The energy efficiency represents the things you can do with some amount of energy, and if you can do more with less, than it reduces the energy consumption.
Explanation:
The answer to this question is actually very simple. Imagine that you use only the half of the energy you produce, an efficiency of 50%. Lets say you need 5kJ, so you would need to produce 10kJ, because you can consume only the half. Now, imagine you increase the efficiency, you use exactly what you can generate, (efficiency of 100%). In this case, if you needed only 5kJ you would need to generate only 5kJ.
