Solar water heaters don’t convert the radiation from the sun into electricity. Instead, they use thermal energy to heat the water. As such, you don’t need solar panels as part of the installation. It is, however, possible for you to use a solar water heater in conjunction with a panel or two.
Some people may opt to use an electric water heater. This is different from the thermal option available in most solar water heaters. In this case, it becomes necessary to connect the heater with solar panels. This type of water heater can also work if you hook it up directly with the electricity in your house.