How about an inverter-genset... with a battery

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techntrek
techntrek Solar Expert Posts: 1,372 ✭✭✭
So inverter-gensets have established themselves in the market. They have advantages like lower gas consumption and less noise when your load is light. They do this by throttling down to an idle, fewer revs = less gas used. All of this is nothing new to most people here.

I get the most out of my (non-inverter) genset by loading it up as much as possible when its running, others here do the same, because they operate most efficiently that way. You get more kW per gallon of gas/LPG or cubic foot of NG. This includes using a battery bank + inverter to time-shift some of that energy. While there is a 25% efficiency loss between the charger and inverter, its 50% cheaper per kW to charge the batteries when the genset is fully loaded vs. half-loaded or even less-loaded, so overall there is a 25% savings. Priuses (Prii?) do the same when they are parked but on and running things like the A/C. Start, recharge a little, turn off, repeat.

That got me thinking, why not take inverter-gensets one step farther and add a battery? You end up buying something the same size as a Honda inverter-genset but you must add a 100 amp-hour deep cycle battery. I'm operating under the assumption that under a light load there is a greater fuel savings running at full throttle for spurts vs. idle. It is entirely possible the opposite is true, but I doubt it or else hybrid cars would always idle instead of turn off. You would have the option of either selecting for best fuel economy (FE) or the quietest operation (QO). When in QO mode it would operate the same as current inverter-gensets, with the benefit of electric start even on smaller models. The battery wouldn't do much except handle brief surges so the engine could stay at idle. In FE mode it would run full-throttle for a while to recharge the battery then shut off for a while, and repeat, when it is lightly loaded. Under a full load it would operate like any genset on the market and run at full throttle, throttling back as the load drops. Maybe at 50% load it would begin cycling on-off, tests would have to determine where it makes sense.

If you remove the QO option so the genset is always loaded up you could even move to a diesel engine and decrease the fuel useage that much more.

Maybe there wouldn't be enough fuel savings to make the additional size and weight of lugging around a battery worth it (but I keep thinking about hybrid cars and believe the fuel savings would be worth it). Additional complexity means a bigger chance of something going wrong, and more maintenance. Your average Joe wants to pull his genset out, start it, and forget it until the tank runs dry - and this system would require a little more "fiddle factor". Things could be made easier by adding something like an Andersen connector so the user doesn't have to mess with thumb screws all the time. I see many reasons for big companies to not bother producing something like this even if the fuel savings is decent. Running at idle is "good enough", so that is what Honda will produce.

But for some segment of the market fuel economy is paramount and noise is secondary. Thoughts?
4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: How about an inverter-genset... with a battery

    The only place that I have read about "Hybrid" generator systems have been setups in Africa where they run the genset in the evening (people home, food prep, homework, etc.) and run off a battery bank for the balance of the day to supply the minimal loads when people are sleeping, at work, etc.

    I think these where "engineered" village sized installations instead of turnkey small setups like you are suggesting.

    The closest turnkey Generator/Battery setup is this Yamaha EF30iseB:
    The Boost Control Unit in the generator automatically senses when additional boost is needed and it uses power from the internal 12-volt battery to produce additional amperage. In fact, the additional amps boost the alternator's 3000-watt output for up to 10 seconds, increasing the output so it's comparable to a conventional 3500-watt generator. Supplying that extra boost for 10 seconds is ample time to power equipment that may need that extra kick to start quickly and efficiently, such as a 15,000 btu air-conditioner or other trailer appliances.

    Unfortunately, I think the change from the above "simple" implementation to full hybrid (with full autostart/engine control, ability to supply AC power while engine is shut down, charge/discharge a larger battery bank) is probably beyond the capability of this genset.

    In the end, a significantly sized Hybrid Battery Bank would well exceed the size and weight of a typical "standard" genset--and increase the costs by several times.

    For a fixed installation--It would seem logical for a Yamaha or Honda to offer a Genset with DC terminals to run the inverter when the engine is shut down for an external battery bank (integrated with solar panel support?). But that would add lots of cost and complexity to be equivalent to the Xantrex, Magnum, Outback level of functionality (it would seem to me).

    What I would like to see is a 1,000-3,000 watt genset with pressurized oil / oil filter system and support with a full automatic start engine controller (including failsafe for non-start/oil/temperature/etc. problems).

