Identifying Research Priorities for the further development and deployment of Solar Photovoltaics

ABSTRACT

Solar Photovoltaics (PV) is considered a highly competitive technology supporting the transition towards a low-carbon energy system. However, increased shares of its deployment have caused a set of mainly regulatory and financial challenges which require solutions. This paper identifies key research challenges for the further development and deployment of Solar PV, aiming to bridge the gap between expressed market needs and scientific research inquiries. The findings revealed a heterogeneous landscape of Research Priorities and Research Needs focused around the issues of renewable energy sources’ variability, the impacts of curtailment, material (re-)use and module efficiency, synergies with the cooling/heating sector, quality criteria and standardisation, as well as new support schemes and business models. These findings can be taken up by academic institutions or technology associations to shape further directions for research. Finally, a list of implications to guide potential end-users involved in the field of policy and practice is provided.

KEYWORDS:

• Photovoltaics
• Solar PV
• Research Priorities
• Research Needs
• policy implications
• support mechanisms

1. Introduction

The ‘Winter Package’, which was published on November 2016 by the European Commission, addresses all areas of the energy system and is anticipated to shape the policy framework for many years post-2020 (Rosenow et al. 2017). European countries will have to (re-)form their climate policies, and develop National Climate and Energy Plans, in order to comply with the mandates of the ‘Winter Package’, and meet the EU emission targets for 2030 and beyond (Hancher and Winters 2017). Achieving temperature and emission reduction goals signals the further development and deployment of Climate Change Mitigation Options (CCMOs). In the context of achieving these climate goals and implementing the ‘Winter Package’, the energy sector’s momentum towards its decarbonisation should be globally maintained to achieve the transition to a zero-carbon, sustainable electricity system by 2050. Given that one-third of the global CO₂ emissions are emitted by the power sector, there is wide scientific consensus that renewable energy technologies, such as Solar PV, are significant contributors towards their mitigation, eventually resulting in global temperature increase mitigation (Cooper 2016; Eurelectric 2016; Vandyck et al. 2016).

Solar PV has been proven to be one of the key technologies of electricity generation from renewable sources (RES-E) for the support of the transition towards a low-carbon energy system. To do so, much research effort was dedicated on ways to reduce the technology’s cost and increase operational efficiency. New business models for sustainable development, followed by novel investment frameworks, centred around industrial growth and employment generation can arise from the further development and deployment of Solar PV (EPIA 2012; SolarPower Europe 2014; EUROBAT, EHPA, and SolarPower Europe 2016). Nowadays, the technological cost reduction is considered of secondary importance. The research challenges that are considered a first priority, to allow the technology to keep its exponential growth rate, are those that have emerged due to the large numbers of deployed systems. Those challenges are mainly regulatory and consequently financial (EPIA 2012) and mainly relate to: the need for novel market business models and financing mechanisms (Papadelis, Stavrakas, and Flamos 2016; Parag and Sovacool 2016), the need to balance the intermittent operation of Solar PV (Brouwer et al. 2016; Burger and Luke 2017) and the need to develop strategies for rational curtailment enforcement (IEA 2014; Jamal et al. 2017).

On the technical aspect, PV technology has already proven its capabilities towards a decarbonised energy system. Nowadays, technical studies and industrial efforts are focused on issues which will enable Solar PV to be more competitive in the energy market – against conventional generating technologies – leading to their wider deployment. Such issues, among other, may include: improving the energy efficiency of PV modules (Nelson, Gambhir, and Ekins-Daukes 2014; Ryan et al. 2016), developing standardised PV handling procedures to maximise efficient operation and lifespan (Munoz et al. 2011; Keating, Walker, and Ardani 2015), developing heat recovery techniques to protect the panels from increased operating temperatures (Siecker, Kusakana, and Numbi 2017), exploring technologies (potentially making use of the recovered heat) promoting synergies with cooling and heating applications (Testi, Schito, and Conti 2016; Al-Waeli et al. 2017), developing recycling procedures to reduce the life-cycle footprint of PV panels (Carnevale, Lombardi, and Zanchi 2014; Dusonchet and Telaretti 2015) etc.

This article considers relevant technology associations and platforms’ perspectives on seven (7) Research Priorities that merit further attention by the research community in order for Solar PV to be further developed and deployed. These insights are supplemented by an extensive academic review extracting more specific and up-to-date Research Needs for each Priority, as raised by scientific and ‘grey’ literature. The main goal is to identify and highlight Research Priorities in order to bridge the gap between market needs and industrial know-how, and scientific research inquiries. Finally, a number of implications for end-users involved in the field of policy and practice are suggested, to assist better-informed decisions and to shape directions for further development and deployment.

The rest of this paper is organised as follows: Section 2 presents an overview of the methodological approach used for the identification of the key Research Priorities and specific up-to-date Research Needs for CCMOs of interest. Section 3 presents the application of the methodological approach for the case of Solar PV. More specifically, Section 3.1 presents the key Research Priorities, for the case of Solar PV, as reflected in the positions papers, of relevant technology associations/platforms reviewed. These Research Priorities guided the scientific literature review, presented in Section 3.2, with the goal of acknowledging additional, specific and up-to-date Research Needs per Priority, raised by the scientific literature. Finally, Section 4 presents conclusions on the main lessons learned and suggests key Implications for Policy and Practice.

2. Methodological approach for identifying Research Priorities and Research Needs for CCMOs

Hundreds of literature reviews and feasibility studies are already available in the scientific literature tackling the subject of CCMO assessment, analysing demonstration programmes, and investigating industry pilots. In addition, technology associations and platforms regularly publish position papers explicitly expressing key market needs, successfully bridging practical lack of knowledge with key scientific research inquiries. Such position papers have been considered in the framework of the H2020 project CARISMA¹ to provide a good basis for prioritising future research on CCMOs of interest. Experts’ knowledge and concerns were also incorporated as a supplementary source of input.

Figure 1 visualises the methodological approach suggested for the identification of Research Priorities and Research Needs for CCMOs of interest.

Figure 1. Approach for the identification of Research Priorities and Research Needs for CCMOs of interest.

2.1. Step 1: identification of Research Priorities (RPs)

Step 1 builds on the stakeholder consultation process (i.e. round tables, surveys, open discussions, meetings-events, etc.) that takes place during the development of the respective associations’ positions papers. In this respect, the identification of Research Priorities incorporates knowledge, from a wide representation of market experts and relevant stakeholders, that has been recently synthesised and further communicated by the technology associations.

