Lack of access to mod­ern forms of energy ham­pers efforts to reduce poverty. The pro­vi­sion of elec­tric­ity to off-​​grid com­mu­ni­ties is there­fore a long-​​standing devel­op­men­tal goal. Yet, many off-​​grid elec­tri­fi­ca­tion projects neglect mid– and long-​​term oper­a­tion and main­te­nance costs. When this is the case, elec­tric­ity ser­vices are unlikely to be afford­able to the com­mu­ni­ties that are the project’s pri­mary tar­get. Here we show that, com­pared with diesel-​​powered elec­tric­ity gen­er­a­tion sys­tems, solar pho­to­voltaic sys­tems are more afford­able to no less than 36% of the unelec­tri­fied pop­u­la­tions in East Asia, South Asia, and sub-​​Saharan Africa. We do so by devel­op­ing geo-​​referenced esti­mates of afford­abil­ity at a high level of res­o­lu­tion (1 km²). The analy­sis illus­trates the dif­fer­ences in afford­abil­ity that may be found at the sub­na­tional level, which under­scores that elec­tri­fi­ca­tion invest­ments should be informed by sub­na­tional data.