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Article

Potentials of Green Hydrogen Production in P2G Systems Based on FPV Installations Deployed on Pit Lakes in Former Mining Sites by 2050 in Poland

by
Mateusz Sikora
1,* and
Dominik Kochanowski
2
1
Faculty of Civil Engineering and Resources Management, AGH University of Krakow, 30-059 Krakow, Poland
2
Sun Energy Group, 88-200 Radziejow, Poland
*
Author to whom correspondence should be addressed.
Energies 2024, 17(18), 4660; https://doi.org/10.3390/en17184660
Submission received: 10 June 2024 / Revised: 29 August 2024 / Accepted: 10 September 2024 / Published: 19 September 2024
(This article belongs to the Special Issue Energy Consumption at Production Stages in Mining)
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Abstract

:
Green hydrogen production is expected to play a major role in the context of the shift towards sustainable energy stipulated in the Fit for 55 package. Green hydrogen and its derivatives have the capacity to act as effective energy storage vectors, while fuel cell-powered vehicles will foster net-zero emission mobility. This study evaluates the potential of green hydrogen production in Power-to-Gas (P2G) systems operated in former mining sites where sand and gravel aggregate has been extracted from lakes and rivers under wet conditions (below the water table). The potential of hydrogen production was assessed for the selected administrative unit in Poland, the West Pomerania province. Attention is given to the legal and organisational aspects of operating mining companies to identify the sites suitable for the installation of floating photovoltaic facilities by 2050. The method relies on the use of GIS tools, which utilise geospatial data to identify potential sites for investments. Basing on the geospatial model and considering technical and organisational constraints, the schedule was developed, showing the potential availability of the site over time. Knowing the surface area of the water reservoir, the installed power of the floating photovoltaic plant, and the production capacity of the power generation facility and electrolysers, the capacity of hydrogen production in the P2G system can be evaluated. It appears that by 2050 it should be feasible to produce green fuel in the P2G system to support a fleet of city buses for two of the largest urban agglomerations in the West Pomerania province. Simulations revealed that with a water coverage ratio increase and the planned growth of green hydrogen generation, it should be feasible to produce fuel for net-zero emission urban mobility systems to power 200 buses by 2030, 550 buses by 2040, and 900 buses by 2050 (for the bus models Maxi (40 seats) and Mega (60 seats)). The results of the research can significantly contribute to the development of projects focused on the production of green hydrogen in a decentralised system. The disclosure of potential and available locations over time can be compared with competitive solutions in terms of spatial planning, environmental and societal impact, and the economics of the undertaking.

