Sure.
First, diesel will be around for decades for essential uses, and in a transitional period commercial consumption will out-bid personal transportation consumers for fuel. Most farmers are small and suffering, but most farm acreage is being managed by large organizations, and is much more profitable. Those organizations will just raise their food prices, and out-bid personal transportation (commuters and leisure travel) for fuel, so they'll do just fine. As farm commodities are only a small % of the final price of food, it won't make much difference to food prices.
For example, "beanfarmer" tells us that diesel is less than 10% of his costs, so that if diesel prices double, and food prices rise by 10%, he'll be better off http://www.theoildrum.com/node/6871/708181 . The distribution system, too, will outbid personal transportation for fuel. Given that overall liquid fuel supplies are likely to only decline 20% in the next 20 years, that gives plenty of time for a transition.
Second, farm equipment isn't optimized for efficiency, and optimization of fuel useage combined with electrification of the drive train could probably double fuel efficiency. For example, GE expects to reduce freight train fuel consumption by 44% with expanded electrification of the drive train. Here's a terminal tractor that reduces fuel consumption by 60%.
Farm tractors can be electric, or hybrid . Here's a light electric tractor . Farm tractors are a fleet application, so they're not subject to the same limitations as cars and other light road vehicles(i.e., the need for small, light batteries and a charging network). Providing swap-in batteries may be easier and more practical: batteries could be trucked to the field in swappable packs, and swapping could be automated, a la Better Place. Zinc-air fuel cells can just be refuelled. Many sources of power are within the weight parameters to power modern farm tractors, including lithium-ion, Zebra batteries, ZAFC's and the latest lead-acid from Firefly Energy, and others.
It's very likely that an electric combine would be an Extended Range EV: it would have a small onboard generator, like the the Chevy Volt. Such a design would be 50-100% more efficient than a traditional diesel only combine, and would allow extended operation in a weather emergency.
The combine described here http://www.theoildrum.com/node/6871 used about 73.5 gallons in a 12 hour day. That's about 450 kWhs (assuming 15% conversion efficiency*), or about 37.5 kW (or about 50HP on average). 450kWhs in a li-ion battery would weigh about 4 tons (at about .125kWh per kilo). Now, the combine we're talking about can carry 60,000 lbs of wheat, or 30 tons. If we reduce it's carrying capacity by 13% (inconvenient, but certainly doable) we can a days' worth of batteries.
On the other hand, we could choose to swap batteries once during the day, and only carry 2 tons of batteries.
Li-ion batteries cost about $350 per kWh these days (online sources range from $440/kWh to is about $2,000, but they're not selling large-format, high volume, purpose built industrial equipment), , so a 450kWh pack will cost about $160k (that's the wholesale price these days, and will be the retail price in 5 years). Over 30 days per year, we'll use 73.5 x 30 = 2,205 gallons, and use 13,500 kWh. If we want a 10 year payback, then we need to save $16k per year. The power will cost about $1,000 (night time power is cheaper, so the average cost/kWh might be $.07), so we need to save $15k on fuel. $15k / 2,205 = $6.80. gallon.
So, when fuel prices rise above about $7/gallon (timing?), or batteries get cheaper than $450/kWh (probably about 5 years out) electric combines will become competitive.
Or, we might get creative with strategies like cheaper shorter-lived chemistries: lead-acid costs roughly $100/kWh: LA would be competitive with diesel at $2/gallon. Now, LA weighs more: about 80 lbs per kWh (at 35 wHrs per kilo and 80% depth of discharge), so 450kWh would be 18 tons. That might mean swapping batteries every two hours to limit the pack to 3 tons. One advantage: with 4 hour fast charging, we'd only need two packs, which would reduce our cost by 2/3!
How fast do they recharge?
Depends on the chemistry: some li-ion chemistries can recharge to 80% in 30 minutes. OTOH, you might charge overnight. 450kWhs over 12 hours would be about 40kW: that's not that bad. That's a 440V, 100A load.
