Module grounding revisited [RE-wrenches]

[Joel Davidson]

Good questions that hopefully will lead to new ways of thinking about PV.

Yes, the experimenters tested unframed glass and plastic modules. The unframed,
ungrounded plastic modules were toast. The glass modules physically survived,
but were electrically dead. It is fairly easy to attract lightning as Benjamin
Franklin discovered. The experimenters wanted natural lightning and induced
laboratory lightning to strike to determine how solar modules withstood
lightning.

Some module design issues are pretty obvious. The cell encapsulant must be
electrically inert and pass the high voltage potential (megger) test. EVA and
glass are preferred encapsulants, but Uni-Solar and others use a plastic
superstrate. Plastic substrates are common, but ASE uses a glass back sheet.
3-layer Tedlar back sheets (plastic-aluminum-plastic) are required in Japan, but
U.S. and most other manufacturers use 1-layer Tedlar. Metal framed modules are
physically strong, ship well, handle well and the frames provide a place to
fasten the module to the site and to earth ground. Plastic frames can also
protect laminate edges, but no one wants to make production grade, commercial
modules with plastic frames because major customers prefer glass and aluminum.
Frameless laminates can be framed in the field or fastened to a back rail with
silicone, but handling frameless laminates requires special care.

Bottom line: aluminum framing is relatively inexpensive, commonly used in
construction and gives the PV module physical strength, protects the laminate,
provides a simple way to fasten and ground the module. That said, business is
booming for Powerlight and their unframed, ungrounded, unfastened laminates
glued to plastic insulation. In the 1880s, Charles Fritts, maker of the first
selenium PV cell, predicted that roofs covered with solar cells would generate
electricity. Stan Ovshinsky, founder of the science of amorphous materials, is
developing "a roof that makes electricity." Some day PV building material and a
variety of fastening methods will be as common as glass, composition shingles
and other roof coatings are today.

matthew tritt wrote:

> Joel,
>
> So, did they also experiment with non-metallic frames? Did the aluminum act
> as an attractant to lightning in this test, and thus become kind of a
> self-fulfilling prophecy? What about modules with no frames at all? This is
> what a composite framed module would, in effect, be.
>
> Matt

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