First over 40 kWh day

[Ian S]

I had my system turned on in Oct of 2013. I finally hit 40.01 kWh's today out of my 6.72 Sunpower system :. The best day before today had been 36 kWh's. Should be interesting to see how much it puts out in the summer.

I just checked and my best day in February last year (first year of operation) was February 24 with production of 41.03 kWh from my 6.9 kW Sunpower system with panels facing due south. That's in central Phoenix. A lot depends too on your panel angle with the horizontal. Mine is 15 degrees so my best times tend to be in late April- May after which the heat starts to build and output is less. This February has really sucked in comparison with a lot of high cloud (but no precip) and unusually hot weather - thanks global warming!

[gregvet]

Just looked at my TED5000 stats. The highest I have measured is 59.178 kWh on March 25, 2013. This is a 7.755 KW system. You can see more details on the PVOutput website (kettBVhome) location: 81211. My average is between 40-50 kWh on a sunny day.

[russ]

Just looked at my TED5000 stats. The highest I have measured is 59.178 kWh on March 25, 2013. This is a 7.755 KW system. You can see more details on the PVOutput website (kettBVhome) location: 81211. My average is between 40-50 kWh on a sunny day.

Not bad! PV Watts predicts approximately 34 kWh/day annually for your zip code.

[silversaver]

I'm very sensitive with the word "predict".....

[russ]

I'm very sensitive with the word "predict".....

Maybe but that is what PV Watts does - predict an output - might be a bit high or low - possibly even totally off but it is a prediction.

PV Watts can nor take into account the precise local conditions such as water, snow, fog, hills, trees etc.

[silversaver]

Maybe but that is what PV Watts does - predict an output - might be a bit high or low - possibly even totally off but it is a prediction.

PV Watts can nor take into account the precise local conditions such as water, snow, fog, hills, trees etc.

can't agree more. Just look at my today's output for a 6.63kW DC Bosch SW245 deg with 23 deg pitch. As you see the output drop at 4pm because there's hill with about 10 to 15 deg higher than my house from SW240 all the way to NW. I also have a big tree @ SW 260 deg. I just hope the tree will not affect my afternoon production. Well....I'm not too worry, because that is less than 3% of the daily production. I add the solar arrays to the house and I can't pick the house that is perfect for solar..

[J.P.M.]

Maybe but that is what PV Watts does - predict an output - might be a bit high or low - possibly even totally off but it is a prediction.

PV Watts can nor take into account the precise local conditions such as water, snow, fog, hills, trees etc.

According to the NREL Website for PVWatts and specifically the page that discusses how to interpret PVWatts results, PVWatts is a calculator that ESTIMATES possible long term future performance for a "typical" month or year, based on system parameters and prior weather conditions. It is not a predictor of output over any individual current or future month, or year, much less individual days. An approximate confidence level for PVWatts estimates as given by NREL seems to be +/- 20% for individual years and +/- 40% for individual months, saying nothing about individual days, but probably more than +/- 40%, maybe by a fair amount. As you wrote: "possibly even totally off". I'd call that confidence level - +/-40+%worse than a WAG, especially if it leads to conclusions/actions that are erroneous due to user ignorance. Using a monthly output from PVWatts and applying it to an individual day seems to imply an expectation of every day being identical to every other day in a month that happened years ago. That makes no sense - to me anyway and seems like a misapplication of the calculator's intent and purpose leading to erroneous conclusions.

There are models available to predict clear day output - usually hr. by hr., some minute by minute. PVWatts is not one of them.

As a possible suggestion, there are websites where PV system owners post their system parameters and output on a daily or more frequent schedule. Comparing those data with another nearby system output (yours, mine, anyone "nearby") may offer a way to estimate what that other system (yours, mine ,anyone "nearby") did on a "clear" day, thus giving a number for estimated clear day output for that time period.

[russ]

Get a life!

[Volusiano]

Get a life!

I'm with Russ on this. I understood perfectly what he meant when he said "predict" because he qualified it with "might be a bit high or low".

