This Technical Report, which is informative in its nature, describes common practices and stateof the art for renewable energy power forecasting technology, including general data demands,renewable energy power forecasting methods and forecasting error evaluation. For thepurposes of this document, renewable energy refers to variable renewable energy, which mainlycomprises wind power and photovoltaic (PV) power – these are the focus of the document.Other variable renewable energies, like concentrating solar power, wave power and tidal power,etc., are not presented in this document, since their capacity is small, while hydro powerforecasting is a significantly different field, and so not covered here.