### Target Model and the Integrated Energy Market in the EU  
Market codes are the most relevant codes for electricity markets. These codes describe the \"Target Model\", which is a totally new design for the internal electricity market of Europe. Corresponding legislation includes: (i) the European Union's Directives 2009/72/EC [4], 2019/944 [5], and 2019/943 [6], which define common rules for the internal market of electricity; (ii) Regulation (EC) 714/2009 [7] defining cross-border electricity exchanges; (iii) Regulation (EC) 713/2009 [8] establishing the Agency for the Cooperation of Energy Regulators (ACER); (iv) Commission Regulation (EU) 2017/2195 [9] outlining specific guidelines for integrating the European balancing energy markets; (v) Commission Regulation (EU) 2017/1485 [10], which establishes harmonized rules for TSOs, DSOs, and Significant Grid Users (SGUs), with the goal of providing the proper legislation for the interconnected transmission system operation; (vi) Commission Regulation (EU) 2015/1222 [11], establishing a Capacity Allocation and Congestion Management (CACM) guideline; and (vii) Commission Regulation (EU) 2016/1719 establishing a Forward Capacity Allocation (FCA) guideline [12]. The Electricity Target Model seeks to integrate various national electricity markets into a common European electricity market [13]. These new markets are depicted in Figure 1.  
The Forward and Future Markets react to events that occur years in advance, all the way up to the day of delivery. Forward and futures contracts are agreements to deliver a  
Figure 1: The different markets in the European electricity market [13]. specific power amount at a future date for a price agreed upon today [14]. The Forward Market allows participants of the market to limit their exposure to the Intra-Day Market by ensuring their position when market prices are volatile [13]. Electricity can be traded in Forward and Future Markets between market zones, as well as within market zones [15]. Transactions of electricity with a requirement for physical delivery on a day (D) are auctioned in the Day-Ahead Market on day D-1. Since the market zone must be balanced at the end of the day, the Day-Ahead Market is critical [15], and after it has been cleared, the Intra-Day Market opens [16]. When deviations from their Day-Ahead Market offers occur, market participants can proceed with corrections. Unlike the Day-Ahead Market, which requires a balanced portfolio, the portfolio of the BRP can be unbalanced after the Intra-Day Market [16]. The Target Model is defined in Commission Regulation (EU) 2015/1222 [11] for the timeframes of the Intra-Day and the Day-Ahead. The Target Model of the Intra-Day Market is defined an implicit continuous trade-matching algorithm that enables the coupling of intra-day EU markets is defined as an implicit continuous trade-matching algorithm that allows the Intra-Day Markets' coupling in the EU [17]. After the Intra-Day Market closes, a balancing mechanism ensures that supply equals demand in real-time [18]. The primary goal of the Balancing Market is to make corrections of real-time imbalances in the electricity system between input and output [19]. TSOs must act in real time to secure balancing differences in demand and real-time production. The TSO must contract three types of reserves in the Balancing Reserve Market (Figure 2). Frequency Containment Reserves (FCRs) are used to stabilize the frequency in seconds using reserves (locally activated or/and automatically controlled) [19]. Frequency Restoration Reserves (FRR), which are controlled and activated centrally, are used to restore system balance and are active for seconds to 15 min [19; 20; 21]. When FRR are insufficient to restore system balance, Replacement Reserves (RR) are used (i.e., in case of major imbalances). When frequency restoration reserves are insufficient to restore system balance, replacement reserves (RR) are used (i.e., in case of major imbalances).