Home-made or imported: on the possibility for renewable electricity autarky on all scales in Europe

Tim Tröndle

Stefan Pfenninger

Johan Lilliestam

v1.0

The original version of this article has been published in Energy Strategy Reviews. article DOI

Abstract

Because solar and wind resources are available throughout Europe, a transition to an electricity system based on renewables could simultaneously be a transition to an autarkic one. We investigate to which extent electricity autarky on different levels is possible in Europe, from the continental, to the national, regional, and municipal levels, assuming that electricity autarky is only possible when the technical potential of renewable electricity exceeds local demand. We determine the technical potential of roof-mounted and open field photovoltaics, as well as on- and offshore wind turbines through an analysis of surface eligibility, considering land cover, settlements, elevation, and protected areas as determinants of eligibility for renewable electricity generation. In line with previous analyses we find that the technical-social potential of renewable electricity is greater than demand on the European and national levels. For subnational autarky, the situation is different: here, demand exceeds potential in several regions, an effect that is stronger the higher population density is. To reach electricity autarky below the national level, regions would need to use very large fractions or all of their non-built-up land for renewable electricity generation. Subnational autarky requires electricity generation to be in close proximity to demand and thus increases the pressure on non-built-up land especially in densely populated dense regions where pressure is already high. Our findings show that electricity autarky below the national level is often not possible in densely populated areas in Europe.

Keywords: localism; cooperation; land use; potential; administrative division; eligibility

1 Introduction

Renewable electricity, nuclear power, and carbon capture and storage are the main supply-side options to decarbonise the electricity system in Europe. Among these three, renewable electricity is the only option to not deplete the energy resource it depends on, but its resource has another unique characteristic: it is available everywhere, in different intensities. This makes it possible to generate electricity from local resources and decrease imports — and it could allow regions to become electricity autarkic, i.e. eliminating imports altogether. This would be in stark contrast to today’s situation, in which the European Union relies on primary energy imports for more than a third of its electricity [1], and in which Member States trade significant amounts of primary energy and electricity within the European Union. A transition to renewable electricity might hence not only allow the European Union, its Member States, or regions in Europe to decarbonise their electricity systems but also to become autarkic.

Proponents of local electricity generation bring up the benefits of increased electricity security, improvements to the local economy and its sustainable development, and community involvement. Local generation is seen as a reliable source of electricity, with supply and price determined within a political unit’s own borders. As such, autarky would decrease dependency on others and increase electricity security [2]. Positive effects on the local economy are expected, as value creation happens within the region, thus decreasing the outflow of capital. Installation of generators, and their maintenance and operation, are furthermore expected to create jobs locally [2,3]. The resulting increase in economic activity will improve the attractiveness of the regions and thereby counteract emigration from peripheral regions to the cities [2,3]. Lastly, [4,5] show that self-sufficiency is important to the local community, and [3,6] discuss case studies, in which the involvement of the local community in transition processes has improved the willingness to change and has reduced public opposition.

There are also arguments against local autarky, in particular concerning the cost and stability of small electricity systems. Larger renewable electricity systems often have lower costs, because of a more efficient use of resources and because the best renewable resources can be used by everybody – whereas in an autarkic setting, one must use what is available locally, regardless of the quality. Electricity demand may rise due to a less efficient use of resources, for example when electricity cannot be used or stored locally at the time it is generated [711]. Positive effects on the local economy through local value creation will be diminished, or eliminated, as both technology and know-how for installation and operation will often need to be imported from other regions or countries — the specialist knowledge is not readily available everywhere. Lastly, the land footprint for electricity generation is high and can lead to land use conflicts, for example with local food or feed production [12]. Thus, some authors have pointed out that the benefits of cooperation and autarky can be combined when full autarky is replaced by local generation embedded in a larger system [11,13].

Because there are advantages and disadvantages, there is no consensus in European policy as to which degree local generation should be promoted or integration should be strengthened. On the one side, there are many initiatives on the global (Go 100% Renewable Energy, Global 100%RE), European (100% RES communities, RURENER), and national levels (CLER, Community Energy Scotland, 100ee Regionen Netzwerk) that promote local generation as part of their agendas. Autarky is often discussed in an on-going debate about decentralisation of the electricity system [1416], but decentralisation (in terms of plant sizes, grid structures, and ownership) and autarky are distinct aspects of the electricity system: decentralised systems are not necessarily autarkic, and autarkic systems must not be decentralised. Existing projects are often in rural areas, while for cities and towns it is acknowledged that autarky will be more difficult and thus, they are advised to focus on improving energy efficiency instead [17]. While these initiatives promote local generation, they do as well promote cooperation, but only on the regional level: between municipalities [18,19], and in particular between cities and their encompassing rural municipalities [17].

