Generac Generator LPG or Natural Gas Fuel Consumption at Low Loads

[Chewwy]

Any one have any experience with the LPG ornatural gas fuel consumption of a Generac generator when operating at low loads (25% or less of rated?

The specs from generac only provide consuption estimates at full losd and 50% load.

 

[MAX-24-Dean]

That is because gasoline and LPG fuel generators burn rate is 50% of the full load burn rate, no matter how low you get the electrical output.
So thier charts are giving you the facts.

The key is to get a generator that meets the load requirements you have at half load and full load.

 

[ning]

So this is from a Kohler 20KW (they provide this in the spec sheet), not a Generac, but the relative amount should be similar.
As in, the difference ratio between 50% load and 25% load in the Kohler is likely to be pretty similar to the ratio of the Generac.

As you likely already understand, in order to provide a 60Hz frequency, these generators are run a specific RPM, regardless of the load; an engine will have a "sweet spot" of power generated at that RPM, and looking at the above consumption chart that sweet spot is likely 100% load - so at very low load you're using a lot more gas per watt.

(nb The ratios will vary somewhat because it's likely that the generators of a given manufacturer may share engines in a different state of tune for different KW targets but in general the fuel consumption will follow a similar curve, +/- a bit)

 

[grsthegreat]

With devices constantly switching on and off automatically, just use the 50% values. I had an actual wifi fuel flow device set on my own 22 kw unit during a summer outage. The full load burn is rated at 3.5 GPH.

I was running basement full of wifes quilting group and the AC unit. The generator never sucked down more than 1.2 gph during a 3 hour outage. Occasionally id see a peak draw against generator during motor startup, but its very short.

I also monitor my unit with a Genmon wifi monitor, so can see load draws.

 

[Tpondel]

Too many letters and numbers for me to convert.

Do I understand on the LPG chart that it would use 2.3 gallons per day at 50%? Trying to understand how long my 500 gallon tank might last.

Thanks.

 

[drumminj]

Too many letters and numbers for me to convert.

Do I understand on the LPG chart that it would use 2.3 gallons per day at 50%? Trying to understand how long my 500 gallon tank might last.

Thanks.

That's 2.3 gallons per hour, not per day.

 

[ponytug]

Too many letters and numbers for me to convert.

Do I understand on the LPG chart that it would use 2.3 gallons per day at 50%? Trying to understand how long my 500 gallon tank might last.

Thanks.

Ok, a few things go into this.
1) your 500 gallon tank has a maximum of 400gallons in it.
2) as the tank gets empty, it cools off and the last portion may not be accessible because it can't boil off. (Better in the summertime, much worse in the winter time.) There are tables to look this up in most manuals.
3) as @drumminj points out, that is 2.3gal/hr
4) 2.3gal/hr assumes that you don't load it up to full load, in which case, you probably want a smaller generator. Ideally, one that can run 80% load much of the time.

Bottom line: probably not more than four or five days, as little as two and a half, and up to seven or so depending on outside temperatures, and actual loads.

If you anticipate mostly small loads, and occasional large loads, a better solution might be to have batteries that can be recharged by the generator quickly, and run the small house loads for an extended period of time. That's likely to be the most fuel efficient solution.

All the best,

Peter

 

[grsthegreat]

Unless theres medical devices needing to run….. let the unit run a few hours, manually shut it down when not necessary, then turn it on again. Refer and freezers can easily last 12-24 hrs without power without excessive opening and closing of doors. They dont need to run during sleeping time. People with cpap machines should get a good battery power supply unit that can power unit thru the night…quietly. And this can be recharged on generator during the day. Some of these even have solar panel to recharge.

 

[Chewwy]

That's 2.3 gallons per hour, not per day.

Per the table, it is 2.3 CUBIC METERS per hour or 82 cubic feet per hour. That equates to 2.25 gals per hour.

 

[Darth_DMack]

We have the 26kw Generac Home GenSet, with a 500 gal Propane Tank as well. I don't have a flow meter, and can only go by what we get refilled when the propane truck comes.

When we built our house, we went above board with the electrical plan. Ours is a modest 2700 square ft ranch style (single story) home, 3 bedrooms, 3 baths. We have it partitioned where we can select what we need for power. We have a Propane on demand water heater, and a propane range / oven.

In case of a long term storm, power outage, I can partition things to only run essential things. We also have Solar panels, battery bank and a large power inverter. I also have a portable dual fuel inverter genset just in case.

 

[ning]

We have the 26kw Generac Home GenSet, with a 500 gal Propane Tank as well. I don't have a flow meter, and can only go by what we get refilled when the propane truck comes.

When we built our house, we went above board with the electrical plan. Ours is a modest 2700 square ft ranch style (single story) home, 3 bedrooms, 3 baths. We have it partitioned where we can select what we need for power. We have a Propane on demand water heater, and a propane range / oven.

In case of a long term storm, power outage, I can partition things to only run essential things. We also have Solar panels, battery bank and a large power inverter. I also have a portable dual fuel inverter genset just in case.

Can your genset directly charge your battery bank?
If and when I set up a backup generator, the plan is for the battery bank to be charged by the generator, and the house runs from the batteries - that way the generator only needs to run for battery recharges, and so assuming the generator size is chosen appropriately it should be running at a pretty fuel-optimal rate and only for parts of the day (assuming an extended bad-weather outage, like, winter - summertime the solar keeps up if the A/C isn't used, and in a disaster/long-term power fail you just deal with the heat).

 

[Darth_DMack]

Can your genset directly charge your battery bank?
If and when I set up a backup generator, the plan is for the battery bank to be charged by the generator, and the house runs from the batteries - that way the generator only needs to run for battery recharges, and so assuming the generator size is chosen appropriately it should be running at a pretty fuel-optimal rate and only for parts of the day (assuming an extended bad-weather outage, like, winter - summertime the solar keeps up if the A/C isn't used, and in a disaster/long-term power fail you just deal with the heat).

That is how I have it configured. The Genset can charge the battery bank. Now my inverter is wired to just cover the appliances that need AC voltage. Most of my stuff is propane... but, I have a few deep freezers and three refrigerators. Those are wired to draw from the inverter if needed. I spent a little bit of money to make this happen, and HOPEFULLY it will work as planned if it gets to that. The few outages I've had, my Generac has covered beautifully.