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Solar Energy System of the Month - Sarnia: The largest operational PV plant in the world

Sunlight, petroleum and prairie

Taking the train through Southwestern Ontario, near the United States border, one comes to a curious sight. On the edge of the mid-sized town of Sarnia, surrounding a central woodlot and ringed with tall-grass prairie, row upon row of black, thin-film solar photovoltaic (PV) modules reflect the sky, covering a total of 440 hectares.

This is the Sarnia PV plant, commissioned by First Solar Inc. (Tempe, Arizona, U.S.) in September 2010 as the largest operational PV plant in the world at 80 MW-AC.

The Sarnia PV plant is the largest operational solar PV plant in the world at 80 MW-AC. Courtesy: First Solar Inc.
The Sarnia PV plant is the largest operational solar PV plant in the world at 80 MW-AC. Courtesy: First Solar Inc.

Sarnia is an interesting location for the the world's largest PV plant, and speaks to the evolution of global energy industries. An oil well dug in nearby Oil Springs in 1858 may have been the first in North America, and the region was an early center for the Canadian oil industry. Another coincidence is that the plant is owned by oil and gas company Enbridge Inc. (Calgary, Canada).


The site: farming the sun

Like many large PV plants, the Sarnia plant was built on former farmland. "It was primarily in agricultural use for mixed crops, between soybeans, sugar beets, corn, winter wheat," states First Solar Vice President of Business Development, Canada Peter Carrie.

However, First Solar notes that this was already changing by the time the site was considered for a PV plant.

"Of the total area of the site, one third of it was zoned for industrial development, and two thirds remained zoned for agricultural purposes, however the city had planned for this area to be used for industrial purposes."

Array blocks at the Sarnia PV plant. Courtesy: First Solar Inc.
Array blocks at the Sarnia PV plant. Courtesy: First Solar Inc.

Development: working with city government and wildlife habitat

The plant's location is within the boundaries of the City of Sarnia, which had an impact on the development of the site. When First Solar originally acquired the site, Ontario had implemented its Renewable Energy Standard Offer Program (RESOP) policy, a precursor of the feed-in tariff.

"Under the RESOP program at that time the approval process for plants, for First Solar projects, was a planning-based project, with the municipality playing a central role in the approvals," notes Carrie. "We worked quite extensively with the city of Sarnia, on official plan amendments to enable construction of the facility."

First Solar says that these meetings influenced the site plan.

"We have installed quite substantial tree screens, around the perimeter of the project," states Carrie. "We've done a lot of landscaping, we've planted some additional woodlot in the central area of the project."

"And part of the project as well involved just under 50 hectares of wildlife habitat, in the form of tall-grass prairie, which is a historical wildlife habitat that was present in southwestern Ontario in the pre-development era, the pre-settlement era."

Ultimately, First Solar says that these improvements have made the site more friendly for wildlife than previous uses.


Design: array blocks follow natural features

OptiSolar (Hayward, California, U.S.) originally built a 1.5 MW PV plant on the site, which First Solar acquired when it purchased OptiSolar's development pipeline, as announced on March 2nd, 2009. This OptiSolar plant, which was built with amorphous silicon modules, was then removed.

Under an agreement with plant owner Enbridge, First Solar provided engineering, procurement and contracting (EPC) services for the plant. The company developed the plant in two phases, with  an initial 20 MW phase. First Solar used its standard array layout for the plant, building a series of 1 MW blocks.

However, even at this phase features of the site required adaptation in planning.

"When we were doing the array layouts, we essentially had to avoid a number of natural features, or drainage features on the site," notes Carrie. He says these site features forced the company to use four different shapes of array blocks.

"The clear choice would have been to use a single shape. So there is some variety in the layout of individual arrays on the site."


Construction part 1: mud

Carrie also notes that early in the construction process, First Solar encountered the same difficulties which had frustrated early oil developers in the region more than 150 years earlier. "The two largest site-specific difficulties, and they were very closely related, are the soil conditions and the weather."

