Correlating Photovoltaic Clear-Sky and Actual Output to Sky Cover Measurements

Published

September 1, 2013

Author(s)

David R. Daily, David Holmberg, John Baras

Abstract

As distributed energy resources are added to existing building systems, and variable priced electricity tariffs are introduced, facility owners may profit from understanding the expected performance of their building systems. Hourly, forecast energy generation from photovoltaic sources allows owners to manage energy storage and consumption for their optimal benefit. This paper documents an empirical method which uses publicly-available sky cover observations to estimate the output of a photovoltaic (PV) array. Two functions are developed which together relate PV array output to sky cover observations reported by the National Weather Service for a nearby airport and results are evaluated by comparison of estimated PV array output with actual output. Results show that this approach can produce useful estimates of hourly and daily PV system output which may be applied to forecast weather data in order to estimate forecast PV array outputs. Although some large deviations are observed between estimated and actual PV output, the method presented uses data that would be available to a building owner with no on-site instrumentation beyond a meter.

Proceedings Title

Proceedings of the 39th IEEE Photovoltaics Specialists Conference, June 16-21, 2013, Tampa, FL.

Conference Dates

June 16-21, 2013

Conference Location

Tampa, FL, US

Pub Type

Conferences

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Keywords

Buildings, correlation, photovoltaic, sky cover, sky condition

Citation

Daily, D. , Holmberg, D. and Baras, J. (2013), Correlating Photovoltaic Clear-Sky and Actual Output to Sky Cover Measurements, Proceedings of the 39th IEEE Photovoltaics Specialists Conference, June 16-21, 2013, Tampa, FL., Tampa, FL, US, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=913901 (Accessed October 18, 2025)