The influence of electric transportation charging modes on the operation of the Ukraine’s Integrated Electricity System and emission levels

This paper studies the potential impact of electric transportation charging modes on Ukraine’s Integrated Power System operation and emission levels. The non-linear integer least-cost model developed by the Institute of General Energy was used. Three electric transportation charging modes were analyzed. Calculations illustrate mainly positive effect of electric transportation on the energy system operation, particularly reduction of fuel consumption and emissions of greenhouse gases and pollutants. The results would support the development of strategies for electric transportation development.


Introduction
Nowadays the humankind is facing the dramatic challenges -the limited technologically available resources of fossil fuels and global climate change.Implementation of electric transportation is effective way to address these problems.Naturally, the part of electricity is produced from fossil fuel combustion, but there are alternative sources of electric energy integrated in national power systems, i.e. nuclear energy, hydro, wind, solar and other renewable sources.Also it should be noted that electric transportation charging stations equipped by solar batteries do not use any fossil fuel and do not produce any greenhouse gases (GHG) and pollutant emissions.
The fleet of electric transportation (ET) rapidly increases worldwide [1,2].The number of electric vehicles per 1,000 residents in EU significantly varies.For example, in 2020 this indicator totals 6.5 in France, 8.5 in Germany, 20.6 in Sweden and 81 in Norway.Ukraine is significantly behind in the number of electric cars (approximately 0.75 numbers of electric vehicles per 1,000 residents).Now Ukrainian government plans to develop national strategy and programs for electric transportation implementation.
The common practice is to compare emissions from ET with petrol cars using average consumption of electricity/fuel per 1 km and specific emissions of GHG and pollutants from electricity/fuel [3][4][5][6].Similar approach is used for evaluating economic efficiency of electric vehicles exploitation.This approach is not comprehensive.We should take into account that ET charging is additional load on energy system operation.Therefore electric transportation causes changes in energy system operation and consequently changes in the emission level.
Although ET presents several environmental advantages, a massive introduction of them could create several issues in the power grid, which has been studied by several researchers [7].For example, in [8], the impact of different penetration levels of plug-in electric vehicles in a distribution system was considered, and it was demonstrated that a significant ET load leads to voltage drop and voltage deviations.In [9], it was demonstrated that charging ET considerably increases the distribution load and, so, the total power losses.Furthermore, ET charging increases the daily peak load.Shafiee et al [10] indicated that ET generate substantial investment costs in distribution systems, and that power losses can reach up to 40 percents for an EV penetration of 62 percents.Lucas et al [11] exposed that ET fast charging leads to harmonic issues and failure to respect IEEE standard limits.Turker et al [12] proposed that the life durations of low-voltage transformers are reduced with a high penetration of ET.
Although ET presents several environmental advantages, a massive introduction of them could create several issues in the power grid, which has been clarified by Clairand et al [7].For example, smart charging of ET is an important area of study, which allows EV users and grid operators to properly manage ET charging profiles in order to obtain technical and economic benefits, as well as considering the specific demand-side management of ET [13].Some other researchers have focused on the management of ET charging stations.In particular, it is crucial to locate the optimal placement of ET charging stations to meet technical grid constraints, considering customer wait times [14,15].
So the fundamental study of the influence of electric transportation implementation on Ukraine's Integrated Power System (IPS) is needed for developing strategies of ET fleet increase.The experience of other countries is not applicable for Ukrainian circumstances.The Ukraine's IPS is unique complex system with different energy sources, partly obsolete equipment etc.
The main factors to consider are the volume of ET and ET charging modes.The specific feature of electric transportation is the opportunity to vary the charging load during the day due to implementing different regulatory and/or incentive measures.
The aim of the paper is to estimate the effect of different ET charging modes on the IES operation, fossil fuel consumption, GHG and pollutant emissions.

