Energy Policy 28 (2000) 983}988

The viability of solar photovoltaics

Tim Jackson!,*, Mark Oliver",1!Centre for Environmental Strategy, University of Surrey, Guildford, Surrey GU2 5XH, UK

"Ernst & Young, Broadwalk House, Southernhay West, Exeter, EX1 1LF, UK

Received 24 May 2000

Abstract

This paper summarises the contributions to a special issue of Energy Policy aiming to assess the viability of solar photovoltaics(PVs) as a mainstream electricity supply technology for the 21st Century. It highlights the complex nature of such an assessment inwhich technical, economic, environmental, social, institutional and policy questions all play a part. The authors summarise brie#y theindividual contributions to the special issue and draw out a number of common themes which emerge from them, for example: the vastphysical potential of PVs, the environmental and resource advantages of some PV technologies, and the #uidity of the market. Mostof the authors accept that the current high costs will fall substantially in the coming decade as a result of improved technologies,increased integration into building structures and economies of scale in production. In spite of such reassurances, energy policy-makers still respond to the dilemma of PVs with some hesitancy and prefer to leave its evolution mainly in the hands of the market.This paper highlights two clear dangers inherent in this approach: "rstly, that short-term cost convergence may not serve long-termsustainability goals; and secondly, that laggards in the race to develop new energy systems may "nd themselves faced with long-termpenalties. ( 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Photovoltaics; Solar cells; Renewable energy; Sustainable energy systems; Clean technology

1. Introduction

Solar photovoltaic (PV) cells have attracted increasingattention in recent years as a technology capable ofdelivering sustainable electricity supplies and reducingthe burden of fossil fuels on the environment.

Originally developed to provide electrical power forthe space programme in the middle of the last century,PVs have subsequently found diverse application in nu-merous o!-grid markets during the last 30}40 years. Stillexpensive by comparison with conventional generationtechnologies, grid-connected applications have beenslower to emerge; but a recent surge of interest in renew-able energy by policy-makers has led to industry growthrates which averaged 21% per annum between 1982and 1997, with growth in the latter years as high as40% per annum (Oliver and Jackson, 1999). A variety of

*Corresponding author. Tel.: #44-1483-300800x2181; fax: #44-1483-259-394.

E-mail address: t.jackson@surrey.ac.uk (T. Jackson).1The views expressed in this paper belong solely to the author in his

personal capacity and are not the views of Ernst and Young.

policy initiatives has set ambitious implementation tar-gets for the installation of building-integrated PVs ingrid-connected situations.

The "rst such scheme was the German `thousandroofsa programme, which by 1995 had achieved its targetof installing small (1}5 kWp) PV systems on the roofs of1000 domestic residences and small company properties(Weiss et al., 1998). Another early initiative was theJapanese Ministry of International Trade and Industryinitiative to subsidise the installation of 70,000 PV roofsby 2005 (Konno, 1998; Luchi, 1998). In 1997, US Presi-dent Bill Clinton announced an even more ambitiousprogramme to install a million solar roofs with the aim ofhelping to reduce greenhouse gases as part of the climatechange programme and supported by funds promotingpartnerships with industry. Tax credits, grants and low-interest loans will all be available to help to encouragethe deployment of solar technologies (Rannels, 1998).The European Union has recently announced targets todouble the renewables contribution to electricity supplyfrom 6 to 15% of total electricity supply by 2010. As partof this aim a target of 1,000,000 roofs has been set, half inthe EU and 500,000 in developing countries (Papoutsis,1998). In addition, signi"cant support has been given to

0301-4215/00/$ - see front matter ( 2000 Elsevier Science Ltd. All rights reserved.PII: S 0 3 0 1 - 4 2 1 5 ( 0 0 ) 0 0 0 8 5 - 9

2Ends Daily 21st May 1997; Ends Daily 5th November 1997.

3 It is to be noted that PVs are of course an intermittent source ofelectricity, so that meeting diurnal and seasonal load variations wouldrequire either considerable electrical storage capacity or backup plant.

PVs in countries such as the Netherlands (NOVEM,1997) and Switzerland (Haas, 1998). An even more ambi-tious target to install a million and a half solar roofs by2002 has been announced by the Indian government.

