Case Study

Subject: Rigid 4x12 polypropylene solar panels installed in 2006 are failing

Location: Rancho Santa Fe, Southern California

History:

20) 4x12 Techno Solis pool heating solar panels were installed on a custom made aluminum rack in 2006. In the first year the entire bank of collectors had to be replaced due to a ďfactory defectĒ. Over the 5 years since, 25 of the solar panels were replaced under warranty.

In 5 years every single panel failed and had to be replaced and some had to be replaced twice! This involved cutting up the bad solar panel and mailing the corners to Florida where a replacement solar panel was shipped at the customerís cost. The warranty, as with all rigid panel warranties does not cover shipping or labor. Technically the warranty only covers manufacturing defects and systems installed to meet manufacturerís instructions which in turn requires meeting installation specifications which sometimes include a limit on pressure and temperature exposure. Thereís no way to stop a black thing in the sun from getting really hot in mid summer with the pool up to temperature and solar stagnating. Solar design to work around pressure is not included in any manufacturerís instructions except those of Hot Sun Industries Inc..

In 2012, the customer, having exhausted the generosity of the manufacturer and its representatives and with no remedy in sight, asked Hot Sun Industries Inc. of Poway California to help. Immediately Hot Sun looked at pressure. This is what we do. Pressure is what solar mechanical design is all about. PRESSURE IS THE KEY TO A SUCCESSFUL SOLAR IMPLEMENTATION. We took on this challenge partially because we needed to demonstrate this most basic cause and effect. Understanding the issue comes first and is relatively straightforward but knowing what to do about it in some cases is tricky. This is why we address this issue on all our installations up front.

DETAILS

The bottom of the solar panels are 19 feet below pool level. Hot Sun VP Mike Adamcik checked the elevation difference with a surveyorís tool. What this means is that with the pump off and everything full of water the head of water alone causes 19 feet of head or pressure on the solar panels. 19 feet equals 8.2 psi (0.433psi=1foot). We generally consider 8 psi our limit. We donít want to see a solar system with our name on it operating over 8 psi otherwise weíre just not comfortable with long term effects of aging and weathering and heat in combination with that much pressure. We have several Powerstrip systems operating at 13 psi and one cycles between 13 and 19 psi 500 times a day with an older in-floor cleaning system downstream of it. Weíve had some problems with that system and itís allowed us to improve our adhesives and materials. Weíre OK up at that pressure. We just donít think its where you want to be if you can avoid it and you can avoid it (usually). In this case we should be able to limit the dynamic component of pressure (the pressure caused by flow restrictions that will add to the static 8 psi). We installed a pressure gage 5 feet below pool level on the pipe to solar. We got a reading of 13-16 psi depending on which mode the Pentair VF pool circulating pump was in. That translates to 19-22 psi at the solar panels because the solar panels are 14 feet or 6psi lower in elevation.

The Pentair VF pool pump introduces another variable in modern day solar application. Variable speed(VS) and variable flow (VF) pumps are great because pool circulating systems are now run at 40 gpm instead of 140. We no longer have outrageous electricity costs and excessive pressure caused by forcing too much flow through too little pool piping. Tying solar in to those older pools (pre 2008) sometimes meant changing out pumps and worrying the vacuuming would be compromised. Sometimes we regulated pressure and returned regulated pressure to the pool via the spa jets or we asked the pool builder to add a separate pipe to the spa. They didnít understand why so they didnít do what we asked. Modifying pools to accommodate solar was never accepted as a standard practice because the biggest and best solar contractors ignored the need for anything but sending all the flow to solar when the sun shines. The major pool equipment suppliers and builders are also guilty of negligence in this regard. To be fair they didnít know because we never published case studies like this one to prove that pressure is a factor. People donít understand pressure. Solar had to be done by more than specialized mechanical engineering companies otherwise it would never gain the acceptance it has.

ANALYSIS:

So we have 8psi static pressure on the solar panels that we canít do anything about other than relocate the solar panels. We canít avoid the 8 psi and we shouldnít have to. The solar panels can do reasonably well under 8 psi for a long enough life. What we have here is 19-22 psi at the bottom of the solar panels. Thatís too much. No question about it.

