The numbers tell a strange story. Across the United States, wind farms, solar arrays, and battery storage facilities representing more than twice the country's entire electricity infrastructure are queued up, waiting for permission to connect to the power grid. Yet most will never make it.

This isn't a tale of waning interest in renewable energy. It's something more insidious.

The Bottleneck Nobody Expected

Imagine proposing to build a power plant. You find the land, secure financing, design the facility. Then you enter what's called the interconnection queue—a process meant to ensure your project won't destabilize the electrical grid. The studies begin. Engineers analyze voltage stability, power quality, transmission capacity.

Years pass.

In 2010, getting through this process took about 33 months. Today it takes 56 months. That's a 70% increase in a single decade. And the costs? They've more than doubled for projects that ultimately abandon the process.

Here's the harsh reality: only 20% of projects requesting grid connection between 2000 and 2018 ever came online. The rest withdrew. More than 80% of proposed capacity simply vanished from the queues, taking investment dollars and climate ambitions with it.

A System Drowning in Applications

Between 2000 and 2010, the United States averaged 500 to 1,000 new transmission interconnection requests annually, representing 150 to 200 gigawatts of proposed generation. Then renewable energy costs plummeted. Federal incentives kicked in. Corporate sustainability pledges multiplied.

The flood began.

Over the last decade, new requests surged to 2,500 to 3,000 per year—anywhere from 400 to 900 gigawatts annually. A three- to six-fold expansion. By the end of 2023, active queue capacity reached 2,600 gigawatts. For context, the entire installed capacity of the US power plant fleet stands at 1,280 gigawatts.

Roughly 95% of this waiting capacity consists of solar, wind, and battery storage. These are precisely the technologies needed to decarbonize the electricity sector.

The Price of Uncertainty

Interconnection costs follow a cruel logic. Nearly a quarter of projects receive cost estimates below $25 per kilowatt—locations where the grid can absorb new generation with minimal upgrades. But another quarter face costs exceeding $250 per kilowatt. Some encounter expenses an order of magnitude higher.

Projects that eventually withdraw face average interconnection costs of $373 per kilowatt. Those that succeed? Just $73 per kilowatt. The difference is stark.

For withdrawn solar projects, interconnection costs would have represented 30% of total project expenses. For wind, 37%. These aren't rounding errors. They're deal-breakers.

The costs have climbed steadily. Withdrawn project interconnection expenses reported during 2019–2023 averaged $428 per kilowatt, up 117% from pre-2014 levels. Completed projects saw a more modest 44% increase over the same period.

Network Upgrades Drive Withdrawals

Two types of costs emerge from the interconnection process. First come point-of-interconnection costs—the local facilities needed to physically connect a generator to the grid. Second are network upgrade costs—broader transmission system improvements that may be located far from the generator itself but become the developer's financial responsibility.

For completed projects, network upgrades account for roughly 43% of interconnection costs. That ratio has held steady over time.

For withdrawn projects, the story diverges sharply. Network costs have risen from 40% to 70% of total interconnection expenses. Projects actively moving through the queue show a median network upgrade cost proportion of 80%, suggesting future withdrawals will remain high.

The implication is clear: the transmission system is running out of capacity. The piecemeal approach of identifying upgrades through individual project studies—rather than through coordinated regional planning—is breaking down.

Geographic Patterns and Proximity Paradoxes

Active queue capacity clusters in regions with high renewable energy potential but also spreads across areas lacking robust high-voltage transmission networks. Wind and solar projects scatter more widely across the landscape than natural gas projects, which tend to locate near existing infrastructure.

You might expect projects farther from transmission lines to face higher interconnection costs. The data show a correlation, but it's weak. In PJM, a major mid-Atlantic grid operator, the Pearson correlation between distance to high-voltage lines and network costs is just 0.20. In SPP, covering the Great Plains, it's 0.16.

Much of the cost variation remains unexplained by simple geographic factors. This uncertainty forces developers to use the interconnection process itself as a price discovery mechanism, submitting exploratory requests to learn what connection might cost. The strategy clogs the queues with speculative proposals.

Regional Variations Tell Different Stories

Texas operates differently. The Electric Reliability Council of Texas uses a streamlined interconnection process that doesn't focus heavily on thermal overloads. Projects there move faster—a median 48 months from request to operation, compared to 80 months in California.

But Texas's approach trades speed for congestion risk. Generators there face higher curtailment rates, reducing potential revenue.

