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A Simple, Rigorous Method for Sizing the Array of a PV Hybrid System

Michael M.D. Ross
RER Renewable Energy Research

Full Text Article
Link to SESCI (conference)


Ross, Michael M. D. "A Simple, Rigorous Method for Sizing the Array of a PV Hybrid System". Proceedings of the 32nd Annual Conference of the Solar Energy Society of Canada, Calgary, Alberta, June 10 to 13, 2007.


Many rules of thumb for sizing the array for a PV-hybrid system have been developed. The rules of thumb include sizing the array so that it meets the average load under the annual average solar irradiance, so that it meets (say) 60% of the annual load, so that it fully satisfies the load during half the year, or so that no more than (say) 25% of its output is rejected in the sunniest month of the year. All of these result in reasonable array sizes under certain conditions. But all of them ignore the financial aspects of array sizing, so in other conditions they may yield results that will not be cost-effective. Ultimately, the optimal array size is based on financial considerations: it minimizes the cost of providing power.

Sizing and simulation software have also been developed for this purpose. Unfortunately, they rarely reveal why a certain sizing is appropriate, so the factors influencing the sizing are not clear. This makes them prone to user error. If simulation software does not automatically search for the best array sizing, it is up to the user to try multiple sizings and figure out the best one. Furthermore, sometimes it is inconvenient to have to learn a piece of software and use a computer.

In fact, the optimal sizing of the PV array does not require simulation, nor is a rigorous solution so complicated as to necessitate rules of thumb. Here a sizing method is presented that is very simple, that makes sense intuitively, that finds the most cost-effective array size, and that can be applied with a pen, paper, and monthly solar data in tabular form—or adapted to the most sophisticated simulation software.