The plant uses PV modules mounted on steel posts, which Carrie describes as similar to I-beams, driven vertically into the ground with a small post driver.

Carrie states that the team benefited from a mild winter in 2009-2010 and was able to continue construction through most of the season, including post installation. However, rain posed other problems.

"We had to halt construction a number of times, just because we would get rain, and it would churn up the mud on the site," recalls Carrie. "There was a fair bit of lost time because of surface conditions that are particular to that part of Ontario: A heavy clay soil which takes time to drain."


Construction part 2: drainage and a rail line

These conditions of the site required First Solar to install significant drainage improvements, including French drains and drainage tiles.

Additionally, the project's location adjacent to a main rail line posed its own set of difficulties. As part of the permitting requirements, First Solar was required to upgrade a main north-south drain running through the site, one end of which is a railroad culvert.

"The railroad track is part of one of the main Canada-U.S. rail corridors, so we ended up with quite a substantial project, even aside from the solar construction, to upgrade this culvert and improve the drainage to the site, of course, working around the train schedules."


Construction part 3: mounting modules

First Solar completed the first phase of the plant in December 2009. During the same month, the company began work on the second 60 MW phase of the plant, which brings the plant to a total output of 80MW-AC. First Solar commissioned the completed plant in September 2010.

Construction worker installing First Solar CdTe modules. The company estimates that 800 workers were employed in the construction process. Image courtesy of First Solar Inc.
Construction worker installing First Solar CdTe modules. The company estimates that 800 workers were employed in the construction process. Image courtesy of First Solar Inc.

The plant uses a total of roughly 1.3 million First Solar FS-272, 275 and 277 cadmium telluride thin-film PV modules, each with an output of 75 watts. These .6 meter by 1.2 meter modules are mounted at a 25 degree angle.

First Solar notes that more than 800 workers were employed in construction of the plant, which uses modules manufactured in First Solar facilities in Perrysburg, Ohio, U.S. and Malaysia.


The rubber meets the road: Output

Upon completion, the plant was transferred to Enbridge, however First Solar continues to operate and maintain the facility. Enbridge sells the power produced to the Ontario Power Authority (OPA, Toronto, Canada) through a 20-year power purchase agreement.

First Solar states that the output of the plant follows its expectations.

"The overall project forecast is in the range of 1250 kWh per peak kW," states Carrie. "And the actual performance is consistent with that, providing enough power to serve the needs of about 10,000 local homes per year with clean and affordable solar energy."

Carrie also notes that while there are a few days of snow during the winter, that this snow tends to melt quickly on the modules and has not significantly affected plant output.

Courtesy: First Solar Inc.
Courtesy: First Solar Inc.

Conclusions: drainage, tall-grass prairie and even larger PV plants

First Solar states that as a result of its experiences with the Sarnia plant, it is looking more closely at site drainage issues.

"Like all developers, and solar EPC contractors, we certainly learn from every project that we do," states Carrie. "Our practice for our future construction projects in Ontario will require particular attention to the soil conditions and we will plan to get in early to the sites to install additional drainage infrastructure to help keep the site well drained during construction."

Carrie and others at First Solar are proud of their accomplishment. In addition to developing the world's largest PV plant, First Solar describes a site with improved environmental features, including greater habitat for local wild animals.

"In and around the arrays that now has been planted with a permanent ground cover, as opposed to the mono-cultivation that was done annually under agricultural use," notes Carrie. "There is significantly increased habitat for small mammals or bird nesting, for example. We are seeing a lot of wildlife and biodiversity in and around the site."

As impressive as it is, the Sarnia plant's position as the world's largest PV plant may last long, given the exponential growth of the solar industry. First Solar joins a number of other companies with plans for larger plants, including its proposed 230 MW AV Solar Ranch One, which the company plans to complete near Los Angeles, California in 2013.