    It seems that any auto-start+ solutions are starting at the ~7.5kW or larger sized units. A well designed home power system with conservation measures should be able to run on even a 1,600 watt genset pretty nicely.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
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    Re: How about an inverter-genset... with a battery

    Yamaha inverter-generator EF3000iSEB has a small battery to provide about 500 watts of boost for surge over what the generator-inverter can produce by itself.

    http://www.yamaha-motor.com/outdoor/products/modelspecs/444/0/specs.aspx

    It is pretty rinky-dink in terms of size of battery and boost power but it demonstrates the principle. It adds a DC-DC boost inverter to take the 12v battery (electric starter battery) up to 190 vdc to feed in parallel with the rectified three phase permanent magnet alternator output which feeds the main sinewave AC output inverter.
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
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    Re: How about an inverter-genset... with a battery

    That's half-way there. Just needs a decent-sized deep cycle battery and auto start (with additional logic).

    Looking at Honda's web site, they claim 40%-20% lower fuel consumption at roughly 25%-50% of rated output. Anyone have exact numbers?

    gg_fuelnoisegraph.jpg
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: How about an inverter-genset... with a battery

    Honda used to advertise for the eu2000i running at 400 watts:
    • Run Time per Tankful 4hrs. @ rated
    • load, 15 hrs. @ 1/4 load
    Now:
    • Fuel Tank Capacity 1.1 gal
    • Run Time per Tankful 4hrs. @ rated load, 9.6 hrs. @ 1/4 load

    I am guessing the lower number is more accurate. :cry:

    If you are running near 100% power--it is possible that the el-cheapo noise makers will actually be slightly more fuel efficient (at least from their advertised numbers).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
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    Re: How about an inverter-genset... with a battery

    A conventional generator running at 3600 rpm to create 60 Hz output, has gasoline consumption become pretty linear for power output above 20% to 25% loading.

    One of larger parts of mechanical horsepower overhead is the flywheel fan for an air cooled engine. For a constant rpm generator running at 3600 rpm this air flow remains the same no matter how hard the engine is loaded, even though the engine heating is lower at lower work load.

    The inverter-generator uses a permanent magnet alternator. The output of power (variable voltage and current capability) is a function of rotational speed of alternator. For a constant rpm, the voltage will rise as the alternator load is reduced. Or you can back down the rpm's to maintain a constant output voltage as the load is reduced.

    The alternator has a three phase output that is full wave rectified to a DC output. The DC-AC sinewave inverter is a MOSFET H-bridge that chops at high frequency with a pulse width modulated track of the 60 Hz sinewave. This is filtered with an inductor/capacitor on output to remove high frequency switching leaving just the 60 Hz sinewave output.

    The DC input to the AC chopper must have a minimum of about 180 vdc in order to make the peak voltage on the AC sinewave (170 vdc for 120 vrms output). On my Yamaha the maximum DC voltage goes to close to 300 vdc if the eco-control is off with the engine running at constant 3800 rpm and no load on output.

    When eco-control is on, the engine speed is adjusted to keep the minimum 180 vdc alternator output based on a given load. If there is a sudden surge load applied there will be a sag in the output sinewave peak for second or two as the engine speeds up to handle the additional load.

    For my EF3000sei the fuel consumption is:

    1/4 load (700 watts) 0.17 gal/hr or 4.1 kWH/gal and 20 hour runtime per 3.4 gallon tank.
    1/2 load (1400 watts) 0.32 gal/hr or 4.4 kWH/gal and 10.6 hour runtime per 3.4 gallon tank.
    3/4 load (2100 watts) 0.47 gal/hr or 4.5 kWH/gal and 7.2 hour runtime per 3.4 gallon tank.
    full load (2800 watts) 0.60 gal/hr or 4.7 kWH/gal and 5.7 hour runtime per 3.4 gallon tank.

    If you can use the higher power, generally, the larger the generator wattage the better the kWH/gal. My 15kW Generac gets 5.9 kWH/gal at 7500 watts , 7.0 kWH/gal at 11.3 kW load , and 8.3 kWH/gal at full 15 kW output. It is a regular 3600 rpm fixed generator. It consumes about 0.6 gallons per hour with no load on generator.