The Standard Geothermal Plant as an Innovative Combined Renewable Energy Resources System: The Case from South Poland

Abstract

Geothermal energy, as one of the more well-known renewable energy sources (RES), is used in many operating installations around the world. Depending on the temperature of the geothermal waters in question, the choices range from installations for generating electricity (high-temperature geothermal energy), to the production of thermal energy for use in recreational complexes, to fish farming (low-temperature geothermal energy). Lindal’s diagram determines the possibilities of using warm groundwater for many investment projects. In light of the drive to avoid climate change, it seems that the conventional “one-way” use of geothermal water resources is insufficient. Therefore, this article presents an optimal innovative solution wherein geothermal water is fully utilized in a geothermal cogeneration installation to produce heat and electricity and to provide cooling. In addition, it was proposed to expand the investment with photovoltaic and hydropower plants to ensure greater energy independence by diversifying energy sources and increasing the share of energy supplies based on renewable energy sources. Such a broad approach allows for the implementation of a sustainable development strategy in the field of environmental protection. The proposed solution involves the modernization and expansion of the existing energy generation sources by a heating plant and a geothermal power plant in Chochołowskie Termy (South Poland), as well as the construction of a power plant based on a photovoltaic installation, hydropower setup, and energy storage. The presented innovative solution may be an excellent example of implementation for similar geothermal facilities in the world. The novelty of the system is the approach of assessing and combining the different RES in one project, based on a geothermal plant. Popularizing this solution in the wider scientific environment may have a real impact in terms of the reduction of pollutant emissions.

1. Introduction

The intention of this paper was to identify an innovative comprehensive design for optimizing the use of renewable energy sources that can be applied broadly and universally. An analysis of existing publications shows a shortage of such solutions. The hydro-geo-solar (HGS) system in question, taking the example of the Chochołowskie Termy (ChT) geothermal pool complex in South Poland, was developed to address these needs; such a course of action may be implemented in similar projects around the world. The analyzed solution contributes to achieving the proposed ecological goals and to the improvement of RES utilization, thus minimizing the effects of climate change. The course of action presented in this paper includes universal criteria for all such projects and, in particular, includes the presentation of a comprehensive and coherent description of the system, together with the needs addressed. The paper includes a presentation of the results of the necessary technical and technological analyses for the implementation of a combined RES system. The economic basis for the implementation of the proposed system is, in the opinion of the authors, strongly case-specific and, thus, cannot provide a model for direct implementation in other similar facilities. Therefore, they were not included in the analysis. Such a comprehensive approach to the proposed RES system ensures that it can be verified at the early stages of planning and preparation for implementation, which increases the chance of successful implementation.

Due to concerns for the broader natural environment, the role of renewable energy sources (RES) is more and more significant in the world today. Such solutions are considered the most environmentally friendly installation solution for electricity generation. The requirement of a percentage share of energy production from renewable sources has been ratified in many legal regulations, including those for the European Union member states [1,2,3,4]. Thus, their pro-ecological stance has been confirmed by law. The coal, oil, or gas resources in these countries are limited and the process of energy generation in conventional power plants is currently related to the emission of many pollutants into the environment. For these reasons, technologies are currently being strongly promoted that enable obtaining energy from RES, a so-called “clean energy”. Unfortunately, the conventional, “one-way” use of the selected sole resource (e.g., water, wind, geothermal) is insufficient. The progress made in the field of RES, as well as the possibilities for protecting the environment from the hazards connected with fossil fuel utilization, are now widely discussed [5]. There are many conference activities, scientific articles, and project descriptions from all around the world that are focused on human priorities, such as the progress made/possible in harnessing renewable energy sources to stop climate change. The methods presented in the various conferences, e.g., the International Conference on Sustainable Energy and Environmental Protection, SEEP 2018 [5], are focused, among other topics, on the development of efficient energy conversion systems with low/no environmental impacts. Many projects show the path toward optimizing RES use and to stop/minimize climate change. Sarma and Zabaniotou [6] proposed various courses of action for a more sustainable and resilient renewable energy sector, based on climate change, the potential biological hazards, and human wellbeing. Kaczmarczyk et al. [7] presented the concept of managing low-enthalpy geothermal waters for the purpose of electricity generation in the first stage of the cascade. Thermodynamic calculations were conducted, assuming the use of the organic Rankine cycle (ORC) or Kalina cycle in two variants. The results indicate that the gross capacity in the most optimistic variant will not exceed 250 kW for the ORC and 440 kW for the Kalina cycle [7]. There is a huge area available in which to implement RES technologies, e.g., in Nepal, where roughly 70% of energy consumption is generated from traditional energy sources, while renewable energy accounts for approximately three percent of its energy [8]. Sowiżdżał et al. [9] analyzed whether RES use could also improve living conditions. Despite a large number of similar projects, access to renewable electricity is still limited in many countries, such as Algeria (with 0% of national electricity generation from RES), Iran (7%) or Egypt (9%) [10]. In the literature, there are many papers titled “combined renewable energy resources” but, in fact, most of them refer to the utilization of water with the supplement of wind and solar energy projects for the proper and efficient management of water resources, e.g., in Tajikistan [11]. Here, there are numerous additional objections against hydropower plants—there is a conflict between the downstream country (Uzbekistan), which mostly utilizes water for irrigation, and the upstream country (Tajikistan), which uses water mainly for the generation of electric power. Bagherian and Mehranzamir [12] reviewed the energy generation of renewable resources, including solar, wind, and geothermal energy sources, until 2020. This article attempts primarily to elaborate on the integration of single renewable energies in combined heat and power systems. Multiple renewable energies in one system are rarely implemented. The conclusions of this review paper are the same as in their previously published paper—the integration of different renewable energy sources is highly necessary to facilitate more efficient and feasible operation. Therefore, an innovative, novel system unlike any yet developed, with combined geothermal, solar, and water resources, is presented in the current paper.

Lindal’s diagram [13] determines the possibilities of using warm groundwater for many investment projects. In light of climate change prevention, the conventional “one-way” use of geothermal water resources appears to be insufficient. Therefore, this paper presents the possibility of the optimum use of several RES on the basis of an existing expanded geothermal installation. All around the world, in geothermally favorable areas, geothermal waters are usually extracted using deep boreholes. Most of the published investigations focused on identifying the geothermal distribution heat flow by, e.g., mapping the subsurface temperatures [14], assessing the geothermal potential, gradients, or steps [15,16,17] utilizing Geograpfic Information System [18,19], as well as the evident geological characteristics [20,21].

