Grid tied 18-20kW natural gas generator options?

lasitterlasitter Solar Expert Posts: 47 ✭✭
Would appreciate links to discussions on this topic. Had good success with solar panel install, but now want install ATS and generator to provide whole house coverage in event of extended outage. Contact pages for Home Depot and Lowes all want to respond with quotes for Generac systems. Nobody wants to install diesel, so I'm looking for a genset that you would have some hope of lasting a week in a prolonged outage.

Thanks in advance.
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Comments

  • BB.BB. Super Moderators Posts: 26,872 admin
    Are you looking for diesel, natural gas, or possibly propane (good storage, many folks already have a large propane tank for stove, water heater, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    One problem with natgas is the possibility that it may be affected by an extended outage as well. Diesel can have longer term (more than a couple of years) storage issues, and also fuel gelling in extreme cold. Both problems can be overcome, just something to keep in mind.

    You may want to see if there's an Onan/Cummins dealer in your area.
    Power.cummins.com

    They have a pretty wide range of generators using a variety of fuels, and a lot of dealers.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    If you are thinking you will need genset long term, plan on several break-in runs and their oil changes, while it's under warranty. My backup genset lost Freq regulation at 50 hours, and it's a factory only adjustment. 200mile drive to dealer
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Dave AngeliniDave Angelini Solar Expert Posts: 3,329 ✭✭✭✭
    500 or 250 gallon propane tank if you can. Natural gas probably will not last a week in many cases. Many of these gen sets will operate either way and propane will not have the diesel storage issue as Estragon pointed out. 
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • MangasMangas Solar Expert Posts: 537 ✭✭✭✭
    edited September 26 #6
    I have a 20 kw CumminsOnan propane genset.  High quality unit. At the time, came with Solar use warranty limited by so many hours. 

    When evaluating choices, I'd ask about manufacturer warranty when used in solar applications in a grid tie set up.

    In my opinion, OEM Generator Dealers a better bet than big box stores.
    Ranch Off Grid System: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF House Construction, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • peakbagggerpeakbaggger Registered Users Posts: 8 ✭✭
    Diesels are pretty much standard for emergency power in critical applications. The trade off is you need to run them routinely and deal with fuel storage. Many folks buy military surplus gen sets. They are way overbuilt. They have newer inverter style units that cut way down on fuel usage. They are generally quite noisy. The big trade off is even the inverter based diesel dont deal well with no loads, you need to use power. Of grid folks have battery banks so they can charge up the bank and then shut off the generator and run off the batteries.

    FYI, I hope your title is misleading. You can not easily "grid tie" a generator. You need to either be running on the grid or on the generator never both unless you want to spend a bunch of money on synchronizing gear and get an interconnect permit from the utility. Unless you sync a generator to the grid properly its highly likely that you will toast the generator.   The typical setup has an automatic transfer switch that breaks the grid connection before it allows the generator to take over the load.
  • mcgivormcgivor Registered Users Posts: 1,304 ✭✭✭✭
    edited September 26 #8
    lasitter said:
    Would appreciate links to discussions on this topic. Had good success with solar panel install, but now want install ATS and generator to provide whole house coverage in event of extended outage. Contact pages for Home Depot and Lowes all want to respond with quotes for Generac systems. Nobody wants to install diesel, so I'm looking for a genset that you would have some hope of lasting a week in a prolonged outage.

    Thanks in advance.

    Edit. The  18- 20 kw was missed, shooting from the hip,sorry.
    Whole house coverage, is pretty vague, what sort of kVA rating are you thinking of, diesel, IMHO is the way to go, especially mechanical injection, steer clear of anything with a rotary injection pump, particularly Stanadyne, inline pumps are far superior, lubricated with engine oil rather than fuel. Considering 80% of engine failures are the result of electrical problems, all the ignition components, distributor, plug wires and so forth are not present on a mechanical diesel. Fuel storage with diesels can largely be controlled with anti bacterial additives, in ten years of servicing standby generators with such additives I encountered no problems, a fuel sample was sent for testing annually, all gensets were run monthly and load tested annually, so some fuel was replaced. Depending on the size, Onan, Cat, Kubota, are good choices, Generac are considered low on the reliability side of things, not my opinion, but that of service a company who conducted the annual load tests. Additionally since grid is available, using block heating is advantageous, to prevent cold start conditions , regardless of fuel choice.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    To minimize critter growth, it helps to locate the storage in a place with a stable temperature. If it varies much daily, the tank exhales as it warms during the day, then inhales cool moist air at night. The critters like living in the resulting condensed water. Keeping the tank full also helps reduce the "breathing".

