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True but PV+wind make our existing dams go much further - recall most of them operate as giant annual batteries, they refill in the rainy season once per year,

True but PV+wind make our existing dams go much further - recall most of them operate as giant annual batteries, they refill in the rainy season once per year, then dispense that energy over the dry season. Adding PV means hydro can save much more of its water, just dispensing to “fill in the gaps”. This is already how the hydro in Norway and Sweden operates, you can see it daily if you look at the hourly power breakdowns by generation type. But I agree, I hope we will get to a point where we can decommission the big dams..

xyzzyz 3y ago
> recall most of them operate as giant annual batteries, they refill in the rainy season once per year, then dispense that energy over the dry season That’s not quite how it works. Consider the biggest hydro project in US, the Columbia river, with its 14 dams. The system does fill up in the rainy season, but the crucial thing is that it’s not the dams that do fill up, but rather the whole watershed, meaning things like snowfall and ground water. This means that we have very limited amount of control over when we let the water through. We can’t just dam the river for an extended period: if we don’t use it for generating power, we must spill (waste) it. This means in practice that the dams are not batteries: to a large degree, it‘s use-it-or-lose-it. To make these into batteries, we’d need to somehow refurbish the dams to tremendously increase the power generating capacity on each dam, so that instead of assumption of continuous flow (either through turbines or spillways), we make the flow more intermittent, so that we can make up for closed times by pushing more water through during open times. This is tremendously difficult in practice: dams are simply not designed to allow for refurbishing with many more turbines or much more flow through them than they were originally designed for, the upstream reservoirs are not designed for quickly varying water levels, etc. Point is, we can’t just “save the water”.
- Arrath 3y ago
  > That’s not quite how it works. Yeah in reality there are two forms of hydropower: the classic reservoir dam, and 'run of the river' powerplants. You're absolutely right, even reservoir dams don't really fulfill the 'annual battery' idea, since they must maintain some minimum outflow for downstream consumers and can't shut it off entirely if it better suits the power generation goal.
- jakewins 3y ago
  > Point is, we can’t just “save the water”. The storage level at Lake Mead has an annual spread of ~100ft; the dam is currently at historic low capacity and could hold about twice its current level: https://www.usbr.gov/lc/region/g4000/lakemead_line.pdf https://www.usbr.gov/lc/region/g4000/lakemead_line.pdf Reservervoir dams certainly can store water and dispense it when appropriate. Like I said, this is happening every day already, you can see it in the hourly data on wind/hydro generation share, and you can see it in the annual storage capacity data for Norwegian hydro.
  - xyzzyz 3y ago
    Yes, we can do this for some dams, but not enough to move the needle. Hoover Dam’s generating power is quite tiny relative to the total storage needs, and if you add up all the other viable dams, you’ll find that it doesn’t add up to a lot. To put it in context: Columbia River basin produces 40% of US hydroelectricity. Out of 14 dams on Columbia River, 12 of them produce (each individually) more electricity than Hoover Dam, most by a factor of 3x or more. Very little of it can be turned into storage as of today, what does not get used must be spilled. This is not to say that using dams for energy storage is a bad idea, it’s not. It just will not work well in practice with most of currently existing dams, at least without huge retrofits and/or screwing over downstream water consumers and upstream reservoir users.

xyzzyz 3y ago

> recall most of them operate as giant annual batteries, they refill in the rainy season once per year, then dispense that energy over the dry season That’s not quite how it works. Consider the biggest hydro project in US, the Columbia river, with its 14 dams. The system does fill up in the rainy season, but the crucial thing is that it’s not the dams that do fill up, but rather the whole watershed, meaning things like snowfall and ground water. This means that we have very limited amount of control over when we let the water through. We can’t just dam the river for an extended period: if we don’t use it for generating power, we must spill (waste) it. This means in practice that the dams are not batteries: to a large degree, it‘s use-it-or-lose-it. To make these into batteries, we’d need to somehow refurbish the dams to tremendously increase the power generating capacity on each dam, so that instead of assumption of continuous flow (either through turbines or spillways), we make the flow more intermittent, so that we can make up for closed times by pushing more water through during open times. This is tremendously difficult in practice: dams are simply not designed to allow for refurbishing with many more turbines or much more flow through them than they were originally designed for, the upstream reservoirs are not designed for quickly varying water levels, etc. Point is, we can’t just “save the water”.

Arrath 3y ago
> That’s not quite how it works. Yeah in reality there are two forms of hydropower: the classic reservoir dam, and 'run of the river' powerplants. You're absolutely right, even reservoir dams don't really fulfill the 'annual battery' idea, since they must maintain some minimum outflow for downstream consumers and can't shut it off entirely if it better suits the power generation goal.
jakewins 3y ago
> Point is, we can’t just “save the water”. The storage level at Lake Mead has an annual spread of ~100ft; the dam is currently at historic low capacity and could hold about twice its current level: https://www.usbr.gov/lc/region/g4000/lakemead_line.pdf https://www.usbr.gov/lc/region/g4000/lakemead_line.pdf Reservervoir dams certainly can store water and dispense it when appropriate. Like I said, this is happening every day already, you can see it in the hourly data on wind/hydro generation share, and you can see it in the annual storage capacity data for Norwegian hydro.
- xyzzyz 3y ago
  Yes, we can do this for some dams, but not enough to move the needle. Hoover Dam’s generating power is quite tiny relative to the total storage needs, and if you add up all the other viable dams, you’ll find that it doesn’t add up to a lot. To put it in context: Columbia River basin produces 40% of US hydroelectricity. Out of 14 dams on Columbia River, 12 of them produce (each individually) more electricity than Hoover Dam, most by a factor of 3x or more. Very little of it can be turned into storage as of today, what does not get used must be spilled. This is not to say that using dams for energy storage is a bad idea, it’s not. It just will not work well in practice with most of currently existing dams, at least without huge retrofits and/or screwing over downstream water consumers and upstream reservoir users.