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Guru

Join Date: Sep 2007
Location: East Texas
Posts: 1398

# Interfacing Grid Power with Home Produced Power

05/03/2013 2:08 AM

Interfacing grid power with home produced power without having to jump through the hoops.

Would it be possible to take steel rings, mount them on old railroad axles, coupled either directly or through a hydraulic converter to a generator on one side and an electric motor on the other?

Would it be possible to feed all of the point of use produced power to the motor to charge the flywheel and feed the local demand from the generator and when the flywheel charge gets below a certain level add commercial grid power to the input side?

Would I still need the fancy gizmos to sync with the commercial grid?

The moment of inertia for a simple disk or cylinder is .5mr^2= I. The stored energy is .5I(w^2)

20,000 KG of 1.5 meter radius rings would easily fit on a standard gauge axle and the axles are designed to handle more than this weight.

I=.5(20000) (2.25) = 22500 KGM

Storing 50 KWH = 180,000,000 J

180^6/22500 = 8000 = w^2

89.44 / 2pi = 14.23 rps = 854 rpm

Would that exceed the yield stress for iron?

If I built a soft sand berm next to it would that keep it from mowing down the town if the axle broke?

A quick peek at storage costs for other technologies given here -

http://prod.sandia.gov/techlib/access-control.cgi/2011/112730.pdf

makes me think this could be made cost competitive in small scale applications.

Looking at Table 4:

I have a little trouble wrapping my mind around the cost numbers, especially the one for Compressed Air Energy Storage where Power Subsystem Cost (power density cost???) was given as \$700/KW and the Energy Storage Subsystem Cost (Energy Density Cost ??) is given as \$5/KWH. Obviously I don't understand the metrics used, I could use some help with that. Also, I don't believe there is a reference to the scale of application. Wouldn't this affect both power density cost and energy density costs?

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Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 31852
#1

### Re: Interfacing Grid Power with Home Produced Power

05/03/2013 1:01 PM

Be sure and get this on film......

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Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8378
#2

### Re: Interfacing Grid Power with Home Produced Power

05/03/2013 6:27 PM

I am not following the logic here.

A few forklift battery sets and a grid tie inverter could be had for less cost and would take up less space plus be a whole lot safer and simpler to operate.

You would be time effort and money ahead plus at minimum be of equal to likely ahead on overall system efficiency plus have no moving moving parts to deal with as well.

Guru

Join Date: Sep 2007
Location: East Texas
Posts: 1398
#3

### Re: Interfacing Grid Power with Home Produced Power

05/04/2013 1:01 AM

So how many forklift battery sets would it take to store 50 KWH?

How many cycles could the battery sets take?

What would be the power density in charging? That is; can they accept charge at nearly the same rate as discharge?

A GTI can only used where it is allowed to be used.

In the past year I have been on islands where grid power costs any where from 48 cents to \$1.08 per KWH. Some means to solve intermittent power production challenges; any means, including forklift battery sets if acceptance rates are high enough, would see a pretty high ROI.

The ideal system for several of these islands would be a Channel Tidal Turbine with a short term storage method to accommodate the slack tide.

TCMTECH: For a guy with your interest, background, knowledge, and experience - the South Pacific could indeed be a paradise. You do see just how wide your horizons span; don't you?

__________________
"The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low, and achieving our mark." -- Michelangelo
Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8378
#4

### Re: Interfacing Grid Power with Home Produced Power

05/04/2013 8:48 PM

Most of the common mid sized forklifts run on 36 or 48 volt battery sets rated around 500 - 1000 Ah at a 6 hour discharge rate and if maintained properly can take being moderately discharged and recharged every day and still put in 10+ year life spans.

Typical price in these parts for a rebuilt or new battery can be around \$3500 - \$5000 depending on brand model and service life ratings.

Used can be anywhere from local scrap price on up.

You can do the math from there.

Personally if I ever had to go full off grid Forklift batteries would be my first choice.

Granted they are big, bulky, heavy, and cumbersome to work with and move but when put in a stationary application and properly cared for as I understand it they have incredibly long service lives given the money spent.

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