You can build systems where unused power can be returned to the power source - take regenerative braking in EVs for example. This helps prevent the unnecessary loss of power, and can substantially reduce consumption.
However, you will never return 100% of the energy you extracted back to the power source. The energy used for work can't be returned because you just transferred it somewhere else! Plus, you'll lose energy to heat.
En_TioN t1_ja6ou05 wrote
Reply to comment by Flapflapimabird in eli5 perpetual motion is impossible but why haven't we made something that just goes on for a really long time that we then service so it can keep going? by FrozenKyrie
You can build systems where unused power can be returned to the power source - take regenerative braking in EVs for example. This helps prevent the unnecessary loss of power, and can substantially reduce consumption.
However, you will never return 100% of the energy you extracted back to the power source. The energy used for work can't be returned because you just transferred it somewhere else! Plus, you'll lose energy to heat.