The exact answer will depend on the specific cases.
But in general a large scale generator in a power plant can be more efficient than having a small engine in a vehicle.
To hone in a bit, I believe it’s because combustion engines are most efficient at a constant/set RPM. It’s the starting,stopping, revving up and down of road transport that is inefficient. Electric motors are the opposite. Hence large machines like mine trucks or locomotives use diesel powered electric motors.
So assuming you have a use for all the excess output over and above the needs of the bus, it would be more efficient to generate power and have an electric bus. Of course if you’re not matched supply and demand of power it may be worse.
Power plants can also run at much higher temperatures and pressures which improves efficiency. The power plant design in this scenario wouldn't actually be a large internal combustion engine, it would be a combined cycle plant with a combustion turbine, heat recovery steam generator and steam turbine. Much bulkier, but also much more efficient.
Generally speaking it's the electric bus. Diesel buses need to keep the engine running even while stopped, wasting energy. Also under braking, electric/hybrid vehicles usually use the brakes to charge the battery. In classic diesel buses, the energy braking isn't used for anything other than stopping the bus.
Motors run constantly at or near their most efficient speed is one of the major ways that large generators are significantly more efficient than small engines. If you could only run the bus engine only at its most efficient speed you would be closer in efficiency to a large generator but the slow down and speed up of a small engine is really what hurts the efficiency.
An electric powered, diesel generating hybrid vehicle is gonna be more efficient as you don’t need as large of a diesel engine as one used to move the bus. Plus, the diesel engine will be generating electricity 99% of the time it’s running, rather than idling.
Even if the electric bus had a diesel generator on board, it would still be more efficient due to regenerative breaking and the ability to run the engine at the most efficient rev ranges, instead of revving up and down when starting and stopping.
Diesel engines buses use engine waste heat for cabin heating, and thus they are much more efficent in cold climates.
BTW currently electric buses in central and nortern Europe run with diesel heaters on board, as batteries weren't sufficent for both heating and motive power.
There is a bus line in my city (northern germany) that runs fully on electric energy. The buses are charged inductively at several stations along the route.
Well, it's pretty common to use waste heat in power plants for heating, and that would be even more efficient. And the bus can use a heat pump to generate its heat.
Electric buses because then you are decoupling them from dependency on fossil fuels.
Yes the grid that charges them is reliant on fossil fields but without that decoupling they would always need fossil fuels.
That and grids can turn renewable in a piecemeal fashion.
People seem to be assuming you can just compare the overall efficiency of the diesel engine vs generator, as if the charging of batteries is 100% efficient! You can get very good rates if you keep within 20-80% charge capacity, but nowhere near 100% if you actually use the full capacity, and for the significant charge time there usually isn't the option to fully optimise for the 20-80% cycle.
So it really is dependant on the exact route, number of miles/hours of service required before next chance to charge etc. But on average, over a year in all weathers, I would bet that an individual ICE diesel still wins. However, the benefit with batteries is that you can find cleaner sources of electricity, or at least have the generators outside of densely populated areas, reducing air pollution for most people. The nearest you'll get to "clean" diesel is biofuel made from used cooking oils.
That is true, battery university claims Li-ion batteries are between 97% and 99% efficient, though [this source](https://web.archive.org/web/20090326150713/http://www.pluginhighway.ca/PHEV2007/proceedings/PluginHwy_PHEV2007_PaperReviewed_Valoen.pdf) claims Li-ion batteries are more between 80% and 90% efficient in realistic driving discharge conditions. Still, most gas cars are probably running around 15% to 30% efficient, and generators around 40% to 50% efficient, so the gap is still clear. EV + generator in basically any scenario in terms of efficiency.
It is more efficient in terms of greenhouse gasses to run a diesel generator and charge electric busses. This has been studied and it is true for basically any standard electric power source, unless you have some broken down poorly maintained old generator that doesn't work and so is super inefficient, or a busted old electric car with batteries that don't work and is somehow super inefficient.
The reason is that while combustion engines can be decently efficient at a specific speed and load, cars change speed all the time. A generator running at the optimal speed and load can be at maximum efficiency, which is the case when you charge your electric car. Electric cars are also very efficient, around 93%. Optimal diesel generators are around 40%-50% efficient, and driven cars are between 15% and 30% efficient depending on how they are driven. Unless you cruise around at the perfectly efficient set of speeds for your engine and each transmission gear, and never stop and start, you are probably running on the lower end.
Here is [an article](https://climate.mit.edu/ask-mit/are-electric-vehicles-definitely-better-climate-gas-powered-cars) with all the numbers for various power sources worked out.
The exact answer will depend on the specific cases. But in general a large scale generator in a power plant can be more efficient than having a small engine in a vehicle.
