Presentation on theme: "The Water Boiling Test for Solar Cookers WBT SC Version 1.0.3 Prepared April 2014 by Bernhard S. Müller, Historian on Solar Cooking, former owner of the."— Presentation transcript:
The Water Boiling Test for Solar Cookers WBT SC Version Prepared April 2014 by Bernhard S. Müller, Historian on Solar Cooking, former owner of the solar cookers manufacturer Mueller Solartechnik, Eschborn, Germany Faustine L. Odaba, Founder and CEO of the NGO NAREWAMA – Natural Resources and Waste Management Alliance, Nairobi, Kenya
The Water Boiling Test for Solar Cookers WBT SC 1.Is designed to measure water boiling performances of all solar cookers. 2.Is based on standard amounts of water – 1 or 2.5 liters. 3.Is easy to understand. 4.Is easy to conduct. 5.Does not need sophisticated test equipment. 6.Is in close proximity to the WBT 4.2.x of Aprovecho Research Center (ARC). 7.Compares solar cooker boiling performances. 8.Depends on data contributions from various latitudes, altitudes and temperatures. 9.Gives users world wide a fair chance to buy what they need and not what they are told by manufacturers.
The Water Boiling Test for Solar Cookers WBT SC Is not intended to run tests with other objectives than water boiling, e.g. drying or distillation.
Not included in the protocol, to maintain its simplicity The consumed solar energy, neither for time segments nor in total. Specifically consumed energy for losses due to reflector material quality, glass refractions or absorber material properties. Losses due to convection, vaporization and insufficcient insulation. However, specialists can extract further data by knowledge of the aperture area, the estimation of the insolation and the specific heat capacity. Contributions for an extension of the WBT SC regarding the energy consumption are appreciated.
Advantages to the WBT SC It is easy to understand and to conduct. No need of sophisticated test equipment. Solar cookers from around the world can be compared – even with other water boiling devices, such as rocket stoves, micro gasifiers, open fires, etc. Wrong or incomplete – thus misleading – statements of solar cooker producers can be uncovered. The WBT SC is widely adjusted to the WBT 4.2.x of Aprovecho Research Center *) with the exception of the documentation of simmering time and fuel consumption. *) See ppt-stove-testing-wbt.ppt of Nordica MacCarthy, Laboratory Manager at Aprovecho Research Center
Disadvantages to the WBT SC The test protocol depends on as many contributions as possible from around the world. It has less value, if users fail to report their results.
Supplies Pot with lid, both with dull black surface. Thermometer or thermocouple. Scale to weigh water and pot. A form to note the data. An Excel TM spreadsheet can be downloaded free at The lid shall have a hole to support the temperature measuring device. Excel is a trade mark of Microsoft Corp.
To conduct the WBT SC properly, please note: Amount of water ( 1 or 2.5 liters). Initial water temperature. Ambient temperature. Type of cooker (box, parabolic, panel, etc.). Sun angle at beginning and end of test. Name and country of test location. Altitude of test location. Coordinates of test location. Date and time. Reflector material (if any). Insulation material (box cookers only) if any. Heat trapping material (oven bag, glass, etc.). Aperture area. Water temperature every 10 minutes.
For reasons of convenience it is recommended to use the downloaded WBT SC Excel file All necessary data shall be entered in the green fields only. The local boiling point is displayed automatically once the altitude of the test site is entered. Explanation tags pop up on hovering over the field. Like the entire test protocol, the Excel spreadsheet is easy to understand.
Presently, the Excel spreadsheet is available in English, German and Spanish language Lower part of the form The time intervals are displayed automatically. Just enter the start time. The initial water temperature is entered also automatically from the upper part of the form. Contact the authors for assistance.
Optional, to allow further elaborations The elapsed time to reach 65°C water temperature shall be noted. This information is helpful to determine the water pasteurization abilities of the solar cooker. It is helpful to note weight and material of pot and lid for future energy consumption calculations – an intended extension of the WBT SC.
The test is done. What to do now? Send the completed form as attachment to Do not forget to enter WBTSC in the reference line of your message to avoid that it will be categorized as spam. The site with all required downloads, including this presentation, is located in the Internet at URL
Annex What is the knowledge of the local boiling point good for? The local boiling point specifies the temperature, at which water comes to a rolling boil. The higher the altitude, the lower the boiling point. This can be important for heat storage devices, such as insulation baskets (fireless cookers) because the temperature decay time is the shorter, the lower the local boiling point is. To mention the local boiling point is also an act of fairness. The user gets clear information that the same cooker performs differently, even on the same latitude and at the same ambient temperature.