# Should I Progress through enough PV incentives to a PV system?



## pring7 (Apr 14, 2011)

Well, Iâ€™m thinking about doing a little more than a 2 kw solar system and I just read yesterday that Progress energy is offering this incentive for NC customers.  With this incentive along with the State and Federal ones (about 75% rebate total) I am thinking that this might be enough carrots to entice me into letting them put the ugly panels on the roof.  I know somebody else recently did from this blog and I was wondering if this would be enough Kool-aid to convince you to do it.  I havenâ€™t done the math yet, but I am guessing that this would bring the payback to less than a decade and I am youngish (33) and probably staying in my home for at least 15-25 yrs Lord willing.  I think that the total system cost would be between 15-22k, but I haven't got the actual estimate yet.  I already have solar DHW and water heating for air heat from another great Progress incentive program, but I have much more due south facing rooftop.

Thanks for your consideration.

Carolinas SunSense Solar PV Program - Benefits

With solar photovoltaic (PV) panels on your rooftop, you could be generating clean, renewable electricity â€“ and incentives from Progress Energy.
To qualify for this residential PV program, you must be a Progress Energy Carolinas (PEC) customer located in North Carolina and a homeowner. You must be the account holder, use the home as your primary residence and own the solar PV system ("System") installed on the home. Renters may not participate.
If accepted into the program, you will receive an upfront rebate payment plus an ongoing monthly bill credit. To qualify, the proposed PV system must be rooftop-mounted and range in size from 2 kW AC to 10 kW AC.  Systems must be installed by a licensed contractor, meet electric and safety standards and be capable of producing a minimum of 1,200 kWh/per kW AC annually.

Participating customers must participate on PEC's TOU-D rate, Net-Meter Rider and Solar Rider for a minimum five-year period with an option to extend each year thereafter.  Participants will receive a one-time upfront rebate of $1,000 per kW AC  and a monthly bill credit based on the same system AC rating at $4.50 per kW. 

The program limit is 1 MW AC each year.  PEC must receive and approve program applications prior to PV system installation or else the incentives cannot be provided. Click here to access the application.

For additional program details, click here to review a list of FAQs. To contact Progress Energy Carolinas about this program, send an e-mail to PECHomeSolar@pgnmail.com.
This program is part of Progress Energy's ongoing commitment to making renewable energy more accessible and affordable for our customers and communities.


Legal disclaimer: All non-energy attributes of the System, including environmental attributes and/or the renewable energy certificates ("RECs") attributable to the amount of energy generated by the System, must be owned by the Applicant and will be provided to Progress Energy under the terms of the program.

FAQ's and other details are here at their site:

http://progress-energy.com/custservice/carres/efficiency/programs/solarpv/index.asp


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## mbcijim (Apr 17, 2011)

Are you certain your cost is right?  Up here in Pennsylvania up front costs are down to $5,000 or so per KW so your estimate seems high, although with such a small system you may need to pay a premium.  

Just an FYI, I'm sweatin' bullets right now, I installed 200KW and since 9/9, production is about 75% of what the projections showed.


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## DaveH9 (Apr 17, 2011)

I would think that NC is a somewhat immature residential market and would expect that you would pay around 13,000 to 16,000 for 2 kw. In the Ashville or Raleigh region perhaps less.  What are you paying per kWh? What is the history of rate increases? Are you on time of use rate now and what are the rates? Mandatory time of use usually results in good savings with solar but not always, depends on the rate structure and if you can reduce your load during peak beyond the solar reduction. The 30% federal tax credit may not last as long as we hoped, so it is wise to look at doing it. The rebate is AC, without running PV watts I would guess that would be about $800 a Kw.  The 4.50 a Kw AC per month I believe works out to about .12 kWh.  Some pretty good carrots.


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## jdemaris (Apr 17, 2011)

mbcijim said:
			
		

> .
> Just an FYI, I'm sweatin' bullets right now, I installed 200KW and since 9/9, production is about 75% of what the projections showed.



With a 200KW array I assume you're running a factory with it, or large business of some sort? Are maybe a neighborhood of 20 homes?

I run my house and barn on a 6KW grid-tie system and I was not allowed to install anything larger - or incentives would not have been approved.  Grid-tie and incentive regs here in New York only allow a system that is projected to make 110% of past annual useage.

When it comes to solar installer "experts", I had four estimates and proposals before I designed my own system.  All four greatly over-estimated what production would be. All over-projected by 20-30%.  Luckily, I did not take their "expert" advice.  I did it my way, and for three years now have made an overage of 6%.


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## DaveH9 (Apr 17, 2011)

mbcijim   
 did your installer give you a projected monthly breakdown of production? If they gave you only a yearly projection it may be close. Try taking the avg of your 2 equinox months actual production Kwh and multiply by 12. should be close estimate to annual. Depending on your azimuth and tilt. Did you get buried in snow last winter?


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## jdemaris (Apr 17, 2011)

DaveH9 said:
			
		

> mbcijim
> did your installer give you a projected monthly breakdown of production? If they gave you only a yearly projection it may be close. Try taking the avg of your 2 equinox months actual production Kwh and multiply by 12. should be close estimate to annual. Depending on your azimuth and tilt. Did you get buried in snow last winter?



