PV array mounting hardware choices 12-12 asphalt shingle roof

[Jerry Liebler]

Did you tell us where you are?
Is this a grid-tied system?
Where I am things get really complicated if you go over 10kW nameplate DC.
If so what does your utility have to say about your system size?
I do not know about your building department but mine starts the permit with a letter authorizing a maximum size.
Do you need an engineer to sign your plans? If so IronRidge is a good friend to have because they will engineer your racking system.
What do you have agents clamps and what are you going to do instead? Is your alternative bless by an engineer or will you have to get one to sign for you?
Quick Mount PV is very tempting but as far as I can tell lacks the engineering required to get a permit.
I came here looking for information on Quick Mount PV. Does anyone have experience with them?
Good luck.

AFICT Quick Mount PV is a roof attachment that uses conventional flashings, consider https://quickbolt.com/catalog?field_...ms_per_page=12

FWIW, I'M in Kentucky. Here the complications get really bad above 40KW & the coal lobby keeps attacking even net metering. I haven't tried to get a permit so don't know about engineering stamp requirement. My objections to clamps have been stated previously and came into being after I found an alternative. By using the "PV Stealth" rails from

https://www.pvracking.com/roof-mount-systems/

conventional clamps are completely eliminated and the rails themselves, in effect, hold the full length of the panels on two sides once the panels are "slid" into position. Note electrical "ground" connection of the panels is separate with this system and is best accomplished by clip on "jumpers" which add $1.5 per panel.

[Ampster]

J.P.M. Probabilities and assumptions aside, tell us why you think the attic will be more damp in winter.?

[J.P.M.]

At the risk of starting a flame war over a post I made on another thread. Is there any benefit to the attic vents from the airflow between the roof and the panels? I am particularly thinking of a hot windless day. My layman's theory is based on the assumption that it is a 12/12 roof and that hot air rises. The OP does refer to convection induced airflow.

Another question for the benefit if the ignorant. Why would the attic become damper in winter? Are you referring to relative or absolute humidity?

Short answer #1: yes, but probably reduced vent effectiveness due to air velocity reductions and flow path restrictions caused by an array.

The wind blowing under an array will have a lower velocity than the free stream velocity over an unrestricted roof. Lower velocities will mean less draw, but not zero draw. (see venture effect). If there was no benefit, that is, the vents weren't functioning at all, there would be no flow and no resulting accumulation of vent effluent on the backside of panels when vents are present under an array.

Wind will help, and more wind will help more, but wind velocity over a roof deck will most always be lower under an array than if the array were not there, and any benefit or penalty from absence or presence of an array or other obstruction will probably not be in a 1:1 ratio of resulting relative wind velocities.

On a windless day, the vent under an array will probably or maybe get some (but likely very small) benefit from the nat. convection caused by the heating of the air in the stack vent that is caused by the vent being heated by exposure to the array that's probably ~ 30 C warmer than the surroundings other than the roof under it. There will also be some nat. convection from the attic's higher temps., but how much will probably depend on the type of vent and its size. flush vents (O'Hagin type) will probably work about the same in windless conditions under or away from an array. Stack vents won't fare as well. FYI, convection is usually thought of as being of two kinds: Natural (buoyancy induced), or forced (including wind, which, confusingly, is also natural, or ultimately so, but not usually considered buoyancy induced - at least not on a local level, and so treated as forced - and unsteady - convection ).

Short but a bit longer than #1, answer #2 : Because dwelling air will leak or very easily get into most attics and crawl spaces via exfiltration or chimney effects up and through stud space, pretty much irrespective of blocking, and also any number of other routes. When it does, and it will, if the attic temp. is lower than the dewpoint of the air from the interior of the dwelling, just like the air that's cooled by an air conditioner, some of the water vapor that's in that air will condense on the cooler surfaces in the attic. Having done a few blower door tests, I got a difference from before/after choking off/closing the attic vents along with a few burping toilets. I can't find any direction on what to do w/ attic vents for blower door tests, but that's off topic.

I'm not referring to either relative or absolute humidity. You can talk of either one if it makes you feel better, but it makes no difference and only confuses the issues here. Read up on psychrometrics and think in terms of dew points.

There's a lot more to this than can be explained in a forum format. I can do it, but for that (format) reason, it'll be inappropriate here. Besides, I'm a poor teacher and a worse enabler of lazy behavior for folks unwilling to do their own work/education.

