Solar on storm water detention basins

The U.S. state of New Jersey is densely populated, meaning available land for ground-mounted solar projects is scarce. Consequently, this renewable energy market is primarily focused on rooftop installations.

However, Pro-Tech, an environmental engineering firm, has come up with the unique idea of installing photovoltaics on storm water detention basins, of which there are thousands in New Jersey.

The company’s first such project is currently underway at Peddie School. The 297 kilowatt system, which is being built with Kyocera photovoltaic modules, is scheduled to be completed in May. "We are drilling all the footings now and setting all the vertical support posts," explains John Drexinger, principal at Pro-Tech. "The rain has hindered us a little, but our anticipation is that the systems should be completed sometime mid to late May."

He adds that the installation procedure is similar to that of a ground-mounted photovoltaic project. "The footings are about four and a half feet deep," he says, adding: "They’re ordered footings, concrete with vertical posts, and then the racking from direct power and water is assembled on those vertical posts.

"In the basin, the only true difference, honestly, than a standard ground mount is the vertical height. The height of the array is 14 feet high at the lowest point inside the basin, because that has to be up at the top level of the basin and above the flood plains. So basically, it’s a very tall ground-mount or really, a carport in a basin."

In terms of costs, Drexinger states that while it is cheaper to install than an elevated carport photovoltaic system, solar systems on water detention basins are more expensive than ordinary ground-mounted projects. "I think it is somewhere around USD$5.25 to $5.35 a watt, because everything’s elevated and there’s a lot more involved in the concrete footing. You also have a lot of wind uplift, because of how tall these are, so your footings are much deeper in depth and your vertical posts are much stronger than standard systems."

Discussing the procedure for installing the water detention basin system, Drexinger explains that Pro-Tech had to obtain approvals from the New Jersey Department of Environmental Protection and the Mercer County Soil Conservation. "One of the things they were concerned about," he says, "was the volume of water displacement, because of the vertical posts, so we had to address that."

He adds: "We did our pre-design and submitted it to the proper parties for approval and we received a permit from that point. We then went out to bid on that project, and we hired a very experienced excavation company to do the work, because there’s certain criteria that you have to adhere to. One is that you can’t displace more than 5,000 square feet of soil when you’re working in the basin area."

Tremendous potential

Once this flagship project has been completed, Pro-Tech plans to install more photovoltaics on water detention basins. Currently, the company is considering several other projects, including one for a university and another for an unnamed "large municipality" in the state.

"Just that municipality alone has 60 detention basins that we have had conversations on," states Drexinger. "What we wanted to do was get the [Peddie] project underway (…) and make sure that we’re comfortable with discussing it with clients, because we knew the interest was going to be very high. We’re at that moment right now and we’re getting contacted on a weekly basis."

Drexinger believes that there is "tremendous" potential for this solar market to take off in New Jersey, due to the limited political and public support for ground-mounted solar systems. Additionally, he says that there are hundreds of thousands of detention basins and landfills available that can be used for solar projects.

In general, the size of solar systems on the water detention basins will range from between 200 and 500 kilowatts.

Speaking about the potential impact that this new market could have on the New Jersey solar industry, Drexinger states: "Companies in our industry should continue to look for projects that will have a public perception of being positive.

"Utility scale solar farms are not going to be very supported in New Jersey, because it is very densely populated, and you’re just not going to have the current Governor’s Office and Environmental Protection Agency or the Board of Utilities supporting utility scale solar where you’re using clean land. But New Jersey has a high concentration of landfills, brownfield sites and detention basins that seem to receive higher public support."