The solar UV radiation coming from the sun is considered as the main source of microbial germicide and environmental sterilization. The objective of this study is to estimate the UV dose amount and time required to inactivate coronaviruses by solar exposure. The published trials on 254-nm UV inactivation dose under ultraviolet light exposure of coronaviruses families and the equivalent microbe in terms of D90 (ultraviolet dose for 90% inactivation), or any other dose or/and genome size was examined and summarized. The mean with its confident interval of the unified D90-254 nm inactivation dose of all trials was assumed as ultraviolet susceptibility of the SARS-CoV-2 (COVID-19) virus. The inactivation dose spectrum (sensitivity envelope) for coronaviruses and equivalent microbes as a function of the UV wavelength equivalent to UVB range (280 to 320 nm) was adopted from literature. The UVB solar measurement intensity at Baghdad's geographical location was used over a year at every fifteen minutes and converted from a lump sum to solar spectrum per wavelength in the range of 280 to 320 nm using a simplified mathematical model. A composite action spectrum was drawn that including the virus sensitivity spectrum normalized to 254 nm, UVB solar measurements spectrum, and inactivation effective dose spectrum for coronaviruses. The area under the inactivation effective dose spectrum was calculated numerically to find the equivalent solar flux. The time required to inactivation SARS-CoV-2 (COVID-19) virus is predicted for each value of UVB lump sum intensity to simulate the time required to sterility the outdoor surfaces at all months within Baghdad geographical station. This work should be useful to provide the decision-makers with a clear picture of the sterilization process management of the outdoor surfaces and curfew timing arrangement.