Battery Storage as Grid Reinforcement for Peak Power Demands

Sammanfattning: An increased amount of intermittent electricity production, more electric vehicles (EV), and an overall electrification of society may all cause a higher variability between the balance of supply and demand on the electric grid. Battery storage has been identified as a solution to the emerging problem asit can be charged during hours of low power demand and then discharged to help meet the power demand during peak loads. This master thesis investigates how characteristics from yearly power demand data can be defined so that a battery energy storage system (BESS) can be dimensioned for it and which parameters are important when dimensioning a BESS. The investment cost of the dimensioned BESS is investigated and calculated, and there is as well a general discussion of potentials, drivers, and barriers for a grid owner to implement a BESS. The master thesis includes a literature study and a case study performed together with Tekniska verken and its subsidiary company Tekniska verken Nät where three cases of varying sizes were investigated:• An EV charging station, with a peak power demand of up to 1 MW.• A distribution station, with an original peak power demand of close to 3 MW.• Purchased power from the regional grid, with a peak power demand of almost 152 MW. By dimensioning a BESS from a year-long data curve of the hourly power demand, a power limit was set. The highest peak power value over the power limit, the longest peak duration, and the highest energy peak were then identified to establish the curve characteristics. A battery storage was investigated to see if it could be used to meet the demand occurring when implementing a power limit to the yearly power demand curve. Batteries store electrical energy in the form of electrochemical energy and then transforms the energy back into electrical energy when needed and does so with varying efficiency according to the type of chemistry that is used in the battery. The so-called lithium ion (li-ion) battery is mostly used today and utilizes lithium in the shape of ions along with a metallic cathode and a carbon anode. The cathode and anode can vary in a li-ion battery chemistry, which varies its characteristics and means that there are multiple types of li-ion battery chemistry types. The specific li-ion battery chemistry lithium iron phosphate (LFP), was established as the most applicable battery due to its high energy density, easy to attain materials, general safety, maturity, and amount of discharge cycles it can handle throughout its lifetime. A BESS could be modelled from the LFP limitations and data curve for each case. The results showed that a short-duration variability of a power demand was a success factor for the implementation of a BESS. It allows the BESS to recharge often and the minimum required energy capacity could be lower and more optimal. An investment cost insecurity was established from literature when comparing estimates, as it could vary depending on the published date, used battery chemistry, taxes, and subsidies in the origin country of the literature. Therefore an estimate given by the Swedish transmission system operator (TSO), Svenska Kraftnät of 5-6 MSEK/MWh from a report published in late 2022 was deemed most relevant. An investment cost for each scenario in every case could be calculated and additional economical benefits relevant in the cases such as comparing to the cost of conventional grid reinforcement or economical gains from a lowered grid subscription were investigated. However, an overall conclusion that the investment cost of a BESS was too expensive to be deemed feasible and that there were no overwhelming economical gains from reducing the peak loads was made. A final generalization and discussion of drivers and barriers concluded that the applicability of a BESS can be identified by the defining characteristics of a demand curve. Moreover, it was found that the BESS investment cost was too high when only applying it for grid reinforcement methods. Although, a BESS can have additional benefits to the grid stability. The grid owner cannot however, own a BESS and use it on the frequency service market which otherwise would potentially make it economically feasible to strengthen the grid. The ultimate goal of the project is to help create a broader understanding of battery storage as part of the electrical network, where and when it can be applicable, and how one could go about investigating its use.