There are two underlying technologies of solar cooking.
One is of trapping the heat from the sun in a box by using the using a sheet of glass or plastic at the entrance. Solar box cookers use this technology.
The second technology is that of focusing the sunlight to achieve a very high temperature at the point focus. Parabolic solar cookers use this technology.
Solar Box cookers give satisfactory results with unattended cooking. ( At the very outset, I would like to clarify the meaning of the term unattended cooking. The term refers to the attention or attendance that is required to be given to the solar cooker to cook a satisfactory meal. It does not refer to the attendance or attention that the meal itself may require during cooking.) Yet they cannot be made very large as their reflectors then tend to tilt the whole cooker in wind. Also often the trapping glass is the most costly component of the cooker and increase in its size increases costs and the weight of the cooker. This renders it difficult to be carried in and out of the house. In some sense, Solar Box Cookers are an ideal means to enjoy a sun -cooked meal in a winter after noon and wonder why the rest of world does not adopt it?
Parabolic cookers are excellent at collecting sun light from large parabolic surfaces.