    Biocides work for minor growth, but if it gets out of hand, the killed critters can end up clogging filters etc. It's worse on boats, because they tend to slough off en masse during rough weather, which is exactly when you don't need the engine sputtering off. Guess how I know that. :#
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • lasitterlasitter Solar Expert Posts: 47 ✭✭
    BB. said:
    Are you looking for diesel, natural gas, or possibly propane (good storage, many folks already have a large propane tank for stove, water heater, etc.).

    -Bill

    My bad. Have natural gas at the house. We replaced our oil burning furnace with gas, so I have 660 gallons of storage for a diesel, but nobody wants to quote me an install / maintain option. I'd love a Perkins Genset, or for that matter maybe a Cummins/Onan, which one guy wants to quote me but as a natural gas, vs a diesel setup. I think it's a Quiet Connect RS20A or something like that ...
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  • lasitterlasitter Solar Expert Posts: 47 ✭✭

    FYI, I hope your title is misleading. You can not easily "grid tie" a generator. You need to either be running on the grid or on the generator never both unless you want to spend a bunch of money on synchronizing gear and get an interconnect permit from the utility. Unless you sync a generator to the grid properly its highly likely that you will toast the generator.   The typical setup has an automatic transfer switch that breaks the grid connection before it allows the generator to take over the load.
    ATS: Yes. Vendors have discussed having the service entrance fed into a 200-amp ATS on the outside of the house, and then having that feed the existing 200 amp load center. I have Edge 3000/6000 inverters, and I'm a bit fuzzy on which piece of my current setup sees the mains power go down and then disconnects from the grid to prevent solar backfeeding. I've also been told that you would have a major problem if the solar panels / inverter ever backfed your genset, so I'd love to see a wiring diagram explaining how you get all three things (inverters / genset / grid) protected from one another. This can all be done with a single ATS?
  • peakbaggerpeakbagger Solar Expert Posts: 335 ✭✭✭
    FYI, natural gas generators really arent a great alternative to diesels for standby. Diesels generally can take sudden load changes a lot better than natural gas engines. The trade off is nat gas engines require far less maintenance.
  • BB.BB. Super Moderators Posts: 26,872 admin
    Generally, the GT Inverters are connected "upstream" of the ATS on the utility side. And your "protected loads" are connected downstream of the ATS. With a whole house ATS--That may require an extra "main panel" upstream of the ATS.

    Or--The GT Inverters are generally 60Hz +/- 0.5 Hz. Most smaller gensets cannot hold that frequency (inverter genset can). Or you can program your genset for 62 Hz and the GT inverters will never connect. (the frequency and voltage have to be stable for 5 minutes before inverter will connect--Most smaller gensets cannot hold the frequency specification that long and will never connect).

    However, looking at the data sheet, your inverters are configurable for acceptable frequency range--So your configuration would have to be confirmed--Or better yet, just go with option A and connect the inverter on the utility side of the ATS. You are correct--back feeding your genset would not be a good idea.

    https://www.solaredge.com/sites/default/files/se-single-phase-inverter-datasheet.pdf

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 3,329 ✭✭✭✭
    edited September 29 #14
    The last option which I may have missed is just AC coupling a battery based inverter. I am not saying to do this but at least it should be thought about. With a reasonable AGM battery or one of the Li-ions in the store here all you would need is an Outback or Schneider inverter. I believe solar edge is compatible. The LG RESU 10H and the Tesla also would fit the bill. By getting the battery inverter you get the transfer switch built in for your generator.

    As I pointed out before, the natural gas may not be there if it is a pretty bad thing that takes out the power grid. An AC coupled system would be and would not need much fuel, just sunlight!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • lasitterlasitter Solar Expert Posts: 47 ✭✭
    Most vendors are quoting me $9k - $11k for a 20kw genset installed. For that kind of money, would it make sense for me to just go with a battery array, and what would that look like?

    My solar system was projected to make 10.9 megawatts per year, but at the moment looks ready to make almost 13mW by early November, my 1st year anniversary date.

    What I don't know how to figure out is how much it will cost to keep the batteries charged, and the difference in service life of AGM versus wet ...window.onbeforeunload = function() {}window.onbeforeunload = function() {}
  • BB.BB. Super Moderators Posts: 26,872 admin
    Typically, AGM batteries only use ~0.1% of their AH capacity for float current (or even less). A 1,000 AH @ 12 volt battery bank would take:
    • 1,000 AH * 12 volts * 0.001 rate of charge = 12 Watts float (plus charger losses)
    • 12 watts float * 24 hours per day * 30 days per month * 1/0.80 charger eff = 10,800 WH per month = 10.8 kWH per month ($0.10 to $0.34 per month utility power cost for AGM, maybe 2-4x more for typical flooded cell floating cost)
    Flooded cell batteries would take around 0.1% to 1.0% rate of charge to keep float.

