A major expansion of battery storage may be the most economical and environmentally beneficial way for Illinois to maintain grid reliability as it phases out fossil fuel generation, a new study finds.

The analysis was commissioned by the nonprofit Clean Grid Alliance and solar organizations as state lawmakers consider proposed incentives for private developers to build battery storage.

“The outlook is not great for bringing on major amounts of new capacity to replace the retiring capacity,” said Mark Pruitt, former head of the Illinois Power Agency and author of the study, which suggests batteries will be a more realistic path forward than a massive buildout of new generation and transmission infrastructure. 

The proposed legislation — SB 3959 and HB 5856 — would require the Illinois Power Agency to procure energy storage capacity for deployment by utilities ComEd and Ameren. Payments would be based on the difference between energy market prices and the costs of charging batteries off-peak, to ensure the storage would be profitable. The need for incentives would theoretically ratchet down over time. 

“As market prices for power go up, your incentive goes down,” Pruit said. “The idea is to provide an incentive that bridges the gap between the cost of battery technology and the value in the market. Over time, those will equalize and level out.” 

The bills, introduced in May at the end of the legislature’s spring session, would amend existing energy law to add energy storage incentives to state policy, along with existing incentives for nuclear and renewables. 

The study noted that Illinois will need at least 8,500 new megawatts of capacity and possibly as much as 15,000 new megawatts between 2030 and 2049, with increased demand driven in part by the growth of data centers. Twenty-five data centers being proposed in Illinois would use as much energy as the state’s five nuclear plants generate, according to nuclear plant owner Exelon’s CEO Calvin Butler Jr., quoted by Bloomberg. 

The North American Electric Reliability Corporation (NERC) found in its summer and winter 2024 assessments that within MISO and PJM regional grids, Wisconsin, Michigan, Minnesota, Illinois and Indiana are all at “elevated” risk of insufficient capacity. 

“NERC, PJM, MISO and the Illinois Commerce Commission have all identified the potential for capacity shortfalls,” said Pruitt. “You do have some options for alleviating that. You can build transmission and bring in capacity from outside the state. You can maintain your current domestic generating capacity [without retiring fossil fuel plants]. You could expand your domestic generating capacity. And an independent variable is your growth rate. All these have to work together, there’s no silver bullet. We know there are major challenges on each of those fronts.” 

Gloomy numbers 

The latest PJM capacity auction results showed capacity prices increasing from $28.92/MW-Day for the 2024/25 period to $269.92/MW-Day — a nearly 10-fold increase — for the following year. That “translates into an annual cost increase of about $350 for a typical single-family household served by ComEd,” Pruitt said. “The increase in costs indicates that more capacity supply is required to meet capacity demand in the future.” 

There are many new generation projects in the queue for interconnection by MISO and PJM, but many of them drop out before ever being deployed because of unviable economics, long delays, regulatory challenges and other issues. A recent study by Lawrence Berkeley National Laboratory noted that while interconnection requests for renewables have skyrocketed since the Inflation Reduction Act, only 15% of interconnected capacity was actually completed in PJM and MISO between 2000 and 2018, and experts say similar completion rates persist. 

“This finding indicates that deploying sufficient new capacity resources to offset [fossil fuel] retirements is not likely to occur in the near term,” said Pruitt. “Just because something is planned doesn’t mean it gets built.” 

Meanwhile the state is running out of funds for the purchase of renewable energy credits (RECs) that are crucial to driving wind and solar development. The 2024 long-term renewable resources procurement plan by the IPA shows the state’s fund for renewables reaching a deficit in 2028, so that spending on RECs from renewables will have to be scaled back by as much as 60%. 

Long-distance transmission lines could bring wind energy or other electricity from out of state. But planned transmission lines have faced hurdles. The Grain Belt Express transmission line, in the works for a decade, was in August denied needed approval from an Illinois appellate court. The transmission line, proposed by Invenergy, would have brought wind power from Kansas to load centers to the east. 

“That sets it back years,” Pruitt said. “Transmission is a very long-term solution. I’m sure people are working diligently on it, but it’s five to 10 years before you get something approved and built.” 

Value proposition, solar benefits 

Pruitt’s study found that if 8,500 MW of energy storage were deployed between 2030 and 2049, Illinois customers could see up to $3 billion in savings compared to if they had to foot the bill for increased capacity without new storage. The savings would come because of lower market prices in capacity auctions, as well as investment in new transmission and generation that would be avoided. 

Pruitt found that $11 billion to $28 billion in macro-level economic benefits could also result, with blackouts avoided, reduced fossil fuel emissions and jobs and economic stimulus created. 

Pruitt’s analysis indicates that the incentives proposed in the legislation would cost $6.4 billion to customers. But the storage would result in $9.4 billion in savings compared to the status quo, hence a $3 billion overall savings between 2030 and 2049. 

