterday.