Which is fine as long as not too many private households sell electricity back to the grid. Not only are there the issues @feld mentions, the more general problem ist that (at least in Europe where I live) the various grid systems are top-down and in need of constant balancing:
• Transmission grids (high voltage 220kV or 380 kV) large distance transportation of electricity
• Distribution grids: transports electricity at high (60 kV to 220 kV), medium (6 kV to 60 kV) and low voltages (230 V or 400 V).
In this top-down structure voltage has to be transformed down from higher voltages to lower voltages.
Usually, homeowners with their solar-to-grid installation feed their electricity at the lowest voltage back into the grid. In order to counter fluctuations in the number of feeding sources as well as their quantities of electricity, the net stability has to be guaranteed by re-dispatch: shutting on and off of various feeders and consumers under the primacy of keeping the net frequency constant (otherwise there will be brown-outs with large sections of the grid shutting down). Every re-dispatch costs a lot of money (which has to be paid by all consumers) and endangers the net stability. And the more households feed back their electricity into the grid, the more instable the net and the more expensive its balancing becomes.
Current grid and net structures can accomodate for up to 30% electricity from renewables. Otherwise, due to fluctuation, net balancing becomes so difficult and expensive that brown-outs become frequent. Adding household-to-grid (e.g., via private solar) or vehicle-to-grid (via car batteries) endangers the overall supply with electricity and increases the electricity prices for industries.
Also not to be ignored: The cost for the re-dispatches to keep the net frequency stable is paid by all consumers. That is: Those who sell their electricity back to the grid can only do so because others pay more for the costs that arise from keeping the net stable than what the feeders pay.
I thus would be very careful to cheer any "down-towards-upwards" feed of electricity. The #infrastructure is not there for such "localized" electricity "production".
simsa03
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