I'm not the guy you asked, but here's what happened here in central NY.  The State incentive programs require annual estimates for electric production. Never monthly.
One big problem in areas with mountains is the micro-climate.  20 miles one direction or another can make a big difference in annual sun.  My specific local area is much darker then the City of Cobleskill that is only 15 miles away.  Same for the city of Oneonta that is 20 miles distant the other direction. 

None of the State certified installers took that into account even thought I had monitored sunlight here for the past 10 years. My projection was dead-on and all the installers that came here were way off.  All said I only need a 3.6 KW system to make my 110% per year.  My system also works when the grid is down, and most do not.


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## pring7 (Apr 17, 2011)

Wow, nobody responded initially, so I thought this would be an unanswered thread.  Let me first say I thank you for all of your inputs.  I would like to get as much feedback as possible before I decide whether to make the solar investment.  

Mbcijim: My estimate IS a little high.  I think that the over the phone estimate was probably no more than 14 thousand for a 2k system.   Iâ€™m a little OCD though, so if there are a funny number of panels on the roof I may end up with a little more than a 2kw system just to make it â€œlookâ€ right to me.  The requirement is a minimum 2k system for Progress though.

DaveH9: IMO we do have a very immature market and here is a link with the rate info and TOU schedule: http://www.progress-energy.com/aboutenergy/rates/NCScheduleR-TOUD.pdf

Rates have not changed much if at all in the last 5 years.  Duke and Progress have hooked up, so Iâ€™ve heard that there may be rate changes, but some have said that they could get worse and some have said that they may actually improve.

The Progress rates here are not terrible, so really that makes the decision tougher.  Especially after nights like last night with high winds, 105 tornado reports across the state, and possible golf ball sized hail in the area.  I guess homeowners insurance would cover solar panels, or would I need a waiver on my policy?
The way I read the rebate it should be a straight $2000 for a 2kw system plus $9 per month for 5 yrs.  You read that differently though, so now I am wondering.

Jdemaris: If I do a system, I would like it to have the capability that yours has to be â€œoffâ€ the grid.  I think that I will have to wait for the 5 year incentive to be over though.  One perk is that NC is one of those states that allows you to sell RECs.


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## mbcijim (Apr 18, 2011)

DaveH9 said:
			
		

> mbcijim
> did your installer give you a projected monthly breakdown of production? If they gave you only a yearly projection it may be close. Try taking the avg of your 2 equinox months actual production Kwh and multiply by 12. should be close estimate to annual. Depending on your azimuth and tilt. Did you get buried in snow last winter?



Yes I had a monthly breakdown of production.  Can't think of the name of the software...  So far I checked the angle facing south (had a surveyor out) that is correct.  I have to start watching as summer solstice approaches, but I think they may have put the rows too close to one another.  The top panel of row 1 was shading the bottom panel of row 2, and so on at 11:00AM in early March.


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## mbcijim (Apr 18, 2011)

jdemaris said:
			
		

> mbcijim said:
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This is a commercial system hooked up to a factory.  If you'd like to see an aerial go to http://mbcdevelopment.com/past.asp


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## mbcijim (Apr 18, 2011)

Firemedic, one thing to consider is why roof mount?  You're already almost guaranteeing the wrong angle.  When you need a new roof your adding take off and reinstall the panels to the project.  

My father had the second rubber roofing installation license in Pennsylvania (circa 1978 or so).  He's literally installed over ten million square feet of rubber in his career.  
When we were doing our 3/4 acre (200KW) system, he was adamant he didn't want it on top of a rubber roof.  I don't pretend to understand roofing but I do know good advice when I hear it.  

If you have any room at all I'd advise ground mount.


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## pring7 (Apr 18, 2011)

For the Progress rebate the system has to be roof mounted.  I think that my pitch and aspect are good for a system too.  It might not be the ideal angle, but it seems to be pretty good.  My evacuated tubes do really well, but I know that they aren't as finicky as the PV panels.  

I have an Aunt and Uncle in Montana that have two ground units that track the sun and they are neat, but for the purpose of taking advantage of the rebates I would like to do a roof system.  My house is only 4 years old and the roof should hold up for a while before it needs changing.  It's definitely a point to consider though.  Have people had panel installations wear out their roof prematurely?


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## jdemaris (Apr 18, 2011)

firemedic said:
			
		

> For the Progress rebate the system has to be roof mounted.  I think that my pitch and aspect are good for a system too.  It might not be the ideal angle, but it seems to be pretty good.  My evacuated tubes do really well, but I know that they aren't as finicky as the PV panels.
> 
> I have an Aunt and Uncle in Montana that have two ground units that track the sun and they are neat, but for the purpose of taking advantage of the rebates I would like to do a roof system.  My house is only 4 years old and the roof should hold up for a while before it needs changing.  It's definitely a point to consider though.  Have people had panel installations wear out their roof prematurely?



There is no ONE perfect angle anyway. Solarization changes summer to winter.  One good average setting is usually used in the Northeast. Expensive tracking systems gain little in this part of the country.

