The present study investigates the possibility of energy saving during the spring period in a conventionally heated greenhouse, using an innovating hybrid solar energy saving system. The greenhouse was divided in two equal parts (experimental and control), where tomato plants were cultivated hydroponically. The control part of the greenhouse covered the heating requirements exclusively by a conventional heating system. The experimental part used the conventional heating system only when the hybrid solar energy saving system could not maintain the greenhouse air temperature above 16°C. The hybrid solar energy saving system was consisted of a transparent cylindrical polyethylene sleeve filled with water and two perforated polyethylene tubes resting on the top of it. Through these tubes, air was pumped in order to inflate them and to be mixed with the greenhouse air. The use of hybrid solar energy saving system led to an energy saving portion capable of decreasing the greenhouse energy cost. Energy saving between the two parts of the greenhouse was recorded to be 36% from March to May. It has been also calculated that the oil consumption was significantly decreased in the experimental part and for the whole experimental period was 149.08 l, while in the control part reached 233.03 l. The application of this system contributed to smoother variation of the greenhouse air temperature and the rockwool slabs temperature, leading up to a better plant growth.