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The Renewable Electron Economy Part VIII.2: The Electric Farm – 2 November 30, 2007

Posted by Michael Hoexter in Green Transport, Renewable Energy, Sustainable Thinking.
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In Part 1 of this post, I started to construct a scenario where a medium-sized farm would do most or all of its work using electric farm equipment. This model of a farm had 1 large tractor with 250kW(335 hp) maximum power output and 4 smaller tractors with 50kW (67hp) maximum power output (though working at 50% power on the peak energy day). I started to sketch out what would be the electric power demand on the peak day of the year and how many battery packs and battery pack exchanges (assuming that a quick battery exchange system was part of the tractor design) would be required to fulfill that demand within a workday of 10 to 14 hours. I have put to one side claims of companies that suggest that they have high energy density ultracapacitors that can charge and discharge very rapidly (EEStor for one). If such ultracapacitors were more than vaporware, a recharge tender vehicle rather than a battery exchange tender would be preferable as tons of batteries would not need to be changed in the field during the workday.

I figured that on this day all tractors would be required to do work for 10 hours and that the large tractor would work at 100% power while the 4 smaller tractors would work at 50% power. Road vehicles do not operate at anywhere near maximum power for most of the time they operate, so farm vehicles in certain tasks (deep plowing in particular or driving a heavy piece of machinery through its power take off drive shaft) are mass energy and power consumers. The diesel equivalent of the large tractor might consume 150-200 gallons of diesel fuel in a 10 hour day if it worked continuously at maximum power.

In actuality most farm tasks do not require maximum power but some do, therefore the variations in power among the tractors even on this peak energy use day. I assumed that half the weight of the tractor could be battery weight as the electric motor would be much smaller and lighter than the equivalent diesel motors it would replace. I assumed the total weight of these tractors would be the same weight as fully ballasted diesel tractors of a similar power rating. Using current lead-acid technology, there would need to be many battery exchanges with the high power tractor operating at full power all day (13 exchanges) but less with smaller tractors working at half-power (3-4 exchanges). Using current lithium-ion technology, there were much fewer if any battery exchanges per workday but of course much greater expense to purchase the battery packs using approximate pricing for 2007.

A table of the calculations for this scenario can be found here.

Charge Infrastructure

The type of battery makes a big difference in the amount of in-field battery exchange required and it also makes a difference in the size and power of the available charge infrastructure. We will assume that the tractors can plug in and recharge their onboard batteries at the same rate as battery packs on the external charger.

The charger and spare battery packs would be installed inside a vehicle-accessible shed or barn, especially in colder and wetter climates; in warmer, drier climates, a open shed with a roof may be sufficient. The battery tender or tractors would need to be able to dock on the recharge racks and have access to the batteries so that the battery enclosures or transport sleeves could interface without unnecessary lifting of the tonne or half-tonne battery packs. The battery packs might be stored on recharge racks with fittings that allow easy lock and release of the packs by horizontal sliding on rollers. A hydraulic mechanism might push and pull the packs in and out of the charge racks into either the battery tender or the tractors themselves.

The number and size of the farm’s battery inventory would depend in this example on the battery technology (lead-acid and lithium ion), its quick-charge potential, and the power of the charge unit. We will assume that all batteries, battery packs and vehicles have the power electronics and wiring to allow complete recharge within 60 minutes, which is within the claims of makers of the current generation of nanostructured batteries. Let’s say the charger operates on a 480V 220 amp circuit with a 106 kW power capacity. This means that the charger can recharge 4 of the lead-acid (25 kWh) packs per hour or takes a little over 70 minutes to recharge one of the 125 kWh lithium ion packs. In my calculations, I’ve allowed for there to be three times as many offboard as onboard lead acid batteries, with a one to one ratio for lithium ion packs as they carry more charge and therefore last much longer in the field than the lead acid packs.

Battery Inventory

The all-electric farm, in order to handle a total peak day energy use for the 5 tractors of 3.5 MWh (3.5 million watt hours) would use an electric tender vehicle (a specially designed truck with cranes or hydraulic battery pack tubes that remove and “inject” battery packs into the tractors or the charger stand) that also uses the same type of battery packs as an energy source to do the work of exchanging and carrying the heavy batteries to and from the charger to the tractors in the fields. I have assumed that the battery tender would need 25 kWh of energy to do one complete exchange whether for a smaller or a larger tractor (though in reality there would be somewhat less energy required to exchange 2.5 {small tractor} rather than 8 {large tractor} tonnes of batteries). The farm total, for all mobile uses, will have energy needs that vary then from 3.55 MWh for lithium ion to the much higher 4.225 MWh for lead acid, the difference being made up by the 25-29 battery exchanges performed by the battery tender with the lead acid batteries versus 2 exchanges with the lithium ion battery packs.

