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Climate & Irradiance

 

The "Climate & Irradiance" window allows you to construct the climate model of your particular site in a few minutes. After you adjust the climate model, you can transfer it to the scene window and save in a scene file. From this moment the climate model of your site will work automatically in all your sessions with other "solar" windows, and Shadow Analyzer will take care of all the complex dynamical calculations of the irradiation of your static or sun-tracking solar collectors including the shading effects. 

 

Key questions for your orientation

 

Why to use a model of solar radiation, instead of to use the solar data itself?

 

To answer this question, we need to explain the main idea of our approach that seems a little bit strange at a first look. Really, why to use a model that calculates solar radiation, instead of to use the solar data itself? And why to search for the additional atmospheric data, when we have the ready to use solar data? 

 

In general, we need a model of solar radiation instead of a fixed data set, because we need to transform and recalculate dynamically the solar data measured on horizontal and normal surfaces into the irradiation of any arbitrary oriented collectors. So we need a model (an algorithm, a procedure) in any case. And this model should to be based on physics of known processes instead of pure solar statistic.  

 

The question is: what should be an entry point of such a model, and what data types are required? Then some known problems with the available solar databases come to a scene.

 

We expect that our users will experience problems just due to the lack of the sufficiently detailed and uniformly represented solar databases. The geography of our actual already registered customers is rather wide. They are living on different continents in so different countries like USA, Uruguay, Germany, Italy, Greece, Israel, China, Australia, etc. The available local databases vary by durations of solar statistic, lists of parameters, and data formats. Most of simple solar databases contain only monthly sums of global solar radiation (or daily sums for average days of the months).

 

Therefore, we propose you to construct your own climate model (a kind of a climate database) of your particular site, composing it flexibly from available sources of information. Just the input data of 12 partial Bird models of the "Climate & Irradiance" window together with 12 monthly probabilities of clear sky and 12 correction coefficients for the diffuse radiation constitute such a database. The input and output data exchange their roles in this approach: instead to enter the solar data directly into the model, you use them as a reference data, trying to adjust the model so that it will be able to generate the solar characteristics of a given site.

 

This model is more flexible than a fixed data set. If you have solar data of your site, but do not have some input data for the climate model, you can consider such input data as the abstract adjustment parameters, thinking of the climate model as an "black box" that will work relatively realistic after you adjust it so that it generates the solar radiation similar to your site statistic. The more types of solar data you have, the more adequate the model will be.

 

The integration of the Bird model into the climate model (that in its turn is integrated into the "Solar Day" and "Solar Year" windows) is itself a substantial improvement of the calculation algorithm, while the tuning of the partial Bird model parameters leads to the improvement of the second order members. What is more important than the Bird model tuning is to make a minimal realistic setting for the monthly probabilities of clear sky (using the distribution of sunny hours by months as a reference data). This setting regulates the relative energy weight of the direct radiation. It is important, because the energy losses associated with the shading are connected with the direct radiation, and occur just within the sunny but not within the cloudy time intervals.

 

Although the first search for an appropriate database take time, the work with the "Climate & Irradiance" window itself takes only a few minutes due to the convenient user interface. After you adjust the climate model, you can transfer it to the scene window and save in a scene file. From this moment the climate model of your site will work automatically in all your sessions with other "solar" windows.

 

So the main advantage of the climate model is that you can adjust the model only by a few key data arrays from a simplest solar database, and then Shadow Analyzer will take care of all the complex dynamical calculations of the irradiation of your static or sun-tracking solar collectors including the shading effects.      

 

How reliable is to use the default Bird model settings for the shading calculation?

 

The usage of the default settings for partial Bird models often is enough for many practical cases of the shading evaluation, especially when you compare different variants of your collector system ranking them by the grade of the shading. The worse variants will remain to be worse practically under any Bird model settings.

 

However, the final percentage of the shading is sensitive to the variations of the atmosphere transparency, because the energy weight of shadows is proportional to the energy weight of the direct solar radiation. Therefore, it is better to consider the balances not only for the global horizontal radiation but also for the direct radiation on the normal surface. If the corresponding reference data are available, you can use the broadband turbidity as the adjustment parameter to refine the monthly balances of the direct component. Do it in an iterative manner adjusting simultaneously the broadband turbidity of the partial Bird models of clear sky and the correction coefficients of the diffuse radiation.

