Hybrid systems are best . My capital ships usually have the following in different sizes . Pure electric systems including batteries , motors , and RTGs not always the last part . Fuel engine good for 2 k or better . Hopefully with 1501 output to fuel ratio . This is easy , but takes a lot of space . Steam turbine system for filling the batteries . I use small turbines and small boilers in equal parts . 6 x of each gives ~ 1200 per second for about . 5 material . Scale to whatever size you need . Steam piston system for providing raw horsepower . Typically for railshields and what not . Generally a large boiler , 24 pistons and 1 wheelgenerator . Producing in the 20 k range at VERY HIGH material use . At least 2 backup fuel engines , typically 200400 power and built to be as small as possible .