The farm’s battery inventory will vary by number, weight and cost of batteries, depending on battery chemistry, given that we are planning for 3 times the number of offboard charging batteries for the lead acid chemistry while just a one-to-one ratio for the lithium ion batteries. The battery packs in this scenario are either one metric tonne (2200 lbs) or a half tonne, for either chemistry. The large 250kW tractor would carry 8 metric tonnes while the smaller 50 kW tractors would carry 2.5 metric tonnes of batteries (we will assume that the larger tonne-sized packs are exchanged on the smaller tractors rather than a single half tonne pack).

As the lithium ion batteries on the four smaller tractors do not need exchanging on our peak day, we will only allow for a single tonne-sized battery pack to remain in reserve for these tractors. The 250kW tractor is working at peak power all day in this peak energy day scenario (on other days, the smaller tractors might work harder and therefore use extra batteries that on the peak day are used by the larger tractor) so requires reserves for all 8 of its battery packs. We are then looking at 12 metric tonne-sized battery packs off the tractors on the chargers with 18 metric tonnes of battery packs on the tractors. The tender requires one metric tonne sized battery pack to do its work (more than enough for 2 battery exchanges). We are then looking at 31 metric tonnes worth of lithium ion batteries for the entire farm distributed in 29 tonne-sized packs and 4 half-tonne packs with a total capacity of 3.87 MWh. Assuming an energy density of 125 Wh/kg (the energy density of the Tesla motors ESS) and a 2007 cost of $.48 per Wh, the 2007 battery cost for the lithium-ion based farm would be $1.857 million dollars.

The battery inventory picture is somewhat different for the lead acid battery-based system. More exchanges, more offboard battery reserve, and lower energy per unit weight means greater total battery inventory tonnage to supply the tractors and a much harder working battery tender. The onboard battery capacity for the 5 tractors will be 450 kWh and offboard will be 1.35 MWh. The battery tender will need to carry two tonnes of batteries for its own use in order to be able have the energy to do 25kWh battery exchanges and exchange its own batteries after pretty much every exchange (the capacity of the lead acid pack is 25 kWh). The battery tender would need to work at a frenetic pace all day to be able to effect 25-29 exchanges. Offboard, then there would need to be 60 tonnes of batteries on the charger and onboard 20 tonnes on the 5 tractors and the battery tender for a total of 80 tonnes of batteries. Despite the increased tonnage of batteries needed, the 2007 cost of the lead acid battery inventory is relative to the cost of the lithium ion battery inventory, favorable: with lead acid batteries at $.12 per Wh and 25 Wh/kg, the 80 tonnes of batteries with a capacity of 2.00 MWh would cost just $240,000. The lower capacity requirement and therefore much lower than 1/4th the total cost of the lead acid batteries is due to the more complete usage of the lead-acid capacity through more battery exchanges; in the lithium ion scenario there is excess battery charge both on the battery charger and onboard the smaller tractors.

Farm Energy Requirements and Renewable Energy

One of the major advantages of using electricity is that it is a highly flexible energy carrier that is particularly suited to using renewable energy as its primary energy source. In addition electric motors are about 3 times as efficient as internal combustion engines, and have high torque at low rpm, perfect for farm work. On a given farm there may the opportunity to use wind, solar, biogas, or waste biomass to generate electricity, beyond the use of the latter two to generate process heat for crop drying and barn-heating. Before we design any renewable energy systems for the electric farm, we first need to determine what are its overall energy requirements. As this is an idealized scenario we are free to make assumptions that would need in the future to be modified by more accurate statistics and real-world prototyping of a renewable and sustainable farm energy system. We will assume that non-mobile energy use on a farm is one-third of mobile farm energy use, which is slightly higher than the 20% of farm energy that was delivered in the form of electricity in 2002.

We have found that a lead-acid based battery-exchange system will require more battery exchanges which on our peak day scenario leads to a total mobile energy usage for our electric farm of 4.225 MWh while for the lithium-ion based scenario the usage is 3.55 MWh, barely over the energy needed by the tractors themselves. For the sake of simplicity, we will take a value in the midpoint between these two numbers and divide it by 3 to arrive at an average daily mobile energy use on a farm, which we will say is 1.4 MWh. We will assume that tractors are used 200 days/year, so annual mobile energy use for the farm will be 280 MWh. If non-mobile use of the energy on the farm is 1/3 of that of mobile usage, then we come up with 450 kWh/day, and assuming that stationary systems must operate 300 days/year we come up with annual non-mobile energy usage of 135 MWh. The proportions and total amounts of these figures will vary greatly depending upon the type of agriculture that is being practiced on the farm, the amount of on-farm processing that goes on, the climatic zone, and the types of crops. Using this scenario we come up with a total yearly energy requirement of 415 MWh.

What size of renewable energy system would deliver this amount of energy per year to the farm?

