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Diesel vs propane generator as backup for solar system?

 
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Which generator type is "better", diesel or propane(dual-fuel) as a backup power source for an offgrid system?

Also, since it may factor into it, which has the best/simplest homemade green fuel alternative?
Where the one generator would be running on biodiesel, and the other could (presumably) be run on woodgas.

What do you think?  What would/did you all go with?

 
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I don't have either. But "the word around here" is that propane is only good for the convenience of hooking up to a large propane tank that your home already uses (and thus, near infinite genny time when the power is out). Other than that I hear that propane is an inefficient fuel source for a generator. No one I know off grid has a propane generator.

What do I know though, mine runs on gas hahaha.
 
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To me, it would come down to local resources.

Diesel generators/engines can be tweaked to run other fuels like biodiesel or kerosene in a pinch. If you are familiar with diesel motors you can generally tinker on your own stuff assuming you have the proper tools.

Propane, as another commenter has mentioned, would be something that I would consider if I had a convenient supply. Hypothetically you could run a 2k watt generator for something like 30 hours on a grill tank.

For my own personal usage, I find diesel generators to be a bit more friendly to work and troubleshoot.

Something to look into are multi-fuel generators, I don't know how reliable they are but some give you the whole gambit of options. I've heard of dual-fuel and tri-fuel options in recent years.
 
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Mine is gas. A dual fuel generator would certainly be a good option.

I would recommend going with whatever fuel you have other things for. I went with a gas generator because my car runs on gas and my mower runs on gas. So I can keep some in storage and use it for all of those. If I had a diesel truck, maybe it would make sense to have that. If I had a propane stove in the kitchen and a propane grill out back... then maybe propane makes sense to keep on hand.
 
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Propane is very stable, but not the most efficient.
Some say it is better for IC engines than gasoline.
Diesel is stable , but it does prefer to be warm.
Gas is unstable, but it's everywhere, for now.
Biodiesel requires more work than wood gas, well I should say , more work than running a generator off of charcoal gas.
You can make charcoal while heating your home or cooking your food, from scraps of wood and/or twigs, and  it keep very well.
This all makes me want to use a dual fuel gas/propane generator, run it on stored propane in blackouts, gasoline in a SHTF scenario, and a charcoal gasifier in an ongoing crisis.

I was already a propane grill user when my FIL bought a duel fuel gas/ propane generator.
He live next door, so that was more than enough for me to start accumulating more and more tanks.
I now have almost 10 propane jugs and a tool crib that sells propane by the pound(marked down Tuesday) around the corner from me.
Making char is an ongoing obsession.



 
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I think Timothy Norton is correct.

Diesel is common, lots of parts availability, many bools/videos, and non explosive.

Much easier DIY repair and much easier to source local repair if a problem.

Propane explosions were not uncommon when I lived in RV parks for several years. Almost all were caused by poor DIY or a lack of local repair services.    

Any off the grid solution that you can't repair isn't really off the grid.
 
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The other question is how and how often do you expect to use it.  Is it only for the big week long storm that happens once a year and you never want to think about it until then—propane. Is it going to run weekly/ semi daily during the winter to offset a lack of sunlight (a $5k generator can save 20-30k on panels and batteries needed to get through winter purely on solar—that pays for a lot of fuel). Then it depends a lot on size, location, and your logistics. For less than a 10kw generator, I’d say gas 100% (not sure if there is even an option in the us for a reliable diesel that size) for bigger it depends on which fuel you need on the homestead anyway, and a bit on your weather. Small diesels can be finicky in the cold. But they are definitely more durable and often actually quieter in this size range—they are just made for regular use where gas are often “emergency backup” so they are built to a price point  
 
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I say it depends. If a generator is a daily runner and a primary power source for your system then diesel wins with longevity and efficiency. If its primarily a winter charger and you want it to start automatically and in cold weather without fail every time then propane wins out.  Chances are good if you are off grid you are handling hot water and cooking with propane so its a natural extension. It depends on local specifics of course.  9 out of 10 installs I've been involved with choose a propane auto start generator. Portables are all over the map.
If you are going to choose an alternative fuel secondary generator I would recommend Charcoal powered. Woodgas sounds great but on variable demand generator applications the changes in engine demand can play havoc with a straight wood gasifier. Check out www.driveonwood.com in the small engines section for the most comprehensive guide to that. Make sure to choose your inverter accordingly to a model with Dual inputs usually labelled "grid" and "Gen" which is much easier that switching back and forth if you only have a single power input port.  
Cheers,  David Baillie
 
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Something I saw was a generator that fed into the batteries, along with the solar. When you need a lot of power for your microwave or oven etc, then you run the generator. The excess goes into charging ( a smallish battery). You get some from the solar during the day too. That way you're not running the generator for very small loads or wasting or losing what you make from the fuel.
 
