Solar-Reports:

Research Agenda provides a Vision
for European Photovoltaic Solar Energy Technology

The European Photovoltaic Technology Platform in June 2007 published a Strategic Research Agenda (SRA) for Photovoltaic Technology. The document shall serve as a reference on short, medium and long term research priorities for Europe in order to consolidate Europe's leadership in photovoltaics on a global level.

The SRA is giving a clear message: photovoltaic solar electricity will be competitive with conventional electricity in Southern Europe by 2015 - and in most of Europe by 2020. Competitiveness due to the EU Photovoltaic Technology Platform (EU-PVTP) will be reached by strong market developments - if appropriate market support mechanisms are in place in as many countries of Europe as possible. Under adequate conditions the European Photovoltaic Technology Platform expects a growth of market until 2010 over 80 % in average per year. In addition Public programmes on short, medium and long term research are to be adopted combined with a doubling of R&D budgets in order to reach the SRA goals.

Quality Control of CIS-Modules at Würth Solar(Germany).
Picture: Quality Control of CIS-Modules at Würth Solar (Germany). Source: Würth Solar

The Solar Report 11/2007, based on the SRA, highlights the agenda aiming to contribute to the rapid development of a world-class cost competitive European Photovoltaic for a sustainable electricity production and it outlines different approaches: traditional technologies as well as emerging technologies.

The SRA was prepared by the Science, Technology and Applications Group of the EU PV Technology Platform, based on thorough consultations with representatives of research, industry and other stakeholders. The members of the Working Group are experts in PV technology working as senior researchers in the public and private sector.

 

A Strategic Research Agenda (SRA) for Photovoltaic Solar Energy Technology

Forschungs-Fahrplan für die Photovoltaik in Europa bis 2030.

Focus on development of PV systems
and reduction of turn-key system prices

The direct conversion of sunlight into electricity is a very elegant process to generate environmentally friendly, renewable energy. This branch of science is known as "photovoltaics" or "PV". PV technology is modular, operates silently and is therefore suited to a broad range of applications and can contribute substantially to future energy needs. Although reliable PV systems are commercially available and widely deployed, further development of PV technology is crucial to enable PV to become a major source of electricity, the EU PV Technology Platform emphasizes. The current price of PV systems is low enough for PV electricity to compete with the price of peak power in grid-connected applications and with alternatives like diesel generators in stand-alone applications, but cannot yet rival consumer or wholesale electricity prices.

Thus a drastic further reduction of turn-key system prices is needed and fortunately possible. This was already emphasised in the document "A Vision for Photovoltaic Technology", published by the Photovoltaic Technology Research Advisory Council (PV TRAC) in 2005. Further development is also required to enable the European PV industry to maintain and strengthen its position on the global market, which is highly competitive and characterised by rapid innovation.

The table below summarises the key targets contained in the SRA. The figures are rounded and indicative.

The table summarises the key targets contained in the SRA. The figures are rounded and indicative.
"Flat plate" refers to standard modules for use under natural sunlight, "concentrator" refers to systems that concentrate sunlight (and, by necessity, track the sun across the sky).

Prices for turn-key systems in 2015 between two and four Euro/Wp

Current turn-key PV system prices vary from ~4 to ~8 €/Wp, depending on system type (roof-top retro-fit, building-integrated, ground-based,...), size, country and other factors. The figure of 5 €/Wp, however, is considered representative by EU-PVTP. Similarly, prices in 2015 may range between ~2 and ~4 €/Wp. The conversion from turn-key system price to generation costs requires several assumptions. This SRA assumes first ?an average performance ratio of 75 %, i.e. a system yield of 750 kWh/kWp/yr at an insolation level of 1000 kWh/m2/yr. In southern Europe, where insolation is typically 1700 kWh/m2/yr, a performance ratio of 75 % translates into 1275 kWh/kWp/yr. Second ?1 % of the system’s price will be spent each year on operation & maintenance and third ?the system’s economic value depreciates to zero after 25 years.

