viability of building a 30-40 hp electric utility tractor?

[westcliffe01]

I would like to question the math used by flusher. Just because an engine is rated 40hp on the dyno does not mean it is loaded to 40 hp in the application.

I probably have a few rounding errors on my back of the napkin calculation, but bear with me:

40hp ~30kw (its actually a tad bit less)
so over 8 hours one consumes 240kWH of power (8h*30kW)
This 240kWh is equal to 240 000Wh (x1000 to get Watts)
Since a Watt is 1Joule/second lets get the timebase to seconds

So 240 000Wh = 860 million Ws (multiply Wh x 3600 to get hours to seconds)

From the definition that 1W = 1Joule/sec I can get the formula 1J = 1Ws

Thus, to plow the field at full rated 40hp we will need 860 million Joules.

The calorific energy of diesel is 38.6million J/liter or approximately 149 million Joules/gal. Now we need to take the thermal efficiency of the engine into account. The most efficient diesels will have a thermal efficiency of about 30%.

Thus to determine the amount of diesel consumed one divides the work required by the calorific energy and then divide again by the thermal efficiency. Thus 860/149/0.3 = 19.3 gal.

That equates to a fuel useage of 2.42 gal/hr. If you use 1gal/hr it is just because you are running the engine at 16.5hp instead of 40hp. Or you are simply not operating for 8 hours. Taking 3 hour long siestas ?

So back to the math: 19.3 gal x $2.50 = $48.32 So at those costs, it would appear that electricity would reduce the operating cost by 50%. If one actually used that amount of power over an extended time (particularly off peak at night) one would expect the utility to cut you a break and get a major discount, thus reducing the bill further.

The other arguments regarding cost of the battery pack are pretty much on target.

Don't forget, there is more to a tractor that a battery and motor ! You still need the tires, wheels, axles. Some sort of frame to hold the whole thing together (and the massive battery box). A charge controller, a motor controller. Steering system. Electric / hydraulic power pack for the hydraulics / 3 point system.

If you convert tractors, a lot of the mechanicals are a given, but if you don't and you don't manufacture those parts you would be buying them from competitors unless you find independant suppliers who build for the aftermarket.

If the machine works in open fields, one can add a canopy of solar panels. You might get up to 3kW/hr at mid day and it will make a nice shade / rain shield. The batteries will never run flat if it stays out in the field, but to get a full charge would take several days of no operating.

This kind of thing has already been done by individuals. But not for plowing fields 8 hours/day. Tractors with dead engines are cheap and particularly if you use a 3 phase motor the control electronics can be quite affordable. No getting around an expensive battery and if it is going to get cold you need a warm place to keep the whole thing and an insulating blanket around the battery pack to keep the cold out while working.

 

[flusher]

I would like to question the math used by flusher. Just because an engine is rated 40hp on the dyno does not mean it is loaded to 40 hp in the application.

I probably have a few rounding errors on my back of the napkin calculation, but bear with me:

40hp ~30kw (its actually a tad bit less)
so over 8 hours one consumes 240kWH of power (8h*30kW)
This 240kWh is equal to 240 000Wh (x1000 to get Watts)
Since a Watt is 1Joule/second lets get the timebase to seconds

So 240 000Wh = 860 million Ws (multiply Wh x 3600 to get hours to seconds)

From the definition that 1W = 1Joule/sec I can get the formula 1J = 1Ws

Thus, to plow the field at full rated 40hp we will need 860 million Joules.

The calorific energy of diesel is 38.6million J/liter or approximately 149 million Joules/gal. Now we need to take the thermal efficiency of the engine into account. The most efficient diesels will have a thermal efficiency of about 30%.

Thus to determine the amount of diesel consumed one divides the work required by the calorific energy and then divide again by the thermal efficiency. Thus 860/149/0.3 = 19.3 gal.

That equates to a fuel useage of 2.42 gal/hr. If you use 1gal/hr it is just because you are running the engine at 16.5hp instead of 40hp. Or you are simply not operating for 8 hours. Taking 3 hour long siestas ?

So back to the math: 19.3 gal x $2.50 = $48.32 So at those costs, it would appear that electricity would reduce the operating cost by 50%. If one actually used that amount of power over an extended time (particularly off peak at night) one would expect the utility to cut you a break and get a major discount, thus reducing the bill further.

The other arguments regarding cost of the battery pack are pretty much on target.

Don't forget, there is more to a tractor that a battery and motor ! You still need the tires, wheels, axles. Some sort of frame to hold the whole thing together (and the massive battery box). A charge controller, a motor controller. Steering system. Electric / hydraulic power pack for the hydraulics / 3 point system.

If you convert tractors, a lot of the mechanicals are a given, but if you don't and you don't manufacture those parts you would be buying them from competitors unless you find independant suppliers who build for the aftermarket.

If the machine works in open fields, one can add a canopy of solar panels. You might get up to 3kW/hr at mid day and it will make a nice shade / rain shield. The batteries will never run flat if it stays out in the field, but to get a full charge would take several days of no operating.

This kind of thing has already been done by individuals. But not for plowing fields 8 hours/day. Tractors with dead engines are cheap and particularly if you use a 3 phase motor the control electronics can be quite affordable. No getting around an expensive battery and if it is going to get cold you need a warm place to keep the whole thing and an insulating blanket around the battery pack to keep the cold out while working.

