RES growth linked to grid development. Case Study: Romania

The paper presents Romania to illustrate how more production capacities from renewable energy sources can be integrated as part of the environmental protection and geostrategic policies, in an accelerated energy transition process. Increasing electricity production, especially for the widespread development of wind turbines and rooftop solar PV systems, requires the development of the electrical grid and increased interconnection capacity. The authors of this report also take into account the behavior in different seasons, cold and warm, in terms of the amount of renewable energy injected into the network. The data used in the study is based on the interpreting and associations of various information at the national and European levels, highlighting that the benefits of renewable energy are not only seen in terms of significant reductions in environmental impact but also in terms of cheaper energy! In summary, it is assumed that in 2023-2026, the electricity demand at the level of quality indicators will be covered by investments in new generation facilities related to grid reinforcement measures.


Introduction
In order to facilitate power plant growth and repowering, the enhanced performance of renewable energy power generation units necessitates the construction of transmission and distribution networks as well as stronger interconnection capacity.
The case study that is being given, which focuses on Romania, emphasizes how new production capacities from renewables can be part of the framework of European policies that support the energy transition process.

National Energy and Climate Plan (NECP) of Romania
There are several points and objectives for the Romanian energy and climate plan: • Achieving sustainability goals through the transmission of renewable energy to the end consumers, domestic or industrial.• The development of the transmission infrastructure to accommodate imports, exports, transits, and the anticipated demand for electricity.• Ensuring the operation of the national energy system and electricity transportation network according to the specifications of the Technical Grid Code [6].
• Ensuring that all applicants receive non-discriminatory access to the transmission network and are connected in accordance with all applicable regulations and rules.• Coupling at the European market on all tiers.
• Minimizing investment costs for transport network development solutions.
The revised Romania's National Energy and Climate Plan (NECP) with reviewed climate and energy targets reflecting the Romanian contribution to the overall EU objectives for 2030, is submitted to the European Commission [2].The summary of Romania's 2030 energy and climate targets are provided in Figure 2: In 2030, an extra 946,80 ktoe of new renewable energy production capacity must be put into place in order to achieve a 30,70% of the total consumed energy that has to be provided from renewable sources in the total energy [1].The breakdown by RES technology is shown in Figure 3   To achieve the 30.7% goal of renewables, share in total consumed electricity, the following additional variable RES production capabilities should be implemented [13] Consequently, repowering is required to maintain the current capacity until 2030 in addition to the installation of new wind and photovoltaic power plants and extra capacities [2].In this sense, it is anticipated that repowering will produce roughly 3 [GW] from wind power plants and 1.35 [GW] PV.

The Ten Years Network Development Plan (TYNDP)
The grid development plan is intended to accomplish the following objectives, as per the most recent TYNDP 2020-2029 that Transelectrica, the Romanian Transmission and System Operator, adopted: ✓ The Technical Grid Code and the Performance Standards for Electricity Transmission Service and System Service outline the requirements and quality standards for the safe functioning of the energy system as well as the transmission of power [7].✓ Development of the transmission grid to handle imports, exports, and transits in order to satisfy the anticipated electrical demand.✓ Increasing the ability of electrical networks to connect.
✓ Meeting sustainability goals through grid integration and transmission of energy from renewables to consumers.✓ Connecting to the European market at every level.✓ Ensuring that each applicant receives non-discriminatory access to the transmission network and is connected in accordance with all relevant rules.✓ Selecting a strategy to develop the transmission grid and keep investment costs as low as possible.
An evaluation of the suitability of the Community-wide ten-year network development plan will be part of this non-binding plan for network growth which should be revised on a biannual basis.
Romanian TYNDP 2020-2029 was built on two scenarios addressing sustainability requirements: Reference (RS) and Green (GS).This was done to accommodate an increased uptake of renewable electricity injected into the grid and, consequently, to develop the transmission grid to meet the increasing demand for renewable energy by the final customers.Figure 5 shows the anticipated new generation capacity between 2024 and 2029 [1].[MW] biomass.For system adequacy purposes, the proposed addition of 1 [GW] in pumped storage (Tarnita) supports the approximately 1 [GW] increase in new RES generation in comparison with the Reference Scenario.The Green Scenario calls for only 620 [MW] of fossil fuel decommissioning to be completed by 2024, with no reduction in capacity in fossil fuels between 2024 and 2029, [11], [12].

