offgrid for 13yrs, Proven wind turbine and solar. Installed it myself as well as installed many other system, offgrid, battery back-up on grid, grid-tied. Mostly Outback. Glad to help you.

500KW a month average? What's your largest use month? What's the total solar wattage being presented to you? Where in Montana? I want to look at sun chart.

Largest use months are in the summer due to irrigation and running the water pump (watering the lawn). Summers are usually about 600. If I go with the grid tie-in with battery backup, I'm not really worried about that high usage as if the grid does go down for whatever reason, keeping the lawn watered will be one of the last things I'm concerned with. If I go with off-grid, I could get a separate grid meter for just irrigation. It would separate that from the house and the rates are lower as well.

Options are 12 panel guaranteed at 4800kWh and 16 panel at 6400. The 12 pole mount is $14K, 16 ground mount is $19K, and 16 pole mount is $21K.

I plugged my info into a website and came up with this sun chart.





(Not sure how accurate those are as in the summer our sun doesn't set until dang near 2200).

Use this chart, let me know.

https://www.nrel.gov/gis/image...ovoltaic_2012-01.jpg

Individual panel wattage?

On that chart I'm in the 4.5-5.0 zone.

330 watt panels.

Forgot about this. I'll compare your numbers to mine. Believe the output being guaranteed is generous. I wouldn't get that NET output here.

Use the default efficiencies

http://pvwatts.nrel.gov/index.php

quote:

Originally posted by Gustofer:
I don't trust our grid as far as I can throw it. I want/need the ability to be independent from it.

Maybe your area is different, but the solar PV system we had put in when living in California was actually required by code to turn off when the grid went down.

There was some logic there, from the electrical utility standpoint - if homes were powered when the grid wasn't, then repair folks could get hurt while trying to fix lines. And it's been awhile since we had that system put in - maybe the transfer switches are fancier/smarter/safer now.

But the upshot is, solar systems like that did not automatically help you in outages.

If that's one of your goals, be sure to ask your designer/installer/contractor if the system would actually power your home when the grid goes down.

I believe Arc posted some very good info on solar a year or two ago. Would be worth trying to get his attention.