Solar PV plant in Spain.
Solar PV plant in Spain: Grid Parity possible in most of Europe by 2020. Source: Corporación Energķaj

Grid Parity for most of Europe by 2020


The overall aim of short-term research is for the price of PV electricity to be comparable to the retail price of electricity for small consumers in southern Europe by 2015. Continued price reduction after 2015 implies that this situation will apply to most of Europe by 2020. This state, where prices are comparable, is known as "grid parity". Larger systems and ground-based PV power plants that are not connected directly to end-consumers will generally need to produce electricity at lower prices before they can be said to have reached ‘grid parity’. To reach these targets, the SRA details the R&D issues related to PV cells and modules as well as the Balance of System (BoS).

Many different technologies with large commercial potential

A range of technologies can be found in commercial production and in the laboratory. No clear technological "winners" or "losers" can yet be identified, as evinced by the investments being made worldwide in production capacity based around many different technologies, and in the numerous concepts developed in laboratories that have large commercial potential. Therefore it is important to support the development of a broad portfolio of options and technologies rather than a limited set. The development of PV is best served by testing the different options and selecting on the basis of the following criteria:

  • The extent to which the proposed research is expected to contribute to reaching the overall targets set
  • The quality of the research proposal and the strength of the consortium or research group(s) involved.


R & D up to 2030:
Challenges for all types of solar cells and modules

Concerning "cells and modules", a distinction is made between existing technologies (wafer-based crystalline silicon, thin-film silicon, thin-film CIGSS and thin-film CdTe) and "emerging" and "novel" technologies (advanced versions of existing technologies, organic-based PV, intermediate band semiconductors, spectrum converters, etc.). It is noted that in addition to the cost of PV electricity generation the value of the electricity generated is important. The latter may be enhanced, for instance, by matching PV supply and electricity demand patterns through storage. The main R&D topics per technology area that are addressed to realise the Vision are outlined below. The detailed descriptions can be found in subsequent chapters of the SRA.

R&D in general focusses on efficiency, energy yield, stability and lifetime. Research aims to optimise combinations of these parameters rather that one parameter at the expense of another. This implies careful analysis of the costs and benefits of individual technological improvements.

Since research is primarily aimed at reducing the cost of PV electricity it is important not to focus solely on initial capital investments (€/Wp), but also on the energy yield (kWh/Wp) over the economic or technical lifetime. High productivity manufacturing, including in-process monitoring & control throughput and yield are important parameters in low-cost manufacturing and essential to achieve the cost targets.

Solar PV module in the solar electric plant "Pocking" (Bavaria; Germany).

Solar PV module in the solar electric plant "Pocking" (Bavaria; Germany). Totally 57.912 High tech solar modules with a peak power of 10 Megawatt (MWp)

 

Picture: Martin Bucher

Achieving a degree of standardisation and harmonisation in the physical and electrical characteristics of PV modules is important for bringing down the costs of installing PV. Ease of installation as well as the aesthetic quality of modules (and systems) are important if they are to be used on a large scale in the built environment.

Wafer-based crystalline silicon technology prevailing

Wafer-based crystalline silicon has dominated the photovoltaic industry since the dawn of the solar PV era. It is widely available, has a convincing track-record in reliability and its physical characteristsics are well understood. A learning curve for the progress in silicon wafer-based technology can be drawn that spans three decades. It shows that the price of the technology has decreased by 20 % for each doubling of cumulative installed capacity. Two driving forces are behind this process: market size and technology improvement. Such progress was not made by chance but is the combined result of market-stimulation measures and research, development and demonstration activities with both private and public support.

Research targets for Wafer-based crystalline silicon technology are a reduced specific consumption (g/Wp) of silicon and materials in the final module, so new and improved silicon feedstock and wafer (or wafer equivalent) manufacturing technologies, with careful consideration of cost and quality aspects are to be developed. New and improved materials for all parts of the value chain, including encapsulation are also to be developed. An increase of 1 % in efficiency alone is able to reduce the costs per Wp by 5-7 %. Small cells with efficiency values up to 24.7 % have been produced in expensive clean room facilities with vacuum technologies used for the deposition of metal contacts.


Solar-silicon silicon atom configuration.
Solar-silicon; silicon atom configuration. Fotos: SolarWorld AG, HMI

Wafers becoming always thinner and bigger

For example, wafers have decreased in thickness from 400 µm in 1990 to 200 µm in 2006 and have increased in area from 100 cm2 to 240 cm²; modules have increased in efficiency from about 10 % in 1990 to typically 13 % today, with the best performers above 17 %; and manufacturing facilities have increased from the annual outputs of typically 1-5 MWp in 1990 to hundreds of MWp for today’s largest factories. Plans for GWp-scale factories have been announced.

