The Terawatt Challenge for Thin Film Photovoltaics

Ken Zweibel

NREL, Golden, CO, USA


It is critical to understand what this report purports to do and what it cannot do. It cannot analyze either company or technology specific information about thin film manufacturing. It cannot give any current actual prices, because they depend on volume and varying specifications. Thin film photovoltaic (PV) manufacturing is changing quickly, and most crucial details are confidential.

So what can this report do? It can assemble in one place a set of technology options, process choices, and device designs and attempt to give a rough estimate of their status and potential. There are long lists of these attributes (e. g., Tables 11.1 and 11.4) that seem to indicate actual costs. But this is not the case. The lists are long to assure that as much as practical is included – missing process steps or major materials components would be a serious shortfall. But the actual costs estimated under each category are simply educated guesses. With time, they will change. This is a snapshot of what the author believes is a fair picture of the landscape of thin film PV. One cannot do more; it is really rather a question of whether one should simply do less, and not publish at all. But in the interest of addressing a bigger question – ‘Can thin film PV meet the Terawatt Challenge?’ – it seems worthwhile to make the effort, especially considering the critical importance of solar (covered in the next section) in terms of climate change and oil depletion. Solar is ‘the only big number out there’ (in the sense of the size of the resource available to meet climate change without carbon dioxide emissions) and this matters. This report should suffice to give a sense of the progress in thin films; their potential; and what remain as major challenges.

Tables 11.16-11.19 summarize the results of the rough, but methodologically consistent cost estimates. They show that a number of thin film module options have system price potentials in the range of $1-$1.2/Wp DC. This translates (in an average US solar location like Kansas City) to about 5-7 c/kWh AC electricity. Such electricity should be inexpensive enough to: (i) provide intermittent, daytime electricity from grid tied systems and (ii) split water and make hydrogen for portable fuels. If PV is to be used for dispatchable electricity, other aspects of system design and cost must be addressed through long distance transmission and storage.

This study was conservative. There are a number of clear avenues for further PV cost reduc­tion (e. g., through less expensive encapsulation) that could take PV prices substantially lower.

Thin Film Solar Cells Edited by J. Poortmans and V. Arkhipov © 2006 John Wiley & Sons, Ltd

In addition to the cost estimates, other topics associated with the ‘Terawatt (TW) Challenge’ include materials availability, land area needs, and energy payback. These were examined as well. In some cases there may be materials availability issues (e. g., indium and tellurium supply), while in others only the prospect of steady growth (e. g., glass). Due to the diversity of PV module options, no supply issue is critical. Land issues turn out to be a red herring – land use is actually a strength of PV since: PV can be used on roofs and other structures, it is the most efficient means of converting primary solar energy to usable form, sunlight is ubiquitously available in sufficient quantities, and only tiny amounts of land (on a relative basis) are in question (about 1 % of land area). Energy payback is also found to be a nonissue, as it falls toward about 1-2 years today, and below that with further technical progress.

The evolution of PV into one of the world’s largest industries is not going to happen without major unforeseen problems. However, this study attempts to address the obvious ones, so that we can put aside the mythology of PV (for example, that it is only ‘boutique power’ or that one must pave the world with it to be useful) and get on with changing the world’s energy infras­tructure. With the years of rapid market growth now underway in PV, the author is sure this will not be the last effort to understand the real potential and pitfalls of meeting the TW Challenge.

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