SunPower SPR-E20-327-C-AC Power Testing

[J.P.M.]

I don't think you understand what the OP is doing - no one is not chasing after max output and spinning wheels. He (and I) are trying to ensure the panels and micros are all performing correctly. You and Mike have indicated he should be satisfied with hitting roughly 80% of STC, even though he previously was hitting over 90%. Yes panels degraded slightly each year, but not much. I also track data (requires no effort on my part it is all logged automatically) to ensure each panel and micro is working correctly. I have proved with data over and over that the panels can hit near their capacity on a regular basis (and have indicated my panels are not optimal in terms of orientation and angle and can also happen in the middle of summer). Excluding Nov - Jan, my panels hit anywhere from 90 to 102% of STC at least one interval in a day over 50% of the days in that period. I'm sorry your system is not performing as well as often.

After reading through this thread a few times, I believe the OP is trying to determine two things: 1.) Is his array operating normally ? 2.) If his array is not operating normally, is it because the replaced micros are either failing or operating incorrectly, or otherwise (re)wired incorrectly or some combination of errors and so causing any under/malperformance?

That about it ?

FWIW, read what I wrote. I believe you'll find I never wrote that the OP or anyone else anyone should be satisfied with 80% of STC. I believe I know what Mike had in mind to convey, and while not attempting to speak for him, I don't think Mike meant what you claim he meant.

I did provide some information about my S.P. 327 W paneled array's general output as f(STC output), but only as a comment for the OP's reference and perhaps use.

As for my array's actual output, it seems fit for purpose. Over the last 8 years it's performance has been slightly better than I had expected. It's daily average specific production, after inverter losses has been 4.70 kWh/(day*installed STC kW). Put another way, that's 1,734 kWh/yr per installed STC kW, or 9,072 kWh/yr. average per 365 days for the entire array after inverter losses, which losses seem to average about 3.1 % or so. The overall output is also after an average of 3.5 % output decrease accounting for late afternoon shading. I determined that my panels are (or were when new), on average, 3.5 % above their STC rating which seems to make sense with the S.P. spec sheet tolerance of +5/-3% of STC and the binning method S.P. was using at that time. There seems to have been a 1st year burn in penalty of ~ 2-3 % or so. The annual average performance regradation after the 1st year seems to be about 17 STC W/yr. or ~ 0.003/yr. which is under the 0.004 warrant the spec sheet shows. No panel has failed or even given unusual output since 10/13/2013, except a few data that was 5,136/16 = 321 W/panel or thereabouts once or twice rue to cloud abedo effects.

I do believe you do not understand why I believe chasing after data at upset or nonstandard conditions or worrying solely about max. output, particularly without any knowledge, use or consideration of, or any way to consistently measure with any precision the environmental input condtions at such times, and also particularly without mention or consideration (or at least mention) of any solar or array orientations is an exercise in futility and will not lead to any conclusions that may aid in possible problem solution(s).

As for what you track, you seem to track some data, a lot of which (the sunpower data) I also track and use - although it's a lot less useful now than when I fired up my system 8+ yrs. ago when there was a lot more very useful data available on the Sunpower site, a lot of which I've found alternate means to procure, and that you do not seem to know about, or at least why a lot of it is necessary to find possible answers to situations such as the one the OP has.

So, what you seem to track is, IMO only, incomplete and insufficient, and how you use it and what conclusions you seem to draw from that data, at least from what I've seen in this thread, seem mostly specious. Part of what you do not track/log is the environmental conditions that influence array input and output and are necessary data for a eaningful estimate of array performance.

I'm not damning you for what you don't know, but because you don't know what you don't know - at least IMO only - as exhibited in this thread, even if you think you're on the right track, you're not. You're spinning your wheels and taking the OP, along with other neophytes who don't know much but are quick to glom onto such inaccurate methods and thinking.

Seems to me what you're doing is sort of analogous to observing a vehicle doing 140 MPH and extrapolating that the vehicle is operating normally without knowing it's going down a long, steep, straight grade in neutral. with a tailwind.

You claim to have proved your panels have consistently exceeded their STC rating. Actually, you've proved nothing. You've measured something, not proved it. In any case, so what ? That means nothing. My array exceds STC rating quite often. That tells me nothing except that maybe the P.O.A. irradiance is >1 kW at that time, and that's quite unusual under normal conditions at any elevation less than maybe 7,000 ft. above mean sea level. BTW, do you have a reasonably precise way to determine P.O.A. irradiance ? How about cell temp. ? How about array/cell voltage or current ?

From reading your posts, you seem to not know why your methods will not get you the desired result of ensuring the OP's panels are performing correctly - primarily because your methods will not give you meaningful results, only data that won't correlate with comparison to that of a nominally performing array under the same quasi steady state conditions might operate at which is necessary to determine array performance.

