Caterpillar's gas-hungry earthmovers are good at upheaving the planet; less so at preserving it. To make its iconic yellow vehicles greener, Caterpillar began R&D on electric and hydraulic-based hybrid excavators. After two years of testing, it chose a winner: this hydraulic model, below, which ships in March. These qualities helped it prevail.
Electric: Technicians would have needed new training to learn the unfamiliar electronics and battery storage system.
Hydraulic: The controls are similar to standard machines, so technicians won't skip a beat.
Electric: The best opportunity to conserve energy is when the arm swings between two points. At each one the excavator has to brake, resulting in lost energy. An electric hybrid could have converted that energy and stored it in a capacitor but would have had to convert it back for use with the motor.
Hydraulic: In a hydraulic hybrid, the braking energy is stored as pressure in an accumulator. When the machine swings, it is aided by the stored pressure. No conversion needed.
Electric: An enhanced cooling system would have been required to remove heat from the electric components.
Hydraulic: The size of the cooling system is actually reduced because overall engine efficiency is higher.
TIME TO RECOUP COST
Electric: Up to eight years due to complex (and costly) systems.
Hydraulic: Caterpillar expects it to be roughly 12 months. Value!
[Image: Flickr user Terinea IT Support]