On a roof-mount system, adjustable racks can be used so the panels have the correct angle without having to match the roof pitch.

Here in NY, there is no mandate for "home roof mounting."  Any roof qualifies, regardless if on the house, barn, four foot high rack, etc.  In my case, I built a new barn to "kill two birds with one stone."  I designed the south-facing roof with the exact pitch required.  It also houses a small motorhome, four farm tractors and two bull dozers, plus my backup battery bank, PTO generator, etc.

It is odd though that the wiring-code requirements are different for a home if using a"roof mount" or "wall mount."  The wall mount is less restricitive and also eliminates any re-roofing problems later.


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## DaveH9 (Apr 18, 2011)

> Yes I had a monthly breakdown of production.  Canâ€™t think of the name of the softwareâ€¦  So far I checked the angle facing south (had a surveyor out) that is correct.  I have to start watching as summer solstice approaches, but I think they may have put the rows too close to one another.  The top panel of row 1 was shading the bottom panel of row 2, and so on at 11:00AM in early March.



You may be able to solve that type of shading issue by 2 methods. One is to lower the tilt, there should not be a panel shading another any time of the year imho. Method two is to add a optimizer like tigo energy or solar magic. I imagine that you are using a central commercial inverter?

Do you have a peak charge? if so lowering the tilt might be beneficial in the summer and help your shading.


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## mbcijim (Apr 18, 2011)

DaveH9 said:
			
		

> > Yes I had a monthly breakdown of production.  Canâ€™t think of the name of the softwareâ€¦  So far I checked the angle facing south (had a surveyor out) that is correct.  I have to start watching as summer solstice approaches, but I think they may have put the rows too close to one another.  The top panel of row 1 was shading the bottom panel of row 2, and so on at 11:00AM in early March.
> 
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What's an optimizer?  I have 13 inverters that are all commercial.

Lowering the tilt, unfortunately, means a $20k-$50k bill.  I may have to fix it, I just don't know yet.  We are talking 3/4 of an acre of panels, not a residential system.  No easy fixes.


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## DaveH9 (Apr 18, 2011)

mbcijim said:
			
		

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An optimizer will help boost performance of a string that is compromised by shading. When one module of a string is shaded, even partially, the voltage of the whole string is effected.
The old fashioned Christmas light syndrome. Optimizers can switch off the affected module(s) and allow the rest of the string to produce optimally.  Are the modules mounted portrait or landscape.?


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## mbcijim (Apr 18, 2011)

Interesting, I'll have to speak with my installer about that.

They are installed 4 atop each other in landscape.  I don't know how many long, but long, probably 100-125' across.


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## DaveH9 (Apr 18, 2011)

another option might be to convert how the strings are wired. You might be able to string the bottom shaded rows together to the same inverters, (if that is not how it is wired now). Long shot, but worth looking at.


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## mbcijim (Apr 18, 2011)

Thanks I'm going to look into it.


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## pring7 (Apr 19, 2011)

Are there systems for residential roofs that will automatically adjust to the ideal angle?  If so, is it worth the (probably) additional expense?  
I like the idea of putting a barn up by the creek with solar panels.  I had thought about one day building a 2 story barn/boat house with a gambrel roof down by our creek.  Something like this:


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## mbcijim (Apr 19, 2011)

The best solution would be to put the back of that building facing due south and build one of the roof pitches at the correct angle.  Then you don't have to worry about any system.  FYI, that's a SMALL roof.  PV's need room.  They aren't small.


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## benjamin (Apr 19, 2011)

mbcijim said:
			
		

> Firemedic, one thing to consider is why roof mount?  You're already almost guaranteeing the wrong angle.  When you need a new roof your adding take off and reinstall the panels to the project.
> 
> My father had the second rubber roofing installation license in Pennsylvania (circa 1978 or so).  He's literally installed over ten million square feet of rubber in his career.
> When we were doing our 3/4 acre (200KW) system, he was adamant he didn't want it on top of a rubber roof.  I don't pretend to understand roofing but I do know good advice when I hear it.
> ...



I don't know squat about rubber roofs, but I know as much about shingles as any Julio.  DON'T install PV on top of shingles.  

A recent Home Power magazine has a photo of a nice new PV install on shingles that have been scuffed to death by the installer traffic, bad idea.  At least now they have a properly flashed anchor point, it was only a few years ago that standard practice was to put a lag bolt through the roof with a dab of silicone?!?!  

Lots of solar systems are removed by roofers and never reinstalled.  I've had people say that of course a $$$ system would be put back up when the shingles are replaced, but a future homeowner may not want to spend $$ to reinstall a $$$ system when the system will only produce $ worth of electricity before it needs to be moved again.


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## DaveH9 (Apr 19, 2011)

firemedic said:
			
		

> Are there systems for residential roofs that will automatically adjust to the ideal angle?  If so, is it worth the (probably) additional expense?
> I like the idea of putting a barn up by the creek with solar panels.  I had thought about one day building a 2 story barn/boat house with a gambrel roof down by our creek.  Something like this:



The angle is not such a big deal these days, the best practice on a sloped roof is to keep it parallel to the roof. If you tilt them, them you may have to reinforce the structure due to increased stress from wind load. The front of that building not so good, with those dormers.


