Can wind flow of moving train generate energy?

Last updated on September 17th, 2014 at 01:18 am

There was a news the other day that moving train wind flow can generate energy and a patent has also been registered. The news if to be believed speaks

The Prime Minister’s Office (PMO) has sent the Railways Ministry into a tizzy over an idea it received from an 81-year-old resident of Gujarat — that windmills be installed along railway tracks to produce electricity, utilizing the wind generated by fast moving trains.
Vipin Trivedi of Ahmedabad, a former employee of Bank of Baroda’s Agriculture and Rural Development wing who retired in 1991, sent the idea by post to the PMO. The PMO, in turn, forwarded it to the Railways Ministry, asking it to explore the “techno-economic” feasibility of the idea, and sought regular updates.

Energy intends to be generated will come from the fuel bill of the train engine only, and therefore, no gain except loss only. It is similar to generating power from the wheel of the train for lighting, air conditioning on the train. The reaction of this power generation is experienced in the form of train resistance. The efficiency of this generation is of the order of 35% due to losses in different conversion from the power consumed at the locomotive and generated at wheel axle.

Indian Railway replied politely

“A train will pass the windmill in less than 20 seconds. Even if there is a train every 15 minutes, a windmill can operate for only 25 minutes per day. This will not be viable economically. Further, the energy produced by the windmills would have to come from the trains only, which will consume extra energy,” said a mail Trivedi received from the ministry on September 1.

IIT Delhi students have also taken a project to use wind flow in the tunnel to generate power. The students, estimated conversion of in a rush of wind flow at the tunnel entrance and exit for the purpose of power generation and total power estimation is 200W.

http://cleantechnica.com/2013/02/27/delhi-students-to-generate-power-from-wind-produced-by-metro-rail/

However, it is not only in India, China is also innovating power generation through the wind flow of running trains as appeared in

http://news.discovery.com/tech/alternative-power-sources/device-harnesses-wind-power-from-passing-trains-110404.htm

Wind flows due to pressure difference at two places being a function of large many atmospheric factors. This pressure difference is actually caused by varying temperature and is result of sun energy. This flow of wind retards while rotating the wind turbine blades. In the similar way, the wind exerts air resistance and if the flow of air is not free from obstruction, the resistance on the train running will increase.

The train resistance is given by a formula = a+bV+cV*V Kg/Tonne. The factor c accounts for air drag. This resistance is directly proportional to the square of the speed and directly with the cross-sectional area of the vehicle therefore; its contribution is more visible with speed going more than 80 kmph.  This resistance can be written as cAV². The factor accounts for the resistance of quite air which the vehicle envelope has to displace continuously during the run. The envelope, thus, is not only the frontal cross-section but also the space in-between vehicle, fittings under the vehicle, skin resistance of the sides, turbulence and draft created at the rear end. The frontal air resistance is less in open area because the displaced air is free to move in all direction; whereas while moving in tunnel, the air volume is pushed continuously thus adding to the train drag. 

For more details read

Train, grade, curve and Acceleration Resistance

Therefore, it is not possible to generate power from the wind flow of running train purposely. However, if there is some another way to produce energy using train air flow, please share.