This acceleration of support for PVs would suggestthat there is a growing con"dence in its long-term viabil-ity, and that, in spite of the current high costs, unsup-ported wide-scale adoption of the technology is on thehorizon. This indeed is the view of several close observersof the industry who argue that a virtuous circle of in-creased demand, expanding production facilities, im-proved performance and falling costs is pushing PVs evercloser towards convergence with mainstream grid-con-nected electricity sources. The Anglo-Dutch oil companyShell believes that the market for PVs could be worth$25billion by 2025 (Herkstroter, 1997). In May 1997, oilgiant BP announced a signi"cant boost in investment inits solar power business, BP solar, with the aim of in-creasing sales from $100million to $1000million over thenext decade (Brown, 1998). Major expansions in PVproduction capacity have also been announced inGermany, which has declared its aim of establishingworld leadership in solar production.2

Set against these signs of massive expansion, it is worthremarking on a number of facts. Firstly, the costs ofelectricity from PVs remain uncompetitive with mostconventional sources of electricity except in isolated loca-tions removed from the grid. In fact, the high cost of theGerman 1000 roof programme prompted one observer towrite that its was `unlikely to be extended in the current"nancial climatea (Grubb and Vigotti, 1997). In spite ofa history of rapidly falling module costs, the balance ofsystem costs may constrain further cost reductions atrecent rates (Oliver and Jackson, 1999). Furthermore,even the ambitious targets set, for example, under theEU's million roofs programme would lead to onlya modest contribution (around 0.02%) to the EU's totalenergy consumption (Jackson and LoK fstedt, 1998).

Such contributions are miniscule by comparison tothe apparent physical resource. The contributions to thisspecial issue all take for granted that the renewableenergy base for PVs is enormous. Solar radiation falls onthe earth at a global rate that is almost 10,000 timeshigher than the rate of anthropogenic energy consump-tion (Twidell and Weir, 1986). Granted, this considerableresource arrives at the surface of the earth as a relativelydi!use #ow &like a very "ne rain... a microscopic mist' asGeorgescu-Roegen (1975) described it. The annual in-solation rate in equatorial Africa is only 250}300W/m2.In northern latitudes, this microscopic mist is even"ner. The average summer insolation rate in the UK(for example) is about 200W/m2, falling to 20W/m2

in the southern part of the country during the winter

and less than half of this in the north. These insolationrates are equivalent to an annual average of only2.5 kWh/m2 per day (Green, 1982). Nevertheless, if thisenergy could be converted to a useful form at an averagee$ciency of only 5% (say), then the aggregate UK elec-tricity demand could be supplied using only 3% of theland area.3 Hill et al. (1995) even calculate that this couldbe achieved by integrating modules into existing buildingstructures without the need for additional land.

However, it is clear from the chequered history ofenergy policy that the viability of a particular energytechnology cannot, with any reliability, be judged purelyon the basis of the physical resource base. Rather acomplex dynamic of economic, technical, environmental,institutional and social factors need to be taken intoaccount. This is particularly true when envisaginga transition from one kind of energy supply system witha particular set of characteristics to another with com-pletely di!erent ones. Lessons from the history of nuclear"ssion (Proops, 2000), hydroelectricity (Sims, 1991), windpower (Jackson and LoK fstedt, 1998), wave power (Ross,1995), and even nuclear fusion (Jackson, 1989) indicatethat technological options can fail* or their implemen-tation falter * for a variety of reasons, ranging fromhidden costs to social unacceptability and from resourceconstraints to institutional failure.

The aim of this special issue is to examine the prospectsfor wide-scale implementation of PVs, and to address thetechnical, economic, institutional, social and policy issueswhich are likely to a!ect those prospects. Thus, weare concerned with a broad range of questions aboutthe viability of PVs as a source of clean and sustainableelectricity generation. What is the current state of the art?What future developments are likely? How will thesedevelopments in#uence the cost of the technology? Howsoon could these costs converge with the cost of conven-tional grid-connected supplies? What are the environ-mental and resource implications of the technology?What institutional demands do PVs place on conven-tional electricity supply structures? How will PV marketsdevelop in the future? How strong is the argument forpolicy intervention and government support? Whatlessons can be learned from experience about thedesign and implementation of appropriate policy frame-works?

Within the scope of single journal issue, it is probablyimpossible to provide adequate answers to all these ques-tions. However, it is to be hoped that the followingcontributions go some way towards addressing the vi-ability of PVs as a mainstream electricity supply techno-logy for the 21st Century.

