Utilityscale Flatplate Thin Film Photovoltaics Land Water and Critical Materials Requirements

Table 4. Resource requirements.

Indicator Name

Base Year 1997

Units

2000

2005

2010

2020

2030

Land

ha/MW

5

4

3

2.5

2.5

2.5

ha

0.08

9.6

24

40

40

40

Critical elements

MT/GWp

NA

50

30

20

10

3

(e.g., In, Se, Ga, Te)

Water

m3

nil

nil

nil

nil

nil

nil

Land area needs are based on calculating the array area required to produce the desired output, amount of energy per square meter of array and then multiplying this area by a factor of about 2.5 to account for packing the arrays without shadowing. At 10% system efficiency, a PV system produces about 100 W/m2 of array. Including the packing factor, this is 40 W/m2 of land area. A MW would thus require 25,000 m2 of land, or about 0.025 km2. In the early years, we expect system efficiency to be below 10% (accounting for the larger land requirements), but by 2010, system efficiency of over 10% is assumed (accounting for the lower land-use numbers). In some cases, PV will be used on rooftops o r other dual-use applications, thus reducing land use below these estimates.

Certain PV technologies require important elements such as tellurium, indium, selenium, and gallium. The availability of these materials is, in principle, limited by economics and geologic factors. However, thin film PV uses very smal l amounts. Typical elemental concentrations in PV are about 3 g/m2 for each micron of layer thickness. Laye r thicknesses vary from about 1-3 ^m . In early years, little effort will be put into reducing thicknesses, because eve n at these thicknesses materials costs are not a driver. But as performance increases and other costs are overcome, materials costs will become important, and layers will be thinner. The theoretical limit on how thin layers can be (from today's understanding) is about 0.1-0.3 ^m, depending on device subtleties such as light trapping to cause multipl e reflections. This evolution of materials needs is captured in Table 4 (above) based on reduced layer thickness (coming down from about 2 ^m to about 0.2 ^m) and efficiency (output per g of feedstock) rising from 8% to 15%. In no case would the very large-scale use of PV put pressure on the availability of these elements. Indeed, this also means tha t other materials that are used in compound semiconductors (e.g., cadmium in CdTe) would not be used excessively , obviating most global-level environmental impacts of these materials. For example, cadmium is used today at abou t 20,000 MT/yr for current uses (rechargeable batteries for entertainment). Using 100 MT/yr for PV (to add over 30 GWp /yr of PV capacity) would change this usage by less than 0.5%.

Ultimately, as PV reaches a steady-state, recycling of outdated thin film modules would allow for another reductio n by half in the amounts of new material needed to make a GWp per year of PV. In fact, the use of materials is so controlled in PV systems (semiconductors are sealed from