1. Is 3 phase power more efficient to generate/use?

  2. How difficult or complicated is it going to be to provide balanced single phase load(s) from a 3 phase service? (equipment & controls required)

  3. If I decide to get connected to the utility at some point, what types of equipment will I need? (3 phase compared to single phase.)

  4. Is there anything else I should be aware of when determining whether to generate single or 3 phase power for my use and potential grid integration?

Here is my scenario:

I am purchasing a 2 acre property that has two buildings:

  • a 16'x24' insulated, wired and plumbed single story steel pole bldg (converted dog kennel/house)
  • a 20'x24' plywood clad, uninsulated, unwired pole shed (workshop).

There is no electric service on the property as the original electrical supply lines were removed and currently the closest transformer is approximately 300' from the closest building.
There is propane service and wood stoves together with a few small solar panels and a small wind generator hooked up with battery banks and inverters that supply a minimal amount of energy and heating for the buildings.

I have the capability to make biodiesel and clean vegetable oil and a couple diesel engines that can be used as power plants. I am looking into getting a PTO generator (tractor driven Power Take Off) to attach to the diesel engine which then can power the workshop and home and potentially a greenhouse in the future.
I envision also reclaiming and utilizing waste heat from this setup for space and/or water heating/cooling.

Looking forward as I start to layout electrical service and outlets in the unwired workshop and contemplate a separate aquaculture greenhouse in the future, I am trying to determine if my needs would best be served by providing 3 phase or single phase power for the tools and equipment I will be utilizing.
I currently do not own any 3 phase equipment but I am aware of the ability to acquire such at considerably reduced cost via auctions and used equipment sales and am cautiously leaning in that direction. My concerns however center around how costly and complicated it is going to be to separate and provide my single phase needs with a 3 phase generator and which scenario would provide the most efficient production and utilization of the electricity I will be producing. The house is already wired and utilizing single phase AC via PV and wind power. The load is small and optimized for off-grid living. Additional generator provided supply would allow conveniences not currently possible.

As it is my intention to start with a 25kW generator, I am also concerned about not wasting the excess capacity of the generator as my initial needs are considerably less than the 25kW potential maximum. Therefore, I want to investigate if it would be cost effective to pursue a grid intertie and dump my excess capacity to the grid as opposed to just dumping it or before designing an alternative storage/utilization capacity somehow (e.g. batteries, water pumping, alcohol distillation, thermal storage, greenhouse lighting, etc. etc.)
I assume that a future aquaculture venture would likely benefit from 3 phase equipment (lighting, pumps, ventilation, etc.)

My desire is self sufficiency. Waste of any kind is a pet peeve. Therefore the thrust of my questions revolve around:

Is 3 phase a more efficient method of producing and utilizing electrical energy and would it be smart to start with 3 phase generation and step down to provide single phase and possibly grid intertie requirements or should I generate single phase and step it up for specific 3 phase applications?

Cost is definitely a factor in this decision-making process. Therefore, I would like to know if installing 3 phase distribution infrastructure (wiring, transfer switch(s), inverters/converters, etc.) would be smarter than installing single phase distribution infrastructure (wiring, transfer switch(s), inverters/converters, etc.)?
I know that without specific equipment specs and firm usage applications it is impossible to arrive at precise cost estimates but in generalities, (conversion and control equipment, wiring and distribution infrastructure, generation, distribution and utilization efficiency, etc.) which is better and why, 3 phase or single phase?

Note: I'm in Wisconsin, USA. I am in a rural area with single family residences and farms. I don't envision needing 3P in the house, only in the shop and future greenhouse(s) or other crazy experiment(s).

Addendum: I will be producing potentially up to 25kW of electricity using very cheap fuel (vegetable oil and/or biodiesel) with a PTO driven generator designed for continuous operation. My conundrum is to find a use for the electricity generated in the most efficient manner. I have the option of generating either 3 phase or single phase primary power. The shop building is not wired for electricity and there currently is no greenhouse or other major loads to utilize generated capacity. Generated electricity will eventually need to be distributed to various structures on a 2 acre property and there is the potential to tie in to the grid (if the utility will permit such). The house will not need 3P power and the shop will definitely need single phase to operate hand tools,etc. but major equipment such as saws, drills, grinders, welders, dust collection, lighting, etc., etc. can be either single or 3 phase. The same would be true for future structures such as a greenhouse. It would be easier for me to just go with single phase since the culture in the U.S. is primarily structured for it except in industrial/commercial applications. Nevertheless, I have to consider future equipment costs and distribution infrastructure costs with a desire to be efficient (line losses, conversion losses, etc.). My posting here on this venue is an attempt to educate myself further through the experience and perceptions of thoughtful, generous individuals who are much better versed in this field than am I so that when I eventually seek a local electrician I will know somewhat what to look for and inquire about. Thank you for your input and enlightenment.

