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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

Video 1: Optimization of "Solo" Cooker

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