“Solar is great, but solar is an intermittent resource; battery storage when paired with solar allows it to be far more reliable,” said Andrew Linhares, Central Region senior manager for the Solar Energy Industry Association. “Battery storage is not as cheap as solar, but its reliability is its hallmark. Combining the resources gives you a cheap and reliable resource.” 

“Solar and storage is this powerful tool that can help reduce costs for consumers and create new jobs and economic activity,” he continued. “I don’t believe that same picture is there for building out new natural gas resources. Anything that helps storage, helps solar and vice versa. CEJA sees these two technologies as being joined at the hip for the future, they are being seen more and more as a single resource.”

Study suggests a big role for grid battery storage as Illinois shutters its coal power plants is an article from Energy News Network, a nonprofit news service covering the clean energy transition. If you would like to support us please make a donation.

As president and CEO of Green Mountain Power in Vermont, Mary Powell developed the first utility partnership with Tesla to attach residential Powerwall batteries to the grid, providing backup clean power for the utility when needed. Customers could earn money by essentially filling the batteries at night and dispatching them during the day, Powell explained in a 2016 interview with Energy News Network. 

Today, such arrangements are increasingly promoted by clean energy advocates, who’ve dubbed distributed grid-connected batteries — plus solar — “virtual power plants” that allow homeowners and businesses to help out utilities during times of high demand. They’re also central to Powell’s current mission as head of the nation’s largest residential solar company.

Powell left Green Mountain in 2019 after two decades with the company, and in 2021 she became CEO of Sunrun. In an interview during a recent conference near Chicago, she spoke about how the culture of her former industry can slow the pace of innovation that’s much needed to address climate, cost and reliability concerns. 

“You’re talking about a 100-plus-year-old system and way of thinking, and you compound that with the fact that utilities’ whole culture is built for ‘slow and no’ and ‘protect, preserve, defend.’ For so many years, it’s been a one-way system,” Powell said. 

Virtual power plants are a prime example of the coming change. Powell said utilities’ experience with energy efficiency in recent decades provides a look at what might be coming for such pairings of solar and storage.

“I would say energy efficiency was the disruption — the first opportunity for utilities to start to think differently about their role and their mandate. And as we know, that took like 20 years, even for the most progressive utilities, to embrace.”

Utilities can generally choose to incorporate virtual power plants into their rate structures and grid services, and state regulators and legislatures can facilitate the concept through decisions, laws and policies that create incentives and provide standards. The Illinois legislature is considering a bill that would essentially allow the agency that procures power on behalf of utilities to contract with virtual power plants.  

Green Mountain Power was an early adopter of energy storage under Powell’s leadership, and broader adoption of the technology is ramping up quickly. The U.S. Department of Energy noted in a 2023 report that, “deploying 80-160 GW of virtual power plants (VPPs) — tripling current scale — by 2030 could support rapid electrification while redirecting grid spending from peaker plants to participants and reducing overall grid costs.” 

That means utilities will have to adapt quickly, and Powell sees a significant role for private developers in that transition. Powell describes Sunrun as a “clean energy lifestyle company,” branching into technologies like smart electric panels and EV charging. 

“When you think about customers having heat pumps, when you think about them having electric vehicles, you make sure that you’re leveraging all of that in a way that’s beneficial for the grid and beneficial for the customer.”

That focus on the end users of electricity is in part a bet that utilities’ need for solar power will eventually catch up to consumer demand.

“When I went to Sunrun I said to the team, ‘We’ve got to stop wandering around trying to convince every Tom, Dick and Harry utility to utilize our resources.’ We’re doing it, we just need to scale as fast as we can. 

“Because guess what, utilities are going to hit the wall, they are hitting the wall in some parts of the country, and they don’t have the ability to meet the kind of capacity demands that are projected over the next five years. They’re going to need our resources.”

Despite that expected market demand, Powell said legislative and regulatory bodies also have a role to “nudge utilities in the right direction.” Illinois in particular, she said, provides a strong example. 

“Illinois has done an amazing job. Making sure that rooftop solar is considered as part of the RPS [Renewable Portfolio Standard] is really thoughtful policy. And I am encouraged with a lot of the conversations about how we could leverage storage more. So yeah, we’re very bullish about Illinois.”

Powell also said she has no regrets about leaving the utility sector to work at Sunrun.  

“Frankly, even the fastest-moving utility was moving a little too slow for me. We weren’t scaling as fast as I would have loved us to be able to scale. It’s awesome to work on mission-driven work that you feel is valuable for the people you serve and for the planet at the same time.”

Sunrun CEO says utilities’ ‘slow and no’ culture gets in the way of energy innovation is an article from Energy News Network, a nonprofit news service covering the clean energy transition. If you would like to support us please make a donation.

For years, utilities have grappled with how to handle the ever-growing number of solar and battery systems trying to connect to the lower-voltage grids that deliver power to customers. That’s especially true for midsize projects like, say, a solar array that might adorn the roof of a multiunit apartment complex or a community-solar project that generates power shared by hundreds of dispersed customers.

