Standby Generators - School Me

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Jun 17, 2013
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556
Location
Texas
Prior to the massive infrastructure failure here in Texas, I have always toyed with the idea of getting a standby generator because I'm in an area that seems prone to outages. After this past week, getting one is at the top of the list now.

I've calculated that I need about 15kw to comfortably power my home using natural gas that I can tap in my neighborhood. Don't need the big 20kw generators that you see at lowes or home depot as I don't intend to power literally everything and my home is not massive either. With that said, can anyone provide info on what is generally considered some of the better standby generators? I see Briggs and Strattons, Kohler, Cummins, Champion, and of course Generac. Any others I should be looking at? And any other considerations I should keep in mind?
 
I recently had a Generac 22KW unit installed. It is enough to power everything in the event of a power failure. I had the local Generac representative come out and sized the unit. I’m happy with it. It’s kicked on once for a 5 hour period. That was from an eighteen wheeler taking out a power pole. It exercises itself regularly. I’m using propane. Propane has more BTUs than natural gas. I don’t know about your city codes or home owner association’s rules. Generac appears to use a rebranded Kohler engine. Biggs and Stratton makes the Cummins air cooled units. Personally, I wouldn’t rely on public utilities to deliver my fuel.
 
Was reading that thread but really didn't see much regarding reliability for specific brands. More of a discussion on capacity. I have a portable, 5kw generator that powered the bare essentials, but pulling that from storage and setting it up is time consuming. Having something that switches on automatically is what I'm going for.
 
I recently had a Generac 22KW unit installed. It is enough to power everything in the event of a power failure. I had the local Generac representative come out and size the unit. I’m happy with it. It’s kicked on once for a 5 hour period. That was from an eighteen wheeler taking out a power pole. It exercises itself regularly. I’m using propane. Propane has more BTUs than natural gas. I don’t know about your city codes or home owner association’s rules. Generac appears to use a rebranded Kohler engine. Biggs and Stratton makes the Cummins air cooled units. Personally, I wouldn’t rely on public utilities to deliver my fuel.
City codes or HOAs are not an issue at my location. I get what you're saying about public utilities, but I saw the lines that were at propane stations...not terribly interested in having to deal with that in the worst case scenario and even at that, there's no guarantee that there will be propane available at those locations. They both have their pros and cons.
 
City codes or HOAs are not an issue at my location. I get what you're saying about public utilities, but I saw the lines that were at propane stations...not terribly interested in having to deal with that in the worst case scenario and even at that, there's no guarantee that there will be propane available at those locations. They both have their pros and cons.
That’s why you have a 200 gallon tank sitting outside. Call and have a delivery when it gets to 30%.
 
What happens if you lose your natural gas? People have lost both electric and natural gas.
That's certainly a consideration. Propane isn't guaranteed to be available either. A storage tank on my property is not something I'd care to have either.
 
Prior to the massive infrastructure failure here in Texas, I have always toyed with the idea of getting a standby generator because I'm in an area that seems prone to outages. After this past week, getting one is at the top of the list now.

I've calculated that I need about 15kw to comfortably power my home using natural gas that I can tap in my neighborhood. Don't need the big 20kw generators that you see at lowes or home depot as I don't intend to power literally everything and my home is not massive either. With that said, can anyone provide info on what is generally considered some of the better standby generators? I see Briggs and Strattons, Kohler, Cummins, Champion, and of course Generac. Any others I should be looking at? And any other considerations I should keep in mind?
I assume you are talking about a true standby automatic generator. The biggest factor for you in texas , is do you want to run your air conditioning during an outage?

That will be the biggest startup load, depending on your a/c tonnage. A 2 ton central air/ heat pump will probably pull close to 60amps startup.

A 17kw briggs standby unit puts out about 63 amps. What size is your a/c heat pump?
 
I assume you are talking about a true standby automatic generator. The biggest factor for you in texas , is do you want to run your air conditioning during an outage?

That will be the biggest startup load, depending on your a/c tonnage. A 2 ton central air/ heat pump will probably pull close to 60amps startup.

A 17kw briggs standby unit puts out about 63 amps. What size is your a/c heat pump?
It's a 3 ton unit.
 
If you have to haul gasoline or propane, just how will you get it if the power is out? The gasoline pumps won’t work and the propane pumps won’t work.
 
If you have to haul gasoline or propane, just how will you get it if the power is out? The gasoline pumps won’t work and the propane pumps won’t work.
A 200 gallon tank on my property isn't an option.
 
It is very likely that a single portable propane bottles like the kind you get to power a bbq will not feed a 15 KW genset very long before the boiling off of the liquid to gas gets the liquid too cold to provide enough pressure, and even if it did provide the pressure ( witch I think it will not) a BBQ size bottle will not run a 15 KW genset very long. I think you would need a set-up of quite a few of them to feed a 15 KW fast enough and also long enough to make it work.

The 200 gallon tank is a realistic approach to what would be required. You need to calculate how long a gallon of propane will run a 15 KW genset, and then figure out how long you need to run your system in the longest outage you will see. And calculate how big a tank you will need.

