The criteria for assessing the quality of the plan include:

• cost: defined as the lowest “net present value” cost of the plan, where the value of reliability is assessed by assigning a “cost of unserved energy” to all energy requirements that are not met by the proposed plan. The cost versus reliability trade-off is at the heart of the optimisation algorithms employed in the ISEP process
• flexibility: refers to the ability of the plan to adapt to changing circumstances with minimum penalty. A key objective is to maximise the amount of flexibility that is available to enable the accommodation of uncertainties without compromising reliability robustness: defines how well committed investments perform under all relevant scenarios
• sustainability: refers to the contemporary (people, planet, prosperity) understanding of sustainability and includes environmental and climate change considerations
• implementation: the ability of the organisation to implement the solution. This includes its ability to raise the required funds, access the necessary skills and source the required fuel and equipment.

ISEP concentrates on the following key uncertainties that impact on the primary planning assumptions:

• Unexpected decrease or increase in electricity demand (short, medium and long term)
• Changes to the load “shape” of the demand for electricity
• Plant failure leading to sustained higher than targeted plant outage
• Unexpected decommissioning, derating or unavailability of Eskom, municipal or imported generating capacity
• Degree of market penetration and sustainability of DSM
• Uncertain and prolonged lead times and cost of building new plant
• CO₂ and other environmental constraints and/or penalties sooner than anticipated
• Fuel supply including increase in supply cost, inflexibility and low availability.