1. Wind energy explained: theory, design and application;Manwell,2010
2. 2020 Wind energy targets, EU wind power now and the 2020 vision;Europe,2011
3. Most states have renewable portofolio standards;U.S. Energy Information Administration (EIA),2012
4. Relays become problem solvers;White,2011
5. Intermittent nature of green power is challenge for utilities;Cardwell,2013