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Someone who sells and installs generators along with the propane tanks could give you exact data on what is required,

But here are some rough calculations of what is going on:

1 gallon of propane has 91,500 BTUs of heat energy when its vapors are burned

15 KW = 51,181 BTUs per hour

An realistic approximation of the efficiency of a small internal combustion engine is 20 %

So the engine will consume 5 times the 51,181 BTUs per hour if the genset is running at 100 % load

So lets be generous and say it is running at 2/3 of 100 % load, .66 X 5 X 51,181 = 168,897.3 BTUs per hour to power the engine

168,697.3 / 91,500 = 1.846 gallons of propane per hour to power a 15 KW genset running at 2/3 load capacity.

in 24 hours that would require 24 x 1.846 = 44.3 gallons of propane per day.

At that rate a 200 gallon tank will last 200 gallons / 44.3 gallons per day = 4.51 days

And a 200 gallon tank is the kind of size required to provide enough surface area to keep the liquid propane warm enough from the cooling effect of the liquid changing into gas to power your 15 KW genset at a rate of 1.85 gallons per hour continuously when the weather is cold.

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These are just some calculation using realistic numbers for the amount of BTU a gallon of propane has, and an approximation of how much an internal combustion engine powering a 15 KW generator running at 2/3 of maximum load will require. I do not work in the propane or generator industry. But I did get straight A in both my college physics courses. So these approximations are probably very close to what you will experience in real life.

BTW, a 20 Lb BBQ bottle has 4.7 gallons of propane. That would run your 15 KW genset for: 4.7 gallons / 1.846 gallons per hour = 2.546 hours ( that is almost exactly 2 and a half hours ) if it was running at 2/3 of full rated capacity.

But if it was cold out the bottle would get too cold and loose pressure from the cooling effect of the liquid propane boiling off and becoming gas, and it probably would not be able to supply enough pressure to run the genset for even one hour before the pressure of the gas coming off of the bottle was not enough to supply what the genset needed to keep running.

And often those 20 Lb bottles are not filled up all the way. Instead of 4.7 gallons, you can expect to get something like 4.4 gallons.

Which works out real nice to show that with the above calculation of 44.3 gallons per day, you would need 10 of the 20 LB bottles to run a 15 KW genset at 2/3 load for one day ( 24 hours ).

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So if you wanted to run that 15 KW genset at an average usage of 2/3 rated load for a one week outage without having a propane truck come out and refill the tank every 3 or 4 days ( which is what would be required if you only had one of the 200 gallon propane tanks ), you would need 2 of the 200 gallon propane tanks on your property. Two of the 200 gallon tanks would last 9 days at 2/3 average load on a 15 KW genset. But you would want to get them refilled every 7 or 8 days.
 
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BTW, in a long outage, do not forget to change the oil often. 50 hours is not too often, and 100 hours with very good oil of the correct viscosity for the ambient air temperature is doable, like when you are running Mobil 15W-50 in the summer, or a good 0W-30 in the winter.
 
It is very likely that a single portable propane bottles like the kind you get to power a bbq will not feed a 15 KW genset very long before the boiling off of the liquid to gas gets the liquid too cold to provide enough pressure, and even if it did provide the pressure ( witch I think it will not) a BBQ size bottle will not run a 15 KW genset very long. I think you would need a set-up of quite a few of them to feed a 15 KW fast enough and also long enough to make it work.

The 200 gallon tank is a realistic approach to what would be required. You need to calculate how long a gallon of propane will run a 15 KW genset, and then figure out how long you need to run your system in the longest outage you will see. And calculate how big a tank you will need.

---------------------------------------------------------------------------------------

Someone who sells and installs generators along with the propane tanks could give you exact data on what is required,

But here are some rough calculations of what is going on:

1 gallon of propane has 91,500 BTUs of heat energy when its vapors are burned

15 KW = 51,181 BTUs per hour

An realistic approximation of the efficiency of a small internal combustion engine is 20 %

So the engine will consume 5 times the 51,181 BTUs per hour if the genset is running at 100 % load

So lets be generous and say it is running at 2/3 of 100 % load, .66 X 5 X 51,181 = 168,897.3 BTUs per hour to power the engine

168,697.3 / 91,500 = 1.846 gallons of propane per hour to power a 15 KW genset running at 2/3 load capacity.

in 24 hours that would require 24 x 1.846 = 44.3 gallons of propane per day.

At that rate a 200 gallon tank will last 200 gallons / 44.3 gallons per day = 4.51 days

And a 200 gallon tank is the kind of size required to provide enough surface area to keep the liquid propane warm enough from the cooling effect of the liquid changing into gas to power your 15 KW genset at a rate of 1.85 gallons per hour continuously when the weather is cold.

-------------------------------------------------------------------------------------

These are just some calculation using realistic numbers for the amount of BTU a gallon of propane has, and an approximation of how much an internal combustion engine powering a 15 KW generator running at 2/3 of maximum load will require. I do not work in the propane or generator industry. But I did get straight A in both my college physics courses. So these approximations are probably very close to what you will experience in real life.