1. Introduction

When the European Green Deal strategy was adopted in 2019, UE activities and projects aimed at protecting the climate became more intensive and accelerated, resulting in the proposal of the Fit for 55 package, adopted in July 2021 [1,2,3]. The main objective was to revise and adapt the EU climate law to meet the new objective of a 55% reduction in CO2 emissions by 2030 and achieving climate neutrality by 2050 [4,5,6,7].
The EU Commission emphasised that in order to meet these targets, major technological changes are required both in power engineering systems and in other industries, such as transportation, construction, or agriculture [8,9,10]. These objectives are included in strategic documents adopted in Poland, and the Polish Energy Policy by 2040 (PEP2040) stipulates that the share of renewable energy sources in the gross energy consumption should be 23% by 2030 and the greenhouse gas emissions in relation to 1990 emission levels should be reduced by 30%. At the same time, the proportion of coal used by the power sector should be constantly reduced. In this context, green hydrogen production, regarded as the fuel of the future, may be one of the strategies with which to meet the targets specified in the European Green Deal [11,12]. Furthermore, hydrogen can be effectively used for energy storage, integrated with the power grid, enhancing its stability [13,14]. To date, the intermittent availability of energy from renewables (wind power and solar systems) has limited the increase of its share in the structure of national power grids [15]. The key postulate in the PEP2040 regulation is the development of low-emission transport, with the ultimate goal being zero-emission urban mobility systems in cities with more than 100,000 inhabitants by 2030. These objectives and regulations contained in the Sustainable Transport Development Strategy by 2030 are in line with this policy, stipulating that the urban mobility in Poland should rely on novel propulsion solutions, including electric cars or vehicles powered by alternative fuels, such as LNG, CNG, ammonia, or hydrogen cells.
According to the EU strategy supporting hydrogen technology, large-scale production of hydrogen should be effected in electrolyser systems with the capacity of up to several hundred megawatts (starting from 100 MW) [16]. In the variant adopted in Poland, the electrolysers are to be powered with surplus capacities from offshore wind farms [17,18]. This strategy might cause the overloading of high-voltage lines, particularly if the projected nuclear power plant is to be located in the seaside village of Lubiatowo-Kopalino, within the municipality of Choczewo.
The design of electrolysers for operation in adverse marine conditions was undertaken by the consortium of Orsted, Siemens, Gamesa Renewable Energy, Element Energy, and ITM Power. This project marks the first step in the development of a commercial-scale method for hydrogen production from offshore wind farms, while the hydrogen is to be generated offshore and transported via a pipeline. This solution ought to foster commercial implementations of hydrogen production systems from offshore wind farms, marking an interesting trend in the development of the hydrogen technology market in Poland. However, the main barrier faced by large-scale producers of green hydrogen from offshore wind farms lies with high transport costs if the dedicated pipeline system has yet to be constructed and with the technology of hydrogen production from marine water, which is still commercially unviable.
There is a certain niche, i.e., the potential of decentralised green hydrogen production in small Power-to-Gas systems [19,20]. Electric power can be converted into gas and stored as reserve for future use (i.e., grid balancing), further distributed, consumed by end-users, or further processed [21,22]. This potential is offered by pit lakes left over after the extraction of minerals (natural aggregates, sand) under wet conditions. Under Polish law, the mining sites need to be reclaimed once the mining operations cease. Due to their previous industrial history, water reservoirs in those sites offer an attractive location for floating photovoltaic facilities and P2G systems generating green hydrogen via electrolysis of H2O.
The topic of developing post-mining areas for the purposes of electricity production and storage has already been discussed. A combination for the development of post-mining areas in the form of electricity production using FPV and energy storage has been proposed by Mert and Dincer. A unique integration of floating photovoltaic with underground energy storage and hydrogen energy storage systems, as well as a heat pump-driven district energy system, is analysed using a thermodynamic approach from energy and exergy points of view. The proposed design exploits unutilised natural bodies and abandoned structures in a sustainable manner [23]. Temiz and Javani describe another project that investigated the possibility of floating PV plant integration with existing basins for wastewater treatment. According to their calculations, water between 15,000 and 25,000 m3 is saved by each MWp. Furthermore, there is a yearly energy yield of up to 10% through the cooling effect [24].
The sources of hydrogen production from renewables can potentially be engaged in providing energy flexibility in the context of involving customers, implementing novel solutions (such as electrolysers), and supporting middle- and low-voltage systems at the local level [25]. It is assumed that the flexibility services should be traded on energy flexibility platforms, and the remuneration thereof can be regarded as an alternative benefit of green hydrogen generation. In the event of an electricity surplus, the hydrogen generation should commence, while in the case of a power shortage, the hydrogen generation should be discontinued and all electricity should be delivered to the grid to meet the current demand. Obviously, these operations need to be synchronised, economic aspects duly taken into account, and business models developed for the key stakeholders.
It has been reported in the literature that the costs of the power supply to the electrolysers must include the high distribution fee. This conclusion could be considered premature, and, in the more secure variant, the electrolyser modules should be implemented in the direct vicinity or close to energy sources [26,27]. Taking into account this uncertainty and the risks involved, it is reasonable to suppose that decentralised, small-scale installations should act as a safety buffer in green hydrogen generation at the national level.
Development work and feasibility studies are being carried out around the world. Publication [28] shows that a Power-to-Gas installation based on FPV can achieve IRR rates of return of 20% in Indonesian conditions.
With regard to the location of P2G facilities, they do not require extensive networks of power transmission infrastructure, thus eliminating the need to obtain grid connection permits from distribution system operators [29,30]. It might appear therefore that there should be no restrictions as to their potential locations. Yet, the expertise gained when implementing projects involving electricity generation from renewables clearly indicates that before a stand-alone wind, solar, or water power facility can be built, numerous constraints have to be met, mostly in terms of environmental and social impacts. It is reasonable, therefore, to expect similar difficulties when implementing P2G systems.
When floating photovoltaic facilities located in lakes in former mining sites are integrated with electrolysers or the systems of electrolysers, the abovementioned administrative and legal obstacles (i.e., restrictions imposed by local land development plans or environmental and social concerns) should be removed. Once the mineral extraction operations under wet conditions (categorised as projects producing severe environmental impacts) receive the required approvals relating to land development and environmental and social impacts, it is reasonable to suppose that after the mining operations ceased, the respective administrative decisions could be easily revised because the environmental impacts of photovoltaic facilities are less severe and risks are lower than in the case of new localities. FPV installations have several advantages. The reuse of degraded areas, mitigating land-use conflicts, more efficiency than ground-mounted PV solar, saving water, improving resilience, and diversifying electricity-producing infrastructures are of FPVs key benefits [31].
There are abandoned mine lands nationwide where minerals used to be extracted under dry conditions (above the groundwater level), which can potentially be reclaimed and reused for industrial purposes (electricity generation from renewables or green hydrogen production) [32,33]. However, these lands are often attractive for reclamation and reuse as farming land or forests, reflecting the preferences of local communities [34]. These aspects are not addressed in this study. As they are located in areas degraded by prior mining activity, pit lakes are often remediated, providing space for recreation, yet such forms of redevelopment are suitable only in the vicinity of major cities, where recreation spaces are readily accepted if not requested by inhabitants. In large cities, there is still demand for rehabilitated water reservoirs to be reused for recreation; the most popular are those located in close proximity to city centres. Good examples of such reservoirs include Zakrzowek Lake and Bagry Lake in Cracow, the open-air bathing spot Morskie Oko in Wrocław, Zwirownia Lake in Reszów, Tarnobrzeskie Lake in Tarnobrzeg, Pogoria I and Pogoria II Lakes in Dabrowa Górnicza, Balaton Lake in Trzebinia, and the Kamionka Bolko reservoir in Opole. Considering the multitude of man-made lakes formed during mineral extraction operations under wet conditions, only a few of them are rehabilitated and reused for recreation.
Obviously, pit lakes are mostly located outside city centres and in areas where aggregate reserves were proved and administrative decisions could be issued to start the enterprise; in most cases, they are some distance from densely populated areas.
The key advantages of accommodating photovoltaic facilities on water reservoirs over locations on land include the higher energy efficiency due to the lower temperature of floating modules and the fact that it should not interfere with the existing infrastructure on land [35].
The key aspect in promoting the implementation of P2G systems relying on electric power supply from floating photovoltaic plants is the ready access to process water. Apart from other obvious advantages, this feature renders the P2G systems an attractive option for investors. The cost of water access is a major component of the variable operating costs; the average demand for water for electrolysers varies from 9 to 11 l/kgH2 [36].
This paper contributes significantly to the scientific community by exploring the potential of green hydrogen production through Power-to-Gas systems integrated with FPV installations on pit lakes in former mining sites in Poland. This research is pioneering in evaluating the feasibility of using rehabilitated mining sites for renewable energy production and hydrogen generation, which is crucial for achieving climate neutrality by 2050. The study uses advanced GIS tools to identify potential sites for FPV installations, assess their capacity for hydrogen production, and model the timeline for site availability, offering a novel approach to decentralising green hydrogen production.
The findings can inform future projects focused on renewable energy and hydrogen production, providing a model for assessing similar sites globally, especially in the Member States of the European Union. By addressing the technical, legal, and organisational challenges associated with such installations, the paper adds valuable insights into the sustainable redevelopment of former industrial areas, contributing to broader efforts in climate change mitigation and sustainable energy transitions.
The paper addresses the following key research questions:
−
Is there potential for green hydrogen production in Power-to-Gas systems operated on pit lakes in former mining sites in Poland by 2050?
−
How can GIS tools be used to identify and evaluate suitable locations for floating photovoltaic installations on these pit lakes?
−
What are the technical, organisational, and legal challenges associated with implementing FPV-P2G systems on rehabilitated mining sites?
−
What is the projected capacity of green hydrogen production from these systems, and how can it support urban mobility in terms of powering city buses in Poland’s West Pomerania province by 2030, 2040, and 2050?
The answers to these questions form the basis for a comprehensive assessment of the potential for green hydrogen production in the study, providing an outline of a roadmap for future developments in this area. To deepen knowledge and refine the direction of this development, further research should be conducted, particularly focussing on the economics of the proposed venture, the logistics of transporting hydrogen supplies to urban agglomerations, and a detailed environmental impact assessment.

