Even Low Efficiency Energy Storage Devices Become Competitiv

[Bret Cahill]

If energy from the grid costs 13 cents/kW-hr and a 1000 cycle battery
costs 27 cents/kW-hr, and diesel is 40 cents/kW-hr, then a 33%
efficient energy storage device that is capable of thousands of cycles
over its lifetime suddenly starts to look interesting.

Maybe it's possible to trade a little efficiency for higher energy
density or lower initial costs.

For example, the flywheel below is 86% efficient but has an energy
density of only 5.5 W-hr/kg.

It would be cost effective to find something that was only 50% or 40%
efficient but with 10X the energy density.


Bret Cahill


http://www.magma.ca/%7efesi/50kW-1000Wh%20Flywheel%20System.pdf

System Description
Continuous rated power 50 kW
Peak power 120 kW
Charge or discharge time 60 seconds at 50 kW
Mass 135 kg
Volume 110 litres
Diameter 24 in (610 mm)
Height 18 in (460 mm)
Specific power 370 W/kg (continuous)
890 W/kg (peak)
Specific energy 5.5 Wh/kg
Typical DC interface 600 - 750V
Self-discharge rate 0.5 - 1.0 kW
Typical Efficiencies at Rated Power
Motor/generator 98%
Inverter 95%
Net one-way 93%
Net round-trip 86%
Flywheel Rotor
General description Composite flywheel rim with
aluminum hub
Operating speed range 15,500 rpm - 31,000 rpm
Polar inertia 0.720 kgˇm2
Energy storage 1,000 Wh @ 31,000 rpm
250 Wh @ 15,500 rpm
Net energy storage 750 Wh
Motor/Generator
General description Permanent magnet, 3-phase,
synchronous, liquid cooled
Frequency range 515 Hz - 1,030 Hz
Line-line voltage 230 Vrms at 515 Hz
450 Vrms at 1,030 Hz
Total inductance 100 ľH
Line-

 

[John Larkin]

On Sun, 10 Aug 2008 10:17:56 -0700 (PDT), Bret Cahill
<BretCahill@aol.com> wrote:

If energy from the grid costs 13 cents/kW-hr and a 1000 cycle battery
costs 27 cents/kW-hr, and diesel is 40 cents/kW-hr, then a 33%
efficient energy storage device that is capable of thousands of cycles
over its lifetime suddenly starts to look interesting.

Maybe it's possible to trade a little efficiency for higher energy
density or lower initial costs.

For example, the flywheel below is 86% efficient but has an energy
density of only 5.5 W-hr/kg.

But its standby power loss is absurd. That's why they are used as a
short-term UPS sources - if that - rather than as daytime-nighttime
energy movers or vehicle sources.

It would be cost effective to find something that was only 50% or 40%
efficient but with 10X the energy density.

Absolutely. If batteries were 10x as dense, and lasted 10x as many
cycles, as they can do now, all sorts of things would change.

Sadly, batteries have to carry all their reactants, and all their
waste, whereas a fuel engine doesn't. And batteries damage themselves
when charged and discharged. And quick charging needs huge power
inputs, with consequential thermal problems; a 50% efficient battery
would cook if you charged it fast.

The ideal battery might use air as one reactant, have its chargable
component refreshed off-vehicle, and dump its wastes. Sure sounds like
a fuel cell to me. Or a gas engine.


John

 

[John Larkin]

On Sun, 10 Aug 2008 13:14:39 -0700, "Rob Dekker" <rob@verific.com>
wrote:

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news8bu94pft0vnpoh62j67rgvnujsovvpqob@4ax.com...
....

The ideal battery might use air as one reactant, have its chargable
component refreshed off-vehicle, and dump its wastes. Sure sounds like
a fuel cell to me. Or a gas engine.

Or a Zinc-air battery.
Which has the additional advantage that it produces no waste.

Rob

The vehicle still has to lug around the zinc oxide, which is heavier
than the original zinc. And it has to be collected and reprocessed.

Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is 12,500.
That's 34:1.

John

 

[Bret Cahill]

The ideal battery might use air as one reactant, have its chargable
component refreshed off-vehicle, and dump its wastes. Sure sounds like
a fuel cell to me. Or a gas engine.

