Chapter 3 · the time series · 120 monthly snapshots

Headroom time machine

One frame per month from … to …. Each county is shaded by the cumulative MW of fossil capacity that's retired — or filed to retire within the snapshot's forward window — on its local grid. Today's retirement schedule didn't appear all at once; press play to watch it build up. Why that's the headroom number ↓

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Map shows:
Click any county to pin its trajectory · up to 5 at a time
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Counties on the board
… GW
Nationwide headroom freed
… MW
Biggest single county
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Top county
Scroll to zoom · drag to pan · Enter pins a county
County-level freed interconnect MW, monthly time series
Source: EIA-860M monthly archives, normalized to county FIPS. Hatched counties have no fossil-retirement history in the window.

Biggest movers — last 12 months

Change in freed interconnect MW between the selected month and 12 months earlier.

CountyΔ MWNow

Top 20 movers · 10-year shapes

Each sparkline is the county's freed-MW trajectory from … to …. Click to pin.
What this shows, and why. Utilities report planned retirements on EIA Form 860M, typically 6–12 months ahead of the physical shutdown — sometimes years. That filing is the earliest public signal that a site's interconnection capacity may open up. This map sums those filed MW by county, cumulatively, so a darkening county is one where more capacity has been filed for retirement. Full details on the methodology & sources page.
What we hold constant vs. recompute, and why
  • The freed-MW number for each month is recomputed from that month's EIA-860M xlsx — this is the component that changes most frequently.
  • Other inputs (transmission, queue, prices, tariffs) are not back-cast. They change much more slowly than retirement filings, so they use current values for all snapshots.
  • "Freed" here means "MW of fossil capacity within the snapshot's forward window that has a published retirement date." It is not the same as "MW that have actually left the bus" — some of those filings get rescinded.