 

Can one use the "Bird" and "Climate" windows for free for the educational and research purposes?

 

Yes. You can use the "Bird" and "Climate" windows for free for the educational and research purposes. These options are fully functional and publicly available in the time-unlimited free Trial version of Shadow Analyzer. Download the Trial version of Shadow Analyzer from our Website. Copy the following string into the address bar of your Internet browser:

 

http://www.drbaumresearch.com/Dnld/Shadow_Analyzer_TW_Setup.exe

 

The "Bird Clear Sky Model" and "Climate & Irradiance" windows are working together with the "Solar Table" window in the Trial version exactly so as they do it in the full version of Shadow Analyzer. So you can learn the behavior of the solar radiation inside the atmosphere, set the climate profile including the monthly probabilities of clear sky for a site on any geographical latitude, and calculate the daily sums of direct and diffuse solar radiation for fully sunny and mean cloudy days over the year. The calculated values are displayed in the "Solar Table" window, and you can copy them into a text document or insert in an Excel table for further numerical analysis.

 

The "Climate & Irradiance" window

 

With the "Climate & Irradiance" window, you can set the climatic characteristics of your site, which include the Bird model parameters for the clear sky radiation (individually for each of 12 months of the year), 12 values of the monthly probabilities of the clear sky, and 12 values of the correction coefficients for the diffuse radiation at the mean cloudiness condition. The window has also its own parameter "Latitude", that is independent from ones of the 3D scene views.

 

If you do not have enough information to set all the parameters of the Bird model for your particular site, use the default settings for the unknown parameters. However, you need to know at least the monthly probabilities of the clear sky of your site (or average amount of sunny hours by months) to calculate the realistic annual energy yield of your solar collectors. 

 

You can select / change the climatic parameters of the "Climate & Irradiance" window using the arrow keys of your keyboard when the window is active. To select a parameter, use the LEFT / RIGHT arrow keys. On the page 1 of the window, you can use also PAGE UP / PAGE DOWN keys to jump from one to another parameter group. The selected parameter is marked by a yellow background. You can change the selected parameter using the UP / DOWN arrow keys.

 

Once the climatic parameters are set (or one of them is changed), the "Climate & Irradiance" window recalculates the daily, monthly, and yearly sums of several components of the solar radiation at the ground level. It shows also the sums of the extraterrestrial solar radiation (out of the atmosphere).

 

The sense of your work with the "Climate & Irradiance" window is to construct a realistic general climatic model of your site to use it further for the analysis of the energy characteristics of your particular collector system. The main criteria for this task is the yearly balance of the total solar irradiance on a horizontal surface -- the yearly sum of Tot_H in kWh/m2 per year.

 

The "Climate & Irradiance" window is independent of any other window. It has its own set of the climatic parameters. And each 3D scene also has its own climatic record of the same structure. The "Climate & Irradiance" window does not react automatically on any changes that occur in 3D views or in other "solar" windows. Also other windows do not react on the parameter settings of the "Climate & Irradiance" window. To use the "Climate & Irradiance" window together with your 3D scenes, you can call a notification dialog for the data exchange between different windows.

 

The direction of the data exchange depends on which the window is active:

 

 

 

The climatic information is a part of the scene record like any other scene parameters. It is updated in the dynamic memory of the scene immediately after the transfer. Later, when you save the scene, the climatic information will be saved in the scene file too.

 

 

So you can use the "Climate & Irradiance" window as an intermediate data storage for the exchange of the climatic data between scenes. In this case, it is useful to use key "L" to lock the window. The locked window prevents the occasional changing of the input parameters. If the window is locked, you can change the parameter settings only through the data transfer dialog, retrieving them as a whole from a scene window or from the "Bird Model" window. 

 

A typical sequence of your work

 

The process of your work with the "Climate & Irradiance" window looks in general as follows.

 

For the beginning, you can left the default Bird model settings that are displayed on the page 1. You start from the page 2, where you set the latitude of your site, and adjust the monthly probabilities of the clear sky. Shadow Analyzer reacts on your actions very quickly, recalculating energy balances of the direct, diffuse, and total (global) solar radiation on a horizontal surface. It calculates also the income of the direct radiation on the normal sun-tracking surface. Just the balances of the global solar radiation on a horizontal surface are published in the solar radiation databases most often. So you need  to meet the monthly balances at least for the global solar radiation. To meet the yearly balance is also important, because it impacts the main characteristics of your system, its annual energy yield. It is a good sign, if you nearly meet the balance at this first step (with the default Bird model settings).

