About to install LG300A1C-B3 300W AC microinverters, got some Q's

[AaronG]

IANATL either, but from what I have read the cost of reinforcing the roof structure to take the weight of the panels and racking can definitely be included in the cost for tax credit purposes. The cost of putting on a new roof so that you will not have to take the panels off to reroof before the 20 year lifetime is up, even though your current roof has 10 years of life left, probably not subject to tax credit. Replacing your roof because it needs it right now anyway, definitely not creditable.

My roof is now 22 years old. I brought this up and they state that my roof should be in fine state and since the tiles are concrete that it should continue to last a lot longer. I worried about this, but I guess it is one of those things that since you've never had a leak or issue, its tough to replace the whole thing when it works well.

But yes item for discussion relating to the tax credit. Thanks.

[AaronG]

Hey thejq,

you have the DC 300w LG panel and per your graphic and your SE link, you seem to be getting on average peak about 265-270W per panel. Your system is real new and I know you dont get 100% efficiency, but did you expect to see a bit better results? a 4.8KW system and your site shows about 3.6-4.0 produced a lot. Is this average? Is the 10% loss on the panel bumped up to 15-17% by the time it goes through the inverter , seem average? Is it feasible that with the LG panels with the LG designed microinverters, that this inherent/expected inefficiency be reduced?

Your 28-30kWh you produced on avg or so, what you expected out of the 16 panels?

This is just my ignorance talking really, I have no idea.

[inetdog]

Hey thejq,

you have the DC 300w LG panel and per your graphic and your SE link, you seem to be getting on average peak about 265-270W per panel. Your system is real new and I know you dont get 100% efficiency, but did you expect to see a bit better results? a 4.8KW system and your site shows about 3.6-4.0 produced a lot. Is this average? Is the 10% loss on the panel bumped up to 15-17% by the time it goes through the inverter , seem average? Is it feasible that with the LG panels with the LG designed microinverters, that this inherent/expected inefficiency be reduced?

Your 28-30kWh you produced on avg or so, what you expected out of the 16 panels?

This is just my ignorance talking really, I have no idea.

Ignorance asking questions is a lot better than ignorance trying to ask them, so you are on the right track.

Because of the difference in real life panel temperature from STC panel temperature, as well as other issues of orientation, atmospheric conditions, etc, panels will rarely produce their rated output. On a cold day, at an elevation of 5000', and with just the right scattering of clouds outside the direct path toward the sun you can get 10% or more above the rated output.

The sizing tools and recommendations for microinverters take this into account and recommend that your panel produce more than the inverter rating, up to some limit.
Then even when the conditions are ideal and the panel overproduces you will only lose some power at solar noon but make up for it the rest of the day compared to a panel which never exceeds the inverter input limit. (Referred to as "clipping".)

And yes, 10% less than rated is not unreasonable for a hot day. Worse if there is not enough air space between panels and roof for proper cooling (4" minimum, 6" better). Then the efficiency of the micro will be somewhere between 90% and 95%, depending on the brand and who you believe.

[thejq]

Yeah, exactly what he (above) said. The rated wattage is measured at ideal conditions, eg direct and full sunlight, low temperature etc. In the 1/2 month that I have owned my system, I have seen it once that the instantaneous power was close to the rated power. With that said the LG300 panels have been phenomenal. According to pvwatt, at my location, my 4.8KW system with premium panel, 0% loss, 96% efficiency, should produce 651 KWh in the month of September. So far from 09/06 - 09/18 (13 days), it produced 320 KWh. If that average holds, I will be looking at 738 KWh for September or about 13% higher than estimate. So if you're mounting it facing SW like mine and use LG300 panels, you should be plenty happy with the results. Don't get too hang up on the instantaneous power numbers.

Since no one has the LG300A1C panels installed, you will be the first to tell the story on how well they work, if you decide to go that route.

[J.P.M.]

Yeah, exactly what he (above) said. The rated wattage is measured at ideal conditions, eg direct and full sunlight, low temperature etc. In the 1/2 month that I have owned my system, I have seen it once that the instantaneous power was close to the rated power. With that said the LG300 panels have been phenomenal. According to pvwatt, at my location, my 4.8KW system with premium panel, 0% loss, 96% efficiency, should produce 651 KWh in the month of September. So far from 09/06 - 09/18 (13 days), it produced 320 KWh. If that average holds, I will be looking at 738 KWh for September or about 13% higher than estimate. So if you're mounting it facing SW like mine and use LG300 panels, you should be plenty happy with the results. Don't get too hang up on the instantaneous power numbers.

Since no one has the LG300A1C panels installed, you will be the first to tell the story on how well they work, if you decide to go that route.

I"d suggest the above is perhaps another of many examples of vendor estimates of performance being way low to observed performance.

[PVAndy]

I"d suggest the above is perhaps another of many examples of vendor estimates of performance being way low to observed performance.

All of what I've been reading in this thread is not the way panels are really rated. Full sun is not a definition of irradiance.


