The growing clean energy backlog, in five charts

For the past four years, researchers at the Department of Energy’s Lawrence Berkeley National Laboratory have been tracking a major threat to the U.S. clean energy transition: the backups and bottlenecks in connecting proposed solar, wind, and battery projects to the electricity grid.

LBNL’s team laid out its latest findings in a recent webinar. The overarching takeaway is that clean power plants can supply enough near-term electricity to avoid building new fossil-gas-fired power plants or keeping coal plants open longer — but only if something is done about the grid backlog.

U.S. utilities and the entities responsible for grid reliability are warning that growing demand for electricity from data centers, factories, electric vehicles, and decarbonizing buildings is expected to outrun the pace at which new clean energy resources can be added to the grid. Already, many utilities are proposing to keep coal plants open past previously planned retirement dates and to build new fossil-gas-fired power plants supplying gigawatts of power — even though those plans threaten to put the country’s carbon-cutting goals out of reach.

At the same time, the U.S. has an enormous amount of proposed carbon-free projects waiting to replace those fossil-fueled generators. As of December 2023, nearly 2,600 gigawatts’ worth of proposed projects, the vast majority of them wind, solar, and battery storage, were making their way through the series of studies and steps required to plug into the power grid — about twice the amount of generation powering the entire existing U.S. electrical grid.

The problem? Grid operators and utilities can’t fit all those projects onto their existing power lines, and they’re buried under the piles of paperwork required to figure out how to expand the grid to accommodate them.

The situation is only getting worse: The interconnection backlog at the end of 2023 was ​“roughly eight times the capacity that was active in the queues as of the end of 2014,” said Joseph Rand, an energy policy researcher at LBNL and co-author of the lab’s latest ​“Queued Up” report. But the pace of transmission grid expansion has slowed to about 1 percent per year over the same period of time.

Still, the amount of clean power and batteries seeking to be built could, at least in theory, provide plenty of headroom for U.S. grids to meet the forecasted growth in demand. These five charts from LBNL’s latest report demonstrate that.

Meeting peak demand without emissions 

The chart on the left shows just how much solar, wind, battery, and ​“hybrid” capacity — batteries combined with renewable energy, almost all of it solar today — is waiting to come online. The chart on the right shows how far those clean resources could go in meeting electricity needs, including those summer and winter peaks in demand that keep grid planners and operators awake at night.

The gray bars on the chart on the right represent the total amount of generation capacity seeking to be interconnected in each region, which is typically far higher than the existing generation capacity in each region, as marked by the black lines in each column.

Since wind and solar may not generate their full capacity when grids need the most power, LBNL’s chart also compares the most important metric for grid reliability: peak loads, or the maximum amount of electricity demand in each region, which usually spikes during hot summer afternoons or cold winter mornings. On that chart above, those regional peak loads are represented by yellow lines.

LBNL also ran what Rand called ​“a rough back-of-the-envelope calculation to estimate the approximate peak load contribution of all of that active capacity in the queues,” shown as the red lines on the chart. ​“Those red lines exceed peak load in all regions, and they actually exceed the installed capacity in several regions as well,” he said.

This does not mean that regions can expect their peak grid demands to be met by yet-to-be-built solar, wind, and battery capacity in the near term. That’s because it’s highly unlikely that most of the capacity in queues will be built.

In fact, only 14 percent of the generation capacity of all the projects that submitted interconnection requests from 2000 to 2018 had been built and brought online by the end of 2023. That completion rate may or may not hold steady in future years, but it does serve as a warning for utilities and grid operators planning to rely on still-unbuilt projects to meet their peak load needs.

How much clean energy could actually get built in the near term? 

To get a better sense of how much clean energy and battery capacity might be ready to meet grid needs in the near future, LBNL’s report examined where projects stood in terms of timing and status. Rand noted that nearly half the projects now in interconnection queues have proposed to come online by the end of 2026, adding up to nearly 1,300 gigawatts of capacity — an amount equivalent to the entire existing U.S. grid.

The most promising projects are those that have already executed interconnection agreements — the key step that allows them to begin construction and start paying for whatever grid upgrades have been assigned to them. About 12 percent of the active projects LBNL studied have reached that point, adding up to 311 gigawatts of capacity — and ​“those are the projects I would say are much more likely to actually reach commercial operations in the relatively near term,” Rand said.

How the likeliest projects could help the grid 

What might be the grid value of the projects that have passed through the interconnection gauntlet?

