Cook and Save Energy with an adjustable Oven

We buy an oven according to the size of our family…..larger families means big meals which needs to be cooked in full sized ovens. However most of us do come across a situation when we just want to cook or heat up a small portion and the whole of this energy consuming gadget needs to be heated up. Matt has designed an oven for such times. He intends to heat only that part of oven that will accommodate the food product without wasting more energy to heat the rest of the space. Going by the image, it seems that this oven can be shelved and portioned according to the usage. Though Matt Gossington has conceptualized an energy saving oven concept, at this stage I am not convinced about its practicality. We would have appreciated improvised and practical eco-friendly features that can actually lure the makers to grab the design for the future kitchens. How about an alternatively powered oven that saves up on all the grid energy?