Diffuse Fraction Model Parameter Estimation

We have constructed software in Excel to allow a user to input a set of solar radiation data, global, direct and diffuse and construct their own diffuse fraction model. This will allow the user to determine their own parameter estimates if they have a set, albeit small, of radiation data. They then can apply their model to infill when there is missing data for their location, or to estimate diffuse radiation for a location nearby. The appropriate file is Diffuse_ modeLxls. Following is a set of instructions for using the software:

1. Open the Excel file – you will be accessing a sheet called Data. It is here that you will run the macro to organise the data. Note that you will have to be able to activate the macros embedded in the file. However, beforehand you will have to copy your data into the sheet RawData under the format given in the file SurfaceSolarFormat. pdf.

2. By clicking on the button Data Collect, you will run the software. You will be asked to enter the number of days of data you have, and then the latitude and longitude, both being the absolute values of these quantities. After this has run, you will have a number of rows of data, all sorted so that there are no rows for before sunrise or after sunset.

3. Highlight the data (not the titles), and copy it to the sheet (starting in row 10) you wish to use for estimation, either Single Predictor or Multiple Predictors.

4. In cell U6 on Single Predictor or U7 on Multiple Predictors, you will have an objective function. You will be invoking the optimisation tool in Excel, called Solver, to perform a least squares optimisation to find the best estimates of the parameters to minimise the sum of squared deviations between your model and the data. Before you invoke Solver, you must ensure it is available. If you are unsure, go to the Tools menu, and Add-Ins. Make sure the Solver option is ticked. If it isn’t, do so, and it will be added, unless it was not loaded as part of the installation of Excel. You may have to re-install it.

5. You will find that we have set up Solver in each instance to perform the pa­rameter estimation. However, before you begin, you will have to make a slight alteration to the sheet. Since we don’t know how many data points you have, we can’t set everything up. So;

6. Highlight T10:U10 and fill these formulae down to the end of the data. Then, alter the sum in U6 to sum the cells from U10 to the end of the data.

7. Go to the Tools menu and Solver, and hit the button Solve. The parameter esti­mation will be performed.

Updated: August 5, 2015 — 3:25 am