More off topic and off my chest:

But to be honest, I doubt your motives for the questions you ask me as being anything more than for the purpose of wasting my time or trapping me with any errors I may and do make. I get, understand and accept that a lot of folks think I overexplain stuff. I usually attempt to provide as complete and as accurate information as possible given this format. Sometimes, those with short attention spans find it irritating. You may think it's pedantic. Take it any way you want. That's one reason for my oft made "Take what you want of the above. Scrap the rest" statement. Not that I think you care, but I'd rather overexplain and be called pedantic but maybe add some information that in their ignorance some folks may find off topic but that may help or spark some curiosity in someone, than underexplain and maybe make the situation less clear.

Rant mode off.

[Jerry Liebler]

Did you tell us where you are?
Is this a grid-tied system?
Where I am things get really complicated if you go over 10kW nameplate DC.
If so what does your utility have to say about your system size?
I do not know about your building department but mine starts the permit with a letter authorizing a maximum size.
Do you need an engineer to sign your plans? If so IronRidge is a good friend to have because they will engineer your racking system.
What do you have agents clamps and what are you going to do instead? Is your alternative bless by an engineer or will you have to get one to sign for you?
Quick Mount PV is very tempting but as far as I can tell lacks the engineering required to get a permit.
I came here looking for information on Quick Mount PV. Does anyone have experience with them?
Good luck.

FWIW I'm in Kentucky, the house is in Georgetown. To get the benefit of fair net metering I'll have to get the PV installed before the end of 2019 ( the coal lobby has gutted a previously fair law).
Here things get really ugly over 30KW below current law mandates approval. I haven't started permit process, may well need local engineer, hopefully equipment supplier engineering is sufficient.
My aversion to clamps started when I "discovered" the alternative called PV Stealth. With the PV Stealth rails the panel's frame sits inside the racking on two sides, the panels are "slid" into position and thereafter held by gravity. Quick Mount PV is not the same as QuickBolt, which offers the "microflashing"..

[Ampster]

Trapping you, J.P.M. ?
Perhaps you dont want to talk about absolute humidity because it will blow holes in the assumptions you made to create your attic moisture theory on cold days. The OP doesn't think he will have a problem with his installation which will be above his roof vents. I agree with him. He knows his environment and how his attic is vented better than you or I.
Perhaps his attic has eave vents. How would that affect things?

[J.P.M.]

Trapping you, J.P.M. ?
Perhaps you dont want to talk about absolute humidity because it will blow holes in the assumptions you made to create your attic moisture theory on cold days. The OP doesn't think he will have a problem with his installation which will be above his roof vents. I agree with him. He knows his environment and how his attic is vented better than you or I. Perhaps his attic has eave vents.

You don't know enough about absolute humidity to know how ignorant that statement is. As for air movement in a dwelling, I base my opinions on education and practice and also as a member of ASHRAE for 38 years. I'm done with this thread.

[Ampster]

............
But to be honest, I doubt your motives for the questions you ask me as being anything more than for the purpose of wasting my time or trapping me with any errors I may and do make. I get, understand and accept that a lot of folks think I overexplain stuff. I usually attempt to provide as complete and as accurate information as possible given this format. Sometimes, those with short attention spans find it irritating. You may think it's pedantic. Take it any way you want. That's one reason for my oft made "Take what you want of the above. Scrap the rest" statement. Not that I think you care, but I'd rather overexplain and be called pedantic but maybe add some information that in their ignorance some folks may find off topic but that may help or spark some curiosity in someone, than underexplain and maybe make the situation less clear.
........

Doubt my motives? Have I once launched off on a multi paragraph rant whose sole purpose is to prove you wrong? Perhaps you are paranoid? Just because you are paranoid does not mean some one else may not be stalking you. LOL. I prefer short answers and clarifying questions which may help inform others. You launch off on tirades, without checking assumptions and you write long paragraphs that seem to be more about demonstrating your knowledge of thermodynamics and irrelevant to the question posed by the original poster. Want examples?

Give me an example where one of your long rants has "sparked curiosity"? When asked to clarify or explain, you dodge the question. Some of us are still waiting for you to respond to the question about why Present Value analysis would be a meaningful tool to compare two bids for a solar installation when all the environmental assumptions were the same. You promised to get back to us but instead you never responded. Want more examples of where you have dodged the question?

We were given two ears and one mouth for a reason, Listening is what we should do most of the time.

[Ampster]

You don't know enough about absolute humidity to know how ignorant that statement is. As for air movement in a dwelling, I base my opinions on education and practice and also as a member of ASHRAE for 38 years. I'm done with this thread.

Now that is a classic case of attacking the person instead of the argument. Then you couple that with an appeal to authority. After 38 years, you can't tell us, the ignorant, why absolute humidity may or may not be important in assessing whether there is more or less moisture in cold air.

