Design, construction, analysis and promotion of solar cookers
Reciprocal Video System for Real Time Solar Cooker
Optimization
Abstract
A new Reciprocal
Video System for use in optimizing the shape of a solar cooker for
optimum performance has been developed and tested. This video system essentially adds a new real time function to
the Reciprocal
Optical Test for Measuring Solar Cooker Performance (Reciprocal Optical
Test).
Reciprocal Video System
When
designing a new cooker, or attempting to improve the performance of an existing
cooker, it normally is difficult to determine whether or not the performance
can be improved by adjusting the shape of the cooker. The Reciprocal Video System, is designed
to make it possible to do real time optimization of the shape of a solar cooker
to maximize the performance of the cooker.
For the optimization procedure, the camera that is
used in the Reciprocal Optical Test
is replaced with
a digital camcorder. A video monitor is
placed near the cooker and attached to the camcorder which is located about 50
feet in front of the cooker. The test
stand, with the cooker mounted on it, and the rest of the test set up, is
unchanged from that used in the Reciprocal Optical Test. The
effective area of the cooker (the area perpendicular to the sun's rays at the
mouth of the cooker for which, in normal operation of the cooker, the incoming
sun's rays will hit the pot) is illuminated on the video monitor.
Figure 1: Test Setup
for Reciprocal Video Optimization
Figure 1
shows the test stand, with the Scott Rundle's "Solo" cooker mounted
on it, and the TV monitor and microphone. The top of the test stand with the cooker is tipped forward 45 degrees forward
to correspond to a sun altitude angle of 45 degrees.
Figure
2: Video System Set Up for Cooker
Optimization
Figure 2 shows
a view similar to Figure 1, but with the video system running. The light source inside the plastic pail that
replaces the pot in the cooker has been turned on. The camcorder that is on a tripod about 50
feet in front of the cooker, at the height of the center of the pot, has been
turned on. The video signal is being
transmitted to the TV monitor which appears in the upper left corner of Figure
2. The illuminated area on the TV screen
represents the effective area of the cooker. The objective of the optimization is to adjust the shape of the cooker
to maximize the illuminated area on the TV screen.
While
performing the optimization procedure, the operator watches the TV monitor, and
adjusts the shape of the cooker as
necessary to maximize the illuminated area. Experience has shown that is helpful, before performing the optimization
process, to place a clear plastic sheet over
the face of the TV. Then, with the video
system on, use an erasable marker to sketch the approximate outline of the initial
illuminated area on the plastic sheet. This allows the operator to compare the
changing illuminated area to the initial illuminated area. Normally, a video record
of the optimization procedure is recorded on the camcorder. Also, the microphone, which is located near
the cooker, allows the operator to add an audio description of the optimization
process to the video record as it is being recorded.
Usually,
the Reciprocal Optical Test for Measuring Solar Cooker
Performance is performed before and after the real time video optimization
procedure to more accurately determine how much the optimization
improved the performance of the cooker.
The camcorder
that is being used with the Reciprocal Video System is a Canon VIXIA
HF R80. The video monitor is a 19 inch
Element flat Screen TV. The TV is connected
to the camcorder with 70 feet of HDMI cable. Also, the dynamic microphone is
connected to the camcorder with 70 feet of microphone cable.
Results of initial Reciprocal Video Optimization Procedure
So far, only
one optimization procedure has been performed. A cooker that Scott Rundle had sent for evaluation was used for this
first test. It was carefully assembled
using photos and videos that he put on Facebook. Reciprocal optical tests were performed
before and after the optimization procedure., and the results are shown on the
graph below. Since the initial test
showed maximum power at 45 degrees sun altitude, the optimization was done for
sun altitude of 45 degrees to see if the maximum power could be increased. As the graph shows, the maximum power at 45
degrees was increased from 121 to 155 Watts by the optimization. Although the front and top flaps were
adjusted a bit, it is believed that much of the power gain was from forcing the
distance between the sides of the cooker to be much larger and using coat
hanger wire to force the sides to stay farther apart. This is a very preliminary test since the
optimization system and procedure are still being perfected.
Figure 3: Performance of "Solo"
Cooker Before and After Optimization
Figure 3
Shows the results of Reciprocal Optical Tests performed
before and after the optimization process. Since the initial test measured maximum power at 45 degree sun altitude
angle, the optimization was done for 45 degree sun altitude angle to see if the
maximum power could be increased by optimization. The maximum initial power of 121 Watts was increased to 155 watts
by the optimization.
Figure 4 is
a collage of the six pictures that were taken during the initial Reciprocal
Optical Test performed before optimization. Each of the 6 photos in the collage is
analyzed to produce the corresponding data point on the Initial curve in Figure 3.
Figure 5 is
a collage of the six pictures that were taken during the Reciprocal Optical Test
performed after optimization. Each of
the 6 photos in the collage is analyzed to produce the corresponding data point
on the Optimized curve in Figure 3.
Figure 4: Collage from Initial Reciprocal Optical Test
Figure 5: Collage from Reciprocal Optical Test after
Optimization