On the other hand, the European Commission and the European Network of Transmission System Operators for Electricity (ENTSO-E) strive for stronger electricity cooperation in Europe. While they do not oppose local generation, they both emphasise the benefits, especially the cost-decreasing effect, of integration and electricity trading among European countries [20,21]. Thus, the Commission is striving for the establishment of a single internal energy market through the harmonisation of market mechanisms, support schemes, and network codes. Regarding autarky on the European level, the Commission seeks to lower import dependency, but it does not target full autarky in terms of European import dependence. Instead, it aims to increase diversity of foreign energy suppliers and energy sources. With this strategy, the EU strives to increase the use of local resources, but it is certainly not striving for autarky on the national or subnational levels.

Despite the on-going debate whether Europe should strive for autarky to reach potential benefits, we do not know whether electricity autarky is possible for Europe, its nations, or regions. The source of uncertainty stems from another characteristic of renewable electricity: its large land footprint compared to other sources of electricity [22]. We know that electricity autarky at the European level or below will require large areas devoted at least partially for electricity generation, but not whether sufficient areas are available in each country, region or municipality — or, if they are, how much of the land needs to be reserved for electricity generation.

The objective of this article is to identify whether and in which places electricity autarky is at all possible in Europe, and which shares of land must be devoted to electricity generation in the cases where electricity autarky is possible.

We do this by quantifying the potential of renewable electricity with high spatial resolution and comparing it to today’s electricity demand. We consider the four administrative levels that exist in nearly all European countries: the continental, national, regional (first-level administrative division), and municipal levels. All units on all four levels have their own local governments which could, in principle, decide to declare electricity autarky. We consider onshore and offshore wind power, and photovoltaics in our analysis as these technologies have the highest potential [22], while excluding biomass and hydropower (see below). The geographic scope of our study comprises the countries with member organisations in the ENTSO-E: EU-28, EFTA without Liechtenstein, and Western Balkans countries. We ignore Iceland which has no connection to the mainland and is already electricity autarkic.

2 Literature Review

Arguments for or against electricity autarky in Europe are often supported through case studies for single municipalities [2,3,6,12] but research is needed on the European scale to understand on which level autarky is possible and to understand the land trade-offs that have to be made. Autarky based on renewable electricity is only possible if enough electricity can be generated locally, i.e. the annual potential for renewable electricity generation is at least as high as the annual demand. A sufficient potential is hence a necessary condition for autarky and as such a crucial aspect to consider when targeting autarky in any region. We acknowledge that, if the potential in an area is sufficient, autarky may still be impossible, impractical, or infeasible, for example when taking fluctuations of renewables into account. Here, we only discuss the necessary condition of sufficient potentials, but not whether autarky is actually feasible.

In the literature, different kinds of potentials have been assessed, for example: theoretical, geographical, technical, and economic. To analyse the possibility of autarky, the most important kind is the technical potential. It defines the amount of renewable energy that can be transformed to electricity given technological restrictions. There is however no consensus for this definition: in [23] for example, the technical potential does not include electricity that could be generated on environmentally protected areas, whereas in [24] it does. For roof-mounted PV, north-facing roof areas are sometimes included in the calculation of the technical potential [25] and sometimes not [26]. The different definitions, but also different assumptions, can lead to diverging results.

We are not aware of studies assessing technical potentials in the context of electricity autarky on the European scale, but there are studies that assess technical potentials of single technologies in Europe. For onshore wind, results differ widely, from 4,400 TWh/a [23] to 20,000 TWh/a [27] or even 45,000 TWh/a [24]. The relatively low estimate of the first study can be explained by three exclusion factors not present in the latter two studies: it excludes areas with average wind speeds below 4 m/s at 10 m hub height as well as environmentally protected areas, and it limits the use of agricultural land and forests. Combined, these constraints exclude around 90% of Europe’s land. Despite the differences in definitions, the three studies agree that onshore wind power could supply all of Europe’s current electricity demand of around 3,000 TWh/a, assuming the technical potential could be fully exploited.

Two studies assess the technical potential of roof-mounted PV at the continental level, finding potentials of 840 TWh/a [26] and 1,500 TWh/a [28]. The difference in results can be explained by different geographical scopes, by the fact that [26] ignores north-facing areas, and by different methods: while [26] uses a statistical approach to quantify available roof areas, [28] uses high resolution satellite images for a few cities in Europe to derive roof area estimates, and then extrapolates these results using population density as a proxy. Both studies show that roof-mounted PV can contribute significantly to supplying Europe’s electricity needs, albeit at a much lower magnitude than onshore wind. Combined with onshore wind, both technologies are likely able to fulfil Europe’s electricity demand entirely.