I once said the air exiting a heat pump water heater was dryer than the air going in. You launched a multi paragraph paragraph treatise about relative humidity which completely ignored the point of my statement which was that heat pumps dry the surrounding air. How did that spark curiosity? How did that help educate others?
Now you are done with this thread? How convenient.

[Mike90250]

Something else you may wish to consider, is Ridge-line Venting, where there is a continuous vent along the roof ridge. It's small, but the length can add up. Not sure if it's a recommended idea in your area, but popular in mine

[john phillips]

FWIW I'm in Kentucky, the house is in Georgetown. To get the benefit of fair net metering I'll have to get the PV installed before the end of 2019 ( the coal lobby has gutted a previously fair law).
Here things get really ugly over 30KW below current law mandates approval. I haven't started permit process, may well need local engineer, hopefully equipment supplier engineering is sufficient.
My aversion to clamps started when I "discovered" the alternative called PV Stealth. With the PV Stealth rails the panel's frame sits inside the racking on two sides, the panels are "slid" into position and thereafter held by gravity. Quick Mount PV is not the same as QuickBolt, which offers the "micro flashing"..

You live in one of the lowest cost states for electricity and you are saying that net-metering has been gutted and you hope to get grandfathered into a good net-metering rate.
Typically when the rates are not forever. There is a strong chance your contract will change before you break even. We are not talking about chump change here. I think there are a lot of other places to put your money than to gamble on this adventure. If you sell the salespeople will tell you that you will get full value but the buyer will not get your rate. The system will not be worth nearly as much to them as it is to you. Would you put this kind of money in on a pool or a tennis court? I can tell you that you most of the time a pool, tennis court and solar do not increase the sale price of your home nearly enough to have it be a factor. I have lived in this house for 46 years, I thought I would die here. Next week I am moving, 3 years ago I put in a 9200 Watt DC solar ground mount. The appraiser said he would give me $12,000, I have generated $6,000 in energy, I have not been able to use all the $9000 non-refundable tax credit and if I did and if I do get the $12.000 sale price bump I will still be $3000 behind. 3 different realtors have told me that $12,000 is very optimistic. One said $0 but it may help it sell faster.

Given what you have said I think there are a lot of safer and more profitable investments out there that you should look at. Solar can be good but it needs to be in a high rate area with a great net-metering contract. Net-metering is, in essence, a great battery combined with a great backup generator equivalent to an off-grid setup. The battery is so good that you can go negative in the winter then make it up in the summer. Such an off-grid setup would cost more than double what the solar costs. Without net-metering, you have to store or lose excess production.

In California Rule 21, also known as smart-grid, give the utility the option of turning off you inverters if they do not want the energy.

[Ampster]

......
In California Rule 21, also known as smart-grid, give the utility the option of turning off you inverters if they do not want the energy.

Interesting anecdote that does not apply to the Original Poster. What do you think thev likeliehood is of that happening in California? Conspiracy theory aside, the left coast seems pretty committed to renewable energy. I live in California and my personal belief is they would put a steam plant on standby before the would shut down my inverter. Even if they did turn off my Inverter it would probably only be in the morning hours so no big deal. In that case the grid would be up so I would still have power.

I am confident that the OP has assessed the risks that you have articulated above for Kentucky. I view solar as a different kind of investment that gives one a hedge against inflation and an opportunity to save money on power. Did you notice his goals at the beginning of this thread? He is only asking for advice about the racking not whether he should spend the money. Perhaps he has a diiferent probability of staying in his house longer than you.

[Jerry Liebler]

[QUOTE=john phillips;n395466]

You live in one of the lowest cost states for electricity and you are saying that net-metering has been gutted and you hope to get grandfathered into a good net-metering rate.
Typically when the rates are not forever. There is a strong chance your contract will change before you break even. We are not talking about chump change here. I think there are a lot of other places to put your money than to gamble on this adventure. If you sell the salespeople will tell you that you will get full value but the buyer will not get your rate. The system will not be worth nearly as much to them as it is to you. Would you put this kind of money in on a pool or a tennis court? I can tell you that you most of the time a pool, tennis court and solar do not increase the sale price of your home nearly enough to have it be a factor. I have lived in this house for 46 years, I thought I would die here. Next week I am moving, 3 years ago I put in a 9200 Watt DC solar ground mount. The appraiser said he would give me $12,000, I have generated $6,000 in energy, I have not been able to use all the $9000 non-refundable tax credit and if I did and if I do get the $12.000 sale price bump I will still be $3000 behind. 3 different realtors have told me that $12,000 is very optimistic. One said $0 but it may help it sell faster.

