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Posts: 3
Reply with quote  #1 
Hi, new to the panel, new to solar.
I have a 1.8kw LiFePO battery bank (12.8v 144Ah) that I'd like to start charging with solar.
I'm looking to get 400 to 500 watts of panels and a 40 amp mppt solar charge controller. Most likely 100 watt mono panels from Renogy. But I'm having trouble deciding how best to configure the PV array.
The only practical south-facing location I have is the overhang above my two car garage. The area could accommodate up to five 100 watt panels end to end. I get a couple hours of mostly unobstructed sun in the middle of the day even in winter. But in the mornings and afternoons, due to power lines and lots of trees, I have quite a bit of shading. I'm not sure if I'd be better off with five 100 watt panels wired in parallel (1s5p) to minimize the effects of shading, or four panels wired as two series pairs in parallel (2s2p) to increase the voltage and take better advantage of the mppt.
Also, I live in Seattle, where we have a lot of cloudy days.
Any insight would be greatly appreciated.


Posts: 174
Reply with quote  #2 
If you have substantial shading then you might(?) be better off using PV panels with micro inverters (eg Enphase M215) to generate 220v and a simple charger to charge your batteries as needed.

Each panel/inverter acts independently and if one is shaded the others will still produce.   You can then place panels tens of feet apart from each other (up to 16 in a string on a 20A breaker) to grab sun/PV from wherever it hits.

Also, if you go with net metering you will get credit for power generated when your batteries are full.

Posts: 3
Reply with quote  #3 
Thanks. That seems a little larger scale than what I'm thinking. This wouldn't be grid-tied in any way. These batteries are primarily for a portable power unit, but I'd like to add solar charging capability so they can be relied on as backup emergency power in case of a long-term power outage.

Posts: 174
Reply with quote  #4 
If you only want to use the PV output in case of a long term power outage, you may be putting a lot of time and cash into something that you never use. (How often do you get long power outages in Seattle?)

With your 'shading' panels in parallel is the only sensible option, any series connections will cause all the series panels to reduce their output to that of the most shaded one, even if one or more is in full sun.

To see you through longer outages you might be better to just put the loot into buying more battery capacity,
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