4 ms·

An individual inverter can usually switch in about 4 ms. A Tesla Megapack can go from 0% output to max output in 100 ms. Conversely, gas turbines (the fastest t

An individual inverter can usually switch in about 4 ms. A Tesla Megapack can go from 0% output to max output in 100 ms. Conversely, gas turbines (the fastest type of traditional power plant) takes about a minute to go from say 40% to 60%. Even in the fastest possible design, there is a mechanical rotor (kinetic energy) that has to change speed. What I mean to say is that solar and batteries are likely an order of magnitude faster to respond to sudden demand changes. So I would expect a more reliable system when more solar and especially batteries are being added.

bell-cot 2y ago
IANAEE (not an electrical engineer), but doesn't a gas turbine spin at a constant speed to drive a 60Hz generator, regardless of whether it's running at 20%, 60%, or 100% of capacity?
- markus92 2y ago
  When there’s a load imbalance on the grid (more load than capacity), the turbines physically slow down as inertial energy is extracted from them. This causes the grid frequency to drop. It takes some time to ramp up production and speed up the turbine etc.
  - bell-cot 2y ago
    The maximum slow-down of the turbines (before the generator trips off-line, removing the load on it) is far less than you seem to assume. The article's graph shows the 60.00Hz grid frequency dropping...all the way to 59.92Hz. That's 0.1333%. For an on-line gas turbine, the time to ramp up production is the second or few needed for the automated controls to open the throttle on the "Gas IN" pipe. It's basically a natural gas-burning turboprop jet engine, with the propeller replaced by a generator. (Yes, this can be less efficient in a combined cycle plant.)
    - jeffbee 2y ago
      The more interesting thing about rotating power plants is that they are routinely destroyed by transmission outages, because when a rotating generator is suddenly disconnected from its load, there are infinity terms in the equations that govern its motion and infinity isn't a thing you can resist. For steam turbines the control system has to slam the valve shut on the steam, otherwise the machine would overspeed, and closing that valve destroys some sacrificial part of the steam plumbing (hopefully). Steam power plants have to be inspected and repaired after disconnects and this is one of the numerous reasons why fission kinda sucks on the reliability front.
      - m463 2y ago
        I don't see why there can't be load resistors (like locomotives use) to gracefully handle these sorts of situations.
        Qwertious 2y ago
        Well if you can solve it, I imagine there's a lot of money to be made - and yet it hasn't been solved.
        jeffbee 2y ago
        An SD40 locomotive can dissipate about 500kW that way, so you would need the equivalent of 2000 locomotives worth of resistors and fans to sink the 1 or 2GW or more that a fission power station produces.
        rcxdude 2y ago
        If you wanted to do so continuously. If you're just handling an impulse you don't need so much, but it's gotta absorb a lot of energy quickly.
      - rcxdude 2y ago
        While the infinity terms may be a useful way to think about how the system loses stability, I think it's better to think of it in terms of energy: at any given time there's some amount of energy that's been injected into the system in the form of hot gas which hasn't been converted yet. Even a few seconds worth is a lot of energy, and if the electrical load is removed, that energy has to go somewhere.
leymed 2y ago
I think you’re missing the point how turbine-generator works. The rpm speed has to stay the same, meaning the rotor speed doesn’t change. As long as you don’t have closed circuit you’ll waste that mechanical energy. If you meant starting from stand still position, then you’re right it takes couple minutes to pick up the load. With that said, turbines responding in couple minutes are more reliable as a baseline when you’re planning load flow of as big as country or wider area. The basic reason is that you have source of energy under your control such as nuclear, water, gas, coal. You cannot have solar, wind as your baseline, I don’t want sound dramatic, but it’s kind of suicidal to do that. Solar’s ramping is not a win when you consider greater scale.
- ViewTrick1002 2y ago
  Reliable until it isn’t. The entire grid is a statistical system where we define the acceptable uptime. Renewables are as good as any other energy source bringing its own fuel, just need to take the variability into account. https://www.nytimes.com/2022/11/15/business/nuclear-power-france.html https://www.nytimes.com/2022/11/15/business/nuclear-power-fr...
  - leymed 2y ago
    You’re correct that the system is statistical, and it’s planned accordingly. However, we cannot omit the fact that it’s the running turbine that responds faster to the unpredictable nature of the grid. The backbone of the grid, aka the baseline plants, are extremely responsive to unpredictable nature of the grid at a greater scale, with enough amount of safety margins to bring into service under unusual circumstances. I really don’t see, at least what we have in hand rn, that happening with solar or wind. Without strong baseline you’d experience supply demand imbalance, in engineering terms frequency decay, voltage collapse.
    - ViewTrick1002 2y ago
      Which means nuclear is the worst companion imaginable. Since nuclear power needs to run at 100% 24/7 to only make an enormous loss. Dispatchable nuclear power to complement renewables has never made sense.
quickthrowman 2y ago
> An individual inverter can usually switch in about 4 ms. A quarter of a 60 hz cycle or a fifth of a 50 hz cycle is really fast. For comparison, it takes a current limiting fuse around a half cycle to clear a short circuit current and a GFCI takes around two cycles to clear a ground fault.
lmm 2y ago
> Even in the fastest possible design, there is a mechanical rotor (kinetic energy) that has to change speed. The point of ramping up the power plant is to make sure that the rotor doesn't change speed (by e.g. burning more fuel to push it harder, because there's suddenly more load on it), and that can happen a lot faster than spinning up the rotor from scratch. Indeed a heavy rotor helps to stabilise the grid "for free" by acting as a flywheel (which, in a way, responds even quicker to the demand change than a battery can).
mariushn 2y ago
How many Tesla Megapacks are needed to replace a nuclear plant temporary outage? And for for long can they provide that power?