For the selection of the position papers the following criteria have been used:

1. Specialisation of technology associations/platforms in the CCMO of interest (mainly on a European level),

2. Legal status and overall activity/duration of the associations/platforms,

3. Associations/platforms’ members and network in Europe and worldwide,

4. A clear statement of the associations/platforms’ positions,

5. Publishing date,

6. Methodology used to support the positions expressed.

7. Reference list.

This analysis was supplemented with direct contacts with associations’ experts, to validate the outcomes of the position papers and receive additional feedback on key research challenges, extra insights and updates, through semi-structured questionnaires. This process highlighted recurrent knowledge gaps that were further distilled into key Research Priorities.

2.2. Step 2: identification of Research Needs per Priority (RPNs)

In the framework of Step 2, literature sources, covering one or more of the Research Priorities identified, went through review. Our aim was to perform a structured literature review process, composed of as many information-rich sources as possible. However, an exhaustive literature review was not our scope, instead, we aimed to cross-reference the key Research Priorities expressed by the technology associations, and to provide evidence of potentially additional, more specific and up-to-date Research Needs raised by the academic community. Thus, from the large number of topic-relevant search results, a randomised sample was chosen as input for our analysis.

The rationale on the literature review was hybrid, including existing knowledge from both scientific articles (i.e. papers in scientific journals, proceedings and book chapters) and ‘grey literature’ (i.e. technical/scientific reports, project deliverables, etc.). Τhe search results were limited to the period of 2000 till 2017, selecting studies from 2010 onwards. However, older studies were evaluated according to their relevance and impact and few of them were considered appropriate to be included.

2.3. Step 3: linking Research Priorities with key policy implications

This third Step provides the main lessons of the previous two steps, by synthesising findings in a way that: (i) shapes specific directions for future research to update experts in the field about the prerequisites of further development and deployment of the CCMO under study and (ii) encourages the design of new policy instruments or the revision of the existing ones, to support policymakers in making better informed decisions.

3. Application for the case of Solar PV

Solar PV is considered one of the key CCMOs for the transition towards a low-carbon energy system. Until a few years ago, research was focused on ways to reduce the technology’s cost and increase operational efficiency. Nowadays, the technological cost reduction is considered of secondary importance. The research challenges that are considered a first priority, to allow the technology to keep its exponential growth rate, are those that have emerged due to the large numbers of deployed systems.

The methodology presented in the previous section has been applied to extract such Research Priorities for the case of Solar PV, as expressed in position papers published by relevant technology associations/platforms and to validate if these Priorities are also reflected in recent studies in the scientific literature. Specific up-to-date Research Needs per Priority are also identified by the literature review, to bridge the gap between market/industry needs and scientific research inquiries.

3.1. Identification of Research Priorities for the case of Solar PV

The position papers identified and reviewed incorporate knowledge and viewpoints expressed by SolarPower Europe², Eurobat³ and EHPA⁴ and are listed below:

1. ‘Developing a Real Industrial Policy for PV in Europe’ (EPIA 2012),

2. ‘Solar and Storage’ (EUROBAT, EHPA, and SolarPower Europe 2016),

3. The SolarPower Europe’s official response to the public consultation on the Renewable Energy Directive (REFIT) evaluation, ‘Preparation of a new Renewable Energy Directive for the period after 2020’ (SolarPower Europe 2016).

To supplement our analysis direct contacts with SolarPower Europe were made, to validate on existing knowledge (as extracted from the review of the position papers above), or provide additional feedback on key Research Priorities.

The outcome of Step 1 of the methodological approach presented in Section 2 is Table 1, which outlines seven (7) key Research Priorities that merit further attention from the research community, in order for Solar PV to be further developed and deployed in the future:

Table 1. Seven Key research priorities for the case of Solar PV according to technology associations/platform.

Research priority (RP)	Why is the research priority required?	Section Number
RP1: Exploring new financing mechanisms and business models	Need to support the phase out of the Feed-in-Tariff scheme by balancing the costs incurred by public funded fiscal support, while ensuring that PV investments are attractive to producers/prosumers	3.2.1
RP2: Assessing the impact of intermittency	For the exploitation of the services that RES-E technologies can provide to the grid and the mitigation of the effects that their intermittency introduces	3.2.2
RP3: Assessing the impacts of curtailment	There is a need for the determination of the optimal trade-off between the costs passed on the producer and the costs for grid reinforcement	3.2.3
RP4: Investigating synergies with the heating/cooling sector	To exploit the potential and benefits of solar assisted heating/cooling applications – either stand-alone or combined with PV power generation systems	3.2.4
RP5: Evaluating the re-use of PV module material in the framework of a circular economy	Since the amount of installed PV system is rapidly growing, the safe disposal of modules is crucial in mitigating their environmental footprint	3.2.5
RP6: Improving PV modules’ energy efficiency	Improving the efficiency of PV will lead in shorter return of investment periods, will increase the system’s lifetime, and will also reduce the need for module recycling	3.2.6
RP7: Establishing quality criteria and standardisation for product development and testing	To ensure high PV quality and operational efficiency	3.2.7

3.2. Identification of Research Needs per Priority for the case of Solar PV

Applying Step 2 of the methodological approach, more than one hundred (100) literature studies went through review. Following the hybrid rationale described in the previous section, we reviewed both scientific publications and ‘grey literature’ to acquire combined knowledge from important scientific reports, such as the ‘High Penetration of PV in Local Distribution Grids’ or the ‘Technology Roadmap’ published by IEA (2014, 2011) or deliverables from EC funded projects, such as the ‘CHEETAH’ (2016), the ‘PV Financing’ (2016a, 2016b, 2016c, 2016d) and the ‘PV GRID’ (Barth et al. 2014) projects.

Figure 2 below presents an overview of the literature sources reviewed, across five (5) key dimensions of interest (i.e. Economic, Social, Environmental, Regulatory and Technological) for the case of Solar PV. Literature findings indicated a plethora of studies focusing on Economic and Technological dimensions, a fair amount of studies addressing the Environmental dimension of Solar PV, while highlighted a lack of studies for Regulatory and Social dimensions.

Figure 2. Dimensions under assessment in the ensemble of the literature studies reviewed.

The Research Priorities identified during Step 1 and presented in Table 1, are further analysed and discussed based on findings from recent scientific literature in the field. The scope of this analysis is to cross-reference these Research Priorities and identify any further Research Needs expressed by the scientific community, in order to bridge the knowledge gap between market and research. The sections below present a discussion for each Research Priority, with each one concluding with a number of more specific Research Needs, as identified from the literature review.

