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Wine Country project provides a taste of floating solar power

The largest American floating solar array was recently completed in California's Wine Country-and there's potential for more to come.

By Tony Kryzanowski

While the high cost of land can sink some solar power projects, White Pine Renewables has found an innovative solution to this hurdle in California's Wine Country by building their commercial-scale solar array without land—on water.

 
   

In fact, they have just completed America's largest floating solar farm: the 4.78 megawatt (MW) Healdsburg, California project. It is supported by a 25-year power purchase agreement (PPA) to supply eight percent of behind-the-meter power to the City of Healdsburg, located in Sonoma County.

"Traditionally, the vineyards in Napa and wine country in Sonoma have been really good places for this type of application just because the land is so expensive and no one wants to take grapes out of production to put solar in," says Dylan Dupre, President of White Pine Renewables.

Industry pioneer for floating racking systems supplied Healdsburg project

Management at White Pine Renewables had previous experience successfully installing a smaller floating solar array in the Sonoma County area of California before the company completed the Healdsburg solar project.

Company President Dylan Dupre says that it was a much smaller 400 kilowatt (kW) project installed at a local winery about a decade earlier, and that a lot has changed in the cost-effectiveness of floating solar development since then.

Although successful and still operational, he says it was extremely expensive to build and fabricate because they did not have access to the type of proven, easy-to-manage engineering solutions available today, like the pontoon and mooring system supplied by Ciel et Terre.

Chris Bartle, Company Director for Sales and Marketing for the Americas, says that Ciel et Terre is headquartered in France and has been a pioneer in providing floating racking systems for solar installations throughout the world. They have supplied 235 systems mostly in Asia and with island nations that have limited land available for solar. Their largest project is an 88 MW system in Taiwan. They have also supplied 18 systems in the U.S., with four systems under construction and two in engineering.

Bartle says that studies show there is the potential for an additional 2.1 terrawatts (TW) of floating solar development in the U.S. Generally, floating solar projects will be smaller than land-based systems simply because of the size restraints of water bodies.

Ciel et Terre designed and customized the floating racking system for the Healdsburg project. Then they provided the floating, racking and anchoring materials as well as onsite training.

The hollow floats consist of high density polyethylene, a material commonly used in food beverage containers. Bartle described it as non-toxic, leaching no chemicals into the water. It has been used in the marine industry for decades by marinas, for floating buoys, and even kayak material—anything that floats on the water and is hollow.

"The function of our floats is what is unique," says Bartle. "The float can be affixed to any Tier One solar panel. Our anchoring system is custom designed to the water body."

Each solar module has its own main float and is surrounded by secondary floats that also function as walkways for maintenance. Ciel et Terre also manufactures the fixation system, which are the brackets that connect the plastic floats and solar panels. In saltwater applications, the materials used in the fixation system are corrosion resistant.

As the floats are expected to perform outdoors for a long time, they are manufactured with an ultraviolet light blocker. The company has also done installs where the floats are frozen into ice for part of the year in cold environments.

Bartle says the Healdsburg system was uniquely designed for section detachment and manoeuvrability so that the city can access and clean the pond liner below.

The Healdsburg solar farm floats on 15 acres of a tertiary treatment pond connected to the city's wastewater treatment system. And it delivers more benefits than just affordable renewable power.

The treated water from this pond is typically used to irrigate local vineyards but the city was struggling with algae growth and evaporation. The Healdsburg solar array solves both these problems, shading the water from sunlight to minimize both algae growth and evaporation.

The project has also contributed to the city's need to meet California's mandated renewable power generation requirements. Because Healdsburg operates its own power utility, they are required to produce half their power from renewable sources by 2025. That requirement increases to 60 percent by 2030. So in addition to providing affordable renewable power, the White Pine Renewables floating solar array is helping the city meet its renewable power requirements and there is room for expansion on the wastewater pond.