On the one hand, utilities have eyed such projects warily, fearing that if the solar panels or batteries inject too much power onto local circuits at moments when electricity demand is low, it might cause grid instability or safety problems. As a result, utilities have thrown up barriers that have delayed or halted grid connections.

But as advocates have been pointing out for over a decade, these distributed solar and battery resources can also be enormous assets: By holding back power when the grid doesn’t need it, and then sharing their extra power during periods of high demand, they can help alleviate grid strains and lower the cost of keeping the grid running for everyone.

It’s taken California regulators, utilities and clean-energy advocates nearly four years to hash out these conflicting ideas. But in mid-March, the California Public Utilities Commission approved new interconnection rules that take into account how, with the right structures in place, solar and solar-plus-battery systems can be more help than hazard to California’s overworked grid.

“This will open up opportunities for distributed energy resources to be designed in a way that aligns with grid needs,” said Sky Stanfield, an attorney who works with the Interstate Renewable Energy Council, the nonprofit group that’s been the main proponent of the new rules. ​“It’s a long time coming to recognize that distributed energy resources are a whole lot more helpful than they’re allowed to be — and that we don’t have to spend as much to upgrade the grid as a result.”

The ​“Limited Generation Profile option” just approved by the CPUC is a complicated set of regulations that determine how solar and solar-battery systems interact with the lower-voltage grids operated by California’s CPUC-regulated utilities Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric.

Today, those utilities make a simplistic set of assumptions when they consider the potential impacts of a project on the lower-voltage grid systems that carry power from substations to homes and businesses, Stanfield said — basically, that each project is producing its peak output at the time of least electricity demand from customers.

That’s pretty much how all U.S. utilities calculate the risks of new generation connecting to their grids, she noted. But this assumption is likely to yield findings that exaggerate how likely a project is to inject too much power onto local grid circuits.

To eliminate those perceived risks, utilities have demanded that project developers pay for grid upgrades themselves or have prevented the projects from connecting at all. Since those grid upgrades can cost hundreds of thousands to millions of dollars and take years to complete, the result either way tends to stop projects in their tracks.

Allowing new solar and battery projects to support the grid

The CPUC’s new policy takes a different tack, one well suited to larger-scale projects that are more likely to trigger grid upgrades. It will allow solar and battery projects to modulate how much power they send to the grid with the help of either solar inverters whose power-control systems can reduce power output from moment to moment or batteries that can soak up excess solar power and inject it back into the grid later.

Limited Generation Profile projects would be able to use these capabilities to alter their grid injections during different periods of the day, based on a set of schedules they can choose from. Those scheduling options are derived from the grid data available in the maps of hosting capacity from Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric. (Here’s a snapshot of PG&E’s hosting-capacity map for a downtown section of the central California city of Bakersfield, with circuit capacity represented in red, orange, yellow and green.)

Most utilities in the U.S. haven’t been ordered by regulators to collect the detailed and accurate local grid data needed to create these kinds of maps, Stanfield noted. In fact, the Interstate Renewable Energy Council has played a key watchdog role in alerting the CPUC to problems with these maps as they’ve been developed over the past decade, as well as in making them more useful for customers and project developers looking for good spots to connect to the grid.

Thanks to those improvements, California’s maps now contain accurate information on the hour-by-hour capacity of individual circuits.

With this data in hand, California’s three largest utilities and clean-energy project developers can finally agree on just how much power solar and battery projects can safely inject onto the grid during different periods of the day and night across each month of the year.

That amount may be close to zero during some stretches — say, on a circuit with many homes with rooftop solar systems during sunny and mild spring daylight hours, when self-generated solar power can exceed customer demand for electricity. Within those hours, Limited Generation Profile projects may export little or no energy at all.

But these ​“minimum-loading” conditions are relatively rare — and at other moments, that same grid circuit may be hungry for all the power it can get. That’s typically during hot summer and autumn evenings, when the state’s ample solar resources are fading away, yet electricity demand for air conditioning remains high — the same conditions that have caused statewide grid emergencies in recent years.

California’s power grid is struggling to deal with the wide swings between times when it has too much solar and times when all available resources still don’t provide enough electricity. In fact, the CPUC and state policymakers have made significant efforts to address this imbalance via state rooftop solar policy — which has reduced the value of solar delivered to the grid while promoting the value of batteries that can store power for when it’s needed — and with utility-scale power procurement policies, which have put gigawatts of batteries into operation over the past few years to store solar power for those evening hours when demand exceeds supply.

But until now, utility interconnection policy ​“has not taken into account, or enabled, distributed energy resources to differentiate when they produce power and when they don’t,” Stanfield said. That’s left interconnection policy misaligned with broader state policy imperatives for how best to use solar systems and batteries, she added.

It’s also put interconnection policy at odds with policy efforts to better manage growing distribution-grid costs, Stanfield noted. Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric are facing tens of billions of dollars of additional grid investment in the coming decades to supply the millions of electric vehicles, heat pumps and electric appliances that the state is asking consumers to adopt in order to reduce carbon emissions.