3.2.1. RP1: exploring new financing mechanisms and business models

Financing mechanisms supporting the deployment of PV differ globally, and to some extent even between EU Member States (Jäger-Waldau 2014). Since grid parity for PV electricity has been reached in certain markets, the main policy ambition is to sustain the growth rates of PV deployment, while moving away from the Feed-in-Tariff (FiT) scheme for renewables, including PV (Papadelis, Stavrakas, and Flamos 2016; Anagnostopoulos, Spyridaki, and Flamos 2017). The first step has already taken place in many EU Member States by introducing alternative financing schemes to support PV deployment. An overview of such support schemes applied in eight EU Member State is presented in Table 2. The criteria for the selection of the countries presented in this table were the information availability and the innovative financing schemes applied. For detailed information on the support schemes, the reader is directed to the European Commission’s ‘Guidance for the design of renewables support schemes’ (EC 2013), as well as the legal database for renewable energy, res-legal.eu (RES-Legal 2017).

Table 2. Financing schemes for PV applied in EU countries.

Country	Support Schemes
Austria	FiT, Subsidy, Loan, Leasing, Crowdfunding
Belgium	Net-metering, Subsidy, Green Certificates, Cooperatives
France	FiT, Premium tariff, Tax regulation mechanism, Loan, Crowdfunding, Cooperatives, Auctions
Germany	FiT, Premium tariff, Loan, Leasing, Crowdfunding, Cooperatives, Auctions
Greece	FiT, Premium tariff, Net-metering, Subsidy, Tax regulation mechanism, Auctions
Italy	FiT, Premium tariff, Net-metering, Loan, Tax regulation mechanism
Sweden	Subsidy, Tax regulation mechanism, Green certificates
UK	FiT, Loan, Tax regulation mechanism, Contracts for Difference, Green certificates, Cooperatives, Auctions

Sources: EC (2013), Dunlop and Roesch (2016), PV Financing (2016a, 2016b, 2016c, 2016d), Fowlie (2017), RES-Legal (2017)

Concerning recent developments, auction-based approaches to finance PV projects can perhaps be considered as one of the most widespread financing mechanisms with 48 countries worldwide having already adopted it and 27 more seriously considering it. With auctions, a national renewable energy capacity target is set, and an investment budget is determined. This budget is then allocated to those projects with the lower bid in terms of subsidy request (Fowlie 2017). With such an auction-based scheme, the cost of renewable electricity is significantly reduced, reaching record low levels for the first time after the FiT phase out efforts (Wehrmann 2017).

Focusing on the more innovative financing schemes, leasing allows a company to install a PV system on a customer’s rooftop, and the customer has to pay a monthly ‘rent’ to the installing company for a specific period of time (Dunlop and Roesch 2016). With leasing, the upfront costs of PV installations are not a barrier for customers (PV Dunlop and Roesch 2016; Financing 2016b). An even more innovative form of leasing is the sales and lease back scheme, which is very promising especially for the commercial sector. In this scheme, the PV owner sells the PV system to an investor in order to lease it back for use. That way the initial owner can use the capital in other innovative projects (Dunlop and Roesch 2016). Another promising form of PV financing is crowdfunding, in which many ‘small’ investors finance a PV project. Crowdfunding can be equity based, in which investors hold ownership shares of the system, in the form of financial grants, or combined with loans (Dunlop and Roesch 2016; PV Financing 2016b). Green cooperatives are a form of crowdfunding in which mainly companies sell shares of a project to ‘small investors’ who in turn receive revenue according to the shares they own (Dunlop and Roesch 2016). Finally, green certificates are tradeable assets which validate the amount of renewable energy produced. These assets are awarded to renewable energy producers, who in turn can sell them to supplying companies who have not reached their renewable obligation target (VREG 2017).

As highlighted in (Dusonchet and Telaretti 2015), the appropriate financing scheme, and the level of support for each financing scheme should be determined for each geographic region separately, to prevent situations of excessive revenues for PV owners in specific regions.

New business models which consider the bidirectional electricity flows in a distributed generation system and clearly define the revenue streams for utilities and new market agents (prosumers) are also needed. The scientific community has already investigated several innovative business models, with a focus on system ownership alternatives and revenue mechanisms. These are summarised in Table 3.

Table 3. New business models for PV deployment.

Implementation Scale	Model name	Description	Identified by
Consumer Scale (electricity parity)	Retail Model	The end-user has full ownership of the PV system, after purchasing it from a private company. For rural electrification, funding can be raised through public funds, multi/bi-lateral aid or the private banking sector.	(IEA 2011)
	Energy Service Model	The supplying company keeps ownership of the system and the end-user pays for the service provided. The capital for the company is raised from public/private sector, loans or equity investors.	(IEA 2011)
	Community Solar Model	Customers can purchase either part of a solar system’s output, or an equity stake or revenues from the plant. The company that owns the PV system gets return for the initial investment by charging the customers who want access to the PV’s output.	(Burger and Luke 2017)
Consumer Scale (Synergies with self-consumption)	Peer-to-Peer model	A platform enables producers and consumers to directly sell or buy electricity respectively from each other. A more complex alternative incorporates energy storage system owners to whom producers store their electricity, and from whom consumers buy the electricity they need.	(Parag and Sovacool 2016)
	Prosumer-to-grid model	Concerns local producers connected to a mini-grid, which in turn can either be connected to the main grid or operate autonomously in an island mode.	(Parag and Sovacool 2016)
	Organised prosumer groups	A combination of the previous two business models. The communities or local authorities can sum-up their ‘prosumption’ to generate a revenue stream for community benefit.	(EDF R&D 2015)

The incorporation of storage facilities in electricity systems is beneficial but also makes their management more complex. Based on this, it is important to note that the Peer-to-Peer model is beneficial in cases of excess generation and low demand. The role of the grid operator, in this case, is limited to distribution services, for which he is paid. Based on this concept, two pilot platforms, the Vandebron in the Netherlands and the Piclo in the UK, enable local direct electricity transactions. Concerning the Prosumer-to-grid model, incentives for electricity production exceeding the demand, exist only in the case that the mini-grid is interconnected with the main grid, enabling prosumers to sell back electricity. Otherwise, in an island mode situation, the excess generation that can be accommodated depends on the storage facilities’ (if any) size and the maturity of demand response (DR) services (Parag and Sovacool 2016).

According to the literature sources reviewed for this section, the following Research Needs should be the focus of new studies and initiatives, so that they bring the most added-value in terms of supporting further deployment of Solar PV:

• RP1N1: Alignment of policy measures with new, successful private financing initiatives.

• RP1N2: Analysis of the conditions and requirements for the replication of successful financing initiatives among EU countries.

