collector orientation calculator - ScanTheSun

[J.P.M.]

Actually it does not matter which solar constant is selected since any difference is consumed by fitting parameters A,X to NASA data, eqn. (1) and (3). The value 1353 is given in the text to know what the fitting coefficients are base on. It does not change the results at all since the the experimental data are the constrain here. Similar, integrals (14),(25),(31) smear the angular dependence of the diffuse radiation. In practice the angular dependence is not necessary. This has been confirmed by a green developer company (more than 1000 green buildings sold in one of the capital in Europe) whose management shared with us their research results. They are preparing their own paper for publishing. The only thing I can say (the diffuse model is not our achievement and we do not have the right to publish the interpretation of the model) here is that the parameterization (6) reproduces best the hourly data from weather stations around Europe. Last thing. It is obvious that proper description of the diffuse radiation of any form requires the transportation theory (see the equation attached here as a picture), or at least the simplified diffusion theory with scattering and transportation cross-sections (the sigmas). Anyone who tried it knows that in case of such unpredictable object like the atmosphere is a pure waste of time.

After being around solar resource assessment and solar modeling for a long time, my impression and opinion of this stuff is that it's a form of charlatanism, and the above explanation, such as it is, sounds like more smoke and mirrors.

I'm not at all against new ideas and ways of doing things but I've never been in favor of using that idea to mask B.S., which is, IMO only, what this stuff is. To those considering using this stuff, I'd sincerely and most respectfully suggest you consider spending your time first reading and studying any reputable solar energy text, Duffie & Beckman being pretty much the accepted bible, or others, before digging into this stuff. Doing so will quickly reveal this stuff for what it is: solar quackery and, if a price is attached to acquisition, another way to separate fools from their money. Even if free, it's a waste of time better spent in learning more main stream methods of resource assessment and solar technology in general.

I'm always on the lookout for better and also different ways to estimate/measure the solar resource.This is certainly different, but it's not something I'd take seriously or invest any money or time in. As such, I'll not waste any more time on reviewing the attachment describing the process. From what I've seen of it, combined with what I think I may know about the subject it deals with, I'd not recommend anyone take it seriously. There are better, more back to fundamental methods to get the information.

[Ernest_Grodner]

Actually it does not matter which solar constant is selected since any difference is consumed by fitting parameters A,X to NASA data, eqn. (1) and (3). The value 1353 is given in the text to know what the fitting coefficients are base on. It does not change the results at all since the the experimental data are the constrain here. Similar, integrals (14),(25),(31) smear the angular dependence of the diffuse radiation. In practice the angular dependence is not necessary. This has been confirmed by a green developer company (more than 1000 green buildings sold in one of the capital in Europe) whose management shared with us their research results. They are preparing their own paper for publishing. The only thing I can say (the diffuse model is not our achievement and we do not have the right to publish the interpretation of the model) here is that the parameterization (6) reproduces best the hourly data from weather stations around Europe. Last thing. It is obvious that proper description of the diffuse radiation of any form requires the transportation theory (see the equation attached here as a picture), or at least the simplified diffusion theory with scattering and transportation cross-sections (the sigmas). Anyone who tried it knows that in case of such unpredictable object like the atmosphere is a pure waste of time.

[J.P.M.]

Mods: How about closing this thread ? Not my call, but there doesn't seem like much more to be learned here except how to separate fly crap from pepper.

[J.P.M.]

RE: 14 years of Total Solar Irradiance measurements by the NASA S.O.R.C.E. satellite indicates TSI = 1,361 W/m^2

I hope that Ernest_Grodner uses 1,361 W/m^2 in his application.

The 1,353 W/m^2 measurement (estimate) was the "accepted" value then ...
The 1,367 W/m^2 measurement (estimate) was the "accepted" value then ...
The 1,361 W/m^2 measurement is an accurate measurement.

The value of 1,353 W/m^2 is in error by ~1/2% too low ( too cold )
The value of 1,367 W/m^2 is in error by ~1/2% too high ( too hot )
The value of 1,361 W/m^2 is very accurate ( just right ! )

The reader could use either of the wrong values of 1,353 or 1,367 since they are both equally wrong at 1/2% error
I won't judge, but now you know that 1,361 W/m^2 is very accurate ( not an estimate ).

