Historical PV Generation Potential for March

The PV Power Map is a report of national solar resource availability as illustrated by the monthly energy output of a nominal 1-kilowatt (kW) photovoltaic (PV) system by location. In addition to showing the estimated PV power output for the month of March, this issue we also highlight how same-month production varies historically.

As seen in the PV Power Map, March experienced above average solar energy production through most of the South as drier-than-average conditions prevailed. The Northeast and Great Lakes regions experienced lower-than-average energy production due to cooler and wetter weather effects. Persistent snow cover in the upper Midwest was in some cases misinterpreted as cloud cover, leading to an underestimation of irradiance in that region.

A soon-to-be released SolarAnywhere update that integrates infrared satellite data to better estimate irradiance under these conditions will reduce these observed effects.

The chart, “Current and Historical Energy Production for March,” depicts the estimated monthly PV energy production at two locations: Flagstaff, Ariz., and Austin, Texas — for every March from 1998 to 2013. This data is compared to the average estimated March PV energy production from 1998 to 2012. As the figure highlights, the monthly production at any particular location can vary as much as +/- 10 to 20 percent from the long-term monthly average.

While monthly PV production variability can be significant, it is important to remember that production variability is significantly less on an annual basis, with most locations experiencing less than 5 percent year-to-year variability. Having access to reliable, long-term historical PV energy production estimates can significantly reduce risk by providing insight into projected monthly and annual production variability.

Using the PV Power Map

To use the PV Power Map to calculate the generation potential of a PV system in a given location, multiply the power output indicated on the map by a project’s capacity, in kilowatts. The result is the total estimated power output for the month.

The PV Power Map is created with power output estimates generated by SolarAnywhere services from Clean Power Research; these include simulation capabilities and hourly satellite-derived irradiance data with spatial resolutions from 1 to 10 kilometers. The calculations are based on a PV system with a total 1-kW nameplate rating that is configured as five 200-watt PV panels with a 1.5-kW inverter; fixed, south-facing panels with 30 degree tilt; noshading; panel PVUSA Test Conditions rating of 178 watts; and inverter efficiency of 95.5 percent.

Visualization and mapping provided by GeoModel Solar. Access free historical irradiance data at solaranywhere.com.

Adam Kankiewicz (askcpr@cleanpower.com) is a research specialist at Clean Power Research.