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Because high-voltage residential panels are getting dirt-cheap now, I overpaneled my system by ~1/3rd more that what it would be designed for.  In the real-world, what this means is that I can fully charge my solar batteries, even on cloudy/rainy days.

The other real-world result is that the gasoline generator I designed into the system sat totally unused for several years, until the piston rusted in the cylinder and froze up the generator.  I was finally able to break it out by removing the spark-plug, spraying in WD40, and finally working the piston free.

Fast-forward to today, and I run the generator every few months, just to run it.  I really don't have any practical use for my generator except welding.

So, instead of investing in a generator, your money might be better spend increasing the amount of solar.  Most charge controllers have an amp limit that you don't want to greatly exceed.  You can overcome this by what's called "virtual tracking", that is pointing some of your panels in directions other than South, which is what most of us here do.

For those that want to see numbers, with my 48V batteries, the math says 3600W of solar is needed.  I started out with 4500W (15 300W panels), facing South.  I've subsequently added an additional 2000W of panels facing due West, instead of South.  This really helps in the late afternoon around dinner time, when power consumption goes up in the kitchen.  So, this almost doubles my total solar, while still staying within the 70A limit of my Midnight controller.

This really works the best on cloudy/rainy days when there is almost no direct light, but a lot of low-level diffuse light coming from all directions.  Although the arrays are only at maybe a max of 10% of what they are capable of, it's enough to get to the end of the day with a full, or almost full charge.

BTW, if you decide to add panels, design carefully if you want to add more solar serially instead of in parallel.  Charge controllers have very closely defined voltage limits that you MUST NOT exceed.  Remember that panel voltage goes up as the temperature goes down.  So, the voltage must be designed for the coldest day of the winter.
 
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Here is the way I see things:

Gasoline:
*Engine/gensets are cheap, ubiquitous, everywhere.  Gasoline is very easy to find.  Gasoline is fairly energy dense (lots of energy per unit of volume).
*Downsides:  Gasoline gets stale quickly, fire hazard, energy density not as good as diesel
*Verdict:  Lots of bang for your buck.  May not be perfect, but hard to go wrong

Diesel:
*Diesel fuel is very energy dense.  Diesel engines are very efficient.  A tank of diesel will run a long time.  Diesel lasts in storage much longer than gasoline
*Downsides:  Diesel engines are EXPENSIVE!  Diesel engines are NOISY (especially if run near a house).  Diesel can be hard to start in the winter.  Diesel engines produce dirty electrical power unless run through a power conditioner which can be another installation chore (necessary for running electronics).
*Verdict:  Diesel is a great option if you need your fuel to last a very long time, but be careful about the electronics and starting during winter

Propane:
*Propane fuel lasts longer than you will, never goes stale.  Propane burns very clean.
*Downsides:  Propane is the least energetically dense fuel of the three by far.  Worse, propane tanks don't really store as much as you might think.
*Verdict:  Propane is great for a backup generator that might sit for years without running but not be the best for running every day.

If it were me attaching a generator to a solar setup for intermittent backup/boost power, I would forgo the propane generator as it would run out of fuel so quickly.  Diesel sounds great as the fuel is less of a fire/explosive hazard than gasoline and diesel will run a long time on a small amount of fuel, but the generator is expensive and the power needs conditioning.  Noise is also an issue.  As much as I am a fan of diesel engines, it is hard to go wrong with a gasoline generator unless I will need to rely on a fuel supply for a VERY log time (go months without a refill).

My 2 cents

Eric
 
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Eric Hanson wrote:  Diesel engines produce dirty electrical power unless run through a power conditioner which can be another installation chore (necessary for running electronics).
Eric



Sorry, what? There’s no inherent reason why the fuel makes any difference to the quality of the power produced.
If anything a diesel should be cleaner because it doesn’t have the spark ignition system or worse a magneto.