Wherever renewable energy (RE) is available for effective use, it should be maximized for various purposes, not only for electricity generation and heating but also, if possible, for other applications, e.g., geothermal water for recreational use or balneotherapeutics. Unfortunately, most often, a geothermal borehole is not combined with any other RES type. In addition, with the recreational use of geothermal water, there is the need to discharge the water used into the environment, which is regarded as a burden on flowing waterways that are usually the recipient of wastewater [22]. It appears that injecting water back into the rock mass is a more environmentally friendly but much more costly solution [17]. Elimination of the used geothermal water is a serious challenge [23,24], and injection is probably one of the most expensive processes in geothermal energy utilization. Most of the published papers on this subject are focused on minimizing the environmental impact and climate change. Liu et al. [25] proposed a new geothermal energy-assisted natural gas hydrate recovery method that can simultaneously exploit geothermal energy and natural gas hydrates by injecting water into a geothermal heat exchange well. The proposed system produces fewer carbon emissions and is more environmentally friendly.

A combined system with optimized RES (as is proposed in this paper), based on existing geothermal plants, should focus on three areas:

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Increasing the products/services offered by the company;

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Ensuring more energy independence for the facility by diversifying the energy sources and increasing the share of those based on RES;

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Implementing a sustainable development strategy for the protection of the environment and to make a contribution to climate protection.

2. Case Study: Chochołowskie Termy Geothermal Complex

The facility where this innovative solution will be applied is the existing geothermal pool complex of Chochołowskie Termy (ChT) facility in southern Poland, in Europe. The thermal waters used to heat the facility and present in the thermal pools are extracted from a depth of 3572 m. The Chochołów PIG-1 borehole, from which the water is drawn, was drilled in 1989–1990 and is one of the most abundant intakes in the region [26,27,28]. The water temperature at the intake is about 90 °C. In the deep boreholes that are used to access geothermal waters, it is extremely important to take the thermal lift effect into account. The main hydrogeological parameters of the Chochołów PIG-1 borehole are shown in

Table 1. Characteristics of the Chochołów PIG-1 borehole.

Exploiting Capacity Q (m3/h)	Temperature at the Outflow T (°C)	Static Water Table (m a.s.l./m a.g.l)	Dynamic Water Table (m a.s.l./m a.g.l)	Chemical Type
160	t = 89.8 °C	945.0/155.46	799.5/10.0	0.11%SO4-Ca-Mg-Na

.

Disregarding this effect invalidates the analysis results and results in incorrect determinations of the basic hydrogeological parameters [29]. The swimming pool complex here is a five-story service recreation building, with swimming pools, leisure pools, thermal pools, catering, a sauna area, and a spa (Figure 1). The total water surface area is almost 3000 m².

There are two main geological and structural units in the study area (see Figure 1 and Figure 2): the Tatra mountains (lower unit) and the Podhale basin (upper unit). The lower unit (lower structural element) uplifted and exposed in the Tatra massif, consists of a crystalline metamorphic series of older and younger pre-Permian granitoid intrusions and a Mesozoic sedimentary series, among which, apart from the dolomites, limestones, and marls, there are also sandstones and shales. The formations of the lower unit occur in two facies or tectonic series: the southern one, known as the Wierchy series, and the northern one, known as the Regle series, stretching along the border with the Podhale basin. The Wierchy series is built around a crystalline core covered, on the north side, with Mesozoic sediments. There are no crystalline rocks within the Regle series. The upper unit from the Paleogene is younger in relation to the lower unit; it covers the Regle series of the lower unit transgressively. The formations of the upper unit fill the Podhale basin. They consist of two different links in terms of thickness and spreading sediment cells. The lower link, carbonate, is represented by organodetritic limestones, conglomerates containing carbonate rock fragments and dolomites. The upper link—flysch, known as the Podhale flysch, consists of slate, mudstone, and sandstone formations. The maximum thickness of the Palaeogene sediments (upper unit) in the Podhale basin, according to the drillings performed so far, is over 3000 m (3067 m, in the “Chochołów PIG-1” borehole). In the Podhale basin, the Quaternary formations are represented by Pleistocene sediments of fluvial and glacial origin, Holocene river alluvials, weathered covers, and landslide collars.

The groundwaters of the Tertiary (Palaeogene) aquifer are associated with the deposits of the Podhale flysch and carbonate sub-flysch formations (Tatra Eocene). The deposits of the Podhale flysch (slate and sandstone) are poorly watertight. On a regional scale, as a whole, they can be considered isolating works. They mainly represent a crevice, or less often, a crevice-pore type of aquifer. The water table is usually a subartesian type. Waters occurring in deeper, sub-flysch aquifers are always subartesian or artesian types. They represent a fissured or fissured karst type of aquifer. The waters of the Mesozoic aquifer are mainly fissured karst waters and karst and are related to the carbonate rock series. There are four aquifers. According to the traditional division, these levels form two levels of deep groundwater: upper and lower. The Eocene carbonate waters are included in the upper layer. The existence of the layers depends on the presence of a clay–mud–shale complex with a thickness of about 100 m. These formations play an insulating role on a regional scale. The area of rainwater supply to the sub-flysch aquifers is located in the Tatra Mountains. The rainwater infiltrating this area moves northward in a system of karst fissures and voids, in the direction of the collapse of the Tatra series. A part of the water has a relatively short circulation because it appears on the surface in the form of springs or drains into valleys. The remaining part of the water penetrates the depths of the rocks, heats up, and is captured through holes in the ground as geothermal water.

Termy has been operating a recreation and tourism business in Podhale since 2016. The existing pool facility is fed from the Chochołów PIG-1 well, for which a conditional license was issued in 2011. The concession will expire in 2036. The company currently extracts up to 120 m³/h of thermal water, which is sufficient to meet the heat demands of the existing pool facility. The conditional concession presumes that the handling of the used thermal water after 2025 will consist of injecting it via an absorption well into the rock mass. A temporary derogation from this condition was obtained and the used thermal waters are currently being discharged into the Czarny Dunajec River.

