ANALYSIS OF SOLAR RADIATION CHANGES IN LARGE CITIES OF
UKRAINE IN THE SUMMER PERIOD

Solar energy is the cleanest and most common renewable energy source. The solar energy market today is almost 103 gigawatts (GW). According to the International Energy Agency (IEA), about 125 GW of solar energy is produced in the world. In Ukraine, the average annual amount of total energy of solar radiation ranges from 1,070 kWh/m? in the northern part of Ukraine to 1,400 kWh/m? and above in the Autonomous Republic of Crimea. Along with a fairly large number of works devoted to the components of the radiation balance, research is mainly conducted to study their spatio-temporal distribution over the territory, and in Ukraine, the main source of data remains the few weather stations at which relevant observations are made.

This exploration uses data from surface observations and reanalysis data. In particular, the surface observation data were taken from the Borys Sreznevsky Central Geophysical Observatory. Reanalysis data - from the European Center for Medium-Range Weather Forecasts, ECMWF [http://www.ecmwf.int/en/research/climate-reanalysis/era-interim].

For the exploration, 5 large cities of Ukraine were chosen, which highlight different parts of the country - Kyiv, Kharkiv, Lviv, Dnipro and Odesa.

Validation was carried out on surface observation data using data covering the period 2008-2020. An exploration of the temporal distribution of direct, diffuse and total solar radiation was carried out on reanalysis data covering the period 1991-2020.

For each city as a whole, for the summer and for a single month of the season, the values of direct, diffuse and total solar radiation were obtained according to the reanalysis data. The minimum and maximum values that occurred are determined. For each city, a general trend for the summer as a whole and separately for June, July and August was obtained.

It was found that the reanalysis tends to underestimate diffuse and overestimate direct solar radiation. According to the reanalysis data, the changes in diffuse solar radiation are insignificant in terms of values for all cities, in terms of the actual direction of changes - for Kyiv, Kharkiv and Lviv, in Dnipro and Odesa at the end of the studied period there is a tendency for it to decrease. In general, these conclusions are confirmed by the data of surface observations, with the exception of Kyiv (for all summer months), as well as for June in Odesa and Lviv, where an increase in its values is observed at the end of the studied period. The largest fluctuations (both according to surface observations and reanalysis) occur for direct solar radiation and, as a result, appear in the amount of total solar radiation. In general, for the summer period in all five cities, there is a tendency to a slight increase in the amount of total solar radiation.

Keywords: solar radiation, surface observation, reanalysis, summertime, climate change