California and New York have developed long-term transmission planning processes that socialize some network upgrade costs across all ratepayers rather than assigning them to individual generators. California's completed projects now show the lowest interconnection costs among analyzed regions, despite high costs for withdrawn projects. New York shows similar costs for both completed and withdrawn projects, suggesting factors beyond price drive withdrawal decisions there.

What Happens If Nothing Changes

Researchers analyzed the current queues to project future renewable energy deployment, assuming historical completion rates and timelines persist. The forecast is sobering.

Through 2027, annual installation rates will fall below near-term capacity requirements modeled in leading decarbonization studies. Beyond 2030, the size of current queues could allow capacity expansion roughly aligned with the lower range of study projections—but only if completion rates don't deteriorate further.

Many decarbonization pathways require renewable energy deployment rates to double again beyond 2030. The queue-based projections don't approach those levels.

Meeting mid-century net-zero targets appears increasingly difficult without fundamental reforms to interconnection processes and transmission planning.

The Reform Challenge

Interconnection processes serve a legitimate purpose. They ensure system reliability as generation and storage resources are synchronized with the grid. Recent disturbance events involving inverter-based resources have reinforced the importance of careful engineering standards.

But the system wasn't designed for this volume of applications. Transmission providers lack sufficient workforce capacity to study thousands of projects simultaneously. The networked nature of the grid means studies must assume completion of projects ahead in the queue. Late-stage withdrawals trigger cascading restudies for remaining projects, compounding delays.

The Federal Energy Regulatory Commission recently enacted new interconnection rules to process applications more efficiently. The order standardizes tiered deposit structures, increasing financial penalties for later-stage withdrawals. Whether these reforms will meaningfully reduce backlogs remains uncertain.

Technological and Policy Options

Making better use of existing transmission infrastructure could help in the near term. Grid-enhancing technologies can increase the capacity of existing lines but have yet to deploy at scale. Some transmission operators are developing hosting capacity maps to guide developers toward optimal connection locations, though such maps require frequent updates to remain useful given the dynamic nature of the network.

Alternative interconnection service agreements that accept higher congestion and curtailment risk—rather than requiring costly network upgrades—might accelerate connections for some projects. Texas, Australia, and the United Kingdom allow "connect and manage" approaches. The trade-off involves faster timelines but greater revenue uncertainty for generators.

Longer-term solutions involve tighter coordination between project-level interconnection processes and regional transmission planning. Some regions assign network upgrade costs to end customers rather than generators. Others propose upfront, average interconnection fees applied broadly to all generators in a region, similar to practices in the United Kingdom.

These approaches involve trade-offs among cost certainty, economic efficiency, simplicity, and stakeholder acceptance. No universal solution exists. Regional contexts matter.

The Data Gap

Collecting the interconnection cost data for this research required extraordinary effort. The team manually reviewed thousands of study documents across six grid operators, spending more than 1,900 hours extracting information. Many studies require special access due to Critical Energy Infrastructure Information designations. Others have been removed from public databases due to document retention policies.

This opacity prevents effective monitoring of interconnection process health. Policymakers lack clear metrics to evaluate reform progress. Developers struggle to predict costs before entering the queue. The information asymmetry compounds inefficiencies.

Governments should prioritize interconnection data transparency. The relative contribution of various barriers to clean energy deployment cannot be accurately assessed without credible, accessible information on how the system performs.

A Constraint That Compounds

The interconnection bottleneck doesn't exist in isolation. It interacts with other deployment barriers: public opposition to new projects, supply chain constraints, land-use competition, manufacturing capacity limits. Each obstacle multiplies the impact of others.

But interconnection barriers are particularly insidious because they operate invisibly. A solar farm blocked by local opposition makes news. A project that withdraws from an interconnection queue after receiving a $500 per kilowatt cost estimate does not.

The cumulative effect is profound. Active queue capacity represents enormous developer interest and potential investment. Yet the system converts less than one-fifth of that interest into operating power plants. The gap between climate ambition and infrastructure reality grows wider.

Closing it will require institutional innovation matching the technological innovation that made renewable energy affordable in the first place.

Credit & Disclaimer: This article is a popular science summary written to make peer-reviewed research accessible to a broad audience. All scientific facts, findings, and conclusions presented here are drawn directly and accurately from the original research paper. Readers are strongly encouraged to consult the full research article for complete data, methodologies, and scientific detail. The article can be accessed through https://doi.org/10.1016/j.joule.2024.11.008