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Review

A Review of the Life Cycle Analysis Results for Different Energy Conversion Technologies

by
Violeta Motuzienė
*,
Kęstutis Čiuprinskas
,
Artur Rogoža
and
Vilūnė Lapinskienė
Department of Building Energetics, Faculty of Environmental Engineering, Vilnius Gediminas Technical University, 10223 Vilnius, Lithuania
*
Author to whom correspondence should be addressed.
Energies 2022, 15(22), 8488; https://doi.org/10.3390/en15228488
Submission received: 9 October 2022 / Revised: 1 November 2022 / Accepted: 9 November 2022 / Published: 14 November 2022
(This article belongs to the Topic Advances in Clean Energies)
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Abstract

:
Technologies that use renewable energy sources (RES) are crucial to achieving decarbonization goals, but a significant number of studies show their relatively high environmental impact during the production phase. Therefore, technologies need to be compared in terms of their life-cycle environmental impact. The life cycle analysis (LCA) methodology is well known and widely employed. However, problems related to the methodological choices prevent taking full advantage of the LCA, as the results of numerous studies are often incomparable. The presented review aims to critically compare the impact of different energy generation technologies—RES (as well as non-RES) energy generators and co-generators. The numeric results are structured and analyzed in terms of the global warming potential (GWP) and non-RES primary energy consumption. The results show that RES technologies are superior compared to conventional fossil-fuel-based systems in most cases, and the high impact during the production and installation phases is compensated in the operational phase. The high variations in GWP from similar technologies result from different methodological choices, but they also show that the wrong choice of the technology in a certain location might cause serious environmental drawbacks when the impact of the RES technology exceeds the impact of fossil fuel-based technologies. Cogeneration technologies using waste as a fuel may even have a negative GWP impact, thus showing even higher potential for decarbonization than RES technologies.

1. Introduction

Energy generation is considered a major challenge throughout the industrial evolution, especially as the global population is exponentially increasing [1]. Despite international commitments, energy-related CO2 emissions have risen by 1% per year on average since 2010 [2], and secure, environmentally friendly, and efficient energy sources are needed now more than ever to solve the global problem of climate change. To limit the effects of the energy sector on climate change, significant reductions in CO2 emissions can be achieved by using the appropriate technologies and policies [3], e.g., performing an energy transition of the global energy sector. Policymakers and scientists see technologies that use renewable energy sources (RES) as one of the main solutions on the road to a decarbonized energy sector. It is estimated that renewable energy and energy efficiency measures can potentially achieve 90% of the required carbon reductions by 2050 [4]. The estimates are based on the impacts of the energy conversion phase, but a significant number of studies show that the environmental impact of RES technologies during the production phase can be relatively high and cannot be neglected. Thus, to reach the deep decarbonization goals, the choice of the technology cannot be based only on the operational phase, ignoring the impacts related to the other life cycle phases of the technology. Energy conversion technologies need to be compared in terms of their life cycle environmental impacts, e.g., employing the well-known methodology of Life Cycle Analysis (LCA).
LCA is applied for two purposes: to quantify/assess the environmental performance of a product or process “from cradle to grave”, and to provide general information for evaluating potential improvements of a product and/or a system. The standard methodological framework for performing the LCA consists of four main phases [5]: (1) goal and scope definition, (2) inventory analysis, (3) impact assessment, and (4) interpretation. However, the LCA detailed methodology can include several different methods, approaches, applications, and software packages. The inventory analysis and impact assessment phases are characterized by a number of methodological choices, such as system boundaries (cradle-to-grave, cradle-to-gate, cradle-to-use, etc.), impact assessment (midpoint and/or endpoint), allocation methods, and impact category indicators [6].
Although LCA methodology is widely employed in many studies analyzing energy conversion systems’ life cycle impacts, problems related to methodological issues prevent taking full advantage of this method when making decisions related to the choice of cleaner energy conversion technologies. A transparent and homogeneous comparison is often not possible to make because of differences in authors’ choices related to LCA methodology, software, databases, boundaries, indicators, functional units, etc. This problem was also noted by [7]. In addition, results can differ because of regional specifics, such as climate.
The breakthrough in the efficiency of energy conversion from burning fuel is undoubtedly linked to cogeneration. The combined production of electricity and heat not only increases the efficiency of energy transformation but at the same time contributes to reducing the negative impact on the environment. Most of the world’s electricity is generated by burning fossil fuels (61% in total): coal (35%), natural gas (23%), and oil (3%). The rest is produced using nuclear energy (10%), hydropower (16%), and renewable energy (12%), the share of which is constantly growing, as well as other resources (about 1%) [8]. Burning renewable fuels in combined heat and power production plants further expands the environmental performance of such systems, making an overview of their LCA performance no less important than other RES technologies. The presented review aims to identify opportunities for a sustainable energy transition path, critically comparing the different energy conversion technologies on the basis of the results of the LCAs performed. Moreover, the authors aim to confirm the hypothesis that renewable energy-using technologies are not always superb in terms of their life cycle impact.
The paper consists of the following sections: (1) Introduction: a short presentation of the background of the paper and goal definition; (2) Materials and Methods: a presentation of the choices related to the reviewed energy technologies, data systematization criteria, and used functional units; (3) Results, which is divided into subsections: a review of the methodological choices used and the different energy sources technologies, comparing collected numerical values for impact categories; (4) Discussion: a critical discussion on individual technologies; and (5) Conclusions. Appendix A features a table (Table A1) with a detailed collection of data related to the methodological aspects of the LCA studies reviewed.

2. Materials and Methods

The review includes (Figure 1) literature related to renewable energy conversion systems classifying them as thermal energy generators, electrical energy generators, and co-generators (electrical + thermal), both RES and non-RES.
The review focuses on studies written in English and published in or after 2010 (with some exceptions). The literature is classified according to the energy source type: hydro, wind, solar (both PV and thermal), geothermal, waste, and cogeneration. Each source of energy is discussed in a separate section.
Methodological LCA choices, such as software, environmental impact assessment method, system boundaries, and environmental impact categories were analyzed. Moreover, the region (country) that was applied in the assessment was taken into account. Methodological choices were analyzed for all energy conversion technologies to find the tendencies, and the numeric results were systemized and analyzed for different technologies separately in terms of GWP (gCO2 eq/kWh) emissions and non-renewable primary energy consumption (MJ/kWh). The overall number of literature sources used in the paper was 120; the number of source studies for the data collected and systemized here was 95.