NASA SORCE Satellite
The Absolute accuracy of 100 parts per million (1 ppm=0.0001% at 1-sigma) and a precision and long-term relative accuracy of 10 ppm per year.

The value of 1,353 W/m^2 measurement did not have the accuracy to justify printing that many digits.
The value of 1,367 W/m^2 measurement did not have the accuracy to justify printing that many digits.
The value of 1,361 W/m^2 is the accurate integer

Per NASA,
One of the most important achievements of SORCE Satellite is ...
The Total Irradiance Monitor data established the new baseline level of Total Solar Irradiance (TSI) at the top of Earth's atmosphere of 1360.8 W/m^2
The SORCE Satellite has the accuracy to justify 5 digits.
That is my main point.

The value of 1360.8 W/m^2 is not an "accepted value" or an "agreed upon value" like the previous "estimated" measurements.
As the sun changes into a Red Giant then the TSI value will change - it will trend higher, and higher, and higher!

I also noted that the 11 Year Sun Cycle can be seen in the data set, as a +/-0.5 W/m^2 cyclic change in the graph ...
http://lasp.colorado.edu/home/sorce/...truction-1.png
The reader may find this interesting and/or important.
We can add compensation factors for the 11 year major cycle and the minors cycles.
But I think, the value of 1,361 W/m^2 is good enough for any of our calculations.

You are still missing my point. The estimates are not wrong or right. they are estimates. Reread what I wrote.

One more time: The value of 1,353 W/m^2 was the accepted value for solar energy applications until about 1977 or so. Everyone then knew it to be and estimate but agreed to it as the value used until a "better" estimate was agreed upon. I was part of the group that changed the assigned value to be used in all transactions and submitted correspondence to 1,367 W/m^2 when I belonged to the Resource Assessment Division of the International Solar Energy Society.

That a product uses the value for a constant that's now fallen out of common and agreed upon acceptance by what's probably the users/customers of a product, no matter how far off it may or may not be from the currently accepted value as understood by its potential customers is not necessarily a disaster, but It doesn't go far to instill a sense of confidence in the product or its creators.

As I also wrote, the rest of what I saw was pretty much of a poor rehash of what's also available in the open literature, one example being the use of isotropic diffuse rather than the more commonly accepted but more rigorous anisotropic diffuse solar radiation component that all serious models suggest.

Truth to tell, I think it's a poor product and the posting here amounts to SPAM.

Add: If you're interested in learning more about the 1,367 W/m^2value, about the most concise and at the same time complete rationale and background on where it came from that I've seen can be found here :

Iqbal, Muhammad, An Introduction to Solar Radiation, ISBN 0323151817, 1983, sec 3.4, PP. 50-53 in my ed. (1983).

[NEOH]

RE: 14 years of Total Solar Irradiance measurements by the NASA S.O.R.C.E. satellite indicates TSI = 1,361 W/m^2

I hope that Ernest_Grodner uses 1,361 W/m^2 in his application.

The 1,353 W/m^2 measurement (estimate) was the "accepted" value then ...
The 1,367 W/m^2 measurement (estimate) was the "accepted" value then ...
The 1,361 W/m^2 measurement is an accurate measurement.

The value of 1,353 W/m^2 is in error by ~1/2% too low ( too cold )
The value of 1,367 W/m^2 is in error by ~1/2% too high ( too hot )
The value of 1,361 W/m^2 is very accurate ( just right ! )

The reader could use either of the wrong values of 1,353 or 1,367 since they are both equally wrong at 1/2% error
I won't judge, but now you know that 1,361 W/m^2 is very accurate ( not an estimate ).

NASA SORCE Satellite
The Absolute accuracy of 100 parts per million (1 ppm=0.0001% at 1-sigma) and a precision and long-term relative accuracy of 10 ppm per year.

The value of 1,353 W/m^2 measurement did not have the accuracy to justify printing that many digits.
The value of 1,367 W/m^2 measurement did not have the accuracy to justify printing that many digits.
The value of 1,361 W/m^2 is the accurate integer

Per NASA,
One of the most important achievements of SORCE Satellite is ...
The Total Irradiance Monitor data established the new baseline level of Total Solar Irradiance (TSI) at the top of Earth's atmosphere of 1360.8 W/m^2
The SORCE Satellite has the accuracy to justify 5 digits.
That is my main point.

