here is one way to do it
the absorber sits towards the top of the device so that it can look at the sun and within the engine, it sends heat down towards the top of the water in the evaporator. like the heat lamps used in restaurants to keep prepared food warm
water surface heats up and begins to steam. steam is fed into condenser which in this example is tubular and tightly wrapped around the evaporator. as steam condenses and releases heat, it preheats to-be-treated water
maximize heat transfer between condenser coil and water in evaporator
minimize heat loss, for example, by insulating the outsides of both evaporator and condenser
the insights of knowledgeable people, perhaps those who are experienced with thermal properties of materials, heat transfer, boiler design, etc are requested to share their expertise, and their inputs are very appreciated
ideas anyone, on suitable evaporator-condenser designs?