In order to converve power, and because we really didn't need that much cold space in the icebox, I designed an insulated partition. It's made out of 1/4" plywood, painted white on the warmer side and insulated on the colder side. It's hinged so that it can be inserted and removed through the opening. Although the plywood is cut to conform to the outside contours of the icebox, no attempt was made to seal it to the contours.
This is the view from the top. It shows the aluminum-faced "bubble wrap" insulation. It's fastened with contact cement. Laying a spare piece over the Adler Barbour evaporator seems to help keep the cold in.
This is an older Adler Barbour unit. Newer units have more sophisticated electronics that allow some power savings due to variable compressor speeds, but in general it costs a certain amount of power (whether the power is electrical, chemical, solar, mechanical, etc,) to bring the icebox down to a certain temperature and maintain it there.