Mount types

When pvwatts estimates the module temperature, looks like there are a number of mount types which affect the module temperature.

a) Open rack
b) Close roof mount
c) Insulated back

a) Open rack would be a classical ground mount pv array, or titled pv array on a sloped or flat roof. Something like these two:
postimg.org/image/l0cvroj4n
postimg.org/image/nilcntlat

What about the other two types?
b) Is "Close roof mount" basically the pv array laid down to sloped roof surface? Like this one:
postimg.org/image/nl3fmpr41
Is "Close roof mount" the same as "Flush mount"?

c) And "Insulated back" mount? How does that mount type look like?


Thank you.

Hello,
The PVWatts model in SAM 2103.1.15 provides two mounting options for fixed arrays, and those options are both described in SAM's Help system:

For systems with fixed arrays, you can choose between an open rack or a roof mount. Open rack is appropriate for ground-mounted systems. It assumes that air flows freely around the array, helping to cool the modules and reduce cell operating temperatures. (The array's output increases as the cell temperature decreases for at a given incident solar irradiance.)
Roof mount is typical of residential installations where modules are attached to the roof surface with standoffs that providing limited air flow between the module back and roof surface (typically between two and six inches).
For the open rack option, PVWatts assumes an installed nominal operating temperature (INOCT) of 45 degrees Celsius. For roof mount systems, the INOCT is 50 degrees Celsius, which corresponds roughly to a three or four inch standoff height.

Best regards,

Paul.

Thank you for the reply Paul.


What about the "Insulated back" mount? How does that mount type look like?
Does this kind of mount type even exist?

Could it be that an "Insulated back" mount type is simply "Glass/cell/polymer sheet" type of module, with "Roof mount"?

The "insulated back" option is available for the cell temperature calculation in the Sandia module model that is part of SAM's detailed photovoltaic model. It is not an option for the PVWatts model. Here is a description of the Sandia temperature correction parameters, again from SAM's Help system:





Glass/Cell/Polymer Sheet

Open Rack


Solar cells are between a glass front and polymer back, and the module is mounted on an open rack allowing air to circulate freely around the module.




Glass/Cell/Glass

Open Rack


Solar cells are between a glass front and glass back, and the module is mounted on an open rack allowing air to circulate freely around the module.




Polymer/Thin Film/Steel

Open Rack


Solar cells are between a transparent polymer front and steel back, and the module is mounted on an open rack allowing air to circulate freely around the module.




Glass/Cell/Polymer Sheet

Insulated Back


Solar cells are between a glass front and polymer back, and the module is mounted directly to a building surface in a building-integrated PV (BIPV) application preventing air from flowing over the module back.




Glass/Cell/Glass

Close Roof Mount


Solar cells are between a glass front and glass back, and the module is mounted on a rack with little clearance between the building surface and module back allowing little air to flow over the module back.





Best regards,

Paul.

Thank you once again Paul. I have just downloaded the SAM-help.pdf.

So basically when my pv module is a part of a building facade (glass steel curtain wall), I would always have to choose the "Glass/Cell/Polymer Sheet, Insulated Back". It does not matter if there's a concrete or masonry wall behind that building facade, or some free air space? It does not matter if the inner part of the building is getting ventilated or not?

Or did I get this wrong?


Here is one example of a bipv modules used as a part of a glass steel facade:
postimg.org/image/xsvx7c4jt
Let's pretend that the back part of this glass steel facade is being ventilated and there for the back part of the pv modules are ventilated too.

Which SAM mount type would I have to choose?