2. Method of Assessing the Potential of Floating Photovoltaic Plant Implementation on Pit Lakes

The method of assessing the potential of accommodating floating photovoltaic plants on pit lakes being rehabilitated is universal. Thus, when all geospatial data required for the analysis are available, the method can be effectively employed to examine each potential location and site-specific boundary conditions.
The key element of the algorithm is the database of national geospatial data BDOT10k made available in electronic form via the browser service, in accordance with the Regulation of 27 July 2021 by the Minister of Development, Labour, and Technology, having relevance to datasets of topographic objects, general geographic objects, and standard cartography studies. This Regulation is the executive act of the Law on Geodesy and Cartography of 17 May 1989 (Journal of Laws 2023, item 1752, consolidated act of 31 August 2023). The BDOT10k dataset and the data made available as public information by the Polish Geological Institute-National Research Institute are the input for geoprocessing analysis, yielding the sequence of intermediate results.
Basically, the algorithm involves three stages:
  • Stage I—definition of analysed regions.
  • Stage II—quest for available locations for FPV plants.
  • Stage III—scheduling the availability of areas for investment.
The structure and operating principle of the algorithm are shown as a block diagram in Figure 1.

2.1. Stage 1—Definition of the Analysed Regions

In Stage 1, the site boundaries are to be defined for the algorithm to yield the result. Considering the fact that the results are of geostrategic importance, it is reasonable to expect that the analysed area should be either the entire area within state borders, a formally defined administrative unit, such as a province, county, or municipality, or other areas with formal or administrative boundaries, such as the areas covered by the electricity distribution operators. The area explored in the analysed case study is the West Pomerania province, and the geospatial data are provided by respective geodesy offices. In the case of Poland, the main sources are data that include the database of geographic features BDOT10k, particularly with respect to land features, listed in Article 3, Section 4.
Land survey data are complemented with data made available by the Polish Geological Institute-National Research Institute, relating to locations of mineral deposits and active mining areas subject to mining license under the Geological and Mining Law of 9th June 2011 (Journal of Laws 2023 item 633, consolidated act of 3 April 2023).

