More “efficient” methods for specifying and monitoring PV system performance

Do you know anyone that has been confused when writing or reviewing proposals providing PV system energy production estimates? Or when monitoring system energy production relative to expectations? Is the rate of commercial adoption being negatively impacted by ambiguity and uncertainty in the metrics used for specifying PV system power ratings and annual energy production? Does the efficiency of communication between the PV industry and the financial community need to be improved? I suspect that the answer to these questions is an unequivocal, yes! Can anyone predict the solar resource for the coming year within 1%? The answer is an unequivocal, no! Are there alternative methods for specifying and monitoring PV system performance that are easier to understand, less ambiguous, more accurate, less costly, and more efficient? I believe the answer to this question is yes. From the distinctly different perspectives of both the PV specialist and the system financier (investor), this paper reviews efficiency, power, and energy rating metrics that have evolved in the last thirty years for specifying performance of cells, modules, arrays, and systems. Then, with PV system performance (energy production) as the specific focus, both modeling and field experience are used to describe an alternative approach intended to minimize observed difficulties in marketing PV systems. A central feature of the approach is a more universal thermodynamic definition of the word “efficiency,” based on system energy production, namely ac-energy produced divided by the solar energy incident. In addition, from the financier´s perspective (performance guarantee) and from the specialist´s perspective (O&M), a few methods are described for efficiently monitoring long-term system performance.