Using solar energy, for example, I am told that excess energy can be sold back to the grid. How does this exactly work? Maybe I am a bit confused due to thinking about the analogy of water pressure / flow rate in a pipe network being similar to voltage / current in an electrical network. If your home generated excess energy, how would it overcome the high voltage / current of the grid?
In: Engineering
The relationship that transfers energy to the grid has more to do with the idea of frequency and “torque” than voltage. Yes, the voltage needs to be matched, but that isn’t what is adding power to the grid.
Solar converts energy to DC power, which is converted by an inverter into AC power which can be added to the grid.
For any kind of electricity generator, before it can be attached to the grid, you must sync up the frequency of AC current between the generator and the grid (as well as the voltage). Once in sync, this is like a bike rolling down a hill at a steady pace. It doesn’t speed up, and no power is added to the system.
After the two are in sync, you can increase the speed of the inverter frequency, which “pulls” the grid speed. Since the grid speed has a much higher “inertia”, it doesn’t change, but that energy has to go somewhere, so it is transferred to the grid as power.
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