Panel orientation sanity check

Started by Barry Fields, October 18, 2024, 11:08:53 PM

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Barry Fields

Panel orientation sanity check

I will attempt to explain what I have done and what I propose to do. Please correct me if I have made any analysis errors.

I presently have 3200w of solar panels (12v - 4series x 4parallel = 48v) . Because of roof orientation, the sun does not directly hit the panels until mid-morning. (see attached)
My plan is to add 800w of panels facing easterly @45degrees. Hopefully this will give the battery bank charging an earlier start. It should also increase the "area under the curve" for solar collection (including sky shine days).
My MPPT controller is a Renogy Rover 60 ( similar to MNMPPT60DIY). The unit is limited to 3200w @ 48v. My best calculation is that the final array would be roughly 7% over that 3200w limitation for an hour or so. My presumption is the final array will probably never reach maximum output.
From page 1 of the MNMPPT60DIY manual "The controller features a limited current charging mode. When the solar panel power exceeds a certain level and the charging current is larger than the rated current, the controller will automatically lower the charging power and bring the charging current to the rated level." The Renogy Rover also has a double flash PV current limit mode. (multiple requests to Renogy and they could not explain the function  >:( ).

SANITY CHECK #1 - I do not believe the Final Array will SMOKE the Controller. It may not yield 100% efficient MPPT settings but should perform acceptably.

Because there is a guarantee that the additional panels will be effectively shaded every afternoon and the original panels will be partially shaded every morning, I believe "BLOCKING DIODES" should be added. On this 48v system with and MPPT point around 80v, the voltage drop across the diode of .8v is only a 1% loss. They are also a fire insurance policy in the case of a catastrophic panel failure.

SANITY CHECK #2 - Is my analysis of any of the above incorrect.
Thanks for your input
20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.

Barry Fields

I really would appreciate some guidance here. :)
20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.

Barry Fields

I can't believe that no one can find something wrong with my analysis. I can't be that right.  :)
20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.

boB

3410 watts is only 1% of what specification, Barry ?

And you want to add something like 800 watts?

If you orient the new array towards the afternoon side, you will get power in the afternoon too.  I'm sure the two arrays will add sometime during the day but maybe not enough to over-load the Classic.

Which Classic is this ?  You should get around 68 amps or so at 50V with 3410 Watts.

boB
K7IQ 🌛  He/She/Me

Barry Fields

Thanks for the response.

Honesty first. My charge controller (as noted above) is a Renogy Rover 60. Can we just pretend that it is a MiNite  MNMPPT60DIY? I believe that they are so similar that we can have this discussion anyway.

My existing array is already biased towards the afternoon sun. The additional 800 watts will be biased towards the morning sun.

My open questions are

How long can the  MNMPPT60DIY maintain it's current limit mode (double flashing light) without damage? The  MNMPPT60DIY has a max input of 3200w (48volt system) hence the 7% over paneling number.

Because the arrays 3200w and 800watt will be "out of phase" (see graph above) it would seem to me that BLOCKING DIODES would be a good idea. True?

Thanks for your time
Barry

20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.

Barry Fields

I do not believe that I have asked any really difficult questions here. Someone must have an opinion.
20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.

Barry Fields

I am reminded of the man who jumped off a skyscraper. As he passed each floor on the way down he yells out "so far so good".

The new panels are up and connected. Blocking diodes (20A10) are in place on all 5 arrays. At 3pm the voltage drop across the diodes on the unshaded arrays was .7volts. The voltage drop on the new array (now shaded) was -2.2volts.

The pv collection on the first full day was hard to judge due to partial cloud cover.

All in all, it seems to be working as expected. The next tests will be a bright sunny day and a monthly total collection.
20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.

ralph day

"I am reminded of the man who jumped off a skyscraper. As he passed each floor on the way down he yells out "so far so good".

Of course, he must have talked fast...terminal velocity of 120mph, he might have said it once on the way down.

Couldn't help myself  ::)

Barry Fields

Did I fail to mention that he was an auctioneer?  :)
20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.

ralph day


Barry Fields

Just an update.
It all appears to be working as I anticipated.
Absorb voltage is reached approximately 1 to 1-1/2 hrs earlier than previously.
Has not been real sunny lately but I am seeing about 2500w being collected around 10:30am.
This time of year I have a partial shading issue about that time. Tree trimmer due to arrive Friday.
One step at a time.
20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.

Barry Fields

My panel addition seems to be working out just fine.

I have attempted to create a crude power distribution graph. (yes, i know I have succeeded)  I added 800 watts of PV on the east side of the house @ 30° inclination.

My original 3200 watt array did not get to the 100% point until 1:30pm.  Output of + 85% lasted from 12:00 to 3:30 (2 1/2hrs)'
With the addition, output of +85% lasts from 10:00am to 3:30 (5/1/2 hrs).
 
That 25% addition yielded the expanded dark green area of +100%. That lasts approximately 2hrs in the winter and summer and 4hrs in the spring and fall.

The maximum power possible occurs in the spring fall period @ 113% which equals  3600 watts . That would only occur under absolutely perfect conditions for what would likely be a short perion of time. if one were to presume a collection efficiency of 90%, that equates to 3250watts.

My Renogy Rover 60A (me thinks equivalent to MNMPPT60DIY)  has a limit of 3200 watts (48v system). My understanding is that the controller will ignore the over wattage and just not collect it. It would continue to process the 3200watts and double flash the PV indicator.The real problem for the controller would be over voltage which my bank limited to VOC of 82v (115v@ minus 11°), which is well below he 150v max.
20 years experience in Field Service and Engineering Support in life support equipment and the computer Industry.
I pride myself in diagnostic skills and NOT knowing everything. I do know how to ask the right questions of those who should know the answers. I can do this politely.