Yes, solar covers work, and clear ones work best. It's just like a greenhouse. The thicker ones let the light in just as well, but insulate a bit better.

My problem is the expensive thick clear ones only last the same three years as the thinner blue ones that cost 1/3 as much. Yes they work better, but not THAT much better.

It's fairly futile to attempt to solar heat your pool without a solar cover, any solar cover unless you get, as Richard says, SO much panel that it's almost the surface area of the pool. But with a solar cover, 1/3 the surface of the pool (like mine) can be very effective.

As long as you have sunshine, that is....................