984 T. Jackson, M. Oliver / Energy Policy 28 (2000) 983}988

2. An overview of the issue

Solar PV systems convert sunlight directly into elec-tricity using the photoelectric e!ect * through whichlight causes matter to emit electrons. In the "rst paper,Green (2000) provides an overview of the technology,setting out the principles and design of PV cells, thecurrent state of the art and the most likely future devel-opments. A number of di!erent cell technologies are nowin use. By far, the most common technology is wafer-based crystalline silicon, which now accounts for abouthalf of European PV production, for example (EC, 1996).But Green argues that a transition is now in progresstowards a second generation of potentially much cheaperthin-"lm technologies. These technologies tend to havelower conversion e$ciencies than crystalline cells, butuse fewer materials in construction, thus reducing themanufacturing costs. The most common thin-"lm tech-nology is amorphous silicon (a-Si) which alreadyaccounts for about 25% of European production (EC,1996). But a variety of other thin-"lm techniques useexotic materials such as cadmium telluride and copperindium diselenide.

Only a couple of decades ago, PVs were dismissedas a non-viable technology because the energy embodiedin the manufacture of the cells was greater than theenergy supplied by the technology over its lifetime(Georgescu-Roegen, 1979). However, the rapid improve-ments in performance that have been experienced in thelast two to three decades have changed this situationentirely, as the paper by Alsema and Nieuwlaar (2000)demonstrates. Assuming medium levels of solar irradia-tion, they "nd energy payback times in the order of 2.5}3years for distributed, (building-integrated) rooftop sys-tems. This payback time rises to around 4 years forcentralised, multi-megawatt, ground-mounted systems.Given that the technical lifetime is in excess of 20 years,these kinds of payback times suggest that PVs have nowcrossed the threshold from being a net energy sink toa technically viable energy supply technology.

Since PVs generate no emissions during operation, theenvironmental impacts are mainly associated with emis-sions generated during production of the technology (andthe disposal of modules and cells at the end of their usefullife). Many of these impacts are associated with the con-sumption of energy in the production process. Forexample, Alsema and Nieuwlaar also estimate the carbondioxide (CO

2) emissions per unit of electricity generated

over the lifetime of the cells. These estimates reveal that,even in the current state of the art, emissions from PVsare considerably lower than for fossil fuel power plants,although slightly higher than those for wind energy or forbiomass. The authors argue that PVs have a signi"cantrole to play in reducing CO

2emissions in the longer

term, but that no signi"cant contributions to this taskcan be expected before 2010.

The question of choosing technologies to mitigate theimpacts of climate change is likely to exercise policymakers increasingly in the wake of the Kyoto Protocol,and in the run-up to the "rst &commitment period' duringwhich industrialised countries (Annex 1 Parties) mustachieve their "rst real emission reductions over 1990levels (Grubb et al., 1999). It seems reasonable to arguethat a rational energy policy would implement "rst thosetechnologies which were most cost-e!ective in terms ofgreenhouse gas emission reduction. Indeed, this assump-tion provides a large part of the motivation for theintroduction into the Kyoto Protocol of a number of&#exibility mechanisms' designed to facilitate cost-e!ec-tiveness in greenhouse gas emission reductions (Jacksonet al., 2000). It is clear therefore that any assessment ofthe role of PVs in climate change mitigation involves anassessment not only of the embodied lifetime CO

2emis-

sions (for example) but also of the economic costs. Thecritical parameter, grams of CO

2per kilowatt hour

(g/kWh), becomes some kind of measure of cost-e!ec-tiveness. Furthermore, it is clear that both environmentalperformance and cost are evolving over time, so thata realistic assessment of the role of PVs in climate policyrequires a dynamic assessment of cost-e!ectiveness.

Oliver and Jackson (2000) go some way towards suchan assessment in the third paper in this special issue.They present the economic costs and environmental bur-dens (speci"cally CO

2emissions) of crystalline PVs as

a trade-o! facing policy-makers, and highlight the dy-namic nature of this trade-o!. A series of analyses ex-plores the sensitivity of both costs and burdens to thevalues of certain key parameters, including module e$-ciency, wafer thickness, technology lifetime, siting andsystem performance factors. On the basis of a number ofassumptions about the future evolution of these factors,the authors highlight a kind of &double dividend' avail-able to PVs over the coming years: as performance-related factors improve, so both the economic costs andthe lifetime environmental burdens of PVs will fall. Theyillustrate the impact of this double dividend in terms ofthe development over time of the net incremental cost ofcarbon abatement (as compared against the averageEuropean electricity mix). The analysis reveals that inspite of the current high cost, PVs may in fact representa &no-regrets'measure for greenhouse gas emission reduc-tion * reducing CO

2emission at no net cost * by the

year 2010. The authors argue that this future potentialjusti"es policy interventions now to promote the dissemi-nation of the technology.

