Where to buy 10 degree east west racking for residential?

[fraser]

I cannot find any resellers for residential solutions. Or a commercial one that might sell to homeowners? Does anyone have a suggestion? I would probably need a roof penetrating solution or at least a hybrid as I am in California. I'm set on the east/west orientation as it maximizes the number of panels on the flat part of my roof, while only losing 16% max from having the perfect southerly tilt angle.

[SolTex]

Check the IronRidge website. They may have a product that would fit your requirements. We used their ground mount components for a 15kW system. Very happy with the installation.

https://www.ironridge.com

[Calsun]

The loss of output is far less than you would imagine from a less than perfect tilt angle and this is inherent in the design of solar panels. Consider that the sun rises and then sets and is never at a single angle to your roof and this also varies throughout the year. Most important is to avoid shading of panels.

I would focus more on avoiding roof penetrations as the system warranty does not cover roof leaks from them. Many more options for attaching panels to a wide variety of roof types are available but the problem is that a local installer usually prefers to use one connection type and use it on all their installations. I would seek out multiple bids and have them specify the connection for the panel racking to the roof.

[fraser]

The loss of output is far less than you would imagine from a less than perfect tilt angle and this is inherent in the design of solar panels. Consider that the sun rises and then sets and is never at a single angle to your roof and this also varies throughout the year. Most important is to avoid shading of panels.

I would focus more on avoiding roof penetrations as the system warranty does not cover roof leaks from them. Many more options for attaching panels to a wide variety of roof types are available but the problem is that a local installer usually prefers to use one connection type and use it on all their installations. I would seek out multiple bids and have them specify the connection for the panel racking to the roof.

Yes, the loss of output is negligible. I calculated it on pvwatts. Max loss (flat), is just 17% loss, but optimum tilt causes a loss of more than 50% of usable roof space. I just can't find a residential solution for 10 degree east/west racking, which is a shame.

[J.P.M.]

Yes, the loss of output is negligible. I calculated it on pvwatts. Max loss (flat), is just 17% loss, but optimum tilt causes a loss of more than 50% of usable roof space. I just can't find a residential solution for 10 degree east/west racking, which is a shame.

Free and true advice:
It took several years before it dawned on me, and I proved it to myself in a couple of different ways, that over the course of a year, and to a rough but pretty good first approximation, the maximum amount of irradiance that falls on a sawtooth arrangement of tilted surfaces arrayed on a flat and horizontal surface such as a roof is about the same as the irradiance falling on that flat, horizontal surface without the sawtooth array (but the tilted saw tooth arrayed surfaces will stay much cleaner).

[bcroe]

Free and true advice:
It took several years before it dawned on me, and I proved it to myself in a couple of different ways, that over the course of a year, and to a rough but pretty good first approximation, the maximum amount of irradiance that falls on a sawtooth arrangement of tilted surfaces arrayed on a flat and horizontal surface such as a roof is about the same as the irradiance falling on that flat, horizontal surface without the sawtooth array (but the tilted saw tooth arrayed surfaces will stay much cleaner).

Agreed, the advantage of the flat array is no issues with shadowing
at some times. Disadvantages of the flat array, it takes more panels
to collect all the energy, and less cleaning with rain. Bruce Roe

[fraser]

Agreed, the advantage of the flat array is no issues with shadowing
at some times. Disadvantages of the flat array, it takes more panels
to collect all the energy, and less cleaning with rain. Bruce Roe

I think this comment while technically correct is a bit misleading. Yes it does take more panels to collect solar energy from a flat array, but that is coupled with an advantage of maximizing the amount of power generated by the roof area. They are not separate advantages and disadvantages. If you want to generate the most power from a flat roof, a flat or 10degree east/west tilt (for cleaning purposes only) is the best as the space efficiency overrides the disadvantage of less efficiency by more than 2:1. With solar panel and inverter prices declining, roof space is the limiting factor, not solar panel efficiency. The difference between maximum gain at 30 degrees tilt and flat is only 16%, but you lose over 50% of your roof space with a 30degree tilt. For 20degree tilt it's only an 8% loss from maximum panel efficiency but the roof space loss is only about 30% depending on how many rows you have. For example, a Flat installation of panels producing 10,000 watts is using 20 panels, the maximum amount the roof will allow in a 5x4 landscape configuration. The same 20 panels tilted at 30degrees would produce up to 11636 watts. 16.36% more efficient, but, each row requires spacing of 86% of the width of panel. Even though the roof footprint of the panel is also only 86%, a 14% space savings, you still can only put 3 rows on the roof (3 rows, plus the space of 2 rows for inter row spacing, so you lose 40% production from that. Playing with the tilts between 20 and 30degrees and the inter row spacing required, you can probably get a 4th row, which would then allow the system to produce almost the same as the flat or 10deg EW system.

[J.P.M.]

Agreed, the advantage of the flat array is no issues with shadowing
at some times. Disadvantages of the flat array, it takes more panels
to collect all the energy, and less cleaning with rain. Bruce Roe

Bruce:

The whole idea of placing an array on a (mostly) horizontal and flat roof with limited space is that regardless of the panel tilt, panel height and row pitch and array orientations (which are all linked), the maximum annual energy harvest of any array of any configuration and/or orientation on a (mostly) horizontal roof is limited (to a rough first approximation) to the energy that a continuous array of the same area as the roof and parallel to it will collect.

I Also more than most understand the penalties and other considerations associated with fouling of horizontal panels, but that's an additional consideration apart from what's mostly an exercise in solar geometry as I raised here.

Self shadowing of sawtooth arrays was and still is a problem in solar geometry that was made a lot easier for me and others when PCs came along in the early '80's. Before that, graphical solutions with paper and pencil for lots of different tilts, azimuths and panel height/row pitch ratios and row length combinations were necessary until I had a blinding flash of the obvious that the practical limiting case of maximum production for a sawtooth array on a limited horizontal space is a horizontal array of the same size as that horizontal space and parallel to it.

[bcroe]

Thanks for expanding the basic premise with more detail.
Bruce Roe