Potential regulatory approaches on the environmental impacts of photovoltaics: Expected improvements and impacts on technological innovation

This work assesses the opportunities for technological development and innovation that may be imposed or created by environmental policy. Working within the legislative framework of European Union (EU) sustainable product policies, a study of the feasibility of four specific policy instruments (Ecodesign Directive, Energy Labelling, Green Public Procurement and the EU Ecolabel) to photovoltaic products (modules, inverters and systems) led to the identification of key performance metrics and design features. Starting from an analysis of the environmental hotspots of photovoltaic products throughout the whole life cycle (from raw material extraction to their end of life and disposal), a number of areas of attention for innovation are identified and a policy approach is proposed to tackle these aspects in regulatory terms by means, in particular, of requirements within the legal framework of the Ecodesign Directive.


| INTRODUCTION
As announced in the 'European Green Deal', 1 the decarbonisation of the European Union (EU) energy system is critical in order to reach climate objectives in 2030 and 2050. To this extent, a power sector must be developed that is based largely on renewable energy sources (RES), complemented by the rapid phasing out of coal and by the decarbonising of natural gas. In particular, the 2018 Renewable Energy Directive 2 establishes a binding renewable energy share for the EU for 2030 of at least 32%, and currently, there is momentum for increasing the EU's greenhouse gas (GHG) emission reductions target for 2030 to at least 50% and towards 55%. A recent analysis of the different decarbonisation scenarios in regard to how to reach these GHG reduction targets concluded that the cumulative photovoltaic (PV) capacity in the EU and the United Kingdom would need to increase to 455-605 GW. 3 Being sure that newly installed PV products in the EU are environmentally friendly and do not create new future burdens on the environment is therefore of primary importance, given the role that this technology is expected to have in the decarbonisation of the EU energy system. Regulatory measures in the field of sustainable product policy could be instrumental to this extent, to ensure the environmental sustainability of PVs by improving their environmental performance as well as their energy yield, in turn reducing the overall life cycle environmental footprint of the products deployed in the field.
To date, EU sustainable product policy 4 addresses different aspects associated with the life cycle of products (and services, to a lesser extent) such as product design, materials, manufacturing, use, end of life and the related use of energy, water, chemicals and other resources. This policy is currently articulated in a number of policy instruments with which the market can be driven towards the production and consumption of more sustainable products. These policy instruments, as summarised in Table 1, include Ecodesign, 5 Energy Labelling, 6 Green Public Procurement 7 (GPP) and the EU Ecolabel. 8 In terms of mandatory instruments, the Ecodesign Directive 5 requires manufacturers placing products on the EU market to improve their environmental performance by meeting mandatory minimum energy efficiency requirements, as well as other obligatory environmental requirements such as water consumption, emission levels or material efficiency aspects. The Energy Labelling Regulation 6 provides consumers with a straightforward informative tool to make a better purchase choice, by grading products according to a well-known A-G/green-to-red seven class label.
In terms of voluntary instruments, the EU Ecolabel 8 was established as a tool to encourage businesses to develop products with a reduced environmental impact throughout their whole life cycle and to help consumers find the best environmentally performing products in their category. GPP 7 criteria are proposed to identify environmentally friendly goods, services and works; their voluntary use by EU public authorities is intended to stimulate demand for more sustainable goods and services, which otherwise would be difficult to bring onto the market.
The two voluntary instruments can be applied to both products and services, the latter being relevant for the PV sector. Specifically in the case of PV products, an important aim of introducing the GPP criteria would be to use the wider potential public sector influence, in particular at regional and local level, by providing guidance and criteria on the procurement of new solar PV systems, or by establishing frameworks for reverse auctions as well as usage rights and power purchase agreements for public assets (lands, roofs) to be exploited for RES electricity generation. The potential to combine the use of reverse auctions with associated procurement criteria to meet solar home PV deployment targets could be particularly important as this has proved a difficult market segment to influence. Service-based business models for circular economy have, moreover, the potential to minimise the environmental impact of production and consumption 9 and may play an important role in the solar sector, especially in the residential segment. Annex V of the Directive also allows for a management system for design through manufacturing to be used for conformity assessment.  best not yet available technology (BNAT) technologies are selected based on the definitions below.
• The BC represents the average product on the market in terms of resource efficiency, emissions and functional performance.
• The BAT point represents the best commercially available product with the lowest resource use and/or emissions.
• The BNAT point represents an experimentally proven technology that outperforms the BAT, but is not yet brought to market; for example, it is still at the stage of field tests or official approval.
The MEErP guidance also notes that: Tasks in the Methodology for the Ecodesign of Energy-Related Products. 28 • BNAT technologies could be accelerated to market by incentive programmes once they have been evaluated as such in an Ecodesign preparatory study and Given that a combined approach between the analysis on Ecodesign/Energy Labelling, GPP and the EU Ecolabel was requested for the JRC study, 27 additional methodological considerations were introduced. This resulted in the adoption of a tailor-made methodology in the JRC study, which was largely built on the MEErP to which specific steps aimed at supporting the policymaking process for GPP and the EU Ecolabel were added. Figure 2 displays the eight tasks of this tailor-made methodology, as well as the specific steps, task by task, for GPP and the EU Ecolabel (the outcomes for the Ecodesign/Energy Labelling are those from the standard MEErP). For example, when developing the EU Ecolabel, the Task 1 scope had to include a review of existing certification and labelling schemes.
This approach resulted in a comprehensive analysis of the technical features, as well as of the economic and environmental impacts and of the various design options under analysis, conducted in parallel on three different products groups (PV modules, inverters and systems). For each of these products, the JRC study also outlined potential requirements within the framework of the aforementioned policy instruments.

| LCA methods
The environmental and economic improvement on the BCs of PV module, inverter and system design improvement options was assessed-as detailed in Section 2.3-and was undertaken using the EcoReport tool. The EcoReport tool was developed as part of the In line with guidance on carrying out an LCA, functional units of reference were defined for PV modules, inverters and systems respectively: These figures have been analysed in detail in the JRC study, and they have been discussed with stakeholders. These service lives therefore represent a notional period for the purpose of the modelling, with the intention that products with extended life spans, slower performance degradation or lower failure rates would be differentiated in the results.
The EcoReport tool then models four principal life cycle stages: • raw materials use and manufacturing, • distribution, • use phase, and • end-of-life phase.
Emission and resource use have been expressed as results for each of the different impact categories that are required by the MEErP methodology.

| Technical analysis
The main assumptions and proxies for the lifetime and performance of the modules, inverters and systems that were used as the basis for conducting the technical analysis are listed in Tables 2 and 3.
These were derived from the analysis conducted in the JRC study and the consultation process. The BCs were selected to T A B L E 2 Main assumptions and proxies for the lifetime and performance of the photovoltaic systems For inverters, 13 design options were selected, with 11 of them considered to represent technology that is available presently, being therefore BAT candidates and 1 being BNAT (Table 6).
T A B L E 3 Main assumptions and proxies for the lifetime and performance of the inverters Option 12: BNAT kerfless silicon Kerfless wafer production eliminates the need for the slicing of silicon blocks or ingots to obtain the wafer substrate.
Note. The options selected for further analyses are highlighted in grey. For solar PV systems, 13 and 9 design options were selected for the residential and commercial/utility segments, respectively (see further details in the JRC study 27 ). The PV system options considered largely consist of combinations (or 'packages') of the module and inverter technology design options together with options that focus on improvements in system performance as a whole. For example, for the residential segment, one system option could consist of the optimised PERC 2020 + the best performing inverter, thus combining the best module with the inverter with longer life and including a smart monitoring system.

| Policy options analysis
Towards the end of the JRC study, a policy analysis was carried out • Ecodesign (ED) requirements on modules and inverters: mandatory requirements could be set that would apply to individual modules and inverters placed on the EU market.
• Energy Labelling (EL) requirements for residential PV systems: mandatory requirements could be set that would apply to either the weighted efficiency of a package consisting of a module type and an accompanying inverter type or, alternatively, the calculated energy yield of a whole PV installation.
• EU Ecolabel criteria set: a voluntary criteria set could be established that would apply to a combination of a package placed on the EU market and the related system design and installation service offered to consumers.
• GPP criteria: a voluntary criteria set could be established that would apply to the process of procuring a solar PV system, from contractor selection through to decommissioning.
• Combined policy options: it was considered to combine the mandatory and voluntary options that were evaluated, given that each of them can act in a different way to achieve improvements in the market.
One of the aims of considering both mandatory and voluntary policy instruments was also to analyse the potential for synergies between them. Two combined policy options were, as result, modelled in order to determine the improvement potential.