The value of 1360.8 W/m^2 is not an "accepted value" or an "agreed upon value" like the previous "estimated" measurements.
As the sun changes into a Red Giant then the TSI value will change - it will trend higher, and higher, and higher!

I also noted that the 11 Year Sun Cycle can be seen in the data set, as a +/-0.5 W/m^2 cyclic change in the graph ...
http://lasp.colorado.edu/home/sorce/...truction-1.png
The reader may find this interesting and/or important.
We can add compensation factors for the 11 year major cycle and the minors cycles.
But I think, the value of 1,361 W/m^2 is good enough for any of our calculations.

[J.P.M.]

14 years of Total Solar Irradiance measurements by the NASA S.O.R.C.E. satellite indicates TSI = 1361 W/m^2

http://lasp.colorado.edu/home/sorce/files/2011/09/TIM_TSI_Reconstruction-1.png

The 11 year solar cycle, which causes a +/-0.5 W/m^2 periodic change, can be clearly seen in the most recent data.

I'm very aware of the cyclic nature of solar irradiance, and the various methods used since the early 19th century to estimate the number, as well as ongoing efforts to improve and update estimates.

My point was that the 1,353 W/m^2 number has not been used by those involved in most solar energy research as it may be applied to R.E. applications since the late 70's. To use it now in something that's mostly a rehash of what's in the open literature anyway, and call it, or at least imply that it's current or academically rigorous belies a level of unfamiliarity with the basics of the subject.

Not to put too fine a point on it, it's a bit like writing about internet protocols and assuming everyone still uses dialup.

It's also not that the number cited for use isn't the still currently and commonly used value of 1,367 W/m^2. The actual value of the "solar constant" - which like most things is anything but constant - is probably not 1,367 W/m^ even as I write this, and even after including adjustments for the sun-earth distance and several other variables. However, most informed folks currently and commonly use the 1,367 W/m^ number by agreement and convention, even though they know it to be somewhat variable. It keeps everyone on the same page. Someday that agreed upon number will probably change again, just like the 1,353 W/m^2 number changed in the late '70's, or like 30 yr. average meteorological data changes and gets updated.

The main point is not that the solar constant isn't (constant). The point is that using a value that no one who's the likely audience/customer for this product uses much anymore by common agreement is a giveaway, to me at least, that the authors may not know as much about the fundamentals or have as much familiarity with the subject as their audience.

What's yours ?

[NEOH]

14 years of Total Solar Irradiance measurements by the NASA S.O.R.C.E. satellite indicates TSI = 1361 W/m^2

http://lasp.colorado.edu/home/sorce/files/2011/09/TIM_TSI_Reconstruction-1.png

The 11 year solar cycle, which causes a +/-0.5 W/m^2 periodic change, can be clearly seen in the most recent data.

[J.P.M.]

We are about to publish the new ScanTheSun beta version for testing. Here a short technical documentation: www.scanthesun.com/docs/tech.php

I began scanning the attachment and noticed in the second sentence of the first paragraph that the model uses the pre 1977 accepted value for the solar constant of 1,353 W/m^2 and not the more commonly accepted value of 1,367 W/m^2 as almost universally accepted these days. Not an auspicious start, or one that inspires confidence in the logic/model being presented.

I also noticed in passing through the attachment that the model considers the diffuse portion of the solar radiation to be isotropic (section II). Most serious modeling either calculates time integrated diffuse irradiance (called diffuse insolation BTW) using isotropic and also other more directional methods, and then compares the results, offering the user a choice based on the situation. Anecdotally, most modelers find anisotropic models of diffuse radiation to be a better and more representative fit to measurements.

My suspicion is that digging further into the attachment would produce a lot more questions about the lack of depth or lack of understanding of the subject. If this information were submitted to a journal as a paper, which is about what it represents in terms of content, my guess it would be rejected in its current iteration. I'd also suspect that lack of knowledge about what's already been done would make its methods mostly inferior to those of other open source literature and also proprietary models. FWIW, I believe I've written more sophisticated stuff, and my stuff is far from sophisticated. I've not got the time and I'm not a journal article reviewer so I stopped reading your attachment after about a 5 min. scan.