3. Results of the Review

3.1. Methodological Aspects of the Studies Reviewed

As was already mentioned, different methodological choices make it difficult to transparently and correctly compare the results of the LCA studies on energy technologies. The methodological aspects of the studies are systemized in detail in Appendix A (Table A1), and Figure 2 summarizes the general aspects of the choices related to the impact assessment methodologies used by the authors, the boundaries of the studies, the LCA software used, and the impact categories. The choices related to functional units were not analyzed in the study. The most commonly used functional unit according to a review performed by Muteri et al. [9] is kWh of produced electricity, and it was further used in this review. As seen from the figure (Figure 2a), most studies used CML methods, yet the ReCiPe method is popular as well. In general, it is obvious that there is not one strongly dominant method. Figure 2b shows boundaries used in the LCA studies and here, the boundaries that are used most commonly are from cradle-to-grave (full life cycle of the system) and from cradle-to-gate. The leading software used in the reviewed studies is SimaPro (Figure 2c); in terms of impact assessment, the most popular category, which is also compared in this study, is still global warming (Figure 2d).
The least unification in LCA methodology is related to the impact assessment methods. Each of them uses different assumptions, thus causing additional uncertainties of the results, and comparison becomes merely indicative. A higher degree of unification in the LCA methodology of energy using systems would be beneficial.

3.2. Hydro Energy

Electricity generated in hydropower stations accounts for the largest share of the world’s renewable energy conversion. In 2019, this share was 60% [10]. It is widely agreed that this technology is among the “greenest” used for power generation. In addition to the papers’ aim to compare GHG emissions for different energy conversion technologies, it also merits to compare results within the same technologies provided by different studies. As expected, the results showed a high level of variation. The widest dispersions can be found in review papers, e.g., in [11,12], and this is logical, taking into account the nature of such papers.
Table 1 summarizes the results obtained from different studies on hydro energy life cycle impact in terms of GHG emissions (a visual representation of the results is provided in Figure 3, together with other reviewed technologies). Looking at the hydropower results on the chart (see Figure 3), three relative zones can be distinguished: “upper”, “middle”, and “bottom”. The clear “upper” zone (3 points over 100 gCO2 eq/kWh.e) corresponded to [11,12,13] (in a descending order of GHG emissions). The highest values (237, 160, and 152 gCO2 eq/kWh.e) referred to the cases with high dams and large reservoirs. The dams were constructed using very large amounts of concrete and steel with a high rate of embodied energy and, consequently, emissions. The reservoirs in this case usually are large, flooded land areas, with biomass decaying under the water and releasing GHG (CO2 and CH4) for the years. Moreover, this share of emissions is even more important because it contributes to such a large dispersion of results, as is shown in [12]. This paper also emphasizes the need to distinguish between “net” and “gross” emissions from flooded land because natural ponds (such as lakes and rivers) also emit some amount of GHG into the atmosphere. Emissions from flooded land presented in [13] as “biogenic” are in line with [12], and they were approximately equal to 160 gCO2 eq/kWh.e (85 gCO2 + 3 gCH4 × 25) with “a multiplicative uncertainty factor of 2”.
The “bottom” zone in Figure 3 (points with values below 20 gCO2 eq/kWh.e) corresponded to the results of [14,15,16,17], as well as the lower parts of [11,12]. All these sources, except for [17], refer to the “run-off-river” cases or reservoir cases excluding emissions from flooded land. In the “run-off-river” cases, the height of dams; reservoir sizes; flooded land areas; and, consequently, biogenic GHG emissions usually are much smaller, and this could explain the large differences between the “upper” and the “bottom” parts of hydropower results (see Figure 3). In this logical sequence, the results of [17] stand out strongly compared to other results referring to the cases with high dams and large reservoirs. Some circumstances, such as the immense capacity of power stations and the pre-impoundment clearance of reservoir areas, could explain this gap, but this case still requires more attention.
Table
Table 1. LCA impact of the hydropower.
Table 1. LCA impact of the hydropower.
SourceCountry, CommentsgCO2 eq/kWh.e
[11]review3.7–237
[13]bGHG only160
[12]review, incl. dams4.5–152
[18]Thailand, micro52.7
[19]Myanmar, large scale, ROR31.17–39.23
[12]review, ROR0.3–13
[12]review, not incl. damsavg. 2.9 (0.2–11.2)
[17]China, mega scale7.6–9.12
[16]China3.1–3.7
[14]Peru, Andes, ROR2.06–2.42
[15]Europe, alpine non-alpine0.107–1.41
The “middle” zone also contained two atypical cases. Both cases were drastically different in terms of power generation capacity, although both fell into the “run-off-river” category. Pascale et al. [18] presented a 3 kW community hydroelectric system located in rural Thailand, and this “micro” scale probably is the main cause of higher emissions. Aung et al. [19] presents the results of five large-scale hydropower stations with a capacity of 120 to 790 MW. These stations also appear unusual because of the combination of “run-off-river” type with large dams and reservoirs.

3.3. Wind Energy

The amount of global wind energy conversion takes second place among renewable energy sources, standing at about 20% [10]. Like hydropower, wind energy is also considered as one of the “greenest”.
Among the results presented in Table 2 (also see the visual presentation of results in Figure 3), [20] is a clear exception with approximately 10 times the values of other sources, ranging from 295.2 to 468 gCO2 eq/kWh.e. It seems that there is a problem with the conversion of units because these figures are not in line even with the data in the review part of this source. The second highest value of 123.7 gCO2 eq/kWh.e is presented in [11], although there are no details provided other than a reference to the source itself. The next two points in descending order represent upper parts of quite large intervals. The 55.4 gCO2 eq/kWh.e value [12] refers to a small turbine (30 kW) with a capacity factor of between 0 and 15%. The 42.75 gCO2 eq/kWh.e value [21] represents the worst case of six scenarios with different life-spans, capacity factors, replacement rates of parts, transport routes, and waste management options.
The remaining points lie (also see Figure 3) in the relatively compact zone between 3.9 and 31.8 gCO2 eq/kWh.e. A closer look at this zone revealed some differences; however, there was no clear trend. These results confirm some already known facts that larger wind farms with larger turbines and especially with greater capacity factor values produce lower GHG emissions per energy unit generated. Another obvious fact that is mentioned in almost all of the sources reviewed is that the main part of GHG emissions is generated during the manufacturing phase of wind farms.

