Heatsink on back of panels?

[Naptown]

I can see this as being more advantageous for pool heating where temps are lower and large areas of collector area are needed.
Domestic hot water will have almost the same high temperature in the afternoons as the cells or little temp reduction.

[PNjunction]

..I wouldn't give up on it that quickly. Our first goal was to see how much PV area was needed to approximate a typical SDHW system in performance..

Ok - I guess if I had a pool, I'd try a passive solar pool cover first. At the very least, this should be a requirement for your system even in winter. The one my friend has looks like a huge sheet of large bubble-wrap packing.

Maybe the pool guys might dig it - for me it was just a thought experiment for quickie DIY passive cooling.