For years, wood and charcoal were the most common source of energy for cooking, but it requires cutting down trees which causes deforestation.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/rwanda-new-alternative-charcoal-burning-technique-save-forests
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/all-africa
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/forests
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/deforestation
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/firewood
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/charcoal
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/wood
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/energy
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/biomass
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rwanda
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/africa