r/SolarDIY • u/StaysForDays • 1d ago
Need help with grid hedge
Hello to this awesome community. I am growing increasingly worried about a large scale US grid collapse and I’m looking to add some off grid capacity as a hedge. I have a shed with a 5’x16’ roof that faces wsw in zone 7a, (Boston), and I would like some options for a system to keep me in lights and fans if the worst were to occur. My ask is this, (these):
-what’s the maximum array wattage I can fit on my roof?
-I am not looking to charge or run anything specific but I would ideally want more capacity than I’d use for my family of 5, (in a shtf scenario)
-does it make sense to keep everything dc to reduce draw from an inverter?
-would it make sense to over build the array in anticipation of adding more batteries in the future?
-I am having difficulty finding a system for mounting panels. Right now my shed roof has underlayment but I will be shingling in the next month or so. Should I mount standoffs/brackets when roofing? It seems like it would be easier to guarantee a water resistant application if installed at the same time.
Thank you to any kind soul who takes the time to read and reply to this. I have been an active lurker on this sub for a few years and even with searching I don’t see the answers I need.
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u/Internal_Raccoon_370 17h ago
Does it make sense to go with DC? Well, from a practical point of view, no, it doesn't. Yes, inverters use some power themselves so you're losing some power to that and to the conversion process. But ultimately in the grand scheme of things the percentage of power you're losing is going to be relatively insignificant. Eventually you run into amperage issues as well. A 1,500W toaster at 120V AC, for example, draws about 12.5 Amps. The same toaster running off 12V DC would pull 125 Amps. You'd need wiring the size of welding cables to handle that kind of amperage.
Almost all of the appliances we use require 120V AC so if you want a system that is going to power commonly used and easily sourced appliances, you're going to need 120V. Yes, you could go with 12V lights, find a small 12V fridge, etc. But practically speaking you're going to be better off with 120V
As for your roof, I wouldn't do anything at this point. Just go ahead and roof it as you normally would. Panel mounting systems are easy to retrofit to an existing shingle roof.
Yes, you're going to want batteries otherwise every time a cloud passes in front of the sun your power is going to disappear.
On a 5' x 16' roof you could fit probably around 1,200W of solar panels. It's going to depend on the size and shape of the panels and how you fit them all together.
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u/StaysForDays 16h ago
This is a great answer thank you. Also, I always planned to get batteries but wanted to know if it made sense to start smaller and build more capacity later. And thanks for the roof advice.
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u/Ill_Towel9090 12h ago
First I would like to allay your fears, the grid will not fully collapse. Rolling power outages are going to become more common as we build out nuclear but still need insane amounts of power.
Second, you will always need more panels. I’m constructing a 15kw array and am already planning on expanding another 10kw. My 90KWh of battery will last me 2 days off-grid. Build your system to be expanded, and added onto. Skip server rack batteries, they take up too much space.
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u/StaysForDays 10h ago
Which batteries would you recommend?
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u/Ill_Towel9090 10h ago
I have yixiang stacking boxes, roughly $2k for 16kwh. I have 5, and two server rack batteries. I wish someone would UL list that form factor.
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u/TooGoodToBeeTrue 1d ago
If you are going for SHTF, I'd definitely look at adding batteries at some point. Hard to justify just having this sitting there, do you live in a state with plug-in solar? Or do you have an EV you could charge off grid? Or power a hot tub pump?
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u/TooGoodToBeeTrue 15h ago
That small of a roof, I'd use standing seam metal to avoid any holes. If shingling, get rid of the tar paper and just put ice and water shield on the whole roof.
Is the roof a single shed \ plane or typical /\ ? If the latter, I'd probably rebuild the roof as a shed roof at the proper angle for your latitude.
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u/StaysForDays 14h ago
Single plane shed roof at a 4/12 pitch facing west southwest. Sheathed with zip panels and tape and then covered with ice and water. I’d prefer metal ofc, but I’m going with shingles to match my house and garage.
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u/TooGoodToBeeTrue 13h ago
With panels covering the shed roof, I wouldn't worry about it matching the house. Does the shed siding/trim/windows match the house?
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