When writing about the activities at ChT, one should not forget about the sustainable development policy it implements. Caring for the environment and supporting the development of the local community while implementing horizontal policies is a very important part of their activities. ChT carries out a number of activities aimed at counteracting environmental degradation. In addition to using renewable energy sources (from a geothermal source) to produce heat for the swimming pool complex, ChT strives to reduce its environmental impact in all its processes. Particularly noteworthy is the use of modern technology in the thermal water treatment process. With the use of nanosilver in the water treatment process, it is possible to remove activated carbon (which is considered a dangerous technological waste) from the filter bed and, using a three-stage disinfection process, can achieve bacteriologically clean and, above all, healthy pool water needing only a significantly reduced dose of sodium hypochlorite.

The implementation of the combined RES system described in this paper is a natural progression towards sustainability. The designed technologies and solutions based on a geothermal source and solar energy will reduce the consumption of primary raw materials and make a measurable contribution to reducing CO₂. The proposed solution can be successfully implemented in other, similar, facilities.

Geothermal Borehole Duplex

With the implementation of the HGS system, a new geothermal borehole, Chochołów GT-1 will be constructed and the currently producing borehole Chochołów PIG-1 will be converted into an absorption borehole (Figure 2). The capacity of the new source will be increased to 160 m³/h. The proposed Chochołów GT-1 borehole will be located on the ground surface approximately 385 m to the west of the existing Chochołów PIG-1 borehole (Figure 1). It is planned that a directional borehole will be drilled with an “S” type trajectory. The directional azimuth of the hole will be 20°. The bottom hole distance from the surface location will be 1102 m, while the bottom hole distance between the existing Chochołów PIG-1 borehole and the proposed Chochołów GT-1 borehole will be approximately 992 m. The distances given will allow the limitation of possible interference between the boreholes and, in the case of the Chochołów PIG-1 borehole being used as an injection borehole, which is very likely, and the re-elevation of the temperature of the thermal water.

To a depth of 100 m MD, the Chochołów GT-1 will be drilled as a vertical borehole; from 100 m MD to 1800 m MD, a gradual angle increase is planned until a maximum of 44° is reached. From 1800 m MD to 3100 m MD, there will be a gradual angle drop. From a depth of 3100 m MD to 4122 m MD, the Chochołów GT-1 borehole will then be drilled vertically.

The ChT development strategy calls for the implementation of measures to expand the product range by diversifying the existing offerings in terms of swimming pools, saunas, and spas, as well as catering. Such a significant expansion of the facility raises the question of the scale of the future demand for heat and electricity. The consequence is to increase the energy independence of the facility in terms of maximizing the use of renewable energy sources and heating and cooling.

Currently, all thermal energy for the ChT is drawn from a geothermal source (the Chochołów PIG-1 borehole), which is more than 30 years old, while electricity is purchased from a national electricity supplier. This energy comes from fossil fuels (and thus is not green). Taking into account the provisions of the concession, which implies the need to have a second well fulfilling the absorption role, and the company’s consistent policy based on ecological sustainability, the plans for ChT must take into account the diversification of energy sources and investment in renewable energy-based installations. It is not without significance that the operation of the existing facility is 100% based on heat from the Chochołów PIG-1 well that was drilled in the late 1980s. The construction of the new Chochołów GT-1 borehole is necessary from the point of view of the security of thermal water supply and the continuity of operations and development with a new infrastructure.

3. Case Study (Methodology and Aim of Combined RES System)

The proposed system includes the modernization and expansion of existing energy generation sources provided by a geothermal heat and power plant, alongside the construction of a power plant based on a photovoltaic installation and energy and heat storage. The combined RES system involves the construction of a hybrid plant for the production of heat, cooling, and electricity based on geothermal and solar energy for CHT. In the remainder of this article, the proposed solution will be referred to as the HGS (hydro–geo–solar) system.

The proposed concept includes a cascade heat collection system equipped with an ORC plant [31] and heat exchangers, a micro hydro turbine, a photovoltaic plant, and energy storage. For Chochołowskie Termy Sp. z.o.o., this is a rational solution that takes into account the directions of development of distributed energy, increasing the use of RES, and protecting the environment by reducing the consumption of fossil fuel resources.

For the development of the concept of the heating plant, including the ORC power plant, the demand for peak power of individual heat receivers was assumed to be the nominal power demand for the equipment, including heat exchangers. The proposed plant will supply both the existing and newly designed facilities, so both demands have been balanced.

In order to achieve the declared objective, it is necessary to drill a new geothermal borehole and build RES generation sources for heat, cooling, and electricity production. The new borehole will allow wider use of the industrial geothermal source to power the current swimming pool facility and the newly built leisure and recreation area. The geothermal energy from the new borehole will produce process heat for heating the thermal pools, heating the pool facilities (e.g., changing rooms and spa), heating the leisure and recreation area in winter, and cooling it in summer. The HGS system will also use two technologies to produce electricity from geothermal energy: an ORC cogeneration plant with a capacity of approximately 220 kWe and a 43 kWe micro-hydro-turbine in the geothermal boiler plant behind the head (Figure 3).

A 693 kWp photovoltaic power plant, located on the roof of the current above-ground car park, will provide a complementary source of electricity for the proposed RES installation at ChT. To maximize the company’s use of RES, an energy storage facility will be built to optimize the RES generation system, energy management, and operation of the company’s stuff and customer electric vehicle charging stations. The energy storage will be recharged from the PV power plant and ORC CHP plant during off-peak periods, and the excess energy will be used for ChT’s own facilities. The expected effect of reducing the facility’s electricity demand from the region’s electricity grid is an average of 25% and varies from 19 to 27%, depending on the month. The environmental effect of the HGS system will be an increase in avoided emissions: CO₂—1900 t/year, SO₂—1691 kg/year, NO_x—1567 kg/year, CO—683 kg/year. and dust—89 kg/year (calculated according to the KOBIZE 2019 methodology and indicators [32]).

3.1. Heat and Electricity Demand

Based on the technology audit carried out for the existing ChT facility for the development of the HGS system, the heat streams within the facility were determined (

Table 2. Thermal power demand in the Chochołowskie Termy complex.

