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Sweden is testing a semi-truck trailer covered in 100 square meters of solar panels
(www.popsci.com)
This is a most excellent place for technology news and articles.
874sq-ft is needed for 15kw a trailer is 450. A reefer is around 15kw and needs to be able to run all day and night some times. Just wouldn't work at all. Especially if you had to carry around the batteries for night. It would just be way too heavy.