Like for example mirrors and stuff but what else??
I find my garden hose heats up in the sunlight. If you want to be very simple, just paint the hose black, leave it in the sun and withdraw the water only at a rate that matches the temperature you want. The good thing it this will be enclosed and at the water pressure of your house, you can then get it to where you want without a pump.
Dig a backyard pond and line it with black plastic sheets. Put copper pipes in the bottom of the pond. Fill the pond with salt water except on the top carefully put a layer of fresh water. Run water through the copper pipes. The pipe water will extract the heat from the salt water.
Go to the tire store and ask them.
