The long read: Canal-top solar solutions


From pv magazine 05/2022

The state of Gujarat on India’s western coast has a long history of industrial forward-thinking and is said to be the home of one of the world’s first seaports, at Lothal. Between 2012 and 2014, Gujarat’s pioneering spirit was again on show along a 750-meter pilot stretch of solar panels atop a canal. The pilot eventually led to a 10 MW solar plant winding above the Vadodara Branch Canal (VBC).

If necessity is the mother of invention, it is probably not surprising that canal-top solar was pioneered in India. Densely populated and regularly struggling with the increasingly global issue of water scarity, Indians saw the potential of canal-top solar to simultaneously reduce water evaporation and generate renewable electricity, without occupying otherwise arable or hospitable land.

In the few years since that pilot project, several canal-top solar installations have been commissioned across India, including two more on other sections of the VBC. In February 2022, the ongoing project successes saw Gujarat government-owned Sadar Sarovar Narmada Nigam (SSNNL) announce a 100 MW solar project to be constructed atop the canals branching off the Narmada River.

According to the Gujarat State Electricity Corp., if 30% of the state’s 80,000 km of canals were converted to canal-top solar, it would produce 18 GW of clean power, and save approximately 90,000 acres of otherwise serviceable land.

California dreaming

India’s success has not gone unnoticed by other regions struggling with water scarcity, land use, and renewable energy integration – most notably, by California. When Albert Hammond sang “It Never Rains in Southern California” back in 1973, the sentiment wasn’t entirely hyperbole. According to the US Drought Monitor, much of the state suffers from severe or extreme drought.

California’s canal system, including the California Aqueduct, typically runs from north to south, bringing water from northern, mountainous regions to the dry and densely populated south.

According to Roger Bales, professor of engineering at University of California, Merced (UC Merced), almost 6,500 km of canals transport water to approximately 35 million Californians and 5.7 million acres of farmland across the state. Bales was among the team of researchers in 2021 who published a study in the journal Nature Sustainability, which showed, following the Indian model, that covering canals with solar panels reduced evaporation and would help California meet its renewable energy goals.

According to UC Merced environmental engineer and the study’s lead author, Brandi McKuin, “using canal infrastructure for solar development can make both systems more efficient. Shade from the solar panels can reduce evaporation of water from the canals, especially during hot Californian summers. And because water heats up more slowly than land, the canal water flowing beneath the panels could cool them by a few degrees, boosting electricity production by 3%.”

This is no small accomplishment in a region as drought-prone and thirsty as California. The California Department of Food and Agriculture notes that the state is the fifth largest supplier of food and agricultural commodities globally, making it not just the breadbasket of America, but the world.

According to Bales, most of California’s rain and snow falls north of Sacramento during winter, while 80% of the state’s water use occurs in the state’s south, during summer. California water management has thus led to one of the world’s largest canal systems, of which as much as 2% of its volume is lost to evaporation annually.

In the UC Merced study researchers were able to show that if all 6,500 km of California’s canals were covered with solar panels it would save almost 300 billion litres (65 billion gallons) of water each year, and generate 15 GW of renewable energy. “That’s enough to irrigate 50,000 acres of farmland or meet the residential water needs of more than two million people,” said Bales.

Turlock and load

Following the UC Merced study and the pioneering example of India, a proof of concept on the Turlock Irrigation District (TID) in the San Joaquin Valley has been established. The $20 million project, funded by the state of California, is called Project Nexus. The project is being developed by Solar Aquagrid with the help of UC Merced researchers and the state Department of Water Resources (DWR), and aims for a capacity of 5 MW. Several different types of solar modules will be evaluated in the project to measure efficiency and performance.

“Research and common sense tell us that in an age of intensifying drought, it’s time to put a lid on evaporation” said Solar AquaGrid CEO Jordan Harris, who also noted that Project Nexus will span both narrow and wide canals and incorporate energy storage.

“Our initial study revealed mounting solar panels over open canals can result in significant water, energy and cost savings when compared to ground-mounted solar systems, including added efficiency resulting from an exponential shading/cooling effect,” said Harris. “Now is the chance to put that learning to the test.”

Similarly, DWR Drector Karla Nemeth said the project “offers great potential” and added that the department is “excited to explore new efforts to advance the integration of renewable energy into our water supply delivery system.”

“The prototypes in this demonstration will help stakeholders refine designs, assess co-benefits, and evaluate how these systems perform,” added McKuin. “With more data, we can map out strategies for extending solar canals statewide, and potentially across the west.”

Main challenges

Of course, no innovation is without its challenges, especially when scaling is concerned. As always, cost is a hurdle, with current costs for infrastructure higher than costs for ground-mounted PV. However, the UC Merced study found the co-benefits of avoided land expenditure, water savings, aquatic weed mitigation and enhanced solar panel efficiency more than made up for the additional cost. There is also the added benefit of avoided greenhouse gas emissions as well.

Project Nexus will see over 2.5 km of the TID covered with solar panels in three sections of canal ranging in width from 6 meters to 30 meters. Construction is set to begin in the autumn of 2022, with a completion date expected by the end of 2023, and quantifiable results available by the end of 2024.

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