Saturday, September 19, 2009

Regenerative braking works!

I had a brilliant tour of the Modec electric delivery-vehicle factory in Coventry, and they let me take a one-hour test-drive in an instrumented vehicle (pictured above).
The vehicle had perfectly good acceleration and its response to the pedals has been engineered to make it feel just like a 'normal' vehicle.
For me the most exciting details from the data from this 3.5-ton vehicle were: 1) three headline numbers - maximum power 80 kW; maximum regenerative power 20 kW; typical power at top speed 40 kW; 2) one nicely measured deceleration event from top speed to zero, which allowed an estimate of how efficient the regeneration is at capturing kinetic energy (the answer was that it was better than 50%; and the Modec engineers mentioned a redesign of the transmission that might further improve this efficiency). 3) overall regeneration figures, showing that the regenerative braking recovered roughly 15% of the energy used during the whole test-drive. The graph above shows by the green area the energy recovered, and by the red area the energy that went out from the battery.
Thank you, Modec!
Full story with factory tour images and data


litsl said...

Do you think it would work on an electric bicycle? The Bionx system claims regenerative braking and looks quite good. I wonder if I could make this work for a 60 mile ride from London to Cambridge.

Unknown said...

Very cool vehicle.

Was the one you tested laden, and how does performance vary with load?

David MacKay FRS said...

@Thomas - My test vehicle was nearly unladen (it was carrying a tail-lift only). I had requested a laden one, but it wasn't possible. The vehicle weight is about 3500kg. In practice, these sort of vehicles are used to carry light goods, so the weight of goods rarely gets up to 1000kg. This means, I guess, that the performance, realistically laden, would be very similar (since the cargo weight is so small compared to the vehicle weight).
@litsl - I'd like to try the electric bicycle - I tried a Sinclair Zike about 17 years ago, and it was very impressive: it had a plastic frame with batteries hidden inside it; the Zike zoomed up Scottish hills very nicely. The Zike did not have regenerative braking. I think regenerative braking on a bike is pretty pointless, unless you live somewhere hilly where you have to brake on descents - my reason is, as a cyclist, I almost never use the brakes except in emergencies, and for the last 2 seconds of a journey.

The Long Future said...

From the Modec Factory web site FAQ:

"How does Modec perform?
Range = 100 miles or 60 miles depending on battery choice
Speed = 50 mph
Payload = 2 tonnes"

The Long Future said...

The lithium batteries under testing at the DOE (USA) are capable of many thousands of cycles. The net energy in/out is vey good, +90%. Power densities are through the roof. I am certain the lithium batteries in this vehicle will perform very well under service.

This Modec would make an excellent prototype for a "last mile" delivery vehicle, or transportation. With 4400 lbs payload, fitting 15 people would be straightforward.

litsl, the electric bike prototypers can do 60 miles--no production vehicles that I am aware of. Google endless-sphere

Unknown said...

38 kWh/100 km is a lot higher than the cars mentioned in the book (Gwiz, Tesla). I guess cos this is a small truck (heavy, non-aerodynamic)? Let's hope so - cars have to do better!

osiris87 said...

To really ascertain the benefits of regenerative braking on this vehicle, don't you have to compare it's energy consumption with a modec that's had it's KERS system removed (making it lighter)?

I'm sure it would be more efficient or the engineers wouldn't have bothered, but the 15% figure must be lower in truth.

Unknown said...

@osiris87, I don't think removing the 'KERS' as you call it would be a substantial weight saving. This is because it basically uses the existing batteries and motor controllers.

Perry E. Metzger said...

This is hardly the first vehicle to use regenerative breaking -- I first test drove an electric car with regen breaking almost 20 years ago -- it was a Geo Metro converted by Solectria in Massachusetts.

Unknown said...

I think the point is that this is the first time he has been able to obtain decent data on how well regenerative braking works.

Hilary said...

In a previous blog entry you stated

"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."

I'm not sure that is a reasonable approach, given your generally critical 'show me' analysis.

You book is great. But there is evidence out there that:
1) Electric vehicles (at the moment) produce more lifecycle CO2 than fossil fuel ones
2) PV panel consume more CO2 during production than they can ever save (in our UK climate, at least)
3) Liquid biofuels (e.g. US bioethanol) releases only about half the energy that went into its production.
4) etc..

Encouraging any of these technologies now does not help in reducing CO2 emissions.


Unknown said...

@Hilary: You say "there is evidence out there that...". So if there is evidence, perhaps you could direct us to it? I for one would be interested in all the claims you list.

Hilary said...


Some relevant links:

No doubt there are lots more. What I'm saying is that we have to be very careful about the new technologies. In contrast, measures to reduce energy usage (e.g. monitor household meters, hypermiling driving techniques, more cycling etc, are less likely to have these unintended consequences.

Unknown said...

You're right of course, care is needed, although I'll look at the links when I have a chance. However I would add that whilst measures to reduce consumption are important (and necessary) they are not the whole story. Also many efficiency measures get swallowed up by increased volume of consumers. This makes sense from a techno-economic perspective - because if people save energy they have more spare cash which they inevitably spend on stuff which takes more energy. I think it's called the boomerang effect. Anyway I'll look at your links and come back to you.

Unknown said...

Solar panels: check out this - and see the second paragraph from the top on page 7. Overall, no need to throw out the baby with the bathwater on this one though. More soon on your other links.

Hilary said...

Yes, you're probably correct - on wider reading, PV looks OK (CO2-wise), still too expensive to be commercially attractive though.

Unknown said...

PV is expensive although hopefully improving. I'm a big fan of concentrating solar power and this project is hugely exciting to me. I hope governments get on with it. After all it's not that they can't spend huge capital sums upfront (they often do, e.g. on defence)... I think this animation puts it quite well:

Milan said...

This may interest you:

From Turbines and Straw, Danish Self-Sufficiency

"Last year, the Danish island of Samso (pronounced SOME-suh) completed a 10-year experiment to see whether it could become energy self-sufficient. The islanders, with generous amounts of aid from mainland Denmark, busily set themselves about erecting wind turbines, installing nonpolluting straw-burning furnaces to heat their sturdy brick houses and placing panels here and there to create electricity from the island's sparse sunshine. By their own accounts, the islanders have met the goal. For energy experts, the crucial measurement is called energy density, or the amount of energy produced per unit of area, and it should be at least 2 watts for every square meter, or 11 square feet. 'We just met it,' said Soren Hermansen, the director of the local Energy Academy, a former farmer who is a consultant to the islanders."