Feedback on proposals for San Diego: LG/Hanwha + Solar Edge

[SunEagle]

Treated as a heat exchanger application, which it really is, it's a real loser.

I never tried to determine the true cost associated with using glycol as a heat exchanger. So maybe in that area it is a loser.

I can tell you that is it used in many Food processing industries mostly in equipment like pastuerizers, filling machines and just about all equipment that transfers a food product that requires cooling without contamination.

It is also used in under floor heating systems to keep the ground beneath a food freezer from building up ice which will cause the floor to heave.

IMO I would say it transfers heat very well.

[J.P.M.]

I was thinking about food grade glycol as the heat transfer medium but I also remembered how glycol degrades certain pipe fittings after a while. Talk about a messy leak from that.

Treated as a heat exchanger application, which it really is, it's a real loser.

[J.P.M.]

One of the so far not discussed issues on this thread is something that many believe to be a very good idea: Inspecting the roof around and under where a proposed array will be, and probably replacing the paper under a tile roof. On concrete or clay tile roofs, that has, in the past, often meant removing the tile from the affected area, replacing the paper on that portion of the roof, and replacing the existing tile while affixing the panel standoffs to the roof followed by, or mostly simultaneous with, the placement of the rest of the solar equipment.

That's one common and accepted way of doing it. For "S'" or "Mission style" clay tiles or some others, that can be a more difficult due to breakage or other issues and can take more labor. A somewhat cheaper way to get new paper on the roof is to use different roof material under the array and (temporarily) out of sight that's relatively cheap, and much less labor intensive - composition shingles. I kind of suspect labor cost is one of the big reasons why that method is becoming the darling of contractors. However, for reasons already discussed, my opinion is that as usually and commonly done and attempted, that is a very bad to do it that will only have the end result of creating more problems. Not only does it seem contrary to what I've seen on roofs all my adult life, it also seems to run contrary to common sense, or at least any common sense I have left.

The tile removal and repaper followed by reinstallation of the tile is a common procedure. FWIW, about half the solar installations in my HOA have done this. Happens all the time.

[jd31]

Let me ask a slightly different question then.

Would you pay a premium to have the solar company, with a roofing background, install a new roof membrane under the cement S tiles where the solar is to be installed? For me it would be about 450 sq ft of roof. The benefit, in my eyes, is that one day when I have to re-roof, they don't have to uninstall the solar. To be clear, this is not the flush mount option, it's a raised install above the S tiles.

[SunEagle]

Might work, but My guess is it wouldn't be cost effective or practical from a maint. standpoint. Might be a fun design project for eccentrics who know something of heat transfer and eng. design, but not much else.

I was thinking about food grade glycol as the heat transfer medium but I also remembered how glycol degrades certain pipe fittings after a while. Talk about a messy leak from that.

[J.P.M.]

Too bad the design did not incorporate some type of heat exchange/cooling system between the panels and roof.

If the entire array was totally sealed around the edges to keep out moisture, yet had a way of also removing the heat from behind the panels (which maybe could be used to preheat a hot water system). It might work.

Unfortunately a system like that would probably cost a lot and be hard to maintain without a way to easily remove the panels to inspect the heat exchanger below.

Might work, but My guess is it wouldn't be cost effective or practical from a maint. standpoint. Might be a fun design project for eccentrics who know something of heat transfer and eng. design, but not much else.

[SunEagle]

What you describe is not what I'm writing about. I'm referring to arrays stood off a roof by 6" or so with the concrete/clay tile under the array removed and replaced with composition shingles under that array, while the original tile remains on the rest of the roof.

Such an arrangement can allow water and whatever is carried with it to flow under the remaining tile below the array through the open slit created at the shingle to tile interface. Lack of drainage from accumulated junk carried with the water and little air circulation will keep things wet and promote mold growth and rot. Not only does my engineering judgment tell me that, but common sense sort of screams the same thing.

My experience of having been a peddler prior to an engineering career also makes me skeptical of some vendors motives and their eagerness to engage in such shenanigans. Seen similar stuff and the often common attitude from the inside. My apologies to all the ethical, honest vendors whose job is only made more difficult by the scumbags.

That roofing system is not a good thing. About the only reason I can think of for doing such a thing is that it is easier and cheaper for the vendor. That benefit however, probably does not transmit to the customer via lower prices and any likely damage may go unseen and unknown until the unnecessary damage is done. Even with a price break, I'm not sure how I'd go about putting a value on increased probability of a built in rot problem.

Too bad the design did not incorporate some type of heat exchange/cooling system between the panels and roof.

If the entire array was totally sealed around the edges to keep out moisture, yet had a way of also removing the heat from behind the panels (which maybe could be used to preheat a hot water system). It might work.

Unfortunately a system like that would probably cost a lot and be hard to maintain without a way to easily remove the panels to inspect the heat exchanger below.

[J.P.M.]

I did SAM base on my system. It probably loss about 400kWh per year if mount less than 0.5". I guess 400kWh isn't much for people who prefer the look. My cross street neighbor install 2/3 of his 8.5kW on NE 65 deg just to avoid the street look.

400 kWh/yr. s probably as good a # as any. That AZ. probably cost more than that for an output penalty.

[J.P.M.]

There is a small subdivision down the street from me that has what you describe in option #2 on every house. I've never been on the roofs, so I can't say how they handled the drainage. In addition to the items mentioned above, I would also be concerned with a lack of air flow under the panels. Normally, you want your panels 4-6 inches above the roof. These installations are pretty much flush. Seems to me option 2 is form over function.

What you describe is not what I'm writing about. I'm referring to arrays stood off a roof by 6" or so with the concrete/clay tile under the array removed and replaced with composition shingles under that array, while the original tile remains on the rest of the roof.