 

Than you go to page 1, and enter those Bird model parameters, which you are able to get from different information sources. For example, you can easily find or simply calculate the site pressure, which depends mostly on the elevation of the site above the sea level. See also the final section "How to set the Bird model parameters" of the previous topic Bird Clear Sky Model.

 

Then you go to the page 3, where you can adjust the correction coefficients of the diffuse radiation, trying to refine the balance.

 

Note that if you try to meet simultaneously two or more balances (for example, at once for global and direct radiation), you need to work iteratively adjusting simultaneously a few parameters. If it is difficult to meet all the balances, try to find an equilibrium point, where the differences between the model results and the site statistic are minimal. Do not be confused by such a situation: working with the statistical variables, remember that average values do not necessarily follow the relationships between momently values -- we can expect only an approximate correlation between them.

 

After you adjust the climate model, you can transfer it to the scene window and save in a scene file.

 

Pages

 

The window has the following pages:

 

1. Extraterrestrial solar radiation and input parameters for 12 partial Bird models 

2. Light day duration

3. Daily sum

 

To switch pages, use the keyboard keys "1", "2", "3", or the right mouse click, when the window is active.

 

The argument of functions of all pages is the same: day of the year (from 1 -- January 1, to 365 -- December 31).

 

To see the numerical values of the calculated function curves, use the "Solar Table" window.

 

Switch window modes with keys "L", "M", "V"

 

 

The locked window (when "L" shows "locked") prevents the occasional changing of the input parameters. If the window is locked, you can change the parameter settings only through the data transfer dialog, retrieving them as a whole from a scene window or from the "Bird Model" window. However, in both "locked" and "unlocked" states, you can move the position of the yellow background that marks the selected parameter.

 

In the "constant month" mode  (when "M" shows "flat month"), all the monthly input parameters stay the same within the corresponding months, while the calculated solar radiation can vary even in this mode due to the permanent changing of the Sun path from day to day. The "constant month" mode is useful when you need to interpret experimental data of a particular day.

 

In the "month spline" mode (when "M" shows "climate spline"), all the monthly input parameters are parabolically splined. Each spline is constructed so that it keeps the average monthly value of the input parameter same as its displayed numerical value. However, sometimes the spline with such a property cannot be constructed. It occurs when the numerical setting is near the upper or lower boundary of its allowable range. Then this parameter stays to be constant within this particular month. Note that splines are applied only to the input parameters and before the calculation of the solar radiation curves, which themselves are not additionally splined. It allows to obtain the same monthly sums of the solar radiation in both "constant" and "spline" modes, what is important when you adjust the climate model to meet the balances corresponding to your site statistic.

 

The switch "V" between "100% clear sky" and "mean cloudiness" modes affects only the daily sums of solar radiation that are represented graphically by curves on the page 3. It does not change the values of monthly sums that are displayed numerically, and that are calculated always under "mean cloudiness" condition.

 

Note in advance that "Solar Day" and "Solar Year" windows also have their own independent "V"-switches, which have the same meaning. In addition, the "V"-switch of the "Solar Day" window has the third "random clouds" mode, which simulates the variable cloudiness within one particular day by a random sequence of fully clear and fully cloudy 10-minutes time intervals.

 

Page 1: Extraterrestrial

 

The page shows the variations of the extraterrestrial solar irradiance during the year. It is also the input page for the parameters of the 12 partial monthly Bird models.

 

 

Curves: 

 

 

Curves of the Bird model parameters:

 

 

Depending on the switch "M", curves of the Bird model parameters are splined or constant within each month.

Note that the Wt parameter curve is multiplied by 0.1 to fit the diagram scale (1 cm corresponds to 0.1 scale unit).

 

Parameters are gathered in the numerical table "Set monthly Bird model data" with the following lines: 

 

 

You can select / change the parameters using the arrow keys of your keyboard. To select a parameter, use the LEFT / RIGHT arrow keys. You can use also PAGE UP / PAGE DOWN keys to jump from one to another parameter group (jump from one to another line). The selected parameter is marked by a yellow background. You can change the selected parameter using the UP / DOWN arrow keys.