There's no need to nitpick and over-analyze to death the difference between "predict" and "estimate" and call it "misapplication ... leading to erroneous conclusions". We all know exactly what PVWatts is and what PVWatts does already as a statistical model and don't need a long winded lecture about it. Schooling is not needed and schooling is not asked for.

[J.P.M.]

Get a life!

I'll take that as a respectful suggestion.

Only trying to express an opinion or two in a professional, non offensive way, perhaps share a few things I've picked up along the way and generate some intelligent discussion without being overly technical about it. Sorry if you found it offensive.

[bcroe]

PV Watts

According to the NREL Website for PVWatts and specifically the page that discusses how to interpret PVWatts results, PVWatts is a calculator that ESTIMATES possible long term future performance for a "typical" month or year

There are models available to predict clear day output - usually hr. by hr., some minute by minute. PVWatts
is not one of them.

That could explain why my attempt to graph PVwatts hourly level doesn't make any sense. So I am still looking
for a tool that will give me ideal sun hourly output. This, to simulate the overall performance of a bunch
of different panel alignments. And runs via an Apple.

Hey, maybe I could use a PC at the library. Use it to down load SAM, where is that link? Bruce Roe

[SunEagle]

According to the NREL Website for PVWatts and specifically the page that discusses how to interpret PVWatts results, PVWatts is a calculator that ESTIMATES possible long term future performance for a "typical" month or year, based on system parameters and prior weather conditions. It is not a predictor of output over any individual current or future month, or year, much less individual days. An approximate confidence level for PVWatts estimates as given by NREL seems to be +/- 20% for individual years and +/- 40% for individual months, saying nothing about individual days, but probably more than +/- 40%, maybe by a fair amount. As you wrote: "possibly even totally off". I'd call that confidence level - +/-40+%worse than a WAG, especially if it leads to conclusions/actions that are erroneous due to user ignorance. Using a monthly output from PVWatts and applying it to an individual day seems to imply an expectation of every day being identical to every other day in a month that happened years ago. That makes no sense - to me anyway and seems like a misapplication of the calculator's intent and purpose leading to erroneous conclusions.

There are models available to predict clear day output - usually hr. by hr., some minute by minute. PVWatts is not one of them.

As a possible suggestion, there are websites where PV system owners post their system parameters and output on a daily or more frequent schedule. Comparing those data with another nearby system output (yours, mine, anyone "nearby") may offer a way to estimate what that other system (yours, mine ,anyone "nearby") did on a "clear" day, thus giving a number for estimated clear day output for that time period.

Well at least an "estimation" is better than a SWAG.

[J.P.M.]

That could explain why my attempt to graph PVwatts hourly level doesn't make any sense. So I am still looking
for a tool that will give me ideal sun hourly output. This, to simulate the overall performance of a bunch
of different panel alignments. And runs via an Apple.

Hey, maybe I could use a PC at the library. Use it to down load SAM, where is that link? Bruce Roe

Bruce: Check P.M's

J.P.M.

[russ]

I'll take that as a respectful suggestion.

Only trying to express an opinion or two in a professional, non offensive way, perhaps share a few things I've picked up along the way and generate some intelligent discussion without being overly technical about it. Sorry if you found it offensive.

Overly technical or professional my foot! You are like an old woman sometimes!

[J.P.M.]

Overly technical or professional my foot! You are like an old woman sometimes!

I respect your opinion and will consider it. In the meantime, I'll be more frugal with my words and opinions. Thank you for your candor.

In the meantime I'd suggest even old women can play the piano and don't deserve to be shot for it.

Assuming I still have opinion privileges, and speaking and trying to think as a (retired) engineer, my opinion and my opinion only, FWIW, is that using PVWatts to predict daily performance is a misuse of that tool and can lead to incorrect conclusions and outcomes. That's all and that's it.

As I've written before, it's a free country. Also, your time, not mine. Your money, not mine. Your opinion, not mine.

I'd respectfully suggest that if you disagree with my opinion, constructive criticism or stating why you disagree with my opinion(s), if you feel strongly about it/them (as your epithet seems to imply), might do more to raise the information exchange bar and, leaving the word professional out of it, might be more appropriate and helpful, to me as least, than name calling. Might help to raise and keep the level of conversation above bickering and quibbling as well.