• 'Combined option 1' (ED + EL + GPP) would be led by implementation of the two mandatory instruments, namely, Ecodesign and
Energy Labelling, to be complemented by voluntary GPP criteria.
• 'Combined option 2' (ED + GPP + EU Ecolabel) would be led by implementation of the two voluntary instruments, namely, the EU Ecolabel and GPP, backed by the mandatory instrument Ecodesign.

| RESULTS AND DISCUSSION
3.1 | Environmental hotspots, impacts on technology innovation and potential policy approaches The results for the environmental profile of the PV module BC are presented in Table 7. They were found to be dominated by the production stage for all the impact categories that are evaluated in the EcoReport tool. Upon analysing the results obtained from the EcoReport LCA tool for the lead indicator of primary energy (GER), the following were observed: • Modules: in the residential market segment, the CIGS thin-film design, and for the commercial and utility segments, the CdTe thinfilm design were the BAT. Composite design improvements based on PERx cell architectures have the potential to deliver a comparable performance to the CIGS design for the GER results. This is particularly the case if BNAT options such as kerfless wafers and design for recycling were to be implemented.
• Inverters: in the residential market segment, the longer life and repairable options were the BAT, with both achieving a significant margin of 54%-61% improvement upon the BC. In the commercial segment, the repairable option comes out as the BAT, showing a 52% improvement. In the utility segment, there appears to be very limited margin to identify a BAT based on the design options modelled.
• PV systems: in the residential market segment, options that include a long life inverter or an inverter designed for repair, as well as options that have had the system PR optimised-either from a design or an operation and maintenance perspective-were identified as BAT.
A sensitivity analysis of the influence of the electricity grid mix in difference global regions was also made, as suggested by other authors. 35 This analysis showed that a variance of up to 38% can be seen in the results when using life cycle GWP, suggesting that GWP could also be used to screen for the geographical influence of electricity and fuel infrastructure. Table 8 gives a more detailed insight into the production stage and shows the relative contribution of the different materials to a certain impact category. The heavy metals (Sn, Pb, Cu) used for interconnections are listed separately.
The PV cell herein is mainly silicon but also contains some other materials such as silver for electrodes (contained in the metallisation paste of the electrodes). The PV cell gives the greatest contribution across the majority of the impact categories considered in MEErP.
The aluminium frame contributes greatly for PAH and HMw and to a lesser extent for GWP, persistent organic pollutant (POP), and particulate matter (PM). Also notable is the consumption of water in relation to the glass fibre in the junction box (Table 8).

| Links between environmental impacts, technological innovation and policy
Based on the LCA review on PVs that was conducted in the JRC study, the environmental hotspots together with the life cycle stages where they assume an importance were identified. To tackle these hotspots and to translate them into possible technical requirements to support improvements, a number of focus areas in the PV production processes were identified. These areas together with the translation of the LCA evidence into possible Ecodesign measures are summarised in Note. In columns are the environmental categories: GER (gross energy requirement), haz./non haz. waste (hazardous/non-hazardous waste), GWP (global warming potential), AD (abiotic depletion), VOCs (volatile organic compounds), POP (persistent organic pollutants), HMa (heavy metals to air), PAH (polycyclic aromatic hydrocarbon), PM (particulate matter), HMw (heavy metals to water), EUP (eutrophication potential). Contribution to impact category 25% < X < 50%. Contribution to impact category 10% < X < 25%. Contribution to impact category X > 10%. [Colour

Requirements on durability
To applications. However, similar to the case of modules, to ensure implementation of the design features upon mass production, the qualification would need to be complemented by factory inspections of product quality.