While in reality, to supply this energy, farms will have access to some combination of wind, solar and biomass energy, as well as grid electricity, we will design this model electric farm using solar arrays for comparative purposes to show how much farm land would be needed to generate the energy needed. While often, solar systems tied to the electric grid are sized to cover the energy costs rather than the actual site energy needs in kilowatt hours, here I will size the system to produce enough energy to cover all on-farm energy needs, assuming that the utility will credit the farmer for excess production. In net metering schemes, the electric utility credits a customer who uses a solar array to generate electricity at the daytime rate that is higher than average per kilowatt-hour costs. So solar arrays are sized to zero-out the bill, even though often this means that in net energy terms, the customer is using more than they are producing. Net metering does not allow system owners to make money from their installation, only to cover costs. The goal here is zero net energy.

A small innovation in the area of switches might take advantage of the PV solar array’s DC output, which is the same current type that batteries need. Sending current through an inverter to transform it to AC can lose from 4 to 8% of the energy. Ideally, a solar array on a farm with high battery recharging requirements would have a smart switch that directs current to the charger or to the grid depending upon the state of charge of the battery packs. For the purposes of this simplified model we are assuming negligible inverter losses in outputting AC to the grid.

To generate 415 MWh per year, the size of solar array depends on where the farm is located and what type of solar array is chosen. In agricultural settings, a typical larger array is mounted on the ground if there is not sufficient space on top of farm buildings. Arrays are usually mounted at a fixed angle to maximize production while minimizing the land footprint, while larger arrays sometimes use a motorized tracking system to follow the sun from east to west every day. Rob Erlichman of Sunlight Electric counsels agricultural customers to use a 10 percent fixed tilt or less to cut down on valuable land usage (higher tilt angles require substantially more spacing between them. Alternatively, arrays mounted on livestock-proof racks at sufficient height would allow grazing and sun shelter for animals below the solar array. In California’s Central Valley, an array rated at 200-250 kW could generate 415 MWh of energy per year. An array such as this would occupy anywhere from 1 to 3 acres depending on the spacing and the angle of installation of the units. In the Northeast an array of around 275-325 kW would be required to generate the same amount of power.

Photovoltaic arrays are very handy sources of power but remain expensive because of a shortage of crystalline silicon. On the other hand, the purchase or long-term lease of a solar array (or wind turbine) locks in energy prices (payments on the purchase of the array as the sunlight is free) for a period of at least 20 to 30 years, when fossil energy and grid electric prices will no doubt rise. Current costs for crystalline silicon PV arrays are somewhere in the area of $8/watt with the additional costs of $1 to $2 per watt being incurred for more distant connections to the grid. Taking a middle course of $9/watt for 2007, the array in California would cost before rebates $1.8 to $2.25 million and assuming a rebate of $2.5/watt, $1.3 to $1.6 million net. In the Northeast, the larger array required would cost from $2.48 to $ 2.92 million at current prices. We would expect pricing in 2009 to be significantly less, when more silicon production capacity is online. Cost projections by manufacturers of new thin film materials, like Nanosolar’s Powersheet, are hoping to reduce the cost of panels to $1/watt or less that may yield installed costs of less than $3/watt. Installations with these less expensive materials may occupy a larger footprint depending on their efficiency which is sometimes half that of the more expensive crystalline silicon arrays.

A farm with these energy and equipment requirements will probably occupy several hundred acres depending of course on the type of agriculture and crops. The solar array, depending on where it is installed and whether the land it occupies can be used for other uses, will use less than 1 or maybe 2% of the farm’s land. Generating electricity on the farm may not be the most efficient use of the footprint of the farm, especially if the farm contains no marginal or unproductive land. On the other hand, using farm buildings or pasture for energy production will duplex energy use upon the primary use, reducing the energy generation footprint to near zero.

Summary and Evaluation of the Electric Farm Concept

Farming will remain dependent on petroleum derivatives or biofuels with questionable environmental effects and efficiency until farm equipment manufacturers apply contemporary and near future electric vehicle technology to tractors, harvesters and other powered farming implements. Somewhat ambitiously, I have taken on a moderately difficult farming task, a peak energy use day on a middle sized farm, to see whether currently available electrical power systems might be able to handle the task requirements with no revolutionary technology breakthroughs.

Working through this scenario has yielded a number of crucial results.

