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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.

That sounds like a huge maintenance headache.

A Concrete slab is usually even cheaper.

not if you want to suspend it above the water.

Tarp, and pitch it across the canal like how you might do a hammock - you just need two anchor points on each side (or 4, at most).

We’re discussing permanent cover. A tarp barely lasts a year (or 3 if using very heavy duty fabric).