2.2. Stage II—Quest for Locations Available for FPV

In Stage II, the geoprocessing tools are deployed to locate the mineral deposits that may extend beyond the analysed site and to determine the category of the object OT_PTWP_A—surface water with the attribute value 03—stagnant water. All areas found in this stage are subjected to further analysis. Considering the insufficient speed of BDOT10k data updating and dynamic changes of surface conditions in surface mining, the remaining (excluded) regions should be verified manually in relation to the current orthophotomap available in geoportals (for Poland), and, in the case of a large number of areas considered, the analysis should be supported by visual image identification tools. The latest available satellite imagery is included in the set of rejected mining areas. Several dozen areas are visually assessed to confirm whether they have been correctly excluded from the calculation procedure or if they are located on stagnant water bodies not yet entered into the BDOT10k database. This solution can be automated in the future. Selected areas are then subject to the standard procedure, while the remaining ones categorised as surface mining sites where minerals are to be extracted above the groundwater table level are thus excluded.
To determine the target areas for accommodating floating photovoltaic plants, it is required that the status of active mining operations be first established. In the case of sand or gravel extraction under the water table, the widely adopted rule is that the documented deposit lies within the limits of the business property remaining in the hands of the entrepreneur and that the active mining site is determined in accordance with the plot boundary plans. The target excavation is profiled in accordance with the current standards, retaining the required safety margins to separate it from real estate that is not under the management of the entrepreneur. It is reasonable to suppose, therefore, that the deposit is extracted by full contour mining or within the contour limited by the boundaries of the mining area, leaving the non-production margins as stipulated by the law.
The sketch in Figure 2 shows the spatial orientation and two excavations in different stages of progressing mining operations.
In excavation 1, the extraction operations have ceased, and the water reservoir has its ultimate contour. The surface area of the documented mining site is 2.425 ha, and the surface area of the water reservoir is 2.087 ha. The area occupied by the water reservoir accounts for 86% of the total area to be surface mined.
Applying the same rule to excavation 2, it is reasonable to expect that the excavation should reach its final profile in the following years (as of or prior to the mining concession expiry date) and the water reservoir should have a surface area of 5.964 ha, while the area of the mining site is 7.190 ha. The water reservoir accounts for 83% of the site area.
The analysis of projects implemented in this area seems to confirm the adequacy of the adopted rule. In the calculation procedure, the proportion of the water table surface area in the reclaimed area is taken to be 80%, which is a pessimistic result in relation to the analysed case studies in the West Pomerania province. This result seems adequate and readily implementable without repeating the verification for mineral deposits in lowland areas, while for areas with diverse morphologies (mostly found in the south of Poland), the procedure needs to be repeated and the percentage of the water body area in relation to the site’s surface area should be confirmed or recalculated. In morphologically diverse terrain, a lower proportion of water surface area should be expected within the mining area boundaries due to the profiling of open pits, which are partially non-waterlogged.
The other constraint limiting the scope of FPV investments is the proportion of the water reservoir area that is available for the installation of FPV facilities; the major determinants are the actual shape of the reservoir and irregular shoreline.
Of particular importance are site management restrictions precluding its reuse for industrial purposes, prompting other reclamation schemes. It could be postulated that all available areas should be effectively utilised and, when making strategic decisions, the assessment of potential green hydrogen generation should rely on the highest possible values of the water coverage ratio. On the other hand, it is unreasonable to expect that all available pit lakes in former mining sites should be put to such use. Reusing a fraction of water bodies for the deployment of FPV is fully in line with the principles of sustainable development. In practical terms, there are no obstacles precluding the use of the part of the lake not covered with FPV modules for other purposes, for industry, for natural site recovery, or, under specified circumstances, also for recreation [37,38].
In the recalled case study, the underlying assumption was that 50% of the available water surface area should be covered by floating FPV modules. Ultimately, that means the coverage of half of the water surface, or, in particularly suitable locations, the coverage ratio could be 100%, with further investments. Actually, a coverage ratio of 50% should be regarded as the average value for the analysed region (West Pomerania province).
Figure 3 and Figure 4 refer to two projected photovoltaic installations covering approximately 50% of the available water surface area. In the case illustrated in Figure 3, the southern part of the lake is left uncovered and can be put to different use; in the case shown in Figure 4, the photovoltaic modules should cover the majority of the available water surface due to irregular shorelines.
In the final step of Stage II, the total area available for FPV deployment should be determined.

2.3. Stage III—Scheduling the Availability of the Area for Investment

In the final stage, the sites selected for investment should be arranged in an order demonstrating their ready availability in time, showing the increment of available areas. The scale of this increment depends on the provisions of the mining law and relevant regulations governing the implementation of P2G installations incorporating floating photovoltaic modules and an electrolyser or a set of electrolysers:
  • Geological and Mining Law of 9 June 2011 (Journal of Laws 2023.63, consolidated act of 3 April 2023)
  • Law on Protection of Agricultural and Forest Land of 3 February 1995 (Journal of Laws. 2024.82, consolidated act of 24 January 2024
  • Law on Public Access to Environmental Information, Public Participation in Environment Protection, and Environmental Impact Assessment of 3 October 2008 (Journal of Laws 2023.1094, consolidated act of 12 June 2023)
  • The Energy Law of 10 April 1997 (Journal of Laws 2024.266, consolidated act of 28 February 2024)
  • The Water Law Act dated 20 July 2017 (Journal of Laws 2023.1478, consolidated act of 1 August 2023)
  • The Construction Law dated 7 July 1994 (Journal of Laws 2024.725, consolidated act of 14 May 2024)
Former mining sites are to be rehabilitated when the lands (and water bodies) are wholly or partly abandoned or left unused for a specified period of time. The reclamation project must be completed by the mining company no later than 5 years after the land has been declared useless. In the analysed case study, the maximum allowable waiting period is taken, so it is assumed that the pit lake should be rehabilitated within 5 years from the expiry of the valid mining license. In practical terms, mining concessions can be issued for periods longer than those based on the current progress of mining operations and the quantity of recoverable reserves. In such cases, land reclamation schemes will be implemented sooner, the allowable time period starting from the moment when the deposit is exhausted instead of the expiry date of the mining concession. Furthermore, mining sites can be rehabilitated in part while the mining license is still standing. Hence, the assumption adopted for the algorithm serves as the worst possible scenario, and the available surface area of water bodies in the analysed region may increase sooner than predicted by the algorithm.
The ceasing of mining activities and converting the site to be rehabilitated for use as a water reservoir is the prerequisite to initiating the investment project aimed at P2G installation. Approximately, it takes about two years to obtain the decision on environmental conditions and on water management, as well as building permits for investment projects in abandoned mining areas. In consideration of the legal status of these sites and the activity of other operators, these projects ought to not evoke social or environmental concerns. Poland to date has had no experience in the construction of P2G installations relying on floating photovoltaic plants and electrolysers, yet the entire investment process and hence the time to obtain the requisite administrative decisions and to initiate engineering work is nearly the same as when planning a standard photovoltaic plant with energy storage facilities. The construction stage usually takes a few months; larger installations may take over a year to complete. In the simulated variant, the P2G installation is to be deployed for industrial use after 7 years from the expiry of the mining license.
Strategic plans for floating photovoltaic plants typically provide the installed capacity of 1 MWp per 1 ha of the water surface area, allowing the projected capacity and timeframe of implemented photovoltaic farms to be effectively scheduled. In the analysed case, the project scheduled is the P2G system to be implemented in the West Pomerania province by 2050.