    "Failing" Lead Acid batteries (and old about to fail flooded cell batteries) could take as high as 2% rate of charge--But they will be pretty warm (from charging energy) and should be replaced as--At this level of float current--Could be a fire hazard. AGM/Sealed batteries would probably not survive a 2% rate of charge before they over heated and/or vented (and eventually worse).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 876 ✭✭✭✭
    In terms of run time (in most applications), there is no comparison between batteries and a generator.
  • jonrjonr Solar Expert Posts: 876 ✭✭✭✭
    > Diesels generally can take sudden load changes a lot better 

    I'd like to see support for this.  

    For emergency backup, I'd use propane.    But review here (no mention of sudden load differences):

    https://www.generatorjoe.net/html/genfuel.html

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    A couple of wild guesses...
    Diesels tend to be much heavier for a given displacement. My 4kw is ~350lbs. I have a 3.5kw gas that weighs maybe 80, and a 2kw (optimistic - really more like 1.5) Honda that weighs maybe 25. Some of the extra weight will be in the moving bits, so the inertia helps the diesel keep rotating.

    Diesels tend to have better low rev torque. Mine runs at 1800rpm, some run at 3600. With gas you could rev higher / gear lower for the same effect I suppose.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • peakbaggerpeakbagger Solar Expert Posts: 335 ✭✭✭
    jonr said:
    > Diesels generally can take sudden load changes a lot better 

    I work on designing large Generator CHP installations. The engines are hooked onto synchronous generators so the RPM is steady compared to a small generator that is going to float around. Sudden changes in loads either adding them or subtracting them are called "step loads". Ask about step load guarantees from natural gas engine vendors and most cant give you one(Jennbachers can to limited amount). Most vendors tell us to buy a diesel as they can handle them far better. These are 24/7 engines and have to meet Tier 4 emissions (or similar stringent numbers like SCAQMD emissions.)

    I think the reason for a diesel having better step load changes is fundamental to the design of the engines. Diesels can vary power output quickly by quickly pumping a very small quantity of highly volatile fuel either directly into the combustion chamber or into a prechamber. Some of the fuel doesnt get burned but the fuel that does adds torque quickly.   This can happen rapidly when the voltage and frequency goes south or overshoots due to step loads. With natural gas, the fuel is quite low btu content so in order to change the Air fuel ratio a large volume of natural gas or propane is required to get a higher output from the engine. Moving this large volume of fuel takes longer than squirting in a bit more diesel. Diesels also generally have higher torque due to their higher compression ratio.

    I think of it is consider mixing a batch of paint, start with white paint and now tint it. The diesel acts like concentrated dye while the natural gas is a very weak dye. They both end up at the same place but the dark dye works quickly while the weak dye takes longer. When it comes to step loads we are talking cycles (1/60 of a second) for a direct driven engine or some multiple if its geared. 

    Ultimately I think the way to go is a generator equipped with short term energy storage. GE is invested in a company that has some large commercial units used in oil and gas. Rather than idling a large generator in case they need short term power when the drill rigs sudden has step load change in power, the system can draw on a charged ultra capacitor bank to make up the short term demand. If there is sudden drop in power the capacitors can absorb the power while the engine ramps down.  GE is also deploying peaking natural gas generators equipped with short term storage. This allows the peaker to ride through short term grid issues withouht even starting the generator by pulling out of the storage. If the issue remains the storage covers the start up time of the turbine.




  • lasitterlasitter Solar Expert Posts: 47 ✭✭
    We've done a lot to reduce our electric consumption over the last year. We've completed a lot of insulation work and installed brand new highly efficient 5-speed Bryant AC units. I've learned how to save even more by turning off computer equipment when not in use. We've gone from a four month summer average of 44931 watt hours down to 20577 this year.

    Since we're generating 60kW to 70kW per day during the best of times, it seems that we should be able to have some battery alternative to a conventional genset. We dropped an electric stove and an electric dryer, and added an electric car that draws a max 7kW during a 1-2 hour charge cycle once per week.

    How many batteries, AGM vs wet, does this translate into, and would that (plus whatever inverter) be more or less than an $11,000 generator?

    Some benefits of batteries that I see is that there are no moving parts or maintenance (to speak of), no fuel costs, no noise, and less real estate. Generators also have a variety of offsets to avoid hazards of CO. Generators, on the other hand, are not limited by available sunlight.
  • jonrjonr Solar Expert Posts: 876 ✭✭✭✭
    @peakbagger, thanks for the explanation.  
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