Now you can certainly continue in your thinking as you wish - free country and all that, but it may not be a good idea to let your stuff get into print, have others read it and think it makes sense without someone pointing out the errors in your methods and logic. I'm offering an opinion as to why I believe you're misinforming the ignorant.

I'd prefer you and I leave it at that.

Deal ?

BTW, there's a double negative in the first sentence of your last post.

The last word is yours if you want it. I'm outa' this thread.

[Mike90250]

Panels generally, produce only 80% of their Lab ratings. ( that's real close to the above mentioned 78%)

I'll pretty much stand by that, panels tested at about 70F, and when baking on a rooftop, their voltage ( and therefor power) will drop. In winter, cold bright days, you may exceed STC ratings, because panels produce higher voltage in the cold.

I've no idea about your micro-inverters, or the quality of your metering. But when a panel mfg bins the panels after testing, they are not going to put tested 430W panels in a bin with 410W stickers, unless they have their back against a wall to ship something.

[ajonestx]

After reading through this thread a few times, I believe the OP is trying to determine two things: 1.) Is his array operating normally ? 2.) If his array is not operating normally, is it because the replaced micros are either failing or operating incorrectly, or otherwise (re)wired incorrectly or some combination of errors and so causing any under/malperformance?

That about it ?

FWIW, read what I wrote. I believe you'll find I never wrote that the OP or anyone else anyone should be satisfied with 80% of STC. I believe I know what Mike had in mind to convey, and while not attempting to speak for him, I don't think Mike meant what you claim he meant.

I did provide some information about my S.P. 327 W paneled array's general output as f(STC output), but only as a comment for the OP's reference and perhaps use.

As for my array's actual output, it seems fit for purpose. Over the last 8 years it's performance has been slightly better than I had expected. It's daily average specific production, after inverter losses has been 4.70 kWh/(day*installed STC kW). Put another way, that's 1,734 kWh/yr per installed STC kW, or 9,072 kWh/yr. average per 365 days for the entire array after inverter losses, which losses seem to average about 3.1 % or so. The overall output is also after an average of 3.5 % output decrease accounting for late afternoon shading. I determined that my panels are (or were when new), on average, 3.5 % above their STC rating which seems to make sense with the S.P. spec sheet tolerance of +5/-3% of STC and the binning method S.P. was using at that time. There seems to have been a 1st year burn in penalty of ~ 2-3 % or so. The annual average performance regradation after the 1st year seems to be about 17 STC W/yr. or ~ 0.003/yr. which is under the 0.004 warrant the spec sheet shows. No panel has failed or even given unusual output since 10/13/2013, except a few data that was 5,136/16 = 321 W/panel or thereabouts once or twice rue to cloud abedo effects.

I do believe you do not understand why I believe chasing after data at upset or nonstandard conditions or worrying solely about max. output, particularly without any knowledge, use or consideration of, or any way to consistently measure with any precision the environmental input condtions at such times, and also particularly without mention or consideration (or at least mention) of any solar or array orientations is an exercise in futility and will not lead to any conclusions that may aid in possible problem solution(s).

As for what you track, you seem to track some data, a lot of which (the sunpower data) I also track and use - although it's a lot less useful now than when I fired up my system 8+ yrs. ago when there was a lot more very useful data available on the Sunpower site, a lot of which I've found alternate means to procure, and that you do not seem to know about, or at least why a lot of it is necessary to find possible answers to situations such as the one the OP has.

So, what you seem to track is, IMO only, incomplete and insufficient, and how you use it and what conclusions you seem to draw from that data, at least from what I've seen in this thread, seem mostly specious. Part of what you do not track/log is the environmental conditions that influence array input and output and are necessary data for a eaningful estimate of array performance.

I'm not damning you for what you don't know, but because you don't know what you don't know - at least IMO only - as exhibited in this thread, even if you think you're on the right track, you're not. You're spinning your wheels and taking the OP, along with other neophytes who don't know much but are quick to glom onto such inaccurate methods and thinking.

Seems to me what you're doing is sort of analogous to observing a vehicle doing 140 MPH and extrapolating that the vehicle is operating normally without knowing it's going down a long, steep, straight grade in neutral. with a tailwind.

You claim to have proved your panels have consistently exceeded their STC rating. Actually, you've proved nothing. You've measured something, not proved it. In any case, so what ? That means nothing. My array exceds STC rating quite often. That tells me nothing except that maybe the P.O.A. irradiance is >1 kW at that time, and that's quite unusual under normal conditions at any elevation less than maybe 7,000 ft. above mean sea level. BTW, do you have a reasonably precise way to determine P.O.A. irradiance ? How about cell temp. ? How about array/cell voltage or current ?