Requirements on reparability
A first category of Ecodesign requirements on repairability typically consists of (compulsory) information requirements.
Concerning PV modules, manufacturers could be required to report information both on the possibility to access and replace the bypass diodes in the junction box and on the possibility to replace the whole junction box of the module.
As for inverters, the requirement could consist of the identifica-

Requirements on recyclability
To increase the recyclability of PV modules, one requirement could consist of reporting on the potential to separate and recover the semi-conductor from the frame, glass, encapsulants and backsheet.
The design measures to prevent breakage and enable a clean separation of the glass, contacts and internal layers during the dismantling operations should be clearly detailed. Moreover, and following identification of relevant critical raw materials and other materials that either represent hotspots for environmental impact or a potential future supply risk, the manufacturer should declare the content in grammes of a set of materials in the product (antimony, cadmium, gallium, indium, lead, silicon metal, silver and tellurium). Consequently, despite being categorised according to the LCA results as BAT technologies in terms their GER results, for thin-film technologies, proper recovery and recycling is an important aspect that has to be taken into account due to the toxicity of the semi-conductor materials. 43 For the encapsulant and backsheet, the type of polymers used (including if it is fluorinated or contains fluorinated additives) and the content in grammes could also be declared by the manufacturer.
As for inverters, and following identification of relevant critical raw materials and other materials that either represent hotspots for environmental impact or a potential future supply risk, the manufacturer could be required to declare the content in grammes of listed materials present in the product as a whole and in the replaceable circuit boards (lead, cadmium, silicon carbide, silver, indium, gallium and tantalum).

| Future prospects for technological improvements
As part of the MEErP methodology, a series of BNAT for modules and inverters technologies were identified that could tackle the environmental problems summarised in Table 9 and offer further, in some cases substantial, potential improvements in performance relative to the BCs in the upcoming years.

PV modules
The most promising PV module technologies currently include, together with a classification of their production status: • commercially available, with limited production lines at present:

Silicon wafer material and energy efficiency
The production of silicon wafers by alternative processes that are more efficient in their use of energy and silicon, such as epitaxial growth or 'lift-off' processes, are currently identified as BNAT, although modules based on this type of wafer production have previously entered the market as BAT in the period 1999-2014. 44 This type of wafer could potentially be introduced into multisilicon module production lines, which in 2016 accounted for around 65% of the crystalline portion of the market, which at the present time is expanded from BSF cells to also now includes some PERx cell variants (PERC/PERL on p-type material). However, this portion is projected to decline to around 10% by 2030, when only multicrystaline PERC/PERL cells may remain, so the scope to bring process efficiency gains into the market may be constrained unless the associated modules are more competitively priced.
'Drop-in' technology such as kerfless wafer production could be particularly important for the residential market segment where the large-scale deployment of the BAT identified by the study for this seg- is not yet demonstrated due to a small market penetration. This should therefore be taken into consideration in the design of any policy interventions.

Crystalline module redesign for recycling
The near BAT 'design for recyclability' silicon module is noteworthy given the need to consider the end of life scenarios for a rapidly increasing module stock. Currently, the majority of module designs present various technical difficulties and challenges at the moment of seeking to dismantle them to recovery materials for recycling. 45 Once the junction box and aluminium frame (if present) have been removed, the main difficulty is to separate the encapsulated components as well as the soldered connections and tabbing of the cells. This requires destructive thermal and mechanical processes to be used, which result in low-grade, cross-contaminated material recovery.
Thin-film module designs to some extent simplify the dismantling process, and processes have been developed at commercial scale that achieve a high recovery of the semi-conductor material. 46 Alternative crystalline wafer module designs have been developed to a precommercial stage that have eliminated the polymer encapsulants and laminates as well as the metal soldering that can hinder dismantling. 47 The same pilot production modules have been certified to have passed IEC 61215 design approval, 39 indicating that the design and material changes do not appear to have compromised the durability of the encapsulation-although this is still to be more rigorously tested in the field. The paper argues, inter alia, that there is the potential for technological innovation throughout the product life cycle of PV modules and inverters, including

PV inverters
• silicon wafer and film semi-conductor designs that further improve performance under variable climatic conditions and that are material efficient; • module design to minimise long-term material and performance degradation and to ensure durability in the field; • module and inverter design for ease of disassembly to facilitate access to/replacement of key components; and • module and inverter design for ease of dismantling to facilitate the recovery of components and raw materials.
This potential can be identified from existing leading (BAT) products on the market as well as by making market entry projections for the future potential of products with