Energy Balance
Potential Energy = Kinetic Energy
Potential Energy - Kinetic Energy = Zero

Energy generating systems take some form of Potential Energy and convert it into useable Kinetic Energy.
A car takes Chemical Potential Energy in the form of gasoline and converts it into a useable form of energy rotating the tires so you can go somewhere.
What you do not see happening in the energy system is the heat energy leaving into the atmosphere and exhaust and  the slipping of the gears also wasting some of the gasoline energy.
Hybrid Cars we have a car with 2 forms of Stored Potential Energy; 1) The gasoline in the tank; 2) The electricity in the batteries.

Did you know that your Hybrid Car not only uses energy it recovers energy as well?

When you start braking when your car is moving the motor switches from spinning driven by electricity to spinning because the wheels are still moving and generating electricity to put back into the batteries.
This is called Regenerative Braking.
Electric Locomotives have been doing this for years.

We regenerate compressed air energy.
Here is what our Energy Balance looks like;
Potential Energy Stored in Compressed Air                                :            4,608,000 Joules
Potential Energy Stored in Compressed Air                                :            1.28           kWh

Potential Energy Stored in Falling H20                                       :            3,868,570 Joules
Potential Energy Stored in Falling H20                                       :            1.07           kWh

Total                                                                                            :             8,476,570 Joules
                                                                                                     :             2.35           kWh
Kinetic Energy Required to Move H2O                                      :            5,943,168 Joules
Kinetic Energy Required to Move H2O                                      :            1.65          kWh

Kinetic Energy Required to Recover Compressed Air Energy    :               714,240  Joules
Kinetic Energy Required to Recover Compressed Air Energy    :            .20             kWh

Kinetic Energy Entropy to Create Compressed Air Energy         :            1,112,943 Joules
Kinetic Energy Entropy to Create Compressed Air Energy         :            .31             kWh

Kinetic Energy Available for Ancillary Operations                     :               706,219  Joules
Kinetic Energy Available for Ancillary Operations                     :            .20             kWh

Total                                                                                            :             8,476,570 Joules
                                                                                                    :             2.35           kWh