I really should get a generator.  We lose power, on average, once a week to once every week and half.   Sometimes for 5 minutes, once for over 24 hours.  

That is just in 2 years.  Tried to speak with the power company, it’s a co-op and they really don’t care.  

No natural gas available.  I’ve decided on propane simply for ease of storage.   I can bury a 500 gallon tank, fill and be done.

I have a 10kW solar panel array with a 16 kWh battery back up.  The battery can power everything except the high draw appliances.  The biggest issue is the battery can not start the AC.  It can keep it going, but can not start it.

We are building onto our house.  We have 900 square feet and will add another 3000 square feet.  Long story.  

Ok. The question.  

I would like the highest quality propane generator, but I don’t need that much raw power generation.  

I’ve heard rumors that to get a quality generator, I really need to look at the 22kW units.

I do not mind spending the money.  I would like to buy quality and have it sized appropriately.  

Any other options?  

I could get another battery for $10k, and I am considering it.  
I also could just get the 22kW generator and be done with it.  

It’s all new so I have options.   Space ain’t a concern.

SO purchased a propane 10K from ebay a few years back because we are in the same boat loosing power all the time. It works well but I need to head out to the shed and start it and then plug in all the cords and appliances that need power. We are going to get a ENERAC or KOHLER 22K whole house with the auto transfer switch and be done with it. They are excellent generators and work very well. I am going to get the natural gas version as we have natural gas in our house....

I definitely would like the auto transfer convenience.  

Half the time we lose power, it’s sunny with high winds.  Almost never have we lost power and the sun was not out in the next day.  However, I can see the potential of that happening.

OP, I could afford any option I wanted, but chose to bury a 1000 gal propane tank and buy two Honda 7000 watt inverter generators.  

I'm ocean front and nothing lasts more then five years outside due to corrosion from salt air. I have a friend that installed a standby generator close by that literally corroded away before he needed it. The power here really only goes out during hurricanes which aren't to often.

I bought the propane gas conversion kits for them.  They were easy to install.    This way the generators are stored indoors when not in use, and I have portability if needed, including moving to higher location or another location.  I have to manually hook up the gens; however, I have a 50amp plug outdoors that ties into my panels with manual lockout breakers.  I can run one of my A/C central units if needed.  I can also run one generator only to save fuel, and have the redundancy of two units over one. Total cost not counting the tank, which I needed anyway for cooking, around 9K.

That’s one of my concerns.  Is having a generator that doesn’t get used often and then fails when it’s needed.  

Yes we lose power often, but the battery has been 100% so far (minus the AC).  

Often, we do not know the power cut off.  

The dual Honda generators seem intriguing.

If you have an ATS you can set the generator to test run at your desired interval.  Mine runs once a week for 30 mins, picks up the house load and then transfers back.  Peace of mind that I know it works.

I’d personally get a whole house unit.  If cost isn’t a concern get a commercial grade unit instead if the consumer ones sold at the box stores.  Liquid cooled is also another plus but costs more.

Any recommendations on the commercial side generators?

I’m staying with propane.  If I have to use diesel, I’ll really have to think on it.  

Right now I’m really thinking about getting another 16-18.5kwh battery.  It’ll give me the amps I need to start everything.

I would definitely stay with propane.

Any of the big name manufacturers are good, Cat has generally gotten out of the smaller standby units (unless you find a used one). Kohler is reliable and is what I use at my house.  I’ll double check the model number tonight but I believe it’s the 30RCLQS6.

We have had an 11.5 kw Generac for three years, no issues. It runs itself for 15 minutes once a week for exercise. Runs everything in the house except the electric oven and dryer.

An 11.5 kw won't run your oven or dryer? The max draw on a dryer should be far less. An oven is a maybe. I have a double wall oven plus cooktop so when the draw of both is combined they exceed 11.5 kw but that's with all burners on...

For point of reference my 6kw genny will run oven/cooktop if I'm conscientious about how many burners I'm running.

We have a 22kw Generac and love it. We are 25 miles from the nearest town and every time a squirrel commits suicide on an electric wire we lose electricity. Not to mention hurricanes and car accidents taking out poles. We have a thousand gallons buried.
Our house is all electric, Electric water heater, airconditioning, electric washer and dryer, electric range, refrigerators, it all runs fine.

To answer your question the highest quality will be what is called a prime power generator designed to run 24/7 except for normal maintenance.
Typically they are 1800rpm liquid cooled.
The one I have which is no longer made is a 21kw Eaton with a Ford lr425 inline 4 cylinder engine.

As far as your situation, how will your power draw change once you add the 3,000 sf ?
I think once you determine that you may have a clearer answer as to an extra battery or adding a generator.

I don't have natural gas in my area so I'll also be limited to propane for a generator.

How long does a 1000 tank last?

No simple answer to that. If an above ground tank it represents somewhere around 700-750 usable gallons (max fill being 800 & you can't use past the point of sufficient surface area for vaporization).  With that in mind, you have to consider the consumption rate of your equipment.  That will depend on power draw & size of the engine.  The size of the engine can define the minimum draw rate (i.e at zero draw) & power draw then adds to that.  Maximum possible power draw will be capped by engine size (& power head).

Based on our electric bill usage numbers, when running, the 22kw standby system at our place is generally be supplying a bit over 2 kw/hour (10% load for system).  If we don't change our usual behavior, based on past use, it burns maybe 1 - 1.25 gallons / hour.  If we run it 23 hours a day (1 off for cool down & oil check) then that's 23 - 29 gallons per day without conservation.  Using 26 gallons per day would use up 700 gallons in 26.9 days without making any significant attempt at conservation as long as our use stayed at that ballpark 2kw/hour rate.

If we were using a  4 or 5 kw generator our fuel use would almost certainly be lower for the same ~2kw average use because of the smaller motor, but we wouldn't be able to run the systems whose startup draw required installation of the 22kw unit.