• RP1N3: Development of business models that are fit for final consumers (residential and commercial) but also for those able to provide services to prosumers (aggregators, DR providers, and utilities).

3.2.2. RP2: assessing the impact of intermittency

The need for addressing the intermittency of RES technologies, has been the focus of both EU feasibility studies (EDF R&D 2015), and the scientific community (Huber, Dimkova, and Hamacher 2014; Lingfors 2015; Brouwer et al. 2016). There is consensus that innovations in demand-side integration, energy storage and smart grid infrastructure will act as enablers for the diffusion of intermitted RES technologies. Specifically:

• Literature suggests that DR and energy management systems (EMS) are capable to mitigate the electricity fluctuation problems observed during the operation of intermittent RES technologies. Relevant technical requirements include advanced converters, energy storage and solutions that enhance and utilise demand-side flexibility (Azzopardi and Gabriel-Buenaventura 2014; Khoury et al. 2016; Burger and Luke 2017).

• Electricity fluctuation problems can be reduced by investigating an optimal renewable electricity mix (mainly PV and wind). By reducing the fluctuation problems, such a mix serves in a stabilising manner while reducing the variation handling necessities (Graabak and Korpås 2016).

• Aggregation of small PV systems can mitigate part of the intermittency issues (CARISMA 2016).

• RES-E production uncertainty can be mitigated with improved meteorological forecast models.

In addition, synergies between PV and Pluggable Electric Vehicles (PEV) have been explored. A potential model has been proposed in the PROSUITE project. The main idea is to charge PEV batteries from the network before departure, and to sell any unused energy back when returning (PROSUITE 2010). The advantages of such a model are the reduced energy losses observed in stationary situations, the reduced electricity demand peaks and the balancing effects on the grid since batteries will act as electricity reserve during then night. A challenge that arises from such a model is the prediction for increased electricity and battery prices due to increased demand, in combination with the slow price decrease rate characterising storage technologies. Considering that even today conventional vehicles are cheaper that electric ones, such a case would not attract consumer interest.

The specific Research Needs that have emerged from the literature review on addressing RES-E intermittency are:

• RP2N1: Re-examination of the energy market’s regulatory framework to account for the intermittent nature of RES operation, with a focus on establishing free, fair, and open markets characterised by a level playing field between different generation technologies.

• RP2N2: Investigation of an RES-based electricity mix which will produce minimum intermittency effects during the operation of the network.

• RP2N3: Improving the technology options and the regulatory framework for the aggregation of small PV systems, aiming to reduce individual PV market-access costs.

• RP2N4: Research on the potential and limits of energy storage, demand side management and ancillary services to act as Renewable Energy Source (RES) variability stabilisers, before powering up thermal plants.

• RP2N5: Research and Development (R&D) on new and advanced meteorological forecast models to increase the accuracy of RES electricity generation projections.

• RP2N6: Investigation of the balancing effects that car batteries may have on the grid (by feeding electricity during stationary situations) and how power flows can be managed with Information and Communication Technology (ICT).

• RP2N7: Construction of a clear hierarchy of functions (including the bidding procedure, forecast tool requirements etc.) among generators and Distribution/Transmission System Operators (DSOs/TSOs) enabling them to overcome the variability limitations, while ensuring the elimination of conflicting interests between parties.

3.2.3. RP3: assessing the impacts of curtailment

As stated in the European directive 2009/28/EC, to the extent that safe operation of the grid is not compromised, all RES generation is by priority injected to the network. When predictions show that the safety limits are going to pe surpassed, certain systems are obliged to contribute with less generation than their nominal capacity – a situation known as active power curtailment (INSIGHT_ENERGY 2017). Curtailment is a proven method that helps avoid costly network upgrades which would be mandatory if excess RES generation was injected (IEA 2011), but should be the last option when network balancing is needed because it also incurs financial burdens for PV generators (Jamal et al. 2017).

A curtailment case study, with high aggregated PV capacity (3 kWp/house), for the Austrian region, has been performed by IEA. The case study considers curtailment application to certain systems so that the system voltage remains below safety limits. In terms of electricity generation, despite the fact that more than 7% loss was observed for each curtailed system, the aggregated electricity loss accounted for only 0.8%. When translated to revenue loss (considering the current Austrian FiT), this is equal to about 23 €/year/system or only 4% revenue loss (IEA 2014).

The level of curtailment applied should consider and balance the electricity loss costs entailing the prosumer and the benefits from the reduced requirements for network upgrades. An assessment by the German Energy Agency, underlines the possibility to reduce network upgrade costs by 30% until 2030 and reduce the needs for capacity reserves provision (due to RES generation forecast errors), if RES generation is curtailed by 30% (INSIGHT_ENERGY 2017).

An important decision criterion to consider before the application of curtailment is the trade-off between the compensation of the PV owner and the costs for network upgrade. According to the PV Grid project, curtailment should be chosen only if the amount of compensation is lower than network upgrade costs (Barth et al. 2014). Kane and Ault (2014) present an analytical plethora of curtailment schemes. Finally, IEA’s assessment for the application of curtailment on Belgian low-voltage systems, reveals a network capacity upgrade up to 50% with only 10% of the network costs without the application of curtailment (IEA 2014).

The specific Research Needs here have been codified as follows:

• RP3N1: Exploring policy schemes capable of balancing the socio-economic effects and costs of curtailment.

• RP3N2: Research on combined curtailment application and flexibility options integration (storage, demand side management, etc.), for better network optimisation with a parallel RES integration capacity increase.

• RP3N3: Curtailment studies determining the national cost–benefit ratios, the boundary conditions and the prosumer compensation rules, aiming to reduce network upgrade costs.

• RP3N4: Evaluating RES-E curtailment on the distribution level.

• RP3N5: Developing inverters with integrated communication capabilities. Local control communication systems are not required for the time being, but they are a useful investment for future network upgrades.

3.2.4. RP4: investigating synergies with the heating/cooling sector

Solar PV, apart from generating electricity, has the potential to offer significant services to the cooling and heating sector as well (see Figure 3). The most well-known and widely used application is solar water heaters, mainly used for providing hot water for domestic use, while many studies have focused on potential synergies of Solar PV with space heating/cooling applications (Papadopoulos, Oxizidis, and Kyriakis 2003; MERE-SL 2011; Nelson, Gambhir, and Ekins-Daukes 2014). Reportedly, annual air-conditioning (A/C) consumption reductions ranging between 30-50% have been reported, with low requirements for direct sunlight and heat recovery capability from the condenser (MERE-SL 2011). An analytical study has been conducted by Testi et al. who explore the life-cycle, cost-optimal sizing of Solar PV installations, combined with a thermal storage unit in a farm hostel in Sicily. Results show that with their proposed set-up, the life-cycle cost reduction was about 11% and the respective energy savings about 67% (Testi, Schito, and Conti 2016).