  • Item 3 depends entirely on the electricity supplier you are dealing with.
    – Móż
    Dec 6, 2016 at 23:48
  • One reason 3-phase is used for high power levels is that the electrical power transfer (given a balanced load) is continuous and even. Single-phase alternators or motors will vary in torque at 120Hz as the voltage cycles 0V to +160V to 0 to -160V sixty times a second. At some power level, that becomes a BIG problem. When you are using (for example) multi-megawatt alternators at a hydroelectric dam, that would mean a LOT of vibration and metal fatigue. quora.com/… Jul 30, 2021 at 3:48

3 Answers 3


I'm going to assume you'e in the USA since you're using Imperial units.

1) Is 3 phase power more efficient to generate/use?

In bulk, yes. Three phase (or sometimes 6 phase/3 phase 220V in low-voltage countries like the USA) has more options for direct driving motors and generators, and the higher voltages mean lower currents and hence lower losses. This is why many workshop tools are 220V or two/three phase.

However, at small scale two or three phase power can easily just mean more parts, more wires and more cost. The inflection point depends on the fine print of what you're doing with the power. If you have a house full of single-phase appliances it's likely to be better to have single phase everywhere, even at the 25kW level (about 30 horsepower, I think). But if you have even one three phase machine in your workshop you're likely to be better off with a mutliphase system of some sort. I suspect the same is true of 220V US appliances - you may find that using a centre tap transformer to get 110V out of a 220V generator is more complex for the user than having a separate generator for the 3 phase/220V stuff.

If you're concerned about waste, a combustion engine generator for primary supply is out of the question (biofuel is at best controversial). There's almost no situation in which a generator is better than the alternatives. The exceptions are in remote, low-insolation, extreme weather locations. If you're living outside Barrow, AK, for example, you are probably going to have to use a generator. In Australia RAPS using petrol or diesel ends up costing more than 50c/kWh (usually much more) and it's been a long time since PV/PbS power cost that much.

If you have a load vehicle (ute, truck, or trailer) you may be able to cobble together a decent PV setup by buying second hand systems from other people. That will involve quite a lot of learning about those systems on your part (not least learning how to identify systems that are worth buying), and likely a complex house wiring setup. But if you DIY it could well be cheaper. This is why people paying an installer almost always put in new systems, BTW, the "save 20% by getting a haywire system that might not work properly" option just doesn't work out often enough to be worth the hassle if you're paying for labour.

2) How difficult or complicated is it going to be to provide balanced single phase load(s) from a 3 phase service?

Either very, or trivial. The usual solution is the brutal one of provisioning the whole system for the largest load on any phase. In practice that means arranging the loads so they're spread as evenly as possible because supply capacity is expensive.

How hard the supply provisioning is depends very much on the power source - with a battery system it's almost irrelevant as the phases are independent inverters and what matters is the total load. Buying a 10kW inverter plus a 5kW 3 phase inverter rather than a pair of 10kW inverters comes down to whether you actually need to drive a three phase machine (you would very rarely want to have only a single inverter, since that means one failure takes your electricity away).

But with a three phase generator the size is directly determined by the largest load - if you have three phases peaking at 10kw, 5kw, 5kw... you need a 30kW generator to get your 20kW output. Most cheap generators have a limit on how unbalanced the load can be, but I've never dealt with that problem (my experience is in music festivals where the dominant loads are typically quite well balanced)

3) If I decide to get connected to the utility at some point

You will need to negotiate with the utility. It's unlikely they'll let you feed a diesel generator into the grid.

4) Is there anything else I should be aware of when determining whether to generate single or 3 phase power for my use?

Yes, you need to work out where you're going to get the parts and who's going to maintain it. Unless you train to become a RAPS-certified electrician you will need someone to work on this for you. It's going to be much cheaper and easier if that person is local to you, which really means finding that person and asking what they recommend. Having the best setup in the world is useless if you have to fly a technician in from Germany every time it flashes a warning light at you.

Also, many modern appliances won't run directly off a diesel generator. You will need a decent UPS just to clean up the power enough to stop your electronics exploding and that includes stuff like washing machines and fridges. So the whole "I use simple machines that I understand" thing will only work if you carefully choose appliances that you understand. That means no fluorescent or LED lights, for example, as the voltage variations from a generator will dramatically shorten their lifespan (I have seen single digit minutes when plugging CF lamps into a generator... flicker flicker pop... ooops). It might be more reliable to refine your biodiesel to kerosene and burn that in lamps.

