Gigawatts for a 10 seconds?

[Charles West]

Hello!

I've been looking at different proposals for electric guns to do space launch. One commonality I've noticed between proposals a large portion of the budget going to energy storage because you needs over a megawatt per kilogram of payload even at relatively modest exit speeds.

The cheapest option I've found so far is high discharge LIPO batteries, but I am wondering if there might be some way to bootstrap off of existing infrastructure (like solar grid storage systems?)?

If I may ask, what is the cheapest way you know of to get 1-2 gigawatts of power for 10 seconds (timing flexible, probably off-peak)?

 

[itsmoked]

You seek a Homopolar Generator.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Charles West]

@itsnoked:
LIPO batteries strongly outperform homopolar generators at these durations and LIPOs scale better. I was more hoping there might be a way to piggyback off of existing infrastructure instead of building millions of dollars worth?

 

[cranky108]

You can only get out of the grid, what someone puts into it. Can you propose a 1-2 gigawatts of power for 10 seconds source?

 

[FacEngrPE]

The only part of the grid that can respond to a 10 second x 1GW square wave load is the system inertia. Even if the utility dispatcher would allow that kind of a load to be connected, you would need significant, costly infrastructure to carry the power to your point of use.

My best guess is that any utility would reject the connection request on the grounds that the proposed load profile would disrupt system stability.

 

[waross]

If you are going to accelerate for 10 seconds, how long is your launcher?
What voltage/current/frequency do you plan?
Have you considered mechanical storage?
A large high-speed flywheel in a vacuum?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[davidbeach]

I know of a 1.2 GW "toaster" that has a maximum connection time of 30 cycles. Used only as a system brake for highly significant system disturbances. Anything you want to trigger at a random time needs to "trickle" charge prior to use and not rely on the grid for anything other than that trickle charge.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[bacon4life]

My initial take was the same as David, but then I was struggling to point out specifically which interconnection rules such a load would violate. Some possibilities include:
1) On a large interconnection, 1000 MW is much smaller than the largest credible contingency. Having an extra load for 10 seconds seems far less extreme than loosing a 1000 MW coal/nuke plant. From a system inertia perspective, light load hours would be worst than peak load hours.
2) From an energy trading point of view in market with 5 minute intervals, 1000 MW for 10 seconds is roughly equivalent to loosing a 35 MW generator for the entire 5 minute interval.
3) From a voltage drop perspective, I was surprised I could add 1000 MW at a major 115 kV yard near me and have less than a 2% voltage change. This is larger than preferred for normal daily operations, but this size voltage change does occur. It may be possible to mitigate this with an injection of reactive power.
4) The energy cost for 1000 MW for 10 seconds is only a few hundred dollars. The cost for equipment that can handle 1000 MW would be many millions of dollars.
5)Utilities do not generally have equipment ratings as short as 10 seconds. Although most utility equipment can handle a very high thermal overload for 10 seconds, typically utilities if utilities have an short term rating it is at least 5 minutes long and more likely at least 30 minutes long.

 

[waross]

To put this in perspective the reactors on a Nimitz class aircraft carrier produce 194 megaWatts of mechanical power.
When the Nimitz class of Carrier is decommissioned, 5 or 6 surplus carriers could provide the power.
The bad news: You would have to source and connect generators to the propeller shafts.
The good news: Able to last 20 years without refueling.
At 10 seconds a launch you would be good for over 60 million launches.
Ramping down the power at the end of the launch may be a bigger problem than originally generating the power.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Charles West]

@waross:
I'm working on a small scale prototype of a low cost coilgun/rail gun hybrid with Barry from

https://www.coilgun.info/about/home.htm

. I've also corresponded with Ian McNab (who has done a number of space launch via railgun papers). For my design, you would want relatively high frequency 3 phase current to run an induction motor onboard the projectile down an aluminum pipe. For his designs, it would be DC.

If you know how to get ownership of 5 or 6, airplane carriers, I would love to do that

@bacon4life:
Does this mean that you think it might actually be feasible to hook up at a 115kV yard without having to build large amounts of energy storage?

 

[cuky2000]

I remember back in the 90's that our company work in the Tokamak Fusion Test Reactor (TFTR) currently abandoned at the Princeton Plasma Physics Laboratory (PPPL) that may be a possible power source for your project. There are several components including a substation connected to PSE&G that may be useful to consider if the University and DOT provide the OK to use it.

I also remember working on a power upgrade project to support the Picatinny Arsenal in NJ that was experimenting with electric cannon. Enclosed is a Link that we hope to help your search.

 

[bacon4life]

I assume someone else will point out reasons it may not be feasible. The particular 115 kV yard I looked at is quite large, so it may be more feasible at 230 kV.

I looked at a 10 second thermal load on an overhead wire, and it appeared the wire could carry about 10 times the steady state value. So for a 1000 MW shot, you would still need at least 100 MW of infrastructure to step down from ~230 kV to something low voltage. I suspect rectifiers do not have such a large thermal capacity for short term overloading.

There may also be an issue of finding a robust substation in an area compatible with supersonic noise.

 

[Charles West]

@cuky2000:
Thank you! I think Dr. McNab might have actually worked on that project.

@bacon4life:
I think my design might actually be OK at that voltage but it would need to get to a higher frequency. If I may ask, do you know of any way to multiply frequency at that voltage/power level efficiently? Are there mosfet like parts that can operate at these power levels (switching in the kilohertz range)?

 

[waross]

The power can be handled with existing technology but I don't know how high you can push the frequency.

Further, building two 500 kilovolt DC lines with a transfer capacity of 2,000 MW each would

I live about one mile from an existing 500,000 VDC line.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[FacEngrPE]

A recient PJM study

https://insidelines.pjm.com/transmission-study-lays-foundation-for-regional-offshore-wind-planning/

provides some current pricing relevant to your question.