"The Skylid has no switches or wires or motors... Instead, the unit contains a series of louvers. Each... is supported and balanced so that it hinges easily around its center and... the louvers are connected with a tie rod so they’ll open and close simultaneously. ...[M]ounted on one of the panels are two canisters—one on the outside and one inside ...connected by ...tubing. ... ...with a very low ...can expand ...in one canister and ...condense in the other with a temperature difference of... 1 degree Fahrenheit. This shifting of the Freon’s weight will open and close the... louvers... and the... sun—even the shade of a cloud—produces... enough temperature variation to boil the Freon from one container to the other. ...[A] locking chain... secure[s] the panels anywhere from full open to full close... to override the automatic mechanism."