What is a Hybrid?

A hybrid is a vehicle is one that can achieve propulsion using either a fuelled power source or stored energy.

The fuelled power source could be:

• An internal combustion engine (diesel, petrol, gas etc)
• An external combustion engine (a Stirling Engine, steam engine etc)

The Stored energy source may be a:

• Flywheel
• Hydraulic reservoir
• Super capacitor
• Battery bank

The majority of Marine Hybrid systems use a diesel engine and a battery bank providing propulsion through an electric motor.

 

Conventional Diesel There are a number of Marine Hybrid configurations. To understand these systems lets start with a conventional Diesel and then move onto Hybrid options. This is a conventional single engine installation. A 100hp diesel is connected directly to a marine gearbox and then to the propeller shaft and propeller. Gearbox losses can vary but for this simple discussion we have set this at 6%. So only 94% of the engine's maximum power can be supplied to the propeller.

Diesel Electric

If we remove the gearbox and replace with a generator, motor controller and a motor we now have a Diesel electric. The engine is mechanically coupled to the generator (usually in the same housing). From this point onwards all transmission of power is performed electrically until the motor converts the electrical energy to mechanical energy at the prop shaft. Every step in the transmission of power has an associated loss, some typical values are shown. At this stage don't worry too much about understanding the losses, we will look at these closer in a more advanced discussion.

 

Serial Hybrid

If we now add in a battery bank to a Diesel Electric we have a serial Hybrid. The propeller can be driven by the engine using fuel and from the battery bank (with engine stopped) using stored energy. Typical losses are shown, these accumulate depending on the mode of operation, so again lets leave this to the more advanced discussion. The main thing to consider is that transmission of power to the shaft is performed electrically and propulsion without the engine running is possible (battery drive).

 

Parallel Hybrid

A Parallel hybrid is quite a different concept. As the name implies there are two different transmission paths connected in parallel to the prop shaft. The mechanical connection from engine to gearbox to prop shaft is maintained. A seperate transmition path is established from battery bank, motor controller, and motor. A Power split device is then used to connect the motor to the prop shaft,  depending on the system this may be before or after the gearbox.

Now we have established the basic Hybrid configurations the next step is to look at the efficiencies of each system.

Hybrid Efficiency >