Image: www.wagner-solar.comFirst there's the tank. That's where your water will be heated. If you have a direct solar water heating system your water will be pumped from the tank directly to the solar collectors, where it will be heated, and then it will be pumped back.
The indirect solar heating systems also usually have an expansion vessel. The heat-transfer fluid goes through this vessel, which is mostly filled with air to protect the water heating system from thermal expansion. If the expansion vessel wasn't there, there would be a risk of the ducts cracking when seasons change.
The last component we'll tell you about here is the solar controller. The controller is the machine that checks what the temperature of the water in the main tank is, and if it below a certain temperature the heating system is turned on. There is also a timer function on many controllers. You can decide some certain times, typically nights, when the heating system is never turned on. During those times normal electricity may, if needed, normally be used to heat water. The controllers are, like the pumps, driven by normal electricity.