  • I will be producing potentially up to 25kW of electricity using very cheap fuel (vegetable oil and/or biodiesel) with a PTO driven generator designed for continuous operation. My conundrum is to find a use for the electricity generated in the most efficient manner. I have the option of generating either 3 phase or single phase primary power. Generated electricity will eventually need to be distributed to various structures on a 2 acre property. It would be easier for me to just go with single phase but I have to consider future equipment costs and determine distribution infrastructure costs.
    – Todd
    Dec 7, 2016 at 17:06
  • I asked whether the "cheap fuel" idea is really correct: sustainability.stackexchange.com/questions/5692/… Friends of mine who ran their van off food-waste vege oil found it hard to gen enough oil every week to make it work.
    – Móż
    Dec 7, 2016 at 20:55
  • @Todd it's usually better to build what you need now, and expand it later. While you're learning about this stuff it's easy to make expensive mistakes. I suggest getting a small-ish single phase generator to power your house as it is now, and use that to learn about the noise and other pollution problems, as well as the difference between "rated for continuous operation" and "capable of keeping the lights on indefinitely". Having a separate circuit and generator for the big loads will almost certainly work of cheaper in the long run
    – Móż
    Dec 21, 2016 at 2:19
  • most houses use 2-5kW as baseload, then another 5-10kW of peaking load (dryers, stoves, heaters), but usually that peaking load is at controllable times and it might be easier to have those on the "big generator" circuit that you start up for the 2-3 hours a day you actually need it.
    – Móż
    Dec 21, 2016 at 2:21

Another option:

  • Generate single phase. Run your house on this. Wiring your electrical system is much simpler, and can be done by anyone who can read and understand the equivalent of "Alberta Electrical Code Simplified"

  • In the shop, buy 3 phase equipment, and get a VFD (variable frequency drive) unit for each one. These have the advantage that you can set them up to start the motor using a lower frequency, and thus making for much smaller surges. Your first VFD unit should be for your well pump. Some pumps (Gould makes a line) have VFD's built into the controller, along with sensors that adjust the pumps speed to the demand.

VFD's run about $50+ $100/hp at the low end.


Importance of Three Phase Electricity

Three phase motors are known to have significantly higher radial power output than a single phase motor of similar design for the same electrical power consumption. [1]

Nicola Tesla demonstrated the math behind that and built corresponding devices to demonstrate the benefits of alternating current multi-phase generators and motors at fairs and exhibits. George Westinghouse successfully partnered with Tesla to make AC the distribution standard on the basis of its improved efficiency (and therefore improved sustainability).

Several others around that time found that three phases provided an optimal balance between motor and alternator efficiency and their manufacturing cost. These same economics and physics principles still apply today.

The Equipment Purchase Decision

If you expect to have motors, they will consume less energy for the same work output if they are tri-phase and the electrical power source is tri-phase.

Equipment exists to convert any of these electrical standards to any other one, however, there is a cost. From a sustainability point of view, the manufacture, installation, and maintenance of conversion equipment is undesirable if there is another way to achieve high energy efficiency without the equipment.

For lighting, LED lighting usually requires single phase and possibly at a Voltage below that of higher power motors. For them you could purchase a transformer at a fairly low cost to provide lighting and other devices like break room appliances with power. Such transformers normally lasts for decades, especially if protected from surges, harsh weather, and moisture.

In Summary

The entire choice revolves around the degree to which you expect to install asynchronous AC motors. [2]

[1] Power loss is reduced, and the devices run cooler as a result.

[2] Synchronous motors, such as stepper motors, use an entirely different strategy to powering their windings.

  • This reads like a very high level overview, rather than a specific answer. Could you explain more how a device to produce single phase power from three phase is more sustainable than a device to do the opposite? Ideally with specific reference to the scenario where the great majority of demand is single phase, as in most residential applications.
    – Móż
    Dec 18, 2016 at 21:20
  • 1
    I meant that the leap from a very high level overview of what sustainability is to quite detailed discussion of motor types is odd, and nothing you've written actually helps the OP make practical decisions. I appreciate that you're trying to answer a practical question without practical experience, but I suggest this isn't the right question for that. In this case the OP is very much "what search keywords do I use to find the device I want" and you're all "given an ideal heat engine coupled losslessly...". In your actual experience, are 3->1 phase converters cheaper than 1->3 phase?
    – Móż
    Dec 21, 2016 at 2:11
  • Typically, 3P power is run at a higher voltage for motor applications (277/480V in the US). Lighting which can run on a single phase of 277V power is readily available. Appliances, of course, typically require 120V, but this can still be supplied from a three phase service. So the transformer is for stepping down voltage, not converting 3P to single or split phase.
    – LShaver
    Jan 21, 2017 at 4:59

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