Alternative module mounting methods?

[K8MHZ]

For roof mounting, flush with about a 3 inch air space, are there any other means beside the custom made rail systems suitable? The rails cost nearly 8 bucks a foot. Adding the cost of the rest of the hardware that adds 50 bucks or so to each 3'x5' module. The 33 module array I just drew up would take over 1500 dollars of mounting materials.

I checked Uni-Strut and although they claim to have a product suitable, I didn't see much other than the stuff I already know about. Uni-Strut isn't cheap, either, and there is going to be extra labor due to having to drill holes for L-brackets.

Would it be a travesty to consider pressure treated lumber?

Module costs are not only coming down, but 'scratch and dent' seconds are now showing up for about $1.30 per watt. Good brand inverters are becoming available used for about 1/3 of what they cost new. Also, new technologies are making inverters much smaller, thus less cost and easier installation.

None of the above is true for the mounting systems. We used Uni-Rac in school. Yes, it is a great product, but it costs about $7.70 per foot, not including hardware.

Uni-Strut would be easy to use if we only wanted 1 5/8" of air space. To get 3 inches, 'back to back strut would be needed, putting an open side toward the roof. Also, the back to back stuff doesn't have holes in it. I have seen electricians use 'front to back' by bolting them together for hanging pipe. Although fine for that, I don't think such a configuration would be sturdy enough for mount solar modules.

Right now, the RROI (rate of return of investment) for systems that cost 6-7 bucks per watt is around 2 percent. (At 12.4 cents per kWh). 2 percent is not worth taking money out of a 4 percent interest rate CD to 'invest' in a PV system.

If we can get the cost down to 5 bucks per watt, the investment return figured as interest starts becoming competitive with CD's and savings accounts.

 

[ggunn]

Would it be a travesty to consider pressure treated lumber?

Yes, it would; PV system lifetime is typically planned to be 20-30 years. That's not to say that the guerrilla solar guys never do it, but if your system is to be inspected, it will fail if the racking is wood.

 

[DTLight]

You could use the slotted 3 1/4" P5000T Strut, although I have no idea what is would cost you. It looks like McMaster-Carr has it for about $7.50 a foot, I presume it would be cheaper through a steel supplier probably.

 

[BillK-AZ]

Lower cost mounting

Lower cost mounting

I have used standard slotted pre galvanized (PG) strut on short pedestals, with and without a sealing boot without problems with inspections in Arizona. Use the zinc rich primer paint on any cut ends and drilled holes. Our structural engineer recommends pedestals every 6' or less.

The usual clips will work if you use spring nuts and standard bolts of adequate length.

Strut comes in 10' and 20' lengths, while the custom Unirac or other rails can be up to 25'. Strut is about $2.00/ft.

 

[K8MHZ]

I have used standard slotted pre galvanized (PG) strut on short pedestals, with and without a sealing boot without problems with inspections in Arizona. Use the zinc rich primer paint on any cut ends and drilled holes. Our structural engineer recommends pedestals every 6' or less.

The usual clips will work if you use spring nuts and standard bolts of adequate length.

Strut comes in 10' and 20' lengths, while the custom Unirac or other rails can be up to 25'. Strut is about $2.00/ft.

Cool!

Where do you get the pedestals?

 

[BillK-AZ]

Illustrated is the Direct Power & Water 3" Power Post Stanchion, part PPP3.

Available from many distributors. There are other similar parts.

 

[BretHeilig]

K8MHZ, do yourself a big favor and don't try to make your margins by using the cheapest materials you can find. Remember that these are 30-year systems. Zinc is going to fail more slowly than pressure-treated lumber, but it will fail. Use aluminum and stainless steel. Racking costs what it costs. If there were a reliable cheaper way, Sun Edison and Solar City would be doing it.

http://solarprofessional.com/article/?file=SP4_4_pg14_QA

Additionally, you shouldn't rely on any blanket assertions about engineering (such as '6 feet on center for posts') - that might work fine if your rail spans that far safely, if the rafters you're attaching to can handle the point loads, and if the lag screws you use can resist the uplift of wind on the array. If you don't know how to perform these calculations for your site, get someone who does.

http://solarprofessional.com/article/?file=SP3_2_pg30_Lee

Don't put the client's investment, and the entire industry's reputation at risk.

 

[jaggedben]

Uni-Rac ... costs about $7.70 per foot, not including hardware.

