Low current levels from solar panels under clear skies?!?

Welcome to the forum Cotter.

I am sorry to read about the charging issues you are having with the Renogy system... Just an FYI, I am just a volunteer on this forum, and I do not work for NAWS. And NAWS does not monitor this forum regarding customer questions/issues--I have forwarded your post to NAWS.

But we can certainly see if we can help you now.

First thing--Solar panels when connected in parallel (4x panels with Vmp~17.5 volts connected in parallel to a single PWM charge controller?)--They generally share current very closely unless there are other issues.

• No shading on any of the panels (even just some shade on one cell in a panel can but current by 1/2 or more). No vent pipes, Cell phone antenna, AC unit, vent fan, etc. casting shadows on the panels?
• How did you measure the current for each panel? One easy method is--If you have a 4 position circuit breaker combiner box--Just turn on one string at a time and read the PWM controller display (if you did this way, did you log the voltage per string too?). Another method is to use an AC+DC Current Clamp DMM--Just clamp one wire at a time (zero meter) and measure the current (hopefully, you measured all panels within a minute or so--Same sun/weather/etc...).

Given that the panels have such varying current per string measurements--Should address that first. If no shading issues for panels, then need to check the wiring--Connections are clean and tight (if screw terminals). If you are using MC4 or similar connectors, Have seen poor crimps cause issues (loose/weak crimps, sometimes 1/2 pulled apart). If this was an older installation, then I would also look for water/corrosion on wiring terminals. You can also look for "blackening" of terminals (signs of heat).

The amount of current (Imp--maximum power current, and Isc--maximum short circuit current) a solar panel will supply is based on the amount of sunlight hitting the cells/panels:

• 100 Watts * 1/17.5 Volts Vmp = 5.71 Amps Imp (estimated)

That is based on 1,000 Watts per sqmeter of sunlight (solar noon, panels pointing within 10 degrees or better at sun).

Unfortunately, our eyes are not very good at estimating solar energy on panels.... More or less, "full sun/clear day" seems to be around 50% to 100% of Imp/Isc (using our eyes for "good sun")...

If it not too difficult, disconnecting the 4 panels (or open fuses/breakers in combiner box)--Two quick measurements. One is Voc (voltage open circuit) typically 20-22 Volts (hot day, voltage a bit less). Not really sunlight sensitive (full or 1/2 sun, same voltage).

And the second test is to short circuit each panel and measure the current (your DMM set to 10 amp max scale, or using a DC current clamp DMM). The short circuit current is a pretty accurate measurement of solar energy (within 5% or better). If you have 4 panels, and quickly measure Isc--They should all read within 5% of each other (6 amps, 5.7, 5.9, 5.8 etc.)... Since you have 4 panels, hopefully all are good and read almost identical Isc (some clouds, you may see 3.1, 2.9, etc.. Amps). The big thing is all should be nearly the same current in this test.

At this point, hopefully your panels will output similar current (under full sun/no shade). Bad wiring, or other issues (solar panels do have "by-pass" diodes in the J-Box. And sometimes those diodes "go bad". Miswired panels (+/- reversed) can surge current through cells or diodes and fry them (possibly nearby lightning strikes damage panels, etc.).

Once all panels have the same/similar operating current--Then we can look at the rest of the system.

-Bill

The forum is for anyone and everyone.

It just happened to be founded by one of the (now retired) owners of NAWS (family business) as an open forum. And NAWS pays for hosting fees and software maintenance.

Other than wanting a forum for all (whomever is interested, wherever purchased, etc.)--We pretty much run ourselves based on the conversations and needs of the members.

It was my misunderstanding of your first post... I thought you were (possibly) a customer of NAWS (...your Renogy solar system...)--And I was trying to get you help from the store.

I am very sorry. Anyway--Let's continue on.

-Bill

This is a PWM controller--So all the string currents "in" from array should equal current "out" to the battery bank/DC loads.

I wanted to focus on the current from each of the 4x parallel solar panels first... With identical panels under identical sun, then the current from each panel should be pretty much the same. Something does not sound right on the "upstream" side of the system.

Once that has been addressed, then we can look at the charge controller (voltage set point, actual measured voltage and current on the battery bus, etc.)... It is true, that you will only get current out of the array if the charge controller determines the battery bank & DC loads need current. If the bank is full and there are no loads (as determined by the charge controller), then there would be near zero current flow from the solar array.

-Bill

A while ago, as I remember, somebody had a pre-wired RV solar trailer setup (or something). Turned out that the wiring was kind of non-standard and he had to trace wiring/replace wiring/connectors to get system installed and working correctly.

I don't know of an RV unit... But there are some "all in one" boxes that do solar-inverter-charger systems (connect solar panels + 120 VAC + genset + Batteries + 120 VAC output all in one box). Would need to know what brand/model to understand what the RV mfg. may have been thinking.

If you now have a direct panels to battery wiring/current path... You should be ready to install the solar charge controller. Ideally relatively close to the battery bank (to keep voltage drop down) and a fuse/breaker on/near the battery for the wiring that goes back to Vbatt charge controller input (if there is a short circuit, the Li Battery can output a crazy amount of current into a dead short--Need fuse/breaker to stop the excessive current flow from melting your wiring and starting a fire).

Secondarly, Li Ion batteries need a charge controller (and usually a battery management system) to prevent over and under voltage at the Lithium bank (Li batteries do not like too high or too low of voltage, and many have a BMS with over current limit/shutdown too).

-Bill