Figure 3. Synergies with the cooling/heating sector.

Solar PV efficiency, degradation rate and lifetime are affected by heat levels. As such, methods incorporating water or air to remove the excess heat in order to maintain stable surface temperature, while utilising the excess heat in other applications, ranging from sanitary purposes to water desalination and drying, have drawn scientific interest (Mahmoud 2003; NEMA-K 2013; Al-Waeli et al. 2017; Siecker, Kusakana, and Numbi 2017; Xu et al. 2017).

Detailed technoeconomic assessments of waste-heat recovery, hybrid energy systems can be found in Nižetić et al. (2017) who investigate the capability of those to cover multiple residential energy needs. The technologies proposed include the modification of existing Solar PV and air-conditioning systems, making them capable of simultaneously generating electricity, powering-up an A/C and preparing hot water. It is worth mentioning that only 10% reduction in the electricity generation is observed from the modifications, and the modifications’ cost is relatively low compared to the installation costs.

The factors influencing the efficiency of solar assisted heating and cooling applications among others include the collector’s tilt angle, the spatial configuration, the total irradiation collecting area, the evaporator mass flow rate, the thermal storage tank (if any) etc. Agrouaz et al. (2017) underline the necessity for research focused on determining the optimal values of those factors.

Based on the above-mentioned studies, the following Research Needs have been narrowed down and specified:

• RP4N1: R&D efforts to increase the competitiveness of solar assisted applications against conventional ones, including performance enhancements (i.e. improvement of chillers’ coefficient of performance (COP)), technological innovations (i.e. thermal storage tanks integration, evaporator flow control depending on the weather condition), and set-up parameters’ optimisation (i.e. collector configuration and area).

• RP4N2: Carbon footprint evaluation using Life-Cycle Assessments (LCA) considering Solar PV and heating/cooling devices as a single unit.

• RP4N3: Research on technological advancements enabling efficient heat removal from the PV surface and its direct use for heating applications.

• RP4N4: Research on minimising the generation losses in hybrid systems incorporating fluid circulating pumps.

3.2.5. RP5: evaluating the re-use of PV module material in the framework of a circular economy

Many studies (Varun and Prakash 2009; Sumper et al. 2011; Peng, Lu, and Yang 2013; Ling-Chin, Heidrich, and Roskilly 2016) conduct LCAs focusing on the Energy Payback Time and CO₂ payback time. The classic LCA methodology, considers all the life stages of a system, ranging from raw material acquisition to final disassembly and disposal, with variable analysis depth according to each study’s scope. Nevertheless, very few studies performing LCAs for Solar PV have included the end-of-life phase in their calculations, because PV is a relatively young technology with more than 20 years lifespan, thus calculating the end-of-life’s environmental consequences was considered to be of secondary importance. However, with the exponentially increasing number of PV installations, a great amount of systems will need to be properly disposed in the following years, so final disposal and recycling should be incorporated in future LCA methodologies.

One of the few studies considering this phase in the Energy Payback Time and CO₂ payback time calculations is performed by Carnevale et al. (Carnevale, Lombardi, and Zanchi 2014). Their findings underline that although system disassembly and material recycling are energy consuming processes that cause emissions to the atmosphere, the benefits from using recycled materials instead of acquiring raw ones greatly overcome the recycling emissions impact.

A prediction of about 40,000 tons of PV waste volume by 2020, and the consideration that existing recycling technologies can salvage more than 90% of a PV system’s materials, reveals both the economic and environmental implications of the end-of-life management. Two existing recycling processes, the Deutsche Solar process for crystalline silicon (c-Si) modules and the First Solar process for thin-film cells, have reported recovery rates reaching up to 95% for semiconductor material and 90% for glass. Further reduction of the environmental footprint of PV could be achieved with the clear determination of recycling procedures for other PV components, such as cables and inverters. Towards that direction financial risks have to be addressed, so that recycling costs remain viable for enterprises (Solar Bankability 2016a).

Furthermore, distributed generation projections for the following years showcase that a large number of storage systems will be deployed and will, at some time, need recycling. Tesla underlines that recycling of the metals contained in Lithium-ion storage technologies can help mitigate at least 70% of their environmental footprint. Several recycling processes for various types of batteries have been prepared but are still at an early stage (Solar Bankability 2016a).

Regarding the PV recycling regulatory framework in the EU region, according to the Waste Electronics and Electrical Equipment (WEEE) Directive, every firm or individual trading or importing PV modules is also responsible for the safe disposal and recycling of those reaching the end-of-life phase (Solar Bankability 2016a). For instance, in Italy only enterprises who are members of an EU recycling organisation are qualified PV producers (Dusonchet and Telaretti 2015). It is worth mentioning that a manufacturer-independent recycling system has been set up in June 2010, with more than 300 active members (IEA 2011).

Finally, carbon footprint mitigation for PV systems and re-use of PV materials can also be realised through the process of PV repowering. As PV systems age, degradation and deviation from the nominal capacity is observed, often leading to shorter lifespan than that of the original design (Balfour 2017; Sun & Wind Energy 2017). In addition, physical phenomena or wrong component specifications for certain geographical areas, may cause damage or early failures to systems (Balfour 2017). Repowering of existing PV systems is the replacement of faulty, unsuitable or degraded modules and components with new, more powerful, in order to restore or boost their nominal operating values and extend their original design lifespan (Sun & Wind Energy 2017). In the framework of a circular economy, the components that are removed during the repowering can be sold for second hand use. Potential second hand cases can be found in the online photovoltaic marketplace SecondSol (2018). PV repowering reveals great financial and environmental advantages, given that a detailed cost–benefit analysis for the repowering procedure has been performed (Fishman 2016).

The relevant Research Needs identified regarding re-use of PV module material are:

• RP5N1: Developing a common methodology according to the Product Environmental Footprint Category Rules (PEFCR) to perform LCAs based on re-use of material.

• RP5N2: Expansion of LCAs to account for global scale challenges, geographical differentiations, rebound effects, renewability of resources, and future scenario modelling.

• RP5N3: Inclusion of module components’ recycling (cables, inverters, etc.) in LCAs to depict their significant contribution in reducing greenhouse gas emissions.

