Last I heard, CARB finally got on board with trolley buses being zero emission. Initially, they only counted battery and hydrogen. Of course, trolley buses only really make sense where you already have a system; starting a new trolley bus system would be horribly expensive, just like adding catenary to a railroad. SF has (almost) always had them, so they have the maintenance and minor modifications built into their budget, but you'll note there haven't been many new lines equipped with wires since they replaced the Market Street Railway's (and a couple of Muni lines) streetcars. And ... modern trolley buses probably meet, more or less, the battery bus requirements too, since nearly all of them have a backup battery allowing a few blocks to a couple of miles of operation off the wire.

SF is a special case, really. They have Hetch Hetchy generating a good amount of hydroelectric power (the cheapest kind, until Chinese solar panels became a thing) from the aqueduct water (the aqueduct runs by gravity from the Sierra to Crystal Springs), that can't legally be sold outright to a private utility. So whatever they don't sell to one of the irrigation districts is "wheeled" from Newark to SF (essentially PG&E delivers in SF what they get in Newark, for a fee of course) and can use it at cost for municipal purposes. Like electric transit. So that tilts the playing field more than a little bit. Most places have to pay commercial rates for power, which makes electric transit less desirable at present. Though with current diesel (and even natural gas) prices...