“Good” power conditioners are very expensive and cheap ones don’t do much. A more effective method of cleaning dirty power from something like a non-sinewave inverter, is to run it into an “online” UPS. That will take your dirty power, dump it into a battery and then generate a nice sine wave from the dc.

Personally I’m more a fan of over speccing your solar panels and running absolute essentials off UPSs.
 
Eric Hanson
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James,

When I stated “dirty power”, I was referring to Total Harmonic Distortion which is quite high on diesel generators without a power conditioner.  The short of it is that diesel engines vibrate a lot and this vibration upsets the precise frequency of the ac power they produce.  I have checked a handful of various diesel generators because I am a fan of diesel in general, but I found that the Total Harmonic Distortion (TDC) is pretty high, much too high to safely and reliably run electronics for any length of time.  Don’t get me wrong, you can certainly plug your computer into a diesel generator and it will turn on and function, but the TDC will tend to reduce its life.  

Even ordinary gasoline generators are not ideal for electronics.  I have a Generac GP 5500 which is a basic level generator.  I have installed a dedicated, code-compliant transfer switch so that I can power my house directly in a power outage.  Unfortunately, I realized the TDC issue *long* after I bought the generator.  A diesel will only get worse.  You can check the basic specs yourself.

And you are absolutely correct about the added expense of a power conditioner.  A properly sized one for my 5.5 kw generator is not exactly cheap.  It almost has me thinking about whether I should install a power conditioner or just buy a low THD generator to replace my existing one.

James, you raise a fair question that gets little attention.  Thanks for bringing it up as I was less than clear with my earlier explanation.  I really wish that TDC got more attention from consumers (and producers) when making the decision to buy a generator.

Again, my thanks.

Eric

 
Matt McSpadden
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I'm with James on using UPS's for electronics. For those who are not familiar with a UPS, it stands for Uninterruptible power supply. Really its just a surge protector with a battery and a few bells and whistles.

While more and more appliances are getting sophisticated electronics, things like a fan, light, or vacuum are less effected by "dirty power" than a computer. So, I tend to protect my computer and TV with a UPS anyway... and don't worry too much about the rest of the appliances and whatnot in the house.
 
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If you have a large source ( residential size tank ) of propane and a moderate gen/fuel need, then propane is a fine choice. Propane has difficulty in cold weather sooner than properly treated diesel. Small tanks, <100lb, have difficulty giving enough vapor at temps of -30C or so and below. Diesel is fine down to -40C if proper winter fuel is available, all water is eliminated from system, and fuel is treated to prevent waxing of filter. Gelling is not usually a problem, waxing and any water always is. Gasoline wins for coldest weather, but is the least safe option.
I'm thinking propane gen set has cheaper up front cost per kw.
If cold is not an issue, then fuel availability and transportation ease, cost,  will help you decide. For us a trip to town for anything is a 4hr time commitment, no delivery of anything out here.

Diesel is beast for longevity, however, propane runs very, very clean, engine oil stays cleaner far longer than with either diesel or gasoline.  Seems good to me. We have a 6kw liquid cooled Honda gen set converted to propane from day one 25 years ago. Light usage, excellent results. To attempt to compare fuel consumption without exact side by side comparison seems a bit shortsighted.

Current crop of quality inverter/generator sets, 7.5kw+ either fuel source, would likely show THD<5%, w/stable or adjustable voltages. How much better do you need. They also derive their current mandated efficiency from complexity, just like an auto. Not as easily repaired as they used to be.

'Clean' pure sine wave power and auto start are great, but probably double the cost of your inverter.

High quality deep cycle batteries are cheaper per delivered kwhour/charge cycle of usage than any 'dual purpose or RV' battery. Best way to shorten the lifespan of any battery is chronic undercharging, and a generator with some little battery charger is the best way to ensure you recycle your batteries early. The harder you use/load your batteries, the better your charge system needs to be. My old Trace SW4024 cleans up and makes good use of 'dirty' generator power, I would not consider charging these batteries in any other way and we run all our house AC needs through it.

