Between fuel costs and emissions regulations do you think there is any possability of a plug-in electric switch engine? It seems a locomotive like this could be usefull a yard where it could be charged, used until its battery was depleted and then recharged at a charging station not unlike those used by electric cars. The technology already exits, it would just have to be scaled up.
Such things do exist, but on a very small scale. RRs sometimes use small battery powered, remote control “locomotives” to move engines around an engine terminal.
On a larger scale, you’d be talking about a Green Goat w/o the small engine generator on board. I think it would be a toss up between the engine gen set and a plug-in in terms of efficiency and cost, but the engine-gen set gives you limp home capability if the batteries run flat.
Even if the battery-driven stopped dead in a large yard or intermodal facility, it might not prove lethal to “rescue” the cab employees and be towed home, but it could sure raise heck with logistics.
I would guess that a “plug-in” Green Goat might have slightly lower initial cost and fuel cost than one with a genset, but as you said, the genset does give limp home capability. One other downside to a plug-in Green Goat is that deep cycling takes a huge toll on the life of the batteries, where the genset would keep the batteries at a decent state of charge. I suspect that the shortened battery lifetime would far outweigh the savings in fuel.
One area where a ‘lug-in’ might make sense is a switcher on a line also used by electric light rail vehicles, such as the San Diego Trolley’s El Cajon line (originally the San Diego, Cuyamaca & Eastern). The switched would run off the overhead wire on the main line and batteries on the spurs - as was done by the North Shore line.
My understanding is that the lead acid batteries used in the Green Goat have been giving a lot of problems. Other battery technologies (e.g. NiMH and Li-ion) would probably be much better suited than plane-Jane lead acid batteries, but they are no where near as cheap