In the city energy consumption page https://virtonomics.com/mary/main/globalreport/energy/city there are three columns on the right: regional powergrid cost, share of players cost and share of players percentage. For the cities with 100% players share, the regional power grid cost is 0. Does that mean the city's energy need is completely satisfied by private power plants? From the regional energy consumption page https://virtonomics.com/mary/main/globalreport/energy/region I see that in many regions, even though each city in those region is 100% privatized, the regional shares of private supply is still very low. Is it because a regional power grid exist separately from city grid and is not the sum of city grids? If every city's need is completely met, is there still demand from the regional grid?
Yes. Share of Players=100% means every subdivision runs on private grid. However citizens also need some energy to live, which city council buys from region. That's where the difference comes from.
Production unit use regional energy or corporate or company. About city energy, this is energy for rented units (like shop or office) and perhaps goverments and citizen.