3.4. Solar Energy

Solar energy is used to generate electricity and thermal energy. Therefore, these technologies are further discussed separately as photovoltaics and solar thermal collectors.

3.4.1. Photovoltaics

Over the decades, solar PV has been one of the most rapidly developing, mature, and cost-competitive renewable energy technologies [27]. The total cumulative installed capacity for PV at the end of 2020 reached at least 760.4 GW [28]. Solar PV is seen as the second most promising source after wind, and it has 21% of the total CO2 emission reduction potential from renewables and energy efficiency measures by 2050.
Over the last four decades, a range of viable PV technologies has been proposed, spanning from conventional single-crystal (s-Si) and multi-crystalline silicon (m-Si) to second-generation panels such as amorphous silicon (a-Si), cadmium telluride (CdTe), and cadmium indium gallium selenium (CIGS). More recently, much research and development have gone into third-generation PV technologies including dye-sensitized (DSC), perovskite, quantum dot (QD), and organic (OPV) cells, for instance [29], and a variety of technologies are expected to continue to characterize the PV technology portfolio. First-generation technologies still account for the majority of global annual production [30]. Newer technologies still have barriers that need to be addressed and overcome (durability, price).
Different environmental impact categories of the PV technology strongly vary because of the different component materials, module efficiencies, manufacturing methods, locations, and modes of disposal used in their life cycle. The environmental impacts of some technologies from different generations are compared in [31], where the second-generation a-Si PV technology seems to be among the most sustainable, taking into account the overall effect in nine different impact categories. The thin-film technologies seem more environmentally efficient, and Bergesen et al. [32] estimates that they have the potential to reach GWP values of 6–7 gCO2 eq/kWh.e. A study by Krebs-Moberg et al. [33] also confirms that m-Si has the highest environmental impacts and that organic thin-film panels have the best life cycle environmental performance.
The concerns about air pollution stemming from PV-system components in all the life cycle stages of the system must be treated with caution [34]; however, most of the CO2 emissions are attributable to the manufacturing processes of the PV modules [35,36], and multi-Si production is the most contributing phase in terms of the energy demand and environmental impacts [37,38].
The life cycle impact of a photovoltaic installation is strongly related to the geographical features of the location where it is installed. Both solar radiation levels and outside temperatures play a role in the efficient electricity generation of the module, and there are multiple studies to prove it. In cold climate zones, solar radiation is lower, but at the same time, the efficiency of PV panels increases due to the lower ambient temperature [39]. Parisi et al. [40] have demonstrated how irradiation influences GWP for different PV technologies at different radiation levels. Low radiation levels, e.g., for North Europe, may have almost twice the impact compared to Southern countries. Akinyele et al. [41] found even three times higher GWP values for locations with the lowest solar radiation levels. The results of a comparative LCA depend also on the local electricity mix used in the life cycle stages of the assessed products [42].
Muteri et al. [9] reviewed 39 LCA studies relating to the different types of grid-connected PV systems (from first to third generation) and have provided a summary of information and critical analysis. The review showed that, even when similar modules are examined, it is difficult to compare different studies because of different methodological approaches, as well as factors such as different configurations of the modules, installations, and efficiencies. Therefore, following the aim of the review, we purposefully searched life cycle assessment results—GWP and non-RES PE of the PV technologies, wherein the functional unit is kWh.e. The results are summarised in Table 3.
As is seen from the table, most of the PV technologies have very low environmental impacts compared to traditional fossil fuel sources (see Figure 3). Perovskite solar cells show extreme variations in the GWP impact category, but the value of 5867 gCO2 eq/kWh.e suggests that it should not be treated as a bad technology because the authors [49] only performed a sensitivity analysis assuming different lifetimes and solar radiation levels, and this is the result of the worst case scenario. In general, Perovskite cells are seen as a new and promising technology, offering superior technical performance at a low cost.
PV systems might also be efficiently integrated with other systems, e.g., Yan et al. [51] presented parametric LCA for the tri-generation system—a combined cooling, heating, and power system with renewable energy and energy storage. They compared the influence of various sizes of solar PV arrays and batteries in such a system and discovered a potential decrease in GWP of up to 46%.
It is obvious from the above that solar technologies impact varies, but it can be minimized with proper selection of the technology, taking into account location specifics, with proper selection of elements and with efficient integration with other systems.

3.4.2. Solar Thermal Collectors

Solar thermal technologies are used in all regions of the world to provide low- and medium-temperature heat, especially when used in domestic applications, but it is still a niche market for industrial processes [52]. Solar systems are considered to be attractive investments, due to their long lifetime of more than 25 years and relatively small maintenance cost. However, the real potential of solar technologies lies in the improvement of their efficiency so that they can achieve satisfactory environmental performance when compared to other renewable energy systems [53].
Compared to what is needed to achieve the Paris Agreement goals, the installation speeds of solar thermal collectors are inadequate. For instance, IRENA’s 1.5 °C pathway requires the global solar thermal capacity to increase from around 4 GW in 2018 to 890 GW in 2030 and 1290 GW in 2050 [10]. In this way, solar thermal technologies—and their applications—are thus far at the stage of development.
The literature review of solar thermal technologies demonstrated that even though the publications covered vacuum and flat-type solar collectors, the focus mainly lay on the latter [52,54,55]. Vacuum tube collectors show higher efficiency and are much less affected by variation in the ambient temperature, but as the price is almost 45% higher, it is the flat-type collectors that are the principal option in southern climates [56].
During the last few years, these solar thermal technologies have been taking a large leap towards the improvement of energy efficiency, the minimization of materials used in the production stage, recycling, and the reduction of environmental burdens [57].
In contrast to the widely discussed solar PV technologies, there have been a limited number of life cycle analyses looking specifically at solar thermal technologies [56], with most research papers concentrating on economic analysis [58].
The results of certain LCA studies show that almost all of the environmental impact of solar thermal technologies is produced during the production phase, while in the operation stage, the emissions were negligible [56,57,59].
Moreover, solar thermal systems show their weaknesses in the acidification and eutrophication impact categories, mainly due to the metals used to produce their main components: collector, tank, and copper tubes [59].
In summary, as there was a limited number of publications on solar thermal technologies, and Table 4 presents life cycle assessment results—GWP of the solar thermal technologies for three cases. In all of them, the analysis was covered in southern climates, and thus the variation of the results was moderate (Figure 3). No results for functional unit non-RES PE were found by us.
Nevertheless, a review by Kylili et al. [52] proved that the geographical location has a decisive impact on GWP. Life cycle assessment results for various European cities (Athens, Barcelona, Milan, Frankfurt, Copenhagen, Oslo) presented a significant difference, with higher latitude locations showing more than twice the GWP values compared to lower latitudes.