Case Study: Comparison between NECP and TYNDP for Romania
As a general observation, the NECP's starting point for 2020 shows about 0.7 [GW] underestimate of generating capacity in comparison to TYNDP, [8], [9].
A notable discrepancy can be seen when comparing the NECP and TYNDP capacity objectives for 2029 and 2030, as Table 1 highlights.This discrepancy is primarily in the RES and fossil fuel capacities.

Entire production capacity [MW]
TYND In comparison to the NECP 2030, the RES capacity in the Green Scenario for TYNDP 2030 is understated by roughly 3.3 [GW].This resulted in an overestimation of 343 [MW] for biomass, an underestimation of 1 [GW] for wind power, and a 2.7 [GW] estimate for solar power [4].
Furthermore, it is highly doubtful that the 3.3 [GW] increase in wind and PV capacity in the NECP will materialize by 2025 as projected.
Although the Green Scenario TYNDP's system adequacy analysis indicates that an extra 1 [GW] of pumped storage will be required by 2029, the NECP predicts a rise in hydropower of more than 1 [GW], which is unlikely to be accomplished as intended by 2025.
Regarding decarbonization efforts, the NECP envisions a considerable 1.5 [GW] reduction in fossil fuel powers by 2025, but the TYNDP projected a drop of only 650 [MW] by 2024 and a steady reduction until 2030.
Upon the analysis of the updated capacity forecasts in the draft TYNDP 2022-2031, [2], it can be seen: -In all, TYNDP has 1.6 [GW] more net generating capacity than NECP.
-Compared to the NECP, the TYNDP estimates an additional 2 [GW] of fossil fuels, primarily new gas-fired power plants, and an extra nuclear unit of 0.66 GW (Cernavoda).
-The forecasts for variable renewable energy capabilities match the NECP values, [13].
-In order to meet the 2030 predicted objective, different amounts of renewable energy must be generated in 2026-2030 because the hydro capacity in 2031 does not account for at least 1.1 [GW].
It is also not possible to compute solid RES penetration numbers [TWh] for the next time periods because the TYNDP 2022-2031 lacks a market simulation for the entire year with a minimum of hourly granularity.

Conclusions
The most recent TYNDP release (2020-2029) served as the basis for the comparison of RES scenarios.The NECP's sustainable energy objectives and the Reference-and Green-Scenarios in the TYNDP release 2020-2029 differ significantly with respect to the installed generating mix.
The Romanian Transmission and System Operator -Transelectrica, anticipates that the TYNDP 2022-2031 will continue to be developed with variable renewable energy capacity, in line with the NECP's goals.Nevertheless, the document only considers one reference scenario, which also outlines the green scenario.Furthermore, for the TYNDP 2022-2031, no precise RES penetration numbers for Romania can be projected due to the lack of an entire year of market simulations with hourly resolution.However, in the scenario that an additional 1.1 [GW] of hydropower is not installed by 2030, extra variable RES capacities in the GW level will be required to contribute to the target of 30.7% clean renewable sources in 2030, per the estimated capacity mix in TYNDP 2022-2031.
The European Commission generally contested the 2030 RES target set in the NECP as being too low, which may lead to an upgrade of the NECP by the Governance Regulation.
The most recent version of TYNDP is still not yet in line with the NECP in terms of RES scenarios or decarbonization strategies.

Figure 4 .
Figure 4. Breakdown by RES technologies : a) Wind power: • an increase of 822 [MW] in new capacities from 2022 to 2020 • an increase of 559 [MW] of new capacities from 2025 to 2022 • 556 [MW] increase in new capacities between 2027 vs 2025 • 365 [MW] increase in new capacities between 2027 and 2030 b) solar PV: • a 994 [MW] increase in capacities in 2022 over 2020 • an increase of 1037 [MW] capacities from 2022 to 2025 • 528 [MW] new capacities from 2025 to 2027 • 1.133 [MW] increase in capacities between 2027 and 2030

Figure 5 .
Total generation capacities by the two reference scenarios While the capacity requirements for the intermediate year 2024 are the same in all scenarios, it can be observed that the total capacity objectives in the Green Scenario vs. Reference Scenario diverge by approximately 3.6 [GW] in 2029.The Reference and Green Scenario predict an overall increase in generation capabilities of almost 230 [MW] by 2024, primarily from a rise in RES capacity of 470 [MW] and a decrease in hydropower capacity of 300 [MW], offsetting a loss in fossil fuel capacity of approximately 550 [MW].In the Green Scenario, nuclear power is projected to reach 1,900 [MW] by 2029 (compared to the Reference Scenario's 1,650 [MW] net) with the commissioning of unit 3 at the Nuclear Power Plant (Cernavoda) and the addition of 300 [MW] wind, 500 [MW] solar, and 180