Is that MSRP? Shop around more, you can get a better price than that.

Also, Pro-Solar is quite a lot cheaper, probably enough to justify the slight extra labor involved.

Those are the ones I know. There are a bunch of other racking companies, including wholly different approaches such as Zep. ... Don't start looking at products not designed for the purpose before you have exhausted those that are.

 

[iwire]

Would it be a travesty to consider pressure treated lumber?

IMO yes, that would be some pretty low end work.

 

[Smart $]

Cool!

Where do you get the pedestals?

An alternative:

Use with single strut bolted to top (replace back-to-back in depiction) and lower flange bolted to roof.

 

[K8MHZ]

Is that MSRP? Shop around more, you can get a better price than that.

Also, Pro-Solar is quite a lot cheaper, probably enough to justify the slight extra labor involved.

Those are the ones I know. There are a bunch of other racking companies, including wholly different approaches such as Zep. ... Don't start looking at products not designed for the purpose before you have exhausted those that are.

Thanks for the Pro-Solar link. I'll check out Zep, too.

 

[K8MHZ]

IMO yes, that would be some pretty low end work.

There is a large market for 'low end' type work in rural Michigan. I doubt that a farmer would consider using hefty pressure treated lumber as slip shod work. Some may even prefer it.

In a sense, 'solar mounting systems' is like 'digital TV antennas' to me. Just because a piece of extruded aluminum rail is used for solar panels it becomes more costly.

People won't buy en-masse until the cost of the systems comes down. For two reasons, one is that the payback period of 50 plus years is too long. The other, even if the payback was only 5 or 8 years, is that there still is thousands of dollars to have to come up with.

I am just looking at ways to challenge the prices of the components of the systems. The cheaper they are, the more we will be able to sell.

For Bob, There are a couple DIY arrays out in the country and that is where they seem to only be. I'll look close, but I'll bet I find at least one (not done by me) mounted with lumber and get some pics.

To me, the 'ballast' system is about as cheesy as it gets. Sand bags and concrete blocks piled on like they were expecting a flood? How many years do you think the sand bags will last or the metal under the concrete blocks, for that matter?

 

[jaggedben]

People won't buy en-masse until the cost of the systems comes down. For two reasons, one is that the payback period of 50 plus years is too long. The other, even if the payback was only 5 or 8 years, is that there still is thousands of dollars to have to come up with.

Three comments...
-Using cheaper materials may not help the payback period at all if they have higher maintenance costs, shorter replacement times, or worse fire risks. It could make the payback time worse.
-Solar 'lease' options have been totally changing the problem of up-front cost lately.
-Not all payback times, even without gov't subsidies, are anything like 50 years. It depends on the location.

 

[K8MHZ]

Three comments...
-Using cheaper materials may not help the payback period at all if they have higher maintenance costs, shorter replacement times, or worse fire risks. It could make the payback time worse.
-Solar 'lease' options have been totally changing the problem of up-front cost lately.
-Not all payback times, even without gov't subsidies, are anything like 50 years. It depends on the location.

Thanks!

In my area we are figuring for 3.5 full output hours per day. I was told that is a bit conservative. Using the same products we are using in our lab, the un-amortized payback is 52 years. Doing some shopping and de-rating the dollar I can cut that to 39 years. Still not good, but better.

The other side of the state had (no longer) a rebate program of $2.40 per watt and also a very generous SREC program for homeowners. That made PV systems much easier to sell. This side (Western Michigan) only has a net metering program and that is scheduled to end once 70 MW is attained (one percent of peak).

 

[jaggedben]

Using the same products we are using in our lab, the un-amortized payback is 52 years.

That number is dependent on the price of electricity you are using. It's quite cheap in Michigan, no? If you figure on average electricity prices for the whole US (~$.10 per kWh) then payback periods can indeed be unreasonably long, or never.

But lots of people pay way more than 10 cents for at least some of their electricity. If they use a lot of electricity, they may land in a higher 'tier', and if they go on a 'time-of-use' plan, they pay more for electricity at peak hours, which happens to be when the sun shines. These things vary by location, but in California these rates can get upwards of 40 cents. So payback periods, even without gov't subsidies, can be less than the 25-year life of a system. Installed prices are coming down to $6/W or less out here. For 25 years at 15% capacity factor, that comes to ~$.1825/kWh.