3.5. Geothermal Energy

Geothermal energy is an important energy resource, largely contributing to limiting the use of fossil fuels. It can be employed for both electricity and direct uses [60]. Geothermal energy can be directly utilized for space heating and cooling, greenhouse heating, aquaculture, bathing, district heating, and industrial uses. The direct utilization of geothermal energy by countries worldwide is reviewed in detail in the study of [61]. Indirect utilization is when geothermal energy is converted into electricity by using different technologies. Geothermal plants tend both to run trouble-free at nearly full capacity for most of their lifetimes and to serve the baseload power demand well [62]. In 2020, the volume of generating energy from geothermal technologies was 94 TWh. Nevertheless, geothermal technology is still not on track to reach the required annual 13% increase in generation over 2021–2030, corresponding to ≈3.6 GW of average annual capacity additions [63]. Different technologies, such as dry steam; binary cycle; and single flash, double flash, and triple flash enhanced geothermal systems, are employed to generate heat from geothermal sources. The energy conversion technology used for exploiting geothermal systems depends on different aspects, such as the reservoir properties (e.g., geological, geophysical, geochemical, physicochemical, and thermodynamic) [64]. In terms of this technology, geological areas with very high geothermal gradients hold the greatest appeal [65]. At sites with less favorable conditions, only certain plant designs can make up for the energy and material input to exploit the energy potential provided by geothermal reservoir [66,67]. Moreover, the type of technology and the characteristics of the wells must be treated with caution [67].
With some exceptions, geothermal systems are considered one of the least GHG-emitting renewable technologies [62]. The authors compared the energy conversion impact from different energy sources using the GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation) model. The results show that the biggest impact in geothermal power plants is made during the construction phase. Comparisons of three different types of plants are presented in Figure 4, where EGS is the enhanced geothermal system, and HT–Binary and HT–Flash are hydrothermal binary and hydrothermal flash plants, respectively.
The authors of the review [64] on different geothermal technologies’ life cycle impact results have concluded that most of the LCA studies report global warming, which is mostly caused by the fuel consumption in the construction and operation stages. The results from this study show that the available information about geothermal power production’s life cycle environmental impacts is still scarce.
Geothermal plants’ contribution to global warming also depends on whether an emission treatment system and substitution of natural emissions are applied or not. Basosi et al. [60] calculated that an existing plant with an AMIS® emissions treatment system emits approx. 0.47 kg CO2 eq/kWh, and without an emission treatment system, slightly less. Meanwhile, when an emission treatment system is applied together with a 40% substitution of natural emissions, GWP is only 0.3 kg CO2 eq/kWh.e.
It is also estimated by some studies that the plants that provide electrical power have larger impacts across all impact categories analyzed, compared to plants that provide both power and heat [66,68]. However, [69] notes that this also highly depends on the heat and electricity mix in the region. Meanwhile, [66] emphasizes that for net power and district heat production, the main aspects of environmentally sound plants are the enhancement of the reservoir productivity, reliable design of the deep wells, and an efficient utilization of the geothermal fluid. It must be also noted that there are allocation difficulties related to impacts associated with joint production processes for electricity and heat [70]; therefore, most of the authors of the studies reviewed only addressed the impacts of producing electricity, despite the fact that the plant also generates heat.
The results of different LCA studies show that the construction phase of the plant is largely responsible for the environmental impacts of the geothermal plant [69,70]. However, Ruzzenenti et al. [68] concluded that the materials and energy used for the drilling, cementation, casing, and development of the wells almost offset the benefits provided by the use of non-fossil resources.
Most of the studies reviewed (Table 5) show low GWP impact results compared to conventional fossil-fuel systems, despite the fact that there have been high variations and values found, depending on the region. As a case in point, for power plants analyzed by [68,69], located in Italy, GWP reaches impacts that are similar to the fossil fuel power plants. Moreover, in some cases and depending on the configuration of the plant, there are high variations of the GWP, such as in a power plant located in Germany [66]. Very high environmental performance is noticed in a geothermal plant located in Iceland [70,71,72], where in some cases it can also be achieved by employing a carbon capture and storage technology [70]. Icelandic rocks are primarily igneous and contain lower amounts of carbonates [73]; this does not only mean lower greenhouse gas emissions, but also enables permanent disposal through mineralization of captured CO2, as demonstrated by the CarbFix project [74]. Enhanced geothermal systems (EGS) also show considerably better GWP results for different regions, namely, the U.S., Germany, and Iceland, as presented in [62,69,72,75,76]; they also showed that using refrigerants with low global warming potential ensures minimal effects.
However, there are studies, such as [67], that prove that CO2 emissions from geothermal energy may be of the same order of magnitude as those from fossil power plants and that demonstrate that geothermal electricity conversion is not exempt from environmental drawbacks. Thus, geothermal systems must be designed carefully with environmental consideration throughout the whole life cycle of the system. For this purpose, even a simplified life cycle assessment (LCA) method to assess the environmental impacts of deep geothermal energy plants—those that are in the pipeline or already in operation—has been developed to help geothermal project developers evaluate the environmental performance of their project, in particular against fossil alternatives (https://www.geoenvi.eu/lca-for-geothermal/, accessed on 9 September 2022).

3.6. Waste

The European Union adopted the Circular Economy Package in 2018, wherein the waste-to-energy (WtE) sector plays a crucial role towards a resource-efficient, low-carbon, circular economy. WtE has several purposes: to reduce the amount of waste sent to landfills by producing usable energy: heat and/or electricity [78].
Waste can be classified as organic and non-organic, while the main technologies used for WtE are direct combustion, thermochemical, physiochemical, and biochemical processes.
According to this review and in the context of LCA, much attention is paid to biochemical–anaerobic digestion processes for food waste [79,80] and municipal waste [81]. This is a tested technology for waste management that has a global application, but it has been given less attention recently in terms of thermal treatment [82].
The LCA modeling techniques applied in the research outlined a large degree of variability in technological systems, with different system boundaries, functional units, impact categories, and geographical features complicating the comparison. Nevertheless, the most widely assessed impact categories are global warming [83,84,85], eutrophication/acidification [86], toxicity, etc. (Table 6).
In this research, we found a problem with the comparability of the WtE LCA results due to different functional units. Most researchers choose the input-based approach with a specific amount of solid, food, or other waste as the functional unit [79,80,85]. It was only in a few cases that the authors followed the output-based approach, wherein the results were presented towards the amount of useful products [86].
The critical review of WtE also stated the major challenges in comparability LCA: while most of the studies analyzed followed an input-based approach (80%), some of them did not clearly state their functional unit, and/or the functional unit could not be retrieved [82].
The analysis of the cogeneration processes using waste appeared to be more informative for the purposes of comparison of the functional units for gCO2 eq/kWh or MJ/kWh; as a result, some of the data are presented in the following section.