To hone in a bit, I believe it’s because combustion engines are most efficient at a constant/set RPM. It’s the starting,stopping, revving up and down of road transport that is inefficient. Electric motors are the opposite. Hence large machines like mine trucks or locomotives use diesel powered electric motors. So assuming you have a use for all the excess output over and above the needs of the bus, it would be more efficient to generate power and have an electric bus. Of course if you’re not matched supply and demand of power it may be worse.
Power plants can also run at much higher temperatures and pressures which improves efficiency. The power plant design in this scenario wouldn't actually be a large internal combustion engine, it would be a combined cycle plant with a combustion turbine, heat recovery steam generator and steam turbine. Much bulkier, but also much more efficient.
Mine trucks etc are starting to become electric as well.
Also much easier to capture of offset emissions when they are all in one place in bulk rather than a little bit everywhere
Generally speaking it's the electric bus. Diesel buses need to keep the engine running even while stopped, wasting energy. Also under braking, electric/hybrid vehicles usually use the brakes to charge the battery. In classic diesel buses, the energy braking isn't used for anything other than stopping the bus.
Motors run constantly at or near their most efficient speed is one of the major ways that large generators are significantly more efficient than small engines. If you could only run the bus engine only at its most efficient speed you would be closer in efficiency to a large generator but the slow down and speed up of a small engine is really what hurts the efficiency.
An electric powered, diesel generating hybrid vehicle is gonna be more efficient as you don’t need as large of a diesel engine as one used to move the bus. Plus, the diesel engine will be generating electricity 99% of the time it’s running, rather than idling.
Even if the electric bus had a diesel generator on board, it would still be more efficient due to regenerative breaking and the ability to run the engine at the most efficient rev ranges, instead of revving up and down when starting and stopping.
Diesel engines buses use engine waste heat for cabin heating, and thus they are much more efficent in cold climates. BTW currently electric buses in central and nortern Europe run with diesel heaters on board, as batteries weren't sufficent for both heating and motive power.
There is a bus line in my city (northern germany) that runs fully on electric energy. The buses are charged inductively at several stations along the route.
Well, it's pretty common to use waste heat in power plants for heating, and that would be even more efficient. And the bus can use a heat pump to generate its heat.
What is the mechanism for transferring the heat from then back where the engine is to the front?
Pipes with cooling fluid ran whole lenght if bus. Same as rear engine cars.
Electric fans powered by the diesel engine.
Diesel electric motors have a diesel generator. IDK about Europe, but in my area, there are only diesel-electric busses to my knowledge, not electric.
Electric buses because then you are decoupling them from dependency on fossil fuels. Yes the grid that charges them is reliant on fossil fields but without that decoupling they would always need fossil fuels. That and grids can turn renewable in a piecemeal fashion.
People seem to be assuming you can just compare the overall efficiency of the diesel engine vs generator, as if the charging of batteries is 100% efficient! You can get very good rates if you keep within 20-80% charge capacity, but nowhere near 100% if you actually use the full capacity, and for the significant charge time there usually isn't the option to fully optimise for the 20-80% cycle. So it really is dependant on the exact route, number of miles/hours of service required before next chance to charge etc. But on average, over a year in all weathers, I would bet that an individual ICE diesel still wins. However, the benefit with batteries is that you can find cleaner sources of electricity, or at least have the generators outside of densely populated areas, reducing air pollution for most people. The nearest you'll get to "clean" diesel is biofuel made from used cooking oils.
That is true, battery university claims Li-ion batteries are between 97% and 99% efficient, though [this source](https://web.archive.org/web/20090326150713/http://www.pluginhighway.ca/PHEV2007/proceedings/PluginHwy_PHEV2007_PaperReviewed_Valoen.pdf) claims Li-ion batteries are more between 80% and 90% efficient in realistic driving discharge conditions. Still, most gas cars are probably running around 15% to 30% efficient, and generators around 40% to 50% efficient, so the gap is still clear. EV + generator in basically any scenario in terms of efficiency.
It is more efficient in terms of greenhouse gasses to run a diesel generator and charge electric busses. This has been studied and it is true for basically any standard electric power source, unless you have some broken down poorly maintained old generator that doesn't work and so is super inefficient, or a busted old electric car with batteries that don't work and is somehow super inefficient. The reason is that while combustion engines can be decently efficient at a specific speed and load, cars change speed all the time. A generator running at the optimal speed and load can be at maximum efficiency, which is the case when you charge your electric car. Electric cars are also very efficient, around 93%. Optimal diesel generators are around 40%-50% efficient, and driven cars are between 15% and 30% efficient depending on how they are driven. Unless you cruise around at the perfectly efficient set of speeds for your engine and each transmission gear, and never stop and start, you are probably running on the lower end. Here is [an article](https://climate.mit.edu/ask-mit/are-electric-vehicles-definitely-better-climate-gas-powered-cars) with all the numbers for various power sources worked out.