Resources

Weather and solar resource data

• European Union - Photovoltaic Geographical Information System A free and very detailed production modeling, system design tool and source for weather data that works in most locations globally. Also available in Spanish, French, and Italian.
• National Renewable Energy Laboratories - PVWatts Calculator A free production modeling and system design tool from the National Renewable Energy Labs (NREL) that works in many areas around the world. Only available in English.
• NASA - Power Data Viewer A detailed global irradiance/meteorological resource provided by the National Aeronautics and Space Administration (NASA) that provides data globally. It is capable of exporting data sets and creating unique maps. Only available in English.
• National Renewable Energies Laboratories - National Solar Resource Database An interative map with downloadable solar resource and weather data sets for the Americas and South Asia.
• World Bank - Global Solar Atlas A detailed global irradiance/meteorological data resource. Also includes a free production modeling tool. Only available in English.

Wiring

• Calculator.net - Voltage drop calculator A simple voltage drop calculator that can be used to quickly determine the percentage of voltage drop for a particular circuit with basic information.
• Smartgauge.co.uk - Battery bank configurations An excellent article on voltage drop and battery wiring with simple diagrams showing good and bad wiring practices for various different battery bank configurations.

System efficiency

• Do the Math - Blow-by-Blow PV System Efficiency: A Case Study for Storage An examination of round-trip effiency of an off-grid PV system.