3.7. Cogeneration

Usually, during the cogeneration process, two types of products are produced: electricity and heat. Different allocation methods are used to distribute the environmental impact between these two products on the basis of energy, exergy, the value of emissions, fuel chargeable to power, shared emissions, and other methods. Variations of up to 88% were identified among the most common methods applied to the allocation of resources and emissions [87]. In some cases, in addition to energy flows, some other co-products can include, for example, combined synthetic natural gas and electricity production from lignocellulosic biomass [88], electricity and cold [89], and electricity and hydrogen [90,91]. Due to electricity cogeneration from excess heat occurring in the production of gas, both gas and the electricity are potential products, with their relative amount depending on the process design. The exergy allocation method is often referred to as the most objective and more precise [87,89,92]. The problem related to electrical and thermal energy allocation in the cogeneration process can be avoided by choosing the primary energy as the functional unit [93]. The case of co-processing sewage sludge and the organic fraction of municipal solid waste shows that anaerobic co-digestion provides better performance than dark co-fermentation, mainly because of the higher energy recovery for electricity and thermal energy production [94]. In looking for better options of cogeneration of waste products, recovery of used cooking oil in cogeneration plants has in general lower values in terms of environmental impacts than its employment in biodiesel production [95]. The effective integration of traditional and renewable sources and the proper operation of thermal storage units increase the system flexibility and sustainability, helping to deal with the intermittent nature of the solar source [96].
A summary of the LCA results for cogeneration technologies is presented in Table 7. The nature of the indicators is very different and depends on the priorities of the authors, the specifics of the technology, and the functional unit chosen (electricity and/or thermal output). The ranges of the indicator values are also very wide. They depend mainly on the type of the primary energy source (RES or Non-RES) and the cogeneration technology. Unfortunately, no clear trends in the dependencies of the indicators were observed in the studies examined.

3.8. Results for Different Energy Conversion Technologies

All results from the previous section related to separate energy conversion sources were consolidated into one comparative graph (Figure 3).
No comparison of the non-RES primary energy demand for different sources was made because of the limited amount of data available. The sufficient amount of GWP indicators, wherein the functional unit is kWh of produced electricity, makes it possible to present differences and ranges for different technologies, comparing them to fossil-fuel-based energy conversion systems (coal, oil, and natural gas). Some values of RES generators are even higher than the traditional fossil-fuel-based technologies, pointing to some design drawbacks or worst-case scenarios. Most of the values are in a range from 0 to 100 gCO2 eq/kWh.e, proving that RES technologies, if carefully designed with the environmental issues in mind, have a high potential to replace conventional technologies and lead to the global decarbonization goals.

4. Discussion

This review aimed to identify any opportunities for comparing environmental impacts of different power generation technologies using the results of the previously performed LCAs. The paper further compared different RES-based technologies—hydro, wind, solar (PV and thermal collectors), geothermal, and waste—with the results of cogeneration technology as an alternative, an efficient way to transform energy with a smaller environmental impact. The comparison was made using kWh of converted energy as a functional unit. The impact was assessed in terms of GWP (global warming potential), which is the most common indicator in similar studies, and demand for non-RES primary energy. There are many differences in the methodological approaches in different LCA studies, which were systematized in Annex A; for numerical comparison, only studies that involved the same functional units were used. Each of the technologies was reviewed separately, and the data were structured and compared to the other alternative technologies as the final result of the review paper.
Electricity generated in hydropower stations takes the biggest share of the world’s renewable energy conversion, and in most cases has the smallest global warming potential (GWP) compared with other RES. However, two typical cases can be distinguished, each with its own level of GWP. In the case of high dams and large reservoirs, the expected GWP value is between 140 and 240 gCO2 eq/kWh.e, and in the run-off-river case, it is below 15 gCO2 eq/kWh.e. Such significant differences occur depending on whether biogenic GHG emissions are included in the assessment or not.
Wind energy is the second largest source of RES energy. The reviewed literature confirms the already-known facts that larger wind farms with larger turbines, especially those that have greater capacity factors, produce lower GHG emissions per energy unit. Another obvious fact mentioned in almost all of the studies reviewed is that the main part of GHG emissions is generated during the manufacturing phase of wind farms. The GWP effect of wind power generation is comparable to PV and hydro energy. The approximate average value derived from the sources reviewed can be estimated as 25 ± 10 gCO2 eq/kWh.e. Any values outside this interval usually are associated with scenarios that are based on near-marginal favorable or unfavorable assumptions.
Solar PV technologies are some of the most rapidly developing RES technologies, where different generations of solar cells are applied and developed. Despite their relatively high environmental impacts during the production stage, these technologies have a small overall impact during the whole life cycle, compared to the conventional fossil-fuel-based systems. Some of the PV technologies, such as thin-film technologies, seem extremely environmentally efficient and are estimated to have the potential to reach GWP values of 6–7 gCO2 eq/kWh. This level of impact is hundreds of times lower compared, e.g., to coal power plants. However, it is important to note that geographic features of a photovoltaic installation have a significant effect on the electricity generation, and therefore it is also an important factor when it comes to assessing the sustainability of the PV technologies within their life cycle, as low radiation levels, such as those that exist in Northern Europe, may double or triple the impacts.
Solar thermal systems are also presented as clean energy conversion systems with quite a long lifetime of more than 25 years and relatively small maintenance costs. LCA studies show that here, the production stage plays the largest role, producing almost all of the environmental impact for different types of solar collectors. Meanwhile, the results for the operation stage are insignificant. The review also proved that the geographical location has a decisive impact on energy and GWP, with northern locations presenting up to twice the GWP values and as much as half the GWP and energy savings of southern locations.
As most of the studies on geothermal system LCA covered in this review showed, these systems have low GWP impact results compared to the conventional fossil fuel systems, despite the high variation and values depending on the region and the type of the system. In particular, low impacts are found in geothermal power plants in Iceland and when enhanced geothermal systems (EGS) are employed with the application of different additional technologies, such as carbon capture and storage, combined heat and power production, or the use of refrigerators with low GWP impacts. These plants may reach extremely low GWP values of less than 2 gCO2 eq/kWh. However, there are studies that prove that emissions of CO2 from geothermal energy sources may have the same order of magnitude as fossil fuel power plants, demonstrating that geothermal electricity conversion is not exempt from environmental drawbacks. Thus, geothermal systems must be designed carefully with environmental factors in mind throughout the whole life cycle of the system.
The review of LCA studies of waste-to-energy (WtE) systems identified many differences in system boundaries, functional units, impact categories, and geographical features. Therefore, a problem was found with the comparability of WtE LCA results, as in most cases the functional unit was found to be a specific amount of waste. Thus, the analysis of using waste as a fuel in cogeneration processes was shown to be more informative and could present some results for GWP (gCO2 eq/kWh) emissions and non-renewable energy consumption (MJ/kWh).
LCA results for cogeneration technologies have a strong variation due to the allocation of the environmental impact between different products such as electricity, heat, cold, synthetic natural gas, hydrogen, and recovery of used cooking oil. Moreover, LCA results for GWP strongly depend on the type of the primary energy source (RES or Non-RES) and the cogeneration technology. For cogeneration plants using natural gas as fuel, the GWP is 260 ÷ 520 CO2 eq g/kWh.e. Meanwhile, for plants using residual waste, it can even be negative: −300 ÷ 1 CO2 eq g/kWh.e. The negative impacts are found when residual materials (residual biomass, bio-waste) were considered more dangerous to the environment than the energy conversion process as such.

