The author did some good testing of various designs and explains his results. DO NOTE that more Peltier units will give faster cooling but require more power. https://www.mdcreekmore.com/how-to-build-a-portable-off-the-grid-refrigerator/ If you already have a larger solar electric array (and battery bank for nighttime power?), then you've already made the investment and the cost of this cooling unit will be less. One link to a source for the Peltier units is buried in the parts list: https://www.allelectronics.com/item/pjt-13/thermoelectric-peltier-device/1.html This is Not the only source for these devices and you can do a (non-google) web search on "Peltier Device" to find other suppliers.