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Flywheel Energy Store Hybrid Light Railcars Selected for UK Branch Line

The chassis of a PPM-50 light rail car with flywheel and 2.0-liter engine visible. Click to enlarge.

The new rail franchisee for the UK West Midlands will introduce two hybrid light railcars equipped with a flywheel energy store to capture braking energy for use in acceleration.

The UK Department for Transport announced that the West Midlands rail franchise, to run from November 2007 to September 2015, has been awarded to Govia.  The franchise, expected to generate annual revenue of £400 million, will be operated under the London Midland brand.

Govia states that one of the key highlights of the franchise will be the introduction of Parry People Movers (PPM) flywheel energy store light railcars to operate all services on the short branch line between Stourbridge Junction and Stourbridge Town.

Two new railcars will be built to cover the operation, replacing the heavy diesel trains that currently provide the service.  The new cars will be based at a new depot on the branch line, eliminating the need for empty trains to run to and from the maintenance facilities at Tyseley.

The lightweight rail service is planned for introduction before the end of 2008, once the two new railcars have been built and tested for public service use.

An experimental service using a prototype Parry People Movers railcar operated by licensed train operator Pre Metro Operations Ltd, ran on this route between December 2005 and December 2006.  With more than 4,000 trips operated in passenger service, reliability and punctuality stood at 99%.  It was calculated that carbon dioxide emissions were cut by 80% compared to the conventional type of train that currently operates the branch.

The new PPM 60 railcars will be built by a British industrial supply chain which includes Clayton Equipment, East Lancashire Coachbuilders, Power Torque Engineering, Linde Hydraulics and Brecknell Willis Composites.

Parry People Movers Ltd (PPML) was founded in 1992 to develop rail transport based on a flywheel energy store for capturing braking energy for use in acceleration.

Twelve PPML vehicles have been built so far, ranging in capacity from 2 to 50 passengers. Between them they have carried more than 100,000 passengers.

Technology. PPM uses a flywheel to capture braking energy that can then power the rail car.  A typical PPM flywheel is made from steel laminates, 1m in diameter and 500kg mass, rotating at a maximum speed of 2,500rpm.

The PPM concept supports other options for charging the flywheel:

  • For zero emission operation with closely-spaced stops, the flywheel can be charged (in approx. 30 seconds) from an intermittent electrical supply at the stations only. The flywheel stores sufficient energy for the vehicle to reach the next stop in normal operation, and a battery is also provided for emergency use.

  • For low-emission, high fuel efficiency and quiet self-powered operation, an on board LPG-fueled automotive engine is used.

  • Alternative possibilities include diesel- or hydrogen-fueled internal combustion engines, or hydrogen fuel cells, while the intermittent electric version can be powered from solar cells or other renewable sources of electricity.

The result is great flexibility in powertrain design for the rail car.

PPM 60 cars, which will be used for the West Midland line. use a 2.0-liter Ford diesel engine in combination with a 1m/500kg self-powered flywheel. (A 1.2m/750 kg flywheel is an option for intermittent electric charging.)

(A hat-tip to JZL!)



This seems like a good application of flywheel technology. I suspect weight is less of an issue on a train car compared to automobiles.


I think the adv. of using flywheel in railway system is to reduce cost.

#1. No need to cover all the railway lines with overhead electric lines. (easier to maintain?)

#2. The brake of the train and wearing of the railway can be drastically reduced.

#3. save electric (lower the bill)

John Latusek

I agree BillW. That issue of reduced weight and reduced track friction seems to be working in favour of Parry being in contention for revived use of certain tracks near me in southwest Wales, where heavier locos with traditional brakes would require a higher grade of track refurb and maintenance. Parry also offer a prefabricated station/platform kit, and because their vehicles accelerate quickly from standstill, a greater number of stops can be (usefully) provided without seriously hindering travel time.

John Latusek

I meant I agree BillW AND Bodyweapon (I get confused by the positioning of authors' names here sometimes!). Sorry.

Michael McMillan

From my calculations. The 1.2 m flywheel holds about 1 KWH. To charge it in 30 seconds takes nearly 200 kilowatts. This seems to be a very realistic and long term low cost solution.

From the drawings, there are two flywheels, which counter rotate. The flywheels are on a common axis.



I calculate the amount of energy too.
Radius = 1/2 = 0.5 meter
Weight = 500 kg
I = 1/2*weight*radius^2 = 62.5 kg m^2

Max RPM = 2500 rev / min
Max RPS = 2500/60 = 41.667 rev/sec
Max energy storage = 1/2*I*(2*pi*Max RPS)^2 = 2.14 MJ (or 0.594 kwh)

Since usually you need 2 discs running in opposite direction of each other on the same axis. therefore the total capacity per "PAIR" of flywheel is 1.188 kwh.


I have always been intrigued by flywheels as a supplement to or battery option.

In a popular mechanics magazine they discussed an e.v. fair in Chicago and the only viable vehicle had a light weight composite flywheel.

I like the flinstone model, could there be an economy in sitting at the lights topping up a flywheel with bicycle gearing?

Any thoughts?

Virgil Hammon

Best wishes on this venture. Recharging at station only is sensible. All those wires above traditional electric buses and light rail between stations are impractical and unnecessary. I have thought about this for years and am so glad someone is testing the idea.
-Do you keep contact with the recharge electrical source long enough during acceleration away from the station to break static friction and overcome initial inertia, thus saving the flywheel electricity for rolling only?
-Do the flywheels have a faster rate of recharge compared to batteries?
-Do the flywheels have a more efficient recharge cycle than batteries ($ electricity/joules stored)?
-Are the flywheels encased in a vacuum container to reduce friction?
-Do the flywheels retain energy during idle or are frictional losses a problem compared to idle batteries?
-During the last run of the day, is all energy drained from the flywheel or can it store rotational energy overnight?
Best wishes,
Virgil Hammon, NASA/Jet Propulsion Laboratory

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