Some of the studies with European scope disaggregate their results on the national level, thus permitting an analysis of renewable electricity potential in light of national autarky [24,26,27]. Other studies have assessed the potential for single countries, e.g. wind in Germany [29], Spain [30], Sweden [31], and Austria [32]. All of those roughly agree with the results from the analyses on the continental level and reveal potentials which are close to or exceeding today’s electricity demand. Again others have assessed national potentials of roof-mounted PV, e.g. 1,262 TWh/a [33] and 148 TWh/a (residential buildings only) [34] for Germany or 18 TWh/a [35] and 53 TWh/a [25] for Switzerland. There are no such potential studies for all European countries and thus national potentials across all of Europe are available only from [24,26,27].

On the regional and municipal levels, there are some studies which assess the potentials across entire countries [29,35], but most studies focus on single regions or municipalities, e.g. [3640]. No study has been performed that assesses renewable electricity potentials on the regional or municipal levels across all of Europe within a single consistent analysis framework.

3 Methods and data

We assess the possibility of electricity autarky for administrative units in Europe on four levels: continental, national, regional, and municipal. For each administrative unit on each administrative level we quantify renewable potentials and current electricity demand. We then reject autarky based on renewable electricity for those units for which annual demand exceeds annual potential. We list all data sources used in this approach in Table S1 in the supplementary material.

3.1 Definition of administrative levels

To identify administrative units including their geographic shape on all levels we use NUTS (Nomenclature of Territorial Units for Statistics) 2013 data [41] and the Global Administrative Areas Database (GADM) [42]. The scope of our analysis is EU-28 excluding Malta (for which no data was available), plus Switzerland, Norway, and the Western Balkans countries Albania, Bosnia and Herzegovina, Macedonia, Montenegro, and Serbia. Together, all 34 countries form the continental level; in isolation they form the national level (see Table 1). Country shapes for EU-28 countries, Switzerland and Norway are defined by NUTS 2013, and for the Western Balkans countries by GADM.

The regional level is defined by the first-level administrative divisions, e.g. cantons in Switzerland, régions in France, or oblasti in Bulgaria, of which GADM identifies 502 in the study area. Macedonia and Montenegro only have one subnational administrative level — the municipal level — which in our analysis is below the regional level. For Macedonia we use a statistical division from NUTS3 larger than the municipal level, and for Montenegro we use the municipal level from GADM as no alternative is available. Lastly, there are 122635 communes which form the municipal level. These communes are defined for most countries by the Local Administrative Unit 2 (LAU2) layer of NUTS 2013. For Albania, Bosnia and Herzegovina, Macedonia, and Montenegro, we take their definitions from GADM. Lastly, we estimate the size of maritime areas over which administrative units have sovereignty by allocating Exclusive Economic Zones (EEZ) to units on all levels. Within a country, we divide the EEZ and allocate parts to all subnational units which share a coast with the EEZ. The share is proportional to the length of the shared coast. We use EEZ shape data from [43].

Table 1: Administrative levels considered in this study.

Level

Number units

Source of shape data

Continental

1

GADM [42], NUTS [41]

National

34

GADM [42], NUTS [41]

Regional

502

GADM [42], NUTS [41]

Municipal

122635

GADM [42], LAU [41]

3.2 Renewable electricity potential

To quantify the renewable electricity potential in each administrative unit, we first estimate the surface areas eligible for generation of renewable electricity and then the magnitude of electricity that can on average be generated annually on the eligible surfaces by on- and offshore wind turbines and open field and roof-mounted photovoltaics. We assess two types of potentials of renewable electricity: the technical potential and a socially constrained potential. The only difference between these potentials is the classification of surface eligibility, i.e. the surface areas available for renewable electricity generation. We furthermore assess land requirements when assuming electricity autarky, i.e. the amount of non-built-up land that is needed for electricity generation to become autarkic.

In our study we do not consider two types of renewable electricity that could contribute to supplying Europe’s electricity demand: hydropower and biomass. We ignore hydropower, because its potential is largely exhausted in Europe [44] and no major new contributions can be expected in the future. We ignore biomass for two reasons: first, its power density in Europe (<0.65 MW/km2 [45]) is lower than the one from wind or solar power and thus wind turbines and open field photovoltaics are always superior in terms of electricity yield per area. Second, we also do not consider combining wind power and biomass production despite the high electricity yield per area because of land use conflicts with food and feed production that biomass production causes.