Or a Zinc-air battery.
Which has the additional advantage that it produces no waste.

Rob

The vehicle still has to lug around the zinc oxide, which is heavier
than the original zinc. And it has to be collected and reprocessed.

Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is 12,500.
That's 34:1.

An EV can go 80 miles. A tractor only needs to go one mile.
That's 80:1

2.3 X more energy density than necessary.


Bret Cahill

 

[Bret Cahill]

If energy from the grid costs 13 cents/kW-hr and a 1000 cycle battery
costs 27 cents/kW-hr, and diesel is 40 cents/kW-hr, then a 33%
efficient energy storage device that is capable of thousands of cycles
over its lifetime suddenly starts to look interesting.

Maybe it's possible to trade a little efficiency for higher energy
density or lower initial costs.

For example, the flywheel below is 86% efficient but has an energy
density of only 5.5 W-hr/kg.

But its standby power loss is absurd.

Depends on the application.

why they are used as a
short-term UPS sources - if that - rather than as daytime-nighttime
energy movers or vehicle sources.

But perfect for farm tractors.

Remember, 33% efficiency is now competitive for high cycling energy
storage devices. This number will continue to drop.

It would be cost effective to find something that was only 50% or 40%
efficient but with 10X the energy density.

Absolutely. If batteries were 10x as dense,
and lasted 10x as many
cycles, as they can do now, all sorts of things would change.

That's not only trivially obvious but also irrelevant to the issue:

Including lower efficiency energy storage devices in a big net search
for higher energy or power density.


Bret Cahill

 

[Bret Cahill]

The ideal battery might use air as one reactant, have its chargable
component refreshed off-vehicle, and dump its wastes. Sure sounds like
a fuel cell to me. Or a gas engine.

Or a Zinc-air battery.
Which has the additional advantage that it produces no waste.

Rob

The vehicle still has to lug around the zinc oxide, which is heavier
than the original zinc. And it has to be collected and reprocessed.

Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is 12,500..
That's 34:1.
An EV can go 80 miles. �A tractor only needs to go one mile.
That's 80:1
2.3 X more energy density than necessary.

When the farmer gets out the tractor, it usually runs for hours and
hours under load. The straight line distance isn't a factor.

That was back in the old days _pre_ peak oil.

Things might not be quite so simple post peak oil.

Some are having difficulty accepting what should be a simple concept:

Pre peak: Easy street.

Post peak: Extra labor suddenly becomes cost effective.


Bret Cahill

 

The ideal battery might use air as one reactant, have its chargable
component refreshed off-vehicle, and dump its wastes. Sure sounds like
a fuel cell to me. Or a gas engine.

Or a Zinc-air battery.
Which has the additional advantage that it produces no waste.

Rob

The vehicle still has to lug around the zinc oxide, which is heavier
than the original zinc. And it has to be collected and reprocessed.

Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is 12,500.
That's 34:1.
An EV can go 80 miles. ???A tractor only needs to go one mile.
That's 80:1
2.3 X more energy density than necessary.

When the farmer gets out the tractor, it usually runs for hours and
hours under load. The straight line distance isn't a factor.

That was back in the old days _pre_ peak oil.
Things might not be quite so simple post peak oil.

The requirements of farming haven't changed since humanity howed the
first row.

The industry has, however.

Some are having difficulty accepting what should be a simple concept:
Pre peak: �Easy street.
Post peak: �Extra labor suddenly becomes cost effective.

Without tractors most everyone will starve.

That's why electrification of agriculture is a pretty sure bet.

Human labor isn't an option.

"Labor" here means some fat guy sitting in an air conditioned electric
tractor.

If it were, Africa wouldn't be starving.

Even I don't go that far.

Americans did pretty well before the first tractor.


Bret Cahill

 

When the farmer gets out the tractor, it usually runs for hours and
hours under load. The straight line distance isn't a factor.

That was back in the old days _pre_ peak oil.

Things might not be quite so simple post peak oil.

The requirements of farming haven't changed since humanity howed the
first row.

Some are having difficulty accepting what should be a simple concept:

Pre peak: �Easy street.

Post peak: �Extra labor suddenly becomes cost effective.

Without tractors most everyone will starve.

