Why surplus interconnection could be one of Wisconsin’s most practical clean energy tools

In Portage, Wisconsin, there is a set of wires that has been carrying electricity for decades. 

They connect a coal-fired power plant called Columbia Energy Center to the regional grid. Those wires run to a substation, and that substation connects to transmission lines that carry power to homes and businesses across the state.

Columbia is scheduled to retire. But those wires are not going anywhere.

That is the idea behind surplus interconnection, and it is one of the more practical and underappreciated tools in the clean energy transition.

How It Works

When a power plant connects to the electric grid, utility engineers size everything for that plant’s full output. The wires, the transformers, the substation, all of it. That infrastructure does not disappear when a plant retires, isn’t running, or scales back. The available capacity is still there, even if nothing is using it.

Surplus interconnection lets a new clean energy project plug into that existing connection instead of building a new one from scratch.

Think of it like a parking lot at a stadium that only fills up on game days. Most of the time, those spaces sit empty. Surplus interconnection lets new projects use that empty space, instead of paving a brand new lot somewhere else.

There is one important rule. You cannot park more cars in the lot than it was built to hold. The total electricity moving across the connection point cannot exceed what the original plant was approved to put on the system.

This is technology-neutral. Solar, wind, storage, existing fossil fuel plants, or any combination of them can share an existing interconnection, as long as the total output stays within the approved limit. It is about reusing the connection, not about choosing one technology over another.

Where the Opportunities Are

Retiring coal plants are a natural place to start. Columbia is a clear example of this principle. Alliant Energy is building a long-duration battery right next to the existing coal facility, on the same site, using the same grid connection. The Public Service Commission approved the project in 2025, construction begins this year, and once it is online, it will be able to discharge clean power for hours at a stretch.

Peaker plants tell a similar story. These are gas-fired facilities that utilities run only during periods of peak demand, often hot summer afternoons when air conditioners are running across the state. A peaker might only operate a few hundred hours a year, which means its grid connection sits idle most of the time. Co-locating solar, wind, or storage at a peaker means putting that connection to work the rest of the year. The peaker stays in place as backup for the rare hours when it is genuinely needed.

The same logic applies to existing renewables. A solar plant’s grid connection is sized for its peak output, which only happens for a few hours of sunny midday. A wind project often generates most at night, when demand is lower. Either way, the connection has room to spare much of the time. Adding storage, or pairing solar with wind to fill complementary hours, lets the project use that headroom and deliver clean power through the same connection when it is needed most.

This is already happening in Wisconsin. Solar developers across the state are pursuing battery additions at existing utility-scale solar projects.

Why It Matters Now

Wisconsin is about to see a major surge in electricity demand, driven in large part by new data center development. Meeting that demand by building new transmission lines and power plants, both of which take 5 or more years, could take longer than we would like. 

Surplus interconnection provides an additional tool to help us meet the timeline required for projected load growth. Projects that reuse an existing connection point can often be built in two to three years. Though not a silver bullet for meeting energy demand in Wisconsin, it gives us an opportunity to meet this increase in demand without setting us back years on our clean energy goals.

MISO Has Already Given the Green Light

Wisconsin sits inside MISO, the Midcontinent Independent System Operator. MISO is the regional grid operator that manages the bulk power system across fifteen states, and it has explicitly built surplus interconnection into its rulebook. MISO’s own guidance steers developers who want to add batteries at existing plants toward surplus interconnection as the appropriate route. In short, the regional path is already open. What MISO does not do is require any utility to go looking for these opportunities. That is left to the states.

Other states are stepping into this space. Virginia recently passed the first-in-the-nation Facilitating Access to Surplus Transmission Act (FAST Act). Virginia sits in a different Regional Transmission Organization, but the underlying mechanism is the same. The law requires regulated utilities to inventory sites where they have unused interconnection capacity and run competitive solicitations to fill that capacity with new solar and storage. The stated goal is to cut interconnection timelines from years to months and avoid major new transmission build-outs that would otherwise land on customer bills

The tools exist. What is missing here is a consistent practice of looking for these opportunities.

Looking Ahead

Columbia is not the only Wisconsin plant on the way out. Oak Creek, Edgewater, and units at Weston are all scheduled to retire or convert in the next several years. Each one is a high-capacity connection point that could host new solar, wind, storage, or a mix of them. Wisconsin’s growing fleet of utility-scale solar and wind projects offers another set of opportunities for adding complementary generation and storage without new grid infrastructure, and the peakers across the state are solid candidates as well.

Surplus interconnection deserves more deliberate attention. The grid we already have is more valuable than we sometimes give it credit for. Reusing it well is how we get clean energy online faster and protect ratepayers from paying twice.

There is an old story from the Mediterranean about an elderly man planting an olive tree. A passerby asks why he would plant something that takes decades to bear fruit. The man replies: “Because my children will need the olives.”

Transmission lines are much the same.

Across southwest Wisconsin, communities are hearing about the MariBell Transmission Project, a proposed high-voltage transmission line that would connect Marion, Minnesota, to Bell Center, Wisconsin. The project is part of an effort to strengthen the electric grid across the Upper Midwest.

