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HeatSpring PV Course Blog

Attaching Solar to SIP Roofs and Capturing Heat Under PV Systems


Q:

There are two questions I have regarding structural. First, with some projects I know they are using SIPS for the roofing layer that could be with at least a 12" foam core. Is attaching to the exterior sheathing enough? If so, how should this be done? Is a good construction adhesive enough to hold the rails in place?
My second question is more esoteric. It seems there must be a way to harvest all that heat coming from the bottom of the panel. Perhaps roof insulation does not need to be as thick since the Delta T would be lower (cooling dominated environment)? Perhaps using a phase-change material at the sheathing layer could store some of that energy? Perhaps creating a closed loop system for air exchange with the interior of the building (a hybrid passive/active) solar solution.
I would love some of thinking, oh wise one.
Thanks

A:

SIPS question:
Structural Integrated Panel (SIP) roofing poses a problem, because it does not have normal structural members to attach to, such as rafters. There is no simple solution to this predicament. SIP roofs are sort of like an ice cream sandwich with sheathing on both sides and insulating foam in the middle. By not having anything besides foam in the middle, it is good for insulating from the cold. Cold can travel through wood better than foam, which makes SIP roofs green.
Some people attach to the outer sheathing, which is often OSB (Oriented Strand Board), which is like particle board and can get soggy over time, which can cause you to lose your array. Ecofasten makes something for this. Many people would not use this method.
Another option is to attach through the roof and to put an anchor bolt through the entire SIP roof with something on the inside of the building to attach to. This would hold better.
The best way of dealing with this is to put a standing seam roof on top of the building and to attach to the standing seam roof with something like S-5! clamps. This is what I would do, because attaching to a standing seam roof with clamps is the easiest, most waterproof way to install solar and the standing seam roofs last a long time.
Question about keeping the heat under the PV:
There was a company that did this called PVT Solar and they changed their name to Echo Solar and then Sun Edison bought them and they sort of exist still. Here is a video of their system:
https://www.youtube.com/watch?v=MSeg9MKo0N4
It was really neat, but it took a long time to install and PV thermal combination systems sound good in theory, but do not seem to work well financially and in practice. We are always trying to make PV as cool as possible and to make hot water as hot as possible. Echo Solar would also blow the hot air into the house.
It will probably come back, but so far nobody has ever made it work.
Thanks,
Sean White



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