The need to study the Kenyan national power system with a view to minimising environmental emissions and energy production costs in the present and the long-term was identified. The overall objective of this research was to develop optimal generation dispatch and capacity expansion in the Kenyan power system, with the aim of minimising the environmental emissions associated with electricity supply without contravening the underlying economic objectives. Pertinent factors that influence the level of emissions were identified through review of recent power system data and reports. A criterion was developed to assess the level of influence of identified key factors and gauge their importance to the emission problem. Modelling was then applied in the next two parts of the study. A model was developed and built for power plant dispatch with year 2006 selected as the base year, being the most recent year with a complete set of dispatch data prior to commencement of this study. Variations of the model were developed based on monthly demand data and two assumed dispatch scenarios: ideal dispatch and limited plant availability dispatch. The models used in the two scenarios were largely similar but the latter was designed to have thermal plant availabilities capped at 85%, which is the normal level expected for thermal power plants in Kenya. The optimised dispatch with limited plant availabilities resulted in 3..+°'0 savings in generation cost compared to the actual dispatch in 2006. Emission penalties were then imposed on power plants and the annual energy generation costs and associated emissions again compared with those of 2006. The actual and Limited Plant Availability cases had close emission levels throughout the year resulting in net CO2 emission reduction of 14,000 tonnes or 1.2% compared to the actual 2006 dispatch. The emission penalties imposed increased the total annual generation cost by US$ 2.3 million and yielded no further emission reductions since plants were penalised but no further dispatch optimization was possible in the absence of alternative non-polluting sources. In the long-term case, the capacity expansion plan for the period 2008-2028 was remodelled with a view to replacing some of the proposed plants with renewable sources without compromising the economics of the plan. The 2007 plan, which had been determined through simulations using the Generation Simulation {GENSIM) software, was remodelled and optimised further using the Wien Automatic Simulation Planning Package (WASP). The WASP optimal solution contained geothermal power plants between 2012 and 2016 and the Low Grand Falls hydropower project in 2020. The GENSIM model was used to further investigate the W ASP output and an optimal plan was developed to simultaneously address the economic and environmental objectives of the study. The remodelled plan had a Present Worth Cost (PWC) of US$ 5,980. million compared to US$ 6,045 of the 2008-2028 least cost plan. The 1.1 % or US$ 65 million difference is sufficient for development of a new 50 MW medium speed diesel power plant. The review enabled displacement of 200 MW coal and 100 MW medium speed plants with 70 MW additional geothermal, 140 MW hydro and 150 MW of imports (also assumed to be hydro). The computed potential emission reduction from the proposed plan was 23 million tonnes of CO2 in the twenty-year period, equivalent to US$ 230 million worth of carbon credits at a conservative rate ofUS$ 10 per tonne. The economic and environmental benefits of avoiding the emissions, though not quantified, are considered much more than the financial value. The three parts of the study collectively contribute towards environmental protection in the present and the future. The dispatch models developed can be used by power planners and operators for daily system dispatch operation. The capacity expansion gives an invaluable insight into the generation planning process in Kenya and forms a suitable reference point for subsequent power planning activities. The entire study is relevant to the national climate change mitigation activities. It elucidates possible areas of intervention and provides information for national reporting under global environmental conventions and possible areas for developing Clean Development Mechanism projects under the Kyoto Protocol. Ultimately, the study makes a contribution towards sustainable development.

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