One Reference Scenario and three variations of renewable promotion scenarios (Renewable Energy Policy Scenario, No Inga Scenario, and an Energy Security Scenario) have been assessed. The Reference Scenario is compatible with the WAPP Master Plan reference scenario, but includes the mining demand (which is about 8% higher than the demand used in the reference scenario of the WAPP Master Plan for 2025). The system was optimised at the regional level, with electricity trade within the ECOWAS region allowed. Only those trans-border transmission projects currently under consideration (decided or candidate) are included as future options to be optimised by the model. Some important differences from the reference scenario in the WAPP Master Plan are:

» Inclusion of decentralised electricity supply options;

» Segregation of rural/urban/industrial electricity demand;

» Updating of renewable energy resource potentials and technology cost data; and

» Annual generation for a given hydropower project is assessed conservatively using a "dry year" generation assumption.

As in the WAPP Master Plan, the decided projects are commissioned at fixed dates while the candidate projects are regarded as investment options from 2014 for the thermal projects, and from 2018 for the hydro power projects. An option to import electricity from Central African region is not included in the WAPP Master Plan thus not included in our Reference Scenario either.

A Renewable Energy Policy Scenario (Renewable Scenario) was set up in which cost reductions for renewable energy technologies due to anticipated technology learning, consistent with the past trends (IRENA, 2013a), are taken into account. This is in contrast to the assumption adopted in the WAPP Master Plan's reference scenario, to which our Reference Scenario was calibrated. Fossil fuel prices are assumed escalated in contrast to the Reference Scenario. An option to import electricity from Central African region where vast hydro resource (such as Grand Inga) is included in all but one scenario.

Two variations of the Renewable Scenario were also defined:

» No Central Africa Import Scenario: Electricity import options from the Central African region are excluded.

» Energy Security Scenario: Import share is limited to 25% of the total electricity demand for each country. Countries that already have a higher than 25% share of electricity imports are modelled so that by 2030, the share is gradually reduced to 25%.

Throughout the analysis, conservative views on the resource potential, firm capacity of intermittent renewable source and penetration limits are retained to ensure that the resulting energy system is reliable. This is a shortcut representation of system reliability, and in the next round of the model improvement, the representation of system reliability would be enhanced by refining the firm capacity of intermittent renewable source according to the geographical dispersion of resource within a country, adding system integration costs of renewables, refining assessment of exclusion zones in solar and wind resource potential estimate, and conducting sensitivity analysis on the hydro generation. Representing the system reliability in the presence of a large share of renewables in energy system models is an on-going research topic elsewhere in the world. IRENA is keeping up with the latest methodological improvements, and trying to implement them wherever possible given the current modelling platform.