Assessment of Solar Parks as Biodiversity Promoters in Rural Areas of the EU

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Assessment of Solar Parks as Biodiversity

Promoters in Rural Areas of the EU

- A Critical Review -

Marlon Sippel (12642355)

Supervised by Dr. Gerard Oostermeijer

30 September 2020

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Abstract

With global energy demand growing by the year, the biodiversity crisis at hand and global warming being one of the most pressing issues of the time, the importance of renewable energies increases by the day. Negative ecological impacts of renewable energies are often forgotten or considered to be outweighed by the benefits of “clean” energy. In the case of solar energy some research and grey literature have taken this a step further and claimed that solar parks can even promote biodiversity.

In this critical review I investigated the validity of this claim regarding Europe. I found that photovoltaic technology will be the most prevalent solar technology in Europe and that in comparison to hydro and wind energy, the negative ecological impact of photovoltaic parks is low.

From more detailed research on the ecological impacts of photovoltaic parks, I conclude that such parks can indeed even promote biodiversity, but only if management meets the following criteria: (1) Choice of construction site must be in an area that was previously humanly impacted and shows low biodiversity compared to natural ecosystems in the relative region. (2) Parks must be monitored regularly, and invasive plant species must be controlled. (3) Management intensity must be as low as possible and cutting should only be performed to maintain biodiversity and provide safety and accessibility. (4) Seeds used in seed mixtures must be regionally sourced (5) Horizontally polarised light reflection of the panels must be reduced. (6) Construction of fences must be avoided. If fencing is mandatory, gaps for mammals should be implemented and adversely affected migration monitored. (7) The inherent disaster risk must be kept minimal through regular safety checks.

A European guideline must be implemented to improve management plans, as photovoltaic parks only promote biodiversity if all seven points are met. More research on the impacts of photovoltaic parks on the ecosystem is necessary, because current knowledge is marginal, and it seems like potential negative impacts may remain unknown to this point. Finally, I recommend investigating the potential for construction of parks on rooftops, to avoid impacting ecosystems in the first place.

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1. Introduction

As part of her agenda, president of the European Union -Von der Leyen- declared a "European Green Deal” to be one of the main aims of the European commission from 2019 to 2024. Two of the central points of this “Green Deal” are to take measures that will make Europe the first climate neutral continent and to restore biodiversity in the EU (Von der Leyen, 2019). The deal states that in order to achieve this goal, the energy sector is supposed to be decarbonised.

Beside nuclear energy, renewable sources, such as wind and solar energy represent the most carbon neutral energy technologies (Sims et al., 2003). Further, fossil fuels are diminishing worldwide and if the current global increase of energy demand will develop further as it does, it is likely that all fossil fuels are diminished before 2120. With the most important of those resources – oil – to be diminished before 2060, even according to low demand calculations (Shafiee and Topal, 2009). These factors present proof that renewable energies will grow in importance throughout the 21st_{century and there is no doubt that wind, water and solar energy will be a}

growing industry throughout this century. However, implementation of renewable energies, can cause a negative influence on biodiversity and ecosystems. From the European

standpoint, negative impacts of the energy transition to biodiversity must be avoided to decelerate further species decline.

To tackle negative trends in biodiversity, many ideas have spread in society as well as in research that suggest the use of solar-parks in rural areas to promote biodiversity such as plant richness as well as pollinator diversity and density (Biesmeijer and Wit, 2020; Hernandez et al., 2014; Semeraro et al., 2018).

Based on this idea, I ask the question: “Under which conditions can solar parks in Europe promote biodiversity?” I investigate the energy potential

of solar technologies as energy source in Europe in respect to solar irradiation and technological developments, to assess if the general performance of solar energy in the EU can compete with other renewable energy technologies. I explore ecological impacts of solar parks in comparison to other renewable energies and present current research on different management strategies that are applied to promote biodiversity in solar parks. Finally, I present alternative approaches to improve solar-park management and assess the potential of urban areas for the creation of solar-parks as opposed to rural areas.

Biodiversity

The term biodiversity (from “biological diversity”) refers to the variety of life in the system of referral including all levels, ranging from genes

to ecosystems and is

commonly used to assess the general species richness of an environment.

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2. Methods

All literature I used in this review was collected from March to August 2020 and can be found using Google scholar or the Google search engine. In order to include the most relevant and state of the art research, I selected literature by number of citations and year of publication. Access to papers was provided through the University of Amsterdam network, using Pulse Secure (version 9.0.4), which means that only a fraction of papers I reviewed will be openly available. For storage of individual papers, I used Zotero (version 5.0.89). All references are in the Elsevier – Harvard (with titles) citation style. Green boxes contain definitions of terms, which I wrote myself and serve merely the purpose of explaining the word as used within the context of this review rather than providing a universal definition. Some papers I explained in more detail. Such papers are outlined as case studies and contain the title of the paper as well as the author at the start.

3. Results

3.1 Solar energies in Europe

Analysis of solar parks in the context of biodiversity in Europe is only sensible if the energetic potential of solar energy is high enough to compete with other sources of energy. To compare technologies using solar energy to other renewable energy sources, a more specific break down of the term ’solar energy’ is required. Kabir

et al. (2018) differentiate solar energies into active

and passive technologies, with passive energies being the “(…) accumulation of solar energy without transforming thermal or light energy into any other form (…)”. For the purpose of this review I will only consider active solar technologies, because large-scale solar parks always involve

transformation of energy into electricity. The active technologies cover photovoltaic (PV), solar thermal (ST) and concentrated solar power (CSP); (Kabir et al., 2018). CSP technology is regarded as a very promising technology especially in regions with strong solar irradiation, because it reaches the highest maximal production. In Europe however, PV technology has a clear long-term advantage over CSP, due to the relatively low average irradiation in Europe (Köberle et al., 2015); (Figure 1). Although Spain is one of the biggest CSP-energy producers, the total CSP-CSP-energy production within the EU reaches just over two GW per year, as compared to 115 GW of PV-energy production (REN21, 2019). This shows that CSP, while being a promising technology in the global context, is clearly outcompeted by PV-technologies within Europe. For ST technologies a comparable trend can be observed. ST-energy requires high irradiative force and only breaks even with PV-energy, once the average irradiative force reaches 1600 kWh/m² (Quaschning, 2004). Because only few regions along the Mediterranean Sea surpass this threshold (“Solar resource maps of Europe,” 2019); (Figure 1) and to enable better comparability, I will focus on PV technologies in this review.

