The expected global warming and rapid population growth associated with limited traditional energy sources have put pressure on governments everywhere in the world. In this regard, this research investigated the behavior of solar energy in the heat storage tank. The study aims to find a solution for energy shortage by increasing solar energy share in heating the solar systems' storage tank. As an arid region, Egypt has high solar radiation throughout the country, which is a promising way to be an alternative energy source. The research investigated the potential of storage tanks for storing solar heat energy over the daytime to use it over inactive periods (night time)—the experimental study was conducted from 18 to December 22, 2018, using a thermosyphon evacuated solar collector. The obtained results showed that the maximum increase of storage tank temperature was 3.7 °C during an hour in daylight.Furthermore, the maximum heating storage tank temperature was 69.9 °C throughout the whole day. The values of solar radiation ranged from 200 to 1200 W/m2 during the experimental period. The heat values in the storage tank were 0.952, 1.072, 3.175, and 1.406 kWh recorded on the 18th, 19th, 20th, and 21st of December. The average heat losses from the storage tank during these days were 0.628, 0.631, 0.637, and 0.565 kWh. These small amounts of heat could be a result of keeping the same amount of water inside the tank was over four days. Consequently, the reliability of heating water by this collector and availability to store heating water were achieved to the level requirements.