| Abstract: | A hybrid energy storage system (HESS) plays an important role in balancing the cost with the performance in terms
of stabilizing the fluctuant power of wind farms and photovoltaic (PV) stations. To further bring down the cost and
actually implement the dispatchability of wind/PV plants, there is a need to penetrate into the major factors that
contribute to the cost of the any HESS. This paper first discusses hybrid energy storage systems, as well as chemical
properties in different medium, deeming the ramp rate as one of the determinants that must be observed in the
cost calculation. Then, a mathematical tool, Copula, is explained in details for the purpose of unscrambling the
dependences between the power of wind and PV plants. To lower the cost, the basic rule for allocation of buffered
power is also put forward, with the minimum energy capacities of the battery ESS(BESS) and the supercapacitor
ESS(SC-ESS) simultaneously determined by integration. And the paper introduces the probability method to analyze
how power and energy is compensated in certain confidence level. After that, two definitions of coefficients are set
up, separately describing energy storage status and wind curtailment level. Finally, the paper gives a numerical
example stemmed from real data acquired in wind farms and PV stations in Belgium. The conclusion presents that
the cost of a hybrid energy storage system is greatly affected by ramp-rate and dependence between the power of
wind farms and photovoltaic stations, in which dependence can easily be determined by Copulas. |