From reading your posts, you seem to not know why your methods will not get you the desired result of ensuring the OP's panels are performing correctly - primarily because your methods will not give you meaningful results, only data that won't correlate with comparison to that of a nominally performing array under the same quasi steady state conditions might operate at which is necessary to determine array performance.

Now you can certainly continue in your thinking as you wish - free country and all that, but it may not be a good idea to let your stuff get into print, have others read it and think it makes sense without someone pointing out the errors in your methods and logic. I'm offering an opinion as to why I believe you're misinforming the ignorant.

I'd prefer you and I leave it at that.

Deal ?

BTW, there's a double negative in the first sentence of your last post.

The last word is yours if you want it. I'm outa' this thread.

Correct. I (OP) am trying to determine two things: 1.) Is this array operating normally ? 2.) If this array is not operating normally, is it because the replaced micros are either failing or operating incorrectly, or otherwise (re)wired incorrectly or some combination of errors and so causing any under/malperformance?

To address the orientation question (mentioned a couple of times in this thread, but not addressed yet), the array is fixed at 34 degrees off the horizontal (8:12 pitched roof) facing due south. I have deciduous trees to the south that shade the array during the months of September, October, November, December, January, February, and March.

From what I am reading, it appears that I need some type of way to measure environmental conditions and understand their impact on the actual power output. I understand that it is impossible to just measure the power and say it is good or not without understanding the environmental conditions that affect the systems performance. For some time, we have been considering getting a weather station. If it had the right accessories, I might be able to capture some of this data - obviously when the panels are not in shaded conditions.

In an attempt to get some type of data, I asked (and paid for) one installer (I specifically asked them to bring an irradiance meter), pull panels down and test the modules (panel plus micro inverters) hoping that I had the right expertise to help. When they showed up, they told me that their "sun eye" was broken and they could not measure irradiance - they only measured open circuit V and closed circuit A. They did not appear to know how to test a MI. Hindsight 20/20, I think the sun eye does not measure irradiance and the field trip did not help much other than the collection of some odd measurements that suggested the 327 panel could generate 359 watts DC and the SP portal reported 270 watts (AC). Yes, it was a very clear and sunny day.

I came here for help and admit that I do not know what to do. What I do know is that over the last year or so (when I realized I MIGHT have a problem), the manufacturer and one installer just ignores the question and tells me things like, "the system is performing as expected" or "there have been less sun hours over the last three years" with no evidence or documentation to support the rebuttal to my claim.

I am attempting to absorb all of this information and hopefully / eventually, answer the questions, Is this array operating normally? If not, why? I think I need a weather station and some way to measure power output.

[J.P.M.]

Correct. I (OP) am trying to determine two things: 1.) Is this array operating normally ? 2.) If this array is not operating normally, is it because the replaced micros are either failing or operating incorrectly, or otherwise (re)wired incorrectly or some combination of errors and so causing any under/malperformance?

To address the orientation question (mentioned a couple of times in this thread, but not addressed yet), the array is fixed at 34 degrees off the horizontal (8:12 pitched roof) facing due south. I have deciduous trees to the south that shade the array during the months of September, October, November, December, January, February, and March.

From what I am reading, it appears that I need some type of way to measure environmental conditions and understand their impact on the actual power output. I understand that it is impossible to just measure the power and say it is good or not without understanding the environmental conditions that affect the systems performance. For some time, we have been considering getting a weather station. If it had the right accessories, I might be able to capture some of this data - obviously when the panels are not in shaded conditions.

In an attempt to get some type of data, I asked (and paid for) one installer (I specifically asked them to bring an irradiance meter), pull panels down and test the modules (panel plus micro inverters) hoping that I had the right expertise to help. When they showed up, they told me that their "sun eye" was broken and they could not measure irradiance - they only measured open circuit V and closed circuit A. They did not appear to know how to test a MI. Hindsight 20/20, I think the sun eye does not measure irradiance and the field trip did not help much other than the collection of some odd measurements that suggested the 327 panel could generate 359 watts DC and the SP portal reported 270 watts (AC). Yes, it was a very clear and sunny day.

I came here for help and admit that I do not know what to do. What I do know is that over the last year or so (when I realized I MIGHT have a problem), the manufacturer and one installer just ignores the question and tells me things like, "the system is performing as expected" or "there have been less sun hours over the last three years" with no evidence or documentation to support the rebuttal to my claim.

I am attempting to absorb all of this information and hopefully / eventually, answer the questions, Is this array operating normally? If not, why? I think I need a weather station and some way to measure power output.

I'll retract or go back on my statement that I'm outa' this thread. I just won't deal with or respond to Ajzwilli.

There are ways to approach this situation that also have not been discussed yet and that may provide some clues as to what's going on.

