Solar Panel Questions

[bobby1017]

So, instead of saying that one panel is better than the other, I think there are enough people who've written here and on other threads saying that Heliocol panels do what they expect them to and are happy with them without significant complaints, so that's encouraging. I know people are happy with Aquatherm Ecosun too.

The key is how panels perform in sub-optimal conditions (cloudy, windy, cold ambient temperatures, etc.) .

You are right - I'm sure that many people have Heliocol systems and are satisfied with the results. It all depends on how and when you use your pool and what are expectations are.

My heliocol panels are working good, the pool is at 78 now and rising after a few 60'ish, windy days. I dont know how the fafco would have done, but even though it was sunny a cool wind kept them from coming on at all one day. There have been days with a cool ambient temp, no wind, sunny that they have worked well, raising the temp, but the wind made a noticable difference.

 

[haz]

bobby1017, are you saying that the Heliocol didn't work well on the sunny but cool-windy day?

I think that's one of the issues that people point to but nobody quantifies: we expect the Heliocol with its separate tubes to have more loss of heat if wind is passing over the tubes vs. the more solid panels like Fafco or Aquatherm. But there definitely doesn't seem to be any data saying how they actually do with wind, and I haven't read anything anecdotal like people saying their pool wasn't heating sufficiently with Heliocol on windy days. We just know that under ideal test lab conditions, the Heliocol are around 5% less efficient than e.g. Aquatherm Ecosun. In most circumstances, this wouldn't be noticeable and could be corrected for by adding another panel, if desired.

 

[FloridaSolarPro]

But there definitely doesn't seem to be any data saying how they actually do with wind

The reason I presume is that wind is variable (direction and strength). There are just too many variables to look at to get any real data that can be of use. No matter what, you will be looking at data under a set of circumstances, and there would be too many comparison points to be manageable.

The real test is real-world. If you set up a test facility with side-by-side conditions with all other variables held as closely as possible, you would have a far better set of data upon which to rely. Recording actual pool temperature over time in relation to other factors like wind, sun, temperature, etc, would provide some useful data (which we do not have as far as I know). But even then, you would have to parse the results. For example, if one panel brand works better at a different flow rate, that would throw off any real comparison. The tests would undoubtedly be refuted on multiple bases by the "loser" in the tests.

Absent real-world hard data, we are left to common sense and anecdotes when evaluating performance. Larger headers, more flow (to an extent), more even flow, surface area presented to the sun, and surface exposure to wind are the main common sense components that I can think of.

We just know that under ideal test lab conditions, the Heliocol are around 5% less efficient than e.g. Aquatherm Ecosun.

And about 11% less efficient than FAFCO, but as you mentioned, that's under just one set of test conditions. Heliocol claims to be the slight winner under SRCC Category A (when you don't even need heat in most cases), but loses badly in SRCC Category B (more typical of the solar pool heating season).

But remember, we're talking about panel performance, not system performance. I hate to harp on this, but the marketing folks want to hammer home the panel ratings because makes for easy comparisons, but the more important factor in my opinion is how the whole system works. For example, one manufacturer's panels do not need opposite end feed and returns in single banks up to 12 panels per the manufacturer's installation manual - the panels have more balanced flow due to the subheader. Is that a factor in determining total system performance. You bet! Balanced flow is critical because too much or too little flow in any given tube results in subpar performance. Manufacturers do have curves that show panel performance under various flow rates for given test conditions - they want and need to know how to maximize the performance of their panels, and all have recommended flow rates on datasheets.

 

[bobby1017]

bobby1017, are you saying that the Heliocol didn't work well on the sunny but cool-windy day?

Yes, that was my feeling, the wind blew away thy heat. My solar system as a whole works good although I have no comparison. I will usually gain approx 4 / 5 deg over the course of the day, then seem to loose about 4 every night, overall the temp will increase about 1.5 degree's each day with sunny conditions. I have 325 sq feet of panels with a direct southern exposure, getting sun from approx 9 am untill 6 pm. I expect the pool to reach 80 by friday, and last year it dropped below 80 in late October.

 

[Isaac-1]

On the topic of solar panel efficiency there are a couple of things that tend to get lost in these conversations:

1, it is not the only metric that should be used in selection, there are also non heat performance considerations, expected life, warranty, etc.

2, often a more important metric is $$$ per btu, if one panel cost $250 and another one that produces 10% more btu's costs $300, if roof space is available it would often make more sense to add an additional cheaper panel. As at the end of the day so to speak it is all about the system totals, the same issue applies to panels that have 3 inch spacing vs 6 inch, but this issue is more about if you are working in limited roof area.

