Clean Energy SF: San Francisco, fog then sun, est. 2026

Vol. 1 - No. 14 - Thursday, September 24, 2026 - Free to readers

Policy ยท Analysis

Diablo Canyon gets about five more years, and who signed off

California agreed to run PG&E's last nuclear plant to roughly 2030. Here is the chain of approvals behind it, and how much of your evening grid leans on it.

Filed November 8, 2026 By the Clean Energy SF editors Reading time: 6 minutes

I. How the extension actually works

The legal path runs through Sacramento first. Senate Bill 846, passed in 2022, cleared the way for PG&E to seek more years out of both reactors, and it handed real review to two agencies: the California Public Utilities Commission (the CPUC, which sets what utilities may charge and recover from ratepayers) and the California Energy Commission (the CEC, the state's energy planning and forecasting agency). Each had to weigh in before the plant could keep running past its original license dates.

On top of the state approvals sits a federal piece. The U.S. Department of Energy awarded Diablo Canyon support through its Civil Nuclear Credit program (a federal fund that pays to keep at-risk reactors from closing early), on the order of $1.1 billion at last public report. Separately, the federal Nuclear Regulatory Commission (the NRC, which licenses and inspects reactors) is still reviewing PG&E's bid to renew the licenses, so the units run under the NRC's timely-renewal rule while that review continues.

II. The honest math on who pays

Keeping two reactors open is not free, and the cost lands on ratepayers across PG&E's territory. Each unit shuts down to refuel on a cycle of roughly 18 to 20 months, and a single refueling outage runs well into the hundreds of millions of dollars once fuel, labor, and deferred maintenance are counted. Those costs move through CPUC proceedings, where they are argued line by line rather than waved through.

Whether that spending buys enough reliability to justify the premium is the open question, and it is a fair one to ask out loud. The state's Legislative Analyst's Office (the LAO, the nonpartisan fiscal adviser to the Legislature) has reviewed the extension's finances and flagged that the final bill depends on outage timing, loan terms, and how long the plant actually stays open. The honest answer to what it costs is that it depends, and the LAO review lays out on what.

III. Who leans on the evening output

Diablo runs steady, around 2,200 megawatts between the two units, or close to 9% of California's electricity at last public report, and almost none of it carbon-emitting. That steadiness matters most during the evening ramp (the fast climb in net demand as solar fades after sunset), which in San Francisco arrives early and hard behind a thick marine layer. The state's grid operator leans on firm, always-on supply in exactly that window.

For a San Francisco ratepayer, the plant is not a line on your bill, and it is not what CleanPowerSF or Hetch Hetchy Power sells you. Its job is statewide resource adequacy (the rule that power providers must line up enough supply in advance to cover demand), managed by the California Independent System Operator, or CAISO, which balances the grid you are plugged into. So the accountability is statewide, which is why the CPUC, CEC, and CAISO records are where a resident checks the promises.

IV. Worth watching this month

1. Watch the CPUC's Diablo Canyon proceedings for new cost-recovery filings, most of which are routine but set what ratepayers ultimately pay.

2. Watch for the NRC's progress on PG&E's license-renewal application, since that federal decision, not the state's, governs how long the reactors may legally run.

3. Watch the CEC's reliability and resource reports for any revised estimate of how much the state still expects to need from the plant through 2030.

4. Watch for the next scheduled refueling outage, which takes a unit offline for weeks and shifts load onto the rest of the grid.

5. Watch the LAO's site for updated reviews of the extension's cost, which tend to land around budget season and are worth more attention than routine filings.

Frequently asked questions

Does my CleanPowerSF or Hetch Hetchy power come from Diablo Canyon?

No, not directly. CleanPowerSF and Hetch Hetchy Power buy and generate their own supply, and PG&E delivers it over shared wires. Diablo's role is keeping the statewide grid reliable, which benefits everyone plugged into it.

Who actually approved the extension?

The Legislature authorized it through SB 846 in 2022, and the CPUC and CEC each reviewed it, with a federal loan from the Department of Energy behind it. The NRC still has to finish renewing the plant's licenses.

Why keep a nuclear plant open if California is building so much solar?

Solar fades at sunset, right when demand stays high, and Diablo runs around the clock. The state treated it as insurance for the evening hours while more storage and clean firm power come online, though whether that was the cheapest path is debated.

How long is the extension, really?

Roughly five more years, not a full decade. The units were slated to retire around 2024 and 2025 and are now cleared to run to about 2029 and 2030, pending the federal license review.

References