3. Potential Effects of P2G System Deployment on Pit Lakes in Former Mining Sites

In the case of photovoltaic plants, power output predictions depend on the solar irradiance factor. Numerous authors have reported that the installation of floating photovoltaic modules is beneficial for the FPV plant’s performance. Güllü, E., et al. described that lab-made modified graphite cathodes were used to design and implement floating PV-assisted alkaline electrolysis cells. The results showed that floating PV panels were more beneficial than land-mounted panels, and the G/Ni/Co enhanced the hydrogen generation performance of the system [39]. Due to the water-cooling effect, the operating cell temperature is significantly lower than the temperature of modules installed on land. This lower temperature can be attributed to the module being accommodated on the water surface and to the flow of circulating air, which tends to be cooler in the neighbourhood of water reservoirs than on land [40,41].
The operating cell temperature is the key determinant of each PV plant’s efficiency. The well-known formula presented by Kamuyu (Kamuyu et al., 2018) [42] and recalled in this study takes into account the water-cooling effect to obtain the cell operating temperature in FPV modules.
T C = e 0 + e 1 · T a + e 2 · G T − e 3 · V w
where Ta—air temperature, GT—solar radiation, Vw—wind speed, e0 = 2.0458 °C, e1 = 0.9458 °C−1, e2 = 0.0215 °C·m2·day·kWh−1, and e3 = 1.2376 °C·s·m−1, are empirically determined coefficients.
At the latitude of Poland and in average atmospheric conditions thereof, yearly electricity generation in this type of plant is up to 1100 MWh per 1 MWp. This value is assumed in the developed model, while the algorithm will admit any value predicted in consideration of specific local settings and average weather conditions, such as the solar zenith angle, the type of PV modules, and the operating time. Table 1 summarises the simulated predicted electricity generation in floating photovoltaic plants accommodated on rehabilitated pit lakes in former mining sites by 2050.
The estimation in Table 1 results from applying the model proposed in Figure 1. The forecast of potential electricity production takes into account the generation of 1100 MWh per 1 MWp of the installed power capacity of the power plant. This value is commonly adopted in feasibility studies for photovoltaic power plants in Poland.
The average annual irradiance value was adopted according to the PVGIS-SARAH2 database. For the West Pomeranian Voivodeship, the value was estimated to be 1315 kWh/m2. Depending on other variables affecting the efficiency of electricity production (system loss, PV mounting position, slope angle, PV technology), this results in a yearly PV energy production level of 1100 MWh per 1 MWp of installed capacity.
Figure 5 illustrates potential rates of increase in electricity generation, showing annual growth (for new floating FPV plants).
The integration of floating photovoltaic plants with an electrolyser or a set of electrolysers in the P2G system has numerous benefits. First of all, the process of green hydrogen production requires large amounts of process water and is energy-consuming [43,44,45,46]. Accommodating P2G installations and photovoltaic plants on a water reservoir provides stable access to process water. Producing green hydrogen at the locality of a renewable energy source enables the off-grid operation of the generating unit, i.e., without obtaining the grid connection permit. Currently, this is one of the major obstacles in the development of distributed renewable energy sources.
Poland is a manufacturer of modern hydrogen-fuelled city buses, which have been extensively tested and commissioned for use in Polish and European cities and also on other continents [47,48,49,50,51,52]. Field tests conducted in city agglomerations in Krakow and Vienna reveal that the city bus Mega (Solaris Urbino 18 Hydrogen) bus uses 20 kgH2O/100 km, while the model Maxi (Solaris Urbino 12 Hydrogen) uses 6.3 kg on average [53]. Table 2 summarises the achievable levels of green hydrogen generation in facilities deployed on pit lakes in former mining sites, related to the size of the bus fleet and the annual fuel demand. According to the Central Statistical Office reports, the average value of km driven by a city bus in Poland is about 80,000 km per year. Generally, municipal transport companies distribute the size of the bus fleet in roughly equal proportions by type. Figure 6 shows the achievable increase in the number of city buses fuelled with hydrogen produced in distributed P2G systems in the West Pomerania province over the years 2030, 2040, and 2050.
Simulations revealed that with water coverage ratio increase and with the planned growth of green hydrogen generation, it should be feasible to produce fuel for net-zero emission urban mobility systems to power 200 buses by 2030, 550 buses by 2040, and 900 buses by 2050 (for city bus models Maxi (40 seats) and Mega (60 seats)).
The Energy Policy of Poland until 2040 focusses on the development of low-emission transportation, with particular emphasis on achieving zero-emission public mobility by 2030 in cities with a population over 100,000. As of the end of 2022, the bus fleet of the West Pomerania Voivodeship consists of 534 units. This suggests that the estimated potential for green hydrogen production could provide approximately 35% of the zero-emission public mobility needs by 2030 and nearly 100% by 2040 throughout the voivodeship, not just in agglomerations with populations over 100,000.
Data from the Central Statistical Office do not differentiate between MAXI and MEGA bus units. Therefore, any deviation from the proposed MAXI/MEGA unit ratio would result in a change in the per-unit hydrogen consumption.

