The Seneca fly-ash landfill is owned and maintained by Metropolitan Council Environmental Services and permitted by the Minnesota Pollution Control Agency (MPCA). The landfill is currently in the third decade of its 30-year post-closure period. Its cap, designed by Barr, has been in place since 1996.

The Met Council and solar developer Cypress Creek Renewables proposed installing more than 3,000 solar panels atop the capped landfill. The installation posed challenges because solar panel foundations for photovoltaic arrays typically extend 6 to 10 feet below the ground surface; at this site, however, a synthetic membrane sealing in the stored ash and sludge lies just 2 feet underground. To avoid puncturing the membrane, the panels (as well as electrical conduits and site perimeter fencing) had to be installed on ballasts—concrete platforms that support weight without penetrating the soil.

Barr performed an engineering analysis of the project’s feasibility and assisted with stormwater permitting through the MPCA. Additionally, we reviewed the panel layout and ballast specifications to evaluate how the installation might affect the site’s surface hydrology. We then prepared a memorandum that documented the negligible effect the panels would have on site hydrology, demonstrated the feasibility of installing the solar array, and explained why the solar farm would not compromise the landfill cover’s integrity or the owner’s ability to comply with the state landfill permit.

In 2018, the U.S. Department of Energy’s Office of Fossil Energy and Carbon Management, along with the National Energy Technology Laboratory, issued a request for proposals as part of its Coal FIRST initiative—a research and development program that aims to advance first-of-their-kind coal generation technologies able to adapt to the evolving electrical grid.

Barr submitted two concepts for the first phase of the project, and in 2019 was awarded a pre-front-end engineering design (pre-FEED) study for a hybrid gas-and-coal concept power-plant design. We teamed with Doosan Heavy Industries and Construction; Envergex, LLC; Microbeam Technologies, Inc.; MLJ Consulting; and the University of North Dakota’s Institute of Energy Studies to develop the plant concept, which combines a state-of-the-art, ultra-super-critical 250 MW coal-fired power plant with an 80 MW natural-gas-fired turbine and energy storage. 

The plant design combines unique features to allow for rapid startup and load changes, including a combustion turbine and battery with an inherently fast startup and ramp-rate capability. When power demand is lower than the minimum load, surplus electricity will be transferred to the energy storage system, which will handle the initial ramp-up for morning or evening peak demand.

Some innovative aspects of Barr’s concept were the integration of a gas turbine and coal boiler; an amine-based post-carbon-capture system with steam plant integration; and a battery-energy-storage-system module.

Barr delivered the study findings in a preliminary engineering report that illustrated the advantages and effectiveness of the proposed system, the business case, and an approach for advancement through the identified technology gaps.