To answer that question, LBNL ran another back-of-the-envelope calculation of those projects’ peak load contributions and compared it with the five-year forecast of peak load growth and power plant retirements for six of the country’s grid operators, using data from the North American Electric Reliability Corporation (NERC), a nonprofit organization that maintains standards for grid reliability.

The results indicate that there’s significant potential for these close-to-the-finish-line projects to meet much of the capacity needs from peak load growth and power plant retirements in the Midwestern and mid-Atlantic regions served by grid operators Midcontinent Independent System Operator, PJM, and Southwest Power Pool. For grid operators in California, New England, and Texas, those projects may even exceed those needs.

To be clear, this is a dramatic oversimplification of how grid operators and utilities would go about determining whether yet-to-be-built solar, wind, and battery projects can be relied on to meet regional peak grid needs, LBNL energy researcher Joachim Seel explained. But it’s still an indication of the potential of the clean energy and battery projects that have secured interconnection agreements.

For its rough calculations, LBNL used NERC data on how much power existing wind and solar resources provide in different regions under typical weather conditions during the historical ​“peak hour” for electricity demand across each region. It also assumed that batteries and fossil fuel and nuclear plants will be available 100 percent of the time during those peak hours.

But utilities and grid operators ultimately need to do a much more complex assessment of the effective load-carrying contributions (ELCC) of solar, wind, batteries, and other generators and energy storage resources, Seel said — calculations that incorporate real-world data on how well individual resources perform.

“There is a big difference between ELCC contributions and peak load contributions, especially in regions with higher renewable penetrations,” Seel said. Take California, which has so much solar power that its ​“net peak load,” which typically occurs during the hottest days of the summer and early fall months, has shifted from late afternoon into early evening after the sun goes down. That makes every additional unit of solar power less and less useful for serving peak load — and every unit of grid batteries much more valuable.

Battery storage is on the rise 

Rand highlighted the rising proportion of hybrid projects, power plants that combine generation and batteries, as an indication of how project developers are planning ahead to make intermittent renewables more useful for serving peak grid loads.

The chart below shows that more than half of all active solar and energy storage project capacity in U.S. queues consists of hybrid projects — especially in California and the U.S. West.

Interconnection agreements aren’t a guarantee

LBNL’s data also reveals that projects that have already received interconnection agreements may not be built and ready to serve the grid on the proposed timelines. In fact, even projects that have reached that milestone can end up being withdrawn entirely, as the chart below shows.

There are a number of reasons why even projects with interconnection agreements may face delays or be withdrawn, Rand said. Supply-chain bottlenecks can prevent them from getting necessary equipment, permitting delays can crop up, and transmission upgrades can move slower than expected, to name a few.

If a higher number of late-stage projects end up withdrawing from queues, that can ​“disrupt the assumptions baked into other projects in our connection studies,” Rand added. When projects that were supposed to pay for grid upgrades drop out, grid operators and utilities may be forced to reevaluate the grid upgrade impacts and costs for all the remaining projects in the queue, which ​“could lead to cascading re-studies and inefficiencies in that interconnection process,” he said.

Utilities and grid operators are working hard on reforming their interconnection processes to deal with these complications. Last year, the Federal Energy Regulatory Commission (FERC) issued Order 2023, which requires project developers and grid operators alike to meet interconnection deadlines or pay financial consequences, reform processes for energy storage and hybrid projects that have complicated their interconnection, and make use of​“advanced transmission technologies” that can expand interconnection capacity on the existing grid.

The reforms adopted by FERC last year ​“will surely help reduce the backlogs and delays,” Rand said, adding ​“that implementation is actively underway now. But at the same time, I think it’s increasingly clear that additional solutions are needed to really resolve these issues.”

Last month, DOE released a report on how to improve transmission interconnection, based on two years of work with grid operators, utilities, clean energy developers, regulators, consumer and community advocates, and other stakeholders. The resulting list of 35 solutions to the country’s interconnection problems ranges from streamlining interconnection study processes — and training and hiring more people to tackle the backlog in that work — to taking on the thorny political challenge of forging compromises between utilities and project developers on how to share the costs of grid upgrades.

One of the first steps on this roadmap is to ​“increase data access and transparency” on interconnection work underway at grid operators and utilities across the country, LBNL research scientist Will Gorman said. LBNL’s report builds on data collected from interconnection queues from the country’s seven grid operators and 44 utilities and federal power marketing administrations representing about 95 percent of U.S. generation capacity.

But that data is sometimes incomplete or out-of-date, and it takes a lot of work from LBNL to make sense of it.

“We really need to benchmark, track, and audit these processes to see how things are changing for the better or for the worse,” Gorman said — an imperative that requires more and better data.