In case of nuclear winter, I don't think renewable energy is going to be the main concern.
However, it is possible to put solar panels on satellites that transmit the energy down to the surface. It's costly and dangerous, but a benefit over surface solar is that the satellites can point at the sun for longer time during days and send the energy to places that are not in the sun, thereby producing solar power 24/7.
It's wildly impractical and expensive, but in case of nuclear winter it may be a realistic solution.
Oh sure, it sounds extremely dangerous, just like standing too close to a radar will poach your brain. The satellite beaming the energy back would have to stay on target and if it didn't it would need a quick and safe way to shut off. Of course dissipation of excess energy in a ground-based grid is a serious issue, so how you would design a satellite to deal with the sudden stop in energy flow is completely beyond me. Maybe you just write it off and launch another one in that case, and you have a lot of redundant paths rather than one critical one.
Nuclear winter is a severe and prolonged global climatic cooling effect that is hypothesized[1][2] to occur after widespread firestorms following a large-scale nuclear war.[3] The hypothesis is based on the fact that such fires can inject soot into the stratosphere, where it can block some direct sunlight from reaching the surface of the Earth. It is speculated that the resulting cooling would lead to widespread crop failure and famine.