FEASIBILITY ANALYSIS OF CONSTRUCTION OF NEW HYDROPOWER PLANTS IN UKRAINE TAKING INTO ACCOUNT THE RISK OF UNUSED POSSIBILITIES

The article presents results of feasibility analysis of construction of new hydropower plants in Ukraine according to the Hydropower development program for the period till 2026, which was approved by our Government in 2016. In particular, there are analyzed perspective plans for building the Kakhovka hydropower plant #2 and six new hydropower plants on the river Dniester, as well as developing small hydropower in the country. The feasibility analysis is based on pairwise comparison of alternatives by the criterion of minimum aggregate risk taking into account the risk of unused opportunities. Components of aggregate risks of alternatives are estimated in dimensionless units for water-energy and operability characteristics and costs of commissioning of new hydro aggregates.


ОСНОВИ ПРИРОДОКОРИСТУВАННЯ NATURAL RESOURCES
The role of manoeuvre power sources in the combined energy systems is best fulfilled by HPPs and PSHPPs. For example, starting hydropower units from a stopped position in a turbine mode with synchronization and a complete set of power is only 1-2 minutes; while at idling speed is 15-30 seconds. Changing the power of the hydro unit or its stop needs only a few seconds [9]. In conditions of significant unevenness of daily power load schedules in the combined energy systems, it is the HPPs and PSHPPs, which have the highest manoeuvrability and the largest regulatory range (Table 2), in general, can best provide a stable, efficient and reliable operation of the national energy system. It is believed that for the stable and reliable operation of the CES of Ukraine, the share of manoeuvrable capacities in its overall electricity balance should be about 15-20% [7][8][9]. At present, the domestic hydropower is capable of reliably providing only about 8-9% of such regulating capacities. As a result, the main regulatory role in the CES of our country is mainly performed by thermal power plants (TPPs) [7]. However, utilization of capacities of the TPPs for adjusting load schedules is uncharacteristic, economically inexpedient and even dangerous for the specified type of power generation. The work of the TPP's equipment with a change in load, frequent systematic shutdowns and start-ups of units, leads to decreasing in their efficiency, fuel overconsumption, accelerated aging of equipment, increasing probability of failures and cost price of electric power. In particular, it is associated with increasing environmental pollution.
Therefore, the decisions on further increase of hydro generating capacity in the country, laid out in the Hydropower development Program for the period till 2026 [7], at first glance, are quite rational. Ukraine requires additional high-manoeuvrability and regulatory electro generation capacities, including because of the development of renewable solar and wind energy, which is characterized by a high degree of dependence on climatic conditions and instability of electricity generation [1,2,[7][8][9]].

Some general remarks concerning current state of hydropower in Ukraine
The main functions of domestic hydropower are the regulation of frequency and load schedules in the CES and the formation of an emergency power reserve providing the technological energy safety of the country [8,9].
Some quantitative characteristics of hydropower development in Ukraine from 2010 till 2018 are given in Table 3. During this period, in the country there have been commissioned three hydro aggregates on the Dniester PSHPP with total capacity of 972 MW in turbine mode (1263 MW in pumping mode) and 31 MW of small hydropower. industry that has been developing in the country in recent years (Table 3) does not have sufficient regulatory capacity compared to large hydropower. Moreover, the work of small hydropower plants according to the "green tariff" in the CES of Ukraine, taking into account the climate, topography, and hydrological characteristics of domestic small rivers [10], can be considered more in the context of renewable energy that needs regulation. The only thing that can be calmed in this situation is that the share of small hydropower in the balance of hydropower facilities in the country is negligible. There is also a tendency for a significant reduction of the share of small hydropower in the structure of non-traditional renewable energy (see Table 3, without large hydropower). From 2009 till the first quarter of 2019 it has fallen from 44% to 3.16%. At present, the power of solar plants in households (see Table 1) in the country is already twice the installed capacity of small hydropower. Household solar, along with bioenergy (biomass and biogas), can be considered as a more acceptable "green" alternative to small hydropower, given that, in general, small hydropower in Ukraine can not be considered as environmentally friendly, including in comparison with the domestic large hydropower [10][11][12].
As for our large hydropower, one of its important features is a significant proportion of hydro-accumulation in installed capacity. In turbine mode, this share already makes up almost 25% (1508.5 MW). Taking into account the pumping storage mode (2016 MW), the overall regulation range in the CES thanks to the large hydropower currently reaches 8064.2 MW. Considering the world tendencies of hydropower development with gradual accent on hydro-accumulation, and limited reserves of hydropower potential of rivers in the country [13,14], an increase in the share of hydro-accumulation can be considered as a positive aspect of the further development of hydropower in the country.

