Generator/Vehicles as Generator fuel usage

AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
Just joined here and saw this thread.

Frankly, I like the idea (Prius as generator).

Having been off grid (both intentionally and forced) many times, my experience has been that modern car engines make for really good generators.

I wouldn't dare to list all the combinations that I've used for emergency power, but they include almost every type of generator, and several cars.

What I found is that I could idle a small car engine (adjusted slightly fast idle) for weeks and end up with better fuel economy, significantly less noise, and lower maintenance than running a generator.

Basically I'm talking about hooking a small battery bank to the vehicle and using an inverter vs running a small generator.

The best I can figure, the car engine as a system is far more sophisticated than almost any stand alone generator. Fuel injection, water cooled, computer controlled ignitions, large oil resevoir... all the stuff that is just normal for a late model car.

Frankly, for the cost of any decent small generator, I could buy a used (maybe ugly) small later model car and adapt a 100amp alternator to it (if required), load the battery bank in the back (mini van would be great for this), and basically have a self contained mobile power station that really I would have a lot more confidence in than say a 2kw air cooled generator.

One time I ran a Pontiac Transport mini van at slightly high idle for almost 2 months doing this without any problems at all when my 2.5kw Honda generator gave up, and really it was so much nicer.
When it got low on fuel, no cans... I'd just drive it to the corner gas station.

While this was jury rigged, at that time I dreamed of creating a dedicated vehicle. Get a fuel efficient mini-van, fill the back with batt's (and inverters and the rest), adapt a pair of 200a alternators, cover the top in PV's...maybe adapt a larger fuel tank...etc.

That thought may be sidetracking the thread a bit, but the point is that I am one who would vote "yes" on using vehicles as generators. The Prius makes for an interesting candidate due to its inherent equipment and I am fascinated by the thought.

Cheers!
Sean

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    Sean,

    Make sure you do a full paper design first before you start buying hardware... I agree that what you are proposing can be a cost effective solution--But sizing the major components (loads, battery bank, solar array, alternator, etc.) is going to be important too for best fuel economy.

    By the way, where you able to measure the kWH/Gallon of fuel from your earlier experiences? In general, idling gasoline engines (and high idle) are not terribly efficient. However, when comparing the "high tech" of a modern automotive engine with the "low tech" of a typical genset--There can be advantages for fuel usage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Using a Prius as a generator

    I agree that fuel consumption when using a traditional vehicle isn't great. Figure on roughly 1 gallon/hr while getting 20 amps (250 watts) at idle from the alternator. I would not want to do that for more than a few days in an emergency.

    That said, the emission controls and over-sized engine on vehicles keep the smell and sound down compared even to the best inverter-generators. Even when my Prius is running it is quieter and doesn't smell like my Honda EU3000is even though they give me the same output and burn gas at the same rate.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    250 WH per gallon is not good at all...

    The Honda eu2000i will give you ~3.5 to 5+ kWH per gallon of fuel (25% to 100% load):

    ~4 hours * 1,600 Watts / 1.1 gallon tank = 5,818 WH per gallon (100% load)
    ~9 hours * 400 Watts / 1.1 gallon tank = 3,273 WH per gallon (25% load)

    I am a big fan for the "right size" genset for the job (or several gensets, one small one for small loads, and one large one for big loads).

    Trying to store fuel on site and difficulties obtaining fuel during emergencies make fuel a precious commodity.

    Even running Natural Gas (relatively inexpensive and don't have to store)--Becomes pretty expensive the typical 7-10+ kWatt gensets that you see advertised for home emergency use (can cost several dollars per hour to just keep the genset "on").

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
    Re: Using a Prius as a generator
    techntrek wrote: »
    I agree that fuel consumption when using a traditional vehicle isn't great. Figure on roughly 1 gallon/hr while getting 20 amps (250 watts) at idle from the alternator. I would not want to do that for more than a few days in an emergency.

    That said, the emission controls and over-sized engine on vehicles keep the smell and sound down compared even to the best inverter-generators. Even when my Prius is running it is quieter and doesn't smell like my Honda EU3000is even though they give me the same output and burn gas at the same rate.

    What?!?
    That just can't be right (I say in the most respectful way).
    A gallon an hour?

    I really wish I'd better documented it, but I recall running that little Transport for around a week on a 20gal ( might be 18 ) tank.

