How much energy is stored in compressed air?

[Jesolar]

Hi all,

My name is Jesse and I love renewable energy and finding ways of beating coal. Right now Solar Photovoltaic energy competes with coal in sunny areas during the day, but at night, you need to store the energy from solar and it's not worth it due to the cost of storage mechanisms (might as well build a coal plant). For new power construction, solar + storage doesn't compete if you want to have more than just a day of backup energy. Coal delivers reliable energy regardless of clouds. Some clouds last for 10 days straight.

I'm looking for a way to store power cheaply. The cheapest way is to pump water back up a damn. The second cheapest is to pump salt caverns under ground full of compressed air. Neither of these are abundant everywhere. However, the ocean and lakes are much more abundant and scale-able. I want to know how much energy you can store using a tough air-proof "bag."

I'm not interested in efficiency since this is for long term energy storage (think weeks, months and even years before you need to use it rather than hours or days). Storing the heat from compression won't be useful for this long term storage.

Questions
How much volume will the bags or balloons take up per unit of energy stored at any given depth?
How much force will the anchor need to withstand per unit of energy stored?
When the air blows back up the pipe, will it be so cold that something unwanted happens?

Also, it would be helpful if you knew anything particular about this technology and wanted to share it with me such as best price performance bag or best price performance air pump.

 

[scottdave]

You may want to take a look at this thread, for a start. https://www.physicsforums.com/threads/internal-energy-of-compressed-gas.920452

 

[Jesolar]

I found a paper answering the first question: https://windenergyigert.umass.edu/sites/windenergyigert/files/OSES_Pete_Storage_Final.pdf
The second questions is still interesting...
The third question is yes, but then how much energy is needed to re-heat the gas? More than what was wasted by compressing it. It depends how efficiently you can rapidly heat gas.

 

[CWatters]

The third question is yes, but then how much energy is needed to re-heat the gas?

http://energystorage.org/compressed-air-energy-storage-caes

Adiabatic Method

A much higher efficiency of up to 70% can be achieved if the heat of compression is recovered and used to reheat the compressed air during turbine operations because there is no longer any need to burn extra natural gas to warm up the decompressed air. An international consortium headed by the German energy company RWE is currently working on the development of the necessary components and the heat storage. The pilot plant is scheduled to start operations in 2018. Thermal oil and molten salt storage is being investigated in the US.