@AstonJ Selling back to the utility company is a legitimate thing and can offset a customer’s cost. A lot of people do this exact thing when they put solar panels on their roof. The majority of the time the home isn’t using enough power at the time that energy is being produced by the panels so that electricity needs to go somewhere. It either needs to be absorbed by some kind of energy storage system at the home (such as a battery) or it will be pushed back onto the grid. It WILL flow somewhere. In the case of this generator, it would be producing at night when most people are asleep so selling back to the utility makes some sense.
With the example of that turbine in that video, the grid would never really notice 500W being pushed back onto the grid. The grid is just so much more powerful that this amount would just be absorbed with no one noticing. The problem comes in when the pushback onto the grid becomes “too much”. When this happens, it can cause voltage and frequency instability that can affect people in very negative ways.
In one example, pushing “too much” back onto the grid can cause the voltage on the grid to rise. Since W = Volts * Amps * cos(theta), higher volts means the watts that you consume increases which causes bills to go up without changing any usage patterns. Just think if your neighbor had a huge solar array on their house pushing back to the grid. If that electricity flow wasn’t managed correctly, your bill could go up without you doing anything just because your neighbor had solar panels.
Another example is protection settings. The grid is designed that when faults happen, devices like breakers and reclosers (basically a type of switch) are programmed to open to protect people from getting hurt or killed. If “too much” is being pushed back onto the grid without it being managed properly, these breakers and reclosers may never see a fault and keep the circuit “hot” putting people and property at risk of electrocution.
Right now, there are several people working on this problem of managing this “reverse” power flow from devices like this generator and solar panels. We just have to make sure that it is managed properly so we don’t cause more problems than we are solving. We want everyone’s lights to stay on. 