Should Network Rail have wind farms?

[Shimbleshanks]

Well it could be done, but the energy produced would be in the realms of negligible, and you would be getting close to testing the law of the conservation of energy.

Always seems to be quite a jolt when a train passes in the opposite direction in Kilsby.

 

[Bald Rick]

Always seems to be quite a jolt when a train passes in the opposite direction in Kilsby.

How long for? It might be 20 seconds, every 3 minutes or so, in the operational day. And for a relatively small frontal area. Compared to a 220m diameter wind turbine, which will be going for the equivalent of full tilt for 40% of the time 24/7, it will be minute.

 

[pelli]

Slightly OT, but is there a way the air pressure from trains entering tunnels at high speed could be harnessed to generate electricity? Putting fans and generators in the ventilation shafts at Kilsby, for example? Or maybe in the Channel Tunnel cross-passages?

That would just increase the resistance felt by the train.

Well it could be done, but the energy produced would be in the realms of negligible, and you would be getting close to testing the law of the conservation of energy.

Always seems to be quite a jolt when a train passes in the opposite direction in Kilsby.

Your main concern should be the bolded parts. The turbine slows down the air that is being pushed away by the train, which builds up a larger pressure in front of the train that must be overcome. We can do an estimate as follows: If the pressure differential across the turbine is P, and the volume of air pushed through the turbine by a passing train is V, then the energy that can be extracted from the air is P*V. This additional pressure P on the train frontal area A causes an additional force P*A on the train, and since the train travels a distance V/A to displace the volume V, the train loses an additional energy (P*A)*(V/A) = P*V due to the turbine. So in the end you're just expending extra train fuel/electricity to generate an equal amount of turbine electricity, except that due to inefficiency at each step in the chain you're really losing energy.

My hunch is that the same applies to road/rail-side turbines drawing energy from passing vehicles: The turbine slows down the air that needs to be pushed away in front of and rush back in behind the vehicle, as well as the air that is being drawn along the sides of the vehicle, thus creating additional pressure and friction forces that cost the vehicle more energy than the turbine gains. (There may be exceptions to this, but you would have to do a very careful analysis and extensive computer simulations to identify locations where energy can be extracted from the air without causing an equal/larger energy cost on the vehicle.)

This means that in itself a turbine extracting energy from passing vehicles is a net waste of energy, but of course there are scenarios in which a roadside turbine can make sense, e.g.
* At remote locations with no electrical grid connection (nor other local generation), where installing such would cost more than installing the turbine plus the continual losses in inefficiently siphoning energy from passing vehicles.
* If the purpose of the turbine is actually to harness the natural wind in the environment, which greatly offsets the energy losses of passing vehicles, and the roadside location was chosen for other reasons.
* If the entity that benefits from the energy generated by the turbine is not the one having to pay for the energy lost by the vehicles.