3.2.6. RP6: improving PV modules’ energy efficiency

As pointed out by Alsema and Nieuwlaar (2000), the energy balance of PV has to be improved, in order to promote the technology as a significant CCMO. Such improvements include (a) reduction of the manufacturing energy consumption, (b) increased module efficiency, and (c) longer system lifetime. Estimations regarding the energy efficiency improvements reckon an increase up to 39% in the energy yield until 2030, as compared to the values of 2017 (Ryan et al. 2016).

R&D efforts since a long time ago have been made towards reducing the manufacturing costs of PV (e.g. production of thinner wafers, development of more efficient wafer production techniques, use of recycled aluminium for the PV’s frame) and improving energy efficiency (e.g. better silicon purification techniques, improved system design) (Alsema and Nieuwlaar 2000). Current trends, indicate that the majority of PV cells are manufactured either from c-Si or thin film, while continuous research is being made towards new, more efficient and less costly technologies (IPCC 2012; Traverso et al. 2012; Tyagi et al. 2013).

c-Si technologies utilise mono crystalline, multi crystalline and ribbon c-Si cells, with mono crystalline being the most predominant, multi crystalline increasing their market share and ribbon c-Si having only 5% market share. Thin-film cadmium tellurium (CdTe) modules have increased their market share from 2–13% in the period 2005–2010 (IPCC 2012; Traverso et al. 2012).

Regarding the efficiency rates, large generation plants (≥100 MW), which use various types of modules, were measured in the Gobi Desert with the following results: 12.8% and 15.8% efficiency for multi crystalline (type a and type b, respectively), 6.9% for amorphous silicon (a-Si), 9% for CdTe and 11% for copper indium selenium (CIS) (Varun and Prakash 2009). More recently, average efficiencies reaching up to 16% for silicon, 21% for back-junction and interdigitated back-contact (IBC), 19% for heterojunction (HTJ), 15% for CdTe thin film (IPCC 2012), and 10% for double-junction and triple-junction thin film a-Si modules (Xu et al. 2017) were recorded.

Alternative materials capable of increasing efficiencies while reducing production costs are also being explored. Such materials include iron pyrite (FeS₂), zinc phosphide (Zn₃P₂), copper indium gallium selenide (CIGS), and CdTe with the most attractive in both cost and availability being FeS₂. It is worth to mention that despite the fact that CIGS and CdTe can achieve significant production costs reduction, relatively to silicon, they are not a safe option for mass production because large quantities cannot be guaranteed. Other, more innovative materials and techniques that are being investigated include: nano-composites and organics which require less material and manufacturing costs, but achieve lower efficiencies; nanowires as lithium-ion anodes (capable of storing 10 times more charge than conventional graphite anodes); and direct liquid-coating methods to substitute vacuum deposition (PROSUITE 2010). Less mature and still expensive solutions are dye-sensitised photochemical solar cells, hot carrier devices, conducting polymer cells, plasmonic solar cells, quantum solar cells, modular organic solar cells, and thermoelectric devices. For specific installations (e.g. skyscraper facades) a low-cost module, the ‘Solar electricity glass’ (Si-pin), may also become commercially available. Efficiencies up to 11% and 12% have been achieved for organic cells and dye-sensitised cells respectively by Mitsubishi Chemical and Sharp (IPCC 2012).

Neij’s estimation attributes the future cost reduction of modules to less use of silicon (8%), to efficiency increase (17%), to a yield increase from 85–95% (4%) and to an economy of scale increasing production volume from 10 to 1000 MWp/year (25%). Variations of these percentages are also mentioned due to material availability uncertainty. On the thin-film technology, 18% efficiency rate is estimated until 2030, with the potential to combine the high efficiencies of silicon with the low material requirements of thin film (Neij 2008).

Originally, thin film technology was introduced as a low-cost (yet less-efficient) substitute of c-Si, since it requires less semiconductor material and less processing stages (it can be directly deposited on glass, plastic or metal foil). However, the increased light absorption capability of thin film modules and the capability of CdTe thin film to operate efficiently both under high solar irradiations and cloudy conditions proved them more efficient than c-Si modules. The absorption of different sunlight wavelengths, and the consequent high operational efficiency, has also been achieved by multijunction (multiple semiconductors layers) solar cells. Under laboratory conditions recorded efficiencies reach up to 44% and 32% in actual installations. The major drawback of this technology is the requirement for direct sunlight to achieve these efficiencies. (Nelson, Gambhir, and Ekins-Daukes 2014). The technology that uses mirrors to concentrate sunlight in small, high-performance multijunction cells is called Concentrator PV (CPV). According to the European Commission CPV is an emerging, highly efficient technology, categorised as high concentration (>300 suns) and low/medium concentration systems (2–300 suns) (Jäger-Waldau 2014). Under high direct normal irradiation, these systems can achieve high efficiencies with smaller system costs due to the small photovoltaic array required. Low concentration, tree-junction CPV have achieved efficiencies up to 38.8%, high concentration, tree-junction CPV up to 44.4% and four/five-junction cells up to 44.7% (IPCC 2012).

Finally, R&D efforts are focused on alternative manufacturing techniques which will enable the production of ultra-thin and epitaxial wafer cells, capable of significantly reducing production costs. Ultra-thin wafers manufacturing processes can achieve 80 μm thickness without the problems observed in wire-sawn wafer manufacturing processes, (i.e. wafer breakage or cell processing). However, in order to reach that target from the current commercial wafers’ thickness (160–180 μm) an industrial predevelopment target of 120 μm thickness (thin-cut wafers) has been set-up. Epi-wafer manufacturing processes can achieve 40 μm thickness, with direct chemical vapour deposition. This process avoids the kerf losses related to wire-sawing, and accelerates the manufacturing process since polysilicon formation, ingot formation, and wafering are not needed. Both technologies can significantly reduce material usage, energy consumption, and requirements in consumables during the crystallisation and wafer processing. The cost reduction assessment, relatively to current commercial wafers, is calculated to be 68.9% for epi-foil wafers, 15.8% for ultra-thin wafers, and 16.1% for thin-cut wafers. The CHEETAH project suggests that future R&D efforts should focus on the reduction of wafer handling and cell processing procedures costs (CHEETAH 2016).

Figure 4 presents the currently used or studied module materials and the module technologies/system designs encountered during the literature review, both aiming to increase efficiencies and reduce costs.

Figure 4. Overview of materials used and module technology development aiming in increasing the efficiency of PV modules.

The relevant Research Needs identified are:

• RP6N1: New material development to increase system lifetime and reduce operation and maintenance (O&M) costs.

