https://phys.org/news/2018-11-insight-rays-mars.html

InSight's twin solar arrays are each 7 feet (2.2 meters) wide; when they're open, the entire lander is about the size of a big 1960s convertible. Mars has weaker sunlight than Earth because it's much farther away from the Sun. But the lander doesn't need much to operate: The panels provide 600 to 700 watts on a clear day, enough to power a household blender and plenty to keep its instruments conducting science on the Red Planet. Even when dust covers the panels—what is likely to be a common occurrence on Mars—they should be able to provide at least 200 to 300 watts.

The panels are modeled on those used with NASA's Phoenix Mars Lander, though InSight's are slightly larger in order to provide more power output and to increase their structural strength. These changes were necessary to support operations for one full Mars year (two Earth years).