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

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

Grid ยท Analysis

BART's power contract: greening the Bay's biggest single rail load

BART is one of the Bay Area's biggest single power users, and it has a plan to make the electricity that moves its trains carbon-free. Here is what is real and what is still a target.

Filed October 27, 2026 By the Clean Energy SF editors Reading time: 6 minutes

I. How BART actually pulls its power

Traction power (the electricity that actually moves the trains) reaches BART through a string of substations spaced along the track, which step grid voltage down and feed the third rail. Because trains run from before dawn until after midnight, this is a steady, heavy, around-the-clock load, not the kind of demand that politely disappears when the fog rolls in off the Pacific. That round-the-clock shape is part of why BART's power choices matter to the rest of us on the same wires.

Regenerative braking softens the picture a little. When a BART train slows, its motors run in reverse and act as generators, pushing electricity back toward the third rail where a nearby train can use it. BART has said this recovers a meaningful share of braking energy, though the exact amount moves with how many trains are running and how close together they are, so treat any single percentage you see with caution.

II. The Wholesale Electricity Portfolio, in plain terms

In 2017 the BART board adopted what it calls a Wholesale Electricity Portfolio Policy, a standing rule for how the district buys power. The policy sets interim targets for low- and zero-carbon electricity and points toward fully carbon-free traction power over the coming years. BART publishes the specific percentages and dates, and because those are targets rather than guarantees, the honest move is to check them against the district's latest reporting rather than trust a number from memory.

To hit those targets, BART has signed long-term contracts for solar and for hydropower, the idea being to lock in clean supply at a known price for years at a time. Hydropower is a natural fit in California, and daytime solar pairs reasonably well with a transit system, but both come with caveats: a drought can thin a hydro year, and solar does little for the trains that run after dark. Where the gaps get filled, and with what, is the question worth keeping an eye on.

III. Who is on the hook, and who is watching

Several bodies share this story. BART's own board sets the portfolio policy and approves the contracts, so its meeting agendas are where new deals surface first. The California Independent System Operator, or CAISO, runs the high-voltage grid that BART draws from and publishes the filings that show regional load and supply. And the California Public Utilities Commission, the state regulator, oversees the broader push to electrify transportation that BART's effort sits inside.

For San Francisco readers there is a local wrinkle. The city's own clean-power programs, CleanPowerSF and the SFPUC's Hetch Hetchy hydropower, green the electricity in many homes and municipal buildings, but BART buys its traction power on its own wholesale terms, separately from your household enrollment. Your CleanPowerSF choice cleans the power at your meter in the Mission or the Sunset; it does not directly change what runs the trains under Market Street.

IV. Worth watching this month

1. BART board meeting agendas, posted on bart.gov, for any new power-procurement or contract items; most months these are routine, but a new solar or hydro deal would show up here first.

2. BART's annual sustainability reporting, usually refreshed about once a year, for updated progress against its carbon-free traction targets; this is where a missed or met milestone becomes visible.

3. CAISO's public grid and load reports, for how Bay Area demand and clean supply are trending overall; routine data, but the backdrop against which BART's load sits.

4. CPUC proceedings on transportation electrification, which move slowly and rarely make news, but occasionally set rules that reach large transit loads like BART's.

5. Any announced in-service date for a BART-contracted solar project, which would mark real megawatts arriving rather than a target on paper; treat early dates as likely to slip.

Frequently asked questions

Does BART buy its electricity from PG&E like I do?

No, not in the ordinary way. BART buys traction power on the wholesale market under its own portfolio policy rather than as a retail PG&E customer, and the exact mix shifts over time. The details live in BART's published power documents.

What is regenerative braking?

It is the trick of using a train's own motors as generators while it slows, feeding electricity back toward the third rail. A nearby train can then use that power, which trims how much BART has to pull from the grid.

Is BART's traction power already fully carbon-free?

Not entirely, at last public report. BART has signed solar and hydro contracts and set carbon-free targets, but reaching fully carbon-free is a goal with a timeline, not a finished fact.

Does my CleanPowerSF enrollment make BART cleaner?

No, not directly. CleanPowerSF greens the power at your home or business, while BART procures its traction power separately on its own wholesale terms.

Where can I read BART's actual power targets?

BART publishes its Wholesale Electricity Portfolio Policy and sustainability materials on bart.gov. Those pages carry the official percentages and dates, which is the right place to check any figure.

References