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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

Europe’s Largest Floating Solar Array Opens This Month

By Catherine A. Cardno, Ph.D.

The largest floating solar array in Europe will be completed in the greater Manchester region of the United Kingdom this month.

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United Utilities, in Warrington, England, will use the electricity generated by its new 12,000-panel floating solar array to power its own water-treatment facility. © Chris Stubbs 2016

February 9, 2016—One of the newest trends in renewable energy appears to be of the floating variety. Late last year the world's first floating wind farm was announced (Read " World's First Floating Wind Farm to be Built Off Scottish Coast" on Civil Engineering online), and this month will see the completion of Europe's largest floating solar array near Manchester, England. United Utilities, based in Warrington, England, is installing the £3.5-million (U.S.$5.1-million) solar array in the Godley Reservoir, which is part of a system originally developed in the Victorian era to provide fresh drinking water to the greater Manchester area. The power generated by the 12,000-panel array will be used to operate the utility company's water-treatment facility.

"The water-treatment works, which is alongside the reservoir, is quite a power-hungry location within the United Utilities system," says Chris Stubbs, the head of renewable energy at the utility company. "So that was a good location to plug into—there wasn't much free land within our ownership around the works, but there was a great body of water.

"We'd seen that [a floating solar array] had been done in Japan, and we decided to investigate what the economics looked like," Stubbs explains. "Ultimately, the system—when it's finalized [and] switched on in February—will supply about 35 percent of the [water-treatment] works' annual energy needs." The project is part of the company's larger goal to be 35 percent self-sufficient overall by 2020, according to Stubbs.

The array will provide 2.7 GWh annually for the use of the utility company. Despite England's reputation as a rainy country, the greater Manchester region sees on average 1,372 hours of sunlight each year, according to the United Kingdom's Metropolitan Office. April through September is the sunniest period of the year, offering between 133 and 186 hours of sunlight a month.

Stubbs notes that 60 percent of the array's output is expected to be gathered in just four months in the early summer, the output of the array tailing off as the nights lengthen in the fall and winter.

"It's not as sunny as it is in California, that's for sure, but there is enough to give a decent output," Stubbs says. "We get between about 850 and 900 kWh per year, per kilowatt of installed capacity." While this is less than an array would get in sunnier climes, it works out economically because the system is a closed loop and the utility company will be consuming on-site all of the energy that the array generates. "It makes sense for us to displace imported power off the grid—that is quite a reasonable cost saving to make," Stubbs says.

In addition to the value of gathering a renewable resource and turning it into energy, the floating solar array offers other benefits. Evaporation and algae growth, while not significant concerns in this particular reservoir, will be further limited. Much as the shade balls installed in a Los Angeles reservoirlast summer covered and protected its drinking water supply, the 12-acre floating solar array will limit the amount of evaporation and—by blocking sunlight and subsequent heat gain in the water—algae growth experienced by the reservoir. This decreases the amount of chemical treatments needed to clean the water.

Although the array was chosen for its energy-generating capabilities rather than its attributes in protecting drinking water supplies, Stubbs is quick to note that the utility company will be monitoring water quality very closely for the next year or so. "We've done preinstallation sampling and we're going to do a lot of postinstallation sampling to monitor any issues," Stubbs says.

All of the materials used to build the array are certified to be in contact with drinking water. "The very last thing that we could ever afford to do is cause a problem with the water supply," Stubbs notes. "There's further treatment downstream, but we don't want to add a treatment burden to that downstream works before the water is adjusted for final-quality drinking water."

The array is composed of individual float modules, half of which hold solar panels and half of which do not. The floats come in two sizes, lock together, and are made of heavy-duty, rigid—yet flexible—plastic. The solar panels are mounted on the larger floats, while the smaller, interstitial floats create space between the solar panels and act as walkways for inspections and maintenance. Because the array is completely modular, an individual panel or an entire float-and-panel module can be removed and replaced as necessary.

"The construction method is to build squares of approximately 20 by 20 solar panels—main floats and interstitial floats—assembling them one row at a time on a temporary jetty at the waterside," Stubbs explains. Each row is pushed out into the water and bolted to the next row of modules until 20 rows have been completed. "The resulting square is then taken away from the jetty and moored up at the side of the reservoir until the team is ready to tow it out to the main array assembly," he says. "The squares, while being fairly massive, move very easily across the water. They can be pulled from the shoreline by very lightweight ropes.

"The whole array—when it's put together—covers about 12 acres of water and is tethered to the banks of the reservoir," Stubbs says. In all, there are 76 cables locked into a total of 48 anchor points in the reservoir's embankments.

Energy is gathered and sent to the water-treatment facility's electrical infrastructure in a straightforward manner. The panels in each row are strung together—much like Christmas lights—bringing all the direct-current power generated to the end of each row. Cables then send the power to a number of combiner boxes located on their own floats, which then send the power into larger cables. These cables then extend along a line of floats 35 to 40 yds to the shoreline, through an underground trench, to a transmission station at which the power is converted into alternating current and stepped up to high voltage, and then finally connected to the water-treatment facility's electrical infrastructure.

The reservoir is privately owned by the utility and located behind fences on land that is inaccessible to the public. This was a key element in enabling the utility company to install the floating array. "If trespass was an issue, we would be concerned with putting a floating electrical system on the reservoir," Stubbs notes. "It's exceptionally dangerous because the water is so cold, but people do swim in some reservoirs and lakes," he explains. "And we just think providing them with a diving platform which has got DC electricity all over it would not be a clever idea, so we would've been really cautious about putting one of these installations onto a reservoir where people are known to trespass."

Work on the array is expected to be completed within the next few weeks, in plenty of time for the early summer sunlight that will shortly arrive.


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