Wednesday, November 30, 2022

Floatovoltaics, an efficient use of an under-utilized resource

Here's interesting proposition: why not cover the world's irrigation and other canals with solar panels (and maybe also reservoirs, aqueducts, waste water treatment ponds, and other bodies of water with little or no particular tourist, environmental or cultural value, while we are about it)?

Solar panels can be installed on rooftops, on farmland, even on roadways, but non-controversial space for siting panels is (and will become even more so) an issue. Canals are an under-utilized alternative, and there are some compelling reasons why it would make a lot of sense. Welcome to the world of floating solar panels, or "floatovoltaics".

Apparently (and I certainly didn't know this), the current design of solar panels works most efficiently at temperatures under 25°C. That's fine in Canada (most of the time), but not so much in India, the Middle East and California, and as the world continues to heat up, this will become increasingly problematic. Locating solar panels over water can help cool them, and lead to increases in efficiency of 15% plus.

There are a lot of other advantages too. In addition to utilizing otherwise unused surface area (thereby saving valuable land that can be used for other purposes), water bodies like canals and reservoirs are generally calm, relatively easy to access, and unlikely to host much in the way of sensitive wildlife or plant life. Solar farms on existing water infrastructure can be installed quickly and more cheaply, with less red tape than on land. 

Covering canals and reservoirs with solar panels also significantly reduces water loss through evaporation (up to 82%), which, in our warming and water-scarce world, is an increasingly acute problem, particularly in hot regions. The quality of the water can also be improved, as the panels block sunlight and reduce weed growth, algae blooms and harmful microorganisms, reducing maintenance costs substantially.

The benefits in potential power production are not to be sneezed at. By some estimates, covering just 10% of the world's hydro dams with solar panels could generate 4,000 gigawatts, equivalent to the electricity generation of all the fossil fuel plants in the world! Countries like Brazil and Canada need only cover 5% of their reservoirs to meet their electricity needs.

Yes, there are some challenges. Wind speed, water current, and the direction of the sun all have to be taken into account, especially on winding, meandering canals. Canals also need to be of the right width, not too wide to make installation difficult, nor too narrow to make the installation economically worthwhile. Maintenance access needs to be ensured, both for periodic cleaning of the panels, and for monitoring potential silt build-up in the water below. Canal-top solar panels can be 10-15% more expensive to install than their land-based counterparts, due to the need for things like rust-proofed galvanized supports, anchors and mooring set-ups, etc.

Taking all that into account, though, water-based systems still tend to have a higher net presence value than land-based systems, of the order of 20-50% more. Payback times are a pretty reasonable 8 years.

Some large-scale canal-top solar farms are already under way in Gujurat, India and in California, USA, and the results look very promising so far. A major University of California project (Project Nexus) is keeping more detailed stats on everything from water usage, power production, environmental factors, etc. 

So, saving water, utilizing under-used space, producing clean energy? What's not to like?

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