    20 gallons divided by 168hrs = .12 gal/hr. That was running at approximately 1200rpm.

    Now granted my 7kw diesel generator gets .16 gal/hr @ 1/4 (1750w) load, and approaches .75gal/hr @ the full 7kw.

    I hate to jump in here as the new guy and make a stir, but that just doesn't sound right.
  • AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
    Re: Using a Prius as a generator
    BB. wrote: »
    Sean,

    Make sure you do a full paper design first before you start buying hardware... I agree that what you are proposing can be a cost effective solution--But sizing the major components (loads, battery bank, solar array, alternator, etc.) is going to be important too for best fuel economy.

    By the way, where you able to measure the kWH/Gallon of fuel from your earlier experiences? In general, idling gasoline engines (and high idle) are not terribly efficient. However, when comparing the "high tech" of a modern automotive engine with the "low tech" of a typical genset--There can be advantages for fuel usage.

    -Bill

    Sorry Bill, I was not able. I have to go by memory of appx' runtime vs fuel capacity.

    What I have found though having done this a couple times is that the small car engine, because of it's tech' advantages, burns roughly the same fuel as the small generator (less in some cases), but that's where the similarities end. The car engine is quiet (and if designing one, you could make it even more so), and of much lower maintenance. Water cooled and large oil reserve (could also be increased), means that you aren't changing your oil every 100 hrs like on some portables, nor filling gas very often.
    Like I said before, you can drive it to the station for fuel, and in fact it serves the alternate purpose (excuse the pun), of being an extra vehicle if needed, and can transport itself to different locations without picking anything up (Sean drives it to Bill's house post hurricane...etc).
    Cheap... pick up a minivan with a good motor for under a grand... 100a alternator is about $100...etc. You could just do two of those for $200. The rest is just how far you want to take it (batt's, inverters, solar...wind...hamster..etc.)

    Considerations:

    1. consider diesel or bio-fuel
    2. You should consider building an RPM governor that works with your charging needs (I just did it manually)
    3. Get the smallest, most fuel efficient, and cheaply replaceable engine you can (Although it might be cheaper to just move the whole system to another used car when it's done)
    4. Adapt an automatic generator start like the one from Magnum Research so it doesn't need to run all the time (as mine did)
    5. Is a mini van more, or less portable than a small generator? Hmm...depends on how you look at it?
    6. What is the cost difference between a used mini van "generator" and a comparable output portable inverter generator?
    7. Can the portable be set up to run only when required? The mini van can (so can the candy man).
    8. What sort of runtimes can you get out of the mini van vs the inverter generator without refueling?
    9. Parts availability (There are NAPA's everywhere). Replace your dead alternator almost anywhere 7 days/week. Honda EU?
    10. Register as occasional use, RV, or farm.

    These were all just passing thoughts as I powered my life from a car in the past.
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    Not trying to argue here--Just suggesting that fuel consumption is critical for longer term operations. If you get good fuel economy (kWH/Gallon) from an automotive solution--That is great.

    I agree that generators are pretty much a necessary evil. And small gensets are probably the most evil. :p

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Using a Prius as a generator

    20 amps (or less) is what you would get from a 100+ amp alternator when the engine is at idle. Even if you run the engine at 2000+ rpm to get 100 amps, the alternator isn't going to last very long at its max rate. They are designed to handle brief bursts at high amperage when recharging the battery after a start but can't do it for long.

    I had a Sienna I had to idle overnight for 2 nights, on a trip to Florida to see a shuttle launch. We slept in the van so we could be on-location for the early-morning launch, and if you've ever been on the water in FL in July you'll know it is impossible to sleep without A/C. Filled up the tank each night, then refilled in the morning, and it burned ~8 gallons, ~8 hours each night. A normal vehicle engine does not use the Otto combustion cycle like a Prius. A normal 150-250 hp engine at idle can not achieve .12 gal/hr, and if you are reving the engine to get 50-60 amps from the alternator you'll burn multiple gallons per hour - however long a tank usually lasts you going down the road at highway speeds.

    My Prius and my Honda both get .13 gal/hr running all of the 120 volt loads in my house normally (no conservation). The Honda's specs don't say what hp the engine is, but at 3000 watts max it would need to be at least 4 hp. I know the engine is oversized to obtain a lower max rpm and lower noise, so even if you double that it is only 8 hp and most of the time it is at idle. The Prius gas engine is rated at 76 hp, uses the Otto cycle, and is on for 10% of the time, at idle.