Human labor isn't an option. If it were, Africa wouldn't be starving.

I believe the author's philosophy is that you operate the
tractor say for a half hour and then spend 5 minutes re-charging
the battery---and that the cost of the tractor operator's
labor spent re-charging batteries is less than the additional cost
you would use with the higher priced fuel (diesel vs electricity).

A 5 minute recharge, right.

The tractor can swap out batteries after every lap and never wait.

Modern agribussiness doesn't run little, bitty tractors like Eddie
Albert drove around on the Green Acres TV show.

We really need a tractor pull.


Bret Cahill

 

[John Fields]

On Sun, 10 Aug 2008 20:27:28 -0700 (PDT), BretCahill@peoplepc.com
wrote:

The tractor can swap out batteries after every lap and never wait.

---
Swap out batteries which don't exist that are charged by chargers
which don't exist which are plugged into an electrical infrastructure
which doesn't exist either?

Way to go Cahill!


JF

 

[John Fields]

On Sun, 10 Aug 2008 20:27:28 -0700 (PDT), BretCahill@peoplepc.com
wrote:

We really need a tractor pull.

---
You need to stop pulling your pud.

JF

 

[jmfbahciv]

Jonathan Grobe wrote:

On 2008-08-11, jimp@specsol.spam.sux.com <jimp@specsol.spam.sux.com> wrote:
In sci.physics Bret Cahill <BretCahill@aol.com> wrote:
When the farmer gets out the tractor, it usually runs for hours and
hours under load. The straight line distance isn't a factor.
That was back in the old days _pre_ peak oil.
Things might not be quite so simple post peak oil.
The requirements of farming haven't changed since humanity howed the
first row.

Some are having difficulty accepting what should be a simple concept:
Pre peak: Easy street.
Post peak: Extra labor suddenly becomes cost effective.
Without tractors most everyone will starve.

Human labor isn't an option. If it were, Africa wouldn't be starving.

I believe the author's philosophy is that you operate the
tractor say for a half hour and then spend 5 minutes re-charging
the battery---and that the cost of the tractor operator's
labor spent re-charging batteries is less than the additional cost
you would use with the higher priced fuel (diesel vs electricity).

The author has no farming experience. How is he going to recharge
those batteries? There isn't any power outlet in the middle of
1000 acres. Run power lines? Then a plow can't plow the soil and
a combine can't harvest. Going around things is not a nice thing
to have to do when farming fields.

/BAH

 

[jmfbahciv]

jimp@specsol.spam.sux.com wrote:

In sci.physics Jonathan Grobe <grobe@netins.net> wrote:
On 2008-08-11, jimp@specsol.spam.sux.com <jimp@specsol.spam.sux.com> wrote:
In sci.physics Bret Cahill <BretCahill@aol.com> wrote:
When the farmer gets out the tractor, it usually runs for hours and
hours under load. The straight line distance isn't a factor.
That was back in the old days _pre_ peak oil.
Things might not be quite so simple post peak oil.
The requirements of farming haven't changed since humanity howed the
first row.

Some are having difficulty accepting what should be a simple concept:
Pre peak: Easy street.
Post peak: Extra labor suddenly becomes cost effective.
Without tractors most everyone will starve.

Human labor isn't an option. If it were, Africa wouldn't be starving.

I believe the author's philosophy is that you operate the
tractor say for a half hour and then spend 5 minutes re-charging
the battery---and that the cost of the tractor operator's
labor spent re-charging batteries is less than the additional cost
you would use with the higher priced fuel (diesel vs electricity).

A 5 minute recharge, right.

Modern agribussiness doesn't run little, bitty tractors like Eddie
Albert drove around on the Green Acres TV show.


Even those who do have that size of tractor cannot wait even a

minute if they're haying and trying to get it baled and inside
before it rains.

