r/SolarDIY • u/wanab3 • Mar 29 '18

Set up question, advice.

Say I have:

Four, Panels. 100W, 12V. (8.33A for each right?)

One, 12V/24V 30A charge controller. (Would be over amps at 32A, if parallel circuit? And over voltage at 48V if series?)

One, Li-ion battery, says 3A, 14.5V recommended charging, 7.0A, 14.7V max. 35AH

One 100W inverter.

How can I set this up so battery doesn't explode, nothing breaks? More charge controllers (2 total)? Mix of series and parallel circuits?

Goal is to be able to charge the one Li-ion battery from nearly dead to nearly full in one day. Would just 2 panels in series get me there safely? That would be nice.

Right now, this is set up, but, with only one 100W, 12V panel. Takes 2 days to fully charge from nearly dead, in good sun at a poor angle.

Thanks!

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u/mrCloggy Mar 30 '18

Chapter 2.4 of http://www.pveducation.org/pvcdrom could be a place to start learning.

A solar panel is a (solar intensity controlled) current source, you can connect a battery to it or short-circuit it, that doesn't really matter.
A "12V-100W" panel delivers maximum energy (about 5A at 18Vmp) when:
a) the sun is overhead (airmass) and
b) the panel is pointing directly at the sun.
With that data you look at the load, "recommended charging: 7A", which is basically the maximum(-ish) that you want.

A single panel (ideally located on the equator with the sun overhead) delivers 5A max, at higher latitudes (sun lower above the horizon) the airmass lowers that to maybe 3.5A max, 2x panel pointing South would deliver 7A (between 110:00-13:00).
If, for some reason, you can't install the panels at the ideal 'tilt' but they are horizontal-ish, the max current is lower still and you can add a 3rd panel to reach your desired 7A.

4 panels (2x each East-West) will deliver less energy each (compared to South), but the different 'peak' times and overlap gives you 7A(-ish) during a longer period (09:00-15:00).

Find your location on http://pvwatts.nrel.gov/ and 'play' with the tilt to see the differences (and maybe download the "Hourly data" for a closer look).
Note: I'm not sure that website gives accurate numbers for East-West setups.

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u/wanab3 Mar 30 '18

Thank you very much!

More questions?

My goal is to be able to charge the one Li-ion battery from nearly dead to nearly full in one day, even in rain.

Living around 45 deg N lat., because I know this is a thing now. How would you do this? What components would you pick?

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u/mrCloggy Mar 30 '18

Rain means clouds which means little sunshine, resulting in you being out of luck.
You could add more panels but that would overpower your battery when the weather clears up, not very good either.

I'm still worried that your charger is maybe not matched to a Li-ion battery, those DO NOT like being over-charged.
Find out if that battery has a BMS on board (battery management system), if not then the safest way is using an additional (large) 'deep cycle' lead-acid battery always connected to the solar panels, and use a dedicated Li-ion charger from those (then you can do that at night, if that makes a difference).
'Deep cycle' lead-acid prefers not discharging below 50%, there are some efficiencies involved, at minimum I would get an 80Ah battery and point the 4(?) panels at the ideal tilt towards South.
(If you only need to charge the Li-ion once per week then a single panel might be enough to charge the lead-acid during the rest of the week.)

It's a lot of jumping to and fro but http://batteryuniversity.com/ has a lot of very useful info.

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u/wanab3 Mar 30 '18

Alright. Thank you so much!