  • Lithium ion batteries, now revolutionizing electric vehicle development, also would make a huge difference in high-energy, high-power requirement farm tasks. Because of the five fold advantage in energy content of these batteries versus lead acid, it may be possible to forgo the use of a battery tender and in-field battery exchange: of the 5 mobile farm vehicles, only the large tractor working constantly at full power all day required 2 battery exchanges, leaving the battery tender idle most of the day. While not ideal, it would be more economical for the tractor to travel back to the battery charger for an exchange even though it would interrupt work flow for perhaps 45-60 minutes twice during the peak-use day. While I haven’t worked out a price for the battery tender, eliminating this aspect of the farm’s workflow would be a large savings; all farm vehicles would either refuel directly from a high voltage charger or by exchanging batteries directly at the charge stand. By contrast lead acid batteries would either require multiple battery exchanges during busy workdays or curtailment of energy intensive tasks.
  • As energy dense as lithium-ion batteries are in the battery universe, lead acid remain by contrast extremely affordable. The 80 tonnes of lead acid batteries might cost around $240,000 while the 31 tonnes of lithium ion batteries might cost $1.9 million. Despite the tonnage of lead acid batteries required and the frequent changes, they cost in this scenario less than 1/7th of the lithium ion battery cost, because, in part, we have allowed spare lithium ion capacity in this scenario.
  • Reducing the power and energy requirements of farm tasks, especially as designed for electricity-powered machines, remains an area of huge potential savings and triple bottom line benefit. No- and low-till agriculture has been a big success as they both save energy and preserve soil integrity. Future modifications of farm tasks may allow farmers to produce as much food with less energy expenditure, less environmental damage, and lower capital expenditures on overpowered machinery.
  • Speculative high energy density ultracapacitors (read the always optimistic EEStor) would if their claimed attributes are real have a revolutionary impact on mobile re-charging of farm vehicles via a re-charge tender vehicle.
  • Reducing peak energy needs, at planting, at harvest, or during other energy-intensive tasks, will have a crucial effect on capital expenditures for energy storage or energy conversion devices. The experience of utility companies in instituting demand response programs may in part translate to helping farmers shift tasks to avoid excess capital expenditures, though the unique needs of plants, animals and the ecosystems in which they live may not be as flexible as commercial and industrial utility customers.
  • Land area required to generate electricity for the farm on the farm was calculated to show symbolically how the use of power implements need not require massive inputs of energy from outside the farm. The land area requirements for an on-farm solar array would under all but the most land-constrained and energy intensive farming conditions be negligible if electric farm equipment is used.
  • At least in the beginning, the capital investment in electric farm equipment is going to be substantially more expensive than that in its diesel brethren, especially if the more energetic lithium ion batteries are used. The lead acid tractor system (5 tractors plus spare batteries) with battery tender, would cost substantially more than 5 diesel tractors of the same size. A 330 hp diesel tractor costs around $200,000 USD while a 65 hp diesel tractor costs maybe $50,000 USD: just the batteries alone for the 5-tractor group would cost $240,000 USD. Despite this expense, costs of lead acid battery driven tractors will be within the same order of magnitude as diesel tractors, especially when the relative simplicity of their drive systems are taken into account. With lithium ion batteries, the costs at the present time are multiplied by sevenfold over the lead-acid option and probably 10 times the cost of the diesel tractor.

Energy Paths to a Sustainable Agriculture

The often-overlooked area of agricultural energy may yield a key area for developing large-scale battery powered or grid-optional work vehicles. In the early 20th Century, over a period of decades, agriculture in industrialized nations became dependent upon fossil fuels; it will not be easy to wean agriculture and by extension our civilization off its dependence on these fuels to produce food. While current arguments about agriculture focus on the size of the farm, its use of toxics, diversity and regional appropriateness of food species and its proximity to its market, the Electric Farm concept is applicable to almost every size of farm, from the market gardener to the largest agribusiness, no matter what their cultivation practices and proximity to markets. Despite the focus on energy here, I hope that all food businesses will continue to move towards sustainability in the use of inputs other than energy.

Analysis of the Electric Farm concept has highlighted some key areas where agriculture can move to greater sustainability and minimize energy and climate risk.

Reduction of Farm Energy Requirements

The movement of the last few decades towards low- and no-tillage farming is a bright sign pointing towards the future of farm energy use. Plowing/tilling the soil has been historically one of the most energy and power-intensive farm activities, for which first animal power was used and in the last century fossil fuel powered tractors. No-till and low-till farming was originally paired with increased use of chemical inputs to control weeds and pest formerly controlled by turning the soil. There are now efforts underway to develop organic no- and low-till techniques; previously organic agriculture has substituted physical and therefore energy intensive methods for chemicals.

Agricultural scientists and farmers might be able to work together to further reduce energy use by developing agricultural machines and implements that use energy more efficiently. Electric farm implements will have greater flexibility than fossil fuel driven implements as electric motors are much easier to scale to the appropriate size and power for a task. Furthermore, automated and robotic farm equipment may facilitate the development of new, more energy effective farm tasks that are less disruptive to the farm ecosystem.

