Creating models that provide incentives for utilities is a challenging regulatory task. The purpose of this study is to conduct the analysis of different regulation methods that regulators implement to ensure the development of the energy market. The study considers the following main regulation methods: social regulation, rate-of-return regulation, retail price index minus X (RPI − X) regulation, sliding scale regulation and yardstick regulation. Special attention is paid to the selection of an appropriate benchmark method for conducting efficiency analysis with the aim of setting the productivity factor X, which is crucial for the viability of any applicable form of the RPI − X incentive regulation. Under the RPI − X regulatory regime for the defined period of 8 years, the results define the curves related to price cap, productivity gain, cumulative inflation and the adjustments relating to unforeseen events beyond the control of utilities. Incentive regulation contributes to the energy supply at the most competitive price.

Varaždin County is rich in mineral resources, attracting considerable investor interest in opening new exploration areas and expanding existing exploitation fields. Since the economic value of mineral resources changes with market conditions, continuous professional assessment is required. Although the proposed methodological framework is broadly applicable to mineral resource management, this case study focuses on the exploitation of construction sand and gravel deposits in Varaždin County. In this way, it addresses the sustainability challenges characteristic of quarry operations rather than large-scale mining projects. The objective of this study was to develop and test a new method for quantifying sustainability indicators in the mineral resource management (spatial, resource-related, environmental, economic, and social sustainability—I_PREGS) and for calculating an aggregated composite index (AK_I) using a pilot project for construction sand and gravel. The research establishes a cause–effect relationship between quantified indicators (I_PREGS) and the newly established aggregated composite index (AK_I). Methodologically, the study applied multivariate analysis to questionnaire data, enabling the selection, weighting, and aggregation of indicators and the design of a conceptual framework for AK_I calculation. The resulting methodology provides an instrument for monitoring and improving sustainable mineral resource management, supporting the objectives of the circular economy. The findings highlight the potential of the AK_I to reduce systemic inefficiencies, guide policy development, and offer a transparent mechanism for assessing both implementation and effectiveness. This significantly improves the current state and strengthens the basis for evidence-based economic policy-making. The case study in Varaždin County further demonstrated that the AK_I not only reproduces administrative decisions with high consistency but also clarifies how applicants should proceed in cases of partial acceptance and how policymakers can interpret conflicting outcomes across different index variants.

In this paper, the authors elaborated on the conversion of excess electricity, generated from renewable energy sources by water electrolysis, into chemical energy and on its underground storing. Specifically, one of potential solutions...

Increasing the share of renewable energy sources (RESs) in the energy mix of countries is one of the main objectives of the energy transition in national economies, which must be established on circular economy principles. In the natural gas storage in geological structures (UGSs), natural gas is stored in a gas reservoir at high reservoir pressure. During a withdrawal cycle, the energy of the stored pressurised gas is irreversibly lost at the reduction station chokes. At the same time, there is a huge amount of produced reservoir water, which is waste and requires energy for underground disposal. The manuscript explores harnessing the exergy of the conventional UGS reduction process to generate electricity and produce hydrogen via electrolysis using reservoir-produced water. Such a model, which utilises sustainable energy sources within a circular economy framework, is the optimal approach to achieve a clean energy transition. Using an innovative integrated mathematical model based on real UGS production data, the study evaluated the application of a turboexpander (TE) for electricity generation and hydrogen production during a single gas withdrawal cycle. The simulation results showed potential to produce 70 tonnes of hydrogen per UGS withdrawal cycle utilising 700 m³ of produced field water. The analysis showed that hydrogen production was sensitive to gas flow changes through the pressure reduction station, underscoring the need for process optimisation to maximise hydrogen production. Furthermore, the paper considered the categorisation of this hydrogen as “green” as it was produced from the energy of pressurised gas, a carbon-free process.

At the end of the second decade of the 21st century, humanity is at a turning point: either it will find effective answers to the global challenge of preventing the devastating changes caused by the sources of greenhouse gases emissions, resulting from human activity, or the world, as we know it today, will disappear. In this context, and starting from long-term trends of using the geostrategic resources and mineral raw materials, it is noticeable that the world is going through an inevitable transition - an energy transition, a thorough transformation of the global energy and economic sectors. A demand for certain mineral raw materials, metals and minerals such as cobalt, lithium, magnesium, aluminium is growing fast. Digitalization, industry and energy transition are transforming and increasing the demand for raw materials. In this context, critical mineral raw materials and their circular use are of significant importance in the economy because mineral raw materials form the basis of the economy and are essential for maintaining and improving the quality of life. There is no doubt that it will not be possible to implement the European Green Plan - strategy without the usage of critical raw materials. Namely, less than 5 % of the world's critical resources are extracted in the EU, while EU industry accounts for about 20 % of the world's consumption of these resources, and in this context, strengthening the European supply of critical raw materials is extremely important for the Green Plan and the resilience of the key industry.