    I'm not picking a fight either, just stating facts.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    The Prius is nice because the engine will auto start/cycle when needed.

    And the traction battery will supply energy when the engine would be inefficient (small loads). Then run the engine to recharge and run the engine more efficiently.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Using a Prius as a generator

    Exactly why it achieves the same fuel burn as the 3 kw inverter-genset. I think it would do even better if it had a "generator mode". For best mpg it will only bring the traction battery up to a minimal level of charge (around 30%, I forget the exact number) when sitting still. I think it would be more efficient when using it as a genset to have it go to its max (around 70%, again I forget the exact number) to reduce the number of engine starts. Even better would be the ability to cut out some of the 200 watt loss that occurs the entire time the car is on.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
    Re: Using a Prius as a generator
    techntrek wrote: »
    <snip>
    My Prius and my Honda both get .13 gal/hr running all of the 120 volt loads in my house normally (no conservation). <snip>

    Ok, .13/hr makes more sense. I thought we were looking at 1.0gal/hr. 0.13 is awesome!

    The thing is though, that in my trials, I was never trying to power a large load with the system, nor have a large continuous load.
    I don't know how many amps the alternator was putting out, but at a fast idea, maybe 30 of it's 60amp rating.
    At the time, I had a mere 1500w consumer inverter and my "rig" was jumper cables from the car batt' to a pair of grp 31 deep cycles on the ground...lol!

    For argument's sake, lets say the alternator was putting out those 30adc...

    That's 300watts... not much.

    I survived on this pretty well... could run my TV, charge cell phones...etc. The inverter allows a bit of a buffer...etc.

    That said, the engine of the vehicle was probably in the 100-120hp range and I seriously doubt that putting a 100a alternator in there (perhaps with an undersized pulley) would phase it much, nor change it's fuel consumption by any more than the hp/load derating.

    I used to be a "upper end" car stereo installer/builder and we would often add additional alternators to vehicles. Adding a pair of 100a (or even exotic 200a) alternators barely required and idle adjustment (ok... a touch), and there are some high end reliable alternators out there (emergency service...etc).

    Point? Well I guess 1-2kw of *charging* power is not out of the question at only a slightly elevated idle.

    Are there losses? Sure. Automatic transmission, parasitic loads (power steering pump...etc), the higher rotating mass and friction of a 100hp engine...etc.

    Are there gains... yep.. Millions of dollars of [email protected] into these engines to make them as efficient, and with the highest longevity as possible. As someone who has sat in gridlocked traffic in LA for 4hrs/day in 100 degree heat, month after month...after month... modern car engines are durable.

    My estimation is that a small car engine can match the fuel economy of many small generators per kw (in an inverter based system), but are much more reliable and pleasant.

    Being forced "off grid" (wife neglected to tell me that she hadn't paid the power bill until it was over $3k and then required a $5k deposit to reconnect), I tried many solutions.
    With the portable generator, I was always going to the "shed" I had to build for it (else the neighbors couldn't sleep) to fill the tank at 3am, or changing the oil every week (supposed to do it every 4 days), and having the things rattle themselves to pieces after just a week or two of constant service...etc.

    Also, portable generators (especially air cooled) are very dirty. Oil isn't cheap...especially the good stuff you want to use. Upwards of $20-$30/gal, and you're supposed to change a gallon of it every 4 days??

    I quickly learned not to like <10k gas generators. I moved to diesel portables from there (7-10kw), still had noise issues, and didn't require 10kw but had that engine spinning 24/7 anyway...

    My current main genny is a Powertech CD7000 (7kw diesel water cooled). It's a reliable beast and does *ok* on fuel (.16-.75gal/hr), but these are upwards of 5-10 grand to get into. Maybe $3000 on the used market. That is for the generator alone, not batt's, no inverters..etc. The total cost is closer to $7k to get a used working 7kw genny and 6kw inverter system up and rolling.

    This all has to fit in my RV, but if it didn't, I'm pretty sure that for $7k, that I could build a minivan power plant that would near equal the performance of my onboard system, and have some distinct advantages as well.

    One needs to consider the intended use as well...

    Is it an emergency backup system? Can you live on 1200w until the power comes back on? Do you have nat' gas for heating/cooking..etc?