Others have done what you attempt and, IMO have done so in much better ways and with a better appreciation for what's come before.

IMO, your stuff is still not ready for prime time. If you're going to foist this on the solar modeling community, get some help, get some background in what's available and then get it right.

[Ernest_Grodner]

We are about to publish the new ScanTheSun beta version for testing. Here a short technical documentation: www.scanthesun.com/docs/tech.php

[Ernest_Grodner]

After one year we are going to publish the largest update of the ScanTheSun app.
Soon, the NASA solar energy data will be implemented for measurements of
- the direct radiation component and
- the diffuse radiation component
together with shading analysis.
Preliminary results of the NASA and ScanTheSun data are presented at the end of the video: https://youtu.be/gZnlx63rJ3c

With best regards,
Ernest

[Ernest_Grodner]

Dear Friends,

I'm happy to announce that the project ScanTheSun was chosen by the jury as Energy Globe National Award winner this year. On June 5 (World Environmental Day) all National Winners will be published at www.energyglobe.info.
I would like to thank all of you for the feedback that allowed decent debugging of the ScanTheSun code and make important changes and corrections.
There are also press releases of the recent year available at:

http://scanthesun.com/papers/sts2.php?langmain=EN

With best regards,
Ernest.

[J.P.M.]

Ernest:

I believe your goals are ill defined and poorly explained. Furthermore, your methods are way off base in more ways than this format allows time or space to describe.

1.) The Helgesson paper you reference deals primarily with solar thermal applications and methods to enhance and improve thermal collector performance, mostly by focusing on one type of thermal collector. It treats the analysis of the solar energy resource as a secondary issue necessary for the main topic which seems to be thermal analysis. I would not agree that, to use your words, it is "One of the most informative and openly accessible material..." on the subject.

2.) There is nothing wrong with that paper, which seems to be a dissertation necessary as part of the requirement for recognition and licensure as a Professional Engineer or something similar. In point of fact, it's methods are quite recognizable. I've seen similar and almost identical methods in print and have used similar methods for thermal analysis. The methods are common but they are not the only ones. The point is, what's in that paper regarding the solar resource is not new, and much of the rest of it. while probably accurate (as much as those things can be accurate), seems a reshuffle of existing methods and material, most of which is not new, and certainly not unique, as is common for dissertation topics.

3.) See a copy of Duffie & Beckman, and/or many others - Iqbal, Lunde, Kreith, NREL, The Solar Energy Handbook, etc. and/or, the references in the Helgesson paper itself. Start with Liu and Jordon (1960), to see the origin of the info in the Helgesson paper about not only resource evaluation, but also most of the thermal analysis. Indeed, most of the material you may think makes the Helgesson paper so informative (but IMO, mostly a rehash) was around for a long time before the publication date of the Helgesson paper (2004), as correctly acknowledged by its cited references. As a respectful suggestion - go to the horse's mouth and use the Helgesson cited references as a start.

4.) From the beginning, that you seem to not understand the folly of not including all of the solar radiation components - diffuse and reflected, as well as the direct component, or (as seems possible at this point), to not even be aware those other components exist until challenged (tipped of ?), or that those components may be important in varying degrees based on the situation, and expect to be taken seriously, particularly when methods are commonly available to evaluate the solar resource, causes me to doubt that you do have the necessary depth of the subject to claim the necessary expertize.

5.) FWIW, depending on the application and in spite of what you may think or not see, collector orientation can and does affect heat loss and (possibly to a much lower degree) thermal capacitance, and, FWIW, many other things in any solar conversion device. That effect is usually most pronounced for thermal devices, but also for PV and other applications as well. I and many others think we know that, and some of us think we know why, when, where, how, or not, in what ways and to what degree, at least to a 1st approximation collector orientation affects things that in turn, affect collector performance.

That you acknowledge you do not believe device orientation affects such things as heat loss and thermal capacitance (again, perhaps to some small degree, depending on application), only gives me more reason to think you may lack the knowledge depth of applied solar energy necessary to expect a reasonably knowledgeable student of the subject to take much of what you present seriously.

