Comment by ggreer | Hacker News Reader

Comment by ggreer | Hacker News Reader

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> Battery EV trucks have had range limits of measured in single-digit kilometers.

I don't believe you. Find me an EV truck that any company has fielded in the past 20 years that has less than 10km range.

Also you're comparing a prototype to a mature technology. One might as well note that early automobiles had less range, lower speed, worse reliability, and higher cost than horses. And unlike horses, automobiles require infrastructure such as roads and gasoline stations. All of those things were true at the time, but horses couldn't be improved upon and automobiles could. Now we're in the same position with respect to gas vehicles vs electric vehicles.

Battery technology is improving at an impressive rate. Energy density has doubled since 2010. Price per kilowatt-hour is 1/9th what it was a decade ago.[1][2] These advances have made EVs competitive on the ground. It's quite likely that improvements will continue and EVs will become competitive in the air. EVs have lower refueling costs, lower maintenance costs, and are simpler designs (making them cheaper and safer). We already have battery-powered commercial drones. Human flight is more conservative when it comes to adopting new technologies, so it'll probably take longer for EV planes to become widespread. But long term? I would bet on EV planes replacing regional jets.

1. https://cleantechnica.com/2020/02/19/bloombergnef-lithium-io...

2. https://www.statista.com/statistics/883118/global-lithium-io...

> I would bet on EV planes replacing regional jets

Energy density of batteries are around 1/40th of that of kerosene (0.9 mj/kg vs 44mj/kg) so we are talking 44x the energy density we need to make up for to get perfect parity. From what I can find I’ve seen 35% thermal efficiency for modern airliners and I believe 95% for electric motors. Ok so this means we can reduce the density gap required for parity to just under ~ 44/2.5 so ~18/19 mj/kg? (I’m doing this in my head so it’s rough). Rough calls show we need batteries with 20x the capacity to replace what we have right now with electric alternatives. While the gains in battery densities have been impressive we need to keep these gains in mind that we need to be making much bigger gains for this to become a reality. Personally I don’t see it being feasible for a very long time given the progress and I believe we’re better off taking fewer unnecessary flights than hoping on some miracle battery breakthrough

(Edited for clarity)

Your calculations are correct, but you've baked a few other assumptions into them.

- Fuel has no structural strength. Batteries are rigid and can double as parts of the airframe, saving weight.

- Combustion engines are complex and expensive. This precludes mounting a dozen tiny engines on a plane and integrating them at just the right spots. Electric fans are cheaper and easier to integrate into the airframe, reducing drag. This also helps with engine-out capability. If you have two engines and one fails, you've lost half your thrust. If you have 36 engines and one fails, you've lost 3% of your thrust.

- Air becomes less dense with altitude. This reduces drag, but it also reduces the power of combustion engines. Electric aircraft don't need oxygen, so their power remains the same at altitude. There are losses due to the fan having to rotate more to move the same mass of air, but in general, electric aircraft become more efficient at altitude.

- Electric fans respond much faster to throttle inputs and are easier to gimbal than combustion propellors or jets. This allows designs with reduced or even eliminated control surfaces. The lack of rudder and elevator reduces drag, allowing for greater range.

That last trick might sound insane for human-rated aircraft, but there are already flying prototypes that use this approach.[1][2]

1. https://www.youtube.com/watch?v=5ukmS9ZJm40

2. https://www.youtube.com/watch?v=ZH7DSFRCqDQ

I wonder if you could significantly charge the batteries from the energy of a vibrating wind. Or (and this is out there) from atmospheric electricity

You can definitely significantly charge batteries from sun - see https://en.wikipedia.org/wiki/NASA_Pathfinder - but it's at the moment far from a convenient commercial solution.

Did we forget that electric vehicles were some of the first sold in 1900's? Now imagine what battery tech we would have if a hundred years of development went into battery technology?

Be patient, we'll figure something awesome out.

The Nikola One has a range of 0km (unless it's powered only by gravity)

BMW's Terberg YT202-EV electric tractor, tested~2015, comes to mind. Its route during trials was 2km, though the claimed range was 100 km. I strongly suspect the latter was slow and unloaded. Speed was restricted in any regard:

BMW and the SCHERM Group have put a massive 40-ton EV into service for a one-year pilot. The Terberg YT202-EV electric tractor will travel a 2 km route eight times a day between the SCHERM group logistics center and the BMW plant in Munich, transporting vehicle components such as shock absorbers, springs and steering systems.

The standard tractor has two batteries (112 kWh), and a third battery can be fitted for extended operations. It is equipped with a 138 kW, 720 N·m Siemens motor and an Allison 3000 transmission. Top speed is 25 mph.

The YT202-EV has a range of up to 100 kilometers (62 miles), theoretically enough for a full production day. BMW says it will be charged exclusively with renewable electricity, and will save 11.8 tons of CO2 annually compared to a legacy diesel truck.

https://chargedevs.com/newswire/bmw-tests-40-ton-electric-tr...