4. Discussion

The article identifies new investment areas that have the potential to support zero-emission urban mobility initiatives. Current changes in spatial planning legislation in Poland are making it increasingly challenging to build photovoltaic plants on land. Nevertheless, such investment areas will still be available.
The performance of the developed algorithm was tested on an example of a case study of the West Pomerania province, leading to definite results and conclusions. Sand and gravel aggregate is extracted country-wide, as it is a vital component in the supply chain for the construction industry [54]. Due to the low value of the product, the key component of its market price is the transportation cost [55]. For those reasons, the proved reserves of sand and gravel aggregate are fairly uniformly distributed all over the country. According to the Balance of Mineral Resources Deposits as of 31 December 2022 (last published), there are 3674 sand and gravel deposits being developed in Poland. In some cases, sand and gravel are extracted under wet conditions (below the water table), leaving a legacy in the form of rehabilitated water ponds once the mining activities cease. These are not the only water reservoirs that emerge during surface mining activities. There are some other minerals that are extracted below the underground water table as well; alternatively, ponds can be formed as interior basins in impermeable strata.
With the development of road investment and construction projects, new resources of sand and gravel aggregates are explored and proven, new surface mining sites emerge, and, when the extraction ceases, are subject to rehabilitation and reclamation schemes, including the rehabilitation of water bodies [56].
The developed and tested model demonstrated that the West Pomerania province has the potential for green hydrogen production on post-mining reservoirs of sand and gravel deposits. The estimation of this potential was made possible through the use of GIS algorithms utilising data from databases provided by administrative bodies. The calculation and scheduling of production potential required the establishment of certain boundary conditions resulting from technical and organisational constraints, such as the shape of the reservoirs, the duration of the mining license, the period of technical reclamation of mining sites, and the legal and formal conditions for venture implementation.
The analysed case study of the West Pomeranian province showed that the potential for green hydrogen production in Power to Gas installations in off-grid technologies can be built on selected water reservoirs in former mining sites, thus solving the problems caused by limited transmission capacity of distribution networks. Floating photovoltaic power plants integrated with a set of electrolysers can be a source of green hydrogen for the region in a distributed system and be used to fuel zero-emission urban mobility based on fuel—cell buses. The demonstrated values of hydrogen production potential for the years 2030, 2040, and 2050 require further work and evaluation regarding their economic feasibility, as well as distribution and utilisation possibilities to achieve the goal of net-zero emission mobility.

Potential for Green Hydrogen Production in Power-to-Gas Systems Operated on Pit Lakes in Former Mining Sites in Poland by 2050

According to the obtained modelling results, it is reasonable to expect a steady growth of installed capacity and yearly electricity generation from FPV to 266 GWh in 2050, while its half value can be achieved in 2032. The service life of photovoltaic installation is about 30 years, yet considering the advancements in PV technology and development of upgraded PV modules with improved energy efficiency, they are likely to be replaced with newer technologies before their 30-year life is over. Thus, the actual electricity production levels can be higher than now predicted.
In fact, without extending and developing the national power transmission and distribution network, meeting the objectives specified in the Fit for 55 package and reaching climate neutrality by 2050 might be hard to achieve [57,58].
Green hydrogen generation requires process water supply to the electrolysers. The unit demand for process water varies from 9 to 11 l(H2O)/kg(H2). In the calculations, a higher value of 11 l(H2O)/kg(H2) was used. It means that in the case of a water body with a surface area of 2.0 ha (1.0 ha being covered with FPV modules, installed capacity of ~1 MWp) the amount of process water to be drawn is 216,071 L per year. Average annual precipitation in the West Pomerania region over the last few years has remained on the level of 500 mm (below that the country’s average), which indicates that the annual demand for process water should not exceed 2% of precipitation supplying the water reservoir. It appears that drawing process water from the reservoir should not directly impact the water balance in the reservoir, while at the same time ensuring the supply of 100% process water.
Fluctuations of water level in the reservoirs are attributable to natural hydrological cycles involving surface run-off, infiltration, supporting vegetation, groundwater, retention (including bioretention), and evaporation and transpiration processes. Covering the water surface with FPV modules will reduce evaporation, which indirectly impacts water retention in the reservoir. Actually, each project involving the implementation of P2G systems is subject to environmental impact assessment, also in terms of process water demand, yet according to general estimates, in most cases the negative impacts should be negligible.
In the light of new technological developments, it is reasonable to expect that energy demand for green hydrogen generation should be gradually reduced. The current demand is at a level of 55.6 kWh/kg H2O and is expected to fall to 44.5 kWh/kg H2O in 2030 [48]. This downward trend is expected to continue until 2050, though the estimates are based on the energy consumption level falling down to 44.5 kWh/kg H2O, to rigorously adhere to underlying assumptions.
To evaluate the potential development of green hydrogen generation in distributed P2G facilities in the West Pomerania province, the study is conducted on the feasibility of using green hydrogen in fuel cells for urban mobility systems [59,60].
On account of a large number of small, distributed sources, hydrogen can be transported within the province by road and supplied to the urban distribution network; for example, for powering the urban mobility systems.
Due to the distributed production model with small volumes, on-site gas storage is not anticipated. The road infrastructure, connected to the current mining production areas, is adapted for the export of hundreds of thousands of tonnes of aggregate. Therefore, there will be no need to expand the road network for the regular transportation of hydrogen by truck to transportation companies in nearby urban agglomerations.
In the proposed model, green hydrogen production is scheduled such that it should enable the fleet of nearly 1,000 city buses to be powered by 2050. According to the West Pomerania bus inventory data as of 31 December 2022, provided by the Central Statistical Office, the fleet size was 534 units. This estimate relies on the number of Maxi and Mega buses, while urban mobility in smaller agglomerations is largely dependent on Midi vehicles, providing transportation for a minimum of eight people, in accordance with the Road Transport Law of 6 September 2001 (Journal of Laws 2024.728, consolidated act of 15 May 2024). These vehicles have lower fuel consumption; therefore, it is reasonable to suppose that green hydrogen supply to net zero-emission urban mobility systems should be higher than the estimated value.
The developed schedule shows that the West Pomeranian province has the potential to produce green hydrogen from distributed sources located on reclaimed water reservoirs in former mining sites. Furthermore, the model demonstrates that the demand for net zero-emission fuel for all buses deployed by urban mobility systems within the province should be fully met as early as 2038.
Attention must be given to geolocational variables that have a crucial impact on the estimation results. These include the quantity of mineral deposits, prevailing geological and mining conditions, exploitation methods, terrain morphology, and geographic latitude and longitude. The model’s operating principle is universal and can be successfully applied in other regions of Poland. Furthermore, with access to geospatial data from other countries and adaptation of the model to the prevailing legislation, estimations can be made for other nations and regions. This is particularly feasible for EU member states, whose legal regulations are aligned with the prevailing Directives of the European Parliament, making the modification and application of the model relatively straightforward.
Despite the fact that, compared to primary extraction activities, the production of green energy and green hydrogen in post-exploitation areas objectively has a lesser impact on the natural environment, a significant barrier may be the reluctance of local communities to neighbour this new type of enterprise. For FPV projects combined with hydrogen production to have a chance of success, it is essential to invest in public education from the initial investment stage.
To confirm the economic viability of the proposed green hydrogen production for urban mobility systems, a series of modelling studies are necessary, including economic models, to compare them with alternative solutions such as Power-to-Gas (P2G) production based on land photovoltaic plants or wind power plants.

