Low Tech Magazine on Compressed Air Storage: Difference between revisions
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https://www.lowtechmagazine.com/2018/05/ditch-the-batteries-off-the-grid-compressed-air-energy-storage.html | =Article= | ||
*Low Tech Magazine article - [https://www.lowtechmagazine.com/2018/05/ditch-the-batteries-off-the-grid-compressed-air-energy-storage.html] | |||
=Notes= | |||
*40-50% efficiency of air storage, compared to 70-90% for batteries. | |||
*Pumping and air engines are 60-70% efficient. | |||
*[[Scroll Compressor]] is nearly 100% efficient, but expensive. | |||
*Highest [[ESOI]] of any energy source - [https://energy.mit.edu/wp-content/uploads/2016/05/2016-02-09_Making-Good-Energy-Choices-The-Role-of-Energy-Systems-Analysis.pdf] | |||
*Conclusion of Reference [7] - ''The sizing of storage tanks for a SHS-CAES has been determine by modeling all the components downstream of the storage tank. To operate the system with SHS load of 29.65W for 12 hours requires a tank size of 18 m3, with an initial pressure of 8 bar and regulator setting 3.511 bar. | |||
**Does this calculation reconcile with the 65 cubic meter figure below? Here we have 0.4 kWhr with 18m3 - so with ~3x that volume we have about 1.4 kWhr - so about 2x worse than the experimental extrapolation of the 65 cubic meter volume (see experimental below). | |||
*8 bar system operates at around 60% roundtrip efficiency - that is impressive. | |||
*P. 60 of thesis [https://eprints.usq.edu.au/24651/1/Herriman_2013.pdf] shows the size of tank required for 3kWhr storage - 65 cubic meter. '''This is based on 5% overall efficiency - abysmally low, but real for off-the-shelf compressor and air tool.''' | |||
*P. 54 of reference [8] [https://eprints.usq.edu.au/24651/1/Herriman_2013.pdf] shows only 5% efficiency of overall system was obtained, calculating the total wattage of output to the total wattage of input. This is about 10x less than a claimed 50% efficiency of air storage. What gives? | |||
*P. 60 of Ref [8] states that tank cost would be $25k and overall $30k. | |||
*Summary: efficiency of small scale prototype was 5% using an off-shelf tool motor (3Whr of usable power extracted from a 65l tank at 8 bar). This translated to a 3kW system being 65k liters. However, this is no-where near the predicted 50% roundtrip efficiency? Thus, indicates that the 65k liter figure is off by a factor of 10 for real, easily achievable results? Why was the efficiency so particularly low here? | |||
=Marcin Comment= | |||
The article seems a bit faulty. | |||
''It appearst that your analysis of the 65 cubic meter tank is faulty. You are implying that the efficiency there is decent (such as the 40-50% promised for 8-bar systems). Wading through Reference [8] - a master's thesis produced only 5% overall efficiency - so the 65 cubic meter figure is based on the 5% overall efficiency. You mention that the 200 bar system was 11-17% efficient. Can you reconcile this? It appears that the truth is - the low pressure systems that utilize off-the-shelf components are extremely inefficient.'' | |||
=Links= | |||
*[[Compressed Air Energy Storage]] | |||
Latest revision as of 21:54, 1 April 2020
Article
- Low Tech Magazine article - [1]
Notes
- 40-50% efficiency of air storage, compared to 70-90% for batteries.
- Pumping and air engines are 60-70% efficient.
- Scroll Compressor is nearly 100% efficient, but expensive.
- Highest ESOI of any energy source - [2]
- Conclusion of Reference [7] - The sizing of storage tanks for a SHS-CAES has been determine by modeling all the components downstream of the storage tank. To operate the system with SHS load of 29.65W for 12 hours requires a tank size of 18 m3, with an initial pressure of 8 bar and regulator setting 3.511 bar.
- Does this calculation reconcile with the 65 cubic meter figure below? Here we have 0.4 kWhr with 18m3 - so with ~3x that volume we have about 1.4 kWhr - so about 2x worse than the experimental extrapolation of the 65 cubic meter volume (see experimental below).
- 8 bar system operates at around 60% roundtrip efficiency - that is impressive.
- P. 60 of thesis [3] shows the size of tank required for 3kWhr storage - 65 cubic meter. This is based on 5% overall efficiency - abysmally low, but real for off-the-shelf compressor and air tool.
- P. 54 of reference [8] [4] shows only 5% efficiency of overall system was obtained, calculating the total wattage of output to the total wattage of input. This is about 10x less than a claimed 50% efficiency of air storage. What gives?
- P. 60 of Ref [8] states that tank cost would be $25k and overall $30k.
- Summary: efficiency of small scale prototype was 5% using an off-shelf tool motor (3Whr of usable power extracted from a 65l tank at 8 bar). This translated to a 3kW system being 65k liters. However, this is no-where near the predicted 50% roundtrip efficiency? Thus, indicates that the 65k liter figure is off by a factor of 10 for real, easily achievable results? Why was the efficiency so particularly low here?
Marcin Comment
The article seems a bit faulty.
It appearst that your analysis of the 65 cubic meter tank is faulty. You are implying that the efficiency there is decent (such as the 40-50% promised for 8-bar systems). Wading through Reference [8] - a master's thesis produced only 5% overall efficiency - so the 65 cubic meter figure is based on the 5% overall efficiency. You mention that the 200 bar system was 11-17% efficient. Can you reconcile this? It appears that the truth is - the low pressure systems that utilize off-the-shelf components are extremely inefficient.