Solar energy in progress and future research trends

Triple solar irradiation estimation model

In the triple solar irradiation estimation (TSIE) procedure the vertical Cartesian axis is allocated for sunshine duration ratio and the horizontal axis is for the relative humidity. The contour lines are then drawn for the solar irradiation ratios as

dependent variable. Both solar irradiation and sunshine duration ratios vary between 0 and 1, because they are expressed as ratios to astronomical solar irradiation amounts during cloudless and without atmospheric chemical com­ponents, i. e. with clear and ideal atmosphere situations. It is known that astronomical solar irradiation and sunshine duration values are the maximum ideal quantities ever possible, but the natural counterparts are smaller than these values. In a way, all the TSIE graphs are dimensionless and rather standard with solar irradiation variable values confined to 0-1 interval. The contour lines of solar irradiation might be drawn at each 0.2 intervals. A representative TSIE graph is presented in Fig. 21. The following general interpretations can be drawn from such a graph.

1. variation of solar irradiation with joint variation of sunshine duration and humidity,

2. solar irradiation variation with sunshine duration for any given level of relative humidity,

3. solar irradiation variation with relative humidity for any given level of sunshine duration value,

4. solar irradiation maximal occurrences at relative humid­ity and sunshine duration values,

5. variation of solar irradiation for any combination of sunshine and relative humidity combination,

6. nearly clear weather condition depiction based on sunshine duration and relative humidity values,

7. nearly overcast weather condition depiction based on sunshine duration and relative humidity values,

8. average and standard deviation values of solar irradiation for given ranges of relative humidity and sunshine duration, and hence, it is possible to obtain the arithmetical average and standard deviation variations of solar irradiation by sunshine duration and relative humidity values. This is very helpful in deciding the error limitations concerning upper and lower boundaries in any solar irradiation estimation, and

9. by making use of the previous step one can obtain estimation of solar irradiation for a given pair of sunshine duration and relative humidity value.

The TSIE graphs may be prepared for different time periods such as hourly, daily, weekly and monthly. Comparison of two or more TSIE graphs at different locations help to identify climatic features. On the other hand, it is possible to extend the concept of TSIE graphs by considering other meteorological variables instead of relative humidity such as temperature or pressure. Hence, it is possible to assess whole the available meteorological variable effects and to derive necessary interpretations for the solar irradiation characteristics at a site.

The TSIE graphs are distinct from the restrictive set of assumptions and readily available for linguistic interpret­ations prior to any quantitative estimation procedure. These graphs help to make preliminary fuzzy logic rule bases.