Using loans is an effective solution for the investment and construction of energy works in general and power plants in particular, especially for developing countries. In economic and financial studies of the project investment preparation stage, the options of using capital and paying interest will be taken into account to minimize risks and increase the project’s ability to pay due debts. However, it is difficult to know which loan repayment option is the most beneficial for the project and when the risk is for the project in the context of debt repayment. The current economic and financial analysis of the project mainly focuses on determining the feasibility of the project through basic parameters, such as net present value (NPV), benefit – cost – ratio (B/C), internal rate of return (IRR), profitability index (PI) and payback period (PP). These parameters do not indicate the most difficult time to pay off the project’s loans. This paper analyzes two options for repayment of long-term loans in Vietnam using the case study of Son La hydropower plant to clarify the above difficult times and recommend a suitable repayment plan for the power project. The analytical method is used to actualize the cash flow of capital and interest during the construction and operation of the works. In Option 1, the debt is paid annually for interest and capital with a constant amount of money during the repayment period. In Option 2, the original dept without interest is paid with a constant amount of money during the repayment period, the interest (due to the remaining original capital) must be paid in the year when the interest is incurred. The study results show that the amount of the annual payment in option 1 is smaller than in Option 2 in the first four years (of ten years of debt repayment). Thus, capital and interest payment in Option 2 may be more detrimental than Option 1 in the first three years of debt repayment, and the amount of money from debt repayment is greater than the profit obtained from power generation. Thus, depending on the profit in the first years when the power plant comes into operation, the investor needs to decide on a reasonable way to repay the loan so that the project can self-finance.

Hydropower use of watercourses has tangible consequences for the environment, society and economy. Based on a literature review and their own research, the authors present current data on changes in the ecological status of waters within run-of-river and reservoir hydropower plants, i.e. changes in biological elements (benthic macroinvertebrates, plankton, ichthyofauna, macrophytes), as well as hydromorphological and physicochemical changes. Previous researchers have noted that the impact of hydropower use of rivers on ecological status of those rivers is extensive, consisting of, among others, changes in species structure and populations of macrophytes, benthic macroinvertebrates, plankton and ichthyofauna (positive as well as negative changes), algal blooms due to increased turbidity, constrained migration of water organisms, changes in temperature within hydroelectric power plants, the phenomenon of supersaturation, eutrophication, changes in hydrological conditions (e.g., increased amplitudes of diurnal water levels and their consequent annual reduction), and increased erosion below the damming and deposition of bottom sediments on the damming barriers. In addition to such changes in ecological status, hydropower use also has a visible impact on socio-economic conditions (e.g., living standards of the population) and the environment (e.g., quality of bottom sediments and biodiversity). The article offers an assessment of the impact of hydropower use of rivers on ecological status (biological, hydromorphological, physicochemical elements and hydrological conditions of such rivers), society, economy and environment; it also proposes a research scheme to assess the impact of hydropower structures.