Smart Use of Battery Energy Storage Systems to Improve Power System Adequacy
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- Institutt for elkraftteknikk 
As the penetration of renewable resources increases in the power system, the utility faces new challenges to secure a reliable power supply. Electrical energy storage (EES) is anticipated to play a significant role in dealing with the intermittent nature of resources such as wind and solar energy. The principal objective of this thesis is to study how EES systems, and then mainly battery energy storage systems (BESS), affect the power system s ability to meet the demand. Using the «Loss of Load Probability» (LOLP), it is possible to investigate how a BESS affects the system adequacy. LOLP expresses the likelihood that the power margin (P_margin=P_supply-P_demand) is smaller than zero. In this project, the LOLP has been calculated for a particular case study in Finnmark and Nord-Troms (referred to as northern Norway). The studied cases are equal to the cases in the corresponding pre-project, where an analytical model was applied to calculate the LOLP. The power demand in northern Norway is anticipated to increase significantly from 2015 to 2030. Six cases (case B to G) represent different scenarios in 2030. These reflect the power system with a new power line and/or increased wind power installations. The base case (case A) represents the power system situation in 2015. Employing Monte Carlo methods, the LOLP, «Expected Energy Not Supplied» (EDNS) and «Expected Capacity Margin» (ECM) are estimated. Two Monte Carlo models have been developed. The first one, Model 1, aims to imitate the case study that was conducted analytically in the pre-project and simulates the system reliability for the peak load hour. The results obtained by Model 1 are approximately equal to the results from the pre-project, and the Monte Carlo model is therefore assumed to work as it should. The results show that investments in both the grid and wind power will be necessary to meet the predicted power demand in 2030. Already in the base case, the system security is deficient, and a new transmission line is needed to secure the power supply. An extension of wind power generation is shown to improve the system adequacy in the case of an outage on the new power line. Due to challenges regarding the reliability, the power system in northern Norway is a suitable case when studying the possible effects of BESS on a power system with limited import capacity. Monte Carlo Model 2 includes BESS into the simulations and simulates the LOLP, EDNS, and ECM based on an hour-to-hour basis. The base of the simulations is equal to case D in Model 1 (includes 1300 MW wind power). However, the energy and power capacity of the BESS are varied. Nine cases have been simulated: P(BESS,rated)= [0 0.25 0.50 1] ∙P(wind,average)E(BESS,rated)= [0 2 8 168] hours ∙ P(BESS,rated) The simulations demonstrate that BESS installations have noticeable positive effects on system adequacy and that the LOLP and EDNS improve with increased rated power and energy capacity of the BESS. If the demand in northern Norway increaes as anticipated, it is likely that action has to be done to obtain a satisfactory system reliability level and BESS might be a good option to achieve this. For energy management applications, it turns out that rated energy capacity has a higher priority than the power rating of the BESS. Another important observation is that the BESS has a smoothing effect on the intermittent nature of the wind power production, as the BESS shifts energy from hours with power surplus to hours with power deficits. The thesis also contains a review of battery technologies for stationary applications that already are accessible, or under development, along with the advantages and disadvantages associated with these technologies. The literature review concludes that it is hard to predict which technologies that will succeed or not at this stage in the development, but that is very probable that BESS will be crucial for the future power system.