$/kWh energy storage technologies

[Warpspeed]

Show me the math that lifting a ten ton bulldozer up to the top of a thirty floor building (300 feet) can be done with only 2.7Kwh.

 

[MattiFin]

One potential method not mentioned would be to use a very heavy suspended weight and a pulley.
This need not be expensive, if you just happen to have a disused vertical mine shaft or a suitable cliff edge nearby.
It might work something like a lift well. If you have a VERY long steep slope, something on rails might be possible ?

The weight could be winched upwards with surplus energy, and return that energy as the weight is allowed to fall back downwards.
This should be about the most efficient mechanical energy storage system possible, and its nothing new.

For centuries, clocks have been powered either by clockwork, or a suspended weight. To rewind the clock just quickly winch the weight back up by hand once a day. Falling weights were traditionally fitted to light houses to rotate the light beacon at the top of the tower, before the age of electricity.

Just looked up the weight of a single cubic metre of concrete, about 5,295 Lbs.
https://www.omnicalculator.com/construction/concrete-weight

One horsepower equals 33,000 pound feet per minute. So our concrete weight needs to rise or fall 33,000/5,295 = 6.23 feet per minute for 1Hp.
One Hp = 746 watts.

A single cubic metre is not very big, and 746 watts is not a lot of power.
It would need to fall roughly 37.38 feet per hour.
Or 444 feet for twelve hours for 8.952 Kwh of storage.
Should be possible to recover 75% to 80% of that in a practical system.

Sounded way off but took a while to fiqure out your math with horses per midnight.
6.23 feet per minute is not 37.38 feet per hour but 10x that.

Thus you need 4440 feet drop to store 9 kWh.

 

[MattiFin]

Show me the math that lifting a ten ton bulldozer up to the top of a thirty floor building (300 feet) can be done with only 2.7Kwh.

You get so much more done with SI units when you have 60 minutes per hour.

 

[Warpspeed]

Sounded way off but took a while to fiqure out your math with horses per midnight.
6.23 feet per minute is not 37.38 feet per hour but 10x that.

Thus you need 4440 feet drop to store 9 kWh.

yes you are quite right. sixty minutes in an hour not six.

 

[wattmatters]

Show me the math that lifting a ten ton bulldozer up to the top of a thirty floor building (300 feet) can be done with only 2.7Kwh.

Gravitational potential energy, U = m·g·h

where:
U = gravitational potential energy in joules
m = mass in kg
g = acceleration due to gravity (9.8 m·s⁻²)
h = height in metres

10 tonnes = 10,000 kg
100 metres

U = 10,000 kg x 9.8 m·s⁻² x 100 m
= 9,800,000 joules
= 9,800 kJ
= 2,720 Wh
= 2.72 kWh

Now I am not claiming that the bulldozer can be lifted 100m with only that much energy. I'm only saying that is the gravitational potential energy required to lift it up that height. That's the minimum requirement.

The process itself of lifting will have energy losses, IOW the total energy required to lift the bulldozer will be more than the amount of gravitational potential required. You ain't getting those losses back when it goes back down.

The second law of thermodynamics is a bitch.

 

[Warpspeed]

10 tonnes x 100 m = 2.7 kWh of gravitational potential energy.

Of which the losses would be substantial. You'd be lucky to get 1 kWh of useable storage capacity out of it.

I have now had a day or so to think about all this.
The only real world machinery I can compare this to, is an electric garage vehicle hoist.
Fairly recently I looked at an electric motor removed from one of those, it was rated for 2Hp intermittent duty and was physically quite small.
Considering what they are rated to lift, and the speed of operation, your figures seem to fall well into line with that.

 

[wattmatters]

Considering what they are rated to lift, and the speed of operation, your figures seem to fall well into line with that.

You'd hope so given its just basic physics.

 

[Warpspeed]

You'd hope so given its just basic physics.

True, but sometimes its not always intuitive how much power is actually required to do something.

 

[OffGridForGood]

True, but sometimes its not always intuitive how much power is actually required to do something.

Elevator hoist motors are not very large motors.
the elevator car is balananced with a counter weight to reduce the load on the hoist, however as you add passengers, the load and balance change.
Anyway the point is, even a high rise elevator motor is not actually very large, since the energy involved to lift against gravity is not really very high.

 

[Warpspeed]

Elevator motors in high rise buildings are a very different thing to a slow vehicle hoist.
The speeds and accelerations/decelerations are much higher.
Although they are counter weighted, there is still a lot of inertia to overcome.