3.2.1 Open field surface eligibility

To decide which fractions of the land and water surfaces of an administrative unit can be used for open field PV, or on- and offshore wind farms, we divide Europe into a 10 arcsecond grid, whose cell size varies with the latitude but never exceeds 0.09 km2. For each cell we obtain the current land cover and use from the GlobCover 2009 dataset [46], the average slope of the terrain from SRTM and GMTED [47,48] or its maximum water depths from ETOPO1 [49], and whether it belongs to an area which is environmentally protected from the World Database on Protected Areas [50]. We additionally use the European Settlement Map (ESM) with 6.25 m2 resolution [51] to classify an entire 10 arcsecond cell as built-up area if more than 1% of its land area are buildings or urban parks. We use land cover and use, slope, protected areas, and settlements as decision criteria because these constraints have been found to be the most relevant for land eligibility studies in Europe [52]. For each potential type there is a set of rules by which we define if a cell is eligible for renewable electricity generation and if it is, which technology type it is used for. We assume that a cell is always used for a single technology only, based on the rules described below.

3.2.2 Roofs for PV

The potential for roof-mounted PV not only depends on the amount of roof area available, but also on the orientation and the tilt of these roofs. We analytically derive rooftop area in each administrative unit. We then use a dataset of Swiss roofs, taking it as representative for Europe as a whole, to correct the area estimation and to statistically amend it with tilt and orientation.

We use the European Settlement Map [51] to identify the amount of rooftop area in each administrative unit. The map is based on satellite images of 2.5 m resolution and employs auxiliary data e.g. on population or national data on infrastructure to automatically classify each cell as building, street, urban green, etc. For each 10 arcsecond cell we sum up the space that is classified as buildings. We consider only those cells that we initially classified as built-up areas before, and which are hence not used for other renewable generation.

We then amend this first estimation with data from sonnendach.ch for Switzerland [53]. We use this dataset in two ways. First, we improve the area estimation taken from the European Settlement Map. Sonnendach.ch data is based on high-resolution 3D models of all buildings in Switzerland and thus allow for estimations of roof areas with high accuracy. For the roofs included in the sonnendach.ch dataset, the European Settlement Map identifies 768 km2 building footprints, where sonnendach.ch finds 630 km2 roof area. Sonnendach.ch also apply expert estimation of unavailable parts of the roof, e.g. those covered with windows or chimneys [54], which reduces the theoretically available rooftop areas from 630 km2 to 432 km2. Thus, for Switzerland, the realistic potential may be only 56% of the building footprints from ESM. We assume this factor is representative for all Europe and apply the factor of 0.56 to all areas identified by the European Settlement Map.

The second use we make of the Swiss data is to identify the tilt and orientation of the roof areas. For that, we cluster all roofs in 17 categories: flat roofs, and roofs with south-, west-, north-, and east-wards orientation, each with four groups of tilt. We then quantify the relative area share of each category (see Table S2 in the supplementary material). Again, we assume the distribution of these attributes of the Swiss housing stock is representative for Europe and apply it to all administrative units.

3.2.3 Renewable electricity yield

Based on the previous steps we can quantify the surface area eligible for renewable electricity generation in each grid cell. To estimate the annual generation for wind power, we first assume a capacity density of 8 MW/km2 (15 MW/km2) based on a rated capacity of 2 MW/unit (10 MW/unit) for onshore (offshore) wind [24] which allows us to derive the installable capacity for each grid cell. We then simulate renewable electricity yield of the years 2000–2016 on a 50km2 grid over Europe from Renewables.ninja [55] to determine the average annual electricity yield from installable capacity on each 10 arcsecond grid cell. We assume onshore (offshore) wind turbines are available 97% (90%) of the time [24].

For open field PV and flat roof-mounted PV, we assume a capacity density of 80 MWp/km2 based on a module efficiency of 16% and space demand of two times the module area as an average for all Europe. Furthermore, we assume modules are installed southward facing and with tilt optimisation as defined by [56]. For PV of tilted roofs, we assume a capacity density of 160 MWp/km2 based on a module efficiency of 16%. Using the statistical model from Table S2 we define 16 different deployment situations. We then use Renewables.ninja [55,57] to simulate the renewable electricity yield of the years 2000–2016 of each deployment situation on the 50km2 grid. We assume a performance ratio of 90%.

3.2.4 Technical potential

We first assess the technical potential which is only restricted by technological constraints. To quantify it, we use the following rules: We allow wind farms to be built on farmland, forests, open vegetation and bare land with slope below 20° (slope constraint taken from [27]). An example of exclusion layers for Romania is shown in Figure 1 (see Supplementary Material for exclusion layers of all 34 countries in this study). We furthermore allow open field PV to be built on farmland, vegetation and bare land with slope below 10° (slope constraint taken from [58]). In grid cells where both onshore wind farms and open field PV can be built, we choose the option with the higher electricity yield. Lastly, we allow offshore wind farms to be built in water depths of less than 50m. Grid cells identified as built-up area cannot be used for open field PV or wind farms, only for roof-mounted PV.