Heavy Load Motor-Generator (Dynamotor) Questions 1

[TRBob]

The motor-generator will be used to pull a load up a mountain side/steep incline on a rail system, the load is between 10 and 300 tonnes, its for a gravitational potential energy storage system. Excess electricity pulls the load up the incline, when there is demand for electricity the load is released driving the generator. Obviously a good gearing system is required.

Is this technically possible? How much do you estimate one would cost? What would be the device’s efficiency?

 

[ScottyUK]

Possible? Yes. Worthwhile? Probably not.

Think how much mass of water a pumped hydro scheme stores - typically thousands of tonnes, many tens of thousands in the bigger ones.

How much power are you wanting to generate, and for how long?


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If we learn from our mistakes I'm getting a great education!

 

[Hoxton]

Is this a student post, if so then it is not appropriate here. Otherwise, I agree with Scotty, It would work, but the cost benefit ratio would not be good enough to make it financiably sound. The problem, in my humble view, with this type of scheme is the high civil engineering cost which compared with the electrical and mechanical plant cost reduces the financial return below other investments

 

[sreid]

There are proposals for energy staorage that use vertical holes in the ground. Not much land is used and drilling a vertical tunnel is not technically challenging. The energy is stored by lifting a mass.

 

[LionelHutz]

It could be done.

I have no idea of cost.

Not sure what you mean by efficiency, but I'd guess you could recover something like 70% of the energy used to move the mass up the hill.

As for the bigger picture, a quick calculation tells me that a 300 tonne block moving 500m vertically stores about 400kWh. What you propose doesn't sound large enough for a utility scale but it might work for small scale storage, say for storage of power from solar panels or a wind turbine.

 

[itsmoked]

Sounds like a great idea to me. Pumping water is lots lamer. Pump efficiency is horrid compared to some gears and steel rollers. Especially if a lot of the mass is free. (rock or scrapmetal)

Is this for solar or wind storage?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TRBob]

The end user would be a small remote community, that derives their electricity from wind or solar power and are not necessarily connected to a grid.

Not had much luck with manufacturers.

 

[itsmoked]

That would definitely be a custom job. I wouldn't expect you to find a single vendor.

Be pretty cool really. Much better than battery storage too. An excellent idea in my view.

1kwhr = 3.6MJ

1 tonne x 1000kg/tonne x 1m x 9.8m/s² = 9,800J

3.6MJ / 9,800J = 367m

You need to raise each tonne 367m per kwhr. A 100tonnes would need 3.67m. Ouch.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

If you have the deep hole available - an old mine shaft perhaps - then the viability increases dramatically.

Keith - water as a storage medium works well on big stations because of the difficulty in suspending a three thousand tonne block over a hole over half a mile deep, which based on Lionel's figures is roughly what is needed to replicate the Dinorwig pumped storage station's capability.


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If we learn from our mistakes I'm getting a great education!

 

[LionelHutz]

The power output would be fairly linear with speed if you assume the tracks and gearing are free-running so the load will produce a fairly constant torque on the motor shaft from 0 speed to full speed. Similar applies for uphill travel, the power input would be fairly linear from 0 speed to full speed.

So, considering this is an islanded system, I'm thinking a 4 quadrant VFD with a custom build control system will be needed. The VFD must be able to synchronize with whatever line power is available and the control system will have to regulate the speed of the motor to match the output power with the system demand.

Most RE will more or less produce more output voltage when producing more power. So, it's possible the control for the weight could use the line voltage, running slower or uphill if the voltage is high and run faster downhill if the system voltage is low.

You'll need to first come up with a more detailed specification than lowering a 10 to 300 tonne block down a hill before you can get any answers on equipment. If you're looking for a turnkey solution then you'll likely need to employ an engineering firm, since I doubt any manufacturers will do this level of engineering.

Well, this is besides the issue of sorting out the control system so it doesn't fail and let the 300 tonne block go flying down the hill on it's rail tracks...

 

[itsmoked]

Yeah Scotty, for BIG I agree you can't beat water for an indestructible and predictable mass.

Sounds like a good plan to me Lionel! You could use a typical Otis Elevator safety for preventing an, um, embarrassing descent rate.

Keith Cress
kcress -

http://www.flaminsystems.com