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## pring7 (Apr 20, 2011)

The back would be the dormer side and the other side would be the south side.


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## DaveH9 (Apr 20, 2011)

firemedic said:
			
		

> For the Progress rebate the system has to be roof mounted.  I think that my pitch and aspect are good for a system too.  It might not be the ideal angle, but it seems to be pretty good.  My evacuated tubes do really well, but I know that they aren't as finicky as the PV panels.
> 
> I have an Aunt and Uncle in Montana that have two ground units that track the sun and they are neat, but for the purpose of taking advantage of the rebates I would like to do a roof system.  My house is only 4 years old and the roof should hold up for a while before it needs changing.  It's definitely a point to consider though.  Have people had panel installations wear out their roof prematurely?



Get some fast jack or quick mount pv flashing, and you will never get leaks on the penetrations. 

The tou is good for you. Our peak starts at noon, yours starts at 10 am. Think you could cool your home enough before 10 am and just throttle  the ac down on solar until 9pm?  The evac tubes are absorbing heat that normally would heat your attic and the pv will do the same. Do you mechanically cool your attic? 

Looks like your electric company wants to claim the recs. Did I read that right? If so That's not very nice of them, even though NC recs aren't worth that much as far as I've heard.

Any way, it still looks good, considering that you will increase your home value, enjoy solar electricity, and save money.


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## jdemaris (Apr 20, 2011)

DaveH9 said:
			
		

> The angle is not such a big deal these days, . . .



Just curious about your statement.  From what I've seen, nothing has changed much in the past 20 years when it comes to the technology.   In fact, with the panels themselves, little of high consequence has changed in the past 50 years.  The needs of solarization are the same.

About some other comments on this thread about adding systems to allow bypass to shaded panels?   I'm not sure what the alledged problem is.   A good installation with good panels will have bypass and blocking diodes.   These stop current backflow, and allow current to pass through shaded panels in strings.  It's a pretty simple solution that I assume has become pretty-much standard.  Without the bypass diodes, shaded panels can overheat in darkened areas.

With my setup, I "killed two birds with one stone."   I built a new barn to keep tractors and dozers in, and built a special angle south-facing roof just for the solar panels.  It's about 500 feet from my house.  Inverters are in the barn, so the run to the house is 220 AC, not  DC.  Panels are wired up for 48 VDC.


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## semipro (Apr 20, 2011)

jdemaris said:
			
		

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Wow, I don't see one thing in those photos that I'm not envious of.  Great scenery, the barn, the equipment, the solar setup.  Damn!  I knew there was a reason I was avoiding this thread.


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## benjamin (Apr 20, 2011)

jdemaris said:
			
		

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Hello? the consequential change has been a huge drop in $$$/watt. Standard practice these days is to put the panels flat on the roof whether it's facing south, east, west, or apparently even north from some of the installations I've seen? In the past the panels were just so expensive that it was ridiculous to not optimize the output. These days it's usually cheaper (and more reliable) to add more panels than put the array on a tracker. 

I'll leave the shading issue to somebody who knows for sure what they're talking about, I thought there was an advantage to the newer technologies, but can't tell you exactly how they work.


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## jdemaris (Apr 20, 2011)

benjamin said:
			
		

> Hello? the consequential change has been a huge drop in $$$/watt. Standard practice these days is to put the panels flat on the roof whether it's facing south, east, west, or apparently even north from some of the installations I've seen?



I doubt that's a standard practice for anybody using state-incentive money - which is usually the case with grid-tie intalls.  Here in New York - a proposal and plan has to be submitted, showing the best use of the sun.   They would not allow payment to someone who wanted stick panels up facing the wrong direction, or a a very bad angle, or even if small percentage of the panels got shaded part of the day.

Fixed mounts here in the northeast have always been the standard.  There is little to be gain here with mounts that track.  If  the latitude is 15-25 degrees, the panels get mounted at the same angle.  If 30-35 degrees, you add 10 degrees.  If 35-40, you add 15 degrees. If the latitude is 40 degrees of  higher, you add 20 degrees.

Now, if someone is sticking in non-grid-tie with no state incentive money - they can do whatever they want.  Much of the equipment can cost 1/2 what the grid-tie certified sutff does.  The downside is - you waste any extra power you make, No way to "save it for later."

The prices on panels have come down, but not by a huge amount for grid-tied systems that require certain certified panels.  My Kyocera panels cost me $3.75 per watt 5 years ago.  Now they are $3 per watt which isn't a huge difference.  Some of the electronics involved have steadily gone up, not down.  Same with standby battery banks. They've doubled in price in the past five years.  Another factor is -  if you live in a state that forces you to use a state-cerftified installer. If so, they often add their own markup to the equipment and don't let you shop around for the best prices.

With off-grid  non-certified panels?  I can sometimes get them for $1.50 per watt.  Five years ago I could buy for $2.75 per watt.
I've got an off-grid setup in the NY Aridoncack woods.  They are facing all over the place.  There is no one spot that gets sun all day, so some point towards the morning sun, some to the noon sun, and some to the afternoon sun. If it was grid-tie, they would no have allowed it.


