Daily estimated radiation reached to the earth surface in Tehran province-Iran (Case study: Mehrabad weather station)

The solar radiation received by the earth's surface is one of the most applicable parameters that are usable in projects and hydrological, agricultural, meteorological, and climatological modeling. This research suggests different experimental equations to estimate solar radiation in different climates, considering very expensive instruments for measuring the solar radiation received by the earth surface. Solar radiation reached to the earth surface (Rs) is the main source of solar energy. Several models have been proposed for its estimation due to its importance. Furthermore, various applications have been represented based on the climate, which most of them have calculated the average daily solar radiation in a month. This research aims to find a way that calculates the amount of daily radiation during a year. Data of sunshine hours, and the maximum and minimum of daily temperature were used in thirty years (1961-1990). The daily measured (Rs) data in the statistical period of 1981-1985 were used for evaluating the model and controlling the results. In the proposed model, the ratio of genuine sunshine hours to possible sunshine hours (during the day) was used to obtain the coefficients of the model for calculating the radiation reached to the earth surface. Moreover, adding the maximum and minimum root square of temperature caused to rise the estimation accuracy. The model compared with several popular models such as NSE, MBE, RMSE, and correlation coefficient indices and the results showed high accuracy. While the amount of coefficient of correlation in this model is equal to 90%, the correlation coefficient for the Triton, Rietveld, and Yazdan-Panah models is 78%, 76%, and 79%, respectively. The model outcomes showed the highest correlation with the actual amounts of radiation. Therefore, this model can be recommended as a suitable model for estimating solar radiation in this climate.

Keywords:

Solar energy , Radiation , Sunshine hours , Atmosphere , Coefficient of determination