How many solar panels do I need for 1 hp motor?

The number of solar panels needed for a 1 HP motor depends on the phase type, solar panel watts and age of pump! A brand new RPS 1 HP, three phase pump utilizes twelve 100W panels, a total of 1200W. You could potentially use larger solar panels like 300W, meaning fewer overall panels but about the same square footage. But if the pump is single phase, expect to use more panels since three phase is more efficient than single phase. And if the pump is old, 10-15 years or older, again expect to use more panels as pumps decrease in efficiency over time and require greater power upon startup.