Large scale energy storage/transmission and freight transportation system

One of the barrier to the use of renewable energy (solar and wind) is their intermittency. As more renewable sources of energy comes online, it become more difficult to balance between production and consumption. In Inner Mongolia, wind farm operators have to turn off ("abandon the wind") their turbines during winter nights because of the lack of demand during those times, having to discard 36 GWh of electricity every night. Storage will also reduce the necessity to have excess underutilized generation capacity to handle peak loads. Renewable sources of energy are usually located far away from where there are needed. The current peak/off peak prices of electricity is an artifact of the limitations of existing technology.

This concept is similar to a flywheel, but it solves its main weakness by eliminating the hub.  This kinetic energy system stores energy in magnetically levitated slugs maintained at high speed inside a loop of evacuated tube. In the constant mass version, energy is injected by increasing the speed of the slugs and energy is extracted by decreasing the speed of the slugs, energy can be injected and extracted at any point in the tube. This version can also serve as a power transmission network. In the constant speed version, energy is injected by adding slugs and extracted by removing slugs at a central station. Both versions can also be used to transport freight that can withstand high G forces. The elimination of air drag and rolling resistance allows most of the energy spent during acceleration to be recovered when decelerating. Energy may actually be gained when going from high elevation to low elevation.

The capital cost $/kW/km is inversely proportional to the square root of the kW or kWh of energy storage required. This system is suitable for energy and power applications that requires more than 5 GWh of storage. This system have much bigger MW carrying capacity than overhead lines and cheaper than underground lines. 

In conjunction with electrification of transport, this technology will allow most the energy requirements of transport, energy and heating to be sourced from renewables.

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ET3-ES Cost Benefit Risk

Large scale and high capacity
Improve capacity and reliability of existing power generation.
Lower cost even further by combining energy storage and transmission
Not limited by geography. The slug momentum can overcome any gradient
Low land use and impact on environment
Encourage more use of superconductivity and expected cost reduction
No external electromagnetic field
Unaffected by sunspot activity
Risks, events or unintended consequences that have to be managed.
Accidents, malfunctions and leaks
Floods, earthquakes or cataclysmic events 
Earth movements, continental drift. Tubes have to monitored by SCADA and actively aligned with actuators
Redundancy is required, e.g. when the system is shutdown for maintenance at weekend. 
The spacing between supports must be random to prevent the build up of harmonics to dangerous levels.
Daily expansion and contraction of tube.
Effect of precession


Capital cost and operational performance of Evacuated Tube energy storage/transmission system

Calculates the cost and performance of the system given the Energy storage capacity required.  Use Google Chrome if the graph does not appear.

Slug centripetal force  Tube diameter m
Slug length/diameter ratio Slug loading on magnet kg/m Slug spacing/length ratio
Comparison with other energy storage system
ET3-ES Pumped Hydroelectric Compressed Air Lithium Ion Flywheel
Efficiency % 80-82 68-75 90-98 90-95
Capital cost $m
Wh/kg 0.5-1.5 30-60 75-200 10-30
Wh/liter 0.5-1.5 3-6 200-500 20-80
Energy Cost $/kWh  250-430 60-125 900-1700 7800-8800
Power Cost $/kW 1500-4300 1000-1250 1800-4100 1950-2200
Payback period
Avoided cost of gas generation. US$/MWh Payback period years
Liquid Nitrogen cost $m per year at $0.05/hour/slug. Each slug needs to be recharged regularly with liquid nitrogen
Tube cost $m Slugs cost $m $ per kW per 1000km capital cost
Tube magnet cost $m Slug YBCO superconductor cost $m MW capacity
Tube Magnet cost US$/m at 111 kg/m loading  Yttrium barium copper oxide bulk crystals cost US$/kg load Hours of storage
Steel Price US$/ton * 2 (for support and construction cost) Currency / USD$
Linear Motor Cost US$/kW % energy loss during storage hours
Tube characteristics
Tube thickness mm ton/km of a single tube Weight thousand ton
Length km  Radius km
Air density Air pressure bar inside tube Depth beneath surface of water m
Loop area km2 Loop volume m3 Temperature rise in tube oK
Electromagnetic levitation kW/ton. Set to 0 for YBCO levitationMagnetic levitation
Slug characteristics
Number of slugs Mass of each slug kg  Pay load kg
Speed of slug km/h Slug spacing m Kinetic energy kWh per slug
Slug length m Slug diameter m Slug loop time
Maximum acceleration. G force Acceleration distance km Slug acceleration time
Air drag kW of all slugs Slug Loading on magnet kg/m Pressure Loading on tube kg/m
Rolling resistance coefficient Rolling resistance/Electromagnetic levitation kW of all slugs
Air drag coefficient Cd Centripetal force on slug. Too much centripetal force may cause the slug to loose cohesion to the track. A higher centripetal force will reduce the length of the tube, reduce the cost and increase the speed.
Billion ton-km/year. Cargo that may be carried includes water heated by waste heat from concentrated solar thermal power stations, bulk commodities and sewerage.
Height difference m Potential power MW Maximum capacity mt/year
Capsule load/unload time in seconds % Capacity used Cargo mt/year
US$/Airlock Airlocks Airlock capital cost $m
Electricity cost US$/kWh % Interest rate Energy cost $m / year
Overall electrical efficiency % cents/ton-km freight cost net ton km/MJ
oC temperature increase to water MWt of waste thermal power from thermal plants that can be transported
Number of days for slug to lose 50% of energy Thermal energy price US$/kWht Thermal energy revenue $m
Grids  GWh/day%Storage required


Evacuated Tube Transport

United States Patent No. 5,950,543 Evacuated Tube Transport

Prospects for Large-Scale Energy Storage in Decarbonised Power Grids

Energy efficient, environmental friendly, cost effective, convenient, safe and fast transportation system for passenger and freight traffic

The Role of Energy Storage in Helping Global Energy Problems Become Gone With The Wind

Electricity Energy Storage Technology Options

Last updated: 20 October 2012