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## DaveH9 (Apr 20, 2011)

"These day"  the lower cost of the equipment combined with incentives makes the tilt much less of an issue then 10 or 20 years ago. Still can get a good return, though better if the tilt is optimum. The blocking diodes will stop back flow and prevent cell overheating but will not let voltage through if all cell strings in a module have a cell shaded. That at least is my understanding. The same thing happens at the module string level, the whole string is effected.


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## benjamin (Apr 20, 2011)

Apparently there is still some debate about mounting flat to the roof vs tilted up. 

Dave, Home Power mag and I believe that the best practice it to lay them flat on the roof, for the structural problems and economic considerations Dave mentioned, and the public acceptance sought by Home Power.


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## DaveH9 (Apr 20, 2011)

Here is a link to solmetric isolation tool. Just plug in your zip, tilt and azimuth and it tells you what to expect from your conditions.  

http://www.solmetric.com/annualinsolation-us.html


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## jdemaris (Apr 20, 2011)

DaveH9 said:
			
		

> ". The blocking diodes will stop back flow and prevent cell overheating but will not let voltage through if all cell strings in a module have a cell shaded. That at least is my understanding. The same thing happens at the module string level, the whole string is effected.



Every panel I own has soldered-in blocking diodes, and all my panel-strings have bypass diodes.  I can't say everybody uses them ,but they certainly aren't rare.


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## jdemaris (Apr 20, 2011)

benjamin said:
			
		

> Apparently there is still some debate about mounting flat to the roof vs tilted up.



I don't know why there is any general debate.  It all depends on the specific intallation and many local factors have to be considered.  
Latitude, highest anticipated wind, snow, install cost, type of roof material, etc.   

Here's some info from my latest Kyocera panel install manual for anybody that's interested.


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## pring7 (Apr 20, 2011)

This has been very insightful.  I am leaning against doing this problem for now because I donâ€™t want my roof torn up or leaking.  The guys I used for the evacuated tube system did a good job, but I can imagine that a larger PV system would involve more trips to the roof and more shingle stones coming off.  I think that maybe one day when the roof needs reroofing I will look into the solar shingles.  


I think that the idea of designing a barn/boat house with a good angle (30 degrees) would be the way to go.  Would the consensus be that the panels are best suited for a metal roof?  I had a metal roof on my house in Georgia and I think that is a good fit for my barn project.


Jdemaris: It looks like you have about 30 panels, and thatâ€™s a 6 kwh system?  I would like to get an idea of what size my roof would need to be to handle a 2 kwh system vs a 10 kwh system.  I know that some panels do better than others.


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## benjamin (Apr 20, 2011)

"the solar modules should be tilted for optimum winter performance" seems to indicate that they are assuming an off grid installation, whereas a grid tie would usually be more concerned with maximum annual production, and not as concerned about a high tilt angle. 

I don't know as much about this stuff, but maximum power point trackers (in the inverter, not a physical array "tracker") are the gizmos I thought offered a partial solution to shading.

Edit: yes, I'll say that a metal roof is the best solution short of using the panels themselves as the roofing material, which is not commonly done yet.


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## mbcijim (Apr 21, 2011)

We seem to have attracted a technical expert or two!  

Question:
On my 200KW project the inverters were 11-12% of the project cost, i.e., very, very low six figures.  When I look at them they aren't much bigger than a standard 200 Amp panel.  Why the hell did they cost so much??????

My installer swears they can be repaired and I'll never have to replace them.  True?


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## DaveH9 (Apr 21, 2011)

firemedic said:
			
		

> This has been very insightful.  I am leaning against doing this problem for now because I donâ€™t want my roof torn up or leaking.  The guys I used for the evacuated tube system did a good job, but I can imagine that a larger PV system would involve more trips to the roof and more shingle stones coming off.  I think that maybe one day when the roof needs reroofing I will look into the solar shingles.
> 
> 
> I think that the idea of designing a barn/boat house with a good angle (30 degrees) would be the way to go.  Would the consensus be that the panels are best suited for a metal roof?  I had a metal roof on my house in Georgia and I think that is a good fit for my barn project.
> ...



Unless your roof is more than 10-15 years old putting pv on should not be a big factor, the solar will be there for 25-30 yrs, so roofs with more than 1/2 the life gone should be evaluated. Installation crews should not be damaging any roof. If the shingles are hot we put down a white cloth to keep them cool and protected from walking. 

I am not a fan of solar shingles, the amorphous ones are not efficient and the crystallized silicon ones are too expensive. Plus the wiring is a nightmare. Standing seam metal roofs are great for pv panels as they can be clamped to the seams without rails.


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## DaveH9 (Apr 21, 2011)

mbcijim said:
			
		

> We seem to have attracted a technical expert or two!
> 
> Question:
> On my 200KW project the inverters were 11-12% of the project cost, i.e., very, very low six figures.  When I look at them they aren't much bigger than a standard 200 Amp panel.  Why the hell did they cost so much??????
> ...



