Composite building energy-saving system utilizing rainwater and light energy and using method thereof

The invention discloses a composite building energy-saving system utilizing rainwater-light energy and a using method thereof, and the system comprises a reservoir which is arranged underground and is used for collecting rainwater; the solar panel system is used for storing and heating water; the heater is used for heating the passing water; the heat transfer pipe is arranged in the wall surface and the ground and is used for introducing liquid to exchange heat with the interior of a room; the pipeline system is respectively connected with the reservoir and the solar panel system, the solar panel system and the heater, the heater and the heat transfer pipe, the heat transfer pipe and the reservoir, the reservoir and the heater, and the heat transfer pipe and the solar panel system; in the cooling mode, water is introduced into the heater from the water storage tank, then is introduced into the heat transfer pipe and then flows back to the water storage tank, and the heater is in a heating stopping state; in t