Thermal Power [kW]	Current	New Facilities	Total
(1) Central heating	329	56	585
(2) Pool heating	8392	1067	9459
(3) Process needs	1686	1588	3274
(4) DHW	480	300	780
(5) De-icing	555	-	555
(6) B8 pool supplementation	256.9	-	256.9
TOTAL	11,698.9	3211	14,909.9

). The heat power requirements of the existing Termy facility include: (1) the CO central heating system (70/50 °C radiators and 38/34 °C underfloor heating, with no delineation of heat streams to different parameters); (2) the pool technology (36/34 °C in most pools); (3) process needs, mechanical ventilation, and air curtain supply (70/50 °C and 30/20 °C, in the case of air curtains); (4) DHW preparation (70/50 °C and preheating 38/35 °C); (5) estimated thermal power demand for de-icing (low-temperature waste heat < 30 °C); and (6) the water make-up in the pools, including B8 (via geothermal water bleed at 37.6 °C). The total thermal power demand of the facility adds up to a value of 11,698.9 kW, which is the peak power value.

The planned expansion of the complex includes a leisure and recreation area. To cover the heat demand for the newly designed facilities, the following heat streams are distinguished (Table 2): (1) the CO central heating system, including 26 kW for the changing room and 230 kW for the rest of the building (radiators 50/35 °C and underfloor heating 40/30 °C, with no delineation of heat streams for different parameters), (2) the swimming pool technology (heated to 36/34 °C in most pools); (3) mechanical ventilation, including 36 kW for the changing room and 1552 kW for the rest of the building (60/40 °C); (4) DHW preparation (70/50 °C and preheating 38/35 °C). The total thermal power requirement for the new facility is, therefore, estimated to be 3211 kW.

To cover the heat demand for the newly designed facilities, 3211 kW is needed. Electricity generation will come from three sources: a 219.5 kW ORC plant generator turbine, a 46.5 kW hydro turbine, and a 693 kWp photovoltaic installation.

The electricity demand of the existing facility will be partly covered by RES (Figure 4). Calculations of the demand and energy coverage from RES were made using 15-minute data from 2018–2019 and computer modeling of PV production, with shadow analysis for the location of the parking shelter installation. Simulations of the operation of the ORC unit with a water turbine were made on the basis of the actual heat demand for 2018.

Due to the nature of the heat source, which comes from the extraction of geothermal water at a temperature of 88 °C, the development of a concept for utilizing this heat requires that attention be paid not only to the need for thermal power but also—and above all—to the temperature range of the individual receivers. It should be noted that the total available thermal output of a geothermal source, calculated as the product of the water mass flow (a maximum of 160 t/h is assumed), the specific heat of the water, and the temperature difference (between the geothermal water temperature of 88 °C and the ambient temperature of 0 °C) can be presented as:

$$P_{\mathrm{geoterm}}=44.4\frac{\mathrm{kg}}{\mathrm{s}}·4.19\frac{\mathrm{kJ}}{\mathrm{kgK}} ·\left(88 °\mathrm{C}-0 °\mathrm{C}\right)=16,317 \mathrm{kW}.$$

(1)

This will not be sufficient to cover the demand at the previously mentioned value if the heat receivers need to be supplied with a medium at a temperature of, e.g., 60 °C. In this case, the recoverable heat output will be:

$$P_{\mathrm{geoterm}}=44.4\frac{\mathrm{kg}}{\mathrm{s}}·4.19\frac{\mathrm{kJ}}{\mathrm{kgK}} ·\left(88 °\mathrm{C}-60 °\mathrm{C}\right)=5209 \mathrm{kW}.$$

(2)

In the case of heat circuits in which the medium with the lowest parameters has a temperature of 30 °C, the maximum available thermal power from the geothermal source will be:

$$P_{\mathrm{geoterm}}=44.4\frac{\mathrm{kg}}{\mathrm{s}}·4.19\frac{\mathrm{kJ}}{\mathrm{kgK}} ·\left(88 °\mathrm{C}-30 °\mathrm{C}\right)=10,790 \mathrm{kW}.$$

(3)

For this reason, in addition to the quantity of available heat, the quality of the heat (temperature) was also taken into account for this concept and was the available temperature that was taken into account in the planning phase.

On the basis of an analysis of the thermal (as well as cooling and electrical) power requirements of the existing facilities, the supply temperatures of the individual heat receivers, and the planned investments and changes to the facility’s energy installations, a concept for a cascade heat exchanger system was devised, taking into account the required outlet temperatures of the circulating medium (28–36 °C for swimming pool systems, 55 °C for domestic hot water systems, 60–75 °C for central heating and mechanical ventilation). The available heat output and heating medium supply temperatures predispose the system to be equipped with cooling systems (sorption chillers) in the future (for a supply temperature of 65–70 °C, among other things, during future expansion or modernization works at the facility, a COP of 0.85–0.90 can be assumed).

The following assumptions were made in the presented conceptual solution:

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Due to the lack of separation of heat streams between the central heating systems of radiators and underfloor heating, the analyses assumed that the entire power associated with the central heating system is disbursed for radiator technology (70/50 °C in existing facilities and 50/35 °C in new facilities).

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Similarly for mechanical ventilation, where it is assumed that the small heat flux for air curtains is included in the mechanical ventilation flux of 70/50 °C, as in the existing facilities (in favor of certainty). In the newly constructed facilities, 60/40 °C has been assumed for ventilation.

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Hot water heating up to 60 °C was assumed (in order to ensure the required 55 °C in water intakes, assuming possible transmission losses).

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The temperature was assumed to be raised by 2 K in the pool exchangers responsible for maintaining the water temperature during the normal operation of the facility.

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A water temperature of 10 °C was assumed in the water supply system.

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The following parameters for the geothermal water extracted from the planned Chochołów GT-1 borehole were assumed for the analysis:

• Temperature 88 °C;
• Pressure 160 kPa;
• Flow capacity 160 m³/h (equivalent to a mass flow of 44.44 kg/s).

3.2. Description of the Process Line

The process diagram of the proposed installation is shown in Figure 5. The capacities in the diagram refer to the differences in enthalpies between the inlet and the outlet (an isobaric heat exchange was assumed). For the thermal water intake and discharge, the values have been referred, using a temperature of 0 °C.

