alt Hacker NewsAren't boats typically highly geared direct drive? Hybrid only really benefits when you have lots of changes in speed or are using it for torque conversion as in diesel-electric trains.
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cromka • today at 4:11 PM
This Nissan is a serial hybrid, as in diesel electric trains.
An every-day diesel-electric locomotive solves the gearing (torque) problem, and can let the engine run at the most-efficient speed that can produce the required power output. The required output power is dynamic, though, so in practice the diesel engine runs at a variety of speeds along a given route across the plains or over the pass or whatever.
It's hard to make an engine that runs at peak efficiency at a range of speeds and power demands. But when batteries are added, the picture can change quite a lot.
The engine can be built and sized to run efficiently at a fixed speed, and its power output never needs to exceed whatever the generator that it drives is able to accept.
So when it runs, the combined engine+generator set can be run full-assed. No half-assing required. It's a binary state. On, or off. Full-staff, or flaccid.
By reducing variables in this way, all of the fuel that is burned gets converted to electrical power as efficiently it can be for the process at-hand. (It's also easier to quiet an engine that runs at a fixed speed than one that runs at variable speeds; things get a lot simpler when there's only one set of identified frequencies to bother with.)
While the engine is on, some of that electrical power can get used for driving an electric motor for propulsion and the rest can go into a battery.
If it is on and the vehicle is stationary, then all of that electrical power can go into a battery while the engine is remains at full-chooch.
When the battery gets full-enough and/or demand is low-enough, then the engine can just turn completely off. In this mode, all of the electrical power used for propulsion then comes from the battery.
It works. There's even some boats[1] that use these concepts.
It's just an unusual arrangement for now. (It may always be an unusual arrangement if the goal is to eliminate localized combustion of fuel. But as we keep being reminded over and over on these pages, whenever a headline about vehicular electrification comes by: We aren't quite uniformly there yet.)
[1]: https://en.wikipedia.org/wiki/Hybrid_ferry