It is important to notice that I only compared theoretical potentials in the EU and did not take regional policies – potentially impacting the solar technology market – into consideration. Instead, this assessment applied more generally to the EU, but can of course be placed in a more specific context as well.

Figure 1: Global horizontal irradiation (GHI) in Europe for the years 1994 to 2016 in kWh/m². (“Solar resource maps of Europe,” 2019).

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Within the EU, the installation of PV-parks is increasing due to rising emission costs and a decline in PV-system prices (REN21, 2019). In 2018, PV was the world’s fastest-growing energy technology worldwide (REN21, 2019), driven partly by PV installations on private homes and industrial buildings, and the creation of big parks in rural areas. This trend is suspected to be caused by relatively low maintenance costs of larger PV-parks (Bizzarri et al., 2015) and accelerated by high subsidies that came with the renewable energies directive of the EU from 2009 (Howes, 2010).

It seems clear that PV-parks will become a regular occurrence within the European landscape, especially in the context of the EU’s aim to turn Europe into the first climate neutral continent in the world (Von der Leyen, 2019). With that established, I will assess the impacts the strong landscape change that is involved will have on biodiversity. Especially in comparison to other renewable energies, it is necessary to investigate the ecological impacts of PV-parks to make a meaningful statement about a park’s overall sustainability.

3.2 Ecological impacts of different renewable energies

Assessing ecological impacts of PV-parks makes a comparison to other renewable energies necessary. Based on data from Eurostat (2018), solar energy is the third most common electricity source of renewable energies, covering 12.2% of the EU-27 market. The two more common renewable energy sources are hydro (36.6%) and wind (27.5%) energy, while solid biofuels (8%) come in on fourth (“SHARES (Renewables) - Eurostat,” 2018). As other renewable energy sources each make up less than 5%, I only compare the above three to PV energies. Major drawbacks reported in connection to wind energy are that they represent a threat to migratory birds. Around on-shore wind-turbines, significantly higher mortality rates in birds have been documented in comparison to equivalently examined powerlines in the area (Barrios and Rodriguez, 2004). Dams to produce hydro-energy often cause habitat change to an extent that biodiversity decreases or shifts (Power et al., 1996) and present a major threat to migratory fish (Larinier, 2001). Although these findings only apply to parts of existing wind and hydro technologies, negative effects of solar energy seem smaller in comparison. While research on avian mortality caused by solar power plants found an increase of bird mortality (McCrary et al., 1986), this research investigated production of solar energy specifically using CSP technology. As explained previously, for the European context only PV-technologies are highly relevant, which are not reported to cause increases in avian mortality. Another review comparing hydro, wind and solar energies from several relative sources (CSP, SP and PV for solar, on- and off-shore wind turbines for wind and dams for water-energy) concluded that wind energy technologies are the least environment and biodiversity impacting energy source, with solar on second and finally hydro energy with clearly the strongest impacts on biodiversity. They argue that solar instalments create a cooling effect on the environment, which may negatively affect biodiversity and plant mass in the area. Nevertheless, they also note that in comparison to wind and hydro-energy, impacts of solar-energy on biodiversity are understudied (Gibson et al., 2017).

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An approach that enables direct comparison of ecological impacts of different energy sources was taken by Fthenakis and Kim (2009). They calculated the relative land transformation area in square meters per GWh of produced energy for different energy sources (Figure 2).

Their results show that of all renewable energy sources PV-energy has the highest land use efficiency. Renewable energy extracted from biomass requires the highest relative land-transformation because of the low energy-production efficiency (Fthenakis and Kim, 2009). This is an important factor to consider, because in various case studies land transformation has shown to negatively affect biodiversity in the area and pose an ecological gap for invasive exotic species to establish themselves (Broadbent et al., 2012; Maitima et al., 2009; Polasky et al., 2011). Besides that, biofuel increases

demand for arable land, which can lead to conversion of natural ecosystems into croplands (Fargione et al., 2010).

To assess environmental impacts and energy performance, Leccisi et al (2016) performed a life cycle analysis of PV technologies. By assessing energy input of all product life stages, from the extraction of raw material to the recycling and disposal of the panels, they showed that energy and environmental performance have improved in comparison to comparable assessments from 2005. This means that panels produce higher amounts of electricity per irradiation and that production demands decreasing amounts of energy input. Further, they showed that net energy return of

modern PV-panels is much higher than often publicly referred to. The life cycle assessment found that depending on location and PV technology, net energy return becomes positive within six months to three years after putting a PV-panel into use (Leccisi et al., 2016). With a lifespan of around 30 years per panel (Fthenakis et al., 2011), even the lowest net return estimation promises tenfold pay-out over time.

These results show that in comparison to other renewable energies PV-technologies have relatively low negative impacts on biodiversity. With that established, I will present the current state of research on whether PV-parks can promote biodiversity in the following chapter.

3.3 Use of PV-parks to promote biodiversity

To this point, I found that harm of PV-parks to the environment seems minor as compared to other energy sources. Nevertheless, if PV-parks are created in a landscape that was previously not humanly impacted, biodiversity will likely decrease strongly through the construction of such parks. In order to achieve neutral or maybe even positive impacts, it is thus of primary importance to choose areas where construction of a PV-park will not cause a significant biodiversity decrease.