True they can be repaired, though "never" need replacing is a stretch. Most come with a 10 yr warranty, PA systems should be close to or past break even by then. Their cost is dropping pretty steadily, as electronics tend to do, so replacement costs are expected to be reasonable. The inverters have a lot of high tech features, balancing the strings, checking for grid voltage, etc. I think they are a good deal overall. Down from over a dollar a watt, to near .50, amazing really.


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## mbcijim (Apr 21, 2011)

DaveH9 said:
			
		

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I do have a 10 year warranty and my payback is 4 years 3 months, but I am 25% behind production in 7 months, so my payback may have to get dragged out a bit but still very good (65% direct subsidy and a very good REC contract).  

If you look at these inverters though I might have 2 pallets worth, for six figures???? What the hell is inside them, solid gold?  I don't get it.  Is it like Microsoft Office I am paying for the technology?


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## peakbagger (Apr 21, 2011)

I wouldnt assume that inverters can be economically repaired so they last "forever". The manufacturers come out with new models every few years and after awhile I expect that parts and know how to fix them goes away. The "brains" of the units are cutom burned microprocessors so the chances that an indepdent repair person can diagnose and repair are low.   Most long term solar folks say plan on replacement ever ten years and hope they last longer. I have a whole house surge protector on my main panel plus lightning arrestors on both sides of my inverters to try to protect them and am actively looking for a better lightning arrestor with lower clamping voltage  than I currently have.

I had one warranty covered fault on my inverter within a year of install and my friend with the same brand has had warrantee replacements due to intermittent faults related that were fixed under warranty in 4 years.


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## pring7 (Apr 21, 2011)

Would this be an equivalent American company, or are these a different type?  http://www.greenstoneslate.com/solar.htm

I like the look of the Brit companyâ€™s solar slate shingles.  My impression is that they are not as effective at the standard panel, or am I mistaken?  

Itâ€™s an exciting technology and if my roof were in need of replacing I would like to upgrade it.  

I think from all of your feedback I am leaning towards designing the barn with solar panels in mind and putting the panels on a metal roof.  

I doubt my wife would like the metal roof on the house, so maybe one day when the house needs reroofing I will be able to do a solar shingle/slate design.


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## jdemaris (Apr 21, 2011)

firemedic said:
			
		

> Jdemaris: It looks like you have about 30 panels, and thatâ€™s a 6 kwh system?  I would like to get an idea of what size my roof would need to be to handle a 2 kwh system vs a 10 kwh system.  I know that some panels do better than others.



Here are some solar panel sizes.  There isn't much difference between brands when it comes to watts per square foot -  11-14 watts per square foot.  The bigger and higher voltage panels tend to be a little more compact.  For 2KW of panels, you'd need around 145 square feet.  

200 watt Kyocera -  39â€ X 56â€   

175 watt Kyocera â€“ 39â€ X 51â€

120 watt Kyocera â€“ 26â€ X 56â€

120 watt Evergreen â€“ 26â€ X 62â€

On any roof, the panels have to be spaced away from the roof material to allow air-flow, for cooling.    For  myself, I'd never consider going over anything but a steel roof.


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## benjamin (Apr 21, 2011)

DaveH9 said:
			
		

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Oops, I didn't mean to recommend solar shingles or the "stick on" collectors on steel. Overlapping the tempered glass to form the watertight roof is what I was suggesting, like this:
http://www.solexenergy.co.uk/

Or using the steel itself for the absorber plate in an unglazed warm water seasonal storage collector. 

I thought I had seen a website of a firm that did PV roofs the same way but I couldn't find it. 

And since I'm so far out in left field already, my completely inexpert take on inverters is to compare them to inverter welders, some of which have proven to be reliable and repairable, and some are disposable. I have a well used Lincoln that I fully expect to last longer than I do, but I sure wouldn't waste $500 on an inverter welder from the fine folks at Harbor Freight.


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## jdemaris (Apr 21, 2011)

benjamin said:
			
		

> I'm so far out in left field already, my completely inexpert take on inverters is to compare them to inverter welders, some of which have proven to be reliable and repairable, and some are disposable. I have a well used Lincoln that I fully expect to last longer than I do, but I sure wouldn't waste $500 on an inverter welder from the fine folks at Harbor Freight.



The "inverter welders" are totally different devices than inverters used to turn DC current into 120 or 220 VAC.  

An "inverter welder" uses AC house current, runs it though rectifiers to "convert" AC to DC, and then uses a device to step down and control that DC current for welding.  I think the title of "inverter welder" has caused some confustion.

The device much more commonly known as an "inverter"  makes DC current into AC and does so with either a true 60 cycle sine-wave - or a simulated sine-wave.   This is what's used in solar.   An off-grid setup can use a much cheaper, and usually more efficient simutated wave inverter.   If grid-tie -the power made must almost perfectly  replicate grid-power with a true Hertz Cycle.  Subsequently, inverters used with grid-tie tend to be very expensive, and complicated.

You can buy a simulated-wave 2000 watt inverter (3500 watt surge) for $150.   A true sine-wave 2000 watt inverter certified for grid-tie can cost $1500-$2500.   A non-grid-certified true sine-wave inverter rated at 2000 watts can be found for $400-$600.