5. Conclusions

In conclusion, of the review, RES technologies can be said to be clearly superior to the conventional fossil-fuel-based systems in most cases (Figure 3), and, despite the high impact during the production and installation phases, their impacts are compensated with miniscule impacts during the operational phase. High variations in GWP results occur because of different methodological choices, but they also show that inappropriate technology deployed in a certain location might be the reason for serious environmental issues when the impact of the RES technology excels over fossil-fuel-based technologies. Thus, RES systems must be designed carefully with environmental factors in mind through the whole life cycle of the system, taking into account the specifics of the location, such as solar radiation, external temperatures, and geological properties. The initial hypothesis raised by us that renewable-energy-using technologies are not always superb in terms of their life cycle impact was confirmed. This critical review might be beneficial for policymakers when making decisions on decarburization of the energy sector.

Author Contributions

Conceptualization, V.M. and A.R.; methodology, V.M.; resources, A.R., V.M., K.Č. and V.L.; data curation, K.Č.; writing—original draft preparation, V.M., K.Č., A.R. and V.L.; writing—review and editing, V.M.; visualization, K.Č.; supervision, V.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research did not receive any external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The study did not report any data except cited references.

Conflicts of Interest

The authors declare no conflict of interest.

List of Acronyms

a-Siamorphous silicon PV technology
CCScarbon capture and storage
CdTecadmium telluride PV technology
CEDcumulative energy demand
CExCcumulative exergy consumption
c-gfrom cradle to grave
c-gtfrom cradle to gate
CHPcombined heat and power
CIGScadmium indium gallium selenium PV technology
CMLimpact assessment method by Institute of Environmental Sciences at Leiden University
comconstruction, operation, and maintenance
c-ufrom cradle to use
daadouble accounting analysis
DSCdye-sensitized PV technology
DHWdomestic hot water
EGSenhanced geothermal systems
FUfunctional unit
GHGgreenhouse gas
gt-gfrom gate to grave
GWPglobal warming potential
HThydrothermal plant
ILCDInternational Reference Life Cycle Data System
IPCCintergovernmental panel on climate change
kWh.ekilowatt hours of electricity
kWh.tkilowatt hours of thermal energy
LCAlife cycle assessment
LC-TECThe Thermo Ecological Cost Life Cycle Assessment
mcmaterials and construction
m-Simulticrystalline silicon PV technology
mudmanufacturing, usage, disposal
non-RESnon-renewable energy sources
ooperation
OPVorganic cell PV technology
ORCorganic Rankine cycle
PA + EEIOAprocess analysis + env extended IO analysis
PEprimary energy
PVphotovoltaics
QDquantum dot PV technology
ReCiPeimpact assessment method by RIVM and Radboud University, CML, and PRé Consultants
RESrenewable energy sources
RORrun-off-river
s-Siconventional single-crystal PV technology
WtEwaste to energy

