alt Hacker News> The angle of this that people may not realize is that San Francisco already owns the power generation (ie, the Hetch Hetchy dam).
My conclusion might be totally wrong because I'm converting from units that aren't meant to be converted, but...
If you filter down to only San Francisco County on this official-looking thingie [0], you see that it claims the city [1] has 5.126 TWh of consumption.
Your link [2] claims Hetch Hetchy Power System provides something like 395 MW of power generation capacity. I'm going to assume that that's a misprint and they meant to write MWh because that's the only thing that makes sense to me for a measure of power generation. While the last page of this PDF [3] indicates that the hydro generation component is capable of powering a bit more than twice the city's municipal demand, it seems like it's not enough to satisfy even 1/1000th of the demand of the entire city.
Perhaps I've totally fucked up my unit conversions (or relied on garbage data), but it looks like only the tiniest fraction of the city's power demands can be satisfied by the Hetch Hetchy dam. (Though, we could easily electrify way more of the Muni lines with the surplus capacity.)
[0] <https://www.energy.ca.gov/data-reports/energy-almanac/califo...>
[1] SF City and County are -AFAICT- the same thing. It's a little weird.
[2] <https://www.sfpuc.gov/about-us/our-systems/hetch-hetchy-powe...>
[3] <https://www.sfpuc.gov/sites/default/files/about-us/WeDeliver...> (found via [4]
[4] <https://www.sfpuc.gov/about-us/our-systems/storage-and-deliv...>
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It generates ~1 TWh per year or about 20% of SFs power. Power generation capacity is always in watts but it also doesn't run at 100% all the time.
Power generation facilities are typically quoted in terms of Watts, not Watt-hours. From an era where these were fossil fuel or nuclear plants or dams that provided a pretty steady level of energy. It indicates what the generation facility/asset can produce at any given moment, although if rivers run dry hydro output can decrease.
I think the numbers you cite in [0] are in terms of total annual consumption.
You did this wrong but drew the right conclusion. Hetch Hetchy system exists but it is nowhere near the scale of powering the entire city of San Francisco.
I would assume 395MW is the nameplate capacity, so you would multiply it by a capacity factor and time to get the energy production in a specific interval. Capacity factor in hydro can vary a lot by season and how much they want to produce vs reservoir levels, but for a back of the envelope 100% capacity factor you have 395 MW × 8,760 hours/year = 3.46TWh/year . Capacity factor could be in the high 90s in good conditions and maximum production but I expect it's a lot lower unless it's a wet year with very few big maintenance jobs needed.