Ironically, the cheap simulated-wave inverters tend to be very reliable and more efficienct then the true sine-wave units.


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## benjamin (Apr 21, 2011)

firemedic said:
			
		

> Would this be an equivalent American company, or are these a different type?  http://www.greenstoneslate.com/solar.htm
> 
> I like the look of the Brit companyâ€™s solar slate shingles.  My impression is that they are not as effective at the standard panel, or am I mistaken?
> 
> ...



I'll assume this is my question.  That looks similar to the link I posted.  Hot water panels commonly come in 4'x10' sizes that could easily be redesigned and built to interlock and form the roof surface.  I couldn't find the site I thought I remembered (German) that had installations with standard size or larger PV that interlocked (or overlapped) to form the whole roof surface.  

I'm assuming the "slate" panels are similar efficiency, but at a significant price premium over standard panels, even including the savings in mounting and roofing.  Plus the hassle of additional wiring as previously mentioned.


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## benjamin (Apr 21, 2011)

jdemaris said:
			
		

> benjamin said:
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Some inverter welders produce DC,  but as I understand it, some take AC, convert it to DC, and "invert" it back to AC, but I don't build the things, I just read the propaganda.


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## jdemaris (Apr 21, 2011)

benjamin said:
			
		

> [Some inverter welders produce DC,  but as I understand it, some take AC, convert it to DC, and "invert" it back to AC, but I don't build the things, I just read the propaganda.



I wouldn't want one, but for me - the weight and size of the welder is a non-issue and I suspect the inverter-welder's only claim to fame is being lighter.

I'll take a good old fashioned Century, Miller or Lincoln AC/DC welder any day - with nice big wire-wound transformers and big rectifiers.  AC 60 cycle current in and my choice of low voltage AC or DC out.  I've got two that I bought used in the 1970s and never had a problem with either. I also have one from the 1940s that still works fine but it's huge.

Now when it comes to portable fuel-driven electric generators, the inverter generators have a huge advantage over the cheaper AC uniits.   Since they start out making DC, and run it through a sine-wave inverter - they can make 60 cycle  120 or 220 VAC current at any RPM.  AC units must run at one pre-set high speed to make proper cycles and often make imperfect AC power that will not work with all applicances.

Back to solar, many grid-tie inverters are extremly complicated and go way beyond what a simple non-grid inverter does.   That isn't necessarily a good thing.    A lot of extra complication without a lot of gain to show for it.     You'll also  notice that they tend to get smaller over time.  That's because of the higher DC voltages being used at the imput.  The higher the DC power is going into the inverter - the less windings it needs to step up the voltage.     If you feed an inverter with 12 volts and want 220 VAC coming out of it, a lot of wire-windings are needed.   Feed 600 volts DC into an inverter and have 220 VAC coming out - and the inverter can be much smaller.  Not as  generally useful though.


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## mbcijim (Apr 25, 2011)

jdemaris said:
			
		

> The device much more commonly known as an "inverter"  makes DC current into AC and does so with either a true 60 cycle sine-wave - or a simulated sine-wave.   This is what's used in solar.   An off-grid setup can use a much cheaper, and usually more efficient simutated wave inverter.   If grid-tie -the power made must almost perfectly  replicate grid-power with a true Hertz Cycle.  Subsequently, inverters used with grid-tie tend to be very expensive, and complicated.
> 
> You can buy a simulated-wave 2000 watt inverter (3500 watt surge) for $150.   A true sine-wave 2000 watt inverter certified for grid-tie can cost $1500-$2500.   A non-grid-certified true sine-wave inverter rated at 2000 watts can be found for $400-$600.



I love this place.  Great, great, great info thank you.

Can you use a non-grid certified inverter on a system that backfeeds onto the grid?


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## peakbagger (Apr 25, 2011)

mbcijim said:
			
		

> jdemaris said:
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The fast answer is NO. Your utility ahs the right to dsiconnect you, and your insurance will be null and void if the unti harms anyone while it is in operation. 


Now for my Soapbox comment 

I dont particularly agree with the description of the difference and uses between and on grid inverter and an off grid inverter. Most off grid system use true sine wave inverters. The term" simulated sine wave' isnt generally used in PV parlance. There are Modified Sine Wave  (MSW)inverters that produce a square wave, some with rounded corners but nowhere close to a true sine wave. When used on many electronics and electric motors, a modified sine wave inverter may work, but can cause damage over the long run to the equipment. Home Power magazine, the gurus of off gridding used to maintain a list of equipment that would not work off grid on MSW inverters. Additionally the warranty on equipment may not apply to equipment supplied from modified sine wave inverters. Sure MSW inverters are cheap as they dont need much for internal electronics. True sine wave inverters are more expensive as they require more sophisticated electronics and are usually built for long term use. They create a sine wave that is essentually identical to utility power. 