bell-cot 2y ago

IANAEE (not an electrical engineer), but doesn't a gas turbine spin at a constant speed to drive a 60Hz generator, regardless of whether it's running at 20%, 60%, or 100% of capacity?

markus92 2y ago
When there’s a load imbalance on the grid (more load than capacity), the turbines physically slow down as inertial energy is extracted from them. This causes the grid frequency to drop. It takes some time to ramp up production and speed up the turbine etc.
- bell-cot 2y ago
  The maximum slow-down of the turbines (before the generator trips off-line, removing the load on it) is far less than you seem to assume. The article's graph shows the 60.00Hz grid frequency dropping...all the way to 59.92Hz. That's 0.1333%. For an on-line gas turbine, the time to ramp up production is the second or few needed for the automated controls to open the throttle on the "Gas IN" pipe. It's basically a natural gas-burning turboprop jet engine, with the propeller replaced by a generator. (Yes, this can be less efficient in a combined cycle plant.)
  - jeffbee 2y ago
    The more interesting thing about rotating power plants is that they are routinely destroyed by transmission outages, because when a rotating generator is suddenly disconnected from its load, there are infinity terms in the equations that govern its motion and infinity isn't a thing you can resist. For steam turbines the control system has to slam the valve shut on the steam, otherwise the machine would overspeed, and closing that valve destroys some sacrificial part of the steam plumbing (hopefully). Steam power plants have to be inspected and repaired after disconnects and this is one of the numerous reasons why fission kinda sucks on the reliability front.
    - m463 2y ago
      I don't see why there can't be load resistors (like locomotives use) to gracefully handle these sorts of situations.
      - Qwertious 2y ago
        Well if you can solve it, I imagine there's a lot of money to be made - and yet it hasn't been solved.
      - jeffbee 2y ago
        An SD40 locomotive can dissipate about 500kW that way, so you would need the equivalent of 2000 locomotives worth of resistors and fans to sink the 1 or 2GW or more that a fission power station produces.
        rcxdude 2y ago
        If you wanted to do so continuously. If you're just handling an impulse you don't need so much, but it's gotta absorb a lot of energy quickly.
    - rcxdude 2y ago
      While the infinity terms may be a useful way to think about how the system loses stability, I think it's better to think of it in terms of energy: at any given time there's some amount of energy that's been injected into the system in the form of hot gas which hasn't been converted yet. Even a few seconds worth is a lot of energy, and if the electrical load is removed, that energy has to go somewhere.

leymed 2y ago

I think you’re missing the point how turbine-generator works. The rpm speed has to stay the same, meaning the rotor speed doesn’t change. As long as you don’t have closed circuit you’ll waste that mechanical energy. If you meant starting from stand still position, then you’re right it takes couple minutes to pick up the load. With that said, turbines responding in couple minutes are more reliable as a baseline when you’re planning load flow of as big as country or wider area. The basic reason is that you have source of energy under your control such as nuclear, water, gas, coal. You cannot have solar, wind as your baseline, I don’t want sound dramatic, but it’s kind of suicidal to do that. Solar’s ramping is not a win when you consider greater scale.

ViewTrick1002 2y ago
Reliable until it isn’t. The entire grid is a statistical system where we define the acceptable uptime. Renewables are as good as any other energy source bringing its own fuel, just need to take the variability into account. https://www.nytimes.com/2022/11/15/business/nuclear-power-france.html https://www.nytimes.com/2022/11/15/business/nuclear-power-fr...
- leymed 2y ago
  You’re correct that the system is statistical, and it’s planned accordingly. However, we cannot omit the fact that it’s the running turbine that responds faster to the unpredictable nature of the grid. The backbone of the grid, aka the baseline plants, are extremely responsive to unpredictable nature of the grid at a greater scale, with enough amount of safety margins to bring into service under unusual circumstances. I really don’t see, at least what we have in hand rn, that happening with solar or wind. Without strong baseline you’d experience supply demand imbalance, in engineering terms frequency decay, voltage collapse.
  - ViewTrick1002 2y ago
    Which means nuclear is the worst companion imaginable. Since nuclear power needs to run at 100% 24/7 to only make an enormous loss. Dispatchable nuclear power to complement renewables has never made sense.

quickthrowman 2y ago

> An individual inverter can usually switch in about 4 ms. A quarter of a 60 hz cycle or a fifth of a 50 hz cycle is really fast. For comparison, it takes a current limiting fuse around a half cycle to clear a short circuit current and a GFCI takes around two cycles to clear a ground fault.

lmm 2y ago

> Even in the fastest possible design, there is a mechanical rotor (kinetic energy) that has to change speed. The point of ramping up the power plant is to make sure that the rotor doesn't change speed (by e.g. burning more fuel to push it harder, because there's suddenly more load on it), and that can happen a lot faster than spinning up the rotor from scratch. Indeed a heavy rotor helps to stabilise the grid "for free" by acting as a flywheel (which, in a way, responds even quicker to the demand change than a battery can).

mariushn 2y ago

How many Tesla Megapacks are needed to replace a nuclear plant temporary outage? And for for long can they provide that power?