1. World Energy Outlook 2015;IEA,2015
2. Photovoltaic System Pricing Trends: Historical, Recent, and Near-Term Projections;NREL,2015
3. Role of renewable energy sources in environmental protection: a review;Panwar;Renew. Sustain. Energy Rev.,2011
4. European Union, DIRECTIVE 2009/28/EC of the European parliament and of the council of 23 April 2009 on the promotion of the use of energy from renewable sources and amending and subsequently repealing directives 2001/77/EC and 2003/30/EC (2003) https://eur-lex.europa.eu/homepage.html [Accessed 12 July 2018].
5. White paper for a regional policy;ECOWAS,2006