    Is it an aux source for an off grid home? Can you replace that diesel generator sitting next to the house with a mini van (or Prius) sitting next to the house?
    Is 1200w enough power to charge your bank in the garage when the sun is down and the air is still?

    I think we're more or less all on the same page. Vehicles can be made into generators and some have some distinct advantages over traditional solutions...whether that be from the manufacturer, or with a custom built solution.
  • AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
    Re: Using a Prius as a generator
    techntrek wrote: »
    20 amps (or less) is what you would get from a 100+ amp alternator when the engine is at idle. Even if you run the engine at 2000+ rpm to get 100 amps, the alternator isn't going to last very long at its max rate. They are designed to handle brief bursts at high amperage when recharging the battery after a start but can't do it for long.

    I had a Sienna I had to idle overnight for 2 nights, on a trip to Florida to see a shuttle launch. We slept in the van so we could be on-location for the early-morning launch, and if you've ever been on the water in FL in July you'll know it is impossible to sleep without A/C. Filled up the tank each night, then refilled in the morning, and it burned ~8 gallons, ~8 hours each night. A normal vehicle engine does not use the Otto combustion cycle like a Prius. A normal 150-250 hp engine at idle can not achieve .12 gal/hr, and if you are reving the engine to get 50-60 amps from the alternator you'll burn multiple gallons per hour - however long a tank usually lasts you going down the road at highway speeds.

    My Prius and my Honda both get .13 gal/hr running all of the 120 volt loads in my house normally (no conservation). The Honda's specs don't say what hp the engine is, but at 3000 watts max it would need to be at least 4 hp. I know the engine is oversized to obtain a lower max rpm and lower noise, so even if you double that it is only 8 hp and most of the time it is at idle. The Prius gas engine is rated at 76 hp, uses the Otto cycle, and is on for 10% of the time, at idle.

    I'm not picking a fight either, just stating facts.

    Hmm...well...
    A 100hp car (for the sake of an arbitrary number) that get's 30mpg hwy is using 2gal/hr pushing multiple thousands of pounds of steel down the road at 60mph against the wind.
    It becomes a fuel/hp ratio. My diesel genny gets 7kw on 10hp. Larger generator fall in line with this (20kw generator at 30hp...etc). You can convert hp directly to kw in a formula not equating losses.
    It requires a certain amount of hp to push the car down the road, and it takes a certain amount to power an alternator (be in in a generator, or in an engine bay).

    Losses and efficiency are not an equal game, but it's not a wild swing either. You can move around maybe 10%. In other words, let's say your 100hp car engine is suffering a 10% parasitic loss, but due to it's design (electronic ignition, variable valve timing, mass air sensors, O2 sensors....etc. etc.) is gaining 10% efficiency over the crude generator engine. It's a wash at that point.

    Imagine this... take some efficient engine (Honda eco type) and replace the nuts and bolts Caterpillar diesel in an actual generator with it. Yes, they use the diesel because of it's simplicity, but cost is also a consideration. Generator manufacturers aren't putting the technology into their engines that car manufacturers are. You might realize (aside from the gas vs diesel aspect), a 10% gain in fuel economy from the "eco" 80hp from the Caterpillar 80hp? So what's the difference if it's in your car? After the initial no load fuel consumption, it's all about load. The 80hp Caterpillar will add fuel for 100w of load just as the eco will. In other words, the Caterpillar could power a 100a alternator or a 20kw alternator (higher actually), and the same is true for the eco.

    We are all in agreement except for your Sienna experience vs my Pontiac transport experience.
    Your Prius falls in line with the portable (gal/kw), my Pontiac fell in line (guessing .15-.20gal/hr), your Honda and my Powertech fall in line, but the Sienna at 1gal/hr is way out there.

    I agree that running your idle up to freeway speed is inefficient, but load is load. 100a (1200w) of load is not going to majorly effect fuel economy. It is only doing so because the alternator requires that speed...and the engine must follow. In other words, that alternator isn't using the fuel and hp to achieve it's output. It only cares about RPM. The motor itself barely cares about that 1200w.
    Remember, that your 100hp engine is making 74kw. That 1.2kw of load is barely taking 1/50th of that.
    Ya...that's pretty rough (losses...etc) but you get the idea.

    So to the drawing board... reduce the pulley size to get the alternator speed at idle (or just above), and you're now back in the game.
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    NOTE: Stupid Math Error Alert:

    Roughly, it is about a 1/2 lb of gasoline per Horse Power*Hour...

