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Building First System - thoughts and advice appreciated

Coil

New Member
Joined
Jan 19, 2021
Messages
27
This place and Will's channel have been hugely helpful. I really appreciate those who've taken the time to organize so many resources.

I live in an area that can experience rare but lengthy power outages and of course the usual shorter outages that happen most anywhere.

My goal is to be able to charge my electronics power some lights, a window AC unit (if power was out for a long time in the summer it can be miserable), refrigerator and freezer. I have 6 320 watt mono panels with an open circuit voltage of 40v (and nothing else, so far).

We'll probably be moving in the next couple years or I would consider roof mounting a system. Instead, I'd like to put together two portable racks of 3 panels each in series and then connect those two sets in parallel. My first area of ambiguity is when it comes to building the racks. Most people do it with 2x4s and that's fine but for the difference in bulk and weight I'd just as soon get some proper rails like you would use to fix panels to a roof. So I suppose in my mind there would be 10' rails parallel to the ground with the panels attached to them in the usual way and then 2x4s running vertically as needed for stability. I just haven't seen anything set up like that which gives me pause.

The other question that I have with respect to the mounting of the panels is when fixing them to the frame. I've looked and haven't really seen anyone discussing that particular piece of hardware in any depth. Most of them look like they just sort of "squeeze" the outer edge of the panel to hold it down. Are the clamps for these things just so universal and trivially simple that there's just no reason to go into any depth on it? I just don't want to do something that seems simple and find out that I damage my panels in some way.

For my needs, it looks to me like the growatt all-in-one (https://watts247.com/product/spf-3000tl-lvm-24p/) will do what I need with a minimum of complexity and cost, particularly as this is strictly an emergency system and will be off most of the time. As far as I can tell this is compatible with the panel setup I described.

For batteries, I think I like this unit (https://bigbattery.com/products/24v-170ah-lifepo4-power-block-preorder-rv/). Frankly though, I find it suspicious. Perhaps I'm looking in the wrong place but it doesn't appear that I could even build a good quality battery for that price/watt.

I have other questions, but I was going to read Will's book first before I waste time on questions that are answered elsewhere.

I would appreciate anyone pointing out considerations that I haven't thought of and any obvious inconsistencies or compatibility issues I've overlooked in my ignorance. Once I've established that these are in fact the main components I'm going with I can get into the nitty gritty of wiring and fuses in earnest.

Thanks.
 
You've identified the things you want to run, but have you characterized their power use?

Step #1: Link #5 in my signature to determine the available solar for you location, panel orientation and tilt.
Step #2: Link #1 in my signature to characterize all your devices, their power needs and daily hours of use.

Without the above, you're just guessing. If you have a goal, it's important to design for the goal.

I'm guessing your 320W panels are around 50#, so three of them mounted in a "portable" system would be 150# + rack. Doesn't sound particularly portable, but they could be temporary in nature for the future move.

The Growatt and Bigbattery items may be fine, but you won't know until you determine your actual need.

Using a broad brush, 6 320W panels is 1920W of solar. This would require 80A charging in a 24V system, which the Growatt provide. Assuming an optimistic daily solar of 4 hours, 1920W of panels, you could harvest 7.7kWh of energy. This may be more in summer, much less in winter. That's enough energy to run 3 full size residential refrigerators.

The battery you have selected is 25.6V * 170Ah = 4352Wh, of which 80% is usable, so 3.5kWh.

Your proposed system can currently utilize 3.5kWh of energy over a 24 hour period with additional energy available during charging hours. This can likely power the devices you stated (fridge + separate freezer + other low power items); it could also power a small 500W A/C unit for about 6 hours/day.
 
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