How can I correctly feed a 60 amp Renogy Controller Charger with eight 12 v 175 watt solar panels?

It can be confusing, but that is why I try to talk about the how and whys, and not a single solution... Because single solutions rarely work for everyone.

Why have the trailers in two different locations (?) when connecting to one "solar shed"? Or are these to power two different solar systems? Then why parallel them?

You can certainly configure for either two trailers and one solar system or two trailers and two separate solar systems with a plug-in/wire in system... Just need to make sure that the details (array voltage vs MPPT charge controller voltages are correct for the application).

What you cannot (generally) do is connect "one array" to two different Vpanel inputs for the charge controllers... MPPT controllers assume each controller has 100% control of its mating array. The MPPT function will not work correctly if you have (for example) two MPPT controllers connected to one array.

-Bill

It is a bit difficult to tell.... Push on the corners and see how the structure flexes... Using triangular gussets is a very good way to add strength/rigidity.

For example, push on the top corner(s) along the width of the panels... If you find flexing/movement, then adding some sort of cross bracing is important:

Ideally, the frame (without panels) should be structurally rigided without the solar panels installed. However, when you install the panels and bolt their frames to the structure they do create shear resistance (middle example above).

You also want to avoid "twist"... I.e., you pull down (or back depending on angle of panels) and see if the panels want to twist--That is not good for the panels either.

Things that can make a difference (I am not there).. The short pieces that connect the panel sides to the next panel... Make those connections with "gussets" (sheet stock like a flat piece of paper) that will resist left to right "parallelograming. The "flat stock" will resist "shear". The angle you have there now is only connected by one bolt to left and right side... That will resist pulling/pushing the frames apart or together... But any left to right forces (top of frame pressed right, bottom of frame resisting to left) will just pivot on the single bolts.

Another suggestion would be to move the tilt anchors up to the top (or near top) of frames... Anchors attached too low will allow the frames to "bend" and break the panels down low (lever action). Wind loading:


Look at at the loading (pounds per square foot) for wind and snow loading (just numbers for a random solar panel):

Each of your panels is probably (guess) almost 10 square feet.. .Or 500 lbs+ of wind loading per panel (dynamic loading). And 2,000 lbs+ of wind loading (rated) for 4 panels on a trailer. And double that for snow loading (static loading).

Moving the tilt struts to the very top of the panels, and the bottoms to the (left in picture) outside edge of the trailer will make the entire "triangular" structure much stronger.

The struts themselves... Cut different lengths (two or four different lenghts, depending on how often you want to adjust the tilt). Or make them in two pieces so you can unbolt the middle of the strut to shorten or lengthen...

Anyway, some quick observations.

-Bill

Regarding the wood... You may wish to paint/preserve the wooden supports too... The panels should last 20+ years. You don't want to rebuild the wood frames in something like 5 years... I assume with your additional supports, the arrays feel much more solid now?

All "exposed" metal work (frames, mounts, trailer frames, metal electrical boxes, etc.) should be connected to a ground rod--Mostly for lightning control. And to a degree, to prevent metal from being "energized" with respect to ground (i.e., walk by in tall wet grass, touch frame, and get electrocuted).

Your panels will be running something like 90 VDC or more--Enough to give some nasty burns.

What you do not want to do is ground the Negative (or positive) solar panel power leads to a "local ground". Generally, what you want is to ground your "solar shed" negative battery bus to its "local metal" and a ground rod too (again, mostly for lightning). 

The idea being that the "ground point" for your DC power system (and AC for that matter) should be a "single point" ground connection. If you connect both a negative solar panel lead (from panel to your shed), and (for example) a 6 AWG cable from panels to shed, and ground both in the shed (usually the correct location) and also ground the negative lead at the remote site (trailer, j-boxes, etc.), you have a parallel current path both through the solar panel negative cable, and the green wire safety ground. With code, this is a "no-no" to have ground circuits carrying power too. Will the solar system work this way... Yes. But I can give you multiple reasons why code (and practice) does not want this--But just take it from code--Don't "multi-point" your safety/power grounds. Single point Power+Safety Ground so that only "fault" currents flow through safety ground connections.

For ground rods/lightning control--Yes, the safety ground itself can (and should be with lightning) be "multi-point" grounded (i.e., tie trailer safety grounds/ground rod(s) with 6 AWG minimum cable back to shed ground rod(s)). Lightning wants to find the shortest (lowest "impeadence" path to ground... And it will not follow (for example) a 6 AWG cable more than 10-20 feet or so before finding a better path.

The "interconnect" ground connection should be a ground lead from the "shed safety ground" to the "remote" safety grounds.... That way if there is (in this case) Panel + to local ground (frame, trailer, etc.), the return current flows back to the shed/DC safety ground....

Ground rods are not good at carrying lots of current at our DC and AC working voltages--A ground rod can have as much as 25 Ohms (or less) and still be "legal". 100 volts / 25 Ohms = 4 amps... Not enough to "short" and trip a fuse or breaker. The green wire from shed ground to trailer grounds is to provide the short circuit return path and prevent "trailer frames" from becoming "hot". Usually suggest a minimum of 6 AWG copper cable as the "safety ground interconnect".

-Bill

Yes, you are correct above (and in the drawing).

Just to clarify the drawing--The +/- (Red/White) wiring carries through from array to MPPT controller to +/- Battery Bus to AC inverter/DC loads... All + (Red) leads protected by fuses/breakers as needed (normally, these over current protective devices are mounted "near" the battery bank/battery bus connections to protect the wiring against short circuits).

There is once ground connection from the Battery Negative Bus connection to the ground rod.

Otherwise, all electrical boxes, metal chassis of various charge controllers/inverters/etc. are also wired with Hot/Return/Green Wire safety grounds as normal).

Technically, the solar panel frames are supposed to be tied to the 6 AWG ground cable with electrical "clips". The NEC does not want "mounting hardware/brackets/etc." to be "grounding connections". They want hardwired ground wire connections.... This has to do with NEC/NRTL regulations that want safety grounds to be separate from normal mechanical connections (i.e., a service person must "consciously" undo safety ground connections on purpose--Not an accidental safety ground disconnect when removing a mounting bracket/case/etc... Again, this is just a code requirement--Your choice if you want to use the mounting framework to provide ground paths.

-Bill

I don't have any suggestions on a "clipping" device on the array side... Yes, there are DC to DC converters that could, in theory, clip the current/voltage of the array, but they are not "MPPT" input type converters--And could cause other issues (such as loss of harvest).

Typically, the limit on array output current is there because you don't want too much current that could "cook" the wiring if there is a controller failure or short in the Array wiring.... I.e., a 100 amp peak output array attached to a 20 amp controller.

From the manual (my quote in above post), it says it should clip. And the controller "clipping" would simply limit the current draw from the array to generate its 60 amp output current. And the controller should not "know" if the array is 1% or 100% over sized.

I guess there is the MPPT algorithm that could draw more array wattage when doing the "mppt scan" of the array (controller trying to solve the Pmp=Vmp*Imp equation) and trigger such a warning.

The short term answer would be to reduce the number of panels in the array. The longer term would be to replace the controller with a "better quality/design" MPPT controller--I would guess.

Otherwise, I have not read about that warning before and I have nothing more to add.

-Bill