> The shade supports don't have to hold up solar panels: Shade supports cost less.
If you look at the photos, the solar panels are mounted directly on the supports. If you wanted a simple shade for the canal, you would have to mount some kind of roof on the supports instead of the solar panels. Granted, the solar panels probably weigh a bit more than simple sheet metal, but that is probably more than made up for by the benefit of generating power.
PV itself (not the inverters etc., the panels) is really really cheap.
Tarp is about the only opaque covering I've found that's cheaper than PV, per square meter.
However, even for a balcony PV system the frame is about 25% the price of the panel, and balcony systems are tiny frames; I don't want to even guess about those huge steel I-beams and concrete pads. For big things like this, the cost of the frame is unlikely to go away because you need to care about wind load.
That really leaves maintenance costs (how often do you need to replace the tarp?) and revenue (PV makes money, a tarp does not).
Based on my experience in NM (higher elevation, similar insolation), the expected life of tarp-like materials in open sunshine here would be 2-3 years.
Sunshade material could be more like 5-8 years, but is significantly more expensive.
If you look at the photos, the solar panels are mounted directly on the supports. If you wanted a simple shade for the canal, you would have to mount some kind of roof on the supports instead of the solar panels. Granted, the solar panels probably weigh a bit more than simple sheet metal, but that is probably more than made up for by the benefit of generating power.