Such an arrangement can allow water and whatever is carried with it to flow under the remaining tile below the array through the open slit created at the shingle to tile interface. Lack of drainage from accumulated junk carried with the water and little air circulation will keep things wet and promote mold growth and rot. Not only does my engineering judgment tell me that, but common sense sort of screams the same thing.

My experience of having been a peddler prior to an engineering career also makes me skeptical of some vendors motives and their eagerness to engage in such shenanigans. Seen similar stuff and the often common attitude from the inside. My apologies to all the ethical, honest vendors whose job is only made more difficult by the scumbags.

That roofing system is not a good thing. About the only reason I can think of for doing such a thing is that it is easier and cheaper for the vendor. That benefit however, probably does not transmit to the customer via lower prices and any likely damage may go unseen and unknown until the unnecessary damage is done. Even with a price break, I'm not sure how I'd go about putting a value on increased probability of a built in rot problem.

[silversaver]

One usual PV design goal is to have the array operating as cool as possible. That goal of a cooler array is partially met and helped by air circulating on both surface of an array - top and bottom. Air circulation on both sides means the array must be stood off from the roof deck. Depending on roof type, tilt, and other things, about 6" or so seems to be a tradeoff distance that gets most of the temp. lowering benefit of the standoff while not becoming visually offensive. More than that helps a bit more, but the improvement is less noticeable for more distance.

Regardless of standoff height, if the sides of an array are skirted, air circulation will be inhibited. Less air circulation will increase the array temp., short circuiting the design goal of a lower array temp.

Without getting real technical, there are several empirical ways to est. performance penalty for flush mounts. Cheap/dirty trick: Use SAM, change the standoff height and notice the diff. in output.

I did SAM base on my system. It probably loss about 400kWh per year if mount less than 0.5". I guess 400kWh isn't much for people who prefer the look. My cross street neighbor install 2/3 of his 8.5kW on NE 65 deg just to avoid the street look.

[J.P.M.]

This method is 100% legit and not a steaming pile of #2 as some have suggested. Look around at the new homes that are built with solar integrated in the roof and they are largely flush mounted. Dead Animals getting stuck under your array causing your roof to leak? If this array was located Costa Rica perhaps because of jungle critters climbing the trees that sprouted because you lived in a rain forest. This is San Diego you could have an open hole in your roof most years and not get water damage because of the rain. Mold? Rotting flesh? a smell emanating from your roof? This thought experiment went way off the rails and yes somebody is peddling you a heap of steaming #2 but it isn't your solar guy. JPM you add a lot to the forum but I think your account has been hacked because that post was very short on evidence and uncharacteristically on high on hype. HOA's wising up on this scam? Evidence perhaps? Is your potential solar array visible from the ground or street? Why the talk of the flush mount?

As far as the airflow when you remove tile and replace with comp you lower the profile of the roof because the comp is 2-4 inches thinner than S tile. If you combine this with a railless mounting system you won't affect the air flow as much as a railed system. While this method of mounting is legit the increase in cost is about 40% too much in my experience and that is why option number 1 seems to be a better value not because rotting flesh and fermenting guano will will stink up your neighborhood .

You're a vendor ?

[J.P.M.]

Friend of mine had his 8kW solar flash mount on his new house with $$$ clay S tiles. They look really nice flash mount to the roof and the only concern I had is the cooling part. I know when these panels heat up, the performance will drop pretty bad. His solar is only been up on the roof about 3 months so I can't really tell if there's any performance drop since Winter/Spring. I have spoken with the installer about the cooling, he said the panels are actually about 3" above the roof. I guess time will tell... I'm just an messanger, so don't fire at me.

One usual PV design goal is to have the array operating as cool as possible. That goal of a cooler array is partially met and helped by air circulating on both surface of an array - top and bottom. Air circulation on both sides means the array must be stood off from the roof deck. Depending on roof type, tilt, and other things, about 6" or so seems to be a tradeoff distance that gets most of the temp. lowering benefit of the standoff while not becoming visually offensive. More than that helps a bit more, but the improvement is less noticeable for more distance.

Regardless of standoff height, if the sides of an array are skirted, air circulation will be inhibited. Less air circulation will increase the array temp., short circuiting the design goal of a lower array temp.

Without getting real technical, there are several empirical ways to est. performance penalty for flush mounts. Cheap/dirty trick: Use SAM, change the standoff height and notice the diff. in output.

[silversaver]

The only steaming pile of #2 here is your defense of a bad practice - you will see considerable loss due to increased panel temperatures.

Friend of mine had his 8kW solar flash mount on his new house with $$$ clay S tiles. They look really nice flash mount to the roof and the only concern I had is the cooling part. I know when these panels heat up, the performance will drop pretty bad. His solar is only been up on the roof about 3 months so I can't really tell if there's any performance drop since Winter/Spring. I have spoken with the installer about the cooling, he said the panels are actually about 3" above the roof. I guess time will tell... I'm just an messanger, so don't fire at me.

[ericf1]

Took a walk past some of these installations this morning and payed more attention. The arrays I saw were not actually co-planar to the roof. The top of the array is slightly recessed below the tile peaks while the bottom of the array is higher than the top, about 4" above the tiles. The mounting surface under the array is also not co-planar to the surrounding roof surface, and appears to drain onto the tops of the tiles below it. These are new construction homes that came with solar as a standard feature. They are 2 story homes, so it's difficult to see details from the street.

[russ]

This method is 100% legit and not a steaming pile of #2 as some have suggested.

The only steaming pile of #2 here is your defense of a bad practice - you will see considerable loss due to increased panel temperatures.