haz said:
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.
haz said:
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.