Figure 2: Life-cycle land transformation for fuel cycles based on 30-year timeframe in m²/GWh (Fthenakis and Kim, 2009, fig. 3).

Invasive exotic species

An exotic species is a species, which is not native to a defined environment. In some cases, they can spread rapidly, harming local ecosystems and often have negative impacts on human wellbeing. In such cases they are also referred to as invasive species.

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Case study 1 represents an approach to enable an initial site suitability assessment via remote sensing, to more successfully choose sites to construct PV-parks on.

Case study 1: “Siting solar energy development to minimize biological impacts” (Stoms et al., 2013)

In order to find areas that are suited for the construction of a PV-park, Stoms et al. (2013) created a map, using geographic information systems (GIS). To answer the question; “What areas in the region could be considered most compatible with conservation of biological resources?”, they made a compatibility index to analyse suitability of different locations in their study area in south-eastern California. The index consisted of the two main components on-site degradation and off-site impact, which were combined in a 90-meter resolution raster file. In the first step, the on-site degradation was determined. To do so, the authors modelled current site degradation based on impacted vegetation and the fragmentation of the habitat. Impacted vegetation was derived from three possible impacts, urbanisation, farming or fires. Depending on how permanent the impact was, scores from 0 (low impact) to 100 (strong impact) were applied. Fragmentation was derived from a set of infrastructure maps and weighted depending on their impacts, ranging from 1 (e.g. pedestrian trail) to 9 (e.g. freeway). Both input scores combined form the score of on-site degradation. The second factor – off-site impacts – was created with a cost surface. Cost surface here means that the potential damage that can be done to the environment is added to the model. From totally degraded areas, as already analysed in on-site degradation zero points were

subtracted, as the land has no ecological value anyway. From other areas, in which creation of infrastructure is forbidden, 10.000 points were subtracted. Also, 1.000 points were subtracted from areas with high ecological value, but where building generally is permitted. Additionally, from the distance of each field to highways, substations and existing transmission infrastructure, a cost distance was determined, increasing the cost the farther infrastructure was away from any given location. From this index a suitability map was created, indicating that the

most suitable areas for the construction of PV-parks are in the south of the analysed area (Figure 3); (Stoms et al., 2013).

This first case study shows an interesting approach to analyse the suitability of location for the creation of PV-parks, implementing both ecological and economic interests in one tool. Unfortunately, the work described here was adjusted to arid and semi-arid landscapes and is would thus need to be adjusted to match the European context. Nevertheless, it presents an example of how the selection of locations could be improved by setting a spatial frame in which development is supposedly the least harmful. If, based on approaches like presented in case study 1 and on-site analysis, only the most suitable areas are chosen, this still does not mean that biodiversity is being promoted, but only that negative impacts are minimised. The following case studies, however, investigated PV-parks and their potential to promote biodiversity.

Figure 3: Map of south-eastern California, showing the site suitability that resulted from the compatibility index (Stoms et al., 2013, fig. 7).

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PV-parks are often constructed in a similar fashion; the photovoltaic panels are placed as several long rows, facing either towards the south or – in the case of more advanced technology – rotating to track the sun. They usually are set on poles, compacting less than 5% of the ground surface, and overshadow on average 25 – 40% of the ground (Parker, 2014). With this, it becomes obvious that PV-parks have a lot of potential for growth of biomass, however, agricultural land-use is not possible anymore, because dense placement of panels and heavy machinery of modern agricultural practices are practically not combinable. This led to the idea to manage vegetation in PV-parks to promote biodiversity. Research investigating effects of PV-parks on biodiversity is still scarce, but in recent years increasing numbers of research projects investigating this potential have been published.

Case study 2: “The effects of solar farms on local biodiversity: A comparative study” (Montag et al., 2016)

The potentially most relevant study on the topic, done by Montag et al. (2016), covers 11 PV-parks throughout the South of England. The researchers gathered data on plant diversity and abundance for the individual fields and compared those to control plots, which were located 6 – 280 meters away from the studied PV-park and used for non-organic agricultural practices. For all 11 plots it was determined how strongly the management focus towards wildlife promotion was and among other factors, the management plan for the PV-parks as well as the date of their creation was documented. Biodiversity data they

collected, spanned the categories botany, invertebrates, birds and bats. Here I will only present the results for botany and invertebrates, as the best data was available for these groups. Independent of management, plant diversity on solar fields was significantly higher than on the control plots (Figure 4). Across all observed PV-parks, the diversity of plants was higher than in the control plots and in 9 of the 11 parks, plant richness was significantly higher than in their relative control plots. Comparison of plant distribution inside the PV-parks did not find notable differences in plant distribution relative to panel location. In contrast to plant diversity, species richness was not significantly higher in the PV-parks for invertebrates. The abundance of invertebrates in PV-parks on the other hand was found to be significantly

higher, especially on fields with a management approach focused strongly on promoting wildlife. Finally, the authors applied a ranking relative to species diversity and abundance of all analysed categories, to compare the eleven plots. They found that the three PV-fields that they had scored as highly focused on wildlife promotion, showed the highest diversity across all analysed species (Montag et al., 2016).

The results of the study by Montag et al. (2016) provide evidence that management aimed at promoting biodiversity can indeed be successful in terms of species richness and animal abundance. Not only did their results show higher biodiversity in PV-parks than in the surrounding areas, but they also found higher densities of pollinators in parks that were managed with the aim to promote biodiversity. Interestingly, although case study 2 did not go into detail about the different management strategies, plans with a strong focus on biodiversity promotion show to have success in doing so. Nevertheless, this research lacks differentiation between management types in more detail. Hence, the practical value of the results is limited to a general trend in relation to management approach. Other studies analysing species occurrence and abundance in relation to PV-parks has been done by Peschel et al. (2019), who found comparable results for PV-parks in Germany, as case study 2 (Peschel et al., 2019). Their publication however does not clearly display the methodology applied and will thus not be elaborated upon in this review.