Before we (I) get more involved, I'll need to know a few things:
1.) How involved do you want to get with both your effort to learn and $$ you want to spend to find possible answers to what's going on ?
A decent weather station will set you back ~ $1K or so, will need some regular attention and siting as near to the array as possible. See Davis Instruments Vantage Pro 2 Plus and Davis Envoy 8X logger. That's part of what I have. Pricey but a tank that doesn't stop.
2.) You'll need some self education in solar energy which, to do correctly, will require some math and engineering tools. A good start will be the Solar Power Your Home for Dummies book as I mentioned previously, but more will be needed to understand solar geometry as well as some understanding of how PV cells and panels operate. The best condensed treatment of the solar resource and geometry I've seen is "Solar Engineering of Thermal Processes", Duffie and Beckman, ISBN # 0-471-51056-4. It's a unversity level engineering text. Also, in spite of the title, it has about the most concise short treatment of PV cells and panels I've seen.
4.) Is you background tecnical at all - not computers but of an engineering type nature ?
5.) What's your zip ? Look for something called PVWatts on the net. It's a model to help design solar arrays but can be used for other purposes such as getting SWAGS of output for existing arrays.That may be a sort of backdoor or additional tool to help determine, get some idea, or get a closer guess as to what the clear day resource availability might be at your site. Read the dummies book before you attempt the model and read ALL the help/info screens before you attampt any input. I and possibly others here will run the model for your zip and array orientation (and size) to better answer any questions you may have after you get up to speed running the model.

[ajzwilli]

I'll retract or go back on my statement that I'm outa' this thread. I just won't deal with or respond to Ajzwilli.

There are ways to approach this situation that also have not been discussed yet and that may provide some clues as to what's going on.

Before we (I) get more involved, I'll need to know a few things:
1.) How involved do you want to get with both your effort to learn and $$ you want to spend to find possible answers to what's going on ?
A decent weather station will set you back ~ $1K or so, will need some regular attention and siting as near to the array as possible. See Davis Instruments Vantage Pro 2 Plus and Davis Envoy 8X logger. That's part of what I have. Pricey but a tank that doesn't stop.
2.) You'll need some self education in solar energy which, to do correctly, will require some math and engineering tools. A good start will be the Solar Power Your Home for Dummies book as I mentioned previously, but more will be needed to understand solar geometry as well as some understanding of how PV cells and panels operate. The best condensed treatment of the solar resource and geometry I've seen is "Solar Engineering of Thermal Processes", Duffie and Beckman, ISBN # 0-471-51056-4. It's a unversity level engineering text. Also, in spite of the title, it has about the most concise short treatment of PV cells and panels I've seen.
4.) Is you background tecnical at all - not computers but of an engineering type nature ?
5.) What's your zip ? Look for something called PVWatts on the net. It's a model to help design solar arrays but can be used for other purposes such as getting SWAGS of output for existing arrays.That may be a sort of backdoor or additional tool to help determine, get some idea, or get a closer guess as to what the clear day resource availability might be at your site. Read the dummies book before you attempt the model and read ALL the help/info screens before you attampt any input. I and possibly others here will run the model for your zip and array orientation (and size) to better answer any questions you may have after you get up to speed running the model.

I only read the first and last part of your long winded thread, pretty sad when you have to resort to calling out typos, yet your posts have them (heck, even your this last post is filled with them and I'm guessing your long response has some as well). Unfortunately, it sounds like I won't get an even longer diatribe this time. The funny thing is JPM has even said he would expect to see production greater than 280 W over several months, yet since the OP hasn't seen it since micro replacement he is spinning his wheels trying to collect data related to production to isolate the problem and help with a warranty claim. I just don't want all readers of this thread to assume a maximum of around 80% instantaneous peak is acceptable over a period of time and that hitting close to STC over a period of time shouldn't be expected. Sure, some systems of course may never hit close to STC given where and how it is installed, but as long as you have a reasonable orientation and angle without continuous shade during peak solar output, then you may want to double check your system that all panels and micros are working. My data has showed it can be hit in summer time with temps in the 90+ F. Maybe for a string system ~80% peak should be seen as acceptable, but JPM has indicated he has hit close to STC with his string system (but doesn't seem to happen near as frequently as I have stated in this thread) What this thread is really about is capturing a baseline of production and monitoring that baseline over time to determine if there is an issue. By using long periods of time for comparison, that isolates most of the noise that JPM is talking about and is over complicating it for these specific purposes. In this specific thread, with micros, one is able to establish a baseline of both AC and DC output for each panel at intra day intervals along with daily production that can be aggregated up, all which are used to ensure system is working properly over time by trending and comparing peak output over time (just to name a few variables.

[ajonestx]

I'll retract or go back on my statement that I'm outa' this thread. I just won't deal with or respond to Ajzwilli.