When people first hear about a transmission project, the natural questions are: Why do we need it? And is it safe?

We can answer both.

Transmission Is Planned Generations Ahead

Transmission lines are not built for today’s electricity needs. They are planned decades ahead for our children’s future.

Much of the infrastructure we rely on today was planned decades ago. Engineers studied population growth and future electricity demand long before many of the businesses and technologies we rely on today even existed.

Regional grid operators like MISO (Midcontinent Independent System Operator) are responsible for conducting these long-range studies. From that work comes the Long Range Transmission Plan, which identifies major grid upgrades needed to maintain reliability across the region. The MariBell project is part of that effort.

Once a project appears on a planning map, it often takes 10 to 15 years before construction begins. Environmental studies, landowner discussions, engineering design, and regulatory approvals are all requirements for this long-term investment.

In other words, transmission is built for the future long before it arrives.

The Backbone of a Reliable Economy

Electricity demand across the Midwest is growing again.

Manufacturing is expanding. We’re electrifying our homes and transportation. At the same time, older power plants are retiring, and new energy sources are coming online across the region.

Transmission connects it all, allowing electricity to travel long distances, balancing supply and demand across states, and ensuring reliability during extreme weather or periods of high demand. It also allows new power generation, from solar to nuclear, to connect to the grid and reach the communities that need it.

Addressing the EMF Question

Another common concern raised during transmission discussions is electromagnetic fields, or EMF.

EMFs are produced whenever electricity flows through a wire, not just transmission lines. Household wiring, appliances, power tools, and TVs also create EMFs.

Because this issue has raised questions for decades, it has been studied extensively. Research conducted by the National Institutes of Health, the World Health Organization, and the National Cancer Institute has examined EMF exposure for more than 40 years.

The consistent scientific finding is that EMF from power lines has not been shown to cause adverse health effects from the levels of exposure typically experienced by the public.

Transmission lines are also designed to naturally reduce exposure. The height of structures and the distance they are placed from homes are both meant to take advantage of the fact that EMF levels drop rapidly the farther you move away from a line. In many cases, household appliances can expose people to stronger EMF levels at a very close range.

That doesn’t mean concerns should be dismissed. But decades of research provide strong reassurance that transmission infrastructure operates safely within established guidelines.

Thinking Like the Man With the Olive Tree

The conversation around the MariBell project is in its early stages. Maps show both proposed and optional corridors, and the final route will be determined through regulatory review and public input.

Those conversations matter. Communities deserve transparency, and landowners deserve to be heard.

The grid we rely on today exists because previous generations believed in planning for the future. They built the infrastructure that powers today’s homes, hospitals, farms, and businesses.

They planted the olive trees.

Now it’s our turn.

Transmission projects like MariBell are not just about meeting today’s electricity needs. They are about ensuring that our children inherit an infrastructure strong enough to support their future.

If we want them to enjoy the harvest, we have to start planting now.

On Thursday, October 30, the Public Service Commission of Wisconsin (PSC) authorized two important transmission projects. These projects are part of the Midcontinent Independent System Operator’s Long Term Transmission Planning (MISO LRTP) processes. They will be jointly owned and operated by Xcel Energy and American Transmission Company (ATC).

The Western Wisconsin Transmission Connection Project (Western Wisconsin Project) will run through the Eau Claire region, connecting Trempealeau County to Clark County. This transmission project will connect with the separate Grid Forward Central Wisconsin Project (Central Wisconsin Project), which will run from the central part of the state to Columbia County. These two projects are a necessary part of the state’s effort to expand renewable energy production in Wisconsin and the broader Midwest region. Updated and new transmission lines support the modernization and decarbonization of the resources that produce energy for Wisconsin’s homes and businesses.

RENEW participated in the legal proceedings for these transmission projects, in which the PSC considered the applications and found that these projects were in the public’s best interest. RENEW’s expert testimony detailed the need for both the Western and Central Wisconsin Projects from the perspective of renewable energy integration and economic development.

According to Xcel Energy, the Western Wisconsin Project alone will “support the full interconnection of over 43,000 megawatts (MWs) of potential new renewable generation in the upper Midwest.”

According to the Wisconsin Zero Carbon Study, Wisconsin will need to rely on an interconnected grid that works with those of neighboring states such as Minnesota, Iowa, and Illinois to integrate renewable energy resources and decarbonize the grid. These two transmission projects will interconnect with another transmission project proposed by Dairyland Power Cooperative, which will be taken up by the PSC later this year. All three of these transmission projects will eventually interconnect with lines in Minnesota. As a result, these projects represent major building blocks for the transmission corridors modeled in the Wisconsin Zero Carbon Study.

As stated by RENEW Policy Director Andrew Kell in his testimony, utility-scale renewable resources will utilize these transmission projects “to support their interconnection and delivery of power to Wisconsin’s homes and businesses. The proposed transmission [projects are key examples] of infrastructure needed for Wisconsin’s clean energy economy.”

RENEW applauds the PSC for authorizing these projects, and we look forward to the many solar, wind, and clean energy storage projects that will be able to deliver clean, reliable energy once these transmission projects are completed.