0 50 100 150 200 solar control To tal n um be r o f pl an t s pe ci es

Figure 4: Overall comparison of solar and control plot botanical diversity (Montag et al., 2016, fig. 5.1).

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Instead, to assess different management strategies, I looked for more detailed research in relation to the individual management approach. An interesting study that was conducted in the Netherlands, used one big PV-park, to assess different management and research strategies within the park. In comparison to previous research, this enables assessment of the effects different management methods have on biodiversity.

Case study 3: “The effects of solar parks on plants and pollinators: the case of Shell Moerdijk” (Biesmeijer and Wit, 2020)

Biesmeijer and Wit (2020) divided one big PV-park located in Moerdijk, Netherlands into seven clusters with six plots. Each plot resembled a different seed mixture to be analysed. Decisions on seed mixtures were based on five requirements:

1. They should improve pollinator biodiversity (e.g. bees and hoverflies) whilst complying with the functional requirements and maintenance of the park.

2. Not grow taller than 50-60 cm, to reduce shading of panels and enable air flow underneath them. 3. Plants should not produce sticky pollen that could cover the panels.

4. Diverse seed mixtures should be created, containing species that either thrive in sun or shade. 5. Mixtures should aim at maximum biodiversity with the lowest possible costs and labour input.

Based on these requirements, they created five distinct seed mixtures and sowed them in assigned plots in six areas of the park. Additionally, in one plot per area, no seed mixture was sown to serve as control group. Each of the 42 resulting plots – 20 * 20 meters (one 20 * 10 meters) – were assessed by sampling insect abundance and results were compared in relation to seed mixture. All insects were collected in pan traps located in the centre of each plot. Pan traps differed only in colour, being either blue, white or yellow. Each of the plots contained 18 pan traps, containing two white, two blue and two yellow traps in sunny, half-sunny and shady locations of the plot. Sampled individuals were identified in a laboratory in Naturalis, Leiden, the Netherlands. No significant differences in insect abundance or diversity between the seed mixtures were observed. This could be caused by the fact that sown seeds made up only a small proportion of the vegetation on each plot. Overall analysis found that diversity of hoverfly and bee species was higher in the PV-park than normally in agricultural and industrial areas, however, it was not explicitly mentioned what the area of referral was. Notably, five red list bee species and a total of 103 plant species were identified, including 22 of the 36 plant species sown as part of the seed mixtures. Of all plants the most common one was Senecio inaequidens, making up 9,3% of the vegetation over all plots. Yellow pan traps showed the highest quantity in individuals collected, followed by blue and white. In general traps located in sunny spots collected higher numbers than those placed in shaded areas. Although soil was categorized into five groups, no results in relation to the different soil categories were provided. The authors suggest keeping maintenance of PV-parks as low as possible and keep wide enough gaps in between PV-panels to provide enough sun for vegetation to establish itself. Finally, they recommend ongoing research, to increase data and enable analysis of long-term impacts of PV-parks (Biesmeijer and Wit, 2020).

Case study 3 provides an analysis of different seed mixtures and although only a limited sample size was analysed, it indicates that the choice of seed mixture may not be as important as the mere presence and diversity of flowering plants in general.

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One thing case study 3 found but failed to point out was that in Senecio inaequidens the most common plant in the PV-park was an invasive species introduced to Europe from South Africa throughout the 20th_century

(Lachmuth et al., 2010). Although this paper provides additional proof that management towards biodiversity can increase species richness in an area, it also shows that PV-parks as an artificial environment pose an entrance way for invasive species to establish themselves and spread.

Besides invasive species, a problem causing species decline in Europe is habitat fragmentation. Growing European transport infrastructure and often small individual conservation areas have created isolated ecosystems that show very low movement in between them (Tillmann, 2005). PV-parks are not protected areas but, if managed correctly have shown to positively affect biodiversity and it is relevant for the European context to analyse their potential as corridors. In south-eastern France, Guiller et al. (2017) took an interesting approach at analysing the impact on PV-parks on landscape connectivity.

Case study 4: “Impacts of Solar Energy on Butterﬂy Communities in Mediterranean Agro-Ecosystems” (Guiller et al., 2017)

In order to analyse landscape impacts of PV-parks, Guiller et al. (2017) created a resistance map using ArcGIS. The aim of the study was to find out if a PV-park in a highly humanly impacted landscape disturbs or enhances species migration relative to other land-use types, such as forest, grassland and urban areas. In particular, the study investigated butterfly migration, differentiating the species into mobile (mean dispersal distance ≥ 254 m) and sedentary (mean dispersal distance < 254 m) species. To conduct the research, eight different resistance sets were created, assigning resistances based on literature to the PV-park and other land-use classes (Table 1).

Values used ranged from one (low resistance) to 100 (high resistance). On-site data sampling was conducted, and the observed distributions compared to the eight different resistance sets. While no significant results were found for the sedentary species, interestingly, mobile species were observed most often along routes that were predicted by resistance maps that assigned a resistance value of one to the PV-park.

Table 1: Resistance sets for individual land-use types, implemented into landscape algorithms. USSE (utility-scale solar energy) represents the PV-parks here (Guiller et al., 2017, p. 3).

Resistance map

A resistance map is a map in which per spatial unit (e.g. 100m²) a value is assigned, which indicates how hard it is to overcome the particular area. Individuals will follow the route with the lowest total resistance between the starting and end point. This method is commonly used to predict animal migration.

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The paper concludes that PV-parks can be beneficial to a landscape, if they are managed to accommodate many flowering plants (Guiller et al., 2017).