“Grid upgrades are expensive,” Stanfield said, ​“and we want to avoid them where we don’t need them” — particularly in cases where new solar and battery systems could actually help reduce grid strains.

Even more fundamentally, rules that bar more solar and battery power from reaching the grid based on outdated and inaccurate methods of determining their grid impacts will rob customers at large of the value those projects could provide.

That’s the conclusion reached by Amin Younes, an electric distribution planning and policy engineer with CPUC’s Public Advocates Office, which represents utility customers’ interests. Younes studied the potential for the Limited Generation Profile option to add more clean energy to California’s grids during hours when energy is in short supply.

This graphic from a presentation of his work indicates how widely the capacity of a typical distribution grid circuit can vary from hour to hour. In this case, limiting a solar or battery project to the minimum loading condition — the red line on the chart — would have forced a project to be sized to deliver no more than 1.5 megawatts of power of maximum capacity. But during many more hours of the year, that circuit could accept far more than that — often more than twice that minimum limit, or more than 3 megawatts of power.

According to his analysis, factoring in that extra capacity across the distribution circuits of all three utilities could add up to tens of billions of dollars per year in additional clean energy that could be delivered. And because that power would supply the grid at hours when electricity costs and threats of grid emergencies are the highest, that ​“could lower costs and increase grid reliability,” he said in an interview.

Finally, implementing the Limited Generation Profile option should allow solar and battery developers to avoid having to pay for grid upgrades and give them a much faster interconnection process, Stanfield said. And, if it works as planned, it could be a useful model for other states to follow.

Solving grid-interconnection challenges across the country

In a 2021 blog post, the Electric Power Research Institute, a nonprofit power-sector research group involved in a wide variety of utility technology projects, highlighted the need for more flexible interconnection policies across the U.S. to prevent the tens of billions of dollars of forecasted investment in EV charging, distributed solar and battery backup systems from being stalled out by grid constraints.

The conservative, expect-the-worst approach that most utilities take with interconnection processes may be a way to maintain grid reliability, the institute noted. But it can also ​“lower customer satisfaction and slow progress toward renewable energy targets.”

It’s important to distinguish the problems plaguing this class of clean energy from the similar but distinct issues blocking hundreds of gigawatts of utility-scale wind and solar farms from connecting to transmission grids across the country. The Interstate Renewable Energy Council’s work in California and other states has focused mainly on distribution grid interconnection policies, which cover everything from rooftop solar systems and home battery and EV charging installations to multi-megawatt solar and battery projects.

While these types of interconnection problems can stymie even smaller-scale home rooftop solar systems, the bigger challenges tend to arise with larger-scale installations like community-solar systems that generate power for many different customers (in California, for example, most projects under 1 megawatt in generation capacity aren’t responsible for paying for grid upgrades). In many states, growing grid-upgrade costs and maddeningly slow interconnection timelines have become increasingly significant roadblocks to connecting these mid-sized projects.

In Minnesota, solar and consumer groups are fighting a utility policy that can assign hundreds of thousands of dollars in grid-upgrade costs to relatively small rooftop solar and community ​“solar garden” projects. In the community-solar-rich state of Massachusetts, some developers are stuck waiting for years for grid studies to allow projects to move forward. 

States including New York, Minnesota and Massachusetts have begun to explore flexible interconnection policies — the more general term for the approach California is taking, according to Stanfield — but only through pilot projects or laborious ​“non-wires solutions” programs run by utilities. They have yet to embrace a standard way for clean energy developers to work with utilities.

Most other U.S. utilities haven’t been compelled by state law and regulatory mandates to produce the detailed distribution-grid-level data collection and hosting capacity analyses that enable the CPUC’s Limited Generation Profile approach, Stanfield noted. But these kinds of tools are starting to be developed in other states. That’s an important precursor to enable flexible interconnection, she said.

Can ​“flexible interconnection” expand community solar and batteries? 

To be fair, utilities have very good reasons to take a conservative, safety-first approach to interconnection. After all, they’re responsible for keeping grids safe and reliable — and distributed energy resources represent potential disruptions to those grids that utilities can’t directly control.

That’s why California’s Limited Generation Profile option won’t go into effect until nine months after certain power-system control technologies are certified by the Underwriters Laboratory standards organization as being able to reliably perform according to schedule. That’s expected to happen sometime within the coming year, Stanfield said.

Utilities have also been concerned that changes on their grids could leave circuits susceptible to dangerous conditions. CPUC’s new policy does allow utilities to curtail a project during emergencies or request a change to the project’s schedule in the highly unlikely circumstance of a ​“sustained load reduction” on a grid circuit — namely, if a major customer using that circuit closes down and permanently reduces electricity demand.

