I'm not sure where you are getting the 250-300W/m2 of irradiance. The standard value used in all solar industry calulations is 1000W/m2, but in practice, you should expect to see 800W/m2 at sea level and moderate lattitude.
I was part of the founding team of a power electronics startup. We constantly tore down our competitors' products to estimate their costs, to see how they corrected design flaws between releases, and also to understand which component suppliers they chose to include (this is a proxy for passing their reliability testing).