There are ways to approach this situation that also have not been discussed yet and that may provide some clues as to what's going on.

Before we (I) get more involved, I'll need to know a few things:

I appreciate your time.

QUESTION 1.) How involved do you want to get with both your effort to learn and $$ you want to spend to find possible answers to what's going on ?
A decent weather station will set you back ~ $1K or so, will need some regular attention and siting as near to the array as possible. See Davis Instruments Vantage Pro 2 Plus and Davis Envoy 8X logger. That's part of what I have. Pricey but a tank that doesn't stop.

ANSWER 1.) I prefer to be involved in every aspect of the process, willing to learn and spend the $$ to gather the right tools. We had already planned to purchase a weather station and figured about a $1k expenditure for the right product. It might cost a bit more to get irradiance and cell temperature sensors added. I was thinking $1K to $2K all in. I’ll check out the Davis Instruments products.

QUESTION 2.) You'll need some self education in solar energy which, to do correctly, will require some math and engineering tools. A good start will be the Solar Power Your Home for Dummies book as I mentioned previously, but more will be needed to understand solar geometry as well as some understanding of how PV cells and panels operate. The best condensed treatment of the solar resource and geometry I've seen is "Solar Engineering of Thermal Processes", Duffie and Beckman, ISBN # 0-471-51056-4. It's a university level engineering text. Also, in spite of the title, it has about the most concise short treatment of PV cells and panels I've seen.

ANSWER 2.) Agree that knowledge is key. Earlier this year, I completed a 7.5 hour “Basic Photovoltaics” class, an online course offered by the Midwest Renewable Energy Association. I plan to attend a few other courses at greater depth. I already have the PV for dummies book in my Amazon cart and will make the purchase shortly. I’ll check out the Thermal Processes engineering text.

QUESTION 3.) Is you background technical at all - not computers but of an engineering type nature ?

ANSWER 3.) Yes, engineering type. I am a licensed Architect, so structural, mechanical and electrical concepts are understood at a basic level.

QUESTION 4.) What's your zip ? Look for something called PVWatts on the net. It's a model to help design solar arrays but can be used for other purposes such as getting SWAGS of output for existing arrays. That may be a sort of backdoor or additional tool to help determine, get some idea, or get a closer guess as to what the clear day resource availability might be at your site. Read the dummies book before you attempt the model and read ALL the help/info screens before you attempt any input. I and possibly others here will run the model for your zip and array orientation (and size) to better answer any questions you may have after you get up to speed running the model

ANSWER 4.) 77008. I have been to the PVWatts website in the past and will check again with additional information in hand. I’ll also start with the PV dummies book before attempting the model.

[J.P.M.]

I appreciate your time.

QUESTION 1.) How involved do you want to get with both your effort to learn and $$ you want to spend to find possible answers to what's going on ?
A decent weather station will set you back ~ $1K or so, will need some regular attention and siting as near to the array as possible. See Davis Instruments Vantage Pro 2 Plus and Davis Envoy 8X logger. That's part of what I have. Pricey but a tank that doesn't stop.

ANSWER 1.) I prefer to be involved in every aspect of the process, willing to learn and spend the $$ to gather the right tools. We had already planned to purchase a weather station and figured about a $1k expenditure for the right product. It might cost a bit more to get irradiance and cell temperature sensors added. I was thinking $1K to $2K all in. I’ll check out the Davis Instruments products.

QUESTION 2.) You'll need some self education in solar energy which, to do correctly, will require some math and engineering tools. A good start will be the Solar Power Your Home for Dummies book as I mentioned previously, but more will be needed to understand solar geometry as well as some understanding of how PV cells and panels operate. The best condensed treatment of the solar resource and geometry I've seen is "Solar Engineering of Thermal Processes", Duffie and Beckman, ISBN # 0-471-51056-4. It's a university level engineering text. Also, in spite of the title, it has about the most concise short treatment of PV cells and panels I've seen.

ANSWER 2.) Agree that knowledge is key. Earlier this year, I completed a 7.5 hour “Basic Photovoltaics” class, an online course offered by the Midwest Renewable Energy Association. I plan to attend a few other courses at greater depth. I already have the PV for dummies book in my Amazon cart and will make the purchase shortly. I’ll check out the Thermal Processes engineering text.

QUESTION 3.) Is you background technical at all - not computers but of an engineering type nature ?

ANSWER 3.) Yes, engineering type. I am a licensed Architect, so structural, mechanical and electrical concepts are understood at a basic level.

