Do practitioners see merit in the irrigation plus solar opportunity?

I do think that there is merit is taking a serious look at covering bodies of water, including irrigation canals, with solar panels.  Studies show that covering bodies of water with solar panels can have a dramatic effect on evaporation, limit pollution to the water, and reduce chemical contamination caused by sunlight's interaction with water.  Many drinking water reservoirs have adopted the idea of placing floating plastic balls on the water to overcome these various issues.  If one thinks of this idea as a classic utility scale solar grid tied project opportunity, there are challenges to having this concept be successful from an economic perspective.  Instead, if the design is conceived of as a self-supporting micro-grid opportunity to support the numerous electrical needs that irrigation channels, and reservoirs have along with the ability to support immediately adjacent properties and their electricity needs, not to mention the significant cost reduction due to reduced evaporation, and reduced water treatment that open water sources present, the economics shift and make this an attractive economic proposition. 

A major portion of all water utility district budgets is for payment of electricity. The amounts that water utility entities pay for electricity in major urban areas is astounding. Technically, water is a free resource. The cost associated with bringing water to agricultural areas, and to domestic drinking water consumers is based on paying for the physical infrastructure to get it there, for water treatment to provide safe water, and mostly for electricity to get it to where it is going. An investment in a solid long term renewable energy solution for water utilities offers the opportunity to keep the cost of water reasonable.

To implement this idea, there does need to be a long overdue rethinking of the role of electric utilities and their associated infrastructure (e.g., not all electricity needs to be delivered through the grid), and water utilities need to be open to implementing renewable energy solutions supported by power purchase agreements that provide long term low cost electricity to the points where it is needed. Renewable energy solutions with adequate energy storage for irrigation canals, and adjacent customers should be thought of as a behind the meter solution that avoids interaction with the energy regulatory environment that is so wedded to the status quo.

Our nation's domestic water infrastructure uses a huge amount of electricity.  With careful thinking and action, those that manage our water infrastructure could lead the way to the move away from non-renewable energy sources for the benefit of all.

Unfortunately, I think that using PV to reduce evaporation on irrigation canals (or reservoirs) is another of those great ideas that is ultimately limited to niche applications due to the economic and engineering constraints of utility-scale solar.   Floating PV (or another form of custom racking that can provide shade) will be more expensive to integrate and operate than a "standard" PV project; for the the economics to pan out, the water resource needs to be in close proximity to existing electric transmission resources.   

At a high level, in addition to the basic challenges of working on/around water vs land, I would imagine that the shape of a canal would require unique string configurations.  This can be done with microinverters or smaller central inverters...but both of these solutions would reduce conversion efficiency and increase costs.  Beyond that, "interconnection" ( ie the availability of transmission) is one of the major limiting factors for all PV; while installing an array on an existing water resource solves the landman portion of the "siting" challenge, in order for the power to be useful, there needs to be a cost-effective pathway to flow to the grid.  This would be particularly challenging for irrigation, as these canals are hundreds of miles long...and power is subject to I2R line-losses that multiply as distance (or "R," resistance) increases. 

I do think that there are niche applications however...specifically, pumping stations along an irrigation canal might already have the right infrastructure in place...