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

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

Grid ยท Analysis

The cruise ship at Pier 27 is running on the city's grid

California's At-Berth rule shuts off ship diesels at the dock. We trace where the replacement power comes from, and what it keeps from burning at the waterfront.

Filed October 19, 2026 By the Clean Energy SF editors Reading time: 6 minutes

I. How the plug actually works

The At-Berth regulation started with a shorter list of vessels about a decade ago and was broadened in a 2020 update from the California Air Resources Board (CARB), the state agency that writes the rules on air pollution. Cruise ships were in the first group. The idea is simple to state: within a set number of hours of tying up, the vessel cuts its diesel auxiliary engines (the generators that would otherwise run the hotel load, meaning lights, kitchens, heating, and pumps) and draws that power from shore instead.

Doing it takes more than an outlet. Pier 27, the James R. Herman Cruise Terminal, opened in 2014 with a shore-power vault and the high-voltage gear to match a full ship's demand. A heavy cable is lifted to a connection point on the hull, the ship's systems transfer over to landside supply, and the stacks go quiet. The Port of San Francisco keeps the terminal records that show which berths are equipped and when the connection is used.

II. The honest math, one ship against a neighborhood

A docked cruise ship is not a small load. Its hotel demand runs on the order of several megawatts, roughly 7 to 11 megawatts at the high end for a large vessel at last public reporting from port and industry sources, which is in the range of what a few thousand San Francisco homes draw at once. For a few hours, a single hull at Pier 27 can look like a dense residential district sitting on the grid.

What the plug displaces is the fuel those auxiliary engines would otherwise burn. Marine diesel at the dock puts exhaust right at the edge of a crowded, walkable waterfront, near North Beach, Fisherman's Wharf, and the ferry berths. Shore power moves that generation off the ship and onto the regional system. Whether the air near the pier is cleaner on a given call depends on the ship actually connecting, which the rule requires but equipment and weather can complicate.

III. Where the dockside power comes from

Here the San Francisco story turns specific. The Port is a city department, and city facilities are generally served by Hetch Hetchy Power (the SFPUC's municipal electricity, generated mostly by hydroelectric dams on the Tuolumne River in the Sierra Nevada and carried west to the city). That supply is largely greenhouse-gas-free at the source, which means the shore connection is not just moving emissions inland. It is likely trading diesel exhaust for hydropower.

We say likely because the exact accounting is harder than the headline. CleanPowerSF, the city's community choice program (where the SFPUC buys cleaner electricity for residents and businesses while PG&E still delivers it over its wires), serves much of the rest of the city, and the precise mix behind any single plug depends on SFPUC's resources that day. The honest version: the waterfront benefit is real and local, and the climate benefit tracks how clean the source power is, which in San Francisco's municipal case is cleaner than most.

IV. Worth watching this month

1. Check the Port of San Francisco's cruise schedule for Pier 27 to see which ships are in on the days you walk past, which tells you whether to expect a quiet hull or a working stack (routine, but it sets your expectation at the rail).

2. CARB posts compliance and enforcement material for the At-Berth program, worth a look if you want to know how often connection actually happens rather than how often it is required (this is where the real-world gaps show up).

3. SFPUC meeting agendas occasionally touch Hetch Hetchy Power and municipal loads like the Port, which matters if you care where the dockside electricity is sourced (usually routine, sometimes not).

4. Watch California ISO grid conditions on hot inland days, since a cruise ship's few megawatts land on the same system that serves the whole region (rarely a problem at this scale, but it is the same grid you share).

Frequently asked questions

Does every cruise ship at Pier 27 actually plug in?

The At-Berth rule requires eligible vessels to connect and shut down their diesels within a set window after docking. In practice it depends on the ship being equipped and the gear working, so compliance is high but not automatic, and CARB tracks the exceptions.

How much power does one berthed ship use?

Roughly several megawatts, on the order of 7 to 11 for a large vessel at peak, per port and industry figures. That is comparable to a few thousand homes drawing at the same time.

Where does the electricity come from?

City facilities like the Port are generally served by Hetch Hetchy Power, the SFPUC's mostly hydroelectric municipal supply from the Sierra. The exact mix behind any single connection varies by day.

Does shore power really clean the air by the waterfront?

When a ship connects, it stops burning marine diesel at the dock, which cuts exhaust right where people walk. The climate benefit depends on how clean the shore power is, and San Francisco's municipal power is relatively clean.

References