/BAH

 

[jmfbahciv]

Rod Speed wrote:

BretCahill@peoplepc.com wrote:
The ideal battery might use air as one reactant, have its
chargable component refreshed off-vehicle, and dump its
wastes. Sure sounds like a fuel cell to me. Or a gas engine.
Or a Zinc-air battery.
Which has the additional advantage that it produces no waste.
Rob
The vehicle still has to lug around the zinc oxide, which is
heavier than the original zinc. And it has to be collected and
reprocessed.
Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is
12,500. That's 34:1.
An EV can go 80 miles. ???A tractor only needs to go one mile.
That's 80:1
2.3 X more energy density than necessary.
When the farmer gets out the tractor, it usually runs for hours and
hours under load. The straight line distance isn't a factor.
That was back in the old days _pre_ peak oil.
Things might not be quite so simple post peak oil.
The requirements of farming haven't changed since humanity howed the
first row.
The industry has, however.

Some are having difficulty accepting what should be a simple concept:
Pre peak: ?Easy street.
Post peak: ?Extra labor suddenly becomes cost effective.

Without tractors most everyone will starve.

That's why electrification of agriculture is a pretty sure bet.

Just another of your pathetic little pig ignorant drug crazed fantasys.

Biodiesel will be used instead, you watch.

Human labor isn't an option.

"Labor" here means some fat guy sitting in an air conditioned electric tractor.

You havent established that there will be any more of that post peak oil.

If it were, Africa wouldn't be starving.

Even I don't go that far.

Americans did pretty well before the first tractor.

The very first did in fact starve.


Because they didn't know how to farm.

/BAH

 

[jmfbahciv]

John Fields wrote:

On Sun, 10 Aug 2008 20:27:28 -0700 (PDT), BretCahill@peoplepc.com
wrote:

The tractor can swap out batteries after every lap and never wait.

---
Swap out batteries which don't exist that are charged by chargers
which don't exist which are plugged into an electrical infrastructure
which doesn't exist either?

Way to go Cahill!

Even if all existed, there wouldn't be enough time to finish
the work before the storm hit. It's not just one tractor.
There are vehicles that haul wagons back and forth (baling).

The last thing my farmer relatives want to do is waste their
time refueling when doing the field work.

/BAH

 

[John Larkin]

On Sun, 10 Aug 2008 18:58:58 -0700, "Rob Dekker" <rob@verific.com>
wrote:

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:c0ou94h6skor1kicrp0brqo6eoq0ruc5on@4ax.com...
On Sun, 10 Aug 2008 13:14:39 -0700, "Rob Dekker" <rob@verific.com
wrote:


"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news8bu94pft0vnpoh62j67rgvnujsovvpqob@4ax.com...
....

The ideal battery might use air as one reactant, have its chargable
component refreshed off-vehicle, and dump its wastes. Sure sounds like
a fuel cell to me. Or a gas engine.

Or a Zinc-air battery.
Which has the additional advantage that it produces no waste.

Rob


The vehicle still has to lug around the zinc oxide, which is heavier
than the original zinc. And it has to be collected and reprocessed.

That is correct, but is keeping the zinc oxide in the vehicle a big problem ?


Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is 12,500.
That's 34:1.

Well, that's kind of comparing apples and oranges.

Not really. My kid's Toyota Echo holds about 12 gallons of gas, which
weighs around 32 KG. That's a practical amount of fuel for a usable
car. 32 * 34 = 1088 KG, so the zinc-air fuel cell weighs over a metric
ton. That's when it's "full"; it weighs more when it's "empty."

Even if the fuel cell is 2:1 net more efficient, that's still 1000
pounds.

Any idea of the overall electrical efficiency of a zinc-air battery,
with the zinc oxide converted back to metallic zinc using electrical
power?

John

 

Well, that's kind of comparing apples and oranges.

The battery drives a very lightweight electric motor, at 95% efficiency
or so.
The gasoline drives a heavy ICE (+drivetrain/exchaust etc), at 20%

efficieny or so (if you are lucky).

The efficiency factor alone reduces the factor 34:1 to 7:1.
And the motor mass difference could make up for another factor of 4 or

so (simple replace the heavy ICE by battery mass).> > So in reality the Zi-air battery should be less than a factor 2:1 off

with a gasoline driven car, and probably at par in many

applications.

You can't just look at the weight of the drivetrain/exhaust, etc--you have
to compare
the weight of the whole ICE car vs the weight of the whole electric car.

Mmm. Is there a reason why the mass of the chassis and chairs and steering
and other stuff not related to powering the car would be much different for
an electric vehicle than for a ICE vehicle ?

