CASE STUDY: MaineDOT Solar Array Program
Project Summary
The Maine Department of Transportation (MaineDOT) installed three solar arrays in transportation rights-of-way: at Interstate 95 (I-95) Exit 109, I-95 Exit 112, and at the Augusta State Airport. All three of the projects are in Augusta, the state’s capital. The arrays generate 8 megawatts of solar energy, equivalent to the amount needed to power 1,000 homes. MaineDOT will purchase some of the power generated to offset the electricity needs of 1.7 million square feet of state buildings and facilities via a Net Energy Billing Credits Agreement. The solar arrays are expected to reduce the state government’s electricity costs by more than $8.8 million over the next 20 years, while also making progress towards state environmental goals
Project Motivation
MaineDOT established the Solar Array Pilot Program in 2020 to reduce its environmental impacts and support renewable electricity generation by installing solar arrays in transportation rights-of-way. MaineDOT also found the FHWA Memorandum on State DOTs Leveraging Alternative Uses of the Highway Rights-of-Way to be a source for motivation, guidance, and support for developing the project.
Project Implementation
Siting Decisions
MaineDOT chose the specific locations for the solar arrays to make use of state-owned land that would otherwise go unused due to its adjacency to highway and airport infrastructure. Proximity to the state’s capital was another benefit, allowing MaineDOT greater access to the project sites and close oversight of construction.
Environmental Review
MaineDOT assembled an interagency and cross-disciplinary team to develop the solar project. The team included individuals from MaineDOT’s Environmental and Legal Offices, the Maine Department of Environmental Protection, and federal agencies, including the United States Army Corps of Engineers (USACE), and the Federal Highway Administration (FHWA). For the projects on I-95 right-of-way, MaineDOT worked with FHWA’s Maine Division Office to obtain a Categorical Exclusion under the National Environmental Policy Act (NEPA) and to accommodate the solar arrays as a utility under MaineDOT’s Utility Accommodation Rules and FHWA regulations (23 CFR part 645), a process that was straightforward and accomplished in a timely fashion. The Federal Aviation Administration (FAA) was the lead agency for the NEPA process at the Augusta State Airport. The project site chosen was a surplus property, consisting primarily of wooded, undeveloped land.
Business Model
Construction at all three sites was completed in 2023. MaineDOT led the interconnection application process with the local utility supplier and awarded the contract through a competitive bidding process to Cenergy Power, an energy developer specializing in solar solutions. Cenergy Power will own and operate the infrastructure at each site under a Net Energy Billing Credits Agreement. Additionally, Cenergy Power is responsible for the cost of construction, maintenance, and a 20-year land lease. The State of Maine is purchasing the electricity generated from Cenergy at a reduced rate via a Power Purchase Agreement. The credits are applied to approximately 118 State of Maine electric bills, including electricity for the Capitol Complex and other state office buildings.
Project Benefits
The electricity cost savings of the solar arrays make them cost-effective over the life of the project. Additional benefits of the project include finding an innovative use for underutilized property, lowering maintenance costs for vacant land, and reducing emissions. By meeting more of the government’s energy demands with renewable sources instead of fossil fuels, the project will reduce greenhouse gas (GHG) emissions by 3,220 tons annually, the equivalent of 776 gasoline powered cars. The project will also generate approximately 300,000 renewable energy credits (RECs) which can be used to help MaineDOT or other agencies meet GHG reductions required by state policy. Alternatively, MaineDOT can sell the credits to generate revenue and allow other organizations to meet their own targets. MaineDOT encourages other state DOTs to assess how solar development in transportation rights-of-way may be feasible for them.
Figure 2. Solar Arrays at I-95 Exit 109. The solar arrays are outside of the clear zone and are protected by a guard rail. Source: MaineDOT
Challenges and Solutions
MaineDOT’s greatest challenge was a lack of internal expertise in solar power. As a result, it took time for MaineDOT staff to familiarize themselves with the clean energy industry and secure the interconnection application during the planning and implementation phases of the program.
Transportation agencies can use procurement to place the responsibility for interconnection on developers. For future projects, MaineDOT intends to lease land to a solar developer and allow them to take ownership of the application and project development.
Some of the required Federal and State environmental review processes were difficult to navigate. MaineDOT did not have prior experience working on environmental review with the FAA, which made that process slower and more challenging. Ultimately, MaineDOT obtained a Categorical Exclusion and an approval for Land Release from Aeronautical Use from FAA. Additionally, airport solar projects may also have glint or glare impacts on aircraft pilots, air traffic controllers, and other light-sensitive receptors, which may require additional study on the effects on safe navigation.
Existing relationships helped MaineDOT to navigate the permitting process. For Exit 109, MaineDOT’s partnership with the FHWA Maine Division helped to expedite the NEPA Categorical Exclusion determination.
Lessons Learned
Technical assistance from external subject matter experts was key to the project’s success. The Solar Array Pilot Program was inspired by success stories from The Ray, a nonprofit organization that has helped other state DOTs implement clean energy projects in transportation rights-of-way. The Ray’s Advanced Right-of-Way Mapping Tool analyzes the potential for solar energy generation along highway right of way. MaineDOT worked closely with The Ray using the mapping tool to lead the I-95 projects to completion. MaineDOT also developed relationships with utility company Central Maine Power and the Maine Public Utilities Commission, which were helpful for permitting approvals and navigating the interconnection process. MaineDOT staff will continue using the Advanced Right-of-Way Mapping Tool to scope location feasibility for new projects.
Robust public engagement can help solar projects move more smoothly. It is important to engage the public because projects in transportation rights-of-way are often close to private property. For these projects, MaineDOT presented at Augusta City Council Meetings, but for future projects they will consider additional virtual and in-person venues for public engagement.
Solar projects provide an opportunity to establish native vegetation. MaineDOT is committed to planting native, pollinator-friendly plants surrounding the arrays. Prior to construction, MaineDOT required the developer to submit a thorough “Seeding Plan for Pollinator Species” that includes weed eradication strategies, site preparation, a map or description of seed mix areas, seeding methods, vegetation establishment timelines, maintenance procedures for established vegetation, and mowing requirements. Seeding Plans are required to follow Maine Erosion and Sediment Control Best Management Practices and incorporate spring and fall inspections of vegetative cover by MaineDOT Environmental Office and Landscape Architecture staff.
Conclusion
MaineDOT’s Solar Array Pilot Program has successfully implemented three solar array projects that will provide the agency with long term cost savings and environmental benefits. The program has the potential to expand across the state with relative efficiency, thanks to the siting analysis capabilities, relationships with utility companies and other public agencies, and experience with nuanced environmental processes MaineDOT built over the course of this project. State DOTs and developers working on future projects can learn from MaineDOT’s experience with renewable energy credits, native vegetation seeding plans, and leveraging resources from industry experts.