SOLAR OVEN DESIGN:
CALCULATING OPTIMAL ANGLE BETWEEN GLAZING AND REFLECTOR

(Updated 7/07/2012)

For additional information, see our other web pages on solar ovens:

--Casa Juliana Solar Oven

--Our Current Solar Oven

 

Following is an explanation of how to calculate the optimal angle between the glazing and the reflector of a solar oven.  I havent found this information elsewhere on the internet, so have devoted this page to the calculations necessary for determining that angle.  

Designing a solar oven usually begins with determining the largest cooking vessel one wishes to use.  The dimensions of the vessel are then used to determine the dimensions of the inner oven box.  The oven box dimensions then determine the length and width of the glazing.  The dimensions of the reflector are then determined (e.g. larger for a hotter oven, smaller for portability, etc). 

Once those decisions are made, its useful to be able to calculate the optimal angle between the glazing and the reflector.  The optimal angle is such that the reflector intercepts as much sunlight as possible and reflects all of the intercepted light onto the glazing. 

Calculating that angle involves trigonometry.  For those unfamiliar with trig, the following formula may seem daunting, but its really fairly simple if one does it carefully step by step.   A calculator with trig functions is highly recommended.  An example is given to help clarify the process.

Keep in mind that if the glazing is rectangular, the calculation needs to be done twice, once for the short side of the glass and once for the long side.  This is because the optimal angle is dependent on the ratio of the glass dimension to the reflector height and that will be different for the short side of the glass vs. the long side. 

Below is a diagram showing the glazing and reflector and the angle to be calculated. 

 

 

 

Here is the formula for determining the optimal angle between the glazing and the reflector: 

Angle = 90 + [sinˉ1 x {-(b4a) + (0.25 x √(b a) + 8)}]

 

Example: glass width (a) = 18              reflector length (b) = 24

 

Angle = 90 + [sinˉ1 x {-(244 x 18) + (0.25 x √(24 18) + 8)}]

Angle = 90 + [sinˉ1 x {-(2472) + (0.25 x √(576 324) + 8)}]

Angle = 90 + [sinˉ1 x {-0.333 + (0.25 x √(1.78) + 8)}]

Angle = 90 + [sinˉ1 x {-0.333 + (0.25 x √9.78)}]

Angle = 90 + [sinˉ1 x {-0.333 + (0.25 x 3.13)}]

Angle = 90 + [sinˉ1 x {-0.333 + 0.78}]

Angle = 90 + sinˉ1 x 0.45

Angle = 90 + 26.7

Angle = 116.7