The approach taken by Guiller et al. (2017) is highly interesting and – although it is limited to butterfly distribution – case study 4 presents a promising approach to assess species movement through PV-parks. Especially in Europe where ecosystem fragmentation is a pressing issue regarding species richness and density (Jongman, 2002; Öckinger et al., 2010), the role of PV-parks as potential green corridors as suggested in case study 4 has to be analysed to finally assess impacts of PV-parks on biodiversity. In comparison to butterfly migration, which could apply to some other insect species as well, effects of PV-parks on mammal migration remain largely unknown. While small mammals may also use PV-parks as habitat or green corridors between habitats, it depends highly on the infrastructure of the PV-park, if it can also serve as green corridor for larger mammals like deer. If PV-parks are surrounded by fences, as it is often the case due to insurance regulations or other safety measures, the parks can result in a less permeable landscape, changing its degree of connectivity permanently. Anthropogenic barriers like these would cause further habitat fragmentation and can negatively affect mammal metapopulations in Europe. Especially larger mammals are threatened by extinction due to decreasing habitat and range size, which in Europe is strongly driven by anthropogenic factors (Crooks et al., 2017). Comparison of the negative potential impacts of such fragmentation effects against positive implications is not possible as quantitative data supporting or falsifying either argument is scarce, but it can be expected that fencing around PV-parks will lower their potential ecological benefits. While research on the direct impact of PV-parks on mammal distribution and migration is lacking, general research on mammal occurrence in Portugal suggests that after availability of water, heterogeneity of the landscape – here estimated by counting the number of vegetation types within an area – is the most important factor enhancing mammal occurrence and distribution (Gonçalves et al., 2012).

The above case studies suggest that under the right circumstances, positive effects of PV-parks on biodiversity in the area of construction can be achieved. The next chapter will investigate the negative impacts on biodiversity caused by the construction of PV-parks.

3.4 Negative ecological impacts of PV-parks

The danger of disturbing biodiverse areas through bad or inconsiderate choice of construction site, increased potential for invasive species establishment and acceleration of habitat fragmentation are all potential negative impacts that I found while researching how PV-parks can promote biodiversity.

In this chapter I present literature that researches negative impacts of PV-parks on the ecosystem. The following approach investigates the effects of horizontally polarised light reflected from PV-panels, which has been observed to adversely affect polarotactic insects.

Case study 5: “Reducing the Maladaptive Attractiveness of Solar Panels to Polarotactic Insects” (Horváth et al., 2010)

The environment directly impacts organisms, of which most organisms are highly adapted to certain environments. Evolutionary traps occur when rapid changes of the environment cause individuals to make maladaptive choices. One example of maladaptive choices is polarotactic insects that use horizontal polarization of light to identify waterbodies to lay their eggs. Previously it was already shown that human-made objects like glasshouses reflect polarised light as well, which misguides polarotactic insects and leads to increased reproductive failure.

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The increasing quantity of PV-parks sparked the authors interest on how photovoltaic panels impact these insects and if different panel designs have differing impacts.

For analysis, Ephemeroptera, Trichoptera, and Dolichopodid dipteran species response to a homogeneously black solar panel and the following five alternative classes of PV-panels were analysed:

1.White-framed solar cells with nonpolarizing surfaces.

2. White- and black-framed solar cells with an underlying polarizing plastic sheet. 3. White- and black-framed solar cells without underlying polarizing plastic sheeting. 4. Shiny black surfaces with different nonpolarizing white grid patterns.

5. White framing of solar cells within a solar panel.

Insects examined for this research originated from a creek in DunaIpoly National Park, Hungary, next to which the panels were set up.

Horizontal polarisation of the different surfaces was measured and for analysis of direct effect on polarotactic insects, they counted individuals landing on the different surfaces within a defined time and spatial frame. Analysis of the first four categories was conducted by counting individuals landing on the surface. For the fifth category sticky tape was used, to rule out individuals that land on a surface several times. It was found that solar panels indeed strongly horizontally polarise incident light (d ≈ 90–100%). Shiny black surfaces also showed strong horizontal polarisation (d ≈ 100%), while matte black (d < 20%) and white (d ≈ 0%) test surfaces showed very weak horizontal polarisation. Accordingly, PV-panels with a black frame attracted insects strongest, whereas white frames showed a decrease in insect attraction. Horváth et al. (2010) noticed the effect of white frames around panels and analysed the effect of orthogonal white stripes on the insects. The results showed that fragmentation of horizontally polarising surfaces decreases the number of polarotactic insects captured (Figure 5). This could be caused by insects naturally preferring larger waterbodies than the fragments offer, thus decreasing the chance of maladaptive choices. The authors furthermore state that measures to create fragmentation that would significantly reduce insect attractiveness of PV-panels could be done with a net energy deficit of 1.8%, which they argue is a relatively low decrease in panel performance. Should no measures be taken to reduce horizontal polarisation, PV-parks can have significant negative effects on populations of polarotactic insects as they may be misguided, lay their eggs on surfaces with virtually no chance of survival and contribute to the the ongoing decline of native insect species worldwide (Horváth et al., 2010).

Case study 5 points to an important ecological impact, that previous research presented here did not consider.

Figure 5: The surface density (captures per square meter) of polarotactic dolichopodid (Diptera), mayflies (Ephemeroptera), and Philopotamus (Trichoptera) trapped by a highly and horizontally polarizing sticky surface with different numbers (N) of orthogonal white strips (Horváth et al., 2010, fig. 4).

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PV-parks represent a man-made impact on the environment, and it cannot be denied that the presence of panels in a field may adversely affect living organisms in its surroundings, like shown here as horizontal light polarisation. No other adverse effects have been investigated yet, however, the example of polarotactic invertebrates shows that there are many factors influencing an environment, which are not obvious to the naked eye. Ultimately, ongoing monitoring and research on PV-parks must be undertaken so that other unexpected adverse impacts can be found and potentially counteracted. Besides that, scientists must see PV-parks as the artificial environment they pose and think of impacts such PV-parks could – in theory – have on the environment. To this point, known negative effects of PV-parks remain modest as long as no accidents occur. This leads me to the other perspective I take at PV-parks, which was to investigate negative ecological impacts PV-parks can have in case of disaster.

