Electricity generated at power plants is collected in one place and sent to homes by Tokyo Electric Power Company and other companies. Therefore, the electricity generated by solar power, biomass, etc. is not delivered directly to your home.
Minna Denryoku has a system in place where a portion of the electricity rate you pay is sent to the power plant.
In addition, by "supporting a power plant," 100 yen from your electricity bill will automatically be sent to the power plant as a donation.