Plug-In, Battery-Exchange Serial Hybrids

The all-electric farm may be a vision for a time in the future when batteries or ultracapacitors increase in energy density and down in price: to bridge the gap, it may be necessary to reduce but not eliminate dependence upon fossil fuels by using flexible fuel electric vehicles. The ultimate flex-fuel farm equipment that would minimize fossil fuel inputs would be a serial, battery-exchange, biofuel-capable hybrid tractor or harvester. Such a machine would be able to use grid electricity, charged batteries, biofuels and petroleum to do farm work. An internal combustion engine or a fuel cell would generate electricity for the electric traction and implement drive motors when the substantial batteries, charged from the grid or from local farm generators, are exhausted. The amount of onboard batteries would be limited by weight considerations and cost but these batteries could also be exchanged as in the Electric Farm scenario.

The addition of an electric generator to the battery-exchange electric tractor outlined in the scenario allows for a significant reduction or elimination of off-board battery inventory as tasks that require more energy can supplement battery energy with biofuel or fossil energy. Lead-acid or lithium ion battery capacity could be sized for all-electric use for 60-80% of farm tasks, reserving fossil or biofuel to cover peak energy use. The cost of the generator, fuel tank and its mount would be small in comparison to the overall cost of the tractor or several battery packs.

Commercialization of Electric Farm Equipment

A market for electric farm equipment will emerge in ethically motivated agricultural concerns that have lower daily power and energy requirements for one or more of their tractors. In addition, air quality regulators in intensive agricultural areas like California’s Central Valley may offer incentives to develop zero or near-zero emissions agricultural equipment.

Initial models of electric farm equipment will probably be serial plug-in hybrids with lead acid batteries at a size that will offer most of the functionality of a 40 to 80 hp diesel tractor. Because of cost concerns and the lesser emphasis on weight reduction in tractors than in road vehicles, lead-acid batteries will be an early choice. Generators for this equipment may be either gasoline or diesel engines capable of using biofuels.

Machine designers may start by mimicking the functions of internal combustion tractors but soon realize that electric drive offers additional flexibility that will lead to a new “no-compromise” farm vehicle that can do more than the equivalent traditional tractor. Another path to commercialization may be for equipment manufacturers to start by building small multi-use vehicles like electric ATVs and garden tractors like the Elec-Trak and gradually build up power and functionality as demand arises. With substantial decreases in cost for lithium ion or other high energy-density mobile electric storage, electric farm equipment will gain greater applicability as most farm tasks will be able to be achieved without emissions, especially when paired with renewable energy.

To speed commercialization efforts, a zero-emissions agriculture consortium could be formed by equipment manufacturers, farmers, farm advocates, inventors, engineers, and agricultural scientists which might help develop a research and development program. This program will help locate the most promising niches for growth in this area and best address issues of farm productivity, energy efficiency, and ecological sustainability as regards farm machinery and mechanization.



1. Homaro Cantu - November 30, 2007

You should write for the New York Times. I like the Eestor mention as I think they have the missing piece of technology to end our fossil fuel addiction.

2. terraverde - December 1, 2007

Thank you for your kind comments…I’m guessing that the New York Times would not allow such a sustained piece of speculation in their pages.

Against my better judgment I mentioned EEStor twice in this post…I am not one to stoke the hype for products that show troubling signs of being vaporware. What keeps them just barely credible for me is that they are backed by Kleiner Perkins, ZENN has invested in them, and their barium nitrate powder was certified to a certain purity by a third party. I am not ready to endorse their product, for what that would be worth, but I am allowing for the possibility that a product not unlike theirs could be produced. In this case, battery exchange schemes would become less attractive than quick charge as a goal for developing recharge technology. Quick charge, however, especially at the rate that EEStor claims for it, will require special cabling capable of handling the transfer of many kWh of electrical energy in a few minutes. Also a much beefier electric grid that can handle the sudden voltage drops that will occur when quick charging takes place.


3. Phil Timmons - March 11, 2008


Read this story after finding a link to the earlier first part. Thought the first was an excellent overview.

I am an EE working on utility scale RE projects, and from prior life experience, electric farming is of particular interest.

Just as observation — it seems this follow-on story falls in the Electric Vehicle “battery trap.”

Why the assumption that it would be needed or desired to operate the equipment on batteries? That tends to be very lossy — first in charging the battery, and then in recovery of the energy from the battery.

Electricity tends to be dynamic and likes to be used as it is generated. Have you began any studies into non-battery farming applications, or have any interest in that?

Thanks for your efforts, I think you are doing very good work.

4. Michael Hoexter - March 11, 2008

The point of the Electric Farm concept and the Renewable Electron Economy idea is that you are using batteries to power devices for a number of reasons outlined below. The Electric Farm wouldn’t be electric without batteries, though I suppose that a PHEV or multifuel tractor are suitable transitional vehicles.

