2. Overview of Methodology
EREP was developed using a modelling platform called MESSAGE. MESSAGE is a dynamic, bottom-up, multi-year energy system modelling framework applying linear and mixed-integer optimisation techniques. The modelling platform was originally developed at the International Institute of Applied System Analysis (IIASA), but has more recently been further enhanced by the International Atomic Energy Agency (IAEA). The modelling platform is the framework within which the actual model is developed.
The MESSAGE modelling platform consists of a database which needs to be populated with energy demand and load projections, economic and technical parameters of energy resources and energy supply options, including power plants, transmission and distribution lines, electricity trades and information regarding the existing capital stock and remaining life span. IRENA developed the EREP model by populating the database, configuring it to replicate the existing power infrastructure in each country and setting up a few scenarios in which alterative visions of the future development of a power system and the factors influencing it are quantified. EREP builds on earlier work done by the IAEA. Decisions about investment and operation of plants under consideration and generic plants are a result of the least-cost optimisation in MESSAGE. The least-cost optimisation procedure defines the operation and investment schedule that minimises the total discounted system costs (including investment costs, O&M costs, fuel costs, and any other user-defined costs) over the planning horizon while various system requirements (e.g., supply meets demand at a given time point, that there should be sufficient resources, capacity need to be in place to supply desired production) and user-defined constraints (e.g., reserve margin, speed of technology deployment, emission limits, policy targets) are met. The model reports on the investment and production mix of technologies and fuels that achieve a least-cost power system configuration to meet a given power demand. Economic and environmental implications associated with the identified least-cost power systems can be easily calculated using the model. The modelling framework allows the model to be configured to assess direct social associations (e.g., external costs, job creation effects, local economic impacts).
The model developed by the IAEA was further enhanced by IRENA in two regards. Firstly, additional aspects were included that are essential for the proper assessment of renewable energy technology deployment and secondly, the latest findings for renewable energy technology potential and cost development, based on a series of IRENA studies for Africa were considered. To better reflect the role of decentralised power options for which renewables can offer a significant cost advantage over fossil-based options, the power demand was split into three categories – industrial, urban and rural electricity use. This is important as the shape of the load curve and the connection to the grid differs markedly between categories. Different distributed generation options are available for each category. The set of renewable energy supply options was also expanded and significantly refined. The latest technology cost data anddata were used, based on IRENA cost-competitiveness and technology assessment studies. Data on the quantity and quality of renewable energy resources was updated and refined, using data collected during work on the IRENA-Renewable Energy Atlas.
In the EREP model, each country is modelled as a separate node inter-linked by transmission lines. Each node representing the power system of a single country is characterised as shown in Figure 1. Once the demand is specified, a technically feasible, least-cost power supply system that meets the given demand while satisfying all the constraints is computed by the model for the modelling period. The "least cost" is defined for the region as a whole and for the entire modelling period. EREP considers four types of power generation options, existing power plants, power plants to be commissioned, site-specific power plant projects under consideration (candidate projects), and non-site specific generic power plants. List of plants in the first three categories are taken from the WAPP Master Plan.
Figure 1. Country Power Sector Model Structure