Even conservatively estimating 80% efficiency and 80% cruise speed, and estimating 25% peak power during cruise, that's:

    83.1 km = (112kWh x 80% x 25 mph x 1.6 km/mile x 80%) / (138 kW x 25%)

which is an armchair number plenty close to the claimed 100 kilometers. And if it only has to go 2 km eight times a day, it's going to use less than a third of its capacity.

Unless they charged it at every stop, that's a 16 km drive between charges, not 2km. 112kWh is enough to run the 138kW motor for 48 minutes full-out. At 25mph, that's 32km, so driving without stops cannot be less than a 32km range, and is probably significantly more (trucks run closer to to full power while cruising than cars, but still not 100%).

I may have understated somewhat.

Will you grant double digit km range? Still two orders of magnitude lower than a fuel-based truck in commercial operation?

150 gallons * 7 mpg = 1,050 mi / 1,690 km.

There’s more than just increasing capacity to address the range issue. Further, two digits of difference will be overcome sooner or later.

Such as?

Petrochemical fuels afford a near unbeatable energy/volume and energy/mass density. The best theoretical battery might attain 1/10th this, practical batteries are nearer 1/100th, if that. A ~100 kWh battery holds the equivalent of 2 gallons / 8 litres of petrol or diesel.

Electrics have advantages of vastly more efficient potential-to-kinetic energy conversion (90%= rather than 30% for an ICE), a more efficient drivetrain (often in-wheel motors), and regenerative braking. Air and tyre drag are equivalent for both domains.

Capacity, energy management, and recharge access are all there is.

Two-order-of-magnitude improvements in any non-informational domain are both very hard-won and utterly transformational. Commercial passenger aircraft are ~2 orders of magnitude faster than walking. A semi-trailer has ~2 orders of magnitude more cargo capacity than a man with a wheelbarrow.

Getting two orders of magnitude out of long-haul road-based heavy-cargo EVs is a very tall order. Mains-fed electric trainsets would be a far more likely technology, and are extant and commercially proven

One option is to have multiple vehicles and switch payloads or batteries.

As others noted, we’ve just started taking a serious interest in renovating rechargeable batteries for this use. Lots more can and will be done once the political will is there.

Possible, though greatly increasing capital costs, also complexity and coordination dynamics.

I wonder how long haul trucks compare to passenger vehicles for energy efficiency.

Diesel engines tend to be more efficient the larger they are, with marine engines hitting 50% in fixed speed applications.

You'd want to compare net capacity as ton miles/gallon. Preferably as cargo rather than gross weight, though I'm using the latter for convenience.

Passenger cars net about 90 or so, for a high-efficiency vehicle, gross vehicular weight, at full capacity.

Assuming 140,000 lb GVWR and 7 mpg, I compute 490 ton-mpg. That's roughly equivalent to numbers given for rail ("move one ton of freight one mile on a gallon of fuel), and is likely high, though 100-250 ton-mpg seems likely.

This is not net cargo efficiency, where that rail number may come from. But gives a sense for numbers.

Well, not in the last 20 years, but how about the last 80? From the wikipedia article on milk floats in the UK:

> In 1937 they produced a ride-on four wheeled vehicle, suitable for a payload of 8–10 cwt (410–510 kg) and with a range of around 35 miles (56 km)

Due to the way that power is delivered in an EV, the lack of a regular gearbox, and the non-linear nature of air resistance, EVs have ranges that increase the slower you go. At 20mph the range of a Tesla damn near doubles by some estimates. This is the opposite of how ICE cars work, which typically get better MPG at higher speeds due to gearbox design and variable efficiency based on engine RPM.

That’s probably why milk floats could go so far at the time despite obviously inferior battery technology; milk floats didn’t go very fast.

To this point I wonder how full autonomy will impact this. A truck that drives itself and doesn't have to stop (besides to charge) will easily make the case for a freight or autonomous lane on highways where the vehicles don't go above a certain speed (67mph or 100kph). I don't really care if it takes me 10 hours to go 500 miles if I watch a movie, go to sleep, an wake up in front of my hotel.

Freight should be done more by rail. It’s way more efficient to ship by rail, and easier to electrify. Our heavy usage of semi trucks is partially due to the hidden subsidy that semi trucks get via road maintenance, where semi trucks don’t pay anywhere near enough gas tax to offset the damage they do. EV trucks will be worse.

Generally speaking, the solution for car troubles is to reduce the scope that cars and trucks are used to solve transit problems. Road damage due to semi trucks? Build more freight rail! Inner city congestion? Add a subway! Long commutes? Build more housing, and if that doesn’t work add dedicated commuter rails. Too much air traffic? Offset local flights onto high speed rail to free up room for long distance flights.

https://en.wikipedia.org/wiki/Milk_float

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