Geothermal water with a temperature of 88 °C and a pressure of 1600 kPa, moving at a rate of 160 m³/h will be drawn from the source. Its potential is 16,436.5 kW of heat when the water is cooled to 0 °C. Assuming that the water injected back into the ground will be 12.8 °C, the maximum heat output to be received from the geothermal water will, therefore, be 16,436.5 kW − 2395.6 kW ≈ 14 MW.

The first step in the process line is the installation of an ORC evaporator, which lowers the feed temperature of the first of the heat exchangers (from 88 °C to 78 °C) and, consequently, limits the high-parameter heating power available in the system. However, the location of the evaporator results from the nature of the thermodynamic transformation of the low-boiling medium, so that, to maintain at least a satisfactory level of electrical power in the system, relocating it within another heat exchanger was not considered (this would have required, among other things, the provision of an additional heat source, preferably with a temperature above 100–120 °C).

Due to the relatively low evaporation temperature of the R134a refrigerant in the ORC line, the heat from the evaporator is usually exported to the atmosphere, e.g., in a fan cooler. In the case of the facility under study, however, it is possible to use some of this heat (134.1 kW), e.g., to maintain the water temperature in pool B15. The ORC circuit, however, primarily yields 221.4 kW of net electrical power.

Then, downstream of the ORC circuit, the geothermal water flows through a water turbine to utilize the available pressure; the drop in pressure to 250 kPa allows 48.3 kW of net electrical power to be generated. The turbine is an example of a system for active pressure reduction, allowing the pressure to be adapted to the conditions in the heat exchangers, with energy recovery (unlike valves and other passive systems). The proposed microturbine is of a Francis type, with an expected efficiency of 86% and a speed rate of 750 r/min.

Another element of the process line is the heat exchanger plant, consisting of six successive heating stages and one geothermal water vent. The heating stages are a series of cascade (series)-located heat exchangers, further reducing the temperature of the geothermal water and cooperating with the appropriate heating circuits with adapted parameters (temperature ranges).

The highest-parameter circuits (70/50 °C)—central heating and ventilation—are supplied in heating stage I. The geothermal water cools down to 67.2 °C, giving off a heat flow of 2015 kW.

Domestic hot water (DHW) is then heated in heating stage II. DHW is heated in two stages: first in heating stage V, initially rising to 30 °C (312 kW), before being reheated in stage II to the required 60 °C (with the remaining 468 kW). This procedure is an example of exergetic rationalization (the quality of the available energy) of the circuit and maximization of the heat output at the set parameters of the individual heating circuits. After heating stage II, the geothermal water is at 64.7 °C.

Heating stage III feeds the heating and mechanical ventilation circuits in the new buildings (60/40 °C), giving off a total of 1844 kW of thermal power and reducing the temperature of the geothermal water to 54.8 °C.

In heating stage IV, due to the low water temperature, it was decided to feed the pool heating nodes. Lowering the temperature to 35 °C allows a maximum of 3700 kW of thermal power to be taken from the geothermal water, out of a design capacity of 9459 kW. This means that, in the event of the most unfavorable external conditions and the operation of the remaining receivers at a nominal capacity, there is not enough heat available to fully heat the pools without disconnecting the heat receivers that are operating at higher parameters (stages I–III). For this reason, it was decided to use an installation with a buffer tank—heat storage—which is described below. In this way, in the event of lower power demand, heat can be stored in the demand valleys and used when nominal operating conditions occur.

Downline of the IV heating stage, some of the geothermal water is vented (withdrawn) to feed the B8 pool. Therefore, the geothermal water flux at this point decreases by 1.75 kg/s, causing the available thermal power in the remaining flux to decrease by 256.9 kW.

After Stage V, the geothermal water has a temperature of 33.3 °C, which means that it still has some potential energy, but is only suitable for supplying low-temperature receivers. The demand analysis assumes 555 kW for de-icing the car park, but the potential for this low-temperature heat is much greater. By cooling the geothermal water to 12.7 °C, 3672 kW of low-quality heat is available. This can be used, for example, to heat the pavements and the car park, to maintain the water temperature in the B15 swimming pool, or to regulate the water temperature in the heating circuits (when it is too high) by mixing.

At the end of the process line, there is an injection pump with an electrical output of 155.5 kW, ensuring that the water reaches parameters that allow it to return to the ground.

4. Results and Discussion

4.1. ORC Geothermal Boiler Plant with Water Turbine

An ORC system working with a geothermal source, unlike photovoltaic cells or wind turbines, is an example of a RES with high availability and flexibility of operation [33,34]. These are units with a low sensitivity to load changes and are thus characterized by a wide range of stable operations (the technical minimum is estimated at 10% of the nominal load). They are equipped with an automatic start-up, grid synchronization, and shutdown system, making their operation more convenient in terms of operating costs.

ORC systems are based on the Clausius–Rankine cycle, widely used in thermal power plants, which uses low-boiling agents, often referred to as organic agents, instead of water [35,36,37]. The substitution of water by the above agents becomes expedient at the time of supplying this type of plant with heating of relatively low quality (mainly due to the temperature of the upper heat source), at which point the implementation of the transformation cycle becomes impossible due to the unfavorable parameters of water, from the point of view of the cooperation of machinery and power equipment and the economics of power generation. Significantly, however, these unfavorable parameters—within the same temperature range of the installation—are not characterized by the selected low-boiling compounds, which allow a true right-hand cycle to be realized within the accepted technical realities. The choice of the right working medium for an ORC plant plays a significant role in optimizing its operation from the point of view of energy conversion efficiency.

ORC technology within the heat source under consideration (geothermal water at a temperature of approx. 88 °C) is proposed to be realized with one of the following operating mediums: R1234yf, R1234ze, or R227ea, where the physicochemical properties and characteristic transformations are favourable, from the point of view of heat recovery, with a temperature not exceeding 100 °C. These are relatively safe agents from the point of view of the risk of intensifying the greenhouse effect and the risk of enlarging the hole in the ozone layer. The upper heat source, in this case, will be the thermal water from the borehole, which, by transferring heat to the compressed working medium, will cause its heating and evaporation (to saturated steam at 80 °C and saturation pressure, related to the technically limited temperature drop in the evaporator). The lower heat source, on the other hand, may be atmospheric air or, if the appropriate permits are obtained, the waters of the Czarny Dunajec River. In the case under consideration, fan coolers are assumed to be used.

