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Power utility engineer here. I keep imagining a giant flywheel located at every substation- could be very useful for load balancing, voltage regulation, even fr

Power utility engineer here. I keep imagining a giant flywheel located at every substation- could be very useful for load balancing, voltage regulation, even frequency control. I guess what I mean is, a large spinning mass could potentially have other benefits than just storage, right? Any research into substation application at that startup?

sgentle 8y ago
I was recently reading about power factor correction and found out that "synchronous condensers", basically just large synchronous motors with no load, are sometimes used at utility scale for PFC and frequency stabilisation. Eg, here: http://www.think-grid.org/synchronous-condensers-better-grid-stability http://www.think-grid.org/synchronous-condensers-better-grid... Since it seems like the main source of stability in that system is the inertia in the rotor, would it be fair to describe it as a kind of flywheel? I didn't see anything about connecting an actual wheel to such a system, but it seems like it would be the same thing with more inertia, right?
- eigenvector 8y ago
  Where "flywheels" in common parlance differ from synchronous condensers is that condensers run at zero torque - so they provide no active power to the system. They provide reactive power, which is needed to regulate and maintain the stability of the power system, but not active power which is used to match generation and demand or shift load. There's no actual source of energy being fed into a synchronous condenser. In a flywheel, you're drawing energy from the grid to spin up a really big mass and then storing it in rotational inertia so you can output it later very quickly. Flywheels can provide reactive power too, through their DC/AC power converters, but since you don't actually need any rotating mass to do that (recall, reactive power requires no torque), you can use a STATCOM - which is functionally like a synchronous condenser just without any moving parts.
bigiain 8y ago
They do this in datacenters - mostly I think to bridge the gap between a power outage and diesel generator startup time. You might also be interested in this: https://electrek.co/2018/05/11/tesla-giant-battery-australia-reduced-grid-service-cost/ https://electrek.co/2018/05/11/tesla-giant-battery-australia... “In the first four months of operations of the Hornsdale Power Reserve (the official name of the Tesla big battery, owned and operated by Neoen), the frequency ancillary services prices went down by 90 per cent, so that’s 9-0 per cent. And the 100MW battery has achieved over 55 per cent of the FCAS revenues in South Australia. So it’s 2 per cent of the capacity in South Australia achieving 55 per cent of the revenues in South Australia.”
eigenvector 8y ago
For an energy storage system, you probably don't want a synchronous machine. You want to be able to deliver (or absorb) rated power over a wide range of rotor speeds, since the difference between your lowest and highest speed is what effectively determines your energy storage capacity. To do this with a synchronous generator you'd need a big, expensive high-speed gearbox similar to what you see in synchronous generator wind turbines. So we used an induction motor/generator + back-to-back converter to tie to the grid, which is a common design very similar to what's used in most modern wind turbines. Therefore, from the perspective of the grid, no rotational inertia is coupled to the power system and the machine doesn't exhibit the inertial response of a synchronous generator that I'm sure you're familiar with. However, if you have a fast enough control and communications system, you can provide the desired response for both frequency and voltage control and that's a big part of what we were trying to do. You can ramp from minimum to maximum active or reactive power very, very fast (like 5 AC cycles), which is much faster than any traditional generator. Due to the fast ramping capability, we also researched the possibility of using flywheels for large unit trip contingencies in small power systems (e.g. Hawaii) where operating reserve is very expensive. At the end of the day, the biggest problem is that anything flywheels can do, batteries can do too - and batteries are getting cheaper every year.
ridgeguy 8y ago
Yes, flywheels are used for phase matching at some grid intersections. For example, http://beaconpower.com http://beaconpower.com has installations that do this. There are FERC rate schedules for this service that make it a profitable application for flywheels.

sgentle 8y ago

I was recently reading about power factor correction and found out that "synchronous condensers", basically just large synchronous motors with no load, are sometimes used at utility scale for PFC and frequency stabilisation. Eg, here: http://www.think-grid.org/synchronous-condensers-better-grid-stability http://www.think-grid.org/synchronous-condensers-better-grid... Since it seems like the main source of stability in that system is the inertia in the rotor, would it be fair to describe it as a kind of flywheel? I didn't see anything about connecting an actual wheel to such a system, but it seems like it would be the same thing with more inertia, right?

eigenvector 8y ago
Where "flywheels" in common parlance differ from synchronous condensers is that condensers run at zero torque - so they provide no active power to the system. They provide reactive power, which is needed to regulate and maintain the stability of the power system, but not active power which is used to match generation and demand or shift load. There's no actual source of energy being fed into a synchronous condenser. In a flywheel, you're drawing energy from the grid to spin up a really big mass and then storing it in rotational inertia so you can output it later very quickly. Flywheels can provide reactive power too, through their DC/AC power converters, but since you don't actually need any rotating mass to do that (recall, reactive power requires no torque), you can use a STATCOM - which is functionally like a synchronous condenser just without any moving parts.

bigiain 8y ago

They do this in datacenters - mostly I think to bridge the gap between a power outage and diesel generator startup time. You might also be interested in this: https://electrek.co/2018/05/11/tesla-giant-battery-australia-reduced-grid-service-cost/ https://electrek.co/2018/05/11/tesla-giant-battery-australia... “In the first four months of operations of the Hornsdale Power Reserve (the official name of the Tesla big battery, owned and operated by Neoen), the frequency ancillary services prices went down by 90 per cent, so that’s 9-0 per cent. And the 100MW battery has achieved over 55 per cent of the FCAS revenues in South Australia. So it’s 2 per cent of the capacity in South Australia achieving 55 per cent of the revenues in South Australia.”

eigenvector 8y ago

For an energy storage system, you probably don't want a synchronous machine. You want to be able to deliver (or absorb) rated power over a wide range of rotor speeds, since the difference between your lowest and highest speed is what effectively determines your energy storage capacity. To do this with a synchronous generator you'd need a big, expensive high-speed gearbox similar to what you see in synchronous generator wind turbines. So we used an induction motor/generator + back-to-back converter to tie to the grid, which is a common design very similar to what's used in most modern wind turbines. Therefore, from the perspective of the grid, no rotational inertia is coupled to the power system and the machine doesn't exhibit the inertial response of a synchronous generator that I'm sure you're familiar with. However, if you have a fast enough control and communications system, you can provide the desired response for both frequency and voltage control and that's a big part of what we were trying to do. You can ramp from minimum to maximum active or reactive power very, very fast (like 5 AC cycles), which is much faster than any traditional generator. Due to the fast ramping capability, we also researched the possibility of using flywheels for large unit trip contingencies in small power systems (e.g. Hawaii) where operating reserve is very expensive. At the end of the day, the biggest problem is that anything flywheels can do, batteries can do too - and batteries are getting cheaper every year.

ridgeguy 8y ago

Yes, flywheels are used for phase matching at some grid intersections. For example, http://beaconpower.com http://beaconpower.com has installations that do this. There are FERC rate schedules for this service that make it a profitable application for flywheels.