Solar Cooking
Last edited: 23 June 2020      

Lightoven I schematic

The Lightoven I in a tilted position.

The Lightoven I has been designed by Hartmut Ehmler, who lives in Germany. The goal of the Lightoven was the ability to heat a significant amount of water until boiling, in less time than other portable cookers with similar weight and packing dimensions. Such a design requires a concentrating reflector and an adapted cooking pot design with low thermal losses.

The design has been inspired by the CooKit, however using instead of a few reflecting panels, the Lightoven I incorporates many segments, which follow a parabolic curve on a reflecting bottom plate. The vertical focal line should ideally hit the cooking pot entirely. However when the angle of incident rays is not perpendicular to the reflector, the focal line tends to elongate. Reflector and cooking vessel are therefore designed in a way that all rays are reflected onto the cooking vessel - provided the sun elevation is at its geometrical optimum. The present design of the cooker is best suitable for medium elevation, i.e. the latitude of central Europe. The parabolic reflector can be tilted from vertical orientation by about 15° backwards to account for higher sun elevation angles.

The Lightoven I packed for transport with the reflector rolled around the cooking container.

At 52°N latitude, the direct insolation, which is a function of the sun elevation and visibility, can reach about 500 W/m2 in winter and up to 900 W/m2 during summer (at 10° and 65° elevation, respectively). Tests throughout the year have shown that the Lightoven can easily reach boiling temperatures in this elevation range, with the best performance between 30° and 50°. The Lightoven therefore turns out to be an all-season solar cooker for this latitude. The dimensions of the reflector in operation are 114 x 45 x 45 cm (width, height, and depth) resulting in a maximum aperture of 0.57 m2 in total including the bottom plate. For transport both parts of the reflector can be rolled around the cooking vessel resulting in a 45 cm long package with a diameter of 17 cm. The total weight of this package is 1.6 kg including a watertight transport bag. Read the test results.

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See Hartmut Ehmler.