not solar power it is the water chnner up to the vacuum tube , then the sun shine on the tube on roof become heated water, the tank there is for when there are no sun raining all the day, at night u need hot water then u can turn on the heater switch to heat the water using electric, so the solar water heater are actually "Hybrid " water heater , use either solar or electric.

they use special vacuum tube to get the sun light so the water flow between , the water can boil eggs at sunny afternoon
one disadvantages is the solar water heater system must install before move in after move in it is difficult need to hack the wall to lay water piping down to all water tap point

Malaysia
Need Heater

Pondan

but instant water heater only 10seconds.