INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Rotating Stored Energy (Centrifuge with M/G Driver): Theoretical Weight & Speed

Rotating Stored Energy (Centrifuge with M/G Driver): Theoretical Weight & Speed

(OP)
Question came up on a different "science" and energy forum about using high-speed (or verylarge) centrifuges to "store" wind or solar energy for use later in the day or at night to balance out their irregular power outputs.

1. Getting outside of the politicals/money/CAGW and usefulness of the idea at large - which is impossible in the real world, but bear with me on that - for a house-sized unit ( 1-2 kw size) what would be the needed weight (inertia) rotating at 15:00 pm to still generate power the next morning at 9:00 am?

2. Could those assumptions be "built up" to a 2-3 megawatt unit - as if one windmill running one centrifuge M-G set?

Overall, I can't see it working at anything but a government-funded Sandia-type national lab.

Problems:

Clearly balancing, bearings, lube oil system and storage and cleanliness and cooling and maintenance.

If the centrifuge were ultra-high speed, seems you be buying the reduction gear issues and problems as cost as well.

Air resistance of the rotating centrifuges and MG-Set, unless a nearly-impossible vacuum or hydrogen-cooled gas cooling system were used. And those are tough to build and maintain even on the big power generators!

Brushes and and all those DC-side problems, or could they be avoided by an AC-AC motor generator with an outlet
AC-AC frequency converter to "pickup" the slowly lowering AC output from the centrifuges as it slows down?

Thus, you'd have a transformer <-> grid connection <-> AC-AC static frequency converter <-> AC motor-generator <-> clutch/coupling <-> (optional reduction gear) <-> centrifuge.

It seems like you'd need to setup the ac-ac MG to be able to over-speed the centrifuge up past the MG set synchronous speed (to build up stored inertial energy in the centrifuge) during off-production hours, then pull that inertial energy down from centrifuge max speed though the unit's nominal speed down to the generator's cut-off speed

As a guess, I estimated a house-sized unit would be about the weight of two cars. Way too big, or way too small?

RE: Rotating Stored Energy (Centrifuge with M/G Driver): Theoretical Weight & Speed

Probably too small; you forgot the scattershield.

There was an article (in ME, I think, before it became a comic book) maybe a decade ago about designing safety containment structures for energy storage flywheels, based on a thick walled lead ring that absorbed the flying pieces, and rotationally accelerated itself within a steel ring, and sort of melt/extruded axially upward as it decelerated.

The accompanying photos were _very_ impressive.

Mike Halloran
Pembroke Pines, FL, USA

RE: Rotating Stored Energy (Centrifuge with M/G Driver): Theoretical Weight & Speed

I was considering a PhD to design such a thing as a replacement for lead-acids in remote areas, twenty years ago. Here is a bigger installation than you had in mind

http://beaconpower.com/stephentown-new-york/

this may be more of a size that is useful

http://www.power-thru.com/industrial.html

Advantages compared with lead acids are very long life times and high round loop efficiency, the latter being remarkably unimportant in these days of cheap pV.

The energy stored is just 1/2*Izz*w^2

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Rotating Stored Energy (Centrifuge with M/G Driver): Theoretical Weight & Speed

Elon Musk has an alternate approach:
http://www.cnet.com/news/teslas-elon-musk-introduc...

TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: Rotating Stored Energy (Centrifuge with M/G Driver): Theoretical Weight & Speed

Yes, the idea of using a different battery chemistry makes a lot of sense. For my off grid house Musk's battery is already half the price of my current setup, per kWh, and that is projected to fall by a further 50% in 4 years.10 usable kWh of battery with intelligent monitoring means we could run an electric kettle woo woo

http://rameznaam.com/2015/04/30/tesla-powerwall-ba...

Back to flywheels

this does half the job

http://www.calculatoredge.com/mech/flywheel.htm

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Rotating Stored Energy (Centrifuge with M/G Driver): Theoretical Weight & Speed

(OP)
Yes, the question came while discussing alternatives to Musk's proposed Li batteries.

I've used high-powered DC-AC MG sets and high-potential lead-acid batteries in the Navy's nuke plants (S1W, S6G, S5W), and serviced very powerful DC-AC MG sets with battery DC sources at several power plants; and have a smaller (625 watt) inverter with a lead-acid deep cycle battery for home backup ... And that's why I can't see a "regular" household ever being able to support hardly form of battery-inverter-backup system. People today just know enough to tighten the bolts after changing batteries.

Assuming they don't sue when they lose their eyes to to acid spilling from a broken battery that fell across their legs.

RE: Rotating Stored Energy (Centrifuge with M/G Driver): Theoretical Weight & Speed

(OP)

Quote (GregLocock (Automotive))


3 May 15 21:52
I was considering a PhD to design such a thing as a replacement for lead-acids in remote areas, twenty years ago. Here is a bigger installation than you had in mind

Interesting idea = good concept.

But,m for industrial use - as a backup BEFORE the generator comes on is their criteria.
Thus,
225 kW at 30,000 to 53,000 rpm =
190 kW continuous for 10 seconds, 225 KW maximum surge, "until generator starts"
.528 KW-hr @ 190 Kw, 1900 kw-seconds at 1300 lbs, underground installation for debris containment (outdoors in the photo's at the site.)

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close