QUESTION 4.) What's your zip ? Look for something called PVWatts on the net. It's a model to help design solar arrays but can be used for other purposes such as getting SWAGS of output for existing arrays. That may be a sort of backdoor or additional tool to help determine, get some idea, or get a closer guess as to what the clear day resource availability might be at your site. Read the dummies book before you attempt the model and read ALL the help/info screens before you attempt any input. I and possibly others here will run the model for your zip and array orientation (and size) to better answer any questions you may have after you get up to speed running the model

ANSWER 4.) 77008. I have been to the PVWatts website in the past and will check again with additional information in hand. I’ll also start with the PV dummies book before attempting the model.

Understood.

Not a plug, but the Davis Pro 2 is a semi professional instrument and is common among serious PV geeks and alt. energy folks for home use. It's also the common choice of Weatherunderground participants. If you go that way, don't buy from Davis. If you shop around you'll get all you want or probably need for about the price of ~ $1K. Read the Davis lit. and holler back w/questions. My weather station has been running 8 + yrs. It's located ~ 4 ft north of the N-S centerline of my array w/ the anemometer cups elevated about 6" higher than the northern edge of the array. I've replaced the anemometer once and replace the solar sensor every 2 years which is cheaper than recalibration. Initial assembly/setup took me ~ 3-4 hrs. and I took my time. I've found the envoy 8X monitoring to be reliable if a bit clunky, but still fit for purpose.

Most all pyranometers are oriented horizontal by convention, including the davis sensors. You'll need an algorithm to convert Global Horizontal Irradiance ("GHI") to Plane of Array Irradiance ("POA"). There are many models to do so. Duffie and Beckman have about the best text as a primer to help separate the wheat from the chaff for solar radiation characteristics and measurement and is an excellent intoduction to a lot of the fine points of solar radiation. Lots to consider when dealing with irradiance, its composition, characteristics, measurement and how a silicon cell handles it. Facinating but I don't want to get too far ahead of the learning process.

Some Davis users simply offmount the pyranometer, make a jig and mount the sensor in the plane of the array, bypassing the GHI to POA conversion. I'm sort of a purist about such things and prefer to use GHI and convert to POA via algorithm. Besides, ensuring that the sensor does indeed get and stay in the same plane as the array can be tricky. Just know that irradiance measurement is as much art as science and many conversion algorithms are available. The journal "Solar Energy" is a good source for such things after the D & B treatment. I've also seen some papers in the Arch. journals from time to time.

Holler back as your needs dictate.

[ajonestx]

Understood.

Not a plug, but the Davis Pro 2 is a semi professional instrument and is common among serious PV geeks and alt. energy folks for home use. It's also the common choice of Weatherunderground participants. If you go that way, don't buy from Davis. If you shop around you'll get all you want or probably need for about the price of ~ $1K. Read the Davis lit. and holler back w/questions. My weather station has been running 8 + yrs. It's located ~ 4 ft north of the N-S centerline of my array w/ the anemometer cups elevated about 6" higher than the northern edge of the array. I've replaced the anemometer once and replace the solar sensor every 2 years which is cheaper than recalibration. Initial assembly/setup took me ~ 3-4 hrs. and I took my time. I've found the envoy 8X monitoring to be reliable if a bit clunky, but still fit for purpose.

Most all pyranometers are oriented horizontal by convention, including the davis sensors. You'll need an algorithm to convert Global Horizontal Irradiance ("GHI") to Plane of Array Irradiance ("POA"). There are many models to do so. Duffie and Beckman have about the best text as a primer to help separate the wheat from the chaff for solar radiation characteristics and measurement and is an excellent intoduction to a lot of the fine points of solar radiation. Lots to consider when dealing with irradiance, its composition, characteristics, measurement and how a silicon cell handles it. Facinating but I don't want to get too far ahead of the learning process.

Some Davis users simply offmount the pyranometer, make a jig and mount the sensor in the plane of the array, bypassing the GHI to POA conversion. I'm sort of a purist about such things and prefer to use GHI and convert to POA via algorithm. Besides, ensuring that the sensor does indeed get and stay in the same plane as the array can be tricky. Just know that irradiance measurement is as much art as science and many conversion algorithms are available. The journal "Solar Energy" is a good source for such things after the D & B treatment. I've also seen some papers in the Arch. journals from time to time.

Holler back as your needs dictate.

I will be doing some research over the holidays (cameras, books, etc.) and will get back to you with questions. Merry Christmas and Happy New Year.

[J.P.M.]

I will be doing some research over the holidays (cameras, books, etc.) and will get back to you with questions. Merry Christmas and Happy New Year.

Understood. I'm in no hurry.

Enjoy the holidays.

[ajonestx]

Understood. I'm in no hurry.

Enjoy the holidays.

Ugg... finally got the PV for Dummies book yesterday. Engineering book will not come in for several more weeks. weather station is bogged down in analysis on the question of "which one" with the boss. Time to start reading. I will probably gloss through the first section about reducing energy use as we have already reduced consumption by about 50% just with LED lamps and other specialty vacancy light switches throughout the house.

