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If you're working with a new construction or a very old roof in need of full replacement, why not forego asphalt shingles altogether when installing solar panels on the roof? It seems like a waste to stack panels on top of new shingles.

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    Most solar panels are not designed to fit tightly together to be weatherproof. Also, panels need a little open air beneath them (between the panel and the roof for cooling. .However, there are panels designed to replace shingles, such as Tesla's Solar Roof. – DoxyLover Mar 15 at 0:31
  • One solar company said roof was in good position, but were not interested since we had steel roof on(replacement of shingle). Unknown if they thought it was just tin on strapping. – crip659 Mar 15 at 0:38
  • Thanks @DoxyLover I'm sure some flashing could be rigged up for weatherproofing. The cooling makes sense, but I wonder if the efficiency hit would outweigh the cost of shingles and shingle installation. Perhaps vents could opened underneath in the summer to mitigate this issue as well. – user1033341 Mar 15 at 0:50
  • And what happens when the solar is past it's use by / doesn't work any more - you're left with whatever is underneath ... In theory in a hot climate it will help keep the amount of heat ingress down. – Mr R Mar 15 at 7:55
  • @MrR -- solar panels will keep on chugging right past the end of their warranties, just with reduced output (only way to make one fall off a cliff is to physically break it -- their EOL mode is a gradual wearout, and the warranty generally is X number of years to Y% of output as a result) – ThreePhaseEel Mar 15 at 11:47
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You need a WRB on that roof somewhere

One thing all roofs need is some way to shed water. Asphalt shingle roofs use the shingles themselves as the primary water-resistive barrier (WRB), often backed up by a secondary barrier (roofing felt). Other roof technologies, such as metal roofs, have their WRB underneath the roof cladding instead. However, this depends on the roof cladding being a full-coverage sort of thing, which isn't true for solar panels as panels need air circulation for cooling and wiring space behind them for connections and equipment.

You can get solar roof products that serve as a roof cladding, but they still require a WRB underneath them, and such building-integrated photovoltaic systems require more care in wiring as well due to issues with the potential for wiring damage from roof incidents. They're also harder to replace than a conventional panel if they do get damaged, say by hail, and pose challenges under the current NEC rapid shutdown rules.

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The roof we put on our prperty has the solar panels being the outer or final weather layer.

It was designed with a 6” gap underneath - well there are a few support beams but it helps keep it cool.

There is a membrane fitted to waterproof just in case.

It is at a 70 degree slope so it is self cleaning and each panel can be removed due to the type of fixings used. But they came with the panels.

The inverter is designed to do the disconnection to the standards in our country.

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