Floatovoltaics, the cute portmanteau adopted by floating photovoltaic (PV) solar power systems, have been around in idea and implementation for many years, but whenever they are discussed they elicit interestingly strong reactions. Those in favor of floating solar argue that it might be an ingenious solution to the need to expand the availability of clean energy across the world, while those who are skeptical scoff at the idea that the added complexity can really deliver results or move the needle on the world’s massive (and growing) energy needs.

I always sort of assumed that floatovoltaics were somewhat akin to the futuristic idea to simply replace road pavement or sidewalk space with solar panels. For these road-based solar solutions, the idea sounded OK in principle and would sound obvious to those who were outside of the industry, perhaps asking “why isn’t this a thing!?” over a couple of beers, but the moment you dug into the science, the economics, and the practical numbers it obviously fell apart as an unrealistic solution (albeit one that sounded really cool and Jetsons-like). For floating solar, I assumed that these installations were intriguing and a clever way to find new areas for much-needed solar energy, but that they were too niche and they represented a classic ‘solution in search of a problem.’

Recently, however, I was compelled to do some deeper digging into the idea of floating solar. And as always, I thought that rather than keep that research to myself I should write up my findings. So without further ado…







Floating Solar…What Is It?

Well, the name kind of tells you the basics. But I’ll still let an official scientific publication (in this case, the Texas Water Journal), explain it clearly:

“The concept of floating solar is simple: PV panels (like those used for traditional terrestrial systems) that float on water bodies. Solar PV plants use the same technologies as traditional ground-mounted PV plants.”

While you may be used to seeing solar panels on rooftops or even in empty fields, harnessing the natural energy of the sun’s rays, floating solar takes that identical technology to the water-energy nexus, allowing solar power to be generated by the solar radiance that would otherwise strike bodies of water.

OK, What Problems Does It Solve?

You may hear that and have the same thought as me: sounds cool, but is that really useful? When you dig into it, it turns out that there are several operational advantages, opportunities for systematic efficiency, and underrecognized problems that floating solar can solve.

Utilizing Unused Space & Harnessing Economics of Land Prices

First, one of the most beneficial aspects of floating solar comes from placing them on bodies of water that were previously unused or even unusable for anything worthwhile. These bodies of water are the aquatic equivalent of brownfields: water that is man-made (meaning ecosystem disruption is less), inland, and calm.

A great use case of this type of otherwise unused body of water is the reservoir behind dams used for hydropower. Not only does this placement get PV panels placed in areas where the physical footprint is cheap (since the water would remain empty otherwise), but by co-locating the solar installation with hydropower generation the solar panels are able to optimize operational and cost efficiencies by simply tapping into the existing energy transmission infrastructure (not to mention the reduced transmission losses from being located right on-site already). Even better, if floatovoltaics are sited on the water of pumped hydropower energy storage, they can be tapped into when solar activity is the greatest and then have the energy stored to be dispatched at a later time when it’s more economical to do so.

Looking at the entire setup economically, as solar cell and PV panel prices continue to fall (which they’re universally projected to do) that means that traditional solar installations will see a greater percentage of their costs going to physical land costs. So, in areas where land costs are particularly high (e.g., island nations and communities with valuable farmland), floating solar bis able to provide a new and critical avenue to implement solar power.

Operational Benefits of Solar on Water

A few less obvious benefits to nautically located solar panels also take hold from a scientific and operational perspective. To start, a source of electric inefficiency in solar panels comes when they get overheated. However, by placing the panels directly over water they can take advantage of the cooling effect of water. Studies find that this feature can account for an increase in average efficiency of 11% when compared with on-land panels.

Additionally, an under-discussed challenge of land-bound solar is what is known as ‘soiling.’ This phenomenon occurs when dust and dirt get kicked up by the wind and other activity to effectively block the sun from fully reaching the panels. Frequent maintenance of some kind is needed to fight this, lest the solar panels lose money in the need for such upkeep (though many installations will have minimal, if any, soiling maintenance requirements as the reality soiling concerns will vary from region to region and location to location). Obviously, though, being located on the water diminishes this challenge.

Benefits to the Water Systems

Lastly, the solar power systems aren’t the only ones to benefit, as floating solar can also create a symbiotic relationship between the panels and the water. To start, panels located above the water provide shade and cooling to the water, which naturally reduces the rate of evaporation. Such an effect is useful for water resources where scarcity is an issue, such as at Lake Mead which has recently lost 5% of its water to evaporation per year.

Further, covering the surface of bodies of water also serves to minimize some of the natural methane emissions that come from standing bodies of water. This tendency of reservoirs to naturally release methane has been responsible for making the carbon footprint of such hydropower generation non-zero, but the presence of floatovoltaics can work to counter that.

Lastly, the shade provided by solar panels will reduce algae bloom in the waters and thus improve water quality. This trend can again be critical in situations where water resources are scarce and thus keeping the quality of the water in those areas high is critical.

Doesn’t It Introduce New Issues?

Those benefits are all well and good, you may say, but are they worth the potential new issues that siting solar panels above water would create? These questions are natural and fair, as the complexity of planning and maintenance needs get elevated by siting solar on the water.

For instance, special planning must be given to how falling and rising water levels will affect the installations, especially in regions prone to heavy storms (hello Florida during hurricane season!). On the other end, winter weather can present issues when snow covers the panels and must be cleared or when the water itself freezes over.

