*2.1. Life Cycle Assessment Methodology*

The sustainability of the Spanish electricity system has been calculated using three methodologies based on a life cycle approach: attributional life cycle assessment (LCA) for the environmental dimension, levelized cost of electricity (LCOE) for the economic dimension and direct life cycle employment generation for the socio-economic dimension. Figure 1 illustrates the scope and system boundaries applied in each one of these methodologies, which varied primarily depending on the availability of inventory data. Thus, the boundaries considered for the environmental dimension included the whole life cycle of the system, as included in the ecoinvent datasets employed [18]. The boundaries for the economic dimension considered all direct costs except decommissioning and the end of life phase [19,20]. The boundaries for direct employment generation only considered fuel generation (where necessary), manufacture and power plant construction and operation [21].

**Figure 1.** Life cycle diagram, system boundaries and input/output consideration employed to evaluate the environmental (green), economic (red) and socio-economic (blue) sustainability of Spain's electricity system.

#### *2.2. Inventory Data of Installed Capacity, Electricity Generation and Technology Mix*

The sustainability assessment of the electricity system was based on the quantification of indicators describing its life cycle performance on the environmental, economic and socio-economic dimensions. This required the collection of official information regarding installed capacity, power generation and technology mix for the time periods considered in the investigation (1990–2015 for historic analysis, and 2030 and 2050 for future projections).

#### 2.2.1. Historic Electricity Data

The core of historic data for electricity generation, installed capacity and technology mix, covering the period 1990–2016, was extracted from La Energía en España, the official yearly report published by the Spanish Ministry for Energy, Tourism and Digital Agenda [22]. This information was validated and supplemented with additional data for 1960, 1970, 1980 and 1990 using updated statistics from Red Eléctrica Española (REE, the Spanish electricity system operator) and the International Energy Agency (IEA) [23,24]. Owing to the higher uncertainty associated with older generation technologies and their environmental, economic and socio-economic impacts, only the period 2000–2016 was evaluated for sustainability. Figure 2 illustrates this historic transformation in the Spanish electricity system in terms of electricity generation (GWh), generation per capita (MWh/capita) and technology mix for the period 1960–2016, and Figure 3 shows the same information for installed capacity for the period 2000–2016 (this parameter was not available for earlier years). The power generation technologies considered in this investigation are those listed in REE [23] and IEA [24] statistics as follows: Concentration Solar Power (CSP), Photovoltaic (PV), Wind, Hydropower (Hydro), Biomass, Nuclear, Oil, Natural gas and Coal. When different technological varieties are available for a given energy resource (e.g., natural gas in the form of combined cycles or CHP gas turbine, or wind in the form of off-shore and on-shore), the analysis is based on a weighted representation of the Spanish situation during the time period considered.

Generation values refer to gross power output, including electricity losses due to power transmission, distribution and other system inefficiencies. Due to its limited contribution, this investigation does not consider electricity imports and exports from Spain, which for the periods considered, accounted for between 2–3% of the power consumed nationally [22]. This investigation covers only power generation systems, overlooking other elements (e.g., storage, transformation, transmission, grid control) that may be essential in future electricity systems, particularly those with a strong dependence on renewables.

**Figure 2.** Historic data for electricity generation and technology mix in Spain (1960–2016).

**Figure 3.** Historic data for installed generation capacity in Spain (2000–2016).

As shown in Figure 2, the commercial electrification of Spain commenced in the 1950s and 1960s with the development of the first large-scale hydroelectric projects. This was followed by a rapid expansion in the electricity sector between 1960 (18,615 GWh) and 2000 (300,777 GW/h), which was supported by the incorporation of oil, coal and also nuclear power to the technology mix. This electrification period was driven by the economic growth that followed the political transition into democracy in 1975 and the opening of the national markets that was culminated with the incorporation of Spain into the European Union in 1986. During this period, Spain developed most of its hydroelectric and nuclear capacity, which has remained rather stable up until the present (19.5 GW and 7.8 GW respectively by 2016).

