Electric cars

AdrianC

Herzlos wrote: »

1. Just requires huge batteries. Adding 2t of battery to something that weights 40t, has a top speed of 4mph and already costs half a million quid isn't going to be that big a deal.

That typical mid-range combine holds about 600 litres of diesel. At 40Mj/litre, that's about 24Tj, or about 6.7MWh.
An 85kWh Tesla battery weighs 540kg, so 6.4kg per kWh gives a battery pack weight of around 43 tons.

And that's ignoring the minor detail that that's nominal capacity, not usable. Let's add 10% for that. Hell, let's just round it to 50 tons!

Ooops. Suddenly, it's no longer drivable on the road without getting into a whole world of extra regulation - and that's ignoring the minor detail that you've just turned a 12t vehicle into a 62t one, with all the knock-ons for the structure and running gear. It'll probably be 70t by the time you've finished.

That's not going to do the field much good, is it?

2. Recharging on the fly either means cables (it's covering a single field at a time in stripes, so it's not going to need miles of cable, a few hundred ft would cover it most of the time) or having something follow it to recharge.

Umm, where are you plugging the other end of this into? Are you assuming the field is right next to the farmyard?

Herzlos

almillar wrote: »

How big will the battery need to be to run a four to five hundred kilowatt combine 24 hours a day for a week? Do the sums.

84,000 kWh. Or, say, 1,000 Tesla batteries. An extreme example of where electric isn't viable yet. Let's put combines to the bottom of the pile, and concentrate on passenger vehicles, then.

Combines are definitely at the bottom of the pile.

But you make a good point. Combines would consume 1000 Tesla batteries (current tech) per week, or about 1 every 10 minutes. Combines are moving across fields at a walking pace.

A combine harvester could (I reckon) easily hold 6 Tesla batteries (1 hour running) without any inconvenience. Do them in a hot-swappable way and you'd need to swap them out every 10 minutes (or 20 minutes with a double pack, or 30 minutes on a triple pack). That can easily be automated to some extent, or using a loader of some sorts.

Then the problem moves from "Can we store 84mWh on a combine harvester" to "Can we charge and deliver 6x 84kWh batteries to a combine harvester in an hour?"

Since you can fast charge a Tesla battery in ~20 minutes, you'd only need 2 fast chargers on the farm and say, 12 battery equivalents, depending on distance from charger to harvester. Potentially you could get away with having 2 workers with loaders feeding batteries to it all day.

So you've got from "totally impossible" to "fairly plausible".

I still don't think it's worth doing unless batteries get much better and diesel becomes much more expensive. Current tech may mean 6 swaps an hour, which is a pain in the rear. But give it a generation or 2 and you could be down to 1 swap an hour which is no big deal. Presumably these things don't carry a full 168 hours worth of diesel at a time?

AdrianC

Herzlos wrote: »

Since you can fast charge a Tesla battery in ~20 minutes, you'd only need 2 fast chargers on the farm

And we're back to monumental cable upgrades to the farm...

Oh, and don't forget transporting all these batteries back-and-forth.

BTW, you might be forgetting that the combine can be refilled in the field quite easily. They're probably getting through 20 litres/hour or so.

Herzlos

AdrianC wrote: »

That typical mid-range combine holds about 600 litres of diesel. At 40Mj/litre, that's about 24Tj, or about 6.7MWh.
An 85kWh Tesla battery weighs 540kg, so 6.4kg per kWh gives a battery pack weight of around 43 tons.

Yeah, carrying it all is a no-go.

Umm, where are you plugging the other end of this into? Are you assuming the field is right next to the farmyard?

There are 2 interesting properties here. 1 is the fields don't tend to move around much, staying roughly where you left them from year to year. 2 Is that cables can cover fairly large distances in a remarkably flexible manner. You probably don't even need a point at every field, if you've got enough battery to get between points.

So it may be viable to run cable to a few hub points around the field infrastructure, depending on distance from a spur, and the surrounding landscape. Again, probably doesn't make any sense right now, but in 25 years?

Herzlos

AdrianC wrote: »

And we're back to monumental cable upgrades to the farm...

I'd hardly call it monumental. They potentially already have some fairly substantial power depending on what processing they do there.

Oh, and don't forget transporting all these batteries back-and-forth.

I covered that.

