Assessment of the intensity and flow of straight solar radiation falling onto the horizontal surface of a room

The paper presents the results of experimental studies of straight solar radiation in the Central Chernozem region of Russia. The intensity and flow of straight solar radiation falling onto a horizontal surface of a room were evaluated. Measurements were made of the flow of straight solar radiation on a horizontal surface through a translucent structure. Experimental data were obtained using a high-class measuring device in the period from July 1 to August 1. The measurement results showed an intense wave-like change in the solar radiation flux over 8 hours. The paper describes a method for estimating the intensity and flow of straight solar radiation falling onto a horizontal surface of a room. This method of evaluating daytime radiation allows one to determine the density of the total and straight radiation flux. Using this estimate to calculate solar installations used in the Central Chernozem region, their efficiency will increase by 10%.


Introduction
Renewable energy sources are of interest at all levels of the world community. Renewable energy sources have gained significance in energetics and politics. This is due to the increased interest in the environmentally safe and sustainable energy supply of mankind in the future [1,2].
Accurate prediction and calculation of solar radiation flows falling onto a horizontal surface at a specific geographical point are not possible in practice, since meteorological information is not always available and reliable [3,4]. To calculate the characteristics of solar installations, it is necessary to use the data from experimental measurements of solar radiation parameters in the considered location. The most reliable information is the amount of straight solar radiation falling onto a horizontal surface.
The characteristics of solar radiation are often presented in different ways, but the following information is important for understanding and using solar radiation data: 1) the results of a momentary measurement or for a certain period; 2) the measurement time interval; 3) the measured radiation (straight, diffuse, or total); 4) the orientation of the receiving surface to the cardinal directions; 5) the averaging period (month or day).
Most of the measurements of the incident solar radiation flux include direct and scattered ones and relate to the horizontal receiving surface. Such measurements can be made using thermoelectric pyrometers. They are used to measure the most popular characteristics of solar radiation. The sensitivity of the sensors of such devices does not depend on the wavelength in the spectrum of solar radiation, and they are protected from external influences. In addition, these devices must not be sensitive to the angle of incidence of radiation. Most of these devices allow one to get instantaneous IOP Publishing doi:10.1088/1757-899X/1035/1/012026 2 data series that are not average or integral values. Therefore, data is stored in the device's memory or on a personal computer and integrated graphically.

Problem statement
To estimate the flow of incident solar radiation, you can also use the results of measuring the time during which the solar disk in the sky is visible when the sky is clear. The average sum of total monthly day solar radiation is the most available data on the flows of incident solar radiation falling onto a horizontal surface. Similarly, hourly amount of the total radiation received by the horizontal surface is available. Data from ground-based measurements of solar radiation fluxes made under the auspices of the world meteorological organization are presented in the archives of the World Radiation Data Center. However, it should be noted that the accuracy of the data obtained differs from the corresponding modern requirements, the error of which is from 5% to 20%.
Measurement of solar radiation flows falling onto inclined or horizontal surfaces is important in determining the energy input of solar collectors. For a long time, the traditional unit for measuring the flux density of incident solar radiation was the calorie/cm 2 . Currently, the more familiar unit of measurement is MJ/m 2 or W/m 2 .

Conducting experiments
Detailed data on solar radiation is necessary for calculating the dynamic behavior of solar installations. They are also used to model the long-term operation of installations. In this regard, we measured the flow of direct solar radiation onto a horizontal surface through a translucent structure. The measurements were made using a high-end device from July 1 to August 1, 2019.  The measurement results showed an intense wave-like change in the solar radiation flux over 10 hours. Figure 3 shows the measurement graphs.

Calculations
The state of the atmosphere and its mass changes during the day. The scattering and absorption of incident solar radiation also depend on time. When calculating the flows of solar radiation falling onto a horizontal surface, it is necessary to use the concept of a standard (clean) sky. In [7], Professor of the Massachusetts Institute of technology Hoyt Clark Hottel proposed a method for assessing the flow of direct solar radiation propagating through a transparent atmosphere, which considers the Zenith angle and height of the measurement site. However, the method allows calculations for standard atmospheric conditions and four types of climate. In this case, the atmospheric transparency coefficient for direct solar radiation τb is equal to the ratio of the scattered radiation flux to the flow of the transatmospheric radiation falling onto a horizontal surface and is determined by the formula: where cos z  -the cosine of the sun's Zenith angle [8,9], and is determined by the following formula: cos cos cos cos sin sin where Аthe height of the observation in kilometers. The transparency of the standard atmosphere for direct radiation can be determined for any Zenith angle and any height. As a result, the flow of direct radiation to the normal surface of the beam in a clear sky is determined as follows: where, Gonthe solar radiation flux density, W/m 2 . But to get a total radiation flux falling onto a horizontal surface, it is necessary to estimate the intensity and flow of direct solar radiation in clear sky conditions. In [10], the following empirical relationship was proposed between the transparency coefficient for direct and scattered radiation in a clear sky:  In this case, using formula (7), we find the ratio of the scattered radiation flow to the flow of the transatmospheric falling onto the horizontal surface.

Conclusion
When using this method of estimating and calculating the radiation flux falling onto a horizontal surface for calculating solar installations used in the Central Chernozem region, the efficiency and accuracy of selecting such installations on a real area will increase, which will give a subsequent increase in productivity of up to 10%.