[J.P.M.]

Ugg... finally got the PV for Dummies book yesterday. Engineering book will not come in for several more weeks. weather station is bogged down in analysis on the question of "which one" with the boss. Time to start reading. I will probably gloss through the first section about reducing energy use as we have already reduced consumption by about 50% just with LED lamps and other specialty vacancy light switches throughout the house.

Sounds (Reads) to me like what you want to do will take a Davis Pro II. Shop around, Spend the $1K or so. From my experience and observation, other stuff from places like Accurite,etc, don't have the quality, flexibility or reliability, particularly with respect to irradiance monitoring.

Still not a plug, but if you're serious about figuring out what your array is (or isn't) doing with a reasonable degree of accuracy and precision, you will need a weather station that's reliable and reasonably accurate, particularly for irradiance monitoring. After doing just that (monitoring) for 8 + years as less than a job but more than a hobby, I don't see how other products I could afford could have done the job as well. The other commonly available stations are pretty much a waste of time and money.

I record weather data at 1 minute intervals. The Davis instruments/monitors have not missed one data point in 8 years. I sure can't say as much for the Sunpower monitoring of the array.

You'll be able to save a few bucks by shopping around. Also, buy the Davis in parts, not the complete Pro II Plus package. I didn't need a UV monitor so I bought the (wireless) pro II station by itself which has temp., humidity, barometer and rainfall measurement built in, then added the anemometer, and pyranometer. You'll also need the envoy 8X monitor which, as I wrote, is a bit clunky, but OK and very reliable.

On other stuff you wrote, that seems like a large %age reduction from lighting changes alone. Lighting amounts to <10% of my usage.

I'd read the conservation sections of the Dummies book with more than a cursory view.

Conservation is hard to beat. Reason: Not using something is always cheaper than buying more of it. Just sayin'.

BTW, how many kWh/yr. of your usage is from A/C ?

Happy New Year.

[ajonestx]

Sounds (Reads) to me like what you want to do will take a Davis Pro II. Shop around, Spend the $1K or so. From my experience and observation, other stuff from places like Accurite,etc, don't have the quality, flexibility or reliability, particularly with respect to irradiance monitoring.

Still not a plug, but if you're serious about figuring out what your array is (or isn't) doing with a reasonable degree of accuracy and precision, you will need a weather station that's reliable and reasonably accurate, particularly for irradiance monitoring. After doing just that (monitoring) for 8 + years as less than a job but more than a hobby, I don't see how other products I could afford could have done the job as well. The other commonly available stations are pretty much a waste of time and money.

I record weather data at 1 minute intervals. The Davis instruments/monitors have not missed one data point in 8 years. I sure can't say as much for the Sunpower monitoring of the array.

You'll be able to save a few bucks by shopping around. Also, buy the Davis in parts, not the complete Pro II Plus package. I didn't need a UV monitor so I bought the (wireless) pro II station by itself which has temp., humidity, barometer and rainfall measurement built in, then added the anemometer, and pyranometer. You'll also need the envoy 8X monitor which, as I wrote, is a bit clunky, but OK and very reliable.

On other stuff you wrote, that seems like a large %age reduction from lighting changes alone. Lighting amounts to <10% of my usage.

I'd read the conservation sections of the Dummies book with more than a cursory view.

Conservation is hard to beat. Reason: Not using something is always cheaper than buying more of it. Just sayin'.

BTW, how many kWh/yr. of your usage is from A/C ?

Happy New Year.

Your "non-plug" for the Davis equipment is appreciated. I do recognize that without irradiance and temperature and wind measurement, any other data collected is not of any value - I hear you. Nice to hear the 1-minute interval / never missed a beat in 8 years. this helps narrow the field. We just have not been able to circle the wagons and get something on order.

You don't miss the smallest details (I like by the way) - Maybe giving all the credit to lighting is an oversimplification and other components have helped over the last 25 plus years in the house such as improved AC / heating, vacancy light switches, floor insulation, wall insulation, attic insulation, radiant barrier roof deck coating, door weather stripping, insulated doors, window weather stripping, improved envelope sealing, blocking at balloon frame opening, programmable thermostats, shade sails, higher efficiency appliances and lower wattage fish pond pumps, Our highest usage was in 2000 at 1,156kWh (average monthly). Right before PV we got it down to 663kWh (average monthly) in 2016. Since then, we have continued to replaced CF and Incan lighting to reduce more, but do not have enough trend data to see how much benefit it was - Agree that conservation is hard to beat - kWh (average monthly usage) graph attached.