• RP6N2: Optimising cell manufacturing and wafer handling processes to reduce product defects, and consequently further reduce costs and increase module efficiencies.

• RP6N3: Continuous research on manufacturing techniques and module technologies which require less material (i.e. thinner wafers), have high efficiencies and low production cost.

3.2.7. RP7: establishing quality criteria and standardisation for product development and testing

Mishandling or machinery errors are factors that may cause damage to PV components during the production process. Damage can also be observed during system transportation and installation. For these reasons technical manufacturing inspections (to identify and repair faulty parts), pre-delivery and on-site inspections are considered key parameters for the optimal operation and guaranteed lifespan of PV systems.

As such, thorough periodic inspections, conducted by testing institutes, have been made mandatory for PV factories. The process aims to assure high-quality, certified products, and eliminate the potential negative impacts that production steps have on the final product and consists of three steps: (a) raw material verification, (b) production line inspection, and (c) review of quality issues (Solar Bankability 2016a, 2016b). During the first part, invoices or delivery notes are reviewed to verify the use of proper materials. Random checks for consistent material use are also performed to recently manufactured systems. The second step inspects whether all the quality controls, both on- and off- production line, are performed and verifies the products’ compliance with the standards. Finally, during the third step, quality relevant documentation (i.e. ISO certificates, quality manuals, error traceability techniques, faulty part handling, etc.) is reviewed and where necessary demonstrated. TÜV Rheinland has prepared an inventory of factory deviations and recommendations that may be encountered during the inspection. Deviations require immediate actions, which if not made, result in certification loss for the PV manufacturer. Recommendations, on the other hand, are not linked to the factory’s certification, but their application is encouraged to improve the final products’ quality (Solar Bankability 2016a, 2016b).

Specific module qualification tests have also been developed and included in the IEC61215 and IEC61646 standards. These are performed on random samples (usually eight modules large) before entering the market to test their compliance to standards. A produced batch is IEC approved if none of the following occurs in the test sample: (a) output power descent exceeds the test limit or the 8% threshold after each test sequence, (b) open circuits are observed, (c) visual identification of defects, (d) poor insulation, (e) observation of current wet leakage (f) failure in specific test requirements (Munoz et al. 2011; Sharma and Chandel 2013).

As mentioned above, standards during the transportation and installation phases should be kept as well. During the transportation phase, certified logistics routines should be followed to ensure the sound delivery of systems. On delivery, visual inspection is considered important to ensure there are no damaged modules and no degradation has affected the modules since the date of manufacturing. The installation standards refer to a certified installer who will assemble the system and will provide ‘as-built’ documents to the system owner. The ‘as-built’ documents verify the installation of the system according to the system’s original design and guarantee its proper maintenance. A certified installer is held responsible for any damage may occur during the installation (Solar Bankability 2016a).

Finally, despite the fact that Solar PV have fewer maintenance requirements relatively to other technologies, proper maintenance has to be carried out in order to maintain the designed efficiency and lifespan of the system. Responsibilities concern both the system owner and an O&M expert (usually the Engineering Procurement and Construction (EPC) contractors). The owner’s responsibilities are limited to periodic visual inspections for potential damages, and maintaining the PV’s surface clean from dirt or snow. The maintenance work performed by the O&M expert is based on the instructions given by the manufacturer and the maintenance guidelines included in the installation manual and range from thorough degradation inspections, to extensive checks of the electrical and electronic components (Solar Bankability 2016a). The ‘Best Practices in PV System Operations and Maintenance’ published by the Solar Access to Public Capital (SAPC) Working Group presents an analytical overview of the standard O&M practices for PV systems (Keating, Walker, and Ardani 2015).

In conclusion, it should be noted that until now O&M practices were omitted by the PV manufacturer because they were considered an unwanted financial burden. However, the specification of detailed O&M strategies in the original system design, facilitates the early identification of defects, reduces the need for costly interventions and drives O&M costs down via knowledge building for the part of the manufacturer. That way the costs entailing the producer and those entailing the system owner are balanced.

The relevant Research Needs identified here are:

• RP7N1: Standardisation of tests and quality standards through the entire value chain of PV (O&M included) to ensure long lifetime and high performance of systems.

• RP7N2: Standardisation of inspection techniques, downtimes, and O&M operations intervals to minimise maintenance power losses.

• RP7N3: Integration of data collection mechanisms tracking PV operation, to reduce the need for visual inspections and costly O&M interventions.

4. Conclusions and implications for policy and practice

Solar PV has been proven to be one of the key technologies of electricity generation from renewable sources (RES-E) and is widely believed that new business models for sustainable development, followed by novel investment frameworks, centred around industrial growth and employment generation can arise from their further development and deployment, assisting global efforts for transition towards a low-carbon energy system. Until a few years ago, research was focused on ways to reduce the technology’s cost and increase operational efficiency. Nowadays, the technological cost reduction is considered of secondary importance. The research challenges that are considered a first priority, to allow the technology to keep its exponential growth rate, are those that have emerged due to the large numbers of deployed systems. Our study highlighted key Research Priorities and more specific and up-to-date Research Needs for the case of Solar PV, combining technology associations/platforms’ perspectives, with cumulative knowledge in the scientific literature, in order to bridge the gap between market needs and industrial know-how, and scientific research inquiries. The main insights on Research Priorities and Research Needs, along with key Policy Implications suggested for each Priority, are summarised below:

I. Novel support schemes and business models

There is a general effort to move away from feed-in tariffs while maintaining the growth rates of PV applications. Several alternative subsidy-free, financing schemes, to support PV deployment are starting to appear and new business models which consider the bidirectional electricity flows in a distributed generation system and clearly define the revenue streams for utilities and new market agents (prosumers) are being investigated. These also include self-consumption models, which allow direct local electricity transactions. New policies supporting this new era’s business and energy trends should ensure a fair, free of retroactive measures business environment while initiating and promoting private funding mechanisms. Policymakers examining the market designs which will enable the adoption of novel energy services, in a manner acceptable for consumers, need to investigate the national requirements to replicate successfully implemented financing initiatives and business models in other countries. The policy design process should also focus on promoting self-consumption, with the development of business models fit for both final consumers and energy service providers.