Most rural power grids are old and close to their load limit now, and many farms don't have large power services or transformers.
True. OTOH, their peak load is during the day, and battery charging would be mostly at night. The farm we discussed would need about 450kWh per day. A 15kW service could provide 1/3 of that in 10 hours: that's not bad. An EREV combine could be 1/3 powered by the grid, 2/3 by fuel.
*The conversions are very straightforward: diesel fuel contains about 40kWh, assuming 100% efficiency of burning. That means that our 73.5 gallons for the day can produce a maximum of about 3,000 kWhs. Now, even the most efficient marine diesels (2 stories high) only get to about 50% efficiency, and that's with a 2 story high 100,1000 HP engine running at the sweet spot of about 80% of rated capacity. A combine engine at best is unlikely to do better than 33%:
Two sources (hat tip to Paul Nash) back this up:
we see from http://www.dieselserviceandsupply.com/Diesel_Fuel_Consumption.aspx that a generator with 150KW output capacity (roughly 200HP) consumes 5.9 gallons per hour at 50% capacity (75KW output). That gives roughly 32% efficiency (75kWh divided by 236 potential kWh (40kWh potential kWh per gallon x 5.9 gallons)).
Another good source for a real world estimate is well known and published naval architect Dave Gerr. If you google Dave Gerr engine fuel consumption, it wil come up with the Google books link to his 2009 book "boat mechanical systems", and on p90, he has his formulas for fuel consumption. For diesel engines, gal/hr = 0.054xhp, so 1 gal/hr =18.5hp or 13.8kW, and for 6gal/hr = 84 kW, so pretty close. A boat engine is a good comparison to a tractor because they tend to run at fairly constant speed for long periods, and often at or near the optimum fuel efficiency point.
The inefficiencies built into the overall mechanical system likely reduce overall efficiency to maybe 15%. I'm really combining several forms of efficiency: engine thermal efficiency, drive train efficiency (including low utilization periods).
Examples of EREV efficiency in large equipment include GE's latest diesel train EREV work) and this new Caterpillar dozer, with diesel electric drive: http://www.cat.com/D7E .This is a production model you can buy today. The electric motor small compared to the engine and generator that power it. They claim a 25% improvement in fuel per ton of earth moved.
I strongly suspect that farm equipment hasn't been optimized for fuel efficiency (note that the majority of the Prius efficiency gains come from outside the hybrid drive train). Sources of inefficiency include hydrostatic transmission & torque converters etc, equivalent of a car automatic; accessory loads powered by always-on mechanical linkages (A/C, brakes, etc); tire and suspension flexing; and aerodynamics (yes, combines move very slowly, but everything adds up).
So, 15% of 3,000 kWhs is 450kWhs for the day.
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Can we really electrify such large pieces of equipment?
Mining gives us a lot of examples of really large electrical equipment: electrical mining equipment. Caterpillar manufactures 200-ton and above mining trucks with both drives. Caterpillar will produce mining trucks for every application—uphill, downhill, flat or extreme conditions — with electric as well as mechanical drive. Here's an electric earth moving truck. Here's an electric mobile strip mining machine, the largest tracked vehicle in the world at 13,500 tons.
A battery pack can fail via a dead short or, for some chemistry types a puncture - in both cases the dense energy can be released in a FAR shorter period of time.
Doesn't this seem a bit alarmist? Doesn't it seem like something the owner of a horse and buggy would have said about those dangerous horseless carriages?
To answer the question directly: the newest li-ion designs are mighty safe, and even the older designs never exploded.
What about just using a very long cable?
An alternative (courtesy of Paul Nash): go mining style, and do it with cable, not batteries. You woul need to have one cable (the A cable) on a reel and trailer, which starts from the SW(say) corner, and will run up the W side of the field. the combine has a B cable, connected to the A cable, and this is started laid out to halfway along the S edge of the field and back to the combine at the corner. The combine moves west to east along the south side, and drags the cable behind it, in the just harvested area. When it gets to the east side, the cable is now at full length, and the combine turns around and comes back, so the cable will be back to being halfway along the field. The A cable is then moved forward two combine widths, so it is behind the next run and you go again.