You're right. 1gal/hr for a 30-40hp diesel running full bore is a tad optimistic. I checked a typical Nebraska test, this one for a 43 hp (engine) JD 5103

http://tractortestlab.unl.edu/Deere/JD5103.pdf

It burns about 2.9 gal/hr at 43.7 hp.

But the OP asked a feasibility question, which I was attempting to answer with my back of the envelope calculation.

 

[candersen10]

Thanks for the responses.

From what I have seen, the batteries and electric motor components do have faults but also have certain advantages. Extra weight from the batteries is in many respects a good thing and I'd imagine that it would be possible to develop a battery pack that could be removed via a hydraulic arm, allowing one to charge one while using another (this would obviously add a lot to the cost). Meanwhile, motors have few parts and produce peak torque from 0 rpm upwards.

The electric motor components seem if anything to be a positive for PTO type components. It is far easier to add a PTO and three point hitch on the front and rear of a tractor if all that is required is a few lines from the battery system to the motor and linear actuators. Mowers and other attachments might even have separate motors that could be more closely matched to the required application, thereby reducing power consumption.

The battery efficiency is certainly a major obstacle as is the cost of the electricity used to charge the batteries. However, it seems to me that the direction that we are heading will soon mean 5 or even 10 dollar per gallon diesel. At this price, I suspect that electricity may become a competitive source for tractor propulsion (assuming it is source from non-oil based electricity production centers which is certainly a big assumption.

Alternatively, what do people think of Hydrogen? New Holland's NH2 seems like a well thought out plan, but hydrogen is dangerous to transport, requires water to produce, and also requires a lot of energy to produce. Meanwhile, the current design can only run for 2 hours. However, the fact that one can refill the machine rather than recharge is a huge benefit.

Just thinking out loud. Thanks for all the responses. Staring at my command center stated 5-6 gallons/hour used on my Deere is really frustrating.

 

[have_blue]

Thanks for the responses.

Just thinking out loud. Thanks for all the responses. Staring at my command center stated 5-6 gallons/hour used on my Deere is really frustrating.

I think utility tractors are a great application for electric. No weight constraints, no aerodynamics, passengers, or ride comfort to worry about.

I have always thought 1 motor per wheel would be the way to go. Instead of having giant rear tires and tiny front tires, average them, and use 1 size. Instead of hydraulics (very inefficinet), use small motors or linear electric actuators wherever possible.

A 40hp tractor would be a monster. You may get by with around half of that and still have more than acceptable performance.

Small tractors usually don't work very long. 2 hours is a long session for most (except for mowing!) Small tractors aren't used every day, making them perfect for solar charging. A 150W solar panel would re-charge a huge battery bank in 5-6 days, if it wasn't drained too much.

Don't let anyone discourage you. When people start pulling out physical laws on you, they often don't think it realistic terms. Realistically, you don't run a tractor for long periods, and that's a huge advantage. I bet my average engine run time per session is well under 30 minutes. I bet it wouldn't be real hard to design a system that would easily get you 3 hours run time at medium throttle. And that would be a serious tractor.

 

[dynasim]

If the purpose is to transfer energy to a device that requires bulk energy energy transfer(like tillage equipment), batteries are a horrible idea.

The overall energy efficiency of those devices is low, and there are not possibilities for energy recovery(like electrical braking) which makes tranportation system better(but still not good). From what I have seen, a battery charging/discharging cycle, at peak efficiency, is somewhat like 75%. This is just the battery efficiency. At non peak efficiency, it is a lot lower.

One has to make the electricity, transport it to your house, convert it to dc, charge it into the battery, discharge it from the battery, control its flow, convert it to power. Every step has significant losses.

The biggest efficiency gain about using batteries is that you bypass the taxation system(for now), which I do not think is a good thing, as everyone ought to pay their share.

The commercial uses of battery powered electrical equipment are in places where the purpose is not to dissipate energy, but provide mobility(which if the system is designed correctly, dissipates very little energy).

If the primary purpose of the tractor is to move thing around the yard with an FEL, or drive a spraying rig, you may have a workable concept.

Best Regards
Chris

 

[BobRip]

On hydrogen, it has more issues than batteries. It takes as much energy to make as it can put back out at 100% efficiency. Of course you don't get 100% efficiency. You also have to compress it, which takes additional energy. I think all of the concepts for hydrogen assume cheap solar or wind energy, which we don't have yet. Hydrogen being a very small and fast molecule is hard to stop from leaking. It also has a low energy density which means large tanks. The Institute of Electrical and Electronic Engineers (IEEE), had a good article on this. If memory serves me right the efficiency from production, through transport, to use was less than 10%. Right now batteries a better.

 

[bw_wis]

Take a look a electric lift truck technology. I used my first one in '94 and wasn't new then.

Great concept. The fact it would be very quiet would appeal to my neighbors since I tend to work very late at night.

Good luck.

 

[Danno1]

.

Here's another angle to think of: if your diesel runs dry a mile fr home you could (theoretically) carry a 5 gal cont of fuel out to it to get it going. If the elec tractor discharges its' batt bank a mile fr home (out in a muddy field) how do you recover it?

.

 

[sizzami]

if you are going to build a battery powered tractor why not just build a coal burning one and cut out the middle man?

 

[slowzuki]

Good point sizzami, perhaps a steam powered unit so we could burn wood or cardboard wastes in it.