# Compressed Air Storage

# Intro

Taking example calculation at https://en.wikipedia.org/wiki/Compressed_air_energy_storage -

a 500 gallon propane tank stores .75 kWhr of energy when compressed to 200 PSI. Pressure rating of propane tanks is 215 PSI - [1]. Taking efficiency of an air engine - generator to be 50% - we have .4 kWhr. So a 500 gallon tank would get us 0.4 kW hr of usable energy.

See comments below:

# Storage Math

- 500 gal propane tank - 66 cu ft x10 = 660 cu ft. Cost is $1500 + installation, so about $2000.
- 250 cu ft is $300 for Type K Cylinder.
- Advantage here is high modularity, scalability.
- Type K tanks are about 2x less expensive than propane tanks.

# Usage

- 7 cfm for .2 hp at $250 [2]
- One type K cylinder at 250 cfm runs this for 35 minutes

# Air Power Cube

- 10 Type K cylinders produce 35 minutes of 2 hp, or 1 hp hour. Not bad.
- Using 700atm storage vessels, we get sufficiency - 10 gal

# Cost

# Calculations

For volume of 500 gallons (propane tank) -

E=Pressure x Volume.

=200 PSI x 1.9 cu meters =1,400,000 Pascals x 1.9 cu meters =2.7 million Joules =.75 kW hr

With 60% efficient air engines - this makes it slightly under 1/2 kWhr of energy storage.

For comparison, one motorcycle battery at $20provides a comparable amount of electrical energy storage, making a weak case for compressed air storage on cost considerations.

- However, a motorcycle bat will last you a year, whereas the tank will be unlimited lifetime.

For comparison - if one could generate an average of 50W via wind power, that appears to be an easier route of power generation.

# Links

- EPRI head states that air will be cheaper per watt hr store than batteries. - [5]
- Cost Comparison of Energy Storage - [6]