Mountain cabin off-grid

Solray said:

I'd have gone with 48 volts rather than 12 or 24.

Not sure what to do with that comment. Good for you, I guess.

I did a significant amount of cost trades, mathematical analysis of loads through the day, and consideration of some ancillary requirements like 12VDC for some loads that are already in the cabin.  I'm guessing you don't know all that.  Anyway, the increased cost for a 48V inverter couldn't be justified, and made some things harder to do rather than easier.  It was considered though.

jonr said:

I predict it will tip over - at > 88 mph of wind :-).

Well, I certainly hope not. It should be OK according to the Snap-N-Rack on-line tool. Although that was set to 90MPH, so maybe you are close. 

With all the cross member bracing and 3,000 lbs of concrete, the thing is pretty rock solid. We don't get much real strong winds up there, except micro-bursts. That pole fence you see behind the ground mount has been there for 42 years (I built it in HS), and I'm not thinking it would still be standing if there was a 90 MPH wind at any time during the last 40 years.  I'll just keep my fingers crossed!

BB. said:

Very clean install.... Kind of went "big" on your system vs your first post in the discussion.

Looks like it will supply your power needs for a long time to come.

Will you have any issue with "heaving" (ground freezing) with using the ballasts vs post holes below frost line?

Enjoy!
-Bill

Yeah, I was talking with my siblings (partners in this effort) on how it grew. They had added some additional future loads to include, but most of the increase was me doing the analysis over and over. As I've mentioned before, I got the epipphany from reading your posts that it makes more sense to size the PV array according to what you need to charge the battery, rather than base it on the daily energy needs. That (and lower prices for panels) led me to a bigger PV array than I would have imagined.  The PV went from two 300+ watt panels, to three panels, to four panels, and finally to five panels (which had to round up to six to make an array for the MPPT). Funny how that always works.

The well pump by itself drove me to a bigger inverter than we would otherwise need. However, it runs so little during the day (2 min, 40 seconds each time, and generally no more than 3-4 runs in a day) that it doesn't have a huge impact on the battery bank.

We shouldn't have any problem with the heaving. That tends to happen where the soil is a little more moist. The ground up there stays pretty dry, and we don't think the 3000 lbs of concrete will get lifted at all.

We would have preferred deeper concrete piers instead of the ballasts, but it's solid bedrock a few feet down. In fact, my plan for one 8 ft ground rod ended up being two 4 ft rods, and even then I had to use a jack hammer in several different candidate places before we could get them down that far.

Solray said:

My system is similar with a few 12 volt loads, I used a 110 ac to 12 volt DC converter for the 12 volt portion. It was pretty straight forward, the other option it a 48 volt dc to 12 volt dc converter made for golf carts, but I wanted to have a little more head room on the 12 volt side just in case.
There are trade offs whatever you decide on. I like the 48 volt set up though and will do the same again on the next project as well.

Obviously a simple 12VDC wall wart could provide the 12VDC from my 120VAC inverter power. That wasn't the point. The inverter we are using can be programmed for start and stop of down times, where it puts itself into standby.  Our design was using a few 12VDC items such as hallway nightlights, phone chargers, etc. so that if we chose to we could use this feature to shut down the inverter every night from 11:00pm to 6:00am or so. This would eliminate tare loss during that period, yet still provide the few things through the night that were needed. Like I said, this was all stuff you didn't know when you made your comment. That's fine.

I did look into 48VDC-to-12VDC buck converters. They are far less common than the 24VDC-to-12VDC converters because of the large market for 24VDC trucks that want to use 12VDC items. Less common mostly meant I was going to be rolling the dice on quality and how hard it would be to replace.