A grid tie inverter is always going to be a true sine wave inverter, but since its synched to the grid it can in theory be less complicated than an off grid unit as it can use the utilities wave form to create its output. The actual grid tie electronics can be programmed into a IC chip that is probably being used for other purposes inside the unit. There is additional cost in that a grid tie inverter has to have an internal GFI interlocked with the unit to shut it down if there a DC current leakage to ground (potentally highly dangerous). An off grid unit doesnt legally need one yet, but if someone gets zapped with a high voltage DC leakage from the panels, I guess they saved a lot of money that can be applied to the medical bills or funeral expenses. 

So why is a grid tie inverter more expensive that an equivalent output MSW inverter?. I expect its mostly due to the quality of construction. There are no regulated quality control standards for off grid inverters. Any third world country can hack off an existing design, build it with substandard components and design it for limited life. If the unit breaks down, the consumer might return it, and the store or distributor will probably eat the cost as the manufacturer is probably long gone. If equipment gets damaged, the consumer is SOL. If someone gets hurt or their house burns down good luck fiding someone to pay the bills. 

A legal grid tie inverter has to be built and tested to UL or some other testing authority. There is a much more  likely chance that if it is made poorly, the testing organization will catch the problem and not give it a rating. If there is an issue it it more likely the company will be in business to fix it.


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## benjamin (Apr 25, 2011)

mbcijim said:
			
		

> jdemaris said:
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I think they call that "guerrilla solar" because there's little chance that you'll get caught with an un-permitted, small, grid tied PV system because there's just so little change in the power usage. I think that as the PV industry has become more mainstream (lucrative) there has been less talk of the wild and wooly days.

That's good to know the difference between grid tied and off grid inverters, I would have guessed the opposite, that the more expensive, "certified" grid tied would be more robust. The other use of inverters is wind and hydro, which produce "wild" AC which is fed to the inverter to be converted to 60hz power.

EDIT: oops, what he said


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## jdemaris (Apr 25, 2011)

peakbagger said:
			
		

> I dont particularly agree with the description of the difference and uses between and on grid inverter and an off grid inverter. Most off grid system use true sine wave inverters.
> The term" simulated sine wave' isnt generally used in PV parlance.



I see nothing wrong with the word "simulated" in this context.   Over the past 50 years that I've been using inverters - I have seen many "work-arounds" to make AC power from DC with an effort to mimic the 60 cycle sine-wave.   My use of "simulate" simply connotes an inverter that does not make a true 60 cycle sine-wave.  It DOES make something close enough that the vast majority of AC applicances will work fine on it.   If you feel better with terms like "square wave" or "modified sine wave" - that's fine but it's just another way of saying the same thing. 




			
				peakbagger said:
			
		

> So why is a grid tie inverter more expensive that an equivalent output MSW inverter?. I expect its mostly due to the quality of construction. There are no regulated quality control standards for off grid inverters.



There are few regulated controls for any of them -when it comes to qualilty, durability, etc.  The oversight involves the quality of the AC power coming out, and little else.  What HAS added some "de facto" regulation is the insistance of some State incentive programs to have a 5 year warranty on ALL equipment.  When I bought my Outback grid-tie inverters they only came with a standard 2 year warranty - but the Outback company had to extend their warrantees or lose grid-tie sales. Note though that they did nothing to make the inverters more rugged.  They just jacked up the price to create their own sort of insurance policy for a longer warranty.

As to price?  Anything that is a specialty product gets priced higher.  Solar grid-tie is a specialty, AND the mind-set is that most who install it are getting price-support somewhere (e.g. State and Federal incentives or grants).  And of course, grid-tie units are NOT just inverters. They are much more complicated then that.

I can buy two identical solar panels - same size, brand, and off the same assembly line.  Yet if I opt to buy one without the UL certification, I can often buy for near half-price.

My experience with off-grid solar electric has obviously been different then your's  The cheaper inverters that do not produce a true sine-wave have been the mainstream of the industry for many years and are still common.  Most installations I know of keep a mix of both.  The more expensive sine-wave inverters are often just used for the few pieces of equipment that need it.  What has changed recently is the availabilty of combo inverter/chargers in the cheaper format.  

For anybody that's asking inverter questions though -keep in mind that "inverters" sold specifically for solar use - grid-tie or off-grid of often not just inverters. They often have many more controls and features added.  

One example is my Trace/Xantrex  DR2412 2000 watt off-grid unit.   It has a built-in automatic 120 amp battery charger, it has a built in demand swith so it can turn itself on when AC power is needed. It also has a battery temperature probe that determines proper battery charge by temp, type of battery and size of total battery bank.  It can also remote-start an electric generator to charge the battery bank if needed when the sun is not available.  This "inverter" weighs 50 lbs whereas a 2000 watt inverter from Harbor Freight or AIMs for $150 will only weigh around 12 lbs. 

Off-grid will have a battery bank and thus must have a battery charger, probably a fuel-driven generator, charge contollers, etc. It will also have low voltage solar-panel array.

A mainstream grid-tie has different needs. Usually no batteries so no charge contollers needed.  Solar panels are usually set up for very high voltage so the inverter does not need a lot of step-up wiring.  The AC power though has to be certified to meet power company regs.  It also has to sense a "grid-down" situation and shut itself off.  These units can be extemely complicated and I many have get design changes fairly often as regs change.  This adds to the prices.


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