CEB can purchase solar generated energy at 10 Rs/kWh from large scale solar power projects. With that opportunity in hand, there is no point paying 22 Rs/kWh for roof top generated solar. By continuing this, the loss of CEB will further increases, it is more like giving free money or Samurdhi. Also, large scale plants allow real-time control of power flow to the grid by system control center. One of the reasons, for taking too much time to restore the last blackout was also rooftop generated solar. That's why CEB discourage rooftop solar and focuses on large scale scale solar.