Appendix A

Table
Table A1. Methodological aspects of the reviewed LCA studies.
Table A1. Methodological aspects of the reviewed LCA studies.
SourceEnergy SourcesConverted EnergySoftwareImpact Assessment MethodBoundariesImpact Categories
RESNon-RES/FossilElectricityHeatNon-Renewable EnergyGlobal WarmingEutrophicationAcidificationOzone Layer DepletionPhotochemical OxidationOther
123456789101112131415
[104]+ + n/aESA ReCiPedaa, com +
[105]+ partly n/an/an/a + +
[18]+ + n/an/ac-g+++++++
[13]+ + n/aBiogenic GHG only as input to LCAn/a +
[12]+ + n/an/a +
[19]+ + n/aLCI, LCIAc-g + + ++
[14]+ + SimaPro v8.3.0.0ReCiPen/a + +
[15]+ + SimaPro 8.5 (ecoin vent)ReCiPe 2016, Impact 2002+, Eco-points 97c-g + +
[106]+ + Umberto NXT; (ecoinvent v3.2)ReCiPe, IPCCc-g+++ +
[107]+ + n/an/an/a +
[17]+ + GHG Risk Assess ment ToolLCA ISO/TS 14067c-g +
[16]+ + SimaProCML2001n/a +++ +
[21]+ + SimaPro 8.0.3.14 (Ecoinvent 3.01)ReCiPe 2008c-g + +
[24]+ + n/aPA + EEIOAmc + +
[22]+ + n/an/ac-g +
[23]+++ n/an/an/a +
[25]+ + n/aILCDn/a + +
[26]+ + n/an/ac-g +
[108]+ + SimaproEco-indicator 99; + “original”n/a +
[20]+ + n/an/ac-g +
[109]+++ SimaProCML 2001o + ++
[110]+ ++SimaPro 8.2n/ac-g + ++ +
[111]+++ n/aCML-IA baseline V3.02/EU25c-g +
[112]+ +SimaPro 8ReCiPe, USEtox, and Ecological footprintc-g ++++++
[113]+ ++n/an/ac-u +
[35]+ + n/an/ac-g +
[36]+ + SimaPro 7.1IPCC 1996 GWP 100ac-g++
[43]+ + GaBiIPCC, USEtox, EUTREND, CML 2002c-g ++ +
[44]+ + n/aMRIO-LCAc-g++
[7]+ ++openLCA® 1.6.3Matrix-based LCA methodc-gt+
[51]++++Simapro 8TRACI 2.1 LCIA modelc-g ++++ +
[36]+ + SimaPro 7.1IPCC 1996 GWP 100ac-g++
[45]+ + GaBi 4.0Ecoinvent 1.01
CML 2001
CED		c-u +
[34]+ + GaBiEco-Indicator ’95c-u +
[37]+ + GaBi 4.3CML 2001c-g+++++++
[42]+ + SimaPro 7.1.8CML 2001mud ++++++
[46]+ + GaBiTRACI 2.1c-gt++ +
[32]+ + n/aTraci1.0
ReCiPe 2008		mud +++ +Etc
[40]+ + SimaProReCiPe 2008,
CED		c-gt +
[29]+ + openLCA v1.4.2ReCiPe v1.0.5,
CED		c-g ++++++
[47]+ + GaBi 6.0TRACI
ReCiPe		c-gt +++ +
[48]+ + SimaPorn/ac-gt+++ +
[49]+ + GaBi 6.0ILCDc-gt ++++++
[33]+ + SimaPro 8.5.2.0ReCiPec-g ++++ +
[50]+ + EMIS v5.7IPPC 2007 CED
ReCiP USEtox
EPB		c-gt + +
[60]+ + OpenLCAILCD 2011 Midpoint +
ReCiPe 2016		c-g ++++++
[67]+ SimaProCML 2002c-u + + +
[66] ++n/aCEDc-g +++ +
[68]+ ++SimaProCML 2011
CED		n/a +++ +
[62]+ ++n/aGREETc-u +
[71]+ ++GabiILCDc-g ++++++
[76]+ ++n/aIMPACT 2002+c-g++++
[77]+ ++n/aCEDc-g +++ +
[70]+ ++SimaProCML-IA
CED		c-gt ++++++
[72]+ ++n/aIPCC 2013gt-g +
[69]+ ++OpenLCAILCD 2011c-g +
[75]+ + n/aIMPACT 2002 +
LCI		c-g +++ +
[94]+ ++n/aCML-IA baseline V3.02/ EU25n/a++ +
[114] +++n/aMixc-g +++ ++
[102]+++ n/an/an/a+++++++
[92] ++ n/an/ac-gt +
[98]+ + OpenLCA 1.10.1ILCD 2018c-g+++++++
[89] ++ColdSimaPro 8.0IPCC 2013 GWP 20ac-gt +
[115]++++n/aLC-TECc-g++
[101]+ + SimaPro 8.1CML IA baseline V3.02; Re-CiPe Midpoint (E) V1.12c-g++++ ++
[91] ++H2n/aManualc-g++
[116] + +SimaPro 7.1Eco-Indicator 99c-g+++++ +
[93]+ ++EcoinventImpact 2002+c-g++ +
[97] +++n/an/ac-g + +
[69]+ ++OpenLCAILCD 2011c-g +
[96]++++n/aManualc-g +
[117]++++n/aILCDc-g++++ ++
[99]+ ++SimaPro V8.1.1.16CML IA baseline V3.03c-g+++++++
[118] +++n/aManualc-g +
[103]+++ OpenLCA, Ecoinvent v3.2Cumulative energy demand, CML, ReCiPec-g+++++++
[95]+ ++n/aCML-IA, CExCc-gt + +
[100]+ ++SimaPro 8ReCiPe (I) 2016c-gt+++++++
[54]+ +SimaPro 7.3:CED; Greenhouse Gas Protocol; Eco-indicator 99n/a + +
[119]+ +n/aEcoIndicator 99, Egalitarian Approachc-g + +
[52]+ +GaBin/ac-u+++++++
[53]+ +SimaPro 8.5ILCD, Impact 2002+, CED, Eco-points 97, Eco-indicator 99 and IPCCc-g ++++ +
[56]+ ++Simapron/ac-g +++ +
[110]+ +SimaPro 8.2n/ac-g+++++ +
[57]+ +n/aEco-indicator’95c-g+++++ +
[59]+ +Gabin/ac-g++++++
[55]+ +GEMISEcoIndicator 99c-g ++ + +
[58]+ ++n/aEcoIndicator 95c-gt + +
[79]+ + Gabi 4.0CML 2001n/a + ++++
[84]+ + SimaPro 8.05Eco-indicator 99o + + +
[83]+ + SimaPro 8.02Impact 2002+c-g++ +
[86]+ ++n/aReciPe v1.12c-g+ ++ +
[120]+ + SimaPro7.7.3Ecoindicator99 2.09c-g+++++ +
[81]+ + Gabi 4.0CML methodo +++++
[80]+ n/aClassic LCAmc + +
[85]+ + GABI 4.0CML 2001mc + +

