Turning a brownfield into a bright field - The Exelon City Solar Plant in Chicago

by Solar Server International Correspondent Christian Roselund

January 4, 2011

When one thinks about record-setting solar plants in the United States, one usually thinks of California, Nevada or Florida, or perhaps even New Jersey. However, Solar Server's January 2011 Solar System of the Month was built in the home town of utility Exelon Corporation (Chicago, Illinois, U.S.), in a former industrial site on the South Side.

The Exelon City Solar plant, developed in collaboration with SunPower Corporation (San Jose, California, U.S.) today stands as the nation's largest urban PV plant, at 10MW-DC (8MW-AC), on once-blighted land. In doing so, the companies articulated a vision of returning abandoned inner-city landscapes to productive use in the new energy economy.

Advantages and disadvantages of brownfield land

"Brownfield" is a planning term used to refer to formerly used industrial sites which may be contaminated, as opposed to "greenfield" land, which has not yet been developed. According to the U.S. EPA, there are more than 425,000 brownfield sites in the United States, including 20,000 square kilometers of industrial land in cities.

Such sites are often seen as liabilities, degrading the value of the land around them, and can be difficult to sell due to real and/or perceived health, safety and aesthetic issues. Renewable energy advocates including the U.S. Department of Energy's National Renewable Energy Laboratories (Golden, Colorado, U.S.) have been investigating the possibilities of using brownfield sites for renewable energy generation, as such uses typically do not disturb the soil, which may or may not be contaminated.

“Think of it,” states Opel Solar inc. (Shelton, Connecticut, U.S.) CEO Leon M. Pierhal, an advocate for the use of brownfields for renewable energy generation. “There are literally thousands of these properties across the United States just sitting there, producing nothing of substance despite the fact that they are often ideal for commercial solar farms, are sited close to existing power transmission lines, and can be redeveloped without much disturbance.”


Expecting the unexpected in brownfield redevelopment

Exelon began their experiment with brownfield redevelopment by leasing a 166,000 square meter parcel of land formerly occupied by an International Harvester (now Navistar International Corporation, Warrenville, Illinois, U.S.) brake pad factory in the West Pullman neighborhood on the Far South Side of Chicago. Like many brownfield sites, the project was not without complications.

32,292 SunPower PV modules mounted on single-axis tracker systems.
32,292 SunPower PV modules mounted on single-axis tracker systems.

"This was a parcel that the city of Chicago had marketed unsuccessfully for ten years, it was overgrown and had chunks of broken concrete and steel, open basements and cisterns, full of physical and health hazards," states Exelon Spokesperson Paul Elsberg.

Site work began in July 2009, with Exelon performing considerable work to prepare the site for a PV plant. "We cleared the site, we filled the basements and cisterns, there were barrels of hazardous materials found that we recovered and removed," recounts Elsberg. As a final step, the ground was paved and 7,300 steel piers were driven into the ground.

According to Elsberg, one of the challenges developing brownfields is that you never know what you are going to find. "During the cleanup process, there were some unforeseen things that we had to contend with like underground storage tanks," recalls Elsberg. "They had to use a pile driver to drive steel piers into the ground. In some cases you did find these underground storage tanks that you had to remove and build around."

The plant: SunPower 310 watt modules, T0 tracking system used

SunPower designed, manufactured and installed the PV plant, which is composed of 32,292 SunPower 310 watt monocrystalline PV modules mounted on SunPower T0 single-axis tracker systems. SunPower states that by using the tracker systems it is able to reduce the amount of land needed to generate the same amount of electricity by 20% compared to systems comprised of fixed-tilt crystalline silicon modules.

Aerial view of the PV plant
Aerial view of the PV plant

“Delivering a 10-megawatt solar plant in a space-constrained, 39-acre area is only possible using SunPower’s high-efficiency solar technology, which generates more power per square foot than competing technologies," states SunPower CEO Tom Werner.

The system also uses Satcon 500 inverters by Satcon Technology Corporation (Boston, Massachusetts, U.S.). The site is located near an Exelon substation, which SunPower notes removes the need for new, large-scale transmission.

With large plants such as the Exelon City Solar, financing is always a concern. Exelon applied for but did not receive a conditional loan guarantee through the U.S. Department of Energy for the USD$60 million project, however it was able to take advantage of the 30% federal solar investment tax credit, as well as an Illinois state investment tax credit.


14,000 MWH/year projected output

According to Exelon's modeling, the Exelon City Solar plant will generate more than 14,000 MWh per year. While Elsberg states that the plant is being used to collect data for the company, he also notes that it is too soon to draw conclusions about output on an annualized basis.

"Most of the lessons that we will learn will be through the operation of the plant itself," states Elsberg. "It is being treated as a demonstration plant and it is the first time that Exelon has built a (PV) plant. We are going to see how it operates in a real-world model."

Site of the Exelon City Solar plant before remediation
Site of the Exelon City Solar plant before remediation
Installation of PV panels
Installation of PV panels

Benefits for the local community as well as data collection

Exelon and SunPower note that there are multiple benefits to the plant beyond the production of electricity. Elsberg notes that it is important for Exelon to give something back to the city it calls home.

Like many areas in the urban Midwest, the West Pullman neighborhood has suffered from de-industrialization following a decline in U.S. manufacturing. In building the plant, Exelon was able to bring 200 jobs during the construction of the plant, as well as additional jobs by hiring a local welding shop to produce the 7,300 steel piers for the plant.

Also important to Exelon and SunPower was the transformation of the site. "We are proud to have built the world's largest urban plant, to have turned a brownfield into a bright field, to create a couple hundred jobs during a recession, and to bring a sense of pride for this community that for thirty years had nothing to show for this parcel of land," said Elsberg.

Exelon City Solar plant will produce more than 14,000 MWh per year
Exelon City Solar plant will produce more than 14,000 MWh per year

Exelon to reduce emissions under Exelon 2020 plan

The Exelon City Solar plant is part of the corporation's "Exelon 2020 Strategy", by which it plans to reduce, offset or displace more than 15 million metric tons of greenhouse gas emissions per year by 2020. According to Exelon, this includes offering more low-carbon electricity in the marketplace.

As a utility, Exelon is already prepared to move towards a low-carbon model of electricity generation, as it is the largest operator of nuclear power plants in the United States with 17 operational nuclear units in 10 plants as of 2009. Exelon also owns 36 wind plants, with three more under development, and the company states that it is the largest marketer of wind energy east of the Mississippi River.


Source: Exelon Corporation, SunPower Corporation
Images courtesy: SunPower Corporation and Exelon Corporation