Solar Panel manufacturers use what is called Standard Test Conditions (STC). This means they put the solar panels in a flash tester in their factory that has been calibrated to deliver the equivalent of 1000 watts per square meter of sunlight intensity, hold a cell temperature of 25'C (77'F), and assume an airmass of 1.5. This flash test gives them their STC ratings.

Note that in real life the cell temperature is considerably above ambient temp. Typically 30 degrees C, Also remember that the airmass comes into play.

You will virtually never be operating anywhere close to STC.

You may find the following interesting which I copied and pasted here.

PTC refers to PVUSA Test Conditions, which were developed to test and compare PV systems as part of the PVUSA (Photovoltaics for Utility Scale Applications) project. PTC are 1,000 Watts per square meter solar irradiance, 20 degrees C air temperature, and wind speed of 1 meter per second at 10 meters above ground level. PV manufacturers use Standard Test Conditions, or STC, to rate their PV products. STC are 1,000 Watts per square meter solar irradiance, 25 degrees C cell temperature, air mass equal to 1.5, and ASTM G173-03 standard spectrum. The PTC rating, which is lower than the STC rating, is generally recognized as a more realistic measure of PV output because the test conditions better reflect "real-world" solar and climatic conditions, compared to the STC rating. All ratings in the list are DC (direct current) watts.

Neither PTC nor STC account for all "real-world" losses. Actual solar systems will produce lower outputs due to soiling, shading, module mismatch, wire losses, inverter and transformer losses, shortfalls in actual nameplate ratings, panel degradation over time, and high-temperature losses for arrays mounted close to or integrated within a roofline. These loss factors can vary by season, geographic location, mounting technique, azimuth, and array tilt. Examples of estimated losses from varying factors can be found at: http://rredc.nrel.gov/solar/codes_al...TS/system.html.

[control4userguy]

My roof is now 22 years old. I brought this up and they state that my roof should be in fine state and since the tiles are concrete that it should continue to last a lot longer. I worried about this, but I guess it is one of those things that since you've never had a leak or issue, its tough to replace the whole thing when it works well.

But yes item for discussion relating to the tax credit. Thanks.

That could be an incorrect assessment of your roof. The tiles themselves are not what prevents water from entering the structure. The paper layer below it is. Ask any roofer, that layer lasts maybe 20 years.

[J.P.M.]

All of what I've been reading in this thread is not the way panels are really rated. Full sun is not a definition of irradiance.


Solar Panel manufacturers use what is called Standard Test Conditions (STC). This means they put the solar panels in a flash tester in their factory that has been calibrated to deliver the equivalent of 1000 watts per square meter of sunlight intensity, hold a cell temperature of 25'C (77'F), and assume an airmass of 1.5. This flash test gives them their STC ratings.

Note that in real life the cell temperature is considerably above ambient temp. Typically 30 degrees C, Also remember that the airmass comes into play.

You will virtually never be operating anywhere close to STC.

You may find the following interesting which I copied and pasted here.

PTC refers to PVUSA Test Conditions, which were developed to test and compare PV systems as part of the PVUSA (Photovoltaics for Utility Scale Applications) project. PTC are 1,000 Watts per square meter solar irradiance, 20 degrees C air temperature, and wind speed of 1 meter per second at 10 meters above ground level. PV manufacturers use Standard Test Conditions, or STC, to rate their PV products. STC are 1,000 Watts per square meter solar irradiance, 25 degrees C cell temperature, air mass equal to 1.5, and ASTM G173-03 standard spectrum. The PTC rating, which is lower than the STC rating, is generally recognized as a more realistic measure of PV output because the test conditions better reflect "real-world" solar and climatic conditions, compared to the STC rating. All ratings in the list are DC (direct current) watts.

Neither PTC nor STC account for all "real-world" losses. Actual solar systems will produce lower outputs due to soiling, shading, module mismatch, wire losses, inverter and transformer losses, shortfalls in actual nameplate ratings, panel degradation over time, and high-temperature losses for arrays mounted close to or integrated within a roofline. These loss factors can vary by season, geographic location, mounting technique, azimuth, and array tilt. Examples of estimated losses from varying factors can be found at: http://rredc.nrel.gov/solar/codes_al...TS/system.html.

All of what you write and more is correct.

However, all of what you write and more has little to do with vendor's often, usual and common method(s) of estimating annual production, which was my point.

The most common method used by vendors, if my experience and that reported by others on this forum, and if my conversations with vendors are close to reality, has been to use PVWatts with the default system derate factor of .77. This method, besides being simplistic, and ignoring the particulars of a situation, some of which you write about, almost always results in oversizing a system by underestimating performance due to that default number being unrealistically low for probably most situations, and in any case, not representative of the actual situation except by luck.

What vendors most often do has little if anything to do with either STC, PTC or other methods of testing or rating performance of solar equipment or other particulars as you describe.

Standard test methods for solar equipment are somewhat analogous to EPA fleet mileage for vehicles. Your performance will vary depending on conditions.

The way most vendors use PVWatts is somewhat analogous to bastardizing an EPA mileage rating for a vehicle by estimating mileage while towing a trailer for the purpose of selling a bigger vehicle. In the solar case however, most customers can't see and are not aware of the trailer or the deception.

