Floating Photovoltaic Farms: An Engineer’s Handbook
Tom Lombardo posted on February 14, 2020 |
Floating solar arrays could generate 400GW of clean electricity.

At the end of 2019, more than 600GW—just over 4 percent of the world’s electricity generating capacity—was generated by solar power. Nearly two gigawatts of that came from floating photovoltaic (FPV) systems—solar arrays installed on rafts that float atop bodies of water. According to a study by the Solar Energy Research Institute of Singapore (SERIS), floating solar could easily reach 400GW of generating capacity. In the U.S., the National Renewable Energy Laboratory (NREL) estimates that FPV, or “floatovoltaics,” could supply up to 10 percent of the nation’s electricity. But with very few existing FPV arrays around the globe, and each presenting its own unique variables, there are not a lot of guidelines on which to base new designs.

To help engineers get up to speed on the many facets of FPV, SERIS produced Where Sun Meets Water: Floating Solar Handbook for Practitioners.

Figure 1. A Floating PV array under construction in Walden, Colo. (Image courtesy of NREL.)
Figure 1. A Floating PV array under construction in Walden, Colorado. (Image courtesy of NREL.)

Floating Photovoltaics 

FPV is most commonly installed on man-made bodies of water, such as hydroelectric dams, industrial cooling ponds, and wastewater treatment facilities, since they tend to be calm and rarely used for recreational purposes. The combination of photovoltaics and water offers mutual benefits, including higher PV efficiency, reduced evaporation, and fewer problems with algae. Floating PV on reservoirs behind large hydroelectric dams could double the generating capacity of the site, even if only a small portion of the reservoir is covered. Finally, in locations where land is expensive or needed for crop production, FPV can take advantage of unused surface area. 

Floating PV Design

Where Sun Meets Water takes the reader through all phases of engineering a floating PV system—from site identification, through design, and all the way to long-term operation and maintenance. At 155 pages, it’s essentially a textbook for a self-study course in FPV (and unlike college textbooks, it’s free!)

Just as is true with rooftop or land-based PV arrays, the first step with a floating PV is site identification and analysis. Engineers will evaluate the solar resource (how much sunlight a site gets throughout the year), available water surface area, water depth, local wind conditions, environmental factors, and grid access. One advantage of adding FPV to a hydropower reservoir is the ability to tap into the existing grid connection, which significantly reduces the cost. On the other hand, sites with industrial cooling ponds may or may not have the capacity to transmit significant amperage to the grid, so the added cost of upgrading the infrastructure must be taken into account. 

Designers will then conduct an energy yield analysis to estimate how much energy the site could produce. The result is weighed against the cost of building the floating solar farm to determine the return on investment and payback period. 

At this point, the fun begins—engineering design! On the surface, it would seem that for the PV panels, inverters and cabling, there’s not much difference between FPV and land-based PV, but dive a little deeper and we see that FPV equipment will be exposed to more humidity, constant movement, and possibly higher winds, all of which could contribute to early failure if protective measures are not employed. Obviously, mooring a PV array is more challenging than simply anchoring it to the ground or a rooftop, and the proximity to water calls for additional electrical safety measures. 

As the rooftop and the ground-mounted solar industry matured, the permitting, inspection, and interconnection process became more streamlined, as did the financing. This has yet to happen with the burgeoning FPV industry, so developers should expect to spend more time with bankers, lawyers and regional authorities. Obviously, financing and permitting occur before the construction phase, while inspection and interconnection take place upon completion.

While it’s imperative that we move to clean sources of electricity, we don’t want the trade-off to be dirty water, so the environmental impact of FPV on the body of water and its associated ecosystems must be thoroughly examined. Hydropower reservoirs frequently hold drinking water, so engineers must ensure that the array doesn’t leach anything into the water supply. 

Material procurement and array construction fall under the purview of the contractor, and given the unique qualities of floating solar, it’s important to select a contractor with FPV experience. Where Sun Meets Water lists more than two dozen reputable FPV contractors, mostly in Asia and Europe, but a few in the Americas. 

To ensure efficient energy production, minimal downtime, and array longevity, designers specify an operation and maintenance procedure that includes preventative, predictive and corrective actions. Preventative maintenance involves regular inspections and replacement of parts at specified intervals. Predictive maintenance uses sensors and software to monitor the array and look for impending failures before they occur. Finally, corrective maintenance repairs parts that failed unexpectedly, because not everything can be predicted by statistical models or sensor readings. The handbook includes maintenance plans for each component.

Figure 2. Solar Module Maintenance Plan. (Image courtesy of SERIS.)
Figure 2. Solar Module Maintenance Plan. (Image courtesy of SERIS.)

Routine maintenance of solar panels is exactly the same for FPV as it is for land-based photovoltaic arrays, but the mechanical side is quite different, as you can see here:

Figure 3. Floats and Mooring Maintenance Plans. (Image courtesy of SERIS.)
Figure 3. Floats and Mooring Maintenance Plans. (Image courtesy of SERIS.)

It’s a Handbook

As one would expect from an engineer’s handbook, every section of Where Sun Meets Water includes details as well as tables, charts and checklists. Those new to floating solar should read the handbook in detail until they have a few designs under their belts, while experienced FPV designers can simply keep the tables, charts and checklists for handy quick references.

Download Where Sun Meets Water: Floating Solar Handbook for Practitioners.

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