Solar panels with different light intensity, how to connect / what controller - Page 1
Forum section: electronics / general

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: December 04, 2021, 11:45:52 pm
content: I'm a total noob to this stuff.Just want to play with solar panels, say 50..100W, like 1m x 0.5m monocrystalline, two of them, positioned in excess window area (indoors) in two different rooms (I can't put them on the roof, I don't own the thing, this is basically an experiment of what's possible from where I am).It's 2 to catch the sun when it goes around a corner. So I guess that's a less economical way of "tracking"But when I have such a MPPT controller with a lead gel battery connected as a buffer, it won't like having two panels e.g. in series with two strongly different amounts of light hitting them.How would one actually do this to get some semblance of efficiency? (in the confines of this suboptimal physical setup)

author: Faringdon
author_rank: Super Contributor
timestamp: December 05, 2021, 12:48:13 am
content: I dont think MPPT will care about the two panels with different light on each.The software of the MPPT.....it ups the reference on the converter, and keeps doing so till the input power starts to go down........then it backs off....and keeps re-iterating so it stays on max power point.

author: fourfathom
author_rank: Super Contributor
timestamp: December 05, 2021, 01:42:21 am
content: Quote from: Faringdon on December 05, 2021, 12:48:13 amIf the panels are in series, the MPPT controller may not "care about" the differing illumination on the panels, but it's hardly going to give you the maximum available power. A solar panel is much like a constant-current source (with a voltage limit), and that current depends on the level of illumination. With two panels in series, the total current will be limited to that delivered by the shaded panel, and most of the potential power of the unshaded panel will be wasted.When you have multiple, possibly shaded panels, the best approach is to have per-panel MPPT controllers. Second-best is running the panels in parallel into a shared controller.When you have many panels, it might make sense to put them in series and let the panel "bypass" diodes shunt around any shaded panels, but you still need enough unshaded panels to deliver adequate voltage to the controller. Two panels is probably not enough.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: December 05, 2021, 01:11:19 pm
content: If using two MPPT controllers - can they go to the same lead battery, or do they disturb each other?Ah I found something:https://cleversolarpower.com/multiple-charge-controllers/Apparently all but one of the controllers then needs to turn off "equaliizing", from what I read a special mode to chemically "refresh" the battery plates.Does every MPPT controller, including cheap Chinese ones on ebay typically do that? They don't tend to mention that it seems.

author: fourfathom
author_rank: Super Contributor
timestamp: December 05, 2021, 03:46:03 pm
content: Equalizing is done by charging the battery until the voltage reaches about 16V (in a 12V system, the voltage depends on the battery type and charger design). This is normally done to FLA (flooded lead-acid) batteries, but some gel and AGM (absorbed glass mat) manufacturers also recommend it. You don't want to equalize too often as this can boil off the FLA electrolyte, requiring that the battery water be topped off. Excessive equalization can also cause AGM cells to vent (not good).I'm pretty sure that a modern MPPT charger, if it has an equalization mode, will let you disable this or at least set the parameters. On my sailboat I have three 100W panels with individual MPPT chargers. These are connected to a 1000Ah 12V AGM battery bank, and this has been working well for 20 years. Each controller performs an equalization every 30 days (so there are three EQ cycles in 30 days), but since this is with a single solar panel the equalization current isn't enough to cause battery stress. The battery capacity has dropped somewhat, but it's still good enough that I have no plans to replace the bank anytime soon.

author: Ice-Tea
author_rank: Super Contributor
timestamp: December 05, 2021, 06:15:30 pm
content: Look for microinverters..

author: fourfathom
author_rank: Super Contributor
timestamp: December 05, 2021, 06:47:41 pm
content: Quote from: Ice-Tea on December 05, 2021, 06:15:30 pmThey're cool devices, but are designed for grid-tie applications, not battery and low-voltage DC systems.[the following not relevant to the OP's question:] Speaking of microinverters, one of the founders of Enphase used to work for me. I retired, he went on to found Enphase with another engineer from our company. Smart guys.

author: Twoflower
author_rank: Frequent Contributor
timestamp: December 05, 2021, 07:24:16 pm
content: There are also panel optimizer that do MPPT per module. Something like MPPT microinverter but DC output. You can mix modules with and without them. The modules that might get partly shadowed should get an optimizer to prevent a drop of the whole string. Keep in mind that the installation still need a MPPT for the whole string.