But under the new rules, utilities are largely required to honor the schedules they’ve agreed to with solar and battery projects, and to take on reasonable costs of grid upgrades to manage them. That’s a vital feature for any successful flexible-interconnection process, Stanfield said, because project developers secure investment for projects based on some level of certainty about how much power they’ll be able to sell over the project’s lifetimes.

Any utility program that injects too much uncertainty into that prospect — by, for example, retaining the right to unilaterally curtail a project’s grid exports without a clear and provable grid problem to justify it — won’t work for developers, she said.

“A flexible interconnection solution, if it’s modeled and can show what the impacts are going to be, might give developers a lot more certainty and more comfort,” said David Gahl, executive director of the Solar and Storage Industries Institute, during a November event held by the Interstate Renewable Energy Council. That nonprofit is leading a flexible-interconnection pilot project in New York state that’s funded by The U.S. Department of Energy’s Interconnection Innovation e-Xchange program.

Utopia Hill, CEO of Reactivate, a joint venture developing community-solar projects for disadvantaged communities, also noted at the November event that the key to future flexible-interconnection processes is increasing their predictability. ​“If we can’t get financing parties comfortable with that, we can’t get the funding to build the projects,” she said.

It’s still not clear if the CPUC’s Limited Generation Profile rules will meet that need for California solar and battery developers, said Kevin Luo, interconnection policy advisor for the California Solar & Storage Association trade group. One big question is whether the scheduling options approved by the CPUC will actually allow developers to design moneymaking projects.

“That’s one of the reasons why we pushed so hard for customers to be able to pick their own schedules,” he said — an option that the CPUC denied. ​“Nobody has done the forecasting work necessary to have the confidence in any one schedule.”

Nor are California’s solar policies and market dynamics aligned to support the 1-megawatt-and-up projects that the Limited Generation Profile option would be best suited to, Stanfield said. California lacks effective policies to promote the development of multi-megawatt, distribution-grid-connected community-solar projects or large-scale rooftop solar projects on warehouses or apartment complexes that would be eligible for the new interconnection treatment — although solar and environmental-justice groups are pushing regulators and lawmakers to change that.

Even so, Stanfield said, starting with a schedule-based approach at least begins to align utilities’ grid needs with the imperative to add far more solar and batteries to California’s grid. That way, ​“you can start to get some of the benefits now — and then we can build on that further.” 

California’s new rules allow solar and batteries to help out the grid is an article from Energy News Network, a nonprofit news service covering the clean energy transition. If you would like to support us please make a donation.

It’s called the “solar coaster:” The ups and downs the industry faces as solar-friendly policies ebb and flow. And in North Carolina, rooftop installers are in the middle of one wild ride.

On the heels of cutting bill credits for residential solar panels in October, Duke Energy is now poised to offer new rebates for rooftop arrays that are paired with batteries. Combined with federal incentives, the new “PowerPair” rebates could cut the cost of solar and battery systems in half and inject new interest in rooftop solar, which many installers say waned last fall.

“We definitely saw a dip,” said Doug Ager, the CEO and co-founder of Sugar Hollow Solar, describing his company’s business in the last quarter of 2023. But at least in the short-term, he said, “PowerPair will change all that.”

Approved to roll out in May, the pilot program will initially serve only an estimated 6,000 to 7,000 households. But proponents say it could pave the way for a new paradigm in which Duke invests in and manages distributed renewable energy and storage the same way it might a traditional power plant.

“It’s opening the door to active load management from Duke that is going to be increasingly important,” said David Neal, the senior attorney with the Southern Environmental Law Center who helped negotiate the program. Heralding the pilot as one of the first of its kind, he said, “it’s going to be a lot more cost effective than just building new generation to meet expected loads.”

Ultimately, advocates are also hopeful that the solar coaster can be smoothed out a little.

“The rooftop solar industry really has experienced quite a bit of ups and downs,” said Matt Abele, executive director of the North Carolina Sustainable Energy Association, which also helped devise the rebates. There’s still the question of what long-term strategies would support installers, he said. “But I would say this is not an insignificant program in the interim.”

‘The result of…negotiations around net metering’

Greenlit by regulators last month, the rebates grew out of a years-long dispute between Duke Energy, advocates, and the solar industry about how rooftop solar owners should be compensated for the electricity they produce. 

About 40,000 rooftops across the state boast solar arrays, the bulk of them on homes and in Duke territory. The figure accounts for a tiny fraction of North Carolina’s roughly 5 million housing units.

Despite these small numbers, Duke, like other investor-owned utilities around the country, has long sought to lower the state’s one-to-one net metering credit, which it says unfairly burdens both the company and customers that don’t have solar panels.  

Solar installers and advocates contend that rooftop arrays provide more benefits than costs, including cleaner air, fewer electrons lost in transmission, and reduced need for electricity from centralized fossil fuel power plants. Their assertion is backed up by most independent studies of rooftop solar, a 2019 analysis found.