Solar was plumbed upstream of a gas heater as depicted in this schematic but because of the VF pump running at such a low flow rate the gas heater safeties were not allowing the gas to fire so somebody had added some restriction just downstream of the gas heater to trick its safety circuit which is illegal according to the heater manufacturer but necessary to take advantage of the VF pump. This was all downstream of solar so it caused excess unnecessary pressure on solar. If the pump speed was turned up the restriction would increase somewhat exponentially. Variable speed and variable flow pumps introduce a whole new set of issues into pool mechanical design with respect to solar. Our solution was control. We had to build our own control system so we could get the solar failsafe and other features we needed to control gas heaters, variable speed pumps, chlorinators and solar together harmoniously and so we could watch these systems over time on the internet to make sure everything worked harmoniously together. But we didn't sell or install this control system or this solar system.

SOLUTION:

Our initial solution was simple. Donít put water through the gas heater when solar operates. The 3 way valve that chooses solar or not was re-plumbed so it chose solar or gas instead.

All the water either went through solar or all the water went through gas. The flows met up downstream before going to pool or spa. Now the only restriction downstream of solar is the piping to the pool and at 36gm (the flow setting of the VF pump) thereís no way we should have any dynamic pressure. The pressure on the pipe to solar (14 feet above solar panel elevation) dropped to 10 psi meaning there was now 16 psi on the solar panels. We measured 13-15psi right at the solar panels with a pressure gage. Techno Solis panels are rated at a much higher pressure than this so we had done what we could and we left the system at that. That was a year ago. It was a two hour service call for Hot Sun. It was 45 panel replacements and 10 shipments and 10 replacement efforts on the part of the solar industry and the manufacturer and customer, all unnecessary if all that needed to happen was the panel pressure dropped from 20 psi to 13-15 psi. Why donít our competitors want to recognize pressure as the culprit, the cause of stress that is the cause of failures? This is not a completely common situation. Usually solar systems are up on rooftops and pressures are lower and there are no major issues that canít be attributed to wear and tear, aging, UV degradation, raccoons, rats etc. It doesnít cost much to supply a new solar panel. Thereís only $18 in polypropylene in a rigid solar panel. Its cheaper to replace them freely under warranty at the customerís freight cost , than it is to assure against this kind of difficulty up front, the way Hot Sun does it. Note Techno Solis had been good about providing the warranty replacements. We stopped selling them due to the fact that shipping cost on warranty replacement was $300 per panel. You canít roll them up and UPS ship them. We didnít buy them by the container so we couldnít support warranties. Other rigid panel manufacturers like Aquatherm and Harter Industries were terrible with warranty excuses. They wouldnít even cough up for known and proven factory defects. Aquatherm in particular transfers all local warranty responsibility to the distributor (through a private label agreement) who makes a very small margin and canít afford to replace solar panels at no charge under warranty when this type of thing happens.

THE CALLBACK

Less than one year later we learned that 3 more solar panels had since failed. Back went Mike 5 more times trying to time weather and pump scheduling to see what was happening in terms of pressure. He surveyed the property to get the elevations and confirmed the various pressure readings. The pressure (at the bottom of the solar panels) was 13-15 psi when solar was operating depending on the operating mode. Due to the fact the solar panels are 80 feet away from the pump it was difficult to go back and forth reading panel pressure vs operating mode. He decided to install one of our SWIM PC monitoring systems and use it to monitor pressure over time. This proved rather interesting. We discovered that there were 4 distinct operating modes and pressures over the course of the day beginning with a high pressure first thing in the morning for about an hour.


January 1, 2013: Pressure at bottom of solar panels.

This one hour of high pressure on solar probably corresponds to a vacuuming (cleaning) cycle where the pump speed is higher. Then solar comes on automatically and operates at about 16psi (minus flow restriction from this pressure tapping location to the solar panels 80 feet away). Then at about 3pm the system switches over to spa mode to filter and heat up the spa. I'm speculating. We'll ask the customner to confirm. The pressure at the bottom of solar drops to about 10 psi at this time. Around midnight the system switches back to pool mode and the pressure on solar comes back to about 13 psi.