Generally speaking, as well, any installation, maintenance, and repair to solar panels have added costs and complexities when they must be performed on the water when compared with on-land installations. However, none of these are technical challenges that have not yet been overcome. The only question with these new issues is the cost they add to the energy generated and comparing those added costs to the previously mentioned benefits. If, in the end, the costs to overcome those challenges do not surpass the economic and whole-system advantages gained, then floating solar is not an ideal solution in that instance. But, as we’ll see, floatovoltaics have found plenty of areas where the math works out.

Where Is It Being Used?

Currently, the global market for floating solar has surpassed 1.1 gigawatts (GW) compared with over 100 GW of total solar energy capacity. The World Bank estimates that the global potential can reach 400 GW in capacity.

When it comes to studying the current and future state of floating solar power in the United States, the recent report from the National Renewable Energy Laboratory (aka NREL, a national lab in the system of the U.S. Department of Energy) set the standard. As reported by NREL, the first U.S. installation of floating solar came over a decade ago, but despite that this type of renewable energy generation has not swelled and pervaded the U.S. energy mix.

By the end of December 2018, only seven total floating solar installations were operational in the United States. Internationally, the outlook was relatively more encouraging, with 100 floating solar plants in place. Notably, 56 of the 70 largest floating PV installations were in Japan, where available land resources on the archipelago are scarce. Taiwan is another key example where real estate cost is high and maximizing land use is important, so floating solar is a convenient solution when looking hyper-locally.

This dichotomy between U.S. installations and global installations reflect how floating solar is a niche ‘nice to have’ use case in the United States compared with being a necessity in other places. Looking forward, this trend feeds into estimates that North American installations are only expected to reach 50 megawatts (MW) by 2022 and that in the same period China would lead the world with 485 MW, followed by India at 216 MW, South Korea at 128 MW, and Japan at 121 MW. The international fascination with floating solar, particularly in Asia, has even resulted in a bit of hot potato of which nation holds the active title for largest floating solar installation, akin to the battle for the world’s tallest skyscraper that started in the 20th century.

Focusing back on the NREL study of the U.S. market, the lab also examined the theoretical potential capacity for floating solar by tapping the market more widely. Based on what they described of a conservative estimate (i.e., only 27% of man-made bodies of water and only 12% of the surface of those bodies would be covered in solar panels), NREL found that over 24,000 U.S. reservoirs could generate 10% of the electricity needed to power America by playing host to floatovoltaics. NREL also echoed the sentiment that this strategy could be particularly valuable in areas where land constraints are an issue and land is highly valuable. In this massive floating solar scenario, about 2.1 million hectares of land would be ‘saved’ from housing solar. However, this data point is a bit misleading: wouldn’t we put solar on the optimal water and land resources where it was needed and wouldn’t we only build out the capacity at the rate at which it was needed and in the places in which it was economically viable? Nonetheless, the figure and study as a whole are quite thought-provoking.

In the United States, the excitement is certainly beginning to build. “A lot of people were waiting to see if our 4.4 MW New Jersey project went as planned because it is almost ten times bigger than any other U.S. floating solar array,” claimed the national marketing lead for an engineering group diving headfirst into solar. He went on to note that they’re “nearly there and now five utilities in five states want us to develop new projects totaling 80 MW.” Indeed, a surprising (at least to me) tidbit of the NREL report was the fact that “every state has floating solar potential” despite the diversity in quantity and type of water bodies and natural solar resources. But in the end, when comparing state-by-state electricity demand, NREL found that Idaho, Maine, New Mexico, and Oklahoma could all exceed needed demand through floating solar alone (see the map below). Obviously this arithmetic comes as an oversimplified generalization (energy storage needed to enable that solar generation to cover all times would be expensive and would use up some of the energy, the solar resources would not necessarily be located directly where they were needed, etc.), but again the potential for floating solar to go through massive expansion seems to be technologically and geographically present.

What’s The Final Judgment?

If I’m to make the final judgment on floating solar, which I’m in no way in charge of doing, I would say after research I’ve softened my stance a bit. Floating solar still seems to have come from a place of ‘Hey, wouldn’t it be cool if we just put the solar panels on water?’ and ‘Sure, but why?’ That said, the ‘why’ question has some very useful answers in designated and specific situations, and those are valuable. Geothermal and hydropower are two renewable energy sources that have found success even though they are geographically limited in use cases, but the economics and the low carbon footprint make them obvious answers in those regions where they work. They are nice to have where it works and is necessary to keep in the tool belt, but won’t singlehandedly mobilize the masses. Floatovoltaics can and should find a way to carve out this niche and these optimal market dynamics in the same way that tidal energy can do for coastal regions.

So, are floating solar installations an example of a solution in search of a problem? Perhaps. But that problem has been astutely identified and now it’s about implementation. Float on to a cleaner and cheaper energy mix in those regions.







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To read more insights into solar energy, see this article the Open PV Project, this assessment of the solar revolution across the United States, and an assessment of solar power use in California wineries.

About the author: Matt Chester is an energy analyst in Orlando FL, studied engineering and science & technology policy at the University of Virginia, and operates this blog and website to share news, insights, and advice in the fields of energy policy, energy technology, and more. For more quick hits in addition to posts on this blog, follow him on Twitter @ChesterEnergy.