The economic analysis used by Oliver and Jackson isbased on conventional engineering-type discounted cash#ow techniques. In the subsequent paper, Awerbuch(2000) presents a compelling argument that this kind ofanalysis does insu$cient justice to the complex bene"tsof many new energy supply technologies, including PVs.He argues that PVs o!er &a unique cost-risk menu' that

T. Jackson, M. Oliver / Energy Policy 28 (2000) 983}988 985

4Silicon is the second most abundant material in the earth's crust.

remains largely invisible to conventional valuationmethods, which were conceived long before such at-tributes became technologically feasible. Using the in-sights gained from modern "nance theory, Awerbuchsuggests that PV technology needs to be valued not interms of its stand-alone costs, but rather on the basis ofits portfolio cost, i.e. the cost &relative to its risk contribu-tion to a portfolio of generating resources'. In this re-spect, PVs o!er bene"ts* such as modularity, #exibilityand reversibility* which might contribute signi"cantlyto mitigating some of the risks associated with othermore conventional electricity technologies. Since theselatter risks are often borne in the social arena and arenot always re#ected in private portfolio risk, Awerbuch'sanalysis has some potentially profound implicationsboth for the regulation of risk in "nancial markets forthe internalisation of external social costs in energypolicy.

Critical to Awerbuch's paper is the suggestion thatPVs represent not just a new energy technology, buta &radical architectural innovation' involving new tech-nical, economic, "nancial, institutional and social charac-teristics. This idea is revisited in the contribution fromAndersson and Jacobsson (2000) which sets out to deter-mine a methodology capable of assessing whether cur-rent rates (and directions) of technological change arecompatible with the development of a sustainable so-ciety. The authors highlight the technological #uidity ofthe PV market and suggest, like Green, that thin-"lmsolar cells are poised to dominate the industry. However,they point out that a critical division exists betweendi!erent thin-"lm designs. Some of them use exotic ma-terials which may be subject to both resource constraintsand environmental concerns. Perversely, these designsare generally more e$cient than the alternative, amorph-ous silicon technology, which is subject to very fewresource constraints at all.4

As Andersson and Jacobsson point out, some kind ofpolicy intervention is required if solar cells are to achievetheir potential in providing a signi"cant alternative tofossil fuels. However, a policy driven primarily by thepursuit of cost-e$ciency runs the risk of promoting tech-nologies which face long-term resource constraints (andenvironmental problems) over those which are currentlyless e$cient. This same issue was highlighted by Jackson(1992) in a special series in Energy Policy devoted torenewable energy eight years ago. In the interveningyears, most Western electricity supply industries havebeen driven by the pursuit of market liberalisation inwhich price and cost-e$ciency have dominated bothpolicy and practice. In such an environment, policy-makers may "nd it hard to introduce measures to protectthe diversity of technologies emerging within the PV

market and promote those which o!er sustainable long-term solutions to energy supply. Nonetheless, it is clearthat encouraging short-term cost convergence falls signif-icantly short of providing a sustainable long-term policystrategy.

One possible means of mitigating the resource con-straints faced by some of the thin-"lm technologies is byrecycling PV modules at the end of their useful lives.Fthenakis (2000) presents the results of a feasibiliy studyfor recycling both thin-"lm solar cells and manufacturingwastes from their production. He argues that even withincurrently limited recycling infrastructures the potentialto recover metals from PV modules already exists andthe costs are not excessive. He stresses however the needto design for disassembly and to provide appropriatepolicy incentives. Economic incentives may be inad-equate to drive the PV industry towards voluntary re-cycling.

The "nal two papers in this special issue present de-tailed PV case studies. The "rst of these is provided bythe Solar Olympic village being constructed in Newin-gton, Australia for the Olympic Games in the summer ofthe year 2000. Spooner et al. (2000) provide the details ofthe scheme * an integrated residential development in-volving solar hot water heating, building-integrated solarphotovoltaics, energy e$cient design and water recycl-ing. The village is a high-pro"le show-case in whicheconomic cost is not a particular priority. Yet itdemonstrates that it is already feasible, using today'stechnology, to integrate solar power into a residentialdevelopment with bene"ts to all participants. Theauthors highlight a number of market barriers to a morewide-scale penetration of the technology and suggesta range of policy measures to overcome these.