Building on water also benefits White Pine Renewables as it improves solar array productivity. The floating location keeps the solar modules cooler in high heat.

The developer expects a moderate production boost as compared to solar arrays located in some hot and dry areas of California that lose productivity, particularly in summer high heat conditions.

"When you start to look at the compounding value year over year in additional kilowatt hours that you are producing, these provide both savings and value to the City of Healdsburg as well as additional revenues to White Pine Renewables. So it becomes quite an easy decision just in terms of benefits on both sides," says Dupre.

The project cost between $9 million and $12 million and consists of 11,700 bifacial solar panels supplied by ET Solar. The inverters were supplied by Chint Power Systems.

The most significant difference between this floating solar array and a land-based system is the replacement of a ground-based anchor and racking system with a pontoon and mooring system to support the solar modules, inverters and wiring. These were provided by California-based Ciel et Terre (see sidebar story).

In terms of project construction, that was handled by Collins Electric. It was essentially a process of assembling each line of pontoon building blocks at the edge of the pond and pushing them out to prepare for the assembly of the next set of pontoons, sort of like lines of knitting. Each section was then transported by boat to where it was attached to the anchored floating array.

Construction required no onsite fabrication or welding with extra features like walkways and cables to streamline future operation and maintenance.

Collins Electric brought experience to this project, having constructed a smaller floating array in that same area. They managed the Healdsburg project smoothly and it was completed in just six months from procurement to commissioning.

The biggest engineering challenge was to develop a system to anchor the array while allowing it to rise and fall with the ebb and flow of pond water levels. Screw anchors were placed on the pond boundaries with cable moorings attaching the solar array to the screw anchors. "The moorings have a certain amount of tension built into them so that when the water rises, they take up slack and then when the water falls, they loosen the tension, sort of like the seatbelt in your car," Dupre says.

 
The most significant difference between the Healdsburg floating solar array and a land-based system is the replacement of a ground-based anchor and racking system with a pontoon and mooring system to support the solar modules, inverters and wiring. These were provided by Ciel et Terre, with the 11,700 bifacial solar panels for the project supplied by ET Solar, and inverters from Chint Power Systems.  
   

By securing a PPA with the City, White Pine Renewables was able to arrange financing and build the project. As the project developer, they could take advantage of tax credits which allowed the company to offer more competitive power rates. Healdsburg expects to save materially in its wholesale energy price over the 25-year lifetime of the PPA.

 
By securing a Power Purchase Agreement (PPA) with the City of Healdsburg, White Pine Renewables was able to arrange financing and build the floating solar project. As the project developer, they could take advantage of tax credits which allowed the company to offer more competitive power rates. Healdsburg expects to save materially in its wholesale energy price over the 25-year lifetime of the PPA.  
   

"We simply have placed the solar modules on floats, using proven plastics that have been in use for the purpose of providing buoyancy since the 1970's," says Evan Riley, CEO of White Pine Renewables. "So it is a proven technology that has been repurposed for the use of floating solar modules."

This is a new application of this mooring technology commonly used in marine applications where floating objects must rise and fall with the tides. The Healdsburg site is also negatively-grounded and well-insulated, with proven marine technology once again playing an important role for operating electrical systems safely in a wet environment.

White Pine Renewables believes that there is a lot more opportunity for floating solar development in today's market, particularly in the right environment.

"In agricultural areas where farmlands have energy intensive businesses for treating water or moving water in the production of crops, these have always been a good application for floating solar installations," Dupre says.

The essential element is that the customer has a large water body available to float a solar array and Dupre sees many potential applications in the commercial, industrial and municipal sectors.

Floating solar development has already grown significantly in places like Europe and Asia.

"We are just getting starting in the United States," Dupre says, especially given the added benefits in water quality as well as improved solar module performance from the cooler air created by the ponds.

He says that White Pine Renewables has a number of floating solar projects in its pipeline. One is twice the size of the Healdsburg solar farm.

 


Q3 2021