Solar Hot Water helps you "save" energy. PV "produces" energy!
Solar hot water panels are referred to as "collectors". They are placed on your roof to heat up water that is pumped into them from your water tank.
The heated water is then stored to supply your home. The electrical heater in the tank is only used if there is not enough solar heated water to satisfy your consumption at the time.
This means that as long as your consumption is relatively close to the hot water produced, you will save money on electricity that would have otherwise been used to heat your water!
Solar hot water helps you save energy on heating up your water.
Whereas, PV helps you collect or produce energy for your consumption!
Solar PV panels are converting solar radiation into DC power. When converted from DC to AC via an inverter, it "produces" energy to power your home!
When both pieces of technology are used, you are left with a green home and less monthly expenses.