BTW, a 20 Lb BBQ bottle has 4.7 gallons of propane. That would run your 15 KW genset for: 4.7 gallons / 1.846 gallons per hour = 2.546 hours ( that is almost exactly 2 and a half hours ) if it was running at 2/3 of full rated capacity.

But if it was cold out the bottle would get too cold and loose pressure from the cooling effect of the liquid propane boiling off and becoming gas, and it probably would not be able to supply enough pressure to run the genset for even one hour before the pressure of the gas coming off of the bottle was not enough to supply what the genset needed to keep running.

And often those 20 Lb bottles are not filled up all the way. Instead of 4.7 gallons, you can expect to get something like 4.4 gallons.

Which works out real nice to show that with the above calculation of 44.3 gallons per day, you would need 10 of the 20 LB bottles to run a 15 KW genset at 2/3 load for one day ( 24 hours ).

----------------------------------------------------------------------------------

So if you wanted to run that 15 KW genset at an average usage of 2/3 rated load for a one week outage without having a propane truck come out and refill the tank every 3 or 4 days ( which is what would be required if you only had one of the 200 gallon propane tanks ), you would need 2 of the 200 gallon propane tanks on your property. Two of the 200 gallon tanks would last 9 days at 2/3 average load on a 15 KW genset. But you would want to get them refilled every 7 or 8 days.
It is very likely that a single portable propane bottles like the kind you get to power a bbq will not feed a 15 KW genset very long before the boiling off of the liquid to gas gets the liquid too cold to provide enough pressure, and even if it did provide the pressure ( witch I think it will not) a BBQ size bottle will not run a 15 KW genset very long. I think you would need a set-up of quite a few of them to feed a 15 KW fast enough and also long enough to make it work.

The 200 gallon tank is a realistic approach to what would be required. You need to calculate how long a gallon of propane will run a 15 KW genset, and then figure out how long you need to run your system in the longest outage you will see. And calculate how big a tank you will need.

---------------------------------------------------------------------------------------

Someone who sells and installs generators along with the propane tanks could give you exact data on what is required,

But here are some rough calculations of what is going on:

1 gallon of propane has 91,500 BTUs of heat energy when its vapors are burned

15 KW = 51,181 BTUs per hour

An realistic approximation of the efficiency of a small internal combustion engine is 20 %

So the engine will consume 5 times the 51,181 BTUs per hour if the genset is running at 100 % load

So lets be generous and say it is running at 2/3 of 100 % load, .66 X 5 X 51,181 = 168,897.3 BTUs per hour to power the engine

168,697.3 / 91,500 = 1.846 gallons of propane per hour to power a 15 KW genset running at 2/3 load capacity.

in 24 hours that would require 24 x 1.846 = 44.3 gallons of propane per day.

At that rate a 200 gallon tank will last 200 gallons / 44.3 gallons per day = 4.51 days

And a 200 gallon tank is the kind of size required to provide enough surface area to keep the liquid propane warm enough from the cooling effect of the liquid changing into gas to power your 15 KW genset at a rate of 1.85 gallons per hour continuously when the weather is cold.

-------------------------------------------------------------------------------------

These are just some calculation using realistic numbers for the amount of BTU a gallon of propane has, and an approximation of how much an internal combustion engine powering a 15 KW generator running at 2/3 of maximum load will require. I do not work in the propane or generator industry. But I did get straight A in both my college physics courses. So these approximations are probably very close to what you will experience in real life.

BTW, a 20 Lb BBQ bottle has 4.7 gallons of propane. That would run your 15 KW genset for: 4.7 gallons / 1.846 gallons per hour = 2.546 hours ( that is almost exactly 2 and a half hours ) if it was running at 2/3 of full rated capacity.

But if it was cold out the bottle would get too cold and loose pressure from the cooling effect of the liquid propane boiling off and becoming gas, and it probably would not be able to supply enough pressure to run the genset for even one hour before the pressure of the gas coming off of the bottle was not enough to supply what the genset needed to keep running.

And often those 20 Lb bottles are not filled up all the way. Instead of 4.7 gallons, you can expect to get something like 4.4 gallons.

Which works out real nice to show that with the above calculation of 44.3 gallons per day, you would need 10 of the 20 LB bottles to run a 15 KW genset at 2/3 load for one day ( 24 hours ).

----------------------------------------------------------------------------------

So if you wanted to run that 15 KW genset at an average usage of 2/3 rated load for a one week outage without having a propane truck come out and refill the tank every 3 or 4 days ( which is what would be required if you only had one of the 200 gallon propane tanks ), you would need 2 of the 200 gallon propane tanks on your property. Two of the 200 gallon tanks would last 9 days at 2/3 average load on a 15 KW genset. But you would want to get them refilled every 7 or 8 days.
Double quotes. No idea how I did that.
Thanks for sharing. 200 gallons for 4.5 days is reasonable. I could probably make it last 9-12 days if I only ran it as needed.

This was another reason I bought a 1000 gallon propane tank. That, and well, it was all they had at the time. It sure is (or was) nice filling up at $.89 a gallon in the spring.
 
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