Under the terms of this licence, you may copy, redistribute and adapt the work for non-commercial purposes, provided the work is appropriately cited, as indicated below. In any use of this work, there should be no suggestion that the World Health Organization(WHO),the International Bank for Reconstruction and Development(The World Bank),Sustainable Energy for All(SEforALL)and the International Renewable Energy Agency (IRENA) endorse any specific organization, products or services. The use of the WHO, the World Bank, SEforALL and IRENA logos is not permitted. If you adapt the work,then you must license your workunder the same or equivalent Creative Commons licence. If you create a translation of this work,you should add the following disclaimer along with the suggested citation:”This translation was notcreated by the World Health Organization(WHO). WHO is not responsible for the content or accuracy of this translation. The original English edition shall be the binding and authentic edition”.