They admit it is not intended for latitudes very far from the equator. It requires the sun to be primarily overhead, and will produces heat for maybe three hours on a clear day. The focal length for a lens this size, which is about 75-100 cm in diameter, is relatively long. This means the lens must be supported overhead with a structure holding it about 2.5 m above the focus area. So probably not the most practical way employ solar cooking. None the less, the lens impressively produces temperatures of 175°C (350°F) to 345°C (650°F). In a survival situation in the tropics, with some clear plastic sheeting, water, and some creative carpentry, a cooking source would be possible.