Given what you have said I think there are a lot of safer and more profitable investments out there that you should look at. Solar can be good but it needs to be in a high rate area with a great net-metering contract. Net-metering is, in essence, a great battery combined with a great backup generator equivalent to an off-grid setup. The battery is so good that you can go negative in the winter then make it up in the summer. Such an off-grid setup would cost more than double what the solar costs. Without net-metering, you have to store or lose excess production.

In California Rule 21, also known as smart-grid, give the utility the option of turning off you inverters if they do not want the energy. [/QUOTE

Yes solar payback is definitely slowed by cheap coal power! According to PVWatts I'll get $0.106/year for each PV watt. So it'll take 10 years to break even at $1/watt.

[peakbagger]

Something else you may wish to consider, is Ridge-line Venting, where there is a continuous vent along the roof ridge. It's small, but the length can add up. Not sure if it's a recommended idea in your area, but popular in mine

Hope I can avoid the various brushfires that seem to be popping up on this thread but a FYI on "Vent a ridge type systems" is they work fine for summertime attic ventilation but not so good for winter ventilation which is important for folks with potential for significant snow as the "vent a ridge" type systems have a very annoying tendency to get covered with snow in the fall and not melt out until spring,. This can impact the attic ventilation up through the soffits on warm winter days which is needed to keep ice damming at bay. Generally gable end vents properly sized with louvers and an interior catch pans for blowing snow conditions are more suitable for snow conditions as they don't get blocked. I have seen various creative roof vents that are supposed to be able to deal with snow but they usually end up really ugly as they need to stick up past the potential snow pack. Note many soffits and gable end vents are substantially undersized for summer cooling unless fan assisted.

[J.P.M.]

[QUOTE=Jerry Liebler;n395578]

You live in one of the lowest cost states for electricity and you are saying that net-metering has been gutted and you hope to get grandfathered into a good net-metering rate.
Typically when the rates are not forever. There is a strong chance your contract will change before you break even. We are not talking about chump change here. I think there are a lot of other places to put your money than to gamble on this adventure. If you sell the salespeople will tell you that you will get full value but the buyer will not get your rate. The system will not be worth nearly as much to them as it is to you. Would you put this kind of money in on a pool or a tennis court? I can tell you that you most of the time a pool, tennis court and solar do not increase the sale price of your home nearly enough to have it be a factor. I have lived in this house for 46 years, I thought I would die here. Next week I am moving, 3 years ago I put in a 9200 Watt DC solar ground mount. The appraiser said he would give me $12,000, I have generated $6,000 in energy, I have not been able to use all the $9000 non-refundable tax credit and if I did and if I do get the $12.000 sale price bump I will still be $3000 behind. 3 different realtors have told me that $12,000 is very optimistic. One said $0 but it may help it sell faster.

Given what you have said I think there are a lot of safer and more profitable investments out there that you should look at. Solar can be good but it needs to be in a high rate area with a great net-metering contract. Net-metering is, in essence, a great battery combined with a great backup generator equivalent to an off-grid setup. The battery is so good that you can go negative in the winter then make it up in the summer. Such an off-grid setup would cost more than double what the solar costs. Without net-metering, you have to store or lose excess production.

In California Rule 21, also known as smart-grid, give the utility the option of turning off you inverters if they do not want the energy. [/QUOTE

Yes solar payback is definitely slowed by cheap coal power! According to PVWatts I'll get $0.106/year for each PV watt. So it'll take 10 years to break even at $1/watt.

PVWatts has shown itself to be pretty good as a model and a tool for preliminary design of residential PV systems, but I've found its estimates of electrical costs and savings are not as good. For my POCO, it is off in both method and accuracy.

While $0.106/kWh cost/kWh from the POCO (if that's what you're trying to convey) will make the path to economic cost effectiveness longer than a higher rate, I'd use other methods for determining your electricity costs.

[john phillips]

[QUOTE=J.P.M.;n395583]

PVWatts has shown itself to be pretty good as a model and a tool for preliminary design of residential PV systems, but I've found its estimates of electrical costs and savings are not as good. For my POCO, it is off in both method and accuracy.

While $0.106/kWh cost/kWh from the POCO (if that's what you're trying to convey) will make the path to economic cost effectiveness longer than a higher rate, I'd use other methods for determining your electricity costs.

Given that data and not knowing system cost there is a significant risk the system will never pay for its self even if you disregard the time value of money. The best posable payback is if the green new deal passes and all coal is shipped to China rather being used locally driving electric rates up your system could pay for its self in 10 years or so. If your net-metering goes away count on requiring storage which will cost as much as your solar install probably with no subsidy. At that point, you yous your power company as your backup generator and cover the shortfall you predict your system will have.

You are looking at a very large residential system. It is 3 times larger than I could install here without special permitting.

I am only trying to help, your choice of racking may not be your biggest problem.