Another important parameter to consider is the time matching of the load and solar energy input. Over the annual seasonal cycle, energy requirements of a building are not constant. For the Northern Hemisphere, heating requirements start around October, the maximum heating load is during January or February, and the heating season ends around the end of April. Depending on the latitude, cooling requirements start in May, the maximum is about the end of July, and the cooling season ends around the end of September. The domestic hot water requirements are almost constant, with small variations due to variations in water supply temperature. Although it is possible to design a system that could cover the total thermal load requirements of a building, a very large collector area and storage would be required. Therefore, such a system would not
be economically viable, because the system would be oversized for most of the
year, i.e., it will collect energy that it could not use for most of the time.