The second case study explores the complexities asso-ciated with a subsidised project aimed at di!using small-scale photovoltaic systems into rural areas of developingcountries. The Global Environment Facility (GEF) Solarproject in Zimbabwe was approved for funding in 1992.Its principal aims were to improve the living standards ofpeople in rural areas, to contribute to the reduction ofgreenhouse gas emissions and to enhance the long-termsustainability of the PV industry. By the time the projectfunding ended in 1997, it had succeeded in installingaround 10,000 PV systems. Nonetheless, Mulugetta et al.(2000) highlight a number of problematic elements in theproject. In particular they point out that, perversely,donor-driven projects can sometimes distort local mar-kets, indirectly undermining indigenous renewableenergy companies. Furthermore, such programmes tendto focus on targets for implementation to be achievedwithin the project lifetime (in this case "ve years).Mulugetta and his coauthors highlight the importance ofdesigning well-coordinated development programmeswhich retain a clear view of speci"c engagements beyondthe period of donor commitment.

986 T. Jackson, M. Oliver / Energy Policy 28 (2000) 983}988

3. Conclusions

It is possible to identify a number of common themesamongst the papers collected in this special issue. Firstly,of course, there is the assumption that the resource po-tential for PVs is enormous. Secondly, most authorsaccept that the resource and environmental advantagesof PVs over conventional technologies are substantialeven though the costs are still high. The technological#uidity of the PV industry has been remarked upon.Several authors argue that a new generation of thin-"lmtechnologies is poised to dominate the market. Thesetechnologies may both improve the economics of PVsand reduce some of its life-cycle resource requirementsand environmental impacts. On the other hand, someauthors point out that there are resource limitations tosome of these new PV technologies, particularly thosewhich employ exotic, and sometimes toxic, materials.

Ultimately, the authors tend to agree that a combina-tion of technological innovation, increased e$ciencies,improved learning and economies of scale are likely todrive costs down appreciably within the next decade.A considerable proportion of the market for PVs isexpected to come from the integration of PVs into build-ing structures, driven in part by government policy tar-gets. The expanded production requirements arisingfrom this emerging market will be one of the factorsinvolved in driving costs down further. Thus, it is pos-sible to envisage a virtuous circle of market growth,expanded production, and further economies of scalethat will shortly allow PVs to compete in their own rightagainst conventional electricity supply technologies ingrid-connected applications.

In the meantime, however, PVs confront energy pol-icy-makers with some novel and some familiar dilemmas.Amongst the familiar dilemmas is the question of how torespond to a technology which appears to show consider-able promise in resource and environmental terms, but iscurrently uncompetitive with conventional supplies.Amongst the unfamiliar is the radical nature of the &archi-tectural innovation' introduced into the electricity supplyinfrastructure by a distributed, capital-intensive techno-logy reliant on a geographically uneven, intermittentpower source.

In the face of such dilemmas, it is perhaps natural to"nd policy-makers hesitant * still, for the most part,prepared to leave the fate of photovoltaics in the hands ofthe market. It is worth highlighting two clear dangersinherent in this approach. Firstly, a market dominatedapproach place the onus on PVs to achieve cost conver-gence in as short a time-scale as possible. We havealready remarked however that short-term cost conver-gence runs the risk of &forcing' the PV market towardsparticular technologies, namely those which currentlyo!er the best combination of high conversion e$ciencyand low material input cost. But these technologies are

not always the most sensitive in environmental terms(for instance, because they employ some toxic materialsin manufacture). Furthermore, they may come up againstresource constraints far sooner than some other tech-nologies. Ideally, policies should be promoting the diver-sity the industry needs to develop and test technologieswhich will be both economically viable and environ-mentally sustainable over the longer term. Forcing costconvergence too soon may undermine these conditions.

The second danger will only really emerge if and whenPV technology begins to take its place as a seriouscompetitor to mainstream electricity supply. As the elec-tricity supply market begins to change from one domin-ated by fossil fuels to one dominated by distributedcapital investments, so the geopolitical distribution ofresources, technology and power will change. The win-ners in the new energy infrastructure will no longer bethose with access to mineral reserves. They will bethose with favourable insolation rates or those who cancreate strong technology export markets. The losers willbe those who miss the fact that the new energy infrastruc-ture is a di!erent techological, "nancial, institutional andpolitical animal, and fail to take action early enough toprotect their long-term interests. Hesitancy now mayhave its own costs later.

It may still be decades before PVs occupy anythingmore than a gradually expanding niche within the elec-tricity supply markets. However, the contributions to thisspecial issue suggest that there is plenty for policy-makers to think about right now if they are serious in thegoal of developing sustainable long-term energy systems.

Acknowledgements

We are grateful for "nancial support from the Engin-eering and Physical Sciences Research Council and fromthe Royal Academy of Engineering during the prepara-tion of this work.

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