Mechanical power transmission: Unit economics
Why compressed air costs 6 to 8 times its electricity
What this tab covers What it costs to move a unit of energy this way: capital and operating costs, tariffs, utilisation and how it compares with the alternatives.Because fluid systems waste most of their input, the useful energy delivered by compressed air costs roughly 6 to 8 times the electricity that drives it (calculated). Mechanical drives are cheap to improve: a better belt or fixed leak often pays back within months to a few years.
Key costs
| Measure | Value | Note |
|---|---|---|
| Synchronous belt saving, 100 hp fan, 75% load | about 16,130 kWh and US$1,290 per year1 | at US$0.08 per kWh, against a 95% V-belt (2012) |
| Cost of a single compressed-air leak | about 1,046 to 16,764 USD per year3 | depends on hole size; at US$0.10 per kWh, continuous operation (2026) |
| Cost of useful work from compressed air | about 0.59 to 0.83 USD per kWh of useful work23 | calculated: US$0.10 per kWh divided by 12 to 17% system efficiency |
| US fluid power energy use | 2.0 to 2.9 quads per year225 | about 2 to 3% of US energy (calculated; 2008 data, published 2012); NREL (2017) put mobile off-road fluid power alone at 0.36 to 1.8 quads |
| Urban ropeway capital cost | 10 million to 25 million USD per km7 | most Latin American systems (2017) |
| Ropeway against tram capital cost | 20 to 50% less%8 | manufacturer claim for similar capacity; no cost basis or source given |
Where the money goes
| Item | Share or amount |
|---|---|
| Compressor stage (electricity to stored compressed air) | About 50 to 57% of input retained (calculated from 12 to 17% overall and 23 to 30% downstream)2 |
| Downstream pipes, valves and tools | 23 to 30% of compressed-air energy turned into useful work2 |
| Leaks | 20 to 30% of compressor output in a poorly maintained plant3 |
The alternative to most mechanical and fluid transmission is an electric cable plus a local motor, which wastes far less energy. Fluid systems survive where their other strengths, such as very high force, explosion safety or simplicity, are worth the energy penalty. For ropeways the comparison is with buses, trams or new roads on steep or crowded routes.
Sources
- Replace V-belts with notched or synchronous belt drives (Motor Systems Tip Sheet #5) US Department of Energy, Advanced Manufacturing Office, 2012
- Estimating the Impact (Energy, Emissions and Economics) of the U.S. Fluid Power Industry (ORNL/TM-2011/14), Love, Lanke and Alles Oak Ridge National Laboratory, 2012
- Compressed Air System Leaks (Improving Compressed Air System Performance, Fact Sheet #7, Rev. 1) Compressed Air Challenge, 2026
- Innovation in the air: using cable cars for urban transport World Bank (Transport blog), 2017
- Urban ropeways: a solution for congested cities (manufacturer presentation) Poma-Leitner Group (hosted by Asian Development Bank events; not an ADB publication), 2017
- Estimating Energy Consumption of Mobile Fluid Power in the United States (NREL/TP-5400-70240) National Renewable Energy Laboratory, 2017