Targeted efficiency above 25 %

Industrial Polysilicon targets are a further reduction of Si Consumption to 5 g/Wp by 2008 – 2013 and a wafer thickness below 150 µm. From 2013 to 2020 wafers shall reach a thickness below 120 µm and from 2020 even below 100 µm. Si Consumption up from 2020 is targeted lower than 2 g/Wp. Targets for module efficiency until 2010 are an efficiency above 17 %, from 2013 to 2020 higher than 20 % and beginning 2020 above 25 %.

Existing thin-film technologies may conquer one third of the market

At present, the market share of thin-film PV within total PV production is below 10 %, but might grow to 20 % by 2010 and beyond 30% in the long term. The availability of large-area deposition equipment and process technology, as well as the experience available from within the architectural glass industry and the flat panel display industry, offer significant opportunities for high-volume and low-cost manufacturing. The monolithic series interconnection of cells to produce modules simplifies assembly in comparison with wafer-based technologies. Flexible lightweight modules can also be produced using thin polymer or metal substrates and roll-coating techniques. Thin-film technology thus has a great potential for cost reduction.

Research and industry focus on reliable, cost-effective production equipment for all thin-film modules. ?Low cost packaging solutions both for rigid and flexible modules will have to be found as well as low cost transparent conductive oxides. Reliability of products will be reached by advanced module testing and improved module performance assessment. A special challenge is developing replacements for scarce substances such as indium.

Device for structuring thin film solar cell.

Ultra thin flexible solar cell.

Left: Device for structuring thin film solar cell. Right: Ultra thin flexible solar cell.
Sources: LPKF Laser & Electronics AG (left), HMI (right).

Two gigawatt thin film production capacity each year expected up from 2012

Thin-film PV has a very high potential for cost reduction if materials and manufacturing can be improved by intensive and effective R&D on the fundamental science and production technology. The challenges facing thin films are to be found mainly in the realm of up-scaling production capacity. The global production capacity of thin films is expected to reach 1 GWp/year in 2010 and 2 GWp/ year in 2012. It is being installed mainly in Japan, the USA and Europe. Europe already has excellent thin-film R&D infrastructure and a number of thin-film factories.

Taking account of the increase in production facility sizes, improvements in module efficiency and differences in the calculation methods used by the PV industry, in 2010, the total manufacturing costs will most likely be in the range of 1-1.5 €/Wp. Further cost reduction to below 0.75 €/Wp in 2020 and 0.5 €/Wp by 2030 may be reached. Little difference in cost between the different thin-film technologies is expected in the long term.

In summary, low cost and high-volume production of thin-film PV modules is achievable and should enable costs to reach 0.5 €/Wp in the long term if intensive R&D work is carried out.

Emerging and novel PV technologies

The PV market is still dominated by crystalline Si solar cells - and by a number of thin-film technologies challenging this position. Both technologies are developing roadmaps aiming at further cost/Wp reductions. Limiting the PV research to these sets of PV-technologies may be risky for two reasons, SRA emphasizes: First, flat-plate modules are limited to efficiencies not exceeding 25 %. Secondly, the European PV industry would miss opportunities afforded by step-changes in technology.

The new beyond-evolutionary technologies can either be based on low-cost approaches related to extremely low consumption of (often expensive) materials or approaches that push the efficiencies of solar cell devices beyond the 25% limit achievable with incremental improvements to cells based on traditional designs. In fact, the goal to develop crystalline Si and thin-film solar cell technologies with a cost below 0.5 €/Wp relies on disruptive breakthroughs in the field of novel technologies. An open attitude towards developments presently taking place in material and device science (nanomaterials, nanotechnology, plastic electronics, photonics) is needed to detect these opportunities in an early stage.

