We went to Forest and Erica's on Sunday. Forest has a large Fernell lens that he focused on a black pot turned upside down with a smaller pot/bowl inside. The Idea is to pump cold water between the two bowls and heat the water with the Sun. We started with 16 gallons of water at 86 degrees F. He had a fountain pump that pumped the water through and back to the tank (Picnic cooler). In two hours, five minutes, from 3:15 to 5:20 pm we got a 39 degree F. rise to 125 F. It has potential for pre-heating water.