I'm afraid this is flawed as a science project as it can't conform to one of the rules "is it a fair test?" the temperature of the sun is variable to start with, and you don't mention the conditions the ice placed on foil is in, a better experiment would be to have a controlled heat lamp and do the test with different materials which reflect the heat and light i.e. Foil, a mirror, white plastic, black plastic etc but all you would glean from that is which material had the best reflective properties and you could find that out without doing the experiment