Good question. Technically DE is a type of electric propulsion, but for this demonstration we'll assume it's not. Non-electric propulsion sees the propeller shaft connected directly to the and engine - the engine directly powers, rotates and varies the speed of the prop and screw. It's pretty much that simple.
Electric propulsion is a tad different though. As stated above diesel-electric is a type of electric propulsion, as are fuel cells, batteries or magnets. In an electric propulsion system the engines don't directly power the prop and screw, rather they power constant or variant frequency motors or electrical controllers. While a controller limits prop rotation and frequency automatically, a motor must do so by varying power output to the prop and screw. The most important thing to remember is that in a non-electric system there is mechanical transmission. Electric propulsion doesn't mechanically control the screw or prop, it's all done electronically.
This illustration takes everything I wrote above and condenses it into a simple graphic. Just remember that the generator engine doesn't have to be electric itself, it can burn gas or oil or be magnetically generated electricity, but to be considered an electric propulsion system it has to power electronic motors which control prop speed and vector.
The article you quoted mentions the UK's Type 45. It uses a system called Integrated electric propulsion, which uses diesel and gas turbines to generate electricity which powers electric motors, but since the motors control the prop this system, a type of CODLAG propulsion arrangement, technically isn't CODLAG. Since there is electronic control, power can be varied or distributed where it's needed, including to advanced gun systems or auxiliary sensors.
Traditional CODLAG designs, not an electric propulsion system, also have both diesel and gas turbines like the Type 45's IEP system, but power the prop and screw directly via electric motors and gearboxes.
Permanent magnet motors are pretty cool. They send power through electric coils, making the coil an electromagnet. The coil is surrounded by permanent magnets (magnets that don't lose their charge), which attract the now magnetized coil and cause the coil to rotate generating electricity. They're quiet, safe and nearly maintenance free expect during extreme abuse.
it's old hat on RC ships and small vehicles, but newer on large ships. The USN's Zumwalt class was intended to have a permanent magnet motor, but due to cost (those ships are one big cost overrun) an integrated electric propulsion system - diesel and gas - was chosen. Permanent magnets are a great alternative to fuel cell or battery systems for submarines.
Speaking of submarines, there's a lot of different AIP designs, but they generally do the same thing and are also a type of electric propulsion, since for noise's sake they're paired with quiet electric motors rather then rotating screws, which if you've ever been in the machine room of a ship with non-electric systems, are rather noisy. This is a German Type 212 showing its compressed hydrogen fuel cells:
Each fuel cell is an anode, a cathode and a proton exchange membrane sandwiched in between. Hydrogen, from a tank onboard the vehicle, enters into the anode side of the fuel cell. Oxygen, pulled from the air, enters the cathode side. As the hydrogen molecule encounters the membrane, a catalyst forces it to split into electron and proton. The proton moves through the fuel cell stack and the electron follows an external circuit, delivering current to the electric motor and other vehicle components. At the cathode side, the proton and electron join again, and then combine with oxygen to form the vehicle’s only tailpipe emission, water.
Drive Clean - Hydrogen Fuel Cell
IN this case the water is off-boarded where its temperature differential quickly dilutes with the ocean or sea's background temperature, but it's noticeable if you know where to look - a type of non-acoustic signature leakage.
Electric propulsion, despite being around for a while on submarines, in cars and on trains, is actually fairly new on naval combatant ships, especially large ones like frigates or destroyers. Most use either CODAG, COGAG or CODLAG propulsion.
That's a small rundown of electric versus non-electric propulsion
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. The P-8I needs a replacement for Harpoon.