Still, a pair of state laws, both heavily influenced by Duke, mandate a change to the current net metering scheme by 2027. To avoid the bruising battles and excessive fees on solar customers seen in California and elsewhere, some of the state’s leading clean energy advocates and solar installers forged a complicated truce with the utility. 

The crux of the agreement is a move toward “time of use” billing. New residential solar owners are charged and rewarded more for electrons they add to or subtract from the grid during peak demand hours of 6 to 9 p.m. in the summer and 6 to 9 a.m. in the winter. On a monthly basis, any net solar electrons added to the grid are credited at the “avoided cost” rate — akin to a wholesale rate and currently about 3.4 cents per kilowatt hour.

Diligent solar owners can squeeze benefits out of this complex billing scheme, some installers say. But to ease the transition, they also negotiated a simpler, lower-risk “bridge rate” with Duke, in which solar customers enrolling before 2027 get a monthly credit at the wholesale rate for any electrons they add to the grid. 

Regulators on the utilities commission accepted these compromises last March and ultimately ordered new rates to begin October 1. But they rejected another component of the deal, which would have given customers with electric heat an extra rebate for enrolling in Duke’s smart thermostat program, in which the utility can make temperature adjustments from afar.  

“Instead, the Commission directs Duke to develop a pilot program,” their order read, “to evaluate operational impacts to the electric system, if any, of behind the meter residential solar plus energy storage.” 

PowerPair is the result. “This program was in many ways a result of our negotiations around net metering,” Dave Hollister, the president of Sundance Power Systems, said over email.

‘Possibly a win-win for everyone’ 

Devised after months of conversations between Duke, solar installers, clean energy advocates, and others, the new rebates would be based on the size of the solar array and battery and capped at $3,600 and $5,400 respectively. Combined with a 30% federal tax credit, the cash back could cut the cost of an average $40,500 system down to less than $20,000. 

For customers, the deal is “actually really, really good in terms of the economics,” one installer said. And for Duke, the rebates could prove a low-cost strategy for smoothing out spikes in demand and strengthening the resilience of the grid.

“Cost effective and dispatchable customer-sited resources are key components of our clean energy transition,” Lon Huber, a senior vice president at Duke, said in an email. “We are committed to expanding the scope and adding ways for our customers to deploy grid beneficial technology.”

Customers will be divided into two equal cohorts. Those subscribed to the simpler bridge will allow the utility to remotely control their battery up to 18 times a year and will earn an extra $37 a month on average. Enrollees in the more complicated time-of-use rate plan, on the other hand, won’t get monthly incentives but would have control of their batteries. 

“It will be interesting to see how many folks will allow Duke to control their battery and who wants to have that freedom and independence to manage their customer-generated electricity themselves,” Hollister said. “ We deal with so many folks who are looking for self-reliance and the idea of ‘smart grid’ is somewhat of a third rail for them.”

Already, batteries are popular options for rooftop solar customers. Installers say between a quarter and 40% of their clients were already choosing them for a variety of reasons, from a desire to save money to a quest for energy security in the face of outages. 

Sugar Hollow Solar’s Ager said residential storage fits with the western North Carolina vibe. “Being in the mountains,” he said, “people just want batteries.”

With the PowerPair, the percentage of solar arrays paired with storage will undoubtedly rise, and many installers predicted it would double. 

“I fully anticipate us selling tons of systems with batteries,” said Brandon Pendry, communications and outreach specialist with Southern Energy Management, one of the state’s oldest installers and a negotiator for both the bridge rate and the PowerPair scheme. 

To avoid the problem installers and their clients faced with the last round of rooftop solar rebates — when demand far exceeded supply each year and available grants disappeared in minutes — the architects of the program gave it an overall cap of 60,000 kilowatts but no annual limits. That way, rooftop solar and battery owners can get the rebates on a rolling basis.  

“In this case, there is only one capacity and it’s not time dependent,” said Pendry. “It’s just: when it runs out, it runs out.”

If customers choose the maximum allowable size of a 10 kilowatt solar array, a total of 6,000 households could benefit. But no one really knows when the capacity will be reached, with some predicting 18 months from May and others estimating as few as four. 

Duke projects it will connect 11,400 residential rooftop systems this year. But a spokesperson said it was simply too early to tell when PowerPair rebates would dry up. 

Once they do, the hope is that data gathered during the pilot will inform whatever comes next. 

“It may possibly be a win-win for everyone,” Hollister said, “especially if it can be extended or transformed into a more permanent program.” 

‘A better and better investment’

Since half of the PowerPair cohorts will be using the bridge rate, there’s some chance a permanent program would extend that rate’s life — a key priority for some in the industry.  

No matter what, while most installers contacted for this article eagerly await the pilot, they’re also clear-eyed about their business plan for the future.

“We have been installing solar in [the state] for over a decade and have certainly seen lots of incentives come and go, said Jesse Solomon, vice president and director of sales for N.C Solar Now, in an email. “But we have always been able to design the investment to make sense for our clients.” 

