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New York City, Chicago, and Philadelphia increasingly view their contaminated inner-city brownfield sites as natural locations for large-scale solar installations. 

At the national Brownfields conference held in Philadelphia this year, Dave Graham, who works on Chicago’s brownfield program, said the City Solar project just “fell into our laps.” He was called into a meeting in the mayor’s office with representatives from Exelon and SunPower and found they wanted to create a massive solar farm on a derelict brownfield site. Actually, massive is an understatement for this project: It’s the largest urban solar plant in the U.S. Its 32,000 photovoltaic (PV) panels provide 10 MW of energy, enough to power 1,500 local homes. 

Heavily contaminated sites can cost up to $150,000 per acre to clean up. The West Pullman site for City Solar, which “has a variety of issues,” would have cost $20 million alone to clean up, “something no one in the city wanted to invest in.” As a result, Exelon simply put solar panels on top of the site, leaving the worst soils untouched underground. In some cases, where PV structures need to be installed, the team did actually discover underground storage tanks, which they then removed.

Washington, D.C. should undertake a comprehensive survey of existing brownfield sites to determine which could be used to form a public/private partnership with a solar power firm. 

Research cited by the U.S. Environmental Protection Agency says if placed strategically, trees can reduce summertime cooling energy needs by 7-47 percent and wintertime heating needs by 2-8 percent. 

The city should encourage the use of smart tree placement around residential and commercial buildings by increasing fines for tree removal and providing direct financial or tax benefits for tree planting near buildings on privately owned property. 

According to one Canadian study, a 32,000-square foot green roof on a one-story commercial building in Toronto reduced energy usage by 6 percent in the summer and 10 percent in the winter. Similarly, the green roof of the American Society of Landscape Architects (ASLA), at just 3,000 square feet, reduces energy usage by 3 percent in summer and 10 percent in winter. To ensure the benefits of green roofs are widespread, cities like Toronto have mandated the use of green roofs for certain types of buildings. 

D.C. should follow Toronto’s lead and mandate the use of green roofs in all new buildings. To address older structures, the District can follow Philadelphia’s lead and introduce a stormwater runoff fine, which will incentivize the use of green roofs, bioswales and permeable pavements – systems that not only cool but also help reduce energy use. The city can also incentivize the use of green roofs in older buildings by providing tax breaks for feasibility studies and other preliminary design assessment costs.

In addition, roofs can accommodate both green roof components along with solar panels. In fact, solar panels will work more efficiently near green roof sedum and plants as the air will be cooler. In the northern hemisphere, solar panels should be installed on commercial and residential rooftops to face south. It’s important that tree shade doesn’t cover the panels.

Incentivize the use of rooftop solar panels, and use in combination with green roofs.