 

[haz]

2, often a more important metric is $$$ per btu

That's why I was saying that in my case Heliocol seems to be a better route to me than my Aquatherm Ecosun installer. 435 ft2 of Aquatherm is at least equivalent to 450 ft2 of Heliocol. I think I should be able to get 500 ft2 of Heliocol for less than 435 ft2 of Aquatherm. The Aquatherm would be 86% of the area of the Heliocol, so the decreased efficiency of Heliocol under windy conditions would have to cause more than 9% less efficiency versus Aquatherm (100%-86%-5%) to be worth getting the Aquatherm instead (Note that the math is approximate). I would not even start to be able to calculate how system performance differs between these two, so I am just calculating panel performance, and I assume the system performance is similar enough between the panel brands.

The Aquatherm do seem to have good quality straps - stainless steel, per the installer, covered with a waterproof-looking coat. As we know, the Heliocol does not need to have the straps to be Florida hurricane compliant.

In regards to fafcosolar's comments - yes, the Fafco may be rated 11% higher than Heliocol. However, Fafco has no installers in the South Florida area, which per a Fafco corporate guy I spoke to, is the 1st or 2nd biggest market for pools in the country. This has been the case for months, probably over a year. Why would this be? Aquatherm has a design that allows some air flow to pass through, which helps with its wind rating. Heliocol allows even more, which hurts its BTU/ft2 and helps its wind rating. Maybe Fafco's panels are more solid, improving efficiency but making them less than ideal for a potentially high-wind/hurricane area like South Florida? As Isaac-1 mentioned

1, it is not the only metric that should be used in selection, there are also non heat performance considerations, expected life, warranty, etc.

Maybe there's some other factor that made them less competitive in South Florida? Maybe they have a great product, but corporate has just been lax in finding a good installer in the area, which can be a haven for shady contractors?

Bottom line is that given I'd like professionally installed panels, Fafco isn't an option for me.

 

[FloridaSolarPro]

The issue is not about what is more suitable for a high wind situation. It's all code nonsense. Again, speaking from hurricane experience... There is no discernible difference in the results between separated tube and full body panels in a hurricane. In most cases where the panels needed replacement, the winds were catastrophic. All panel types get damaged equally from flying debris. In most cases where catastrophic roof damage occurs, the panels are toast anyway. Insurance steps in and covers the replacement cost.

Regarding the Aquatherm straps, I'll refrain from posting pictures of the "waterproof-looking coat" having rotted away leaving exposed metal rubbing on panels. Are they strong? Yes. So is 1600# tensile strength Dacron. Straps, by far, are not the weakest point in any mounting system.

I wish they had someone to serve you in South Florida (to be clear, Southeast Florida). We're doing well over here in Southwest Florida, but we can only go as far east as Collier County/Everglades. Miami is a potentially lucrative but difficult market, and FAFCO corporate only selects highly qualified individuals to represent the brand. Stay tuned...

 

[Isaac-1]

Jason, I was wondering if you as a professional in the field could comment on the various strap material options, it seems that there are a variety out there ranging from coated stainless steel (exact coating material and grade and thickness of stainless varies) along with various dacron and other synthetic strap materials. To an outsider like me it seems that a good quality coated stainless steel strap would work best as the synthetics are prone to needing periodic retentioning.

Ike

 

[FloridaSolarPro]

Jason, I was wondering if you as a professional in the field could comment on the various strap material options, it seems that there are a variety out there ranging from coated stainless steel (exact coating material and grade and thickness of stainless varies) along with various dacron and other synthetic strap materials. To an outsider like me it seems that a good quality coated stainless steel strap would work best as the synthetics are prone to needing periodic retentioning.

Ike

Dacron straps do stretch a bit, but not enough to require retensioning. Stainless steel straps do not have the same coefficient of thermal expansion as a roof, and do not stretch, so presumably this causes stress on the attachment points, but there is only minimal evidence to suggest this is problematic. Expansion and contraction are not an issue with synthetic fiber materials that stretch. Any coated metal strap is fine... until the coating comes off and sharp strap edges make contact with the panel. Don't let anyone tell you it doesn't happen. I can provide dozens of pictures of real systems, some of which are just a few years old. Again, strength is not an issue because the tensile strength of all of the strap materials typically used well exceeds any possible loads they will experience. Dacron straps typically last the lifetime of the panel, but can experience some drying out. Fortunately, it's not costly to replace. One downside of stainless steel straps is that they are only held between panels with butterfly type brackets. They are not secured in place. Dacron straps can be positively secured between each panel with a cap and base. This means that the tension is not carried across the whole array to just two attachment points at the ends. This virtually eliminates any issues with lost tension. On that note, you don't really want much tension anyway, given the stress that tension can pass on to attachment points. The straps are just there to prevent uplift (in the unlikely/uncommon event of uplift). Even with the potential problems with each strap type, the straps should not be a major determining factor in your selection of panel, system, or dealer. The vast majority of systems have no problems with straps in their lifetime.

 

[Beer tunnel]

Anyone care to share their technique of how to locate the trusses under the shingles and plywood? These systems all seem pretty simple to self install, I just want to make sure I'm screwing into more than plywood...


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