We do exactly as was mentioned at times. My 4.5kw Cummins/Onan delivers 20+ amps to an L-16  battery bank that would like to see 40, but we run it to take the occasional heavy load off of the system. 15-20% less power on propane than gasoline, believe. Another 1200w of panels/controllers if I made the space w/daylight usage, would be far cheaper and more cost effective long term than the 7kw generator/fuel I would need to get those 40 amps. That gen set would also cost 3-4x the 1000.00USD I paid for that efficient little Onan.
We get along by not needing power and by giving in to gasoline/propane generators for my welder and heavy/non-battery power tools. Simple.

Don't forget, cold ( well below freezing ) solar panels deliver as much as 20+% more voltage (not amps) than warm ones. that's real power if your MPPT controller can make use of it.
My south facing front yard slopes down to a 400ac lake that freezes over in November. All that snow, Nov. to Apr., means my solar gain is not as diminished by winter days as a lot of folk's.  
Been off grid part time/most time in B.C. for about 30 years. That's my experience.
Not enough information in the original question, why the thread answers are so varied.
 
James Alun
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Eric Hanson wrote:James,

When I stated “dirty power”, I was referring to Total Harmonic Distortion which is quite high on diesel generators without a power conditioner.  The short of it is that diesel engines vibrate a lot and this vibration upsets the precise frequency of the ac power they produce.

Eric



Wow, I hadn’t considered vibration causing harmonic distortion. Just checking but when you say frequency, you’re not referring to the fundamental (I’m assuming 60Hz)? But to other induced harmonics?

I’m curious about how these harmonics are being transferred. A belt drive to a separately mounted generator would eliminate chassis transfer but would let some of the vibrations be transmitted by the output shaft through to the belt.

Are you seeing lots of noise on top of a consistent 60hz sinewave (caused by harmonics) or a clean sinewave at 60hz but with an ever changing phase angle (caused by subharmonics)?
If it’s the former then a power conditioner may help as a massive inductor (any big coil) will act as a low pass filter. If is the latter then you’ll need to create the waveform again with an inverter or UPS.

I kinda wish that we had settled on 48V DC as standard power distribution (telephone standard) cos generating it cleanly is easier.
 
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Matt McSpadden wrote: Uninterruptible power supply. Really its just a surge protector with a battery and a few bells and whistles. .



Good point, I was thinking about server grade UPSs. The little single computer ones are little more than surge protectors with batteries. The “online” bit I said was to say that those actually convert ac to dc and back to ac again. You should be able to feed those the nastiest power and they will still output clean AC.
 
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James Alun wrote: Good point, I was thinking about server grade UPSs. The little single computer ones are little more than surge protectors with batteries. The “online” bit I said was to say that those actually convert ac to dc and back to ac again. You should be able to feed those the nastiest power and they will still output clean AC.



If you look, even the cheaper ones have pretty good specs including what you are calling online. I believe this is the same idea as a pure sine wave inverter being built in... but don't quote me on that. It can take whatever and gives off a nice clean signal back out. The expensive server grade ones can last longer and take more of a beating, but you can get fairly small ones for a few hundred that will do that too.

Probably not going to get good results with a $50 one from staples.
 
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James,

Regarding THD, you are right on track with your thinking.  If the diesel engine was replaced with a gas turbine (Just as an example—I can’t imagine a home backup gas turbine powered backup generator for a house!), then you would be absolutely correct that the generator would produce 60hz frequency (50hz in some countries, but that would be another machine) and given that turbine engines are incredibly smooth running, practically nothing would disturb that perfect, smooth 60hz sine wave.

But since the whole generator is a vibrating machine, the armature does not make a perfect circle as it completes a cycle.  It still completes its cycle on a 60 hz frequency, but the tops and bottoms of the sine wave are not perfectly smooth but in fact there are many little mini-peaks with each cycle.  These little mini-peaks act like little power spikes—nothing of the sort that will instantly zap out your electronics, but they are hard on electronics nonetheless.  In fact, these mini-power spikes are not great for batteries either and can lead to premature battery failure.  Obviously the rate of battery failure will depend on a number of factors including size of battery compared to the overall system, battery chemistry, etc.).

This is why some type of power conditioning is important.  Certainly one possibility is to run the generator power into a battery bank which then can be fed out to the rest of the system in an extremely stable, safe, clean form of power.  There are other types of power conditioners that can also protect batteries, but they are another expense and installation.  And has already been mentioned, diesel does burn dirty in that the oil will turn dark quickly.  Gasoline is second place in this category and propane is tops for clean burning.

