This is one of those questions that is best answered as "it depends." If a satellite outside the Earth’s atmosphere were to aim a flat plate at a right angle to the sunlight coming toward it, the amount of solar energy striking that flat surface would be 1,367 Watts per square meter (abbreviated W/m2), if you measure it as a light energy source.
This number is called the Solar Constant and is a measure of the amount of power available from the sun (745.7 W = 1 horsepower). If this energy is considered in terms of heat content, the Solar Constant can be stated as 442 British thermal Units (Btu) per square foot per hour (or 4773.6 Btu/m2/hr since one square meter contains 10.8 square feet).
While a vast amount of solar energy strikes the Earth’s atmosphere, not nearly so much can actually be captured for use at the Earth’s surface. Once solar radiation starts passing through Earth’s atmosphere, much of it is either scattered as it bounces off air molecules, water and dust, or it is absorbed into ozone, water and carbon dioxide molecules. This absorption of solar energy by molecules in the atmosphere is why we feel cooler when a cloud comes overhead and casts a shadow.
Provided below are tables that show how much solar energy is available for use, on average, in Missouri. While data for four different locations are provided, the fact is that very small differences in actual values exist from one location to another. This information can be used to calculate an estimate of how well your energy needs can be met using solar energy. We have included some explanatory information at the end of each table to clarify the use of that data.
The data provided for Columbia (16K), Missouri are called primary data, which means that actual solar insolation data was collected in the immediate Columbia area. Kansas City (15K), St. Louis (15K) and Springfield (16K) data sets are secondary data sets, meaning the values for these three towns were developed by extrapolating the data from Columbia, based on certain weather data values, such as cloud cover, that were different for these three towns versus Columbia’s conditions. The data presented in these tables comes from the Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors, 30-Year Average of Monthly Solar Radiation, 1961-1990.