Why we will still need natural gas plants even if we get to 80 % clean, renewable electrical power

Sometime in the future in the United States we are going to increase our percentage of renewable, clean energy from sources such as solar and wind. It may be a policy to have around 80 % renewable, clean energy by 2035 or so. However, other than the transmission problem we face in bringing in that energy to urban cities from the rural areas, renewable energy faces two major challenges that it is hard to overcome on its own. One, these sources aren't meant to provide the additional power we need in short period of times during peak power demand and two, sources such as solar and wind aren't able to provide what we need at night or during cold storms. The best solution for this is to utilize smaller, more networked natural gas plants that can provide power on demand during these critical times. How are we going to be able to do this otherwise?