Things you mention and others are more of what a thorough analysis and estimate of system performance would include but is usually and conveniently ignored - that deception allowed largely because of the solar ignorance of most customers.

Perhaps the new PVWatts will reduce some of what, IMO, is a deceptive and dishonest but common misuse of information.

My apologies to the honest peddlers who do not do misuse information in the way I describe.

[russ]

All of what I've been reading in this thread is not the way panels are really rated. Full sun is not a definition of irradiance.

If you read what is on the site it says that - many times over.

Some things get shortened such as the term "sun hours" which allow the newbie to understand more easily.

[sensij]

I'm almost certain I was right regarding roof.

http://www.gpo.gov/fdsys/pkg/USCODE-2011-title26/pdf/USCODE-2011-title26-subtitleA-chap1-subchapA-partIV-subpartA-sec25D.pdf

Page 94, under solar panels, the text explicitly excluded roof, because it's part of the structural component.

I realize this isn't totally related to the thread, but I didn't want to let this misinformation go unanswered. The relevant text from your link is this:

(2) Solar panels
No expenditure relating to a solar panel or other property installed as a roof (or portion thereof) shall fail to be treated as property described in paragraph (1) or (2) of subsection (d) solely because it constitutes a structural component of the structure on which it is installed.

In other words, structural costs are eligible to be included in the solar property costs. Your CPA / tax lawyer can help you figure out how to apply that in the best way for your situation, but roof structures are *not* explicitly excluded.

[thejq]

I realize this isn't totally related to the thread, but I didn't want to let this misinformation go unanswered. The relevant text from your link is this:

In other words, structural costs are eligible to be included in the solar property costs. Your CPA / tax lawyer can help you figure out how to apply that in the best way for your situation, but roof structures are *not* explicitly excluded.

Ok, I just reread it again. Maybe you're right -- now I'm not so sure any more. Thanks for pointing out.

[Hillsider]

Less than $500 for equal LG panels

I got 4 quotes. Two were not on the same kind of level. Then these two without even bidding them against each other came down to less than $500 for equal LG panels. Then the way the one company (Sun Craft Solar) got my business was the promise of these LG AC panel, which the other guy said he couldnt get until at least 2015. Now part of me second guesses that if I am on the SW side. On the NE side either micro-inverters or the power optimizers is needed beacuse part of the day my chimney will case a shadow over a few panels.

I really think I am going to go with the SW option and move my thermal. 0.00% change of any shade from anything, so not as critical there.

I was following your thread, until it got off on roof issues. You said "2 guys came down to less than $500 for equal LG panels". Did you mean less than a $500 quote for the LG300A1C panels for your project? I still cannot find any pricing for those panels, without "biting" on Gogreensolar's preorder trap ( no prices, just an invitation to sign up for 4 or more of the panels ). Have you received any mote updates from your bidding contractors or their site engineers? Multi-distributor availability of the panels in early 2015 is no problem for me, as I am still negotiating with trenching and/or electrical sub-contractors, for the conduit run from my field-array site to the back of my house.

[inetdog]

In other words, structural costs are eligible to be included in the solar property costs. Your CPA / tax lawyer can help you figure out how to apply that in the best way for your situation, but roof structures are *not* explicitly excluded.

Those bureaucratic double and triple negatives keep tripping people up.

No expenditure relating to a solar panel or other property installed as a roof (or portion thereof) shall fail to be treated

[AaronG]

Been a while, got a question for anyone who may have an idea here. I so truly appreciate your input.

I am reviewing the plans submitted for 21 LG300N1C-B3 panels at 6.3kWh system.
The company is specifying the use of:
Inverter = Solar Edge SE6000-US
Optimizers = Solar Edge P300

the P300 power optimizer seems like the right way to go. It shows it on their site and seems to be correct. Any input beyond that?

The inverter I wonder though, its 6000w right? Yet my system is 6300w? Any concerns? I see the next step up unit is the 7.6kWh system. Does it mean that *IF* my system was absolutely perfect and each panel did indeed generate 300W and I was at greater than 6000W that it would cut off the extra 300W? I assume that will (can never) never happen to generate 300W per panel at 100% efficiency, but I do wonder about this whole sizing thing.

[inetdog]

Been a while, got a question for anyone who may have an idea here. I so truly appreciate your input.

I am reviewing the plans submitted for 21 LG300N1C-B3 panels at 6.3kWh system.
The company is specifying the use of:
Inverter = Solar Edge SE6000-US
Optimizers = Solar Edge P300

So I wonder. Is this SE6000-US appropriately sized for 6300W system? Do I need a larger one since I am not 6000W? How about those Power Optimizers, are there many models. Is this the one to go with?

In general, because the panel array will rarely if ever produce its full STC rated output, some overpanelling of the inverter (like 6300 into 6000) should not be a problem. The question is what the next size up of SE inverter is and what the cost difference is. I would definitely not recommend a system with two SE string inverters just to avoid clipping.