5. Conclusions

The study presented examines the potential for green hydrogen production using Power-to-Gas systems integrated with floating photovoltaic installations on former mining lakes in Poland, forecasting to 2050. This novel approach not only highlights the feasibility of utilising unused water bodies for renewable energy production, but also addresses critical energy and emission issues faced by regions undergoing energy transition.
The results show that integrating FPV systems with P2G technology at former mining sites presents a significant opportunity for green hydrogen production. The use of FPV in former mining lakes, often considered environmentally burdensome, transforms these sites into valuable assets in the renewable energy landscape. The modelling and analysis of the study suggest that the energy generated by FPV systems can be efficiently converted to hydrogen, which serves as a versatile energy carrier. This approach is in line with global efforts to decarbonise both energy and transport.
One of the key contributions of this study is the identification and quantification of the potential hydrogen production capacity in specific post-mining lakes in Poland. By integrating advanced geospatial data, the study provides a comprehensive assessment of the potential of FPV-P2G systems to contribute to the decarbonisation of public mobility. The results reveal that with appropriate technological and infrastructure investments, these systems can play a key role in the Polish hydrogen economy by 2050, offering a sustainable alternative to fossil fuels.
The study fills a significant gap in the literature by addressing the intersection of renewable energy production and post-mining land use. Previous studies have largely focused on land-based PV systems, often on large-scale agricultural areas, or have treated hydrogen production and PV plants as separate domains. This paper brings these areas together, offering a coherent strategy for integrating renewable energy generation with hydrogen production in a way that leverages existing land-use conditions. The novelty of this study lies in its interdisciplinary approach, combining the successive remediation of post-mining areas with renewable energy and hydrogen production.
Furthermore, this study provides valuable insights for researchers, policymakers, and stakeholders involved in the transition to zero-emission urban mobility. The results suggest that decentralised, small-scale FPV-P2G installations can serve as key elements of a national green hydrogen production strategy, especially in countries with similar post-industrial landscapes and legal regimes. The study also highlights the importance of addressing potential challenges, such as environmental impact and social acceptance, that are key to the successful implementation of these ventures.
The developed model and research results contribute to the growing body of knowledge on green hydrogen production and offer a scalable, innovative solution to post-mining area development challenges. The study not only addresses existing gaps in the literature but also lays the foundation for future research that could investigate the optimisation of FPV-P2G systems in post-mining areas, the integration of other renewable energy sources, and the socio-economic implications of widespread implementation. The results of this study have the potential to impact both research and practical applications, contributing to the global transformation towards a sustainable energy future.

Author Contributions

Conceptualization, M.S.; methodology, M.S. and D.K.; software, M.S.; validation, M.S.; formal analysis, M.S. and D.K.; investigation, M.S. and D.K.; resources, M.S.; data curation, M.S.; writing—original draft preparation, M.S.; writing—review and editing, M.S.; visualization, M.S.; supervision, D.K.; project administration, M.S. and D.K.; funding acquisition, M.S. and D.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by AGH University of Krakow, Faculty of Civil Engineering and Resource Management; subsidy number: 16.16.100.215, 501.696.7996/L34.

