Solarglass Roof in partial shade?

[abasile]

We have a property (small A-frame cabin right next to our primary residence) on which we would like to install solar. I've been debating whether we should just install traditional solar panels, or perhaps hold out for a Solarglass Roof. In terms of aesthetics, Solarglass would be much nicer, particularly if/when a slate-like option becomes available. Going with Solarglass would also give us an "excuse" to tear off the existing composite roof (admittedly in great shape) and add a good layer of foam insulation, since the cabin is not so well insulated.

The big challenge is that the cabin's south-facing roof gets quite a bit of partial shade. If we install traditional solar panels, likely as a DIY project, then I would compensate for the shading by installing as many panels as possible and by using micro-inverters.

I'm aware that Tesla uses string inverters with Solarglass, so I called Tesla to ask if they could use power optimizers for our cabin, but was told that I'd have to put in an order and have their engineers look at our specific property before they could address that question. I then asked if, in general, power optimizers are an option available to their system designers when appropriate. They couldn't answer that. I'm not sure about ordering Solarglass right now, partially given the non-availability of "slate" and macro-economic uncertainties, but if I were to rule out Solarglass then I'd likely want to get started on a DIY solar install.

Does anyone here have a Solarglass Roof with active solar tiles that encounter partial shade? If so, how is that handled by your system? Does a little bit of shade seem to shut down most of your solar production, or is it handled as one might expect of a SolarEdge string inverter with power optimizers?

 

[SolarRoof2020]

I'm pretty far along in my solar roof order. I can't say with 100% certainty, but I don't think you can use power optimizers with the solar roof. At least they never offered to use them for my roof.

I've got the site plan they were submitting to the permit office with schematics. They were doing some really dumb things like connecting south facing and north facing strings together.

The only thing they have to "optimize" is a diode trunk harness, which can disconnect N modules per harness (N = 3 to 5) when they would bring down the efficiency. The details of which aren't really public.

 

[charlesj]

I think SolarRoof2020 made the case for micro inverters as they would maximize output per panel. I have it and the data and daily reading show how well each panel can perform from one to another.

 

[abasile]

The only thing they have to "optimize" is a diode trunk harness, which can disconnect N modules per harness (N = 3 to 5) when they would bring down the efficiency. The details of which aren't really public.

That might not be too bad if all of the modules are on the same roof plane. The modules in shade would be shut off, leaving the remainder to produce at hopefully close to optimal efficiency. I'd be more concerned about the loss of production on systems with modules on multiple planes, i.e., the north/south roof planes at your home. Perhaps that could be addressed by having a separate inverter for each plane, but that would add cost.

At our cabin, there are two roof planes, at different pitches, that face south. If we were to limit the use of solar tiles to the larger roof plane, then Tesla's approach of disconnecting low-producing modules might work out fine. However, the downside of limiting ourselves to one plane is that we would not be able to match the production of a system with traditional panels, assuming that the building code prevents Solarglass modules from occupying all possible locations. I wonder if Tesla has made any progress in lobbying code authorities to allow Solarglass solar modules very close to the peak and sides of the roof. (My understanding is that traditional panels have to be at least 18 inches below the roof ridge, etc.)

EDIT: I found a post by @SolarRoof2020 on another thread that states that, at least in their jurisdiction, Solarglass modules can legally be installed basically anywhere on the roof. That is good news.

I think SolarRoof2020 made the case for micro inverters as they would maximize output per panel. I have it and the data and daily reading show how well each panel can perform from one to another.

I agree that micro-inverters can be very helpful in partial shade and when some panels are covered in snow. We have micros on the roof of our primary residence. Even when most of the panels are buried by snow and only one or two panels are clear, we get some production, which is more than can be said for systems with string inverters of any type, even with power optimizers.

 

[DrSmile]

I agree that micro-inverters can be very helpful in partial shade and when some panels are covered in snow. We have micros on the roof of our primary residence. Even when most of the panels are buried by snow and only one or two panels are clear, we get some production, which is more than can be said for systems with string inverters of any type, even with power optimizers.

I can attest to this being completely false. I have had several panels completely covered by snow and with optimizers the rest of the panels on the string still produce 100% (as far as I can tell on the Solaredge app) of their power.

 

[abasile]

I can attest to this being completely false. I have had several panels completely covered by snow and with optimizers the rest of the panels on the string still produce 100% (as far as I can tell on the Solaredge app) of their power.

Completely false is a little strong there. On a nearby property where we have a SolarEdge inverter with power optimizers, my experience has been that roughly half of the 14 panels have to be clear of snow before the system will start producing at all. That roof is easy to clear of snow, so I've experimented with this! By contrast, on our residence with micros, the system will produce power even if only one panel is clear.

This is less of a consideration for our A-frame cabin, by the way. The main roof plane is so steep (~58 degrees) that snow doesn't stick to it for long.

 

[SolarRoof2020]

That might not be too bad if all of the modules are on the same roof plane. The modules in shade would be shut off, leaving the remainder to produce at hopefully close to optimal efficiency. I'd be more concerned about the loss of production on systems with modules on multiple planes, i.e., the north/south roof planes at your home. Perhaps that could be addressed by having a separate inverter for each plane, but that would add cost.

Most inverters have multiple MPPT ports that are basically as good as having multiple inverters. Each plane should be hooked to its own MPPT port. In my case Tesla was hooking the planes to the same port, even though it was trivial to separate them. Made me question just about everything else they were doing.
Make surey review the site plans.

 

[abasile]

In my case Tesla was hooking the planes to the same port, even though it was trivial to separate them. Made me question just about everything else they were doing.

It seems possible that the designer was just being a bit lazy and that this would have been easily corrected in the field during installation. But I can't blame you for wanting to nail it down correctly; I would want to do the same! Thanks for your input.

So, if Tesla can shut off modules that are shaded, while using a different MPPT port for each roof plane, it seems that Solarglass Roof could work for our A-frame cabin. I think I'll rule out traditional solar panels for now, and hope that Tesla starts selling the "slate" Solarglass within the next year or two. Aesthetically, something more brownish or grayish in color, as opposed to bluish, could be better on this mountain cabin.

 

[charlesj]

... Even when most of the panels are buried by snow and only one or two panels are clear, we get some production, which is more than can be said for systems with string inverters of any type, even with power optimizers.

Right on the money.
Even when sun shines fully, it makes a difference over time, years and years, small differences in panel production adds up.
Daily sun shade variations gives full advantage to mico's independence.