Solar cooking works year-around, in all seasons. As long as you have clear, bright sun shining into your oven, food will cook.
Some people will say ambient temperature affects solar cooking.
Imagine cooking with a propane stove. It doesn’t matter whether it is zero degrees outside. Your pot over the flame will get hot & the food inside will cook. The same is true of solar cooking. As long as sun’s rays shine into the solar oven directly on the pot, it will heat & the food inside will cook.