Approaches to Designing a Solar Oven
All good engineering design starts with a clear understanding of the project’s needs, goals,
budgetary constraints, material constraints, performance tolerances, and criteria (termed the
“Performance Index” or P.I.) for judging the effectiveness and success of the final product.
Once all of these design specifications are clearly understood, the process of actually
designing the product may begin.
(Note that in the “real world” any or all of these
specifications usually change many times throughout the design process.
For this project in
ENGR102, they are clearly defined and are not likely to change during your work on the
One possible approach to producing a solar oven would be to design and build an actual
oven, within the limits of the design criteria.
You would then test the oven and measure the
Performance Index that you achieved with your first design.
Unless you were extremely
lucky, it is highly unlikely that this first oven would achieve the desired P.I.
You would then
have to redesign and build many other ovens, hoping with each cycle of design and test to
achieve the P.I. that the customer needs.
Even with something as seemingly as simple as a
cardboard solar oven, this could take weeks, if not months!
Another approach would be to use Design of Experiments (DOE).
Using DOE, one could
(hopefully) identify the most important factors in a solar oven, and then make good decisions
about the levels to test them at.
Once these values were chosen, you could build all of the
ovens needed to test a full-factorial combination of these factors and levels.
Then, using the
resulting DOE predictive model, you could build additional ovens and test them, until you
achieved the desired Performance Index.
Again, this could take a very long time.
The solar oven project allows yet another approach to design, that of first building a
used to predict a value for the Performance Index.
Based on knowing
the physics of how a solar oven actually works, we are able to write down equations that
predict the flow of energy into and out of the oven cavity.
For the solar oven, this works
because these equations are simple equations with closed-form solutions that are easily
This allows you to calculate and predict the internal temperature of the oven cavity.
In turn, an equation for the Performance Index can then be written down and solved for, and
used as the basis for the actual design of a specific oven.
If a spreadsheet is used to solve these equations and to calculate the Performance Index, it is
easy to iterate solutions by changing the input variables (in effect, changing the oven design),
until the desired P.I. is achieved.
(At this point, no time or money has yet been spent on
actually building any ovens.)
Finally, the oven that achieves the highest calculated P.I. can
then be built and tested, using the values of the input variables in the spreadsheet.