After the year 2000, two different phases may be discerned. The first stage, between 2000 and 2008, is characterized by a progressive growth in power generation (35% increase from 225,000 GWh to 305,000 GWh) and, more notably, in installed capacity (91% increase from 51,000 MW to 97,500 MW) which aimed to provide stability to the national network. During this period, the technology mix was reinforced with a strong contribution of natural gas (both in terms of capacity and generation) and an incipient incorporation of renewables. The second stage, between 2008 and 2016, describes a less expansive and modernized economy where the power demand was rather stable or slightly decreasing due to the increase of sharing tertiary sector activities and the offshoring of energy intensive industrial activities. In terms of technology mix, that period sees a progressive expansion in the installed capacity and generation of renewables, primarily wind power (35% increase from 31,800 GWh to 48,900 GWh) and to a lesser extent PV (68.6% increase from 2500 GWh to 8000 GWh), CSP and biomass. Nuclear, oil and hydropower generation remained stable during that period, while coal and natural gas fluctuated to adapt to national strategies aimed at the promotion of national fuels (coal) and international commitments expected to tackle global warming [25,26].

### 2.2.2. Future Projections

The electricity projections investigated in this paper were defined by the think tank Economics for Energy and published in a document titled Scenarios for the Energy Sector in Spain 2030–2050 [27]. This data was revised and validated in a subsequent document titled Analysis and Proposals for Decarbonisation, commissioned by the Spanish Government and produced by the Commission of Experts on Energy Transition [28] The scenarios proposed incorporated the national objectives set under the Spanish Renewable Energy Action Plan 2020 [29], the international commitments assimilated in the ensuing European 2030 Climate and Energy Framework and the European 2050 long-term strategy [9,10].

Table 1 describes the scenarios analysed for sustainability, which are cited throughout the paper as follows: decarbonisation (DC), current policies (CP), accelerated technical advance (AT) and stagnation (ST). Figures 4 and 5 provides a graphical account in terms of power generation, installed capacity and technology mix.


**Table 1.** Summary of projected electricity scenarios for Spain, as extracted from [27,28].

**Figure 4.** Projections of electricity generation and technology mix in Spain (2030–2050) compared to reference year 2015.

**Figure 5.** Projections of installed capacity and technology mix in Spain (2030–2050) compared to reference year 2015.

The decarbonisation (DC) scenario assumes the implementation of ambitious strategies to confront climate change and achieve a 40% reduction in GHG by 2030 and a 95% one by 2050, according to the objectives set by Member States of the European Union [9,10]. As shown in Figure 4, the DC scenario assumes a small increase in overall power consumption by 2030, as well as a complete elimination of coal and oil, a continuation of nuclear power and a slight reduction of natural gas from the electricity mix. This scenario also considers a significant increase in power demand by 2050, which is covered entirely by renewable sources, primarily PV and wind (hydropower remains stable due to limitations in the availability of additional hydroelectric resources in Spain).

The current policies (CP) scenario assumes a linear evolution of international geopolitics concerning the use of renewables and restraints in the emission of GHG. This scenario considers complete elimination of coal and oil from the electricity mix by 2030, assuming that this is largely replaced by natural gas, which absorbs 33% of the demand. By 2050, the CP scenario describes complete coverage of power demand from renewables, for an overall generation that is 15% lower than that in the DC scenario. The CP scenario would not accomplish the 95% GHG cuts proposed by the European Commission by 2050 [10].

The accelerated technology advance (AT) scenario presumes a rapid reduction in the cost of technologies related to renewable energies, energy storage and electricity consumption, including a fast transition into the electrification of transport. As shown in Figure 2, this would result in higher power demands than observed in the other scenarios and higher penetration of renewables as well as an achievement of the targets set by the European Commission for emission of greenhouse gases. The projections for this scenario consider elimination of coal and oil by 2030, which is compensated by a sustenance of nuclear power and a notable growth in natural gas and renewables that represent 54.5% of the mix. The predicted high power demands require a large penetration of PV and wind, and the continuation of nuclear energy in 2050.

The stagnation (ST) scenario considers a limited economic growth throughout this period and a limited development of new energy technologies leading to a time extension in fossil fuel dependence. In this scenario, overall demand remains fairly stable up until 2030, with a limited penetration of renewables and a strong presence of fossil fuels. The ST scenario assumes a prevalence of natural gas in the electricity mix by 2050 and a limited expansion of renewables in the long term.
