The primary innovation over the Whiller design is the use of an evacuated tube solar collector as the collecting element of the cooker. Evacuated tubes have been used in solar hot water systems, and are considered a mature, efficient technology. By replacing the copper pipe and fin in the Whiller design, John Grandinetti claims during his media interview that his indirect cooker design can reach temperatures of 400°F in direct sunlight. The Grandinetti design replaces water with oil for the heat transport mechanism in order to sustain these temperatures.
The large diameter vacuuum tube (120mm OD) houses a separate sealed glass tube inside (triple cavity), which displaces most of the interior liquid volume. The resulting fluid space allows for only one gallon of vegetable oil to perform the heat transfer function to the heat retention cook box. The steel cook pan, housed within the insulated cook box, is specially designed to integrate with the glass vacuum tube. A silicone coupling hose (120mm ID) is band clamped to both the glass tube and the cylindrical portion of the steel pan outer dimensions. Tests have indicated that the unit, placed in the sun at 8:30am will achieve a cooking temperature (300° F) by 9:30am and cooking, water pasteurization and autoclaving can be readily achieved throughout the remainder of the solar day. The heat retention cook box and the thermal mass of oil and food within, permits cooking to continue through prolonged cloudy intervals and allows deliverery of hot cooked food as late as 10pm. Cook times are similar to an electric stove making this device a true solar appliance. An example is the 15 liter stove-top autoclave, which can achieve the required 17psi steam pressure within 40 minutes of placement within the insulated cook box. Frying, baking, boiling and steaming have all been successfully accomplished.
Mr. Grandinetti is working through his non-profit organization Developing World Solar, to have his design placed into production. A fact-finding trip to China is planned for July 2008 to locate a manufacturer and finalize pricing. Developing World Solar will offer manufactured units to other non-profit organizations at the manufactured cost. Commercial manufacturing and distribution of the cookers will be permitted based on supporting Developing World Solar’s humanitarian efforts.
- John Grandinetti interview on KITV (Honolulu, HI) http://www.kitv.com/video/16158443/index.html