Our new pool has an APC auto pool cover. The fabric is a very heavy vinyl. I'm wondering if everyone thinks it makes more sense to keep it closed or leave it open to gain heat from the sun. Their website claims it acts as a solar cover also, but that fabric is so heavy, I'm not sure how well it would generate heat. I don't want to turn the heater on yet, since it is just still so chilly. But I'd like to take advantage of what few sunny days we are having.