Exploring the use of flexibility indices in low carbon power systems

The term `flexibility´ describes the system´s ability to cope with variations and uncertainties in both generation and demand side and maintain the system reliability with minimum cost. This work presents two different ways of establishing flexibility metrics so that the flexibility of individual units as well as the whole system can be quantified offline without using complex multi-temporal simulations. The first metric is named Normalized Flexibility Index´ (NFI). It is obtained by analyzing the adjustable space of generators and the flexibility level is expressed as a normalized positive number less than unity. The second index, named Loss of Wind Estimation (LOWE), assesses the flexibility level of a system by its capability for accommodating wind. It measures the probability that wind curtailment occurs during a year. The performance and potential applications of the two indices are discussed in the paper. The results indicate these indices provide a convenient way to get a quick, consistent overview of how flexibility different systems are.