The proposed system is a cascade system of heat extraction from thermal waters. The first stage is the evaporator from the ORC plant—in the studied case, the thermal output of this air exchanger is 1937 kW. Expansion of the water in the water turbines generates 46.6 kW of electricity, while in the exchanger room, the total output of the exchangers is 12,113 kW (this output can also be used to generate a cooling action in the absorption chiller). The turbine within the ORC plant delivered 219.4 kW to the generator, which, with a circulating pump drive requirement of 20.8 kW, resulted in 198.6 kW of net electricity. The thermal power for condenser cooling was 1739 kW. The efficiency of the ORC plant was 10.3% net. The results that were obtained make it possible to estimate an exemplary electricity production rate for the installation of 1.241 kWh/tonne of thermal water being fed to the evaporator in the case study. The resulting installation would have a net electrical output of 198.6 kW and a thermal output of 12,113 kW (assuming the active extraction of thermal water until it cools to 15 °C).

The ORC cycle is a promising energy process for converting low-temperature heat from, among other things, geothermal sources into electricity. The principle is based on extracting thermal water as the upper heat source and feeding it to a heat exchanger (preheater, evaporator, or superheater), where it gives up its heat to a medium with increased pressure and a temperature lower than that of the thermal water. The heat thus supplied leads to the heating of the working fluid, its evaporation, and eventual superheating. The vapor (either saturated or superheated) is directed to a turbine (or other expansion machine) coupled to a generator, where the vapor is expanded in successive turbine stages, leading to the mechanical energy of the rotor’s rotation and then, when it is already in the generator, to the generation of AC voltage. In the next heat exchanger—the condenser—the expanded medium condenses and then, via a feed pump that raises its pressure, it is fed back into the heater and evaporator. The thermal water leaving the evaporator is directed to the water turbine—to reduce the pressure from 1600 kPa to 250 kPa—and the heat exchanger, where, thanks to the still relatively high temperature in terms of low-temperature heating systems (70–85 °C), it feeds a cascade of heat exchangers operating the individual heat receivers in the facility (using the existing infrastructure as an example). The design assumptions used for the calculations and further analyses are shown in

Table 3. Design data for the ORC plant within the system under consideration.

Working Medium in an ORC Plant	Upper Heat Source	Thermal Water Parameters Downstream of the ORC Plant	Lower Heat Source
Toluene, R-114, R-135a or R-152a	Thermal water from a borehole with a temperature of 88 °C and an absolute pressure of 16 bar, with a water flow of 20–160 t/h	temperature 85–70 °C	Atmospheric air (fan coolers) or river water (open system, heating the water by no more than 3 °C)

.

It is extremely important that the proposed in-line hydropower turbine is not subject to the risk of solution failure, as is the case with the implementation of standard hydropower plants, where it is extremely common for there to be an issue with, for example, the permeability of a watercourse for bi-environmental fish [38,39,40].

4.2. Cooling Plant

The planned expansion of the ChT complex with the addition of new facilities provides for a sharp increase in the demand for cooling power. The plant capacity of the newly designed facilities will be 3803 kW, giving a total cooling power requirement of 4353 kW. The cooling capacity requirements are summarized in

Table 4. Cooling power requirements.

Cooling Power (kW)	Current	Newly Designed Facilities	Total
Demand	324	3803	4127
Actual power installed	550	3803	4353

.

In terms of covering the cooling demand, sorption chillers will be used. The cooling power demand will be met by the geothermal boiler plant installation.

4.3. Photovoltaic Installation

The PV panels that are proposed as part of the HGS system will be installed over the current parking spaces. Due to the large surface area of the car park and the need to cover 298 parking spaces at three different azimuths, the size of the structure will vary. The photovoltaic panels will be made using passivated emitter rear cell (PERC) technology. They are characterized by higher efficiency compared to classical monocrystalline cells, as well as higher mechanical and static load resistance [41,42,43]. PERC refers to the cell construction technology for the bottom passivation of the emitter. The PERC cell is distinguished from the classical cell by the construction of the underside of the cell. Between the top electrode and the bottom of the P-N junction, there is an insulator insert, the function of which is to limit the attraction of electrons to the aluminum bottom electrode. In addition, the underside passivation of the junction causes solar radiation to be reflected back to the base of the cell. The cell achieves a higher power output. This is all thanks to the improved use of long-wavelength infrared radiation. In a conventional cell, this releases electrons at the back of the cell or passes through the cell, generating heat. The ability of PERC cells to use longer-wavelength light translates into higher efficiency—especially in the mornings, evenings, or on cloudy days [44,45]. Monocrystalline panels are made from a whole-crystal element and guarantee significantly longer operation and life without loss of efficiency for more than 30 years, compared to polycrystalline panels.

The amount of gross and net (DC) energy generated by the photovoltaic cells planned for the 693 kWp installation according to the months of the year, taking into account the shade thrown on the car park shelter area, is summarized in

Table 5. Energy production from the PV installations of 691.3 kWp.

Month	Global Horizontal Irradiance (kWh/m2)	POA Irradiance (kWh/m2)	Shaded (kWh/m2)	Nameplate (kWh)	Grid (kWh)
January	37.0	45.4	42.2	27,082.2	18,032.4
February	45.1	51.5	50.0	32,320.0	21,568.0
March	72.5	77.4	76.1	49,510.8	31,330.0
April	97.5	101.4	99.9	65,138.9	40,092.6
May	130.3	132.5	130.7	84,963.5	50,198.5
June	142.0	142.9	140.9	92,006.3	52,864.1
July	146.1	148.5	146.4	95,432.1	54,114.6
August	127.2	131.3	129.6	84,694.0	47,904.7
September	88.4	94.4	93.0	60,476.6	36,207.9
October	59.9	65.1	64.0	41,553.7	27,173.6
November	31.8	35.1	34.2	22,064.8	16,073.8
December	29.0	34.3	31.7	20,403.9	14,717.9

using the HelioScope software.

The shadow report for the lowest sun (longest shadow) is shown in Figure 6.