Case study 6: “Public health issues in photovoltaic energy systems: an overview of concerns” (Moskowitz et al., 1987)

This paper points out different threats that are posed by the installation of large-scale PV-parks. Two main threats occur in the production and maintenance of PV-parks.

Firstly, there are chemical hazards. During the production of PV-panels, chemicals like arsenic can be released and be a threat to neighbouring communities and production workers. Although this risk is mostly urgent during production rather than maintenance, chemical pollution risk is inherent in parks as there is constant potential for accidents on the plant and the building parts contain materials that can be highly toxic if ignited. To keep such risks as low as possible, the authors suggest establishing prevention measures, such as quality control and early warning systems. They also suggest creation of disaster response measures such as evacuation plans and provision of local hospitals, informing them about the risks that may occur in case of a disaster related outbreak of toxic chemicals.

Second, physical threats are high in parks themselves. Because PV-parks start generating high amounts of voltage as soon as sunlight hits them, damaging the panels can lead to electric shock or even fire. To prevent exposure of individuals to such dangers, the authors suggest regular control of panels for malfunctions and implementation of warning signs to keep unqualified people off the property and decrease the chance of potential harm (Moskowitz et al., 1987).

The results of case study 6 stand in conflict with my previous findings, as fencing would help reducing disaster risks, but potentially negatively impact habitat fragmentation. Warning signs and regular control of panels may help reducing human risk; however, a malfunction of panels cannot systematically be avoided and in the occurrence of malfunctions, animals will not recognise warning labels. This poses the danger of electrical shock, which beside putting individuals at risk, will also increase fire hazards, especially if vegetation surrounding the panels is dense. A PV-park placed in an area in which it could serve as ecological bridge between ecosystems, animal movement through the park would be high and consecutively the risk of disaster increases.

Literature on negative impacts of PV-parks on the ecosystem was marginal. It is important to note that I did limit my research on the impacts of PV-technologies and that this assessment, as mentioned in chapter 3.1, did not take other solar power technologies like CSP into consideration. Based on these positive and negative impacts of PV-parks presented, I look at how successful current guidelines have been at implementing scientific findings in the following chapter.

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3.5 Conceptual weaknesses of biodiversity management and research

Current research on ecological impacts of PV-parks on ecosystems is marginal and especially in comparison to other energy sources like wind energy, knowledge on ecological impacts is often based on limited data and research.

This lead to the existence of guidelines for PV-park management aiming for biodiversity enhancement that are not based on scientific findings, but rather expectations raised from unrelated research or even just general knowledge (England, 2011; Parker, 2014; Semeraro et al., 2018). Research presented previously as well as most management plans aiming at improvement of biodiversity, do so by cultivating plants that are known to promote insect abundance. This management method completely fails to recognize the risk that introduction of new plants or even just the artificial alteration of the natural environment can have major negative impacts on native species. This is not just the case when invasive species establish themselves, but also in case native species are imported from a foreign environment, as Keller et al. (2000) show.

Case study 7: “Genetic introgression from distant provenances reduces fitness in local weed populations” (Keller et al., 2000)

This paper by Keller et al. (2000) investigate the consequences of increasing frequency of man-made wildflower strips on the fitness of local weed populations, specifically in relation to genetic introgression of foreign plants into the environment. The argument made by the paper is that repeated introduction over several years prevents natural selection and with that prevents the recovery of native species from loss of fitness caused by introduced foreign species. To investigate these effects, Keller et al. (2000) raised five central research questions:

1. Do intraspecific hybrids between agricultural and ruderal weeds and distant provenances show increased performance in the F1 generation (heterosis)?

2. Do the same hybrids show decreased fitness in the F2 (outbreeding depression)?

3. How strong are ecological and physiological components of outbreeding depression expressed?

4. To what extent are heterosis and outbreeding depression related to the geographical distance of the foreign population?

5. Is the rare, inbreeding species, Agrostemma githago, more affected than the two ruderal outbreeders

Papaver rhoeas and Silene alba?

To answer the research questions, the three plant species Agrostemma githago, Papaver rhoeas and Silene

alba (S. latifolia ssp. alba), were obtained from different commercial suppliers in Switzerland, Germany,

England and Hungary. Crossbreeding experiments were undertaken in greenhouses, in which a first generation was bred, by one-way crossing female individuals bought from the Swiss provider with other Swiss (bought and wild) and alien individuals.

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To obtain the F2, F1 generations were backcrossed with an individual of the female population (Figure 6). Four-week-old plants were transplanted into randomised 2 * 2 m² blocks. After a growing period in the plots, which was long enough for all species to grow seeds and similar for all species, weeds were cleared from the plots and seeds collected.

For analysis, the seeds of the F1 and F2 were individually weighed (Silene in groups of 50 because of their small seeds), and above-ground dry matter, as well as survivorship of the mother plants (F1 and F2) measured. While results differed slightly in among species, overall results show for above-ground biomass as well as seed weight that the first generation (F1) increased in biomass. The backcrossed generations (F2) however, show negative effects. For the less common

Agrostemma, the same trend was observed, however in this species results were less strong. The authors

suggest that the initial improvement in the F1 could be attributed to the heterosis effect (increased performance of hybrid offspring, because many deleterious recessive alleles are being masked), while after that generation the negative impacts of outbreeding depression decreased seed weight and above-ground biomass. Outbreeding depression is here described as the manifestation of decreased fitness in hybrid offspring, caused by loss of local adaptation due to ongoing import of foreign genes. As to the geographical relation of outbreeding effects to plant origin, Keller et al. (2000) give no final recommendation, because the effect can vary greatly between species and distances can affect populations in diverse ways. Nevertheless, adjusted to the individual region, management guidelines for seed origin and monitoring of wildflower strips is recommended. In general, the authors suggest to only use plants of relatively local origin, without going into more detail on what ‘relatively local’ strictly means (Keller et al., 2000).