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Energies 15 08488 g001 550
Figure 1. Overall classification of the reviewed sources presenting the results of LCA for energy conversion systems.
Figure 1. Overall classification of the reviewed sources presenting the results of LCA for energy conversion systems.
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Figure 2. Methodological aspects used in reviewed studies: (a) impact assessment methodologies; (b) boundaries; (c) LCA software; (d) impact categories.
Figure 2. Methodological aspects used in reviewed studies: (a) impact assessment methodologies; (b) boundaries; (c) LCA software; (d) impact categories.
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Figure 3. Comparison of GWP of different energy conversion technologies.
Figure 3. Comparison of GWP of different energy conversion technologies.
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Figure 4. GHG emissions (gCO2 eq/kWh) by the life cycle stage for various power-generating technologies (Source: [62]).
Figure 4. GHG emissions (gCO2 eq/kWh) by the life cycle stage for various power-generating technologies (Source: [62]).
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Table
Table 2. LCA impact of wind energy.
Table 2. LCA impact of wind energy.
SourceCountry, CommentsgCO2 eq/kWh.e
[20]onshore295.2–468
[11]review9.7–123.7
[12]review4.6–55.4
[21]Ethiopia33.6 (15.72–42.75)
[16]China25.4–31.8
[22]China, onshore16.4–28.2
[23]China31.36
[24]USA, onshore14.45
[25]Colombia, Higher wind speed12.93
[26]China, onshore3.9
Table
Table 3. LCA impact of the PV technologies.
Table 3. LCA impact of the PV technologies.
SourceTechnologyCountrygCO2 eq/kWh.eMJ/kWh.e
[35]Silicon solar modulesChina60–87
[36]Sc-Si and mc-Si with power conditioning system and BOSKorea25–41.80.35–0.56
[43]CIGS/Si, CZTS/Si, and AZTS/Si tandem solar modulesn/a25–29
[44]Concentrated solar power plantChina350.514
[45]Sc-Si PVBrazil14.54–18.68
[34]Poly-Si, a-Si, CdTe, CuInSe2 (CIS)Greece12.28–58.81
[37]mc-SiChina510.041–0.87
[46]Mono-Si, Poly-Si; Fin films: a:Si, CdTe, CIGS, Zn3P2, CZTSUnited States18–38
[32]Thin-film PV technologies: CIGS and CdTeUnited States20–22
[40]DSSC systemNorth/Central/South Europe30–125
[47]PerovskiteUSA99–147
[48]PerovskiteSouth Europe35–373.98–4.15
[49]PerovskiteEurope, USA187–5867
[50]OPVGermany, South Europe5.8–8.2
Table
Table 4. LCA impact of the solar thermal technologies.
Table 4. LCA impact of the solar thermal technologies.
SourceTechnologyCountrygCO2 eq/kWh.t
[56]PV and solar thermal (flat and vacuum collectors)Greece22.2–23.8
[59]Flat-plate solar collectors for DHWSpain92.4
[55]Flat-plate collectors for space heating and DHW Greece8–16
Table
Table 5. LCA impact of geothermal technologies.
Table 5. LCA impact of geothermal technologies.
SourceTechnologyCountrygCO2 eq/kWh.egCO2 eq/kWh.tMJ/kWh.e
[62]EGS, geothermal flash, hydrothermal binaryU.S.5.7–103
[60]Plant with AMIS® emissions treatment systemItaly470
[67]Four plants: 1 single flash and 3 steam with entrained water separated at the wellheadItaly380–1045
[68]Small combined geothermal heat and power plantItaly309–921
[66]Binary plantsGermany7–7507–650
[76]Hydrothermal binary plantGermany38.2 0.185
[77]Binary power plants: various geothermal ORC power plant concepts and working fluidsGermany13.2–130.1
[69]Enhanced geothermal systems (EGS)Germany29.5–54.92.7–9.2
[75]Enhanced geothermal systems (EGS)Germany, Switzerland16.9–49.8
[70]Double flash combined heat and power with and without CCS (carbon capture and storage)Iceland11.2–15.9
[72]Enhanced geothermal systems (EGS)Iceland1.6–17.4
[71]Double-flash combined heat and power plantIceland15–24
Table
Table 6. Assessed impact categories in the investigated studies [82].
Table 6. Assessed impact categories in the investigated studies [82].
LCIA-CategoryShare
Global warming98%
Eutrophication/acidification79%
Toxicity57%
Respiratory effects57%
Energy/resources52%
Ozone depletion33%
Land use12%
Table
Table 7. LCA impact of the cogeneration technologies.
Table 7. LCA impact of the cogeneration technologies.
SourceTechnologyCountryEnergy SourcegCO2 eq/kWh.egCO2 eq/kWh.tMJ/kWh.eMJ/kWh.t
[92]CH4-fueled combined liquid fuel and power co-production based on chemical looping combustion and CO2 storageChinaNatural gas52 ÷ 57 1
[97]Micro cogeneration systems with fuel cell, Stirling, and reciprocating engine configurationsGermany260 ÷ 520
[98]A bioenergy power plant integrated with a juice factory Residual biomass (citrus peel)ItalyResidual biomass−330 ÷ 1 −7.53 ÷ −2.06
[99]Biomass direct combustion steam turbine cogenerationTurkey40 ÷ 50100.670.16
[100]A biomass combustion cogeneration (heat and power) plant and a district heating plantItalyResidual and crop biomass 50 ÷ 330 1.01 ÷ 4.27
[101]Electricity generation from the combined use of energy cane locally cropped with imported pelletFranceCrop biomass220 ÷ 260 2.20 ÷ 2.55
[69]Geothermal heat and/or power plantsFranceGeothermal sources20 ÷ 503 ÷ 9
[94]Biogas turbine and internal combustion engine cogenerationItalyWaste 8.634.27
[93]Municipal solid bio-waste combustion/gasification with electricity recovery, anaerobic digestion with energy cogeneration from biogas/biomethaneItaly−30 ÷ 670 −0.07 ÷ 2.7
[102]Electricity import, supply of biomass, and CHPDenmarkCountry mix170 ÷ 550 2.1 ÷ 8.1
[103]Hungarian gridHungary500 12.2
[69]Electricity supply systemFranceGeothermal sources20 ÷ 503 ÷ 9
[94]CH4-fueled combined liquid fuel and power co-production based on chemical looping combustion and CO2 storageItalyWaste 8.634.27
[93]Micro cogeneration systems with fuel cell, Stirling, and reciprocating engine configurationsItaly−30 ÷ 670 −0.07 ÷ 2.7
[102]A bioenergy power plant integrated with a juice factory Residual biomass (citrus peel)DenmarkCountry mix170 ÷ 550 2.1 ÷ 8.1
[103]Biomass direct combustion steam turbine cogenerationHungary500 12.2
1 with carbon capture and utilization.
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Motuzienė, V.; Čiuprinskas, K.; Rogoža, A.; Lapinskienė, V. A Review of the Life Cycle Analysis Results for Different Energy Conversion Technologies. Energies 2022, 15, 8488. https://doi.org/10.3390/en15228488

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Motuzienė V, Čiuprinskas K, Rogoža A, Lapinskienė V. A Review of the Life Cycle Analysis Results for Different Energy Conversion Technologies. Energies. 2022; 15(22):8488. https://doi.org/10.3390/en15228488

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Motuzienė, Violeta, Kęstutis Čiuprinskas, Artur Rogoža, and Vilūnė Lapinskienė. 2022. "A Review of the Life Cycle Analysis Results for Different Energy Conversion Technologies" Energies 15, no. 22: 8488. https://doi.org/10.3390/en15228488

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