The Braintree Electric Light Department in Massachusetts is using a grant provided by the American Public Power Association’s Demonstration of Energy & Efficiency Developments (DEED) program to explore a solar power project that would float on a reservoir.
The 10-megawatt array of solar photovoltaic panels would occupy about 40 acres or about 25% of the Great Pond Reservoir in Braintree. The reservoir is actually the property of three towns – Braintree, Holbrook and Randolph – but the solar panels would be entirely inside Braintree’s town limits.
Under the current proposed design, the floating solar project would be able to provide about 5% of Braintree’s electric power. Between wind and hydropower renewable energy credits the city controls, renewable power comprises about 13% of the public power utility's electric supplies.
Braintree used the $7,500 DEED grant to fund about half the cost of studying the feasibility of the floating PV project. The grant was helpful in getting the project planning process going, William Bottiggi, general manager of Braintree Electric Light Department, said. “Without it, we probably would have dragged our feet a little more.”
Braintree received the grant in the late spring and contracted with construction firm AECOM to conduct the feasibility study, which was completed in mid-October.
The AECOM report found that the floating solar photovoltaic project in the Great Pond Reservoir would be feasible. The technology has been proven many times over in Europe, Asia and South America on a “scale many times larger than what is being proposed” in Braintree, the report said.
“If we can complete the solar project by 2020, that would be really good,” Bottiggi said. However, “there are still a variety of concerns that need to be addressed.”
On the top of Bottiggi’s list is assuring that the solar project will not harm quality of the drinking water from the Great Pond Reservoir. “The town will be very sensitive to water quality,” Bottiggi said. “I want to get one of the pontoons to be installed and have it tested.”
The project design calls for 37,632 solar PV modules configured in two separate arrays, each mounted on plastic floats configured to form two square raft like structures. The floats or pontoons would be made mostly of high density polyethylene.
The AECOM report says HDPE and polypropylene – used to make the connecting bolts – are the “preferred materials for this application as they resist weather and UV degradation.” They are also inert and do not degrade or leech materials or chemicals into the surrounding environments, and they are the same materials used in the construction of HDPE water line pipes used to convey drinking water in municipal water distribution systems, the report noted.
Bottiggi said he does not want to just rely on published reports, so he is going to have the pontoons tested. He also said he would reach out to the water company in London to learn from their experience.
Developer Lightsource Renewable Energy installed a 6.3 MW floating solar farm for Thames Water Utilities on its Queen Elizabeth II reservoir near Walton-on-Thames.
The size of the British project pales in comparison to floating solar projects in China and Japan. In 2017, China installed a 70 MW floating solar farm on a series of adjacent reservoirs in Anhui Province. In Japan, the capacity of floating solar panel arrays is set to exceed 400 MW by 2024, according to the AECOM report.
Aside from making use of scarce real estate, floating solar farms can also help reduce water evaporation from reservoirs and, by reducing water temperatures, can inhibit the growth of algae. Braintree now applies a spray to reduce algae growth in the summer, but the solar farm could reduce that need, Bottiggi said.
Proximity to water also reduces the temperature of the solar panels, which can improve their efficiency. The research is ongoing, but cooler operating temperatures could improve the energy output of the solar panels by 5% to 15%, the AECOM report said.
Bottiggi estimates that the cost of the power from the floating solar panels would be about 8.4 cents/kWh, making it more expensive than conventional generation but putting it “in the middle of what renewables cost. That puts it in the realm of possibility.”
Bottiggi still needs to secure permission from the mayor of Braintree and from the town council, and he will have to negotiate a payment for the use of town land, i.e., the reservoir. Several other permits will also be required, including approval by the Tri-Town Board of Water Commissioners, which is responsible for the reservoir.
In terms of financing, Bottiggi said he is looking at two broad options. The Braintree Electric Light Department could undertake the project itself and finance it with general obligation bonds, or it could put the project out to bid and sign a power purchase agreement with the developer that allows the utility to retain the renewable energy credits.
In the near term, Braintree should be able to get the water tested over the next six months, Bottiggi says. “That could be the hardest thing.” And then he would hope to move forward with the project.
For additional information about the Association’s DEED program, click here.
Florida public power utility installed floating solar array in 2017
Florida public power utility Orlando Utilities Commission in 2017 installed a floating solar array on a pond near its operations center in southwest Orlando, Fla.
In late 2017, OUC dedicated a 13-megawatt solar facility on the site of a former landfill that was once designated for the construction of a future coal plant. The utility also unveiled plans to construct floating solar arrays at the site.