 

[iwire]

There is a large market for 'low end' type work in rural Michigan. I doubt that a farmer would consider using hefty pressure treated lumber as slip shod work. Some may even prefer it.

It makes no sense to mount equipment with a design life of 25 to 30 years on wood, PT or not.

Any savings will be more than offset once it starts falling apart.

In a sense, 'solar mounting systems' is like 'digital TV antennas' to me. Just because a piece of extruded aluminum rail is used for solar panels it becomes more costly.

No doubt.

People won't buy en-masse until the cost of the systems comes down. For two reasons, one is that the payback period of 50 plus years is too long. The other, even if the payback was only 5 or 8 years, is that there still is thousands of dollars to have to come up with.

Welcome to solar.

I am just looking at ways to challenge the prices of the components of the systems. The cheaper they are, the more we will be able to sell.

Uh huh.

But you did ask for opinions and mine is that PT is a bad idea.

 

[iwire]

In my case I work for a company with a truly enforced safety program, we own hundreds of feet of roof railing systems, countless types and numbers of tie off equipment and the slowed production that goes with applying all of it. We have guys trained and licensed to operate cranes and telehandlers.

But we have to compete against companies that have some home depot ladders and and master mechanic tool kits.


Point being ........it ain't easy money yet.

 

[K8MHZ]

It makes no sense to mount equipment with a design life of 25 to 30 years on wood, PT or not.

Any savings will be more than offset once it starts falling apart.

The modules look like they would last more than 30 years, actually. But methinks you underestimate the longevity of good wood. Look at the cyprus power poles that have been outside, unprotected for nearly 100 years. Same for rail road ties.

I know that at some point I will be asked why 'good wood' isn't used instead of expensive extruded aluminum. At this point all I can say is that an experienced installer (that would be you) feels that any wooden mounting system would fail or create problems at some point during the life of the array. I have no proof, I have seen no lab tests. But I, like many others, have seen wooden structures that are much more than 100 years old. There is an old building I work in occasionally that has wooden floors. The wood is end for end, meaning thousands of foot long pieces were put together like bricks, but with the end of the grain exposed. That building is over 100 years old, has been in use since day 1 and has several areas where the roof failed exposing the floor. The wood on that floor is like concrete.

But you did ask for opinions and mine is that PT is a bad idea.

And I do value your opinion. The fact is, I have no real proof that wooden supports manufactured specifically for outdoor use will fail before the life of an array. All I am able to do is to take a 'conservative' approach by using industry standard materials. The problem is that it would not be cash that gets conserved. Also, our industry standards are so new that we really have no way of actually knowing how long the suggested materials last, all we can do is predict.

 

[K8MHZ]

That number is dependent on the price of electricity you are using. It's quite cheap in Michigan, no? If you figure on average electricity prices for the whole US (~$.10 per kWh) then payback periods can indeed be unreasonably long, or never.

But lots of people pay way more than 10 cents for at least some of their electricity. If they use a lot of electricity, they may land in a higher 'tier', and if they go on a 'time-of-use' plan, they pay more for electricity at peak hours, which happens to be when the sun shines. These things vary by location, but in California these rates can get upwards of 40 cents. So payback periods, even without gov't subsidies, can be less than the 25-year life of a system. Installed prices are coming down to $6/W or less out here. For 25 years at 15% capacity factor, that comes to ~$.1825/kWh.

In my area, juice is 12.4 cents per kWh. Not the cheapest, but still low enough to make for a long payback.

For capacity factor, I use 14 percent (3.5 hours per day).

Another wrench in the gears is going to be when Consumers Energy meets it's 70 MW goal. At that point, they will stop net metering and also stop allowing for grid ties. They get to decide who hooks to their system and who doesn't.

 

[K8MHZ]

In my case I work for a company with a truly enforced safety program, we own hundreds of feet of roof railing systems, countless types and numbers of tie off equipment and the slowed production that goes with applying all of it. We have guys trained and licensed to operate cranes and telehandlers.

But we have to compete against companies that have some home depot ladders and and master mechanic tool kits.


Point being ........it ain't easy money yet.

I am all for safety and applaud your company for going the extra mile to keep you guys safe.

What I do wonder about is why the guys that put the shingles on the roofs never have fall protection, but the guys that put the rails and modules on the same roof have to have it. Outside new commercial / industrial construction I have never seen a roofer with a harness on.