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Solar in uncommon spaces

Sep 08 , 2021

With land-use concerns on the rise, large-scale solar projects are increasingly being built on everything from landfill sites to water reservoirs. Here’s an overview of the state of the art.


Image: Image: NREL/Dennis Schroeder

From pv magazine USA


Solar is at the forefront of climate mitigation efforts, but comes with some environmental baggage of its own. One concern is the amount of land needed for the energy revolution, especially as more utility-scale solar projects are brought forward.


In July, for example, developers of a proposed 850 MW solar plant in the desert north of Las Vegas pulled their application with the U.S. Bureau of Land Management in the wake of local opposition. Residents argued that the array, proposed to cover more than 14 square miles, would be an eyesore and could hurt area recreational activities.


A study by Clemson University estimated that energy production for domestic use and export will rise by 27% by 2040. Roughly 124,000 square miles of land will be needed to site all of the related facilities. With spacing requirements included, nearly 500,000 square miles of land will need to be dedicated to new energy production – an area larger than Texas.


To be sure, locations across the built environment (rooftops, carports, and the like) are common places for solar installations. The benefits of these distributed sites are numerous. But if the nation is to rapidly hit clean energy penetration targets, then large-scale projects with big footprints are needed as well.


Not all large-scale solar deployments need to be sited on vacant spaces or farmland, however. Three options include floatovoltaics, landfill solar, and highway rights-of-way. Let’s have a look at each in turn.


Land or sea?

Floatovoltaics are a hot PV trend set to double in capacity in 2021. The structures largely take land use debates off the table, as the solar array floats on top of a body of water. Typically, these installations are found buoyed-up on a lake or basin, where the water is calmer than the ocean.


Dual-use locations are often sites for these projects. Reservoirs, hydroelectric dam water sources, and wastewater treatment ponds are all potential candidates to host floatovoltaics.


Take the Far Niente Winery in Napa Valley, California, for example. Completed in 2008, it is widely considered to be the first grid-connected floatovoltaic array in the world. To meet annual demand of 800,000 kWh, the solar array uses 2,296 panels, 1,200 of which sit on top of the winery’s irrigation reservoir, reserving nearby vineyard space for grape production.



Far Niente Winery in Napa Valley, California Image: Wikimedia Commons


The buoyant structure that supports the panels was a simple, yet clever solution. Pontoons made of 18-inch ribbed pipe filled with styrofoam sit beneath the panels and are attached to four concrete mounts. The array can freely rise and fall 18 feet as water is used, and the concrete mounts prevent the modules from rotating and ensure an optimal azimuth.


What’s more, the array reduces evaporation by covering and cooling the water. This same effect also prevents the spread of unwanted algae. In turn, the pond benefits the panels, acting as a stable thermal mass that regulates temperature, slowing panel degradation and increasing efficiency.


An example of how such projects be effective comes from the Sembcorp Floating Solar, a 60 MW FPV array on the Tengeh Reservior in Singapore, which recently entered service. The system’s 122,000 Trina Solar 210 Vertex dual-glass modules, which cover a surface area the size of 45 football fields, deliver green energy from Singapore’s main reservoir of drinking water via a 25-year power purchase agreement with the National Water Agency.



Sembcorp Floating Solar Singapore Image: Sembcorp


Singapore’s Public Utilities Board said it selected Trina Solar modules due to their double-glass protection, which will aid in making them durable enough to perform in wet and humid conditions for 25 years. The panels are supported by high-density polyethylene (HDPE) floats. The floats are UV-resistant, a necessity to protect them from degradation.


When evaluating the effectiveness of floating PV, cost is likely a first concern as these structures have unique construction mounting (or docking) needs. However, cost parity may be closer than one may expect. Floating PV has slightly higher capital costs, but lower operation and management costs, no land costs, and increased efficiency benefits the cost structure.


According to Stetson Tchividjian, director of business development at D3Energy, an FPV developer, the price to install floating solar is about 10% to 15% higher than land-based PV. However, O&M cost reductions may help close the gap. If the externalities that stem from developing otherwise-useful land are included, then the economics behind floating solar may keep a project above water.


Landfill opportunity

Landfills and other contaminated brownfield sites are another area for growth. The U.S. Environmental Protection Agency tracks solar-landfill topping installations as part of its RE-Powering America’s Land initiative, and has recorded an 80% rise in installations in the last five years. Nearly 60% of the tracked projects sit on landfills, and more than 90% of the RE-Powering projects are solar PV.



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