6.) Much of what you seem to be attempting has been done before. You seem to be trying to reinvent the wheel. Looks to me like some of the dimensions on your new wheel come out of the imaginary plane.

I believe you are out of your knowledge depth for what you are trying to do with respect to applied solar energy. The shading portion of your application may have some merit. I'm of the opinion that most of the rest of what you claim and provide is simplistic, incorrect in both approach and execution, and therefore prone to error. In its current form, and in my opinion, your application will not find what is likely the best collector orientation with a reasonable probability of success or accuracy. That the comparison and agreement in output between PVWatts and your app that you present seems to be quite seasonally dependent would be a red flag to me. Try comparing your app to SAM or TRNSYS and see what you get. My suspicion is you'll find those two produce results a lot closer to PVWatts than your app.

Respectfully,

J.P.M.

[Ernest_Grodner]

Sensij,
You are right, to get total assessment of usable energy form the cell you need to solve all factors and do parameters measurement for each type of a panel.
No question about that. And this will not be calculated in the app.

Just to clarify what is stated above "The new functionality will be based on angular efficiency of a panel for direct irradiation. ".
Maybe some sentences I wrote are misleading (I'm not a native english speaker). Insolation in my language relates only to beam radiation - and that I have used above.
Do you think I should change
"1)measure the total solar power on your collector." to "1)measure the solar power on your collector from direct irradiation."?
and
"4) Measure the hours of water warming/electric energy generation along the year." to "Timing of beam irradiation"?
to be more precise?


Returning to Lund paper.
The app is intended to find best orientation of the panel. Only first component plays a role as orientation dependent.
I do not see how heat loss or thermal capacitance may strongly depend on collector orientation.

Some of you asked for a comparison of app calculation with , say PVatts.
I have chosen obstructionless environment (that PVatts is only able to calculate online).
I have choosen Egipt location and horizontal panel orientation.
The location is chosen intentionally in order to lower the dependence on weather statistics and increase the relative effect of diffuse irradiation.
kWh per day of solar irradiation are listed starting from January up to December.

ScanTheSun PVatts relative difference
(direct) (direct,diffuse, weather)

3.6 4.43 18%
4.7 5.33 11%
5.9 6.4 7%
7.1 7.31 3%
7.7 7.4 4%
8.0 8.03 0.3%
7.9 7.9 0%
7.4 7.58 2%
6.5 6.8 4%
5.2 5.7 9%
4.0 4.8 16%
3.4 4.16 18%

The relative difference - on the average - on the level of 10%.
Ernest.

[sensij]

The app calls ScanTheSun
with which you can

1)measure the total solar power on your collector
2)measure the solar energy loss in the shade
3)measure the best collectors orientation considering surrounding obstacles like trees and buildings.
4)Measure the hours of water warming/electric energy generation along the year

One of the most informative and openly accessible material on how to treat different factors for output power assesment You can find on the web is from Lund University:

http://www.ebd.lth.se/fileadmin/energi_byggnadsdesign/images/Publikationer/Bok_EBD-T-04_1_web_Anna_H.pdf

Please take special care on equation 7.1. The only component sensitive to panel angle (theta) is the first one and relates to beam (direct) irradiation.
Since ScanTheSun aims to help in proper panel orientation - only the beam irradiation component will be included (basing on IAM data) in the the next release of the app in Spring this year.

Based on what you've described in this thread, it appears that, at best, you are able to meet item (3) of the stated goals of the software, and maybe a bit of item (2). Items (1) and (4) require the full solution of Eq. 7.1 of your citation, along with supporting data to estimate each of the parameters of that equation. It is seriously misleading to suggest that the software in its current or near-term state could hope to meet either of those goals.

[J.P.M.]

I would respectfully suggest you consider withdrawing this application from public use until you get a better working knowledge of applied solar energy and provide something better.

From what I've seen of it and from what you have written, I'm pretty sure both this attempted application and your working knowledge of applied solar energy are not ready for prime time just yet.

I've seen better undergraduate projects than this. Maybe it has some use as a shading tool, but the rest of what I've seen of it is pretty amateur and borderline nonsense.

I'd never recommend its use in its current form. I suspect others more knowledgeable than I would say the same and have a similar opinion to mine.

Respectfully,

J.P.M.