Except for some limited uses, electric propulsion is not yet ready for prime time, I hope it will be. The problem in truely green mechanical propulsion is the source of electricity and efficiency of storage.
"Green" diesel may be a more rational interim solution, diesel produced from the waste stream.
A project under contract for the navy at Philadelphia Navy Yard will produce marine diesel from residential and industrial waste;
page 1, bar on left trash to diesel http://www.navyyard.org/uploads/file...ews_5-2008.pdf
The loss of efficiency, diesel generator to battery to electric propulsion even with "green" diesel may be less optimal than diesel propulsion with a smaller generator for use as systems demand.
The energy source will be diesel either way but consumption of diesel may be higher due to efficiency loss with the battery to electric propulsion.