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Let’s talk generators...

Discussion in 'BBS Hangout' started by Xerobull, Feb 18, 2021.

  1. Xerobull

    Xerobull You son of a b!tch! I'm in!

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    I ordered a $450 3500w gas genny from Amazon last week. It showed up with the box beat to hell, so I tried to set up a return. The automated returns said it wasn't eligible. I jumped on the chat and they said I could keep or toss, and they would refund.

    So now I have a freebie stopgap (if it works). Now to shop for natural gas.
     
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  2. lpbman

    lpbman Member

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    50.5 kwh Thursday. That would be ~5 dollars of electricity on a good day but for Louisiana having a payback rate of 3.4 cents per kwh.

    Would be a total bust except that, for roughly half of the 50.5 kwh I produced, I'm avoiding the 11 cent cost from the electric company.


    Of all the permutations I've done on saving on electric bills, the fastest roi I have found would be solar hot water (pv). Well, I am sure it could be done cheaper by building solar thermal panels with a heat exchanger and pumps and thermostats and relief valves and that is a world of complexity I'm not willing to deal with.

    But, changing out one of the heating elements on a conventional hot water tank for a dc element and high temperature thermostat (in the 160-170 range) and adding a thermostatic mixing valve to drop the temp back down to a safe temperature for human use allows one use hot water as a thermal battery of sorts. ROI in the 10-14 month range which is better than going from a window unit to a mini split (~24 mo).
     
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  3. Andre0087

    Andre0087 Member

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    So anyone else purchased or looking at getting their generator yet? Hurricane season is around the corner. Last week had my electrician install the interlock kit on my inside panel, just waiting on my unit to come in.
     
  4. KingCheetah

    KingCheetah Contributing Member

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    Ug, here we go with the generators again.
     
  5. Andre0087

    Andre0087 Member

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  6. Andre0087

    Andre0087 Member

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    What did generators do to you? They are certainly Cheetah-Friendly™.
     
  7. KingCheetah

    KingCheetah Contributing Member

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    It's what they might do.
     
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  8. DonkeyMagic

    DonkeyMagic Contributing Member
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    Just purchased a 13000 dual fuel (gasoline/propane). I will be tying it into an inlet to the circuit breaker to be able to run 1 ac unit, fridge, freezer and miscellaneous lights/one-offs. Hopefully.

    I’d like the ability to run a line from the house natural gas main so I don’t have to have a bunch of gallons of gasoline/ propane tanks on standby since ideally I’d like to have 5 days supply ( give or take depending on how continuous the system is run). However, I’m not familiar or confident with some 3rd party propane to nat gas converter kits I’ve seen. It makes me a little nervous mod-ing out something that involves fire and fuel.
     
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  9. Icehouse

    Icehouse Contributing Member

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    Ok, truly ignorant questions coming. I got some quotes and it seems like they are recommending the Kohler over the Generac. I'm trying to wrap my head around this whole load managed thing, and see what size I truly need. The salesman is telling me I need a 24 kw Generac or a 20 kw Kohler. Either would allow me to use my AC units as long as I wasn't using over 67% of my capacity (something like that). Using the Generac as an example, does the 24 kw = the unit handling 24 kw a day, or 24 kw a hr? I'm trying to use my energy bills to figure out my typical usage. So if I used 1,000 kw last month then that would be 32.2 kw a day. Does that mean I'd have to reduce my usage to get under the 24 kw of the Generac?
     
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  10. Icehouse

    Icehouse Contributing Member

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    I received a similar quote for a 24Kw Generac, at 15K. So is your unit maxed out at 22Kw a day? Is that how it works? Thanks.
     
  11. lpbman

    lpbman Member

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    Ideally you breakdown every single thing that'll be run by the generator at one time plus headroom for starting surge. If your generator can produce 24kw that means theoretically you can produce seventeen thousand kwh per month, but peak usage is what causes headaches like tripped breakers low voltages and the like. Take inventory of all the things you aren't willing to compromise on like AC, fridge, hot water, stove etc and find out how much power they use. Add 500w for miscellaneous things like laptops, routers, phone chargers and lights and such. If you're under 2/3 of your generator rating with everything that might run simultaneously - you're golden.

    If that 1000kwh a month you mentioned is your actual number it strongly suggests that you'll be fine with 24kw generator... but it's not a guarantee... it's all about what you need at one time.
     
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  12. Icehouse

    Icehouse Contributing Member

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    Thanks. Are you saying if I’m under 2/3 of seventeen thousand kwh per month? Also, how did you get to that number, based on a 24kw generator?

