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Off grid treehouse 48 v

Toddburkett

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Sep 24, 2021
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Hi I’m definitely a newbie, live in Nashville Tennessee, have an off grid 650 square-foot treehouse. I recently just installed a geothermal loop for my treehouse, 55 Chevy radiator box fan 600 feet of ground loop, uses 135 W to produce 65° air-conditioning I decided to get a real solar system, bought 24 used panels off of Will‘s recommendation and an all in one in PPT 6.5 kW 48 V system also off of his website! Have not purchased my battery system yet I was thinking of waiting until after the panels and charge controller are installed to see what actual power I’m going to receive, I’m in a valley so not sure how many hours of sunlight I’m going to get. Minimum battery I’m going to get would be hundred amp hour Sok lithium iron phosphate probably? But I am considering custom building to get more
capacity!
I don’t know what connectors I need yet or fuses for the DC from the panels and I’m looking for some advice, plus best place to ground the system ?from the panel? To the ground like a normal house? I plan on building a wooden support structure for the panels as I have a band sawmill, but not sure how to attach the panels to that or should I consider something else?
 

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You can use PVWatts - https://pvwatts.nrel.gov/pvwatts.php - to get good estimates of incoming power. However, I see nothing but trees and any shading will *greatly* reduce PV power - so try to find a spot or even spots where the panels can be 100% in the sun as much as possible. Even if you did 2 panels here and 3 there etc - its just wiring... and full sun is key.

You said 24 panels but didn't say their wattage. If you share the panel wattage and consumption info (or even guess) we can give a pretty good estimate of the battery size you'll need to optimize power from the system :)
 
The geothermal uses 135 W continuously, probably won’t need to run all the time, the biggest power need is i want to run a full size regular refrigerator
And then minor compared to that will be Soundsystem TV type stuff
 
24 * 250w panels = 6000w PV array.
135w +90w refrig average + 100w other = 300w (continuous) * 24hrs = 7200watts / day.

With a 6kw PV array, this is enough to achieve 7kwh/day in dead of winter and 4 times that in summer.

Battery - 80% DOD of a 9kwh battery = 7,200wh - e.g. let you run 300w continuous for 24hrs...
As an example, 16 x 200ah LifePo4 cells (e.g. 48v nominal) would be 9.6kwh.
You might get by on 1/2 that to start - e.g. 16 x 100ah = 4.8kwh - but leave room to grow (double, triple, quadruple).

At 6000w PV, you could go up to (aprox) 18kwh battery bank and be matched for efficient use of the larger consumption available in summer of 28kwh/day thru the 24hr cycle.

In fact, that's my general advice on all this... OK to start smaller and if possible put things / plan things so you can expand because once you have a working system as you'll probably become a huge fan of solar power and you'll want to expand once you see how cool it is. :)
 
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I’m going to have four strings of six panels in series and then two strings parallel ! plan on using the regular connectors out at the panels and run the four conductors in conduit underground to my treehouse and up inside! Some people have said to use a combiner box down by the solar panel it has DC disconnects and stuff in there but it’s $216 versus for DC Cut off‘s up in the treehouse before I get to my all in one MPPT do I need anything else? Dc fusing ?system should be at 2:40 V
 
DC Cut off‘s up in the treehouse before I get to my all in one MPPT do I need anything else? Dc fusing ?system should be at 2:40 V
OK, if you have the DC cut-off at the treehouse you can make the cut-off a breaker - can serve as both a on/off 'switch' but also a fuse.
I'd use a high quality breaker as the cheap ones don't do on/off very well - maybe something like this - https://www.amazon.com/MidNite-Solar-Breaker-300VDC-MNEPV30/dp/B00A6XHCMK/ref=sr_1_13 - 300vdc@ 30a.

The primary reason I did combiners is for quick disconnect requirements within 10ft of the array per my local jurisdiction. The quick disconnect box requirement gives an easy place for combining. The advantage of local array combining in my case is that I can toggle on/off individual strings at the array which might be useful to debug a failing array - but then I have 15 strings of 3s.
 
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The breaker says rail mounted I assume is to go inside a box but can you mount it where it’s not an electrical box? Or how do you mount them?
 
The breaker says rail mounted I assume is to go inside a box but can you mount it where it’s not an electrical box? Or how do you mount them?
They mount on standard DIN rail - https://www.amazon.com/gp/product/B015E4EIOK/ref=ppx_yo_dt_b_search_asin_title - like this.
Yes, you typically put the DIN rail and wiring in an electrical box for safety. Any box (electrical for code or even plastic for safety) will do but it should have a lid that closes for safety :)
 
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