Some general remarks concerning the Hydropower development program for the period till 2026
The Hydropower development program for the period till 2026 [7] was approved by our Government in 2016. This Program has envisaged achieving an ambitious goal, namely, increasing the share of hydrogeneration in the overall electricity balance of the country from the current 8-9% up to 15%.
Although the achievement of the hydropower share of 15% in the total balance of the CES due to the implementation of the Program [7] is quite questionable, in any case an increase in highly manoeuvrable regulatory capacity of hydropower in the national energy system will have a positive effect.
In particular, according to the Program, the following actions are foreseen to provide (See also Table 4 − as well as rehabilitation and construction numerous small hydropower plants (with the participation of private investors and state support for their activities through the "green tariff"). Provided the Program [7] is fully implemented, the installed hydrogeneration capacity in the national energy system will increase by 39%. The share of hydroaccumulation in the overall balance of hydrogeneration in the country will also increase and reach 43%. It can be concluded that the development of hydroaccumulation in the near future is a priority objective of the Program [7].
In particular, the Program [7] states that according to the National Renewable Energy Action Plan [1,2], the total installed capacity of wind power plants and solar power stations, which are non-manoeuvrable power generating capacity, is expected to increase almost fivefold. It is also indicated that an increase in installed power of objects of power engineering using these renewable energy sources should be carried out within the limits that are technically feasible to ensure the reliability of the functioning of the CES of Ukraine. Finally, it is recognized that the use of pumpedstorage hydropower plants is a universal mechanism for solving the problems that exist in the CES of Ukraine.
However, the Program also provides for the modernization and reconstruction of existing hydropower plants and the construction of new HPPs. At the same time, with the total capacity of additional hydrogeneration at large HPPs of about 947 MW, which is more than three times less than the expected new hydrogeneration capacity at the PSHPP (2900 MW), the total costs for commissioning of additional hydrogeneration at the HPPs will be even slightly higher than the costs concerning the PSHPPs. Small hydropower, which is financed by private investors, practically does not change this negative relation between hydrogeneration at the HPPs and the PSHPPs.

