Though the practice of “over-sizing” solar modules relative to the inverter has existed for decades, it remains one of the trickiest topics to explain. And, even among solar professionals, conversations about over-sizing become more like religious debates than scientific discussions.
The reason for all the confusion: there is no right answer. No matter what sizing ratio you recommend, there are costs and benefits. And, the “right” choice depends on where you see the most value.
But, an Enphase Energy study that examined the cost/benefit trade-offs and came to the conclusion that there are two reasons to recommend over-sizing as standard practice: one based on the fundamentals of solar product ratings and the other based on the economics of today’s solar industry. In fact, the study recommends a change of terminology: “Over-sizing and inverter clipping imply that you’ve made a mistake in designing the system. This terminology is an outdated vestige of an industry focused solely on module cost and module performance.” Read this classic exposition of engineering economics