Nano surface technologies and plasma based procedures offer a broad range of texturing and coating solar cells Flexible organic solar cell developed by Fraunhofer ISE.
Left: Nano surface technologies and plasma based procedures offer a broad range of texturing and coating solar cells. Right: Flexible organic solar cell developed by Fraunhofer ISE.
Pictures: Fraunhofer-Institut für Werkstoff- und Strahltechnik (IWS); Fraunhofer ISE

Regarding new technologies improvement of cell and module efficiencies and stability to the level needed for first commercial application is crucial. Demonstration of new conversion principles and basic operation of new device concepts are one focal point. Research for instance deals with processing, characterisation and modelling of (especially) nanostructured materials and devices.

Concentrator technologies

For new and improved Optical PV systems reliable, long-term, stable and low-cost solutions for flat and concave mirrors, lenses and Fresnel lenses and their combination with secondary concentrators are to be deployed. Materials and mounting techniques for the assembly of concentrator cells and optical elements into highly precise modules that are stable over the long-term using low-cost and fully automated methods are on the agenda. Also tracking constructions which are optimised with respect to size, load-capacity, stability, stiffness and material consumption are to be developed.

Demonstration plant by Concentrix Solar GmbH in Lorca (Spain).
Demonstration plant by Concentrix Solar GmbH in Lorca (Spain). The concentrating PV system consists of three 5,7 kW-trackers and serves for real condition test of the FLATCON-Technology. Picture: Concentrix Solar GmbH
Materials and production technologies for concentrator solar cells with very high efficiencies, i.e. Si cells with efficiencies greater than 26 % and multi-junction III-V-compound cells with efficiencies greater than 35 % in industrial production and 45 % in the laboratory will be probed, to find the optimum concentration factor for each technology. In addition an optimised design, production and test methods for the integration of all system components; methods for installation, outdoor testing and cost evaluation of concentrator PV systems are pending.

In the long term thermophotovoltaics, a third approach, could be used in concentrating solar thermal power applications (CSP). Before that happens, the technology could be used in CHP systems. Although some R&D is still needed on the individual components of a TPV system (cell, monolithic module integration, emitter, filters), the main challenges are to integrate the components in a system, boost reliability and the demonstrate electricity costs less than 0.1€/kWh and a system efficiency of 15%.

Europe and the international competition

Europe’s photovoltaic industry competes with companies from Asia, the USA and other parts of the world. Two of these countries have instituted programmes to support their domestic PV industry – Japan and China. The effectiveness of the programme sponsored by Japan’s Ministry of Economy, Trade and Industry (METI), is already apparent. Due to long term planning, support schemes, investment security, and a substantial domestic market, the Japanese PV industry has around 50% of the world market share in PV products.

China is the second country with an industrial strategy geared towards building up a highly competitive PV industry. China wants to cover the whole value chain from silicon feedstock to complete systems. The fruits of this relatively new strategy are already visible. Chinese cell and module manufacturers are rapidly establishing a significant share of the world market and their production capacity increases are unrivalled.

With the solar PV power Beneixama (20 MW) the German City-Solar-Group is leader of the global PV ranking. Solar modules by the Chinese producer Yingli Solar mounted at the soccer stadium at Kaiserslautern (Germany).
Left: With the solar PV power Beneixama (20 MW) the German City-Solar-Group is leader of the global PV ranking. Right: Solar modules by the Chinese producer Yingli Solar mounted at the soccer stadium at Kaiserslautern (Germany). Pictures: City Solar AG; Solar-Energiedach GmbH

If Europe does not react to this challenge, there is the danger that PV production will move to China, in common with many other manufacturing technologies. So far, Europe still has a competitive edge due to the excellent knowledge base of its researchers and engineers. However, without steady and reliable R&D funding and support from the public purse, this advantage could be eroded in a short time. More support for innovation and clearer long-term strategies are needed for the European PV industry to continue to invest in Europe and to ensure that European companies increase their market shares and become world leaders.

Global PV installations.
Global PV installations. The blue bar shows the chances of an active promotion policy for PV. Source: EPIA

Strategic Research Agenda on the internet

The Strategic Research Agenda is available to Download at http://www.eupvplatform.org/fileadmin/Documents/MG_SRA_Complete_070604.pdf. More information on the platform is accessible at: http://www.eupvplatform.org.

Source: European Photovoltaic Technology Platform. Editorial adaption: Rolf Hug.

Further Information:

Organic photovoltaics: solar power from extremely thin tinted films and polymer films

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