ANALYSIS PHASE 2:

The first question is why are we seeing 13-15 psi at the solar panels with solar on? There is only 8 psi worth of static head. This implies 5-7 psi downstream of solar and there's nothing downstream of solar except 2" pipe carrying 36gpm..........and the inlets to the pool. Could the inlets to the pool be plugged with plaster or debris or could they be overly restrictive? Sometimes pool builders think they need to restrict return line flow to create pressure so they get more flow?? We'll have to look carefully at those inlets. Could the pipe from solar back to the pool be plugged with gravel or dirt? Could the installer have been sloppy about debris? A pressure gage downstream of this solar pipe at the tie in will tell us if this extra pressure is before or after the solar return piping.

The second question is ,ĒWhy is solar seeing the pressure in cleaning mode?Ē Solar is off and fully isolated at this time by the return line check valve and the positive sealing motorized valve. The only way solar sees that pressure is if the check valve or the positive sealing motorized valve leaks. We didnít install this system. There is a common motorized valve used by many in the solar business. Its supplied by the big manufacturers and its called a solar valve. This is a regular 3 way valve with a small check valve built right into the spool.

The idea is that when solar is off water can drain down through this internal check valve emptying the plumbing and solar panels. You donít want water in the solar panels when it freezes in the case of rigid panels because they will freeze and burst and warranties donít cover that. They donít cover that stupid little internal check valve seizing up either by the way. Obviously (obvious to you if youíre understanding all this pressure talk) that internal check valve isnít going to let any water out of any solar panel if the solar panel is below pool level or if the system pressure (in feet of head) is higher than the height of the solar panel. We donít bother with the ďsolar valvesĒ. We use regular pool industry standard valves. They seal 100%. Maybe this is a solar valve and maybe the SLCV (stupid little internal check valve) is leaking. That would be ironic. The solar specialty valve is the cause of the solar specialty failure to the tune of 45 solar panels! Maybe the seals just failed. Maybe the installer removed the seals on purpose? Maybe itís the check valve on the return line that is leaking. Maybe solar was on when the pump was on the higher speed. If the SWIM PC was the solar controller weíd know that but we think its pretty safe to say solar wasnít on. We see this same pattern for the 5 days we logged data and this is mid winter and the days werenít all sunny days.

MORE ANALYSIS - PREVENTION AND FAILSAFING.

In mid summer its likely solar could be on during a cleaning cycle. This cleaning cycle needs to be timed further away from a time solar could operate. If solar and cleaning cycle happened together the solar pressure would be even higher, probably much higher due to the much higher flows through the lengthy solar piping. . These are major issues introduced by the advent of variable speed pumps. Now instead of an issue with a 2HP pump overpressuring solar we have the issue of a pump that could operate at 3 HP and it could be scheduled to happen any time and there is no solar failsafe provision built into any solar control system other than our SWIM PC. We canít replace the Intellitouch here with a SWIM PC because the Intellitouch is a full blown and expensive and well developed pool automation system. Our SWIM PC is not at that level. Its just an online solar and VS pump controller with the failsafe and energy logging and transparency every solar heater needs. Weíre in conflict with the fact the pool industry doesnít accept that they need this level of capability in a simple backyard pool. This situation is the end result and its becoming more and more common as mysterious solar panel failures start to show up more and more now that variable speed pumps have been implemented extensively for 4 years now.

Rigid solar panels, in particular Techno Solis aka Vortex (if you buy them from Solar Direct) are not capable of handling much pressure. 20 psi for an hour a day in the morning when it isnít hot is enough to kill them. Its heat and pressure in combination that is the real killer. This is the middle of winter. Thereís no heat component to these failures. 20 psi in the winter morning is probably like 5 psi in the middle of a sunny day, maybe less, maybe less than the 8 psi rule of thumb we use in design.

