In Sustainable Energy - without the hot air, one of my main conclusions is "electrify everything" - in particular, I recommend electric vehicles. At a recent talk, someone in the audience said, yes, maybe electric cars are now viable. But surely you couldn't electrify freight? Leaving aside two possible answers (namely 1: for local freight deliveries, electric trucks are already genuinely in use, and are manufactured by a couple of companies in the UK; 2: we could make electric freight like eletric trolley buses, using overhead lines), I thought it would be interesting to investigate, using the same model I used for cars in my book, the possibility of making long-distance freight vehicles with on-board batteries.
The model assumes that energy goes into air resistance, into rolling resistance, and into brakes. The model includes regenerative brakes (assumed to be 50% efficient, round-trip), and includes energy inefficiency in the energy-conversion chains (from grid to battery and from battery to wheels). The frontal area is assumed to be 8.6 m2 and the freight carried is 26 tons. The other main assumptions are the distance between stops (500m? 5000m?) and the typical speed (50km/h? 100km/h?).
The figures above and below show the theoretical energy consumption (in kWh per ton-km) for two different batteries' energy densities (corresponding to lead acid and lithium), compared with a fossil fuel truck with the same frontal area and load, versus the range (ie the distance between refuelling stops). The top figure is for the case of 500 m distance twixt stops and 50 km/h speed. The bottom figure (just above) is for the case of 5000 m twixt stops and 100 km/h speed.
The bigger the battery, the bigger the range and the bigger the energy consumption. The main conclusion of these figures is that, on energy grounds, trucks with big batteries are viable. They are superior in energy consumption to the fossil fuel truck. (The point at the top, by the way, is the fossil fuel truck benchmark from the book, which is obtained from government statistics; the lower point is the theoretical performance of a fossil fuel truck according to the model. The latter is presumably lower because the former includes a load of empty-running journeys.)
Of course many other factors need to be borne in mind - could a truck stop provide a 120-kW outlet for charging each truck parked at the truck stop, for example? And what is the capital cost of the batteries? And could they be recycled?
But I find it interesting that in principle, long-distance electric trucks would be more energy-efficient than fossil-fuel trucks. As usual, I have declared one unit of grid electricity to have the same value as one unit of chemical energy. Yes, yes, with today's electricity mix in Britain, blah blah blah, inefficiencies in conversion, ... a factor of 2.4 or some such... But as usual I am focussing attention on the future energy system we should be building, not the details of today's obsolete fossil-fuel electricity system. We want to electrify transport in order to get the whole energy system off fossil fuels as much as possible.
16 comments:
BG, you didn't actually *read* the posting did you? That might have been polite before spouting off on someone else's blog, and, BTW, in the UK we call 'gas' at the pump 'petrol' and already pay twice what you ever have...
As to the subject in hand: can I make a wild generalisation and hope that any land-based transport can then in principle be electrified because of the possibility of regular places for recharging batteries, or the ability to tap the grid every 2.54cm of the way?
And, conversely, electrified air travel is completely out for now because battery energy density is too low, and (long-distance) sea travel is out because frequent recharging points aren't there other than for short or shore-hugging journeys?
Rgds
Damon
Yes, electrified air travel over long distance is impossible - you would have to land to recharge every 50 miles or so.
Electrified boats? I think electric boats would probably work fine, in principle, even over large distances. I would have to work out the model to check, but (if we are allowed to have as many lithium batteries as we want) I think it might be just as energy efficient as a regular boat, and the range could be large. I'll check.
Ah, now here is an outlandish idea for you on the electrified air-transport front.
Supposing the aircraft were light, possibly just about neutral density/buoyancy so that staying up (and coming up/down) doesn't require much effort.
Then equip the aircraft with (say) supercaps to be able to absorb energy very quickly.
Then assume that at regular intervals in the main air corridors, at considerably less than 50-mile intervals you have 'filling stations' with energy beamed up (microwaves/light/etc that can be kept in a tight beam and with efficient conversion to/from electricity) to a dish on the aircraft from the ground on demand...
Now, I don't think any of that is utterly sci-fi and surely a simpler proposition than the oft-cited orbiting solar power stations beaming energy to the ground...
Just my brain-fart for today...
Rgds
Damon
eg http://www.freepatentsonline.com/5890676.html
Interesting, thanks Dr MacKay. Of course in an eco-friendly economy, road transport would be minimised vs rail transport and the complete nonsense of current supply networks (like the famous prawns being fished in East Anglia, skinned in Scotland, and sold in London) would be rationalised, so hopefully we'd need less transport.