The 15% round-trip loss of batteries charging and discharging I don’t consider to be very significant in comparison to the energy losses associated with competing fuel cycles. With biofuels or petrodiesel you lose 70% of your energy to heat in the engine which doesn’t even include the highly inefficient process of turning sunlight into biofuels via plants (as well as all the other issues associated therewith) which contains perhaps 0.5% of the original solar energy in it. The hydrogen fuel cycle loses 65-75% of the original energy of the renewable electricity and hydrogen has its storage problems as well.

So if we are to create a sustainable, affordable, mechanized agriculture, we will either need to prioritize and subsidize the use of petroleum in ag until the point when batteries and RE comes down a lot in price, or certain brave souls and companies will start pioneering the use of electric drive tractors fueled by renewable electricity. It will help if there emerges a discipline called “agro-ergonomy” which studies and reduces the amount of mechanical work per unit crop output, thereby reducing the amount of mechanical energy required to produce food (no- and low-till organic ag would be starts). It could be that we become so clever in our use of mechanical energy to farm and biofuels progress to the point where we won’t need much of them to cultivate food. But you will still be able to do many times more work with less of an ecological footprint with electric tractors and renewably generated electricity, stored in batteries that will be more energy dense than the current crop.

5. Phil Timmons - March 12, 2008

I guess I am still lost on the MUST-HAVE-BATTERIES dogma. (or bio-fuel for that matter).

Sorry, but I did not see any reasoned connection between converting available electric power to battery stored power and then converting it back to electric power just to use the electric power that was present to begin with. Does doing that make sense to you?

Not only are the losses (already mentioned present), but the start-up costs are much higher for including those batteries, as well as long term maintenance and replacement as they are limited life equipment.

Like I said, I think you started hard on the right track with citing the local generation of renewable energy to power equipment. That is great. But to not just use the power directly while it is there does not make sense. To borrow an old farming phrase — Make hay while the sun shines.

Your targeted numbers — 250 kW for example — is an excellent farm scaled application. (btw, while the exact math may say that is over 300 hp, in practice we do not budget much more than 1 hp per kW.) 250 kW / 250 HP is a reasonable output from an acre of solar thermal electric generation — which already is cheaper than coal — not talking PV, but rather solar thermal.

So sitting one acre aside can run all the power consumed by 100’s of acres. If this is roof mounted, a couple of large barns, as well as housing and garages can be placed under this.

So that 250 HP can easily run irrigation during solar prime time, as well as most other equipment during other times.

Maybe the battery thinking is from being sort of stuck on a model of equipment that goes round and round and back and forth across a field? As you may know center pivots (irrigation) and linear irrigation already do that with electric drive and no batteries.

Further, large scale electric equipment does not need batteries by virtue of its size, either. I have worked with 1500 hp draglines (large shovel cranes that could eat a whole farm in a day) and these use no batteries — just cord connections from line power.

While I can see the use of some battery vehicles to zip hither and yon (have put an forklift drive motor on a small tractor, myself, and run it both by cord and batteries), to do the mass grunt work with batteries is not real sensible to me when straight up direct power (DC or AC) is available.

Maybe this is a concept conversion thing we are stuck on? Sort of like a farmer of old looking over a modern tractor to figure out where the hay and oats go in? (still thinking in “horse” mode).

Electric farming would not need or probably even want to have equipment that was designed and optimized around petrol in a post-oil world, any more than one would want or need a harness or whip to drive a tractor.

But if you are interested in doing an exploratory essay on methods for profitable post-oil, all electric farming without batteries, I would be happy to help.

6. Michael Hoexter - March 13, 2008

Thank you for your out of the box thinking. It may very well be that electric farming implements or vehicles will be able to remain plugged in as they do their work. I have seen pictures of old Soviet farm equipment that uses trolleybus style poles on overhead wires.

Staying plugged in may be an option for some farms or types of farming but in other settings it may soon require too much electrical infrastructure built around some fields.

Also, I think commercial farmers would have a lot to say about the inability to use energy when the sun ISN’T shining. Our agriculture has evolved both under animal and now fossil fuel energy inputs to be able to work at night or under poor light conditions. At harvest or planting time, some farmers will work around the clock. There are so many timing issues involved that I wouldn’t want to dictate to farmers when they would have to use energy. There are going to be a lot of crop losses if farmers can’t use their machines whenever they need them.

Batteries (or a grid connection if the implements /vehicles can remain plugged in) will be well worth the investment. As I point out in my essay, the extra weight of batteries can be used as ballast for pulling heavy loads: now tractor operators need to add weights when they need extra traction. Plus having a stack of batteries connected to the grid will give farmers an additional source of income to help stabilize the grid (selling ancillary services) or store cheap nighttime wind power from neighboring wind farms. So, while I can see that you engaging in a thought experiment, my sense of the future indicates lots of electric energy storage. On the other hand, experimenting with different task requirements with different energy requirements will continue to occur, perhaps minimizing the need for storage.

