Figure 6. The outdoor solar heating performance of double-sided heterochromatic nano wrinkled photothermal membranes. (a) The test location. (b-e) The outdoor solar heating test on a sunny day at 0-1am (b), 7-8am (c), 12-13pm (d) and 17-18pm (e). (f-h) The outdoor solar heating test at 14-15pm on a sunny day (f), a cloudy day (g) and a rainy day (h).