- #1
derick
- 1
- 0
I have an idea I would like to analyze but I'm practically ignorant of physics and engineering so I'm hoping you folks can give me some informative feedback.
First, something tells me this idea is ridiculously uneconomical and/or impractical, but I'm still curious to find out and it will be a good exercise for me.
The idea is to store energy, input and output as electricity, as the gravitational potential energy of a heavy mass. I am interested in this for off-grid autonomous facilities because it seems to me it would provide a high level of reliability and a very low level of maintenance (because of its simplicity), a high level of energy efficiency (because the mechanics would only lose a tiny amount of energy to heat and sound (?)), and it would store energy long-term with virtually no loss.
The basic design would be: a shaft down into the Earth in which the mass moves up and down. To store energy, a motor lifts the mass, and to release energy the mass is allowed to fall and drive a generator. My very limited knowledge of physics, materials, and engineering prevents me from being able to explore and analyze the idea very much, but if it could be made practical somehow, I think the benefits I mentioned above would make this type of energy storage highly attractive.
Of course, the amount of energy stored is given by the equation
energy = mass * gravity * height
My target minimum for stored energy capacity is 100 kWh = 360 MJ, which gives
mass * height = 360e6 / 9.81
and for a reasonable (?) shaft height of 30 m, requires a mass of (approx.)
mass = 360e6 / (9.81 * 30) = 1223242 kg
So then, my questions are:
Are there any types of cables and winches which can support this much weight and interface with a motor/generator? Could anything else be used to lift and drop this mass? How much would these things cost?
What are the densest and cheapest materials which could be used for this much mass? I already looked at cement and iron but they would be way too expensive. Might rock, with a general density of 2500 kg / m^3, in the form of waste dust/pieces from industry or shale from mountain slopes, be cheap and practical to assemble into some sort of a mass block? With this density of rock, a mass with volume 489 m^3 would be required, and as a cube shape it would require a shaft width of more than 7.88 m. How much would it cost to make a 30 x 8 x 8 m shaft into the ground, for various types of ground?
What are any other issues with the entire idea?
Thank you very much for any feedback :)
--Derick
First, something tells me this idea is ridiculously uneconomical and/or impractical, but I'm still curious to find out and it will be a good exercise for me.
The idea is to store energy, input and output as electricity, as the gravitational potential energy of a heavy mass. I am interested in this for off-grid autonomous facilities because it seems to me it would provide a high level of reliability and a very low level of maintenance (because of its simplicity), a high level of energy efficiency (because the mechanics would only lose a tiny amount of energy to heat and sound (?)), and it would store energy long-term with virtually no loss.
The basic design would be: a shaft down into the Earth in which the mass moves up and down. To store energy, a motor lifts the mass, and to release energy the mass is allowed to fall and drive a generator. My very limited knowledge of physics, materials, and engineering prevents me from being able to explore and analyze the idea very much, but if it could be made practical somehow, I think the benefits I mentioned above would make this type of energy storage highly attractive.
Of course, the amount of energy stored is given by the equation
energy = mass * gravity * height
My target minimum for stored energy capacity is 100 kWh = 360 MJ, which gives
mass * height = 360e6 / 9.81
and for a reasonable (?) shaft height of 30 m, requires a mass of (approx.)
mass = 360e6 / (9.81 * 30) = 1223242 kg
So then, my questions are:
Are there any types of cables and winches which can support this much weight and interface with a motor/generator? Could anything else be used to lift and drop this mass? How much would these things cost?
What are the densest and cheapest materials which could be used for this much mass? I already looked at cement and iron but they would be way too expensive. Might rock, with a general density of 2500 kg / m^3, in the form of waste dust/pieces from industry or shale from mountain slopes, be cheap and practical to assemble into some sort of a mass block? With this density of rock, a mass with volume 489 m^3 would be required, and as a cube shape it would require a shaft width of more than 7.88 m. How much would it cost to make a 30 x 8 x 8 m shaft into the ground, for various types of ground?
What are any other issues with the entire idea?
Thank you very much for any feedback :)
--Derick