So, I don’t see the emphasis on batteries as a lack of imagination or a fixation: the functionality they offer is well worth the 10-15% charge-discharge energy loss they represent.

Still, you may well yet invent the grid-tied farming systems of the future, I would assume in close collaboration with commercial farmers!

7. Phil Timmons - March 13, 2008

Hey Michael, interesting discussion, thanks.

Used to do commercial farming back a life-time ago. Corn, wheat and soybeans.

Can’t remotely take credit for any invention in this regard, just observation of another industry that tends to use non-battery electric power day or night, in 24 hour operations, year around, with all sorts of weather (far more demanding than farming).


Typically mining operation have far more material moved, are far more remote than most farms, and much larger footprints. (all challenges to full electric power). But the typical mine operation uses almost all electric — either self-grid or commercial grid operations.

Electric mine cars trains for underground, dragline shovels above ground, and conveyors and electric trains above ground. Even the typical large Terex dump trucks (diesel) that we tend to associate in popular culture with mining (sort of like tractors are associated with farming) are used less and less, and now only until the conveyor(s) (all electric) get built.

Like I was mentioning above, a solar thermal electric system (and again NOT PV) of about one acre produces power to more than cover the heaviest use by most farming applications. Most of the year would just be sending power up to the grid. During times of heavy operation or off-hours the farm can draw from the grid. But when looking at electric power sales versus electric power costs, that should be a net money maker for the farm, as well.


I know the following is not your issue, but for other readers, I probably need to jump into some myth busting at this point . . .

There is no electricity shortage in the US. At most there is a time of use issue. Only during times of “peak” use do we come close to using what is available. Peak in the market I design for – Texas and the West – only happens in the middle of Summer, in the middle to late afternoon. Everyone has on the Air Conditioning. And that is it. We turn on all the Gas plants and hydro in addition to the base load coal and nuke plants and run them into early evening while the day cools down.

Most of the time, there is so much base-load power available that entire coal plants are shut down and taken off line for rebuilds in the Spring and Fall, when electric power use drops.

The sham “need to build more nukes” you hear from folks with no knowledge of the power industry is ALL marketing hype being mindless repeated. The proposals for building of new nukes are that it would 80% government funding. Not only costs more, but takes years and years to build. This is a huge welfare program for the contractors/builders. Costs more to operate and then leaves a mess to clean up, as well. Build, operate and then clean up – all losses.

There are lots (and LOTS) of surplus electricity on the grid. Base load power is cheap to buy and there are large discounts to use it off-peak. Solar thermal electricity produces best during the peak use – the methods discussed here would put MORE power on the grid during peak and only consume from the grid during off peak.

With that out of the way . . . back towards what drives all the tractor and energy use on the typical crop farm . . .


Creation of the seedbed.

The need for a good seed bed is what drives the use of a plow. A mold board plow flips the dirt like a slow motion wave breaking along a sea shore. This places weeds and organics at the bottom of the wave to compost, and fresh dirt to the top. For tmi — http://en.wikipedia.org/wiki/Plow

The entire mold-board plow system is what created the need for the high pulling power for the high traction and high power tractor. Often a tractor is described in draw bar horse power – which is essentially its pulling power. An interesting aside — the “traction” portion of the word Tractor is now what we now totally associate with farming just as somewhere around 100 years ago, draft horses would have been totally associated with pulling plows (hence “horse power”).

The rest of the seedbed creation — After the mold board plow turns over the soil, a disk harrow is pulled over it to break up the clumps, and then a wide “drag” is pulled to smooth the soil to plant seeds. So that is typically four passes across the field just to get the seeds in the ground.

The “lite” version uses what is called a chisel plow that is a one pass plow to break up the top of the soil, followed by a drag and then planting. Again that is covered in the wiki article.

But in al that, it is the high traction / pulling power tractor is needed for plowing that is driving the methods – which are modeled after the horse methods they replaced. The other implements are made wider and wider to attempt to efficiently use all that horse power available.

There are a couple of alternatives to using this method to create a seedbed. Like you mentioned the Soviets did have some creativity. Even using surplus Army tanks (high power and high traction) to pull plows.

One alternative to tractors I have seen from the Soviet era was a cable pulling method that would drag a plow across a field to a stationary winch. The winch was moved down the edge of the field, so the motive device was required to only be mobile in one dimension. A present day electric grid application of this may be to run a power line down the edge of the field to power the winch and pick the power from the line as the winch moved along.

Current US farming does something like the cable pull method in a system called “travelers” for irrigation. An anchored cable is pulled onto a winch on a mobile wagon-mounted irrigation water gun. The power of the pumped water pulls the cable onto the wagon, moving it across the field while dragging a large water hose behind. These are often electric (grid) powered via a motor and pump which provides the water pressure that makes the whole system work.