Data Availability Statement

The data can be accessed upon request any of the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Energies 17 04660 g001
Figure 1. Algorithm in the universal method of assessing the potential of implementing FPV facilities on rehabilitated pit lakes in former mining sites (author’s own sources).
Figure 1. Algorithm in the universal method of assessing the potential of implementing FPV facilities on rehabilitated pit lakes in former mining sites (author’s own sources).
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Figure 2. Predicted area of water reservoirs based on identification of proved mineral reserves and in the light of standing mining concessions (author’s own sources).
Figure 2. Predicted area of water reservoirs based on identification of proved mineral reserves and in the light of standing mining concessions (author’s own sources).
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Figure 3. 50% coverage with FPV modules for the water reservoir with regular shoreline (author’s own sources).
Figure 3. 50% coverage with FPV modules for the water reservoir with regular shoreline (author’s own sources).
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Figure 4. 50% coverage with FPV modules for the water reservoir with irregular shoreline (author’s own sources).
Figure 4. 50% coverage with FPV modules for the water reservoir with irregular shoreline (author’s own sources).
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Figure 5. Predicted electricity generation in FPV facilities deployed on the pit lakes in former mine sites by 2050.
Figure 5. Predicted electricity generation in FPV facilities deployed on the pit lakes in former mine sites by 2050.
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Figure 6. Predicted number of hydrogen-fuelled city buses powered from distributed P2G sources.
Figure 6. Predicted number of hydrogen-fuelled city buses powered from distributed P2G sources.
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Table 1. Predicted electricity generation in FPV installations deployed on pit lakes in former mining sites.
Table 1. Predicted electricity generation in FPV installations deployed on pit lakes in former mining sites.
YearIncrement of Lake Surface Area [ha]Increment of Lake Surface Area Available for FPV Installation [ha]Increment of Installed Capacity [MWp]Predicted Electricity Generation [kWh]
202422.7311.36--
20257.283.64--
202661.4430.7211.3612,501,324
202717.658.8215.0016,504,620
202812.146.0745.7350,298,556
202910.375.1954.5560,004,604
2030109.8254.9160.6266,681,296
203119.669.8365.8172,385,764
203210.405.20120.71132,784,168
20332.581.29130.54143,598,928
20342.561.28135.74149,318,004
203532.5516.27137.03150,735,508
203623.2511.63138.31152,140,780
2037--154.58170,042,972
2038--166.21182,831,352
203951.8425.92166.21182,831,352
20409.674.83166.21182,831,352
204119.039.52192.13211,342,296
2042--196.96216,659,960
20430.750.38206.48227,127,384
2044--206.48227,127,384
204554.1627.08206.86227,541,336
204613.406.70206.86227,541,336
20472.461.23233.94257,330,480
2048--240.64264,703,076
2049--241.87266,054,932
205051.6525.82241.87266,054,932
Table 2. Achievable levels of green hydrogen generation related to consumption by net-zero emission urban mobility systems (MEGA and MAXI bus types).
Table 2. Achievable levels of green hydrogen generation related to consumption by net-zero emission urban mobility systems (MEGA and MAXI bus types).
YearPredicted Electricity Generation [kWh]Electricity Consumption Ratio [kWh/kgH2]Hydrogen Production [kgH2]Bus Range [km/year]Bus Fleet Size- Number of Mega Busses
[Item]		Bus Fleet Size-NUMBER of Maxi Buses
[item]
2024-56.0----
2025-56.0----
202612,501,32456.0223,2382,232,3791816
202716,504,62056.0294,7252,947,2542322
202850,298,55655.5906,2809,062,8037167
202960,004,60455.01,090,99310,909,9288680
203066,681,29654.51,223,51012,235,1009690
203172,385,76454.01,340,47713,404,77110698
2032132,784,16853.52,481,94724,819,471195182
2033143,598 92853.02,709,41427,094,137213199
2034149,318,00452.52,844,15228,441,525224209
2035150,735,50852.02,898,76028,987,598228213
2036152,140,78051.52,954,19029,541,899233217
2037170,042,97251.03,334,17633,341,759263245
2038182,831,35250.53,620,42336,204,228285266
2039182,831,35250.03,656,62736,566,270288268
2040182,831,35249.53,693,56336,935,627291271
2041211,342,29649.04,313,10843,131,081340317
2042216,659,96048.54,467,21644,672,157352328
2043227,127,38448.04,731,82147,318,205373347
2044227,127,38447.54,781,62947,816,291377351
2045227,541,33647.04,841,30548,413,050381355
2046227,541,33646.54,893,36248,933,621385359
2047257,330,48046.05,594,14155,941,409441411
2048264,703,07645.55,817,65058,176,500458427
2049266,054,93245.05,912,33259,123,318466434
2050266,054,93244.55,978,76359,787,625471439
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Sikora, M.; Kochanowski, D. Potentials of Green Hydrogen Production in P2G Systems Based on FPV Installations Deployed on Pit Lakes in Former Mining Sites by 2050 in Poland. Energies 2024, 17, 4660. https://doi.org/10.3390/en17184660

AMA Style

Sikora M, Kochanowski D. Potentials of Green Hydrogen Production in P2G Systems Based on FPV Installations Deployed on Pit Lakes in Former Mining Sites by 2050 in Poland. Energies. 2024; 17(18):4660. https://doi.org/10.3390/en17184660

Chicago/Turabian Style

Sikora, Mateusz, and Dominik Kochanowski. 2024. "Potentials of Green Hydrogen Production in P2G Systems Based on FPV Installations Deployed on Pit Lakes in Former Mining Sites by 2050 in Poland" Energies 17, no. 18: 4660. https://doi.org/10.3390/en17184660

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