4.4. Electricity Storage

Energy storage is at the heart of intelligent energy management. It integrates all the energy sources available in the installation and makes them available to the user in a way and at a time that suits them. The energy store itself performs the management functions automatically by means of intelligent software and its connection to energy meters. The most important priority is to minimize drawdown from the grid or to configure it in such a way that electricity is drawn during the night and released during the day, for example. Such functions are seamlessly implemented by the energy store.

The available energy storage functionality is as follows:

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The expansion is modular and scalable;

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A long service life and a high number of operating cycles;

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High operating efficiency;

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Energy management for charging stations;

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Peak power management;

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Energy consumption control for photovoltaic installations;

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Peak-shaving, i.e., the limitation of peak loads beyond 15 min to avoid higher charges when overconsumption occurs at the time of supply restrictions by the distribution system operator;

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Remote access to data and monitoring is made possible via the internet.

The HGS system proposes an energy storage system using lithium-ion cells with a capacity of 996 kWh and 500 kW, along with an energy management system (SPS-R500).

The stored energy from RES sources during peak-demand periods will reduce the need for power and electricity to be drawn from the grid. The system will also install car chargers, which will be powered by photovoltaic cells and/or energy storage.

4.5. Heat Storage (Buffer)

The proposed concept is mainly aimed at confirming the possibility of obtaining the assumed district heating capacities resulting from the identified or estimated instantaneous power demand, during the operation of the facility in periods of peak heat demand. The proposed solutions may, therefore, require some reorganization of the operation of the exchanger system—above all, to carry out exergetic optimization, allowing fuller exploitation of the heating potential of the available geothermal intake. For this reason, it is proposed that the facility equips the system with a buffer tank, allowing heat (water at a temperature of approx. 70 °C) to be stored, e.g., in the valleys of the facility’s heat demand, and then diverted to the peak circuit or used to correct the parameters of individual circuits. This forms the basis for rationalizing the operation of the district heating system and exploiting the potential of the geothermal borehole. A schematic of the proposed installation is shown in Figure 7.

A tee was added to the process line described in Section 3.2 (Figure 5) upstream of the first heating stage, to divert some or all of the geothermal water flow to a buffer tank, which acts as heat storage. Assuming a constant flow of 160 t/h of geothermal water at a temperature of 78 °C (after cooling in the ORC evaporator), over a period of 12 h and its cooling, in the above-mentioned heat store, to a temperature of 50 °C (which, in simplified terms, will form the basis for direct feeding of the swimming pool technology), the maximum thermal capacity of the reservoir would be just over 225 GJ (in the case of smaller reservoir volumes, a conversion factor of 672 MJ/K/h can be used, i.e., 672 MJ of heat at a temperature at least a few degrees lower than the outlet temperature of the geothermal water for each hour of charging the accumulator, for each 1 K of cooling of the heating medium). The cooperation of the system with the heat storage using, inter alia, the PTES (pit thermal energy storage) technology is part of the energy storage policy, also in the form of heat [46,47]. This is related to the regulation of supply between the peaks and valleys of demand, mentioned, inter alia, in the document “Energy Policy of Poland until 2040” [48].

The principle of storage shown in Figure 7 is relatively simple. At peak operating times, receivers of up to 70 °C (central heating, domestic hot water, mechanical ventilation) can be supplied from the storage tank, as well as indirectly through an additional heat exchanger to the swimming pool heating circuits. In this way, it is possible to cover the missing 5759 kW of nominal capacity—without having to increase the geothermal water intake. In addition, the surplus thermal power can be channeled directly into the pool technology system by venting and diverting part of the geothermal water flow to the heat exchanger. Depending on the degree of cooling of the geothermal water, its return from the buffer tank can take place before the first or sixth heating stage.

The capacity for heat storage depends on the space available and the target degree of compensation for heat shortages (maximum output) within the heating system. For relatively small capacities, it is suggested that the system uses a battery of pre-insulated (insulated) buffer tanks with a capacity of 10,000 liters, as used in municipal or industrial systems; these are generally available on the market due to the increasing demand for district heating RES systems (solar collectors and heat pumps). For larger capacities, the target for facilities that are the size of Chochołowskie Termy, it is proposed that they use individual above-ground, surface, or underground thermal storage solutions. The former setup is already in operation, for example, at the Theiss thermal power plant in Austria, where there are reservoirs with a thermal capacity of 7200 GJ and a water capacity of 50,000 m³, with a height of 30 meters and a diameter of 50 meters [49]. The second type, i.e., surface reservoirs (pit storage), are shallow pits filled with gravel and water, as are operating, e.g., in Vojens, Denmark, where there is the world’s largest underground thermal storage pit, with a capacity of 200,000 m³ [50].

The use of underground reservoirs generally comprises storing water in impermeable geological strata or in underground tanks. The choice of storage technology should be preceded by additional geological investigations and an analysis of the area that would be occupied by the storage facilities.

Assuming that the buffer at the Chochołowskie Thermal Springs site would be loaded every day for 12 h with 160 t/h of water, cooled from 78 °C to 30 °C (thus allowing the temperature in the reservoir to be at least 30 °C), the amount of heat stored in it can be determined—in this scenario, it will be just over 387 GJ—with a storage capacity of about 1920 m³. This calculation is an example and is intended to demonstrate the principle of tank selection for similar facilities. The selection of the correct capacity needs to be individualized and must be based on specific assumptions about the loading and unloading times of the tank, as well as the storage temperature. Discharging the tank in the example above for 10 h results in an instantaneous heat output value of 10.75 MW at a temperature of at least 30 °C, thus providing a basis not only for covering the missing heat demand in terms of pool technology but also for investing in sorption heating systems, further water attractions, or accommodation. These values, therefore, provide a sound basis for considering the concept of heat storage—either indirectly (taking heat from the thermal water and accumulating it in an intermediate medium such as circulating water) or directly (storing thermal water and discharging it during the daily peak demand)—as part of a facility expansion.

There is also justification for the construction of smaller reservoirs, which are charged during the normal operation of the facility with temporary surplus heat. The resulting buffer storage capacity cannot be determined directly at the concept stage, but—due to the series of buffer storage tanks available on the market, including those with capacities of up to 8–10 tonnes, and the possibility of combining them in series or parallel—there are no technical counter-indications for such a task.

