Mike, I think you are exactly right. All phase change materials do is act as thermal mass. While adding thermal mass enables one to keep the refrigerator cool longer without running it also will require you to run the refrigerator longer to get it down to the desired temperature. What you add on one end requires subtraction on the other and does not add anything to the efficiency of the refrigerator. It's basic physics.
If you have free energy from solar then it makes sense to use pcm to maintain the low temperature when the sun goes down. If you don't have a cyclical free energy source you are just spinning your wheels putting in pcm materials.
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