Economike, seems you and I are on the same page, I would also like to add to your comments that according to reports I've read and seen, that in an open pond system, light will usually not penetrate more than an inch or two below the surface depending on the saturation of algae in the water. BEHL is using 9" tubes IIRC and thus only the TOP HALF of the tube is directly exposed to the light of the sun as the bottom half is of course shielded by the top, and based on light penetrating just a few inches deep into the tube the BEHL system is left with approximately 60% of the volume of their tube receiving almost no sunlight at all. So far, all of the vertical systems I have seen can get 100% penetration through their bladders. Meaning if you put the bladder between you and the sun, you can still see light penetrating through. As long as light can be seen, you can claim 100% efficiency on your system exposure. BEHL cannot make that claim.