We should be able to operate solar at the 8 psi static plus only about 2 psi dynamic. Why is there an extra 5 psi in restriction in all this 2Ē pipe at only 36GPM? At the tie in 5 feet below the top level of the pool weíre seeing 10 psi on the gage and that corresponds to the 10 psi we monitored midday with solar on in spa mode or pool mode. At this time the solar panels should have been at 16 psi and we measured them at 13-15 psi. Thatís pretty close given that we are using regular pressure gages at the solar panel location. It looks like there could be a 3 psi max difference caused by restriction in the pipe to solar. If there was another 3 or 4 psi restriction coming back from solar and to the pool then we could account for the full 13-15 psi reading at the solar panels. There could be air pockets in the piping to and from solar. There could be blockage as mentioned earlier. WE could open the pipes up at the bottom of the slope where the solar panels are and try to flush them with the full flow of the VF pump. First we'll do the pressure test to see if the restriction is in the pool plumbing downstream of everything exccept the actual inlets to the pool. We've seen plaster (from the initial pool installation) clogged inlets before.

The primary culprit however, is the 20 psi on solar when the system is in cleaning mode. We should address this as the first step. Ideally we need to devise a way to failsafe the panels from this pressure. In fact all solar systems with variable speed or variable flow pumps need pressure protection. If our SWIM PC is the controller it forces a speed appropriate for solar when solar is on. When solar is off other speeds can be programmed. If pressure goes over a setpoint the SWIM PC can be programmed to react with an alarm output of anything we choose to implement. We could configure the SWIM PC as a pressure alarm but that is expensive as a stand alone solution doing nothing but alarming us if a seal fails. If we can get rid of the restriction to flow we won't see as much of a pressure spike in cleaning mode even if a seal fails.

With the advanced features of the Intellitouch youíd think that solar failsafes would be standard features but that isnít the case again because the industry isnít made up of mechanical engineering specialty companies like Hot Sun. Its made up of contractors and contractors need to have a standard to work from. Engineers need to create those standards but engineers donít deal with residential solar installations. In commercial applications they do but they defer to the body of knowledge available to them and that body of knowledge is polluted with the incorrect thinking that pressure is a non issue in solar design.

One final note is that the back of the solar panels are exposed to wind. That doubles the wind loss. Wind is what takes energy away. Sun is what puts energy in. Its worth sheeting in the back of the rack if these panels are to stay.

PROPOSAL:

Replacing the 3 way valve seals and adding an extra check valve on the return side will further ensure solar isisolated when speeds are higher for cleaning.

it is important that higher speed functions (cleaning) be programmed to occur well away from hours solar may be active.

We'll check the pressure downstream of solar equipment and the new tie in to see if we have a problem with clogged inlets or pool piping.

CONCLUSION:

These rigid solar panels can not handle 20psi short term for short times and not in combination with temperature extremes. Weíd expect the failure rate to be much higher at a lower pressure with longer exposure at higher temperature.

Note that Fafco (another rigid panel manufacturer) solar panels have much smaller flow core passages. In theory this greatly reduces the stress on the material for any given pressure. The specification for a Fafco Sunsaver solar panel is a maximum intermittent pressure of 5 psi at 212F. Solar panels can get that hot although more typical high temperatures are more like 185F. We think Fafco is being responsible with this specification. They should train their dealers to understand this specification and how to meet it. They may get the specification right but their field personnel arenít trained to implement them and situations like this can result. If no-one understands the problem how can anyone be expected to solve it?

What we have here is a situation weíve run into many times with almost every rigid solar panel on the market. Solar panels have to be married to pool mechanical systems with intelligent design and expert knowledge. We have yet to learn of a competitor that does that. Hot Sun is unique in this regard.

If the pool problems are solved we should be able to operate solar close to only 8psi and reduce the occurance of solar panel splits due to pressure. The manufacturer believes at its own discretion that the failures are due to manufacturing defects. I guess their idea of a defect is a weakness in the technology they promote. If they understood that their competitors solar panels were no more pressure tolerant I wonder if they wouldn't have to feel so obliged to have to replace solar panels on an ongoing basis. More elite brand name manufacturers certainly aren't replacing solar panels endlessly without finding something else to blame the issues on. Kudos to Techno Solis for standing behind their product as long as a customer is willing to pay $300 to ship a new one every few weeks.

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