II. The issue of RES variability

The intermittent operation of RES-E technologies inserts certain limitations concerning the system’s stability and requires balancing actions to ensure the safe operation of the electricity network. With a large number of PV systems predicted to enter the energy market until 2030 beyond, policymakers will have to re-examine the energy market’s regulatory framework to account for the intermittent nature of RES operation. The new markets have to be free, open and fair in terms of competition for RES generating technologies, after determining a national RES-based electricity mix which minimises the intermittency effects on the grid. Towards addressing the high variability of RES options, R&D initiatives should also be promoted regarding the methods for integrating energy storage technologies (including PEV batteries), demand side management and ancillary services in the new energy market. In parallel, a relevant policy framework making use of those in combination with advanced meteorological forecast models and ICT should be in place. This framework should be set up under the close cooperation and open discussions between DSOs, TSOs, and generators to ensure that no conflicting interests between parties exist, which may lead in unwanted retroactive policy changes.

III. Assessing the impacts of curtailment

Curtailment is a proven method that helps maintain the safety limits of the electricity network and avoid costly network upgrades which would be mandatory if excess RES generation was injected, however, should be the last option when network balancing is needed because it also incurs financial burdens for PV generators. As such, there is a need to explore policy schemes capable of balancing the socio-economic effects of curtailment with the network expansion costs burdening the grid operator. Such policy schemes should be considering curtailment in combination with flexibility options (storage, demand side management, flywheels etc.), for better network optimisation, with minimum curtailment need and a parallel RES integration capacity increase. On a national level, curtailment-related studies should consider the national cost–benefit ratios, the boundary conditions and the prosumer compensation rules, aiming to reduce network upgrade costs. The examples of other countries on the compensation levels and schemes could be a useful source of input for policymakers. Finally, RES curtailment on distribution level is still missing. In a distributed generation regime curtailment studies on distribution level should be promoted with parallel technological R&D investments in novel network components (i.e. inverters with integrated communication capabilities).

IV. The synergies of PVs with the cooling/heating sector

Solar PV, apart from generating electricity, has the potential to offer significant services to the cooling and heating sector as well, making solar assisted cooling/heating applications a significant CCMO. Many studies until now have performed environmental and economic evaluations of solar assisted systems, stating that the main challenge is to make them more efficient and competitive than conventional systems. As such, R&D efforts should be promoted and incentivised on technical topics including performance enhancements, technological innovations, heat removal techniques and electricity generation loss minimisation on hybrid systems. Investigating LCAs considering Solar PV and heating/cooling devices as a single unit would give a better overview of their environmental and financial benefits.

V. The re-use of PV module material in the framework of a circular economy

To date, very few studies performing LCAs for Solar PV have included the end-of-life phase in their calculations. However, with the exponentially increasing number of PV installations, a great amount of systems will need to be properly disposed in the following years, so final disposal and recycling should be incorporated in future LCA methodologies. A such a common methodology according to the PEFCR, to perform LCAs based on re-use of material should be developed. LCAs should also be expanded to account for module components’ recycling (apart from modules themselves), global scale challenges, geographical differentiations, rebound effects, renewability of resources and future scenario modelling. On the policy side, standardisation of the recycling procedures should be accelerated to ensure the safe disposal of PV system components. Furthermore, frameworks and directives like the WEEE (2012/19/EU) holding specific market entities responsible for the recycling of PV systems should be further standardised.

VI. The subjects of material use and module efficiency

R&D efforts since a long time ago have been made towards reducing the manufacturing costs of PV and improving energy efficiency of modules. To achieve those targets, efforts were made towards both the use of materials with better operational efficiencies and the use of less material. Nowadays, Solar PV has reached a satisfactory level of maturity, thus material studies should be made with regard of other aspects as well. More specifically, new material development should be aiming to increase system lifetime with reduced needs for O&M. Furthermore, considering the low availability of certain materials and the environmental impact of raw material acquisition, research relevant to manufacturing techniques and module technologies which require less material, increase efficiencies and reduce production costs should be strengthened. Finally, the cell manufacturing and wafer handling processes should be optimised and standardised to ensure certified products, with long lifespan and reduced costly O&M interventions.

VII. The need for quality criteria and standardisation for product development and testing

To the best of our knowledge, few studies in the scientific literature have focused on assessments relevant to the quality standardisation of PV systems. Damage in PV components can be caused both in factory space and during transportation and installation. Standardisation of the necessary tests and quality standards through the entire value chain of PV, including O&M practices, can help ensure long lifetime and high performance of PV systems and thus should be regulatorily promoted. The O&M practices should be prescribed in a way that balance the costs between the O&M contactor and the PV owner, so that none of them in burdened with excessive costs. Towards that direction a clear specification of the inspection techniques, downtimes and O&M operations intervals is required, to minimise maintenance power losses for the PV owner and also increase the original financial planning flexibility for the manufacturer. The O&M contractor should also be held responsible for any deviation from the predefined practices and the consequent operational losses/system damages. A quality certificate system to help supervise the quality compliance along the whole value chain of PV is considered a good measure. Finally, on the grounds that reduced O&M costs are desired from both manufacturers and owners, the integration of ICT on PV systems should be investigated in terms of data collection mechanisms, which reduce the need for on-site inspections and help to the early identification of deviations from the nominal operational specifications.

Acknowledgements

The authors would like to acknowledge the support from the EC. The authors would also like to thank the reviewers of this article, who provided useful comments and helped to significantly improve it. The content of the paper is the sole responsibility of its authors and does not necessary reflect the views of the EC.

Disclosure statement

No potential conflict of interest was reported by the author(s).

ORCID

Serafeim Michas http://orcid.org/0000-0002-9391-7429

Vassilis Stavrakas http://orcid.org/0000-0003-1073-4561

Niki-Artemis Spyridaki http://orcid.org/0000-0001-7628-196X

Alexandros Flamos http://orcid.org/0000-0001-9279-9638

Additional information

Funding

This paper is based on research conducted within the EC funded Horizon 2020 Framework Programme for Research and Innovation (EU H2020) Project titled ‘Coordination and Assessment of Research and Innovation in Support of Climate Mitigation Actions’ (CARISMA) [grant number 642242].

Notes

1 Coordination and Assessment of Research and Innovation in Support of Climate Mitigation Actions, http://carisma-project.eu/.

2 SolarPower Europe, the new EPIA (European Photovoltaic Industry Association), is a member-led association representing organisations active along the whole value chain and aiming to shape the regulatory environment and to enhance business opportunities for solar power in Europe.

3 EUROBAT is the association for the European manufacturers of automotive, industrial and energy storage batteries. EUROBAT has 52 members from across the continent comprising more than 90% of the automotive and industrial battery industry in Europe.

4 The European Heat Pump Association (EHPA) represents the majority of the European heat pump industry. Its members comprise of heat pump and component manufacturers, research institutes, universities, testing labs and energy agencies. Its key goal is to promote awareness and proper deployment of heat pump technology in the European market for residential, commercial and industrial applications.