Harnessing the sun’s energy in new ways

A small tract of land in the southwest corner of the former Horace Williams Airport property is slated to house the University’s latest renewable energy project, this one powered by the sun.

Plans are being finalized for a state-of-the-art solar farm on the 2.7-acre site, combining photovoltaic panels that convert sunlight into electricity with a battery storage system for any electricity that is not immediately consumed. The energy stored by the batteries can be discharged as needed, either very slowly or as quickly as within four hours.

The solar + storage project will offset some of the University’s energy purchases and advance its goal to become greenhouse gas neutral. The reductions in both energy costs and greenhouse gas emissions are key to the Three Zeros initiative, which aims to reduce the University’s environmental footprint through net zero water usage, zero waste to landfills and net zero greenhouse gas emissions.

The solar panels will help power the buildings along Airport Drive, explained Brad Ives, associate vice chancellor for Campus Enterprises. At its peak, he said, the solar output could handle about a third of the load for that area on a given day, which would decrease the electricity that had to be purchased from Duke Energy.

In addition, the battery storage system provides flexibility in deciding when to use solar energy and how much to store for future use. The battery storage system also can be charged from Duke Energy’s grid at times when low-cost power is available.

Although the technology itself is not new, the solar array with battery storage is a first for the University and will be one of the largest battery installations for Duke Energy.

More commonly, solar projects use rooftop panels like those on the Frank Porter Graham Student Union, the Bell Tower Parking Deck and the North Carolina Botanical Garden’s Education Center. A freestanding solar farm requires ample space, and battery storage adds another layer of complexity.

The University is like a utility within a utility because it is an energy customer with a fairly extensive electric distribution system of its own, said Trevor Rogers, electrical engineer with Electric Distribution Systems. Whereas most Duke Energy solar projects connect power directly to the grid, Carolina’s system will connect from the former airport property to switches on Airport Drive, with the interconnection to Duke Energy on Homestead Road, a couple of miles away.

“Duke had no preconfigured template for this situation,” Rogers said, “so this project will be the first to put battery storage indirectly on their grid as a customer.”

The design for the innovative project began in January 2017 with the development of a simulation model, and the plans have been fine-tuned multiple times in conjunction with Carolina and Duke Energy engineers. The project is expected to be ready for bid early this fall, with anticipated completion in spring 2019, said Cindy Register, assistant director of engineering services in Energy Management.

The fixed-structure array will include 1,350 two-feet by four-feet raised panels, oriented and angled to capture optimal energy from the sun, she said. The panels generate direct current voltage from the sun’s energy and are connected in groups that, in turn, are connected to power inverters. The inverters produce useable alternating current, like the power we get from wall outlets.

The photovoltaic panels can power the electric distribution system or can charge the battery storage system, which then can discharge power when the EDS engineers send the signal to do so, Register explained. That’s where the strategy comes in.

Reducing the need for power supplied by Duke Energy, especially during times of peak demand (such as a hot summer day when air conditioners run constantly), can help reduce costs and energy use for the Airport Drive buildings.

EDS engineers will be able to monitor the energy generated by the photovoltaic panels and where it is distributed, including whether energy is being stored in the battery system or is being used to offset energy consumption.

“That’s pretty significant because we haven’t done that kind of daily monitoring and control before,” said EDS electrical engineer John Lindberg, who retired at the end of the summer.

Current projections are for the project to cost $1.7 million, with a break-even point in a little more than 15 years.

“We actually expect to do better than that, though, depending on battery pricing, plus the expectation that Duke will raise its rates over the next 15 years,” Ives said. “During the 20- to 30-year life of the project, we should see substantial savings.”

A $75,000 solar rebate from Duke Energy also will help defray some of the initial costs.

Project bids will be based on a flow battery system, with an option for a lithium ion battery system, Register said.

In a flow battery, reactants are kept in a liquid storage system and pumped through a battery stack, which provides the current flow. Flow batteries, which are not commonly used in the United States, have the advantage of longevity and flexibility in increasing capacity, the engineers explained, but they tend to be more expensive.

From the outset, the project was to be unique and sustainable on many different levels, Ives said. And that includes the capability to move the entire photovoltaic array and battery if the University should decide to use the site for something else in the future.

It also includes the creation of a pollinator habitat, not only for aesthetics but also to address the important environmental issue of pollinator decline. And Carolina happens to have a resident expert in that area.

Damon Waitt, director of the North Carolina Botanical Garden, has worked with the National Renewable Energy Lab and others on pollinator-friendly plantings for solar farms, so the project planners reached out to him about creating a pollinator habitat here.

A variety of plantings native to North Carolina, including Black-eyed Susans and Bee Balm, will be chosen to attract bees, butterflies and other pollinators, Waitt said. In addition, the plantings below and around the solar panels will help control erosion and stormwater runoff on the site.

Project plans also include ways to engage people on and off campus.

To help students learn about solar + storage technologies, Dana Haine will develop a suite of educational materials and activities geared for a diverse audience, from high school and community college students to Carolina undergraduates. Haine, a science educator for the Institute for the Environment, said she plans to collaborate with the project’s design team and members of the Renewable Energy Special Projects Committee in creating the curriculum.

As the solar project nears completion, planners hope to create a viewing area on site for the public to see real-time data – weather, solar output, etc. – affecting energy use and the decisions that go into utilizing solar energy.

Virtually every aspect of the project is designed to be a living-learning laboratory in some way, from best practices in solar energy management to multi-level lessons in sustainability.