Solar installers also focus on the overall trends buoying their industry: Fossil fuels are becoming more expensive, while the materials designed to harness and store forever-free sunlight are getting cheaper.

Every year Duke raises rates, said Pendry of Southern Energy Management, “solar becomes a better and better investment.”

In North Carolina, Duke Energy to offer rebates for rooftop solar paired with batteries is an article from Energy News Network, a nonprofit news service covering the clean energy transition. If you would like to support us please make a donation.

When Wisconsin’s largest coal plant, the Columbia Energy Center, closes in the next few years, a carbon dioxide-filled “battery” developed by the Italian company Energy Dome will take its place. 

The installation is billed by its backers as a potentially crucial development in the clean energy transition. The European Investment Bank announced at the COP28 climate conference this month that it is backing a similar project by the same company in Italy.

The balloon-like facility will use electricity to compress carbon dioxide when demand is low. When demand is higher, it can generate electricity by letting the carbon dioxide expand to drive a turbine. 

While energy storage can lower emissions, clean energy advocates say the climate benefits depend on whether the projects also drive development of wind and solar. A single pilot project is unlikely to do so, but a successful test could show new ways to manage those variable sources in the future that don’t require natural gas as a “bridge fuel.” 

“Right now we have nothing that can buffer a 4 megawatt solar field,” said Oliver Schmitz, director of the Grainger Institute of Engineering at the University of Wisconsin and a technical adviser on the Energy Dome project. “If we show this works now using whatever energy mix we have, we have the certainty” to deploy more renewables paired with it in the future.

Last year, Wisconsin got 37% of its electricity from natural gas and 36% from coal, according to the Energy Information Administration. Nuclear provided 16% of electricity used in Wisconsin and non-hydro renewables provided less than 1%, according to the EIA. These energy sources will largely power the battery until the state’s energy mix changes drastically. 

A goal of Wisconsin’s Energy Dome, slated to be the first commercial-scale application of the technology, is to drive more renewable development, according to Alliant Energy, the utility that co-owns the Columbia coal plant.

“The expansion of energy storage infrastructure is key to accelerating the transition to cleaner, more sustainable renewable energy,” said Alliant Energy spokesperson Tony Palese. “As we retire older fossil fuel facilities and add additional renewable resources to our generation portfolio, energy storage solutions help to ensure system reliability and meet customer needs.

“Importantly, energy storage systems can complement the variable nature of renewable resources and help balance energy demands. This in turn can help reduce reliance on traditional, dispatchable fossil fuel resources.” 

But the 20 MW Energy Dome alone won’t likely drive new renewable development. Even if the project is successful and more Energy Domes are built, as Palese said is possible, some other challenges still stand in the way of deploying more renewables.

Alliant Energy is the largest utility owner-operator of solar in Wisconsin, with over 250 MW deployed and 839 MW more slated for completion by mid-2024. Since Wisconsin is part of the MISO grid, the Energy Dome also pulls from a system where renewables are expanding quickly, but also plagued by a clogged interconnection queue, transmission constraints and other issues.

Alliant owns 1,700 MW of wind across Wisconsin, Iowa and Minnesota within the MISO grid, Palese noted, and is also expanding solar in Iowa. Meanwhile, in the future an Energy Dome could draw energy directly from wind or solar farms rather than the grid, Palese added.

“As we operate and evaluate various aspects of the Energy Dome system’s performance, we envision it could become a model for additional energy storage development for grid applications or directly connected to wind or solar developments,” Palese said.

Citizens Utility Board executive director Tom Content said CUB would likely only support the project if it is genuinely aimed at expanding renewable deployment, and he would oppose any new natural gas generation to feed the Energy Dome.

“Energy storage technologies beyond lithium-ion batteries are being actively studied and can be key elements of the nation’s energy future,” he said. “It’s encouraging to see innovative concepts such as this get funding to be explored, proven and become more economical over time.”

A promising pilot

In September, Alliant Energy received a grant of up to $30 million from the U.S. Department of Energy to develop the Columbia Energy Storage Project. It will cover 12 acres of the coal plant site south of Portage, Wisconsin, including a large dome holding a balloon that can inflate and deflate as carbon dioxide is compressed and decompressed inside it.

When wind or solar power is abundant, the energy can be used to compress carbon dioxide gas into a liquid. When extra energy is needed, the liquid will be allowed to decompress, turning back into gas and powering a turbine to generate enough electricity to power up to 20,000 homes. 

The dome and balloon are part of a closed loop system, meaning no carbon dioxide will be released, and no carbon dioxide delivery is needed after the initial setup. The project will tap into the grid infrastructure already onsite at the 1,112-MW coal plant, the last coal plant in Alliant’s fleet.

This is billed as the first-ever test of the technology at commercial scale. A much smaller 2.5 MW project is operating in Sardinia, Italy, where a new 20 MW Energy Dome is planned with the funding announced at COP28 — $25 million from the European Investment Bank and $35 million from the firm Breakthrough Energy Catalyst.