 

Page 2: Light day duration

 

The page shows the light day durations, and the time intervals for some diapasons of the sun elevation E (above horizon). It is also the input page for 12 monthly probabilities of clear sky.

 

 

The sun elevation above horizon E is the complementary variable for the zenith angle Z, that is E + Z = 90 degrees.

 

Curves:

 

Depending on the switch "M", the curve for the probability is splined or constant within each month.

Note that the Prob parameter curve is multiplied by 0.1 to fit the diagram scale (100% corresponds to 10 scale units).

 

Curves for some diapasons of the E value:

 

 

Parameters:

 

 

 

You can select / change the parameters using the arrow keys of your keyboard. To select a parameter, use the LEFT / RIGHT arrow keys. The selected parameter is marked by a yellow background. You can change the selected parameter using the UP / DOWN arrow keys.

 

The table "Monthly probabilities (%) and sunny hours graded by E" shows (in the lines after its first line) the total number of hours in a month when the sun is higher than 0, 15, 30, 45, 60, and 75 degrees above the horizon. 

 

The table "Average days: sunny hours and Tot_H sums kWh/m2" shows the characteristics of "average days" for each month. Just these characteristics are most often published in the solar radiation databases. The first line shows the calculated amount of the sunny hours in the average day of a corresponding month, which is equal to the average light day duration multiplied by the probability of clear sky. The second line shows the average daily sums of the total solar radiation on a horizontal surface Tot_H, that is calculated taking into account both the probability of clear sky (which you set on the page 2) and the correction coefficient for the diffuse solar radiation (which you set on the page 3). So this line is also shown on the page 3.

 

The line below the title "Yearly probability (%), sunny hours, and Tot_H sum kWh/m2" shows the corresponding yearly values of the probability, sunny hours graded by E, and Tot_H.

 

Note that the switch "V" between "100% clear sky" and "mean cloudiness" modes affects only the daily sums of solar radiation that are represented graphically by curves on the page 3. It does not change the values calculated for "average days" that are displayed numerically, and that are calculated always under "mean cloudiness" condition.

 

Page 3: Daily sum

 

The page shows daily, monthly, and yearly sums of the different components of solar radiation. It is also the input page for 12 monthly correction coefficients for the diffuse solar radiation.

 

 

Curves: 

 

Depending on the switch "M", the curve for the correction coefficient is splined or constant within each month.

Note that the Dcs parameter curve is multiplied by 10 to fit the diagram scale (1 corresponds to 10 scale units).

 

Curves for the different components of solar radiation:

 

 

Parameters: 

 

 

 

You can select / change the parameters using the arrow keys of your keyboard. To select a parameter, use the LEFT / RIGHT arrow keys. The selected parameter is marked by a yellow background. You can change the selected parameter using the UP / DOWN arrow keys.

 

The table "Monthly Dcs-corrections and sums kWh/m2" shows (in the lines after its first line) the monthly sums of the following components of solar radiation Dir_N, Dir_H, Dif_H, Tot_H, and Ext_H in kWh/m2.

 

The table "Average days: Tot_H sums kWh/m2" shows the characteristics of "average days" for each month. Just these characteristics are most often published in the solar radiation databases. Namely, it shows the average daily sums of the total solar radiation on a horizontal surface Tot_H, that is calculated taking into account both the probability of clear sky (which you set on the page 2) and the correction coefficient for the diffuse solar radiation (which you set on the page 3). So this line is also shown on the page 2.

 

The Line "Yearly sums kWh/m2" shows yearly sums of the following components of solar radiation Dir_N, Dir_H, Dif_H, Tot_H, and Ext_H in kWh/m2.

 

Note that the switch "V" between "100% clear sky" and "mean cloudiness" modes affects only the daily sums of solar radiation that are represented graphically by curves on the page 3. It does not change the values calculated for "average days" and for yearly and monthly sums that are displayed numerically, and that are calculated always under "mean cloudiness" condition.

 

Note that we show also the extraterrestrial solar radiation Ext_H in both the "Bird" and "Climate" windows. This variable is useful for some research purposes, because there is a correlation (known from the solar radiation statistics) between two values D = <Dif_H> / <Tot_H> and T = <Tot_H> / <Ext_H>, where brackets < ... > mean the averaging over a daily or monthly interval. The function D = f(T) helps sometimes to verify or correct data from solar databases, or to reconstruct the unavailable data of direct solar radiation.