4.6. Power Balance of Loads

In order to fully regulate the operation of the system, it is necessary to equip it with valves, by-passes, and the necessary controls and measurement apparatus for automation. The selection of equipment, with its installed power and characteristics, is shown in

Table 6. Characteristics of the equipment selected.

Name of Heat Receiver acc. to Figure 7	Heat Receiver Capacity, kW	Description of the Receiver
ORC	1864.8	Heat from the ORC to maintain the water temperature in pool B15 (13–15 °C)
Surplus/buffer	5759	Use of a buffer (thermal energy store) to stabilize operation during peak times of the district heating section
I stage	2015	Central heating 329 kW (existing facilities) and ventilation 1686 kW (existing facilities)
II stage	468	DHW—II stage 288 kW (existing facilities), DHW—II stage 180 kW (new facilities)
III stage	1844	Central heating 256 kW (new facilities) and ventilation 1588 kW (new facilities)
IV stage	3700	Pool technology up to 8392 kW (existing facilities), pool technology up to 1067 kW (new facilities).
Supplementing water in the pool	276.5	Water discharge at 35 °C and flow rate of 1.44 kg/s for supplementing swimming pools
V stage	312	DHW—I stage 192 kW (existing facilities) DHW—I stage 120 kW (new facilities)
VI stage	3688	Reheating of other streams, pool water control, pool water exchange, car park heating, pool temperature maintenance of B15
TOTAL	18,062.5

.

Table 7. Heat flux balance for the proposed process line and comparison with demand.

Heat Load Capacity (kW)	Total Demand (kW)	Heat Load Used at Nominal Conditions (kW)	Heat Load Withdrawn from Source, Including ORC (kW)	Demand from Receivers with Temperature > 30 °C (kW)
1864.8	18,062.5	12,303.5	14,168.3	14,374.5

summarizes the heat fluxes for all receivers, also taking into account the missing heat power to feed the pool technology, taken in the event of excess heat or from the buffer tank. The columns on the right show the sums of the selected fluxes. The first value indicates the heat power requirement when taking into account the full use of low-temperature heat—18,062.5 kW. The second value (12,303.5 kW) represents the thermal power that can be taken from the geothermal source at the point of peak operation. In this case, the buffer is not charged, and the thermal power is reduced in accordance with the missing 5759 kW. The next value shows the power that is actually received from the geothermal source (14,168.3 kW), taking into account the feed-in of the ORC circuit. The last value is a total by which to check the calculations. All receivers above 30 °C, and the missing 5759 kW, give a value of 14,374.5 kW. Adding the de-icing heat demand of 555 kW gives a value of 14,909.5 kW, which is in line with the demand (as shown in Table 2).

4.7. Environmental Indicators of the Proposed Solution

The ecological indicators were calculated from the value of the energy withdrawn as heat for further use. For this reason, the balance takes into account the value of the heat extracted in the evaporator of the ORC circuit (and not the electrical power generated in this circuit). Also included in the balance sheet are: I, II, III, IV, and V heating stages and the pool water make-up. In the case of heating stage VI, which has a temperature of less than 30 °C, only the car park heating data, i.e., 555 kW, was taken into account for the calculation of the index value. Obviously, with a larger heat outlet, at such a low temperature (<30 °C), the installed capacity could be higher (max 3672 kW), as shown in the diagram. Nevertheless, a safe variant, i.e., 555 kW, has been adopted as the indicator value at this point.

Considering the above, the indicator value consists of the following values from the scheme: 1864.8 kW + 2015 kW + 468 kW + 1844 kW + 3700 kW + 256.9 kW + 312 kW + 555 kW (relating to the heating of the car park, with a safe value assumed) = 11,015.7 kW, i.e., 11 MW.

The indicator value does not take into account the value of 5759 kW, which can be provided if the surplus is stored.

The value of the second indicator relates to the production of thermal energy in relation to the newly created infrastructure, as this is an indicator of the increase in energy production from renewable sources. Therefore, in this case, only the newly built part of ChT (the leisure and recreation building) has been taken into account. This indicator is presented in

Table 8. Heat production, based on power demand for the new leisure and recreation area.

	Power [kW]	Hours/Day	Days/Month	Months/Year	Unevenness Factor	Total [mWh]
Cloakroom (level -1), central heating	26	6	30	6	1.2	33.7
Building (other levels), central heating	230	6	30	6	1.2	298.08
Cloakroom (level -1), ventilation	36	24	30	6	1.2	186.62
Building (other levels), ventilation	1552	24	30	6	1.2	8046.71
DHW	300	24	30	12	1.0	2592.00
Swimming pool water technology	1067	24	30	6	1.5	6914.16
Total	3211					18,071.27

.

5. Conclusions

Confronting the existing heat storage technologies in Europe and the energy requirements of the Chochołowskie Termy facility in question, it can be concluded that commercial solutions now exist to implement the proposed innovative combined renewable energy resources system, which we have called Hydro-Geo-Solar.

This new design:

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Optimizes the use of RES;

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Minimizes the use of conventional sources of energy (pollutant emissions are reduced);

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The geothermal plant is expanded into a multiple geothermal-photovoltaic-water plant;

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The heat and electricity produced can be stored;

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Sustainable development of geothermal power plants is needed to avoid climate change;

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The environmental effect of the HGS system will be an increase in avoided emissions of CO₂—1900 t/year, SO₂—1691 kg/year, NO_x—1567 kg/year, CO—683 kg/year, and dust—89 kg/year.

The presented course of action is individualized for the presented specific case, but can nevertheless be implemented in many similar solutions worldwide. It optimizes the use of renewable energy sources while taking advantage of the latest solutions for energy and heat generation, storage, and maximum utilization. Such systems could be an example of the environmentally conscious use of renewable energy sources. The implementation of similar solutions allows for the development of commercial facilities in a sustainable manner that does not generate additional pollutants in the environment. The benefits of such solutions are tangible—they significantly reduce emissions from conventional sources and protect the climate. Technological schemes and calculations can and should be modified for similar facilities; nevertheless, the authors hope that the presented article will set a new trend in the use of geothermal water, where such facilities will be enriched with installations for obtaining energy and heat/cooling from other renewable sources.