I've mentioned this before on alt.origins. If they have a compromised
reasoning ability it's pretty much a farce to try to discuss science
or tech issues with them. For example, the creationists will say
something like, "two hearts beating = two souls" and all these
Carlinish jokes come to mind, "does a mechanical heart have a soul
too?" etc.

Try as you will to be polite but there is no practical way you can
avoid ridiculing them.


Bret Cahill


"Math is applied logic."

-- Nietzsche

 

[Bret Cahill]

The ideal battery might use air as one reactant, have its
chargable component refreshed off-vehicle, and dump its
wastes. Sure sounds like a fuel cell to me. Or a gas engine.

Or a Zinc-air battery.
Which has the additional advantage that it produces no waste.

Rob

The vehicle still has to lug around the zinc oxide, which is
heavier than the original zinc. And it has to be collected and
reprocessed.

Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is
12,500. That's 34:1.
An EV can go 80 miles. ???A tractor only needs to go one mile.
That's 80:1
2.3 X more energy density than necessary.

When the farmer gets out the tractor, it usually runs for hours and
hours under load. The straight line distance isn't a factor.

That was back in the old days _pre_ peak oil.
Things might not be quite so simple post peak oil.

The requirements of farming haven't changed since humanity howed the
first row.

The industry has, however.

Some are having difficulty accepting what should be a simple concept:

Pre peak: ?Easy street.

Post peak: ?Extra labor suddenly becomes cost effective.

Without tractors most everyone will starve.

That's why electrification of agriculture is a pretty sure bet.

Just another of your pathetic little pig ignorant drug crazed fantasys.

Biodiesel will be used instead, you watch.

Even if it is likely that biodiesel will predominate why risk even a
20% chance of bio diesel not being cost effective when that risk isn't
necessary?

Ralph Nader made a career of safety technology and safety doesn't
improve your chances of survival, let alone quality of life, nearly as
much as having backup energy technology.

Human labor isn't an option.

"Labor" here means some fat guy sitting in an air conditioned electric tractor.

You havent established that there will be any more of that post peak oil.

You haven't established that bio diesel will cost less than $10/
gallon.

Has anyone _ever_ gotten more than 2,000 gallons / acre-year?

If it were, Africa wouldn't be starving.

Even I don't go that far.

Americans did pretty well before the first tractor.

Much better than the Africans today.

The very first did in fact starve.

They were English subjects, not U. S. citizens.

The difference is the early English settlers had funny ideas about
personal hygiene. They thought bathing was unhealthy. They stunk so
bad all the game fled before it could be hunted and killed.

Oysters can't run or swim and therefore would have the perfect food.
There were thousands of tons of oysters in the James River but the
settlers were too stupid to eat them.

You're making the exact same mistake right now.


Bret Cahill

 

[Bret Cahill]

The ideal battery might use air as one reactant, have its chargable
component refreshed off-vehicle, and dump its wastes. Sure sounds like
a fuel cell to me. Or a gas engine.

Or a Zinc-air battery.

Which has the additional advantage that it produces no waste.

The vehicle still has to lug around the zinc oxide, which is heavier
than the original zinc. And it has to be collected and reprocessed.

That is correct, but is keeping the zinc oxide in the vehicle a big problem ?

Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is 12,500.

That's 34:1.

Well, that's kind of comparing apples and oranges.

The battery drives a very lightweight electric motor, at 95% efficiency or so.
The gasoline drives a heavy ICE (+drivetrain/exchaust etc), at 20% efficieny or so (if you are lucky).

Some posters here have no education in thermodynamics which is why we
must constantly explain that an electric motor is 3X - 4X more
efficient than a diesel.

The efficiency factor alone reduces the factor 34:1 to 7:1.

And the motor mass difference could make up for another factor of 4 or so (simple replace the heavy ICE by battery mass).
So in reality the Zi-air battery should be less than a factor 2:1 off with a gasoline driven car, and probably at par in many
applications.

Not worth worrying about.

Advantage is that the Zi-air technology is very simple.
Disadvantage is of course that an infrastructure has to be put in place to replace and recycle the Zi-oxide.

Gotta spreadsheet it including the cost of oil quagmires and then
convince the general public as well as Congress.


