"To help feed the country’s population, an inventor, Toufic Hamdan, created a commercial bakery to bake bread in solar ovens. The startup “Partners With Sun” has installed a solar convection oven on the bakery’s roof. The Solar Oven uses large silver mirrors to capture and magnify the sun’s rays to build heat. The heat is transported by a transfer fluid which is then used to help operate a convection oven, allowing it to reach a baking temperature of between 300 and 400 Celsius. The heat is used directly in food and beverage production. " Baking Bread in a Solar Oven | Happy Eco News
According to the company website, “The Solar Oven cuts up to 80% of the bakery’s fuel bill.”
How well does it operate during sub-optimal conditions? Electricity can be stored in a battery, so you can spread your power out over time. I would expect some flexibility in this, since heat doesn't instantly dissipate, but if conditions remain poor for an extended period, I would think this would be much less resilient.