Capacity planners in developing countries frequently use screening curves and other system-independent metrics such as levelized cost of energy to guide investment decisions. This can lead to spurious conclusions when evaluating intermittent power sources such as solar and wind. Use a system-level model for Kenya to evaluate the potential of using grid-connected solar photovoltaic in combination with existing reservoir hydro-power to displace diesel. Different generation mixes are evaluated with a unit commitment model whereby Kenya’s extensive reservoir hydro-system compensates for solar intermittency. Results show that the value of high penetrations of solar in 2012 exceeds their potential investment cost. Under three 2017 generation scenarios, the investment value of solar remains high if planned investments in low-cost geothermal, imported hydro, and wind power are delayed. The methodology can be used to estimate renewable potential in other African countries with comparable power generation situations.