batteries (Zebra's, sodium/sulfur etc) are excellent :
Energy density ? 150 Wh/kg has been reported. Similar to Li-poly.
Even higher for NaS.
Cost ? That's a bit tricky.
Currently only one factory in the world produces these batteries.
But I'm looking into this.
Remember that this whole large battery business is in it's infancy.
The site give the specs for a Zebra battery at 90 Wh/kg.
The 300 kWh tractor used as an example in the thread
would require well over 7000 pounds of those batteries,
which would occupy over 78 cubic feet. That volume
computation is based on the example given of a 195 kg
Zebra at .13 cubic meter. See
The battery operating temperature is 250 C and must be
kept under charge when not in use to keep the temperature
there. If you allow it to cool, it can take up to 2 days
to get it up to temperature again before you can use it.
The farmer who has a tractor powered by this type of battery
is going to have one helluva job removing 7333 pounds of
batteries and hauling that to the recycler, and another
helluva job of installing the 7000 plus pounds of replacement
I did not find recharge time, but it will certainly cut into
the farmer's productivity, as compared to diesel.
Based on what is posted on the Wiki site and the thread
here, the idea that this technology, as it is today, can
be a practical alternative to diesel in tractors is totally
ludicrous. And that is without considering the purchase
price of the batteries and charging equipment, or the
cost of installing the charging equipment.
_My_ example was for the tractor crossing the field in the typical 6 -
10 minutes. (See above.) The 6 - 10 mph typical tractor speed figure
has been confirmed by other posters citing government and industry web
A 400 hp tractor running wide open moving at 0.5 mph would require
several months to work one square mile and, in 6 years, at the present
rate of spiraling fuel costs, run up a debt of a half a million
dollars just for the diesel.
The 0.5 mph strawman was generated by a useful idiot who unwittingly
helped me build the case for grid-battery.
Almost all field operations allow the tractor to recharge every 6 - 10
minutes requiring only 10 - 30 kW hrs/charge.
30 kW-hr/(0.09 kW-hr/kg) = 733 lbs. The overall drive train will be
lighter than the diesel + fuel tank.
I've mentioned this several times and everyone dodges this issue:
Grid battery farm electrification is possible with low density energy
storge devices, an advantage not shared by road hybrids or EVs.
Any argument for EVs or hybrid electric is, a fortiori, an argument
for grid-battery tractors.
And, _no_ pausing at the end of the field to recharge is _not_ a big
Right now farmers are paying truck drivers $100/trip to run 8 peso/
litre diesel from Mexico at a savings of only 40% over U. S. prices.
This ties up truck and driver time.
Instead of paying a truck driver to sit in line at the border why not
pay a tractor driver to sit at the end of the field?
At least you don't getting pestered by customs agents and junk food
peddlers sitting out at the edge of a field.
The hay guys seem to move fast -- they get across the field in 2
minutes -- but the rest spend 15 minutes each lap screwing around at
the end of the field lining up their lasers or whatever anyway.
You have to be kidding. Do you think farmers work almost every
waking moment during planting season because they like the hours?
Patience is in short supply during the spring. Any delay due to
breakdowns and such drives them nuts. The goal is to keep the planters
moving until the job is done.
Planting season starts around April 10 or so in my area of Nebraska.
Things generally get wrapped up by the second or third week in May.
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Instead of one 700 lb battery that stays in the tractor, two 350 lb
batteries would be cantilevered off both sides of the tractor with a
wire on both ends of the field. The batteries have a verticle rod
mounted on top to contact the wire.
When the tractor reaches the right hand U turn end of the field the
left outrigger scoops up a recharged battery. After the U turn the
discharged battery is dropped off for charging and can be picked up on
the next lap.
The right side battery is swapped out at the other end of the field
when the left hand U turn is made.
The batteries only last a few weeks and are changed - recycled like
Battery cost is about twice grid cost -- the combination is just now
about equal to the cost of diesel -- so in the long run it might be
cheaper to trolly wire the entire field or go with the super pivot.
There are all kinds of farm situations and there will be all kinds of
The original single battery single wire idea where the driver waits at
the end of the field for a recharge was the absolute cheapest easiest
electric tractor to prototype and demonstrate. It was just a way to
get a foot into the extension center door.
Sorry for the mis-quote.
I DID find a manufacturers folder that reports 119 kWh/kg (better than NiMH) :
MES DEA is constantly improving their batteries, and they are still quite far
from the theoretical limit, so we should see higher
numbers in the future.
Thanks for the correction
I agree. Although ludicrous is a big word, 'currently unrealistic' is certainly
Batteries are nice for small tractors for lawnmowers etc (replacing noisy,
inefficient 2-tact motors), but not for 400 hp diesel
workhorses in the big fields.
Electric drive (like the Caterpillar tractor mentioned earlier) make much more
sense currently for efficiency and torque
improvements on big-ass farm equipment.
Energy density just isn't a factor when you can recharge or swap out
batteries several times/hr.
. . .
We really need a tractor pull to show a 350 lb battery just isn't a
Barring some breakthroughs in algae, diesel will soon be prohibitively
expensive, with _any_ kind of drive. Why risk the food supply when
there is such an effort to go EV or plug in anyway?
The EV and plug in industry will require much more metal and other
materials for their batteries than agriculture will ever use.
And if battery costs don't drop very much, then there's always
straight grid, either a lot of trolly wires or something based on a
pivot irrigation system.
It is not 350 pounds. Using the numbers posted in the thread
(300kWh equivalent tractor, 90Wh/kg battery) it is over *7333*
pounds of batteries. Energy density most certainly is a
huge factor, if those numbers you & Rob have been posting
A 350 pound Zebra battery would yield 14318 Wh. That is
the equivalent of 19 horsepower - way too small for a
tractor on a farm.
SINCE ENERGY DENSITY ISN'T SUCH A BIG DEAL, WHAT ABOUT CAPS?
Sorry, no pun intended. My keyboard made an honest mistake.
Anyway, this would need to be spread sheeted to optimize and to
determine competitiveness but several wires over the field could
recharge multi farad capacitors in seconds.
Sure the caps would weigh more than batteries but they'ld last
forever . . .
Because the tremendous cost of the batteries
must be factored into the cost. I have two dead
batteries for my ThinkPad laptop, because I bought
a spare for nearly $100. This laptop has not used
anywhere near $100 worth of electricity, and the
batteries didn't last long at all.
Because unlike a car, you are beating on the
batteries at a far higher rate -- about two orders
of magnitude higher. What is barely feasible
for a car is obviously unfeasible for a tractor.
So instead of burning through a set of batteries
in two weeks, it could be one week or less than
one week. The cost of batteries would greatly
exceed the cost of the vehicle or the cost of
electricity. If the other killer arguments
against your proposal were not sufficient, this
one by itself is sufficient.
It does, but on a time-scale that is two orders
of magnitude longer. Farmers aren't going to be
spending tens of thousands of dollars every one
or two weeks to replace batteries. Your proposal
is an obvious non-starter. Calling people morons
who point this out to you does not increase your
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