Ultimately the choice is yours.  James, I hope this helps explain what I tried to explain earlier.

Eric
 
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Eric Hanson wrote:Here is the way I see things:

Gasoline:
*Engine/gensets are cheap, ubiquitous, everywhere.  Gasoline is very easy to find.  Gasoline is fairly energy dense (lots of energy per unit of volume).
*Downsides:  Gasoline gets stale quickly, fire hazard, energy density not as good as diesel
*Verdict:  Lots of bang for your buck.  May not be perfect, but hard to go wrong

Diesel:
*Diesel fuel is very energy dense.  Diesel engines are very efficient.  A tank of diesel will run a long time.  Diesel lasts in storage much longer than gasoline
*Downsides:  Diesel engines are EXPENSIVE!  Diesel engines are NOISY (especially if run near a house).  Diesel can be hard to start in the winter.  Diesel engines produce dirty electrical power unless run through a power conditioner which can be another installation chore (necessary for running electronics).
*Verdict:  Diesel is a great option if you need your fuel to last a very long time, but be careful about the electronics and starting during winter

Propane:
*Propane fuel lasts longer than you will, never goes stale.  Propane burns very clean.
*Downsides:  Propane is the least energetically dense fuel of the three by far.  Worse, propane tanks don't really store as much as you might think.
*Verdict:  Propane is great for a backup generator that might sit for years without running but not be the best for running every day.

If it were me attaching a generator to a solar setup for intermittent backup/boost power, I would forgo the propane generator as it would run out of fuel so quickly.  Diesel sounds great as the fuel is less of a fire/explosive hazard than gasoline and diesel will run a long time on a small amount of fuel, but the generator is expensive and the power needs conditioning.  Noise is also an issue.  As much as I am a fan of diesel engines, it is hard to go wrong with a gasoline generator unless I will need to rely on a fuel supply for a VERY log time (go months without a refill).

My 2 cents

Eric


Eric total harmonic distortion in my experience is more a function of the quality of the generator than the fuel type. I personally don't like the single cylinder diesels due to noise and vibration. If thd is a major concern the inverter generators offer a cleaner signal regardless of fuel.
 
Eric Hanson
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No doubt, inverter generators have the best, cleanest power.  They are also very quiet.  They would be the absolute perfect generators were they not so expensive compared to regular generators, but absolutely they are very nice generators.

Eric
 
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K Eilander wrote:Which generator type is "better", diesel or propane(dual-fuel) as a backup power source for an offgrid system?

Also, since it may factor into it, which has the best/simplest homemade green fuel alternative?
Where the one generator would be running on biodiesel, and the other could (presumably) be run on woodgas.

What do you think?  What would/did you all go with?



Mine is propane, hooked up to my 500 gal. tank and with auto transfer switch. Only issue with a permanent set up is that it is taxed. They assess a generator by the size of the house which is ridiculous. That would be like vehicle registration being based on the size of the driver. I'm still fighting this with the assessment company. Assessor is suppose to bring it up at their Nov. 18th meeting and I will hold his feet to the fire until they change how it is assessed, by the size of the generator (amps and kilowatts) like the size of a shed.
 
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I think distorted harmonics has more to do with the rotating mass of the generator than the type of fuel burned.

We often think of a generator has having a light load because its unattached physically, but that is not the case. Every time the home has a change in consumption whether it be turning on a light or shutting off a well pump, there are small, and large fluctuations to the load that the governor must account for.  The less rotating mass, and the more sensitive the governor has to be, and most governors are not that sensitive.

The clean power factor was amazing when I went from a portable generator to my tractor-driven PTO powered generator. Mostly because there was a huge difference in rotating mass. Instead of armature, flywheel, piston and crankshaft turning that might add up to 50 pounds, I was turning an armature, gear box, pto shaft, transmission, flywheel, pistons, and crankshaft that added up to hundreds of pounds. Since physics states that a body in motion wants to stay in motion, fluctuations in load were absorbed by all that mass flying around. Since only 1 RPM on the armature will change the frequency/hertz by one, and clean power factor is measured in one-tenth of a hertz/frequency, you can see why rotating mass has such an impact on the clean power factor.

 
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