Methodology
Author use program and information complex simulating the operation of Ukraine's Integrated Power System developed in the Institute of General Energy of the National Academy of Sciences of Ukraine [16].
This complex is based on non-linear mixed integer least-cost dispatch model.It contains information of all power units in the Ukraine's IPS mentioned below.
Nuclear energy provides a reliable base load and covers more than half of the electricity production in Ukraine (55.5% in 2021).There are four nuclear power plants (NPPs) in Ukraine with a total installed capacity of 13,835 megawatt (MW) (15 reactors in total, including 13 reactors with a capacity of 1,000 MW and two reactors with a capacity of 415 MW and 420 MW, respectively) [17].
At the beginning of 2022, there were 12 thermal power plants (TPPs) in Ukraine with a total installed power capacity of 21.5 gigawatt (GW).Most TPPs are using coal as a primary fuel.In 2021, the TPPs' share in electricity production was 23.8% [18].At the beginning of 2022, the total installed power capacity of combined heat and power plants (CHPs) was 6.1 GW.Most CHPs are using natural gas as a primary fuel.In 2021 the share of CHPs and cogeneration units in electricity production was 5.5%.
At the beginning of 2022, there were ten large hydropower plants (HPPs) with a total installed power capacity of about 4.7 GW (101 units in total) and three pumped storage plants (PSPs) with an installed capacity of 1.5 GW (11 units ranging from 33 MW to 324 MW per unit).Hydropower plays a crucial role in the functioning of the Ukrainian power system, as HPPs and PSPs are the main providers of auxiliary services to meet the peak demand of the power system and balance intermittent Renewable Energy Source (RES) capacities.PSPs also contribute to flattening the night "gaps" of electricity consumption.In 2021, the share of HPPs and PSPs in 3 electricity production was 5.8% and 0.8%, respectively [19].
The photovoltaic (PV) sector had the highest growth rate among other renewable energy sources in Ukraine during 2019-2021.At the beginning of 2022, the total installed PV capacity reached 7.6 GW or 80% of the total RES installed capacity in Ukraine (including 45,000 prosumer installations with a total capacity of 1.2 GW) [20].
At the beginning of 2022, Ukraine's total installed capacity of wind power plants (all onshore) was 1.6 GW.Almost all wind power plants in Ukraine were built in the southern regions nearby the Azov and Black seas coasts (Kherson and Zaporizhzhia regions), where natural conditions   for wind power plants are the most favorable.
A set of calculations was carried out for assessing influence of electric transportation charging modes on Ukraine's IPS functioning, fuel combustion and emissions of carbon dioxide and  Four scenarios were considered.First scenario assumes the ET fleet at the 2020 level (Baseline).Next three scenarios assume that a number of EV in Ukraine increases by five times and consider three charging modes; standard (xFive Standard), equal (xFive Equal) and night (xFive Night) (figure 1).Evidently, two last modes are ideal and not achievable really.However, the results indicate the direction for development of strategy and regulatory acts to get better results.

Results
Diagrams at the figure 2, figure 3 and figure 4 illustrates structure of Ukraine's IPS operation under four scenarios in January, July and annual.Author choose January and July, because usually these months differ each other significantly in consumption level, as well as wind, solar and hydro characteristics.
The results show that the share of nuclear power plants increases practically for all scenarios except for the scenario xFive Equal in Winter.Therefore it is expected the decrease of fuel consumption as well as GHG and pollutants emissions.The table 1 (January), table 2 (July) and table 3 (annual) illustrate this fact.The figure 5 and figure 6 show the behavior of fuel

Conclusions
Electric transportation (ET) volumes rapidly increase around the world.Ukrainian government also plans to develop strategies for ET implementation.For these purposes, it is necessary to study the influence of ET as additional load on Ukraine's Integrated Energy System operation.The main factors to consider are the volume of ET and ET charging modes.ET implementation may affect both positively and negatively the IES operation depending on the share of additional ET load.The calculations were carried out using information and program complex developed in the Institute of General Energy.This paper analyzed the influence of ET charging modes on fuel consumed by IES, fuel intensity and emissions levels.Three charging modes were considered, specifically standard, night and equal.Evidently, two last modes are ideal and not achievable really.However, the results indicate the direction for development of strategy and regulatory acts to get better results.

Figure 2 .
Figure 2. Structure of Ukraine's IPS operation in January.

Figure 3 .
Figure 3. Structure of Ukraine's IPS operation in July.

Figure 5 .
Figure 5. Energy intensity compared to baseline.

Figure 6 .
Figure 6.Carbon dioxide emissions compared to baseline.

Table 1 .
Fuel combustion and emissions in January.

Table 2 .
Fuel combustion and emissions in July.

Table 3 .
Fuel combustion and emissions annual.