This thesis report studies three off-grid diesel mini-grids in Kenya with peak demands ranging from 100kW to 1000kW, in order to determie their optimal degrees of hybridisation through solar PV technology. To do so a techno-economic analysis tool was developed which is based on a steady state energy balance in 30-miutes intervals. The methodology was defined during a feasibility study with the scope to maximise renewable energy shares in 20 KPLC off-grid plants, and is tailored to local capacities and data availability. The Excel based and automated tool is able to compare eight different hybridisation layouts characterised by different PV capacities, control and operation strategies, and energy storage capabilities. The systems are assessed both from a technical and economic point of view. The different layouts can be evaluated based on performance indicators and ranked through a multi criteria decision matrix. Furthermore, the study assesses the attractiveness of hybrid systems to private investors and characterises the systems through the use of sensitivity analyses.