This is similar to how traveling irrigators (the big gun type, not centre pivot) drag their supply hoses. You then pick up the whole thing , move it over to the next line, and go again.
This might be easier, and cheaper, than messing with batteries. You just need to find an armoured cable to drag along, but those do exist. http://www.generalcable.com/NR/rdonlyres/3F3084D7-6B80-4FA8-9E99-A832A93B620A/0/PG03TypeWPwr.pdf
These are designed to be dragged behind mining equipment, so they can take some punishment, and being driven over etc.
For 100kW, and three phase, 480V, you would be looking at about 150amp/leg, so the #1 sized cable would do it. Not light at 3kg/m, but much lighter than any battery pack, and cheaper too.
Taking the wired concept a step further, you could set up the field in lanes, and run overhead wires for each pair, and use a trolley bus style pickup. Drive to the south side of the wires on the way out, U turn at the end, and come back on the north side, then switch over to the next set of overhead wires for the next lane.
They wouldn't even have to be over head, they could just be at chest height, like a normal farm fence, with a side pick up from the tractor/combine - think a heavy duty, two cable electric fence, and you just energise each length as you go.
Won't we just stay with fuel?
We might. Diesel farm tractors can run on vegetable oil, with minor modifications. Ultimately, farmers are net energy exporters (whether it's food, oil or ethanol), and will actually do better in an environment of energy scarcity.
Battery costs will continue to decline, and liquid fuel costs will likely rise at least a little. At some point those lines will cross, but it may well be long after most of the rest of the economy is electrified.
A grid-sourced approach might work best, in farm areas close to the (Many) new windfarms that are rising in the MidWest. This isn't just to hang the loads on that windpower, but to take advantage of the Grid improvements that the Windfarm brings along with it.
We really don't need one-size fits all solutions: we need a diverse portfolio.
6 comments:
Nick,
You have clearly answered your own question, with so many fuel options, farm machinery will definitely survive.
Farmers have a good history of mechanical innovation - they invented the combine plow, etc so, they will invent ways to keep them going.
Probably the simplest though,for now, is to grow their own oilseeds and run on straight vegetable oil.
It will cost more than using electricity, but the up front cost setting up for electricity, for large equipment, would be expensive, until the conversion equipment becomes off the shelf.
But that day too, is nearing...
Good points all. I watch the neighbors drag hoses full of manure all over creation while injecting in the spring and fall, easy to do something similar with a big wire. I think the overhead wire could be done with similar efforts and rather simple infrastructure. Diesel engines can also run on a substantial fraction of methane that can be created from manure on the farm. Veggie oil and methane could power much of the midwest's equipment. As you imply, eating will always be a priority.
I hope so, otherwise real hard times are waiting for me and my farm. I've worked so hard to put it on the run, that I'm not gonna stop now looking for solutions. Still, equipment replacement is the last solution. We don't have the money yet.
Nick,
I'm enjoying reading your blog, which I just discovered. I will continue to grit my teeth, however, at your constant use of BTUs, pounds per acre/foot, horsepower/gallon and other barbaric US measures. Makes it doubly difficult to follow some of your comparisons which use inconsistant measures between them.
Your wikipedia reference in this article (electric mobile strip mining machine) shows how it can be done.
Other than this obstructionism, good work and thank you!
Expat,
Good point.
Many sources and specifications are in English units, so in the past I've often stuck with those. Further, I suspect the majority of my audience are in the US, and I'd like this blog to be friendly to non-engineers. Finally, I like some aspects of English units, like the human familiarity of feet and horse-power, and the use of more convenient bases (inches and hours in base 12, minutes and seconds in base 60, etc).
Nevertheless, I'm using metric more lately...
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