Solar PV or solar thermal collectors?
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PV produces electricity; solar thermal collectors produce heat. Their most direct overlap is domestic hot-water heating. Compare the building's useful demand and complete system costs rather than choosing from the number of panels or a single efficiency figure.
When the main need is hot water
Thermal collectors can use a smaller roof area for the same summer hot-water task, but add a fluid circuit, pump and controls that need appropriate maintenance. The tank, pipe route and seasonal demand affect the actual installation.
PV water heating needs a compatible electrical and control arrangement. A dedicated system and a surplus controller on a whole-home PV installation are different options with different scopes.
When electricity has other useful jobs
PV electricity can also supply appliances, cooling or vehicle charging, with surplus handled under the appropriate grid and commercial arrangements. That flexibility can matter if daytime demand goes beyond hot water.
Neither technology should be assumed to provide all hot water throughout the year. Include the alternative heat source, winter performance, service and genuinely useful output in the comparison.