    30 MPG and 2 gallons per hour and 6 lbs per gallon:
    • 2 gallons per hour * 6 lbs/gallon * 1/(1/2) lbs per HP*Hour = 24 Horse Power from motor
    • 1,200 Watt alternator * 1/0.50 efficiency * 1/746 Watts per HP = 3.2 HP from car motor
    • 24 HP needed to move car / (24 HP + 3.2 HP for alternator) = 0.88 efficiency (~12% reduction in efficiency)
    So, 1,200 watts of "alternator load" on a 30 MPG car could increase fuel usage by 12% or cut mileage by *0.88 or:
    • 30 mpg * 0.88 = 26.4 miles per gallon with 1,200 Watt load on Alternator

    General Motors, years ago made daytime driving lights "standard" to turn on whenever the car was running. This cut their fuel MPG rating. And GM went to the government and had the MPG rating on the sticker based on running lights turned off (which the customer could not do) to keep their MPG ratings higher (safety trumped fuel efficiency).

    Standard headlights are about 55 watts per bulb (110 Watts total). So, not as bad as 1,200 Watt alternator--But still noticeable.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
    Re: Using a Prius as a generator
    BB. wrote: »
    Roughly, it is about a 1/2 lb of gasoline per Horse Power*Hour...

    30 MPG and 2 gallons per hour and 6 lbs per gallon:
    • 2 gallons per hour * 6 lbs/gallon * 1/2 lbs per HP*Hour = 6 Horse Power from motor
    • 1,200 Watt alternator * 1/0.50 efficiency * 1/746 Watts per HP = 3.2 HP from car motor
    • 6 HP needed to move car / (6 HP + 3.2 HP for alternator) = 0.65 reduction in fuel efficiency
    So, 1,200 watts of "alternator load" on a 30 MPG car could increase fuel usage by 50% or cut mileage by *0.65 or:
    • 30 mpg * 0.65 = 19.5 miles per gallon with 1,200 Watt load on Alternator

    General Motors, years ago made daytime driving lights "standard" to turn on whenever the car was running. This cut their fuel MPG rating. And GM went to the government and had the MPG rating on the sticker based on running lights turned off (which the customer could not do) to keep their MPG ratings higher (safety trumped fuel efficiency).

    Standard headlights are about 55 watts per bulb (110 Watts total). So, not as bad as 1,200 Watt alternator--But still noticeable (call it around 5% MPG reduction in my above example.

    -Bill

    Very interesting.

    Could you define what you mean by "6hp to move car"? Do you mean it requires 6hp idle the engine? Obviously 6hp isn't running you down the road at the speed limit.

    Rounding the alternator out... 1/2lb per HP = 1.5lbs/hr for the 3hp 1200w alternator, or .25gal/hr. (or 4 hours per gallon). That's not a very efficient alternator when my generator is turning a 10hp engine and produces 1750w from it's alternator at .16gal/hr (6 hours per gallon at that wattage)?
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    Roughly 24 HP to move the car at 60 MPH that is getting 30 MPG. (fixed from stupid error above)

    50% efficiency is pretty common (at least for older cars) efficiency for a belt driven alternator.

    This are historic numbers of fuel usage... For a Prius, the numbers are probably different.

    For a genset, they are direct drive, and that gives better efficiency.

    A Honda eu2000 outputs around 1,600 watts at ~0.25 gallons per hour. So--pretty close to your 1,200 Watts @ 0.25 GPH using the calculation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
    Re: Using a Prius as a generator

    Thanks Bill, let me digest that.

    Been looking at GPH numbers @ Idle for different types of engines... some are as low as .11 gph, others in the .30 range, some in the .5 range with A/C on...etc.

    This is interesting stuff... probably should have been it's own thread.

    Sean
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    Moved to own thread--Original thread was:


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Using a Prius as a generator
    Audiomaker wrote: »
    Very interesting.

    Could you define what you mean by "6hp to move car"? Do you mean it requires 6hp idle the engine? Obviously 6hp isn't running you down the road at the speed limit.
    Possibly a reference to the fact that when you are stationary with the system in Drive and your foot on the brake some power is being consumed keeping a minimum torque on the drive motors? This makes it act like a standard vehicle with automatic transmission in terms of what happens when you let off on the brake without depressing the accelerator.
    SMA SB 3000, old BP panels.
  • Badfish740Badfish740 Registered Users Posts: 13
    Re: Using a Prius as a generator
    BB. wrote: »
    The Prius is nice because the engine will auto start/cycle when needed. And the traction battery will supply energy when the engine would be inefficient (small loads). Then run the engine to recharge and run the engine more efficiently.