A method that I am looking at for total electric (non battery) creation of seed bed is use of tiller/cultivator methods – and yes, this is typical small garden method, but there are commercial farm tractor methods of using tillers – here is an example — http://www.riouxinc.com/BushHogTiller.htm

As these require mostly rotational power – and not traction power, like a plow – they are well suited to be turned by electric motors. As they churn and pass through the soil they create a seed bed that is suitable for planting, and a planter can pass along behind in the same travel. This does the entire 4 pass (plow, disk, drag and plant) in one pass.

I am looking at mounting large scale electric motor powered tillers on a frame like a center pivot, with electric motor wheels – again like a center pivot. So all this could be done while using no batteries, hydrocarbon based fuel, nor bio-fuel, just electric line power, either produced at the site or from the grid, with the power coming down the frame.

After planting comes fertilizing, irrigation and cultivating (mechanical removal of weeds) if desired. As you are probably familiar center pivots and other style irrigators, you can probably see that using liquid fertilizer can directly deliver fertilizer to the field without use of petrol, bio-fuel or batteries. Again just line power driving the pump and drive wheels.

Mechanical cultivation is one area I can see use of small battery power tractors such as you are discussing, however, with current planting methods and weed herbicides, this is not often done in commodity grain crops anymore.

And then finally getting the crop out of the field. The largest challenge with a combine/harvester is tire floatation – or bearing of the weight — on the soft field surface – not really a power or traction issue. Adding battery weight to this would not be a good thing.

It is often the weight of the grain being collected on board that bumps the limits of design capacity. A 300 bushel grain tank holds 9 tons. (300 bu. X 60 lbs/bu = 18,000 lbs = 9 tons).

I recall one Thanksgiving Day some years ago — working 23 hours straight as a Canadian blizzard was bearing down on us. Only stopping to refuel and grab some turkey and keep going. What forced the situation were wet fields and the weight of the combine would sink and get stuck in the mud. We had to wait until the ground froze and then beat the snow. Finished the last hour as snow was blowing in about horizontal in a 40 mph wind.

But what drove all that fun was the equipment and the methods used – which is still about the same today — 25 years later.

A method I am pondering for this is again using the center pivot style frame with small grain heads (the front end of a combine) attached, feeding a cylinder (the part of the combine that breaks the grain from the shell or cob) and then vacuum/blowing the grain back to a central collection point down the structural pipe that would normally be used to provide water out along the irrigator. Again, no petrol, bio-fuels, or batteries required. This keeps the weight of the collected grain back at central storage area, rather than being hauled around the field.

If folks really really wanted to use the conventional tractor methods, I have considered some options for that as well – one could take an old Steiger and put a 200 to 400 HP industrial electric motor in it in place of the diesel and have a super tractor for about 1/5 the cost of a new diesel. Run it from dragline cable – like the mine shovels discussed above, and off you go. That would last for decades and save its cost many times over in the (non) use of fuel.

8. Dennis Rowan - April 4, 2008

Thank you so much for blogging. I am trying to start a company in Pa. and I am trying to learn as much as I can about PV. CSP may not work here but they are using it to the north in Ontario so who knows. I love the quote “Don’t let the perfect be the enemy of the good.” Use it myself. I am working with some big box owners trying to implement BIPV on their stores. Supply is a problem at this point. wish I could hook them up with some Nanosolar or Unisolar. And Pa Senate dragging feet on Gov. Rendells Energy Independence Act.
And yes if EEStor is for real then the new game has truly reached not the first inning but the fourth.
Look forward to reading more of your posts!

9. Exchange with Phil Timmons Re: the Electric Farm « Green Thoughts - April 7, 2008

[…] alert readers of this blog to an interesting exchange I had a few weeks back with Phil Timmons on my posts on the Electric Farm from last November.  I appreciate Phil’s expertise in this area and willingness to think out […]

10. Sirc Revilo - June 12, 2009

Is this thread still active? I have an interest in developing electric farm machinery but lack of comment on the concept is not encouraging, isn’t anyone interested….or do most people think their food keeps appearing on the shelf by magic. I think a little bit of starvation would do a lot to clarify the thinking!

11. Phil Timmons - August 2, 2009

Hello Sirc Revilo,

Sorry, I do not stop by too often, so just read your note.

Yes, still interested, and am building some now. I do not take any lack of comments or answers as anything good or bad, as this is a relatively new field and is way outside of many folks backgrounds, knowledge or understanding of the application.

In addition to these projects and the usual business of Engineering / Building stuff, I am teaching part-time at a Technical College, so I am bringing these projects in for building practice for the students.

If you would like to email me with specific questions, comments or requests for experimental builds and/or test runs, please email me directly at:


And put something like — ELECTRIC FARM EQUIPMENT — in the subject line, so that it will catch my attention if the Spam Filter grabs your email.


Phil Timmons

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