Case study 7 demonstrates that import of seed mixtures from spatially distant sources can negatively impact the genetic makeup of local plants. It opens a very important debate that needs to be included in the assessment of ecological impacts of PV-parks, especially because previous research did not account for the problem of potential outbreeding depression.

On the search for suitable management plans, I only found one that recommends considering origin of the seeds and recommends to only use native seeds for seed mixtures. Namely the “Biodiversity Guidance for Solar Developments” by the British BRE National Solar Centre (Parker, 2014) is an outstanding management plan, as it includes diverse recommendations for improving biodiversity with a PV-park, while taking the various potential negative factors into consideration. Other guidelines, like the “Leitfaden zur Berücksichtigung von Umweltbelangen bei der Planung von PV-Freiflächenanlagen (Guide for the consideration of environmental issues when planning ground-mounted PV systems)” commissioned by the German federal ministry for the environment, nature conservation and nuclear safety (Günnewig et al., 2007) base management recommendations on existing law, ensuring to comply with legal obligations rather than striving to improve biodiversity. In general, not many guidelines aiming at improving biodiversity in PV-parks exist and research on the ecological impacts is often not taken into consideration in such plans.

Figure 6: Crossing design to produce hybrid lines. Abbreviations of the provenances: CH, Switzerland; D, Germany; GB, England; H, Hungary; NJ, New Jersey, USA; W, Swiss wild populations, Zurich (W1) and Basle (W2); (Keller et al., 2000, fig. 1).

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Individual research projects like those described above often fall through the raster, because they usually involve small scale research looking at individual dynamics rather than the entire ecosystem, are hard to find and in some cases not publicly available. In the last chapter of the results, I investigate what alternatives exist to construction of PV-parks in rural areas.

3.6 Spatial paradox of energy production in rural areas

Previous findings indeed suggest that – under ideal circumstances – PV-parks can promote biodiversity. However, the question must be raised, why PV-parks are built in rural areas in the first place. The highest demand for electric energy is found in urban areas and transport of electric energy always results in energy loss of some extent, as well as construction and maintenance costs for infrastructure. Looking at a city, I see many buildings with – often flat – concrete roofs, which could surely support instalment of PV-panels and necessary infrastructure for energy transportation and storage would be avoided or in any case cheaper. So why don’t we build PV-parks on the roofs in cities?

Strupeit and Palm (2016) described three major barriers PV-technologies face when it comes to consumer attraction. The first being consumer inertia; meaning that awareness of potential for PV-technology is low. Second, the consumer does not feel safe in investing in the technology and third, it is often hard to finance initial installation of PV-panels for individual homeowners. These problems reduce the speed at which individuals invest into solar technology within the urban setup, leaving big investors – often energy companies – as the main driver of PV development with the goal of selling produced energy rather than self-sustaining. This leads to the other problem, which is that property in cities is usually small and often every house is owned by another party. For a company or an investor, installation of a PV-park of equal energy and financial potential as in a rural setup, multiple parties would have to be involved. The bureaucratic effort and accessibility of rooftops for maintenance could not or only at high effort be provided. Nevertheless, potentials of rooftops for solar energy production should not be discarded too quickly, as the following case study presents an interesting approach to overcome ownership and accessibility problems.

Case study 8: “Urbane Photovoltaikproduktion auf österreichischen Großparkplätzen: ein Beitrag zu

nachhaltiger Energieversorgung, zukünftiger Elektromobilität und Bewusstseinsbildung bei

Entscheidungsträgern/-innen” (Salak et al., 2017); (“urban photovoltaic production on big Austrian parking lots: a contribution for sustainable energy supply, future electro mobility and awareness raising in future decision makers”).

This Austrian source suggests one interesting approach to avoid the bureaucratic effort and accessibility problems for investors. Salak et al. (2017) suggest usage of large communally owned spaces, like parking lots for the creation of PV-parks.

In their assessment, parking lots with an area > 600 m² were considered and a space usage efficiency of 40% was set, to account for limiting factors like shading. Additionally, they were analysed relative to adjacent industry, but as this is of no relevance for the subject of this review, I will not elaborate on this part of the research.

The solar potential of all parking lots analysed in Austria after reductions such as atmospheric, physical and spatial irradiation decrease, technical efficiency and potential inaccessible areas of parking lots, resulted in an estimated 4.2 TWh/a. To put this into perspective, current photovoltaic production in Austria is 0.9 TWh/a and the total energy demand in Austria herein estimated is 100 TWh/a.

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The conclusion is that parking lots show a high potential for energy generation with photovoltaic panels and societal acceptance as well as potential implementation of PV-parks on parking lots should be investigated (Salak et al., 2017).

Urban parking lots or other communal areas have shown to be promising locations for the creation of PV-parks. Considering case study 8, creation of solar parks in rural areas can ecologically only be justified if a clear advantage to the surrounding environment can be expected. If there is enough space in the urban setup to create PV-parks, opportunity costs must be considered. Whenever a PV-park is built, this land cannot be used for food production or conservation anymore. If you take a system in which food production parallels demand, creation of one PV-park in location “A” leads to expansion of agriculturally used area in location “B”. This relationship is often referred to as telecoupling effect and has shown to indirectly negatively affect ecosystem diversity (Liu et al., 2013; van Vliet, 2019). As the biodiversity crisis is an issue of global concern, these indirect effects of PV-parks on biodiversity elsewhere should be taken into consideration as well. However, quantifying such indirect impacts is complicated and even if they were raised, setting them into context of individual PV-parks is hardly possible. Nevertheless, rooftops or parking lots do not show this trade-off, as they are built for a specific use, which they will fulfil with or without PV-panels installed.