BTW, you might be forgetting that the combine can be refilled in the field quite easily. They're probably getting through 20 litres/hour or so.

I covered that too. It's not really any harder to swap a batter or provide 3-phase to a moving vehicle than it would be to pump diesel into a moving vehicle. You'd just need to do it more often.

AdrianC

It's a LOT harder to swap tons of batteries in a field than it is to pump fuel from a bowser...

And you seem to be forgetting that the fields may be miles from base. The combine may not even belong to the farm - it's very likely to belong to a contractor.

Yes, it IS monumental - a supercharger pulls 145kW. At 415v three-phase, that's 350A. Times two, you said? 700A...

Herzlos

AdrianC wrote: »

It's a LOT harder to swap tons of batteries in a field than it is to pump fuel from a bowser...

Not really, beyond alignment it's largely the same job.

And you seem to be forgetting that the fields may be miles from base. The combine may not even belong to the farm - it's very likely to belong to a contractor.

Nope, I'm not. The ones using contractors tend to have small enough farms that it's not viable to own their own. In which case it's unlikely to be running for as much as a single day without down time, as it'll need to be shipped from farm to farm, and you've just reduced the problem set. So you tend to have 2 use cases:

1. Small farms all over the place, harvester runs for maybe a 12 hour shift (72 Tesla battery equivalents), and then gets transported somewhere else. Would potentially need to be shipped with all 72 batteries.
2. Huge farms, where you can charge the batteries on site and deliver them to the harvester.

Yes, it IS monumental - a supercharger pulls 145kW. At 415v three-phase, that's 350A. Times two, you said? 700A...

Yet we can get at least 4 of these things at every service station in the country?
It's only monumental if you're adamant it won't work for some reason. It's a fairly big one-off installation cost, but it's definitely not monumental.

Like I keep saying; it's possible, but not feasible now. You can't let what isn't feasible currently stop you advancing or we'll never get anywhere.


I think we've done harvesters to death - you refused to believe it could be possible, that's fine. At least you're not going to be responsible for the innovation.

What about tractors - why won't they work?
What about bobcats / mini diggers - why won't they work?
What about tele-loaders - why won't they work?

mumstheword4

17 Aug2017 -Jonathan,
I have had an electric car (from a traditional car manufacturer) for 4 years. Things to consider are:
1. Can you afford to wait for the latest car from the newest car manufacturer to enter the market? (They make a mid-range luxury model now). If you can wait till it hits the shops here, then do so.
2. If you can't wait & have to buy from a traditional car manufacturer, then choose one that has been DESIGNED FROM THE GROUND UP as an electric car only. ( That should be lighter & a simpler design).
3. Traditional car manufacturers offering electrics have a mileage limit per annum.
4. Traditional car manufacturers offering electrics have similar servicing costs to petrol cars, even though there are at least half the number of parts in an all-new electric model.
5. Traditional car manufacturers offering electrics allways use old, energy-intensive (& non-renewable) manufacturing processes (this at least doubles the CO2e that is necessary).
6. Buy green electricity from a renewables-tariff to charge it.
7. ONCE YOU BUY AN ELECTRIC, YOU WILL NEVER WANT TO GO BACK TO smelly- old carcinogenic, explosive, and conflict-fuel-sourced petrol/diesel cars! BTW you will save a minimum of £1000 p.a. on ownership cost.

mumstheword4

I think Mitsubishi have withdrawn their MPG claims ( in TV ads, I have seen). Re. the comment, 'As a low-use second vehicle, sure. But just replacing low-use second vehicles is not going to make any meaningful impact on emissions.'
I disagree; to manufacture a new petrol/diesel car uses approx. 17 Tonnes CO2e (unless the company making it has a completely new ethos & uses renewable-energy manufacturing techniques -one company does).
To use that vehicle with petrol/diesel will generate between 1 and 4 times that CO2 over its life.
Jo

mumstheword4

Like making anything new, the earlier the country up-takes new technology (electric motors & batteries) , the greater the benefits.
You just have to look at the Norweigians, with North Sea Oil exploration- they spent money investing in their own technology and Norway has annual budget surpluses. They are up amongst the world leaders. The UK (Thatcher et al) bought in all the UK's N. Sea oil technology and simply taxed the oil. UK is not a major player in oil rigs. The UK has a buget deficit of £1.2Tn.