language is not clear

but the main effect of renewable energy sources on the grid is an increased requirement for load-following reserve, and ramping-reserve.

Major weather events are usually predictable and foreseeable ahead of time (such as eclipse, storms, etc.). the system can prepare itself for such major events; so RE integration has no effect on contingency reserve; however, operating reserve requirements are larger. a lot of papers in the literature focus on smoothing RE output, which is regulation reserve. but in reality, applied studies (in contrast with academic studies), highlight and emphasize the need for more load-following reserve. that is, reserve of medium size, which has to deploy within 15-minutes after it is recalled.

check out my paper:

A review of power system flexibility with high penetration of renewables

B Mohandes, MS El Moursi, N Hatziargyriou, S El Khatib

IEEE Transactions on Power Systems 34 (4), 3140-3155

Baraa Mohandes thank you sir for your response

In view of dispatching, it is more difficult or more effort to keep control of small system because of intermittence of RES. However it is good to voltage stability due to the fact that inverter of RES having capability to adjust the reactive power.

It will mainly depend on percentage of renewable in the total grid. If it is very low, absence of it in the grid may not have much impact. But if it is significant in terms of instantaneous power (say, even 20% or so), not energy, to hold the grid intact would itself be a serious issue until and unless there is Battery Energy Storage System to the rescue of grid.

This might be useful:

Poster Field Data of Grid Response and Scheduling for Variable Rene...

You can read this adequate topic at URL:

https://www.oas.org/dsd/publications/Unit/oea79e/ch05.htm

With integration of renewable sources the system can take more load if sufficient reactive power is available at the load