The Wisconsin project will explore whether the high efficiency rate of up to 75% achieved at the small project can be replicated when a much larger volume of gas is compressed. Carbon dioxide is especially suited for such an application since unlike other gases, it can be liquified at ambient temperatures.

Mike Bremel, Alliant director of engineering and customer solutions, said Alliant put out a request for information on battery storage proposals in spring 2022, seeking projects that could provide 10 hours or more of reliable energy.

“Energy Dome was at the top of our list, basically because of its round-trip efficiency of 75%, and even more importantly the fact that it’s a really simple process that uses off-the-shelf components,” Bremel said. “The compression of CO2 to liquid has been done for over a century. It’s a reliable process that the industry and folks understand.”

Alliant was planning on a capital outlay of about $5 million, he said, whereas about $60 million would be needed for the Energy Dome project.

Around Thanksgiving of 2022, the company “stumbled upon” notice of a DOE Office of Clean Energy Demonstrations grant specifically for long-duration energy storage projects, Bremel said. The grant allows the project to move forward as a 50% cost-share between the federal government and Alliant as well as the two other utilities that own the Columbia Energy Center, WEC Energy Group and Madison Gas and Electric.

Unique attributes

Eight other projects received DOE grants, including one developing iron-based batteries at retiring coal plants in Minnesota and Colorado; and one using zinc bromide batteries in tandem with renewables in Manitowoc, Wisconsin. Bremel noted that Energy Dome was the only mechanical energy storage technology selected; the others involve thermal or chemical (battery) energy storage.

Schmitz said that compared to the many energy storage systems he’s studied — including lithium ion and flow batteries, thermal systems, molten salt — “this one is a huge storage solution at scale.”

“It can really be used to buffer renewable energy production,” Schmitz said. When excess solar or wind energy is being generated, “you can absorb it and spit it out again when the grid needs it. The specific technology uses very traditional subsystems: compressors, regular turbines, materials that withstand pressure. It’s standard engineering combined into a high-performance system.”

Compared to batteries that involve precious metals and potentially other supply chain challenges, the Energy Dome can be built on-site using domestically sourced technology, including as many components as possible from Wisconsin, Bremel said. If the project is successful, more similar domes may be built on the Columbia coal plant site, he added.  

“Because it does use up substantial amounts of space, it’s pretty well-suited for rural solutions, rural resiliency,” said Bremel, noting a local microgrid could be built around the energy storage.

The utilities will be studying how the project can be used for load-following, providing less energy than its total capacity at a given time and extending how long it can provide energy.

“We could potentially have twice the duration,” Bremel said. “Once we understand this project more, there is potential to marry several domes to a single generation and compression source.”

Community involvement

There has been much public concern about carbon dioxide pipelines and carbon sequestration, including in light of the disaster in Satartia, Mississippi, during which a carbon dioxide pipeline ruptured, the gas displaced oxygen and scores of people were sickened.

But Bremel said the dome poses little risk. There will be sensors to detect leaks in and around the facility, and “in the event there was a leak at the gas stage, it’s not going to leak at a very fast rate because it is at atmospheric pressure — it’s not at thousands of PSI” as in a pipeline, Bremel said. 

He said the project also involves very little environmental impact, including after its decommissioning expected after 25 to 30 years. Concrete will be poured around the dome perimeter, and the land directly underneath will be relatively untouched, Bremel said. The largely steel and plastic components can be recycled.

Alliant plans to seek needed approvals from the state Public Service Commission in the first half of 2024, and hopes to begin construction in 2025 and operation in 2026.

The University of Wisconsin, which works with Alliant through its Clean Energy Community Initiative, is helping lead a community engagement process and development of a community benefits agreement, conditions of the DOE grant.

“There is supposed to be a two-way engagement around energy justice, environmental justice, workforce and good jobs,” Schmitz said. “Communities guide the process, bring in their priorities and concerns.”

Madison Area Technical College will help develop a clean energy jobs pipeline around the storage project, building on its role leading a national consortium of community college energy programs. And University of Wisconsin faculty will likely study issues like whether the dome impacts birds, Schmitz said.

Schmitz noted that the Energy Dome itself won’t create many jobs after construction is done, since “it is very low maintenance, very reliable.” But clean energy advocates hope the large dome’s presence will help raise awareness about clean energy more generally and encourage locals to work in the clean energy economy. That means the benefits for renewable deployment could go beyond the role of bridging intermittency.

“The best thing that can happen is visible projects like this have an immediate impact because they excite potential workers to think about this sector,” Schmitz said. “Maybe they become a solar installer or wind technician. Our workforce is strong on manufacturing and building things, so we want to upskill people into the clean energy domain.”

Can a balloon-like battery move the needle on clean energy in Wisconsin? is an article from Energy News Network, a nonprofit news service covering the clean energy transition. If you would like to support us please make a donation.