Technologies - Fly-wheels (storage technology)

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Fly-wheels (storage technology)

evaluated

The fly-wheel is an electro-mechanical energy storage system based on rotating masses. It is a powerful storage technology which may be used both for on-board and for stationary applications.

Technology field: Regenerative braking and energy management



General information

General criteria

	Status of development: in use

	Time horizon for broad application: 5 - 10 years

	Expected technological development: dynamic

	Benefits (other than environmental): not applicable

	Barriers: high

	Applicability for railway segments: medium
	Type of traction: electric - DC, electric - AC, diesel
	Type of transportation: passenger - main lines, passenger - regional lines, passenger - suburban lines, freight

	Grade of diffusion into railway markets:
	Diffusion into relevant segment of fleet: 0 %
	Share of newly purchased stock: 0 %

	Market potential (railways): low

Environmental criteria

Economic criteria

	Vehicle - fix costs: high
		WTZ Rosslau that the market price of the fly-wheel currently developed (6 kWh / 350 kW) will be roughly 200.000 EURO. This is the market price and does not cover the total development costs of the joint project between Alstom and WTZ Rosslau.

	Vehicle - running costs: significant reduction
		Energy costs Energy costs are significantly reduced. Maintenance The only known in-service use of fly-wheels in railways is a stationary fly-wheel storage system in a substation at Kölner Verkehrs-Betriebe AG (KVB), Cologne, Germany. There is however no data available on maintenance experience. Maintenance experience with Magnetmotor fly-wheels used in Basel trolley busses The maintenance intervals of the fly-wheels used in trolley busses in Basel are defined to 3500 operation hours. The manufacturer Magnetmotor claims that specific tests with bearings and lubrication prove that maintenance intervals of 6,000 h are possible and that for the power electronic the statistic MTBF (mean time between failure) is more than 40,000 hours. Currently the maintenance of the MDS fly-wheel is done at Magnetmotor, i.e. the system has to be removed from the vehicle sent to the manufacturer. Typical maintenance includes checking of components and the system as a whole, cleaning and lubricating or exchanging the bearings. The average maintenance time is about one working day. By 2000, the average repair requirements was down to one repair every 38,000 hours of operation (equivalent to one repair in 8 years per fly-wheel).

	Infrastructure - fix costs: none
		(no details available)

	Infrastructure - running costs: unchanged
		(no details available)

	Scale effects: low
		Scale effects are to be expected from a more wide-spread use of fly-wheels. However, a mass market for fly-wheel technology will not exist in the foreseeable future. According to WTZ Rosslau production of 100 fly-wheels will not yield any price effects. This would require selling at least 10.000 systems, a figure only to be reached in automotive mass market where fly-wheels have little or no potential.

	Amortisation: > 5 years
		Payback time depends on application context but is generally long. Study at NS In a study made in 1998, NS calculated that the energy savings pay off the investment to a great extent but not completely. The amortisation period is between 17 and 30 years. For an energy price of 13 ct/kWh at NS, the return on investment is 0,35-0,6. NS expects that this situation could improve in the future by growing energy prices. The payback time is quite pessimistic. Lirex The situation should have improved in the meantime due to technological progress. DB AG assumes that the investment for the Lirex fly-wheel system will pay off easily within the lifetime of the vehicle currently planned to be around 15 years. Diesel-electric vs. stationary applications in DC systems According to WTZ Rosslau, stationary applications in local DC systems will generally have a better cost-benefit ration than on-board storage systems in regional diesel-electric stock.

Application outside railway sector

	Status of development outside railway sector: in use
		Since 1988, small fly-wheel systems (2 kWh, 150 kW) have been in use in electric busses for urban transport in several European cities. Fly-wheels made by the Magnetmotor GmbH have been in use in diesel-electric city buses since 1988. Since 1992, 12 trolley buses with fly-wheels have been running in Basel, Switzerland, with a total of more than 200.000 operating hours.

	Time horizon for broad application outside railway sector: in 5 - 10 years
		(no details available)

	Expected technological development outside railway sector: highly dynamic
		Energy densities of current fly-wheels attain 20 kWh/m³. Experts claim that a 5-fold increase of this figure is possible. The use of superconductors instead of conventional magnets for the bearing of the fly-wheel would lead to a further reduction of losses.

	Market potential outside railway sector: small
		Since an application of fly-wheels in private cars is highly doubtful, there is no mass market for fly-wheel technology in the foreseeable future. The main market is diesel-electric busses and city rail systems. This means that demand will no exceed a few hundred fly-wheel systems.

Overall rating