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Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

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Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#191

Post by svnt »

Retric wrote: post #188
svnt wrote: post #176

Earlier quoted context omitted.

Sure, but what does this have to do with what I said? You need design and operating margin, and the engine is always running.

Reducing the load is always going to save fuel. There’s no difference between energy used to move a boat and energy used to run the lights. Put another way if there was excess torque being generated it would go somewhere such as increasing the engine RPM.

What you seem to be missing is that your understanding is not true because of the practical realities of operating large internal combustion engines.

For example, one tonne of fuel is about 11 MWh. So if you run the calculations, you will see that adding solar panels to a diesel boat, even if the energy they provide is free, essentially never ROIs, and makes the boat less reliable and useful as a boat.

These kinds of engines generate tens of megawatts when they are on, and they are always on when the ship is moving.

Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#192

Post by cryptonector »

perilunar wrote: post #178
cryptonector wrote: post #173

Earlier quoted context omitted.

Airplanes don't get to do regenerative braking except briefly upon landing, but you're not going to put generators in the wheels just for that, and you need active thrust reversers, so really there is simply no room for regenerating power in electric planes.

There’s no reason why you couldn’t do regen when descending with an electric-powered prop plane. It would give a steeper descent than normal, and may not be more efficient overall than cutting power earlier and descending more gradually, but it could be done.

That would be terrifying.

Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#193

Post by cryptonector »

jmward01 wrote: post #189
perilunar wrote: post #178

Earlier quoted context omitted.

There’s no reason why you couldn’t do regen when descending with an electric-powered prop plane. It would give a steeper descent than normal, and may not be more efficient overall than cutting power earlier and descending more gradually, but it could be done.

Electric will start smaller and build up to big just like everything else. The single and twin engine world is pretty dominated by structure so the gains are easy to see there. As new capabilities and designs are prooven out things will grow or, and this is what I really hope for, we will find that we don't need the massive aircraft to be profitable anymore and we will just get more smaller electric aircraft providin…

> One of the biggest efficiency gains we could have is not forcing people into a hub and spoke mega airport model

The airlines have already switched from that model.

Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#194

Post by Retric »

svnt wrote: post #191
Retric wrote: post #188

Earlier quoted context omitted.

Reducing the load is always going to save fuel. There’s no difference between energy used to move a boat and energy used to run the lights. Put another way if there was excess torque being generated it would go somewhere such as increasing the engine RPM.

What you seem to be missing is that your understanding is not true because of the practical realities of operating large internal combustion engines. For example, one tonne of fuel is about 11 MWh. So if you run the calculations, you will see that adding solar panels to a diesel boat, even if the energy they provide is free, essentially never ROIs, and makes the boat less reliable and useful as a boat. These kinds of…

One tonne of fuel is more like 5.5 MWh. You did a mathematical calculation while ignoring engine efficiency.

The reality of large internal combustion engines is you still pay for every single kWh. These ships already have extremely complex electrical systems with multiple redundancies and load balancing etc.

The dealbreaker is R&D as unlike a house or sailboat you can’t just yolo where panels are placed and wires run etc, this is all bespoke engineering with few of any give design being manufactured and little available space.

Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#195

Post by Animats »

ViewTrick1002 wrote: post #177
Animats wrote: post #165

Earlier quoted context omitted.

Not in shipping. See "Slow Steaming".[1] Most container ships could go much faster than they normally do. Sadly, the S.S. United States, the fastest transatlantic liner ever, is about to be disposed of by sinking.[2] 35 knot top speed. Southampton to New York in 3.5 days. No market for that once air travel crossed the Atlantic. [1] https://en.wikipedia.org/wiki/Slow_steaming [2] https://6abc.com/post/what-are-doing-s…

The difference is for short distance passenger transport, I.e. commuting. A route that used to take 1 hour suddenly becomes 30 minutes and suddenly your daily commute becomes bearable.

Good point. The SF bay has some hydrofoil ferries. Trip length is about right for that.

Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#196

Post by svnt »

Retric wrote: post #194
svnt wrote: post #191

Earlier quoted context omitted.

What you seem to be missing is that your understanding is not true because of the practical realities of operating large internal combustion engines. For example, one tonne of fuel is about 11 MWh. So if you run the calculations, you will see that adding solar panels to a diesel boat, even if the energy they provide is free, essentially never ROIs, and makes the boat less reliable and useful as a boat. These kinds of…

One tonne of fuel is more like 5.5 MWh. You did a mathematical calculation while ignoring engine efficiency. The reality of large internal combustion engines is you still pay for every single kWh. These ships already have extremely complex electrical systems with multiple redundancies and load balancing etc. The dealbreaker is R&D as unlike a house or sailboat you can’t just yolo where panels are placed and wires run…

No, one tonne of diesel fuel contains about 11 MWh of potential energy as determined by calorimetric methods. One tonne of fuel when consumed produces a variable amount of useful energy output depending on the efficiency of the engine.

If you said fuel was 5.5 MWh per tonne people would wonder what you cut it with.

The reality of outputting 80MW is that the power to your lights is a rounding error and you’d be better off buying a robot to regularly clean the hull.

Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#197

Post by wkat4242 »

lawrenceduk wrote: post #139
pfdietz wrote: post #118

Earlier quoted context omitted.

One possible path is the hybrid aircraft, where combustion turbines or fuel cells produce electric power that drives small ducted fans via electric motors. The enabling technology here is superconductors. Airbus is working on superconducting motors and generators for such hydrogen-powered aircraft. One can imagine regenerative braking in the fans, for example to recover energy as aircraft descend, and also with batte…

Pilot here, I don’t think this is right. Aircraft typically operate at 80-100% power output. It’s not the average 20% power output of your car. Weight is pretty much everything, the savings from regenerative braking in an aircraft are almost 0% but the cost of enabling it is some tons. This tech makes loads of sense in a car but I’ve never flown an aeroplane in stop-start traffic because that’s not how the sky works.

Indeed and an aircraft never really 'brakes' like a car does, except for 20 second on the ground (including thrust reversers). Even in a descent you would have significant forward thrust. The drag does all the braking. And you can't regenerate that.

PS I'm a hobby pilot so please correct me if I'm wrong but I don't think even an airliner would idle their engines during descent.

Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#198

Post by Retric »

svnt wrote: post #196
Retric wrote: post #194

Earlier quoted context omitted.

One tonne of fuel is more like 5.5 MWh. You did a mathematical calculation while ignoring engine efficiency. The reality of large internal combustion engines is you still pay for every single kWh. These ships already have extremely complex electrical systems with multiple redundancies and load balancing etc. The dealbreaker is R&D as unlike a house or sailboat you can’t just yolo where panels are placed and wires run…

No, one tonne of diesel fuel contains about 11 MWh of potential energy as determined by calorimetric methods. One tonne of fuel when consumed produces a variable amount of useful energy output depending on the efficiency of the engine. If you said fuel was 5.5 MWh per tonne people would wonder what you cut it with. The reality of outputting 80MW is that the power to your lights is a rounding error and you’d be better…

> No, one tonne of diesel fuel contains about 11 MWh of potential energy as determined by calorimetric methods. One tonne of fuel when consumed produces a variable amount of useful energy output depending on the efficiency of the engine.

That’s almost correct, good try.

> lights is a rounding error

Ships use electrical power for far more than lighting, and no electricity is not a rounding error compared to profit it’s a significant expense for cargo ships.

Re: Electric Propulsion's Dirty Secret: Why Lithium Can't Fly (Or Float) Profitably

#199

Post by generalizations »

cagenut wrote: post #143
generalizations wrote: post #77

Earlier quoted context omitted.

Those were; many were not. Someone who takes issue with the middle class of the USA might not be.

you're committed to the username bit

yup
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