Mounting bifacial panels at 90 degrees?

softdown · November 19

Any studies on this? Should be effective I would think.

But proper anchoring could be onerous. And what kind of winds can large bifacial panels hold up to when mounted at 90 degrees?

East/west orientation of course.

BB. · November 19

For the first pass, assume that you have two panels (mono-faced) back to back, here is PV Watts for 90 vertical facing West (270) for Sterling Colorado:

https://pvwatts.nrel.gov/pvwatts.php

Facing West, 90 degree (vertical):

Facing East:

Facing South at 40 degree tilt from horizontal (best year round):

Image: https://us.v-cdn.net/6024911/uploads/editor/be/yl7hgjbwwjr1.png

At least from a first pass PVWatts point of view, having a "true" East West 90 degree mounted set of panels, vs just a south facing 40 degree set of panels, the harvest is pretty much the same.

Next question that I do not know the answer too: Are the Bi-facial panels really 100% harvest from front and back, or is there a loss on the "back side" of the panel harvest.

In theory, if you properly mounted bi-facial panels on the south facing array, 3 feet or more above a light colored "ground" ("white gravel", free of grass, etc.), then you may get 5-30% more harvest from the single south facing array (now better harvest than "true" bi-facial panels mounted 90 degrees).

https://www.itekenergy.com/solar-panels/best-practices-for-installing-bifacial-solar-panels/

Your thoughts?

-Bill

softdown · November 19

I don’t believe the outcome is as dreary as these figures indicate. That is assuming that one bifacial panel is able to duplicate the output of two mono panels mounted at 90 degrees. Could be more with high mounting and reflective material at base? Could be less?

South facing panels provide good output from ~9am to 3pm. Depending on the time of year the batteries may be draining from ~4:30pm to 7:30am. Fifteen hours.

East and west panels should, theoretically, reduce the battery draining period from ~ 15 hours to ~ 10 hours during peak summer hours. Summer time is when my system struggles unduly due to hot panels mounted at 45 degrees and a large demand from freezers and fridges.

These figures are estimates and vary, a lot, with the seasons of the year.

Then we may encounter cloudy mornings or afternoons. Increasing the capture period from ~6-8 hours to ~11-13 hours effectively counters many uncooperative solar days.

Nevertheless I have a suspicion that simply laying large mono panels on the roof may be equally effective overall. And roughly 1000% easier and less problematic. Very little anchoring needed. Flat panel orientation does pretty well during the summer when the sun is almost directly overhead.

softdown · November 19

Month	Solar Radiation ( kWh / m2 / day )	AC Energy ( kWh )
January	2.88	73
February	4.10	95
March	5.42	137
April	6.59	158
May	7.40	177
June	7.98	179
July	7.18	163
August	6.51	149
September	5.62	128
October	4.41	108
November	3.40	82
December	2.77	70
Annual	5.36	1,519

This is assuming 1000 watts of panels mounted at 2 degrees. Pretty strong summer time figures.

BB. · November 19

For Lead Acid batteries, more hours on sun is going to be better.

I was not saying what mounting for the array was optimal... Just some quick examples. Another option would be to try different tilt and orientation angles (i.e., south west/south east, 40 degrees tilt, more, less, etc.).

I was surprised that East/West vertical panels were so close to "optimum" tilted/fixed array in hours per day.

A field of vertical panels was not my first choice--Worried a bit about shading from one array string to the next (east panels shading west panels unless substantial spacing between strings, etc.)... However, modeling and research may prove that other options may work better.

Of course, there is always 2 axis tracking, tilting array by month/season, etc. But I am a big believer is keeping is simple and well mounted--Less maintenance/fiddling with the system over the next 10-20 years.

-Bill

BB. · November 19

And I would avoid cheeping out/fewer hard mounts for an array flat against roof. Seen too many shingles rip off roof during a wind storm. All is takes is a corner to lift, and/or a branch/neighbor's lawn chair, etc. to wedge itself into the array and let the wind do the lift and separate of the array.

-Bill

softdown · November 20

I’ve left a panel sitting on a flattish roof for years now. Seems pretty stable 12’ off the ground.

The 90 degree bifacial mount works ok on the ground using specialty fence posts for mounting. Takes very little room and snow doesn’t stack. On a roof? I’m not presently planning to try and anchor that mess.

Plenty of youtube vids on it. Funny that youtube recommended viewings shortly after I studied the scenario?

Mounting bifacial panels at 90 degrees?

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