    This is the million dollar winner right here. I've poured over hundreds of threads on alternative energy forums from folks who have made "genverter" systems work with some combination of a conventional gas/propane/diesel generator, a battery bank consisting of lift truck or golf cart batteries, and sometimes PV panels. Some operated the system entirely manually, monitoring battery voltage, water levels, etc...running the generator when the batteries got too low or running the generator for loads that the batteries could not supply. I've also seen some sophisticated setups where a controller monitors the batteries and starts and stops the generator as needed, but the price tag quickly scared me off. Manual operation also comes with it's risks, as I heard many a horror story about battery banks being ruined by undercharging, overcharging, low water levels, freezing, etc... Full disclosure, I am a Toyota fanatic to begin with, but why bother with all of that when a team of Toyota engineers has done all the work for you?
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    And automation can fail too--Motor does not start, out of fuel, low oil, low water, etc... Either the automation system toast the engine, the starter, or battery bank--Or all three at the same time. :cry:

    The more complex the system, the more wild and wonderful ways it can fail.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Using a Prius as a generator

    Just adding a point of information here. My Suburban, which usually gets 18 mpg for daily driving, was using about 25 hp to maintain 60-65 mph on flat terrain this morning. I have an accessory that plugs into the truck's computer that feeds me info like that. Since that number is calculated and not measured I'm sure there is some error margin.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    :blush::blush::blush:
    BB. wrote: »
    NOTE: Stupid Math Error Alert:

    Roughly, it is about a 1/2 lb of gasoline per Horse Power*Hour...

    30 MPG and 2 gallons per hour and 6 lbs per gallon:
    • 2 gallons per hour * 6 lbs/gallon * 1/(1/2) lbs per HP*Hour = 24 Horse Power from motor
    • 1,200 Watt alternator * 1/0.50 efficiency * 1/746 Watts per HP = 3.2 HP from car motor
    • 24 HP needed to move car / (24 HP + 3.2 HP for alternator) = 0.88 efficiency (~12% reduction in efficiency)
    So, 1,200 watts of "alternator load" on a 30 MPG car could increase fuel usage by 12% or cut mileage by *0.88 or:
    • 30 mpg * 0.88 = 26.4 miles per gallon with 1,200 Watt load on Alternator

    General Motors, years ago made daytime driving lights "standard" to turn on whenever the car was running. This cut their fuel MPG rating. And GM went to the government and had the MPG rating on the sticker based on running lights turned off (which the customer could not do) to keep their MPG ratings higher (safety trumped fuel efficiency).

    Standard headlights are about 55 watts per bulb (110 Watts total). So, not as bad as 1,200 Watt alternator--But still noticeable.
    -Bill

    Fix my mistakes above...

    -Bill :cry:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
    Re: Using a Prius as a generator
    BB. wrote: »
    :blush::blush::blush:



    Fix my mistakes above...

    -Bill :cry:

    Lol, I just told two of my friends "Can you believe a car that gets 30mpg is only using 6hp at 60mph?!"

    They were as amazed as I was!
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator
    Audiomaker wrote: »
    Lol, I just told two of my friends "Can you believe a car that gets 30mpg is only using 6hp at 60mph?!"

    They were as amazed as I was!

    Ouch. :blush:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AudiomakerAudiomaker Solar Expert Posts: 100 ✭✭
    Re: Using a Prius as a generator
    BB. wrote: »
    Ouch. :blush:

    -Bill

    No worries, I'll just tell them later that I had the flu and slightly blurred vision :D

    I am compiling some data and theories... I may want to start a new thread unless that messes with your forum housekeeping Bill?

    I would call it: "The viability of automobiles as generators"

    Sean
  • BB.BB. Super Moderators, Administrators Posts: 29,189 admin
    Re: Using a Prius as a generator

    To quote Barbie:

    Attachment not found.

    "Math is Hard".

    If you wish to start a thread specifically for a project/concept--Sure, go ahead.

    Bits and Bytes are cheap these days.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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