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4. Discussion

This review found that in comparison to other renewable energies, PV-energy is one of the least ecologically disturbing renewable energies. Although I found that PV-energy is particularly understudied in terms of environmental impacts, its space efficiency alone makes it a promising source of renewable energy. Besides that, the question, whether PV-parks can promote biodiversity, cannot be answered with a simple yes or no. It does indeed seem like PV-parks can be beneficial to the ecosystem, however, very particular circumstances must be met to enable biodiversity promotion:

1. Choice of construction site: The very first and most important factor that needs to be addressed, is the location of a park. It must be in an area that was previously humanly impacted and shows low biodiversity compared to natural ecosystems in the relative region. To enable ideal choice of location, I recommend initial site analysis through remote sensing. Case study 1 represents an example of how such a model can be created. In a second step, an on-site environmental impact assessment should be undertaken.

2. Parks must be monitored constantly. As seen in case study 3, PV-parks represent a suitable habitat for invasive plants. Ongoing monitoring of plant diversity in parks, can ensure that no uncontrolled spread of invasive species happens and potentially provide information that can help management to adjust seed mixtures to the specific region.

3. Management intensity must be as low as possible to decrease costs and enable plants to establish themselves. Nevertheless, cutting should be performed in the necessary extent to sustain high plant diversity and provide safety and accessibility.

4. Seeds used in seed mixtures must be regionally sourced to prevent or at least decrease the probability of outbreeding depression in native populations (Keller et al., 2000).

5. If the site assessment finds that polarotactic insects occur regularly in the area (often around aquatic ecosystems), horizontally polarised light reflection of the panels must be reduced. Case study 5 suggests that fragmentation of horizontally polarising surfaces can already strongly decrease these negative effects. Besides that, production should already aim at usage of less horizontally polarising materials.

6. Construction of fences must be avoided as it would present an impermeable landscape. If fencing is mandatory, gaps for mammals should be implemented. Should such tunnels not be created adversely affected migration of larger mammals must be monitored. Warning signs or ecological bridges should be created to avoid wildlife accidents along the new migration routes.

7. The inherent disaster risk must be kept minimal through regular safety checks. Further, to reduce damage in case of disaster, case study 6 suggests informing citizens and hospitals in the region about the dangers to improve the reaction to disaster.

Finally, options for creation of PV-parks within the urban landscape should be utilised maximally, before opening rural areas up for development. Nevertheless, creation of PV-parks in rural areas should still be considered in the transition to renewable energies in the EU, as current production of energy through crops (biofuels) is much less space efficient and increases the indirect damage to biodiversity even more (Fthenakis and Kim, 2009).

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5. Conclusions

Because of fast technological development and best performance, PV-technology will be the leading tool to produce solar energy in Europe. In comparison to other renewable energies, PV-panels impact the environment marginally and show outstanding space efficiency. Assessment of ecological impacts found that PV-parks can promote biodiversity. In order to achieve that potential, a management plan for each individual park must be set in place, which specifically aims at improvements of biodiversity. A European guideline should be created, and incentives or regulations put in place to make sure that management plans are created and based on scientific findings. An example for how this advice could look is the guideline “BRE National Solar Centre Biodiversity Guidance for Solar Developments”, coincidentally partly funded by the EU, which represents a very promising guide, being both concise and clear in the recommendations. Should the applied management plan of a PV-park not account for the requirements I outlined in the discussion, no positive impacts on the environment can be expected. To enable ongoing management improvements and increase understanding of ecological impacts of PV-parks, I advise to intensify research and to raise more empirical data on PV-parks.

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Illustration sources

https://www.uva.nl/over-de-uva/over-de-universiteit/huisstijl/huisstijlelementen/logo/logo.html#Basislogos (accessed: 15.06.2020) https://ibed.uva.nl/ (accessed: 18.08.2020) https://phys.org/news/2018-09-physics-ekg-solar-panel-health.html (accessed: 22.08.2020)

Tables

TABLE 1: RESISTANCE SETS FOR INDIVIDUAL LAND-USE TYPES, IMPLEMENTED INTO LANDSCAPE ALGORITHMS. USSE (UTILITY-SCALE SOLAR ENERGY) REPRESENTS THE PV-PARKS HERE (GUILLER ET AL., 2017, P. 3). 11

Figures

FIGURE 1: GLOBAL HORIZONTAL IRRADIATION (GHI) IN EUROPE FOR THE YEARS 1994 TO 2016 IN KWH/M². (“SOLAR

RESOURCE MAPS OF EUROPE,” 2019). 5

FIGURE 2: LIFE-CYCLE LAND TRANSFORMATION FOR FUEL CYCLES BASED ON 30-YEAR TIMEFRAME IN M²/GWH

(FTHENAKIS AND KIM, 2009, FIG. 3). 7

FIGURE 3: MAP OF SOUTH-EASTERN CALIFORNIA, SHOWING THE SITE SUITABILITY THAT RESULTED FROM THE

COMPATIBILITY INDEX (STOMS ET AL., 2013, FIG. 7). 8

FIGURE 4: OVERALL COMPARISON OF SOLAR AND CONTROL PLOT BOTANICAL DIVERSITY (MONTAG ET AL., 2016, FIG.

5.1). 9

FIGURE 5: THE SURFACE DENSITY (CAPTURES PER SQUARE METER) OF POLAROTACTIC DOLICHOPODID (DIPTERA), MAYFLIES (EPHEMEROPTERA), AND PHILOPOTAMUS (TRICHOPTERA) TRAPPED BY A HIGHLY AND HORIZONTALLY POLARIZING STICKY SURFACE WITH DIFFERENT NUMBERS (N) OF ORTHOGONAL WHITE STRIPS (HORVÁTH ET AL.,

2010, FIG. 4). 13

FIGURE 6: CROSSING DESIGN TO PRODUCE HYBRID LINES. ABBREVIATIONS OF THE PROVENANCES: CH, SWITZERLAND; D, GERMANY; GB, ENGLAND; H, HUNGARY; NJ, NEW JERSEY, USA; W, SWISS WILD POPULATIONS, ZURICH (W1)

AND BASLE (W2); (KELLER ET AL., 2000, FIG. 1). 16

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