So, What does it mean to achieve 100% renewable grid?
While there is a global move toward increasing the share of low-cost solar and wind electricity in the grid, there is a debate started to explore the impact of achieving a 100% renewable share in the grid. Though there are countries such as Norway, Costarica, Brazil, and Canada, that have a share of hydroelectricity ranging from 60%-97% which is also considered renewable electricity. However, solar and wind are variable sources of renewable electricity (VRE) which create grid instability and need to be addressed in case we wish to achieve 100% VRE in the grid. The countries such as Denmark and Germany have already to 20% VRE penetrations in their grid, while India has about 10% share of VRE in the grid electricity, and by 2030, we target to reach about 50% of VRE in the electricity grid.
The increasing share of wind and solar has a different impact on grid stability. Already the states such as Gujarat, Tamilnadu, and Karnataka have reached close to 70% VRE penetration during the peak season. During peak times, both wind and solar have higher generation, and curtailing these generators is the most economic option to maintain grid stability. Through the introduction of energy storage in the grid, we can temporarily shift the peak generation. Demand response technologies can be effective to address the high ramp-up and ramp-down rates and shifting the load demand when it coincides with the VRE generation.
The conventional power generation sources in the grid are synchronous generators, while the solar and wind technologies are connected through inverters with the grid. An increasing share of inverter-dominated VRE generation in the grid leads to increased voltage and frequency variations in the grid. While the conventional power generators have strong kinetic energy in the rotating mass and can withstand the grid fluctuations effectively. As we have the inverter-dominated future grid, we need to address grid stability through multiple approaches. The current inverters are grid-following inverters, and the market has to shift towards the grid-forming inverters. While some of the coal-based power plants are in the early retirement stage, their synchronous generators can still be adopted to be part of grid inertia to absorb grid fluctuations. The DFIG wind generators can also provide grid stability through active power control, inertia, and reactive power and voltage control. The throttling of inverters at solar plants can also provide the active power control in the grid. Finally there is also need to introduce the energy storage systems in the grid as we increase the larger share of VRE electricity in the grid.