Bret Cahill

 

[rlbell.nsuid@gmail.com]

On Aug 11, 7:33 am, BretCah...@peoplepc.com wrote:

Mmm. Is there a reason why the mass of the chassis and chairs and steering
and other stuff not related to powering the car would be much different for
an electric vehicle than for a ICE vehicle ?

I've mentioned this before on alt.origins. If they have a compromised
reasoning ability it's pretty much a farce to try to discuss science
or tech issues with them. For example, the creationists will say
something like, "two hearts beating = two souls" and all these
Carlinish jokes come to mind, "does a mechanical heart have a soul
too?" etc.

What does this have to do with the weight of an electric tractor?

An electric tractor will be just as heavy as the comparable diesel
tractor, or it will not be able to pull the same equipment in the same
conditions. Electric forklifts are exactly the same weight as ICE
forklifts, but replace the heavy steel counterweight with a heavy lead-
acid battery (high battery weight for a forklift is a feature, not a
bug). My experience with electric forklifts is that the battery is
sized to last, under expected use, at least as long as the recharge
time, so that you can get away with only two batteries.

Tractors pull ploughs through soil and haul heavy loads around (hence
the name tractor), so long as it does not sink into the soil, weight
is a feature of a powerful tractor, not a bug. Traction is a function
of weight and friction, so heavy-duty tractors need heavy weights. A
light weight tractor is only capable of light work.

Unless your farm is really small, driving to and from the battery
station, even if the battery change itself consumes no time, is going
to be a serious usability issue. If the battery pack will not run
from at least dawn to noon, there may be acceptance issues. For
bringing in the hay, after cutting, but before the rain, may
necessitate a tractor that can have its battery changed in the field,
so it can run 'til dusk. Farming is a business with such slim
margins, that if an electric tractor does not save money in the
current crop, the savings may be too distant to be worth considering
the expense.

The best way to figure out if your electric tractor scheme is on the
right track is to go to a farmer and ask what sacrifices he will
accept for a cheaper to run tractor.

 

[rlbell.nsuid@gmail.com]

On Aug 11, 8:31 am, Bret Cahill <BretCah...@aol.com> wrote:

The ideal battery might use air as one reactant, have its chargable
component refreshed off-vehicle, and dump its wastes. Sure sounds like
a fuel cell to me. Or a gas engine.
Or a Zinc-air battery.
Which has the additional advantage that it produces no waste.
The vehicle still has to lug around the zinc oxide, which is heavier
than the original zinc. And it has to be collected and reprocessed.
That is correct, but is keeping the zinc oxide in the vehicle a big problem ?
Wiki puts zinc-air fuel cell density at 370 WH/KG. Gasoline is 12,500.
That's 34:1.
Well, that's kind of comparing apples and oranges.
The battery drives a very lightweight electric motor, at 95% efficiency or so.
The gasoline drives a heavy ICE (+drivetrain/exchaust etc), at 20% efficieny or so (if you are lucky).

Some posters here have no education in thermodynamics which is why we
must constantly explain that an electric motor is 3X - 4X more
efficient than a diesel.

Only if you ignore the efficiency of whatever makes electricity. We
cannot just pump electricity out of the ground, nor does it fall from
the sky in a readily collectable form. It has to be converted from
some other energy. Our best option, efficiency wise, is natural gas
fired, combined cycle plants with thermal efficiencies advertised at
60% (GE H1), so the electric motor is limited to 57%, not counting
transmission losses, and assuming a connection from the power station
to the vehicle without having to store it in a battery.

Diesel engines for a tractor can feasibly hit 35%, even if it spends
time idling between tasks. Really large diesels can hit 50%
efficiency through nothing fancier than turning slowly enough to get
an optimum burn. Turbocompounding can push the efficiency of a
tractor's diesel to 50%, too.

With battery charging inefficiencies factored in, the overall
efficiency of an electric tractor is not even twice as efficient as
the diesels currently in use, and not as efficient as an improved
diesel, so the only question is whether the electricity is cheaper
than the energy in the diesel fuel and that the farmer can afford the
investment.

This is why I think that producing synthetic oil from coal is probably
a better short term bridge between oil and fuel cells than battery
powered tractors.