Not sure I can isolate the A/C usage. Our Sense meter says the compressor outside runs at about 2,400 watts, but it also says that it used only 190 kWh last year, but it also says we have three of them - I am not sold on Sense and the data is collects. One of these days, I will replace the electrical panel with breakers that measure each circuit. Just looking at energy usage, our six summer months use about 1,400 kWh more than our six winter months (about 233 kWh per month).

Happy New Year.

[J.P.M.]

Your "non-plug" for the Davis equipment is appreciated. I do recognize that without irradiance and temperature and wind measurement, any other data collected is not of any value - I hear you. Nice to hear the 1-minute interval / never missed a beat in 8 years. this helps narrow the field. We just have not been able to circle the wagons and get something on order.

You don't miss the smallest details (I like by the way) - Maybe giving all the credit to lighting is an oversimplification and other components have helped over the last 25 plus years in the house such as improved AC / heating, vacancy light switches, floor insulation, wall insulation, attic insulation, radiant barrier roof deck coating, door weather stripping, insulated doors, window weather stripping, improved envelope sealing, blocking at balloon frame opening, programmable thermostats, shade sails, higher efficiency appliances and lower wattage fish pond pumps, Our highest usage was in 2000 at 1,156kWh (average monthly). Right before PV we got it down to 663kWh (average monthly) in 2016. Since then, we have continued to replaced CF and Incan lighting to reduce more, but do not have enough trend data to see how much benefit it was - Agree that conservation is hard to beat - kWh (average monthly usage) graph attached.

Not sure I can isolate the A/C usage. Our Sense meter says the compressor outside runs at about 2,400 watts, but it also says that it used only 190 kWh last year, but it also says we have three of them - I am not sold on Sense and the data is collects. One of these days, I will replace the electrical panel with breakers that measure each circuit. Just looking at energy usage, our six summer months use about 1,400 kWh more than our six winter months (about 233 kWh per month).

Happy New Year.

Your pre-EV usage is similar to mine: 14 yr. running average = 6,970 kWh/365 days.
Prior 365 day usage = 7,482 kWh before PV contribution. More house guests from back east in the winter this year.
Ave. annual A/C usage = 780 kWh/yr. but varies a lot as f(ambient air temp, dew point temp.).
House is 3,218 ft.^2, built 1980, zip 92026. Warm to hot summers, mild winters.

[ajonestx]

Your pre-EV usage is similar to mine: 14 yr. running average = 6,970 kWh/365 days.
Prior 365 day usage = 7,482 kWh before PV contribution. More house guests from back east in the winter this year.
Ave. annual A/C usage = 780 kWh/yr. but varies a lot as f(ambient air temp, dew point temp.).
House is 3,218 ft.^2, built 1980, zip 92026. Warm to hot summers, mild winters.

WOW... your 3,218 SF house must be pretty tight for you to have similar energy consumption. Our 1,200 SF gets tighter every year though with repair projects. Built in 1910, we have lots to do. I was in your area just a couple months ago for the Komen 3-day walk for breast cancer - beautiful country by the way. As we are in 77008, our "climate" (as PV for Dummies calls it) might be a little more extreme than your area. We also built in a little expansion into our PV system for the future EV, but have not pulled the trigger yet.

I did make it through PV for Dummies Chapter I - interesting read and a few tid bits of good data so far - hope to get into a little more detail in subsequent chapters.

[J.P.M.]

WOW... your 3,218 SF house must be pretty tight for you to have similar energy consumption.

Not really. It was built in 1980 and is reasonably tight by construction/building codes of that time, but nothing too off the wall. However, probably about half of a low electric bill is lifestyle choices and common sense energy conservation measures. For example, extensive use of nighttime ventilation during cooling season allows limiting annual A/C air handler run time to an average of ~ 120 - 150 hrs./yr. depending on weather (BTW, I'm inland, not coastal so summers get quite toasty here relative to downtown/coastal San Diego as well as about 20 % sunnier. But then, I set the summer thermostat at 80 F and shut the A/C off when we're not home. I've also got a solar thermal water heater that provides ~ 90-95 % of my annual DHW load. That alone replaces ~ 1,900 kWh/yr. of the annual electrical usage.

My overpriced, oversized, non cost effective but otherwise well designed Sunpower system (with 327 STC W panels same as yours) provides the rest of the much reduced electrical load. Why I got the overpriced, oversized S.P. system is a long, boring story, but I knew it wasn't going to be cost effective from the beginning and economics had nothing to do with it.

If one goal of the exercise is a lower electric bill in the most cost effective way(s), the key is to first reduce the load as much as possible through lifestyle adjustments, then conservation measures, and only after all that is done to the greatest extent possible within lifestyle choices and lifecycle costing methods, see if/what kind of alternate energy devices (if any) make economic sense.

Then, of course, all that needs to be balanced against other priorities, but that's another topic altogether.