Editorial - International journal of sustainable energy planning and management volume 21

This editorial introduces the 21^st volume of the International Journal of Sustainable Energy Planning and Management. This volume present research on overall national energy planning development with a case from Nigeria. This is followed up by a sustainability assessment of nine sample countries. Moving on to the more local scale, potentials and barriers for photo voltaic systems with cases from Germany, Nigeria and Tanzania are presented. Finally, analyses focusing on the spatial dimension of energy system are presented. This last part addresses both the delimitation between rural and city energy systems and how they should combine and the optimal design of district heating systems.