Performance evaluation standards for photovoltaic modules and systems

Abstract

The photovoltaic (PV) industry is growing rapidly and has moved into a new era of selling energy rather than units. As the scale of systems climbs, so do expectations of the energy produced by these systems. PV system integrators and their customers are less concerned with the numbers of units they are selling than they are with supplying a specific amount of annual energy production, for a specific amount of money, at a specific location. The peak power rating of the PV modules is one of the most important elements in predicting system performance. Translating a module manufacturer's peak power rating into energy produced is confusing and oftentimes frustrating for solar integrators and customers alike. A 150 Wp module may be priced the same or higher than another 150 Wp module but its overall performance and value to the customer can be quite different. Standard test conditions (STC) by which most modules are rated are almost never realized in real world conditions. Various methods exist for determining actual power of a module to account for real world conditions but none have been-adopted universally. Add to that, different manufacturers apply different quality standards, measurement uncertainties, and tolerances to their nameplate ratings. Known effects such as light induced degradation (LID) and manufacturing variances are either not addressed or handled in different ways. Furthermore, module performance is only one part of net PV system performance. Standard methods of evaluating system performance should also be developed which accurately capture loss factors for PV systems. Standardized, third party methods of determining module and system performance reduces confusion and frustration for integrators and customers alike and leads to a respectable due diligence that would foster the whole industry. This paper focuses on identifying issues with PV module and system ratings to demonstrate the need for universally adopted, third party standards.