Panel Tilt: Any Benefit to 8° West?

MrM1

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Fascinating discussion all.

Sorry, the lines were just for location purposes. 8° tilt really is not much at all. I think the crinkle idea is cool.

I'm now thinking of using threaded rod instead of a second versabracket stacked on the first. Will lift and tilt more.

A second SCC is clearly the better idea. Can't afford it now, but I'm setting up the new array with it's own combiner box and home run so it will b easy to add a second classic 150 when I can afford it.
 

Hedges

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But if you want to consider an interesting option, have a think about putting your array in a crinkle cut arrangement, sort of like this:


These can be very space efficient arrangements if the tilt is modest since there is no real need to put space between rows (columns?).

I've thought about that, but can't convince myself it produces any increase in power harvesting, maybe decrease.
When sun overhead, it presents less area to the sun than a flat array of the same panels.
To produce more power when sun is off to the side, it has to present more area to the sun than flat would have, but I think at that point each panel shades the next.

I think a single inverted V can spread hours of production vs. all flat.
Multiple inverted V, I think they need to be spaced apart.

In the photo shown, panels sloping down from the higher roof to lower could be good.
 

wattmatters

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I've thought about that, but can't convince myself it produces any increase in power harvesting, maybe decrease.
It depends on your load profile.

If you can extract every watt from an array (e.g. you can export any excess energy to the grid), then a single tilt south facing array will produce more energy overall than a split orientation array provided there is not excess current clipping by the MPPT(s).

But most off-grid systems can't use every watt an array is capable of supplying at every moment. In particular they may not be able to use the array's peak output capability during the middle of the day.

Perhaps there is a limit to the charge rate of the batteries, and/or insufficient other loads such that output from the array is curtailed during the peak production period.

In this case it may be advantageous to widen the production curve through the day by having a more east + west arrangement - this reduces the middle of the day peak while providing more useable power earlier and later in the day. If you can't use power above a given load limit, then there's no point in having it, so set the array up to instead produce power when you can use it.

While this diagram is crude and perhaps exaggerated a little, it's just to explain the concept:

Screen Shot 2021-11-21 at 10.34.49 pm.png

If your loads (actual loads + battery charger) can only pull so much power at any one time, then middle of the day peak PV output isn't realisable. It will be clipped to not exceed the red load limit power line.

But if the array has a split orientation, the peak will be lower and the curve wider, the system won't clip PV output nearly as much, meanwhile extra production earlier and later in the day is available.

So depending on your load characteristics and level of over panelling, you may in fact get more useable energy overall from such a split orientation array configuration.
 

wattmatters

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Multiple inverted V, I think they need to be spaced apart.
I depends on the height of the peak in the inverted V. If the peak of the "crinkle" is not too high, then casting shadows on adjacent panels is not a problem and you can have them without spacing. Like shown here:

mounting-savings-of-five-to-ten-euros-per-kilowatt.jpg


Or just a little spacing:
Bristol-Airport-Solar-Panel-System-Solarsense.jpg


This one is a little steeper - it depends on latitude what's a good compromise:

Ten-K-DUO-Roof.jpg
 

12VoltInstalls

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think a single inverted V can spread hours of production vs. all flat.
if the array has a split orientation, the peak will be lower and the curve wider, the system won't clip PV output nearly as much, meanwhile extra production earlier and later in the day is available.
I actually didn’t have a lot of data when I tried the bi-directional orientation. Knew it was a thing and experimented this past spring- at the small solar scale it was a BIG improvement for me in daily watts harvested.

The other weird thing I didn’t expect: vertical panels (at my latitude) are way better year ‘round than flat panels particularly with directional planning for early and late. 90* separated, sun hits both arrays for half the day, in my case until a bit after noon.

This whole thread is a very educational read.
 

Hedges

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It depends on your load profile.

If you can extract every watt from an array (e.g. you can export any excess energy to the grid), then a single tilt south facing array will produce more energy overall than a split orientation array provided there is not excess current clipping by the MPPT(s).

I agree with two orientations to extend hours.
My concern with the "crinkle" arrangement is I think shading negates any benefit.

To produce more power at off-angles like earlier and later in the day, it has to present more area to the sun without shading the next panel which is sloped same direction. (To the first order I think power is proportional to area presented; angle of incidence of light to panel will affect reflection and absorption.) And and a small angle doesn't shrink area occupied much, doesn't reduce peak power. Needs to be steep enough angle to occupy smaller area.

A steep single inverted "V" casts a longer shadow than a single flat array; it presents more area to the sun when sun is to the side. 90 degree angle between panels reduces presented area to 0.7 as much, 60 degree angle reduces area to 0.5 as much (but loses more of its potential production to sun being below horizon.)

The "crinkle" with multiple inverted small "v" would have to cast a longer shadow, but not shaded its own panels. Only works to the angle where sun is lined up with edge of other panels, below that shades its own panels. So I think it takes significant space between each inverted "v", doesn't save area. Given large area, can be used to reshape power curve without being tall like a single "V"

Think of it this way - the array has to steal light from your neighbor by shading his house in order to give you more power harvesting in the same area. A large inverted "V" does that (but on a flat surface faces due East and West). Better is a large inverted "V" on your sloped roof. or two arrays oriented SE and SW, not joined in a "V".
 

Cal

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The larges impact of solar harvesting is the sun's angle during summer vs. winter. Winter is the worst case scenario. In that respect, if you're already over paneled, then tilt all panels for optimum winter production. That would mean tilting panels at an angle of your latitude plus 15 degrees to the south.
 

wattmatters

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My concern with the "crinkle" arrangement is I think shading negates any benefit.
As I said, it depends on latitude and load profile as to what's a good compromise. As well as local conditions and available roof area.

The OP was talking about an 8° tilt. That's pretty shallow and is not exactly going to create much of a shadow problem, only very early and very late in the day but as you say it doesn't spread the production curve out by much.

But they already have a morning shade issue from trees so they are not gaining much by avoiding a panel tilt shadow cast onto east facing panels. And by what time of day does having some shadow not matter so much? That's going to depend on the load profile.

Personally I think a shallow crinkle arrangement is a good choice for flatter rooftops as it can help with better panel drainage in the wet while being very space efficient.

A downside is tilting panels on rooftops is more expensive. The rails and mounts needs to be designed for it and it creates a different wind load profile and so on.
 

MrM1

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Wind load is my concerns if I west tilt my 9 new panels. Unlike a crinkle orientation, there will be and open side that I don't like
 
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