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It's a gauge nonetheless. Sorry, I'll say variance or difference in the future.
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It isn't about words. It's about misunderstanding the use and purposes of simulation tools.
Use them as you wish, but know that if you think you can predict future performance from things like PVWatts, or any other simulation program, know that you're not going to have much success in the reliability dept.
Get angry or whatever you want about it, but don't shoot the messenger. I'm simply trying to help others avoid the same type of erroneous thinking.
Take what you want of this post, leave the rest.Comment
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Weather were different most days. predict,forcast,estimate...etc. really just numbers for comparison.
I looking at what I can get off solar in a sunny day and what I can get off solar annually. What's the peak instantaneous output.....etc. With all these numbers, I can pretty much get any answer I need. The graphs show under perform in May, Aug and Sept just becasue the system were off for 25 days with 2 bad inverters replacement. In general, we just gathering all the available infors and make them useful.Comment
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To any and all who are of the opinion that PVWatts is a valid tool to PREDICT output, or that past performance allows prediction of the future, especially over short periods, or who say a system is preforming better or worse than PVWatts "predicted" : Please, can you explain to me your reasoning why you think that way and the logic you used to come to those conclusions ? I'm here to ask questions and learn as much as anyone. Any help would be appreciated. Thank you in advance.Comment
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Although highly unscientific , this is how I initially came to justify going solar.
On my 6.5 KW system, it is expected to make 30 Kwh's per day in the winter months, and 45 Kwh's in the summer months.
30+45 / 2 = 37.5 Kwh's per day average.
37.5 x 365 = 13,687 Kwh's per year.
13,687 - 20% ( cloudy days , rainy days, solar eclipse, etc...etc...) still leaves me with 10,950 Kwh's generated.
10,950 Kwh's annually for 5.5 years meets my payback goal.
Maybe I'll have more sunny days, I doubt I'll have less.
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Historically, their are 277 sunny days per year. 365 - 20% = 292. Partially sunny / cloudy days are to be expected to bridge the gap between the two figures.
These basic calculations are good enough for me.
If anything, it makes errors that create a bigger cushion to support these figures. Example: The summer months are more likely to offer sunny days, than the storm prone winter months.... but in these basic figures, number of sunny days and expected daily output are both equally weighted.
In reality, summer will offer higher daily generation numbers, and more of them.
I'm not going to lose sleep over the final numbers, they are what they are.
Like you stated JPM... its just fun to look at the short term numbers.... long term is anyones guess.
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Regardless the wording of PREDICT or ESTIMATE, you are using the these historical calculated numbers to EXPECT output base on approximation. Your assumption are really base on prediction or estimation which both are educated guess of available infor you received. Hypothetically, the weather of next 2 decades will never be the same as last 2 decades, what are we here talking about it?Comment
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Maybe it can be explained this way...
If you take the averages of flipping a coin every month for the last 50 years, and apply that average to flipping a coin every month for the next 12 months, you are likely to not get the results the historical data "predicted"6k LG 300, 16S, 2E, 2W, Solaredge P400s and SE5000Comment
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Although highly unscientific , this is how I initially came to justify going solar.
On my 6.5 KW system, it is expected to make 30 Kwh's per day in the winter months, and 45 Kwh's in the summer months.
30+45 / 2 = 37.5 Kwh's per day average.
37.5 x 365 = 13,687 Kwh's per year.
I'll say this, I never used PVWatts even for design. My solar guys used their own calcs and my attitude was I take what I can get wrt to actual production. Roof real estate and panel wattage were the only factors for me. I just jumped in on this perpetual discussion. However, if you think you can get the numbers you are stating here, show me what your basing this off of.Comment
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solar31.JPG
Well... here we are in the dead of winter....
The Christmas parties are over, the lights and tree are down.
The cooking and endless baking are over
Everyone is home 24x7 due to the school and work holidays
And.... on a sunny day, I'm over producing by 4 Kwh's... ( 30 Kwh's produced, 26 Kwh's consumed)
Things will only improve with "generation season" coming soon.
Perfect.Comment
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24 x 270 watt panels
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Generation for the 29th. 30 Kwh's ( Rounded up)
solar31.JPG
Consumption for the 29th... -4 kwh's.
Useage: 26 Kwh's.Comment
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