Topicality, general objective and particularities of the research
In practice, not only cost indicators and ratio of expected results determine feasibility of projects. Projects may be effective but not feasible. The effectiveness of any project can be stimulated by various kinds of preferences, for example, in the form of a "green tariff" for produced electricity, etc. However, a feasible project does not necessarily have to be absolutely effective too. For example, the Program's [7] project for the reconstruction of existing hydropower plants of the Dnipro and Dniester cascades may be considered quite feasible. Provided it is needed, various alternatives to its implementation may be analysed to find among them a more efficient (optimal, etc.) one.
It is known that hydropower projects, like any other projects, may be burdened with various risks, including the risks of unused (lost, etc.) possibilities (or opportunities, etc.). The latter risks should also be taken into account when comparing alternatives and making decisions. It is also known that traditional hydropower can have a significant impact on the environment [15,16]. Besides of the expected positive effects, unexpected negative socio-environmental and economic effects may occur, affecting other perspective fields of human activity, limiting possibilities for other natural resources users. Taking into account even the most significant socio-ecological and socio-economic effects is a complicated task of analyzing and comparing alternatives. It is quite difficult to get rid of the influence of various subjective conclusions while solving similar tasks. However, the task could be simplified if, at the final stage of decision-making, the best alternatives are compared in their spheres, fields, etc. These chosen alternatives may be considered more feasible than others.
In the research, a method of decision-making was used on the basis of a pairwise comparison of alternatives taking into account the risk of unused possibilities (opportunities). The fundamentals of the method are given in [17]. The method has already been used to solve several tasks related to development of the national hydropower. The first task concerned selecting the optimal variant for the development of the Dnipro HPPs cascade taking into account the risk. The task had been considered in 2010 [18] before approving the Program [7]. There had been established the feasibility of construction of the Kaniv PSP in comparison with the construction of the Kakhovka HPP#2. As the next feasible option of the cascade development it was determined the construction of the Kakhovka HPP#2 with three or four additional units and total installed capacity of 168-224 MW. The second task concerned grounding of an optimal scenario for setting of new hydrogeneration capacities at PSHPPs in Ukraine in accordance with the Program [7]. In particular, it was concluded the feasibility of the commissioning at first of the fourth aggregate of the Dniester PSHPP with the subsequent construction of the Kaniv PSHPP in comparison with other possible alternatives [19].
The purpose of this article is to ground the feasibility of building new hydropower plants in Ukraine in accordance with the Program [7] taking into account the risk of unused possibilities. Among the possible options is the construction of the Kakhovka HPP#2, the Upperdnistrovsky cascade of the HPPs and the further development of small hydropower (See Table 4). The problem is solved on the basis of a pairwise comparison of alternatives according to the method [17]. The peculiarity of the solution of the problem is that the project of the second stage of the reconstruction of existing hydroelectric plants of the Dnipro and Dniester cascades in the Program [7] is accepted as a "zero" alternative.

Formalization of the research: Risks of alternatives and decision making
According to the method presented in [17], the aggregate (or total) risk of each of alternatives is determined in the form of a linear combination of possible costs or other negative effects and results l associated with the corresponding decision, and the expected positive effects or results (benefits, gains, achievements, advantages) g that can be obtained in the case of an alternative solution.
The task of multicriteria optimization on a countable set of admissible alternatives , while their pairwise comparison, is reduced to the next optimization problem: In general, various positive and negative effects or results may have different units of measurement. Therefore, the quantitative assessment of the relevant components of aggregate risk is carried out in dimensionless units (scores) based on a universal log scale (see also [17][18][19]). Then, the score of some value k y of the corresponding characteristic will be like that: where k  is module,

Solving the problem and results obtained
While researching there were considered and pairwise compared eight alternatives. They were ordered and numbered according to increasing installed capacity. These are alternatives 7 0 a a  (See their characteristics in Table 5 where k E is the total quantity and k v is score value of tariff of the unit of electricity produced by the source of hydrogeneration with the index k . For our research, if electricity is produced at large HPPs score value of tariff k v is equal 1. If electricity is produced at small HPPs, let k v will be 5. As characteristics, from which the components of the risk of unused possibilities g were formed, the power capacities reg N , which can be used in adjusting the load schedule in the CES of the country, and power generation E depending on alternatives  Table 6. The results of their pairwise comparison in accordance with the rule (1) are given in Table 7.

Conclusions
The results of our research show that the best alternative to build new hydropower plants in the country among the considered alternatives the alternative 2 a is. This is the second stage of reconstruction of the HPPs of the Dniprovsky and Dnistrovsky cascades and also the construction of the Kakhovka HPP#2. This alternative should be considered the most feasible to improve situation in the domestic hydropower without significant risks.
As well as, it should be noted that alternatives, which provide for the further development of small hydropower in the country, are worse than alternatives which neglect its development. It may indicate that decision to develop small hydropower in the country under the current conditions and thanks to the "green tariff" is questionable and ungrounded.