Solar Efficiency Record – Solar Griller – BBQ

Photovoltaics is not suitable for façades and window sills, as well and loses (areas) efficiency. Not so with vacuum tubes solar ovens – Griller – BBQ. These bring up to 60% efficiency to the area and are already to have little money or from defective tubes so it is also in the city with freshly grilled or dried – without smoke nuisance and fine dust.
How do I calculate the efficiency to the area? Here is an example from the Himin (whose very special production I was already allowed to visit) Solar BBQ Page: Solar vacuum tube Solar Coker stove Vacuum tubes 1000w / m2 x 0.67m2 * efficiency (which is about 60%) = 402w
Free offers and a solar cooker as a gift here: Himin Solar Kitchen in Hand oder via amazon.Unbenannt