    Over the past 12 months I’ve used between 1,226 and 4,920 (Aug/Sep) kWh, between my house and my garage apartment tenant. We are on the same breaker. I’m trying to see if a 24kw unit can support us if we load manage.
     
  13. lpbman

    lpbman Member

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    No, that's not what I'm saying. I got that number by saying if your generator was running flat out for a month and it was sending power back to the utility company like my solar panels, you'd come up with around 17 thousand kwh. 24kw x 24hrs x 31days. But in the real world your peak usage is way, way higher than average usage. At 6:30pm, you might be cooking and someone else showering. Your microwave ~1200w, stove ~1500w, oven ~3000w, hot water heater ~4500w and A/C ~5000w might be on at the same time. In that scenario would be 15200w from the previously mentioned, add in 500w of constant draw from junk like routers and lights and phone chargers and whatever.... and you are still under 16000w. You're golden. Even if the fridge kicks on you've got the overhead to handle it. At 6:30am if you're still sleeping you might have almost nothing on, your hot water is already hot, your lights are off, the fridge cycles off and on and you're probably using less than 1000w total and your generator is basically at idle. The morning is not what you size your generator off of.... nor is the average of the day/week/month.


    It's everything that *has* to run at the same time.

    I'm saying that you need to actually walk the house/garage and write down everything that *HAS* to run in SHTF times. Look up the actual power consumption of the items and add them up. if those items that you can't compromise on added up go over 16000w you need a bigger generator or you need to do things like get a gas stove/water heater or similar.
     
  14. KingCheetah

    KingCheetah Contributing Member

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    This endless generator talk has honestly been quite shocking.
     
  15. Icehouse

    Icehouse Contributing Member

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    Gotcha. So it seems like the 24KW generator = 24KW an hour? If you’re saying 24x24x31 = 17K. Correct? I see how you added everything up that will be on at once. I’m just trying to make sure I convert it back correctly, to the size unit that’s necessary.
     
  16. lpbman

    lpbman Member

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    If the generator produces 24,000w and you run it for a hour you made 24kwh. If you ran it for half an hour it'd make 12kwh. That's at full output, the generator will only make as much power as you ask from it until you exceed it's ratings. In other words it'll happily hum along powering the little things late at night, and then when you wake up and turn on a coffee maker and electric stove etc and then it'll run harder to make the extra power you ask from it.

    If you are running a really high draw item, like an instant electric hot water heater, and it draws 30,000w when it runs, it won't matter that your generator can make more kwh than you use on average for the day/month. You will have to turn off the hot water when the grid goes down.
     
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  17. Icehouse

    Icehouse Contributing Member

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    Thanks. That makes sense. I was lost on what 24KW represented. Now that I see it’s per hour, I can do my calcs. So if my high was 5K a month thats roughly 167 a day. I can back into the hourly rate that way (estimate) and do the add up everything thing you said, to stay under 17K. So if my max was 5K with no restrictions, I should be fine load managing with a 24KW.

    It seems like they oversell you, unless you plan to run stuff 24/7, since everything won’t be on at the same time.
     
  18. PhiSlammaJamma

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    Welcome to Gattaca, your new gene rater has been installed, and you are in fact a degenerate. So good luck. It was the big nose and your inability to screw in a working lightbulb.
     
  19. Supermac34

    Supermac34 President, Von Wafer Fan Club

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    It is better to look at the amperage. A 24Kw puts out about 75 amps at once. That's enough to run 3 "big things" at once in most houses, plus all the other stuff for the most part. "big things" are AC/furnace and 220 plugs (kitchen oven, electric dryer).
     
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  20. jchu14

    jchu14 Contributing Member

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    You shouldn't look at it in terms of per hour and you cannot just take the average hourly used based on your monthly used and divide up by 30*24 since your usage pattern is not going to be evenly distributed.

    24kw means it can ouput 24kilowatt of power at any given instant. Exceed that number and your generator will either generate out of spec power (can't maintain 60hz anymore) or just shut down.

    Keep in mind that the amount of power required to start a device is often higher than the sustained power usage.

    So the right way to size a generator would be add up all the devices that you think you would power at the same time then add a buffer to account for increased starting power requirement.

    Some of the common large power draw items are:
    AC (3 ton) - 5kw sustained, 7kw starting
    ac/furance fan - 1kw
    water heater (electric) - 4kw
    electric stove - 3kw
    electric dryer - 3kw
    electric water kettle - 1.5kw
    microwave - 1.5kw
    dishwasher - 1.5kw
    hairdryer - 1.5kw

    24kw generator can power quite a few things unless you have big air conditioners. If you can load manage (not turning on multiple power hogs at the same time) or if your water heater stove are gas then it's very likely it's enough.
     
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