I have to say I had myself been thinking about electrifying airplanes. Given my bias (astronautics engineer), I had kind of not thought about the ships, it's a very good question...
For airplanes, a quick search seems to show that there are electric airplanes being developped, at least for general/personal aviation. Of course it's a far cry from this to plug-in A320. But then what's the solution? Biofuels or other alcools produced using decarbonised energy?
Air travel is a tough one to crack from that point of view, I think...
To reply to Damon: Well... It's true that beamed power is being researched at some level. But, being myself a rocket scientist, I'd say this is waayyyy further away than space solar power. There's all sorts of issues associated with beamed power (safety, pointing, tracking, etc...). It's my personal opinion that the "next" generation of global PV power systems will be spaceborne, whereas the first will likely be similar to what David outlined in his book. Think about it: ground-based systems can manage 10 W/m2, whereas space-based can likely manage at least 100 or more. If you solve the launch cost issue (which is of course a big one), this is a serious fact, isn't it?
A.
Hi Arnaud,
I just think that the costs of getting spaceborne PV are so huge (how much does it cost us to get 1kg into orbit right now?) that the plane issue is easier to start with and a useful intermediate step pssobly (only a rectenna needs to get airbourne, plus the supercaps and bulk storage).
Rgds
Damon
@ David MacKay - Electrified boats? I think electric boats would probably work fine,...
check out these links:
http://www.solarwave.at/index.php/en.html
http://www.planetsolar.org/index.en.php
I wonder who's gonna be first ;-)
If all gasoline cars, trucks, and suv’s instead had plug-in electric drive trains, the amount of electricity needed to replace gasoline is about equal to the estimated wind energy potential of the states. What a powerful resources we have neglected. I think electric boats would probably work fine,...
FYI: http://www.treehugger.com/files/2009/03/electric-airplanes-symposium-california-san-carlos-cafe-foundation.php
Rgds
Damon
on the topic of electric freight vehicles, it seems they already are possible! http://www.smithelectricvehicles.com/
and
http://www.modeczev.com/
D
We actually already have long distance electric freight vehicles. Trains.
Freight haulers come in many sizes. I'd be interested in purchasing a plugin electric small pickup truck with towing capability, providing it had 700+km range, or 400km range and a 3 hour recharge time. Even as hybrids, this is a portion of the market not well served currently. I currently own a 2000 Ford Ranger E85-capable pickup because I couldn't find anything smaller and more fuel efficient in the US market. I speculate that is somewhat because of crash test requirements.
Regarding electric freight vehicles, it seems to me there are strong economic reasons to switch to autonomous vehicles.
The consideration is: the labor cost of the driver becomes the largest cost item in delivery and freight vehicles when the average speed of the vehicle drops below 35 miles per hour (56 km/hr).
(I used $20/hr labor, various vehicle mileages and an old rule of thumb: Double your gasoline cost to estimate fuel, insurance, registration and maintenance.)
Now, from a low energy low CO2 emissions design standpoint, the slower the vehicle goes the less energy it uses and the easier it is to build a vehicle with present day technology.
At design speeds of 2 to 10 miles per hour then solar panels, super capacitors and various small power sources installed in de-engined long haul trucks are possible.
If a conventional truck goes 65 mph with a 400 kw diesel, how fast could the same vehicle go with 20 kwh of non-combustion power devices?
If energy required is proportional to the square of the vehicle speed:
65^2/x^2 = 400/20
x=14.53 mph
But the labor cost of a 14 mph top speed truck is too high.
Instead install a laptop PC running Linux with a wireless Internet connection, several safety cameras, a GPS, and software and hardware such as was used in the recent DARPA autonomous vehicle competitions.
A driver in Portland Oregon might "launch" a 32,000 pound load of lumber. About 10 days later the load would arrive in Los Angeles, a trip of 1000 miles, and another driver would ride his bike over to the freeway and "catch" the delivery truck by calling the truck on his cellphone.
Electric freight vehicles certainly are possible. The Swiss ski resort of Zermatt runs on them -http://belsizelibdems.blogspot.com/2009_02_08_archive.html
The technological development in recent years has enabled us to not only build electric cars but also electric machines for work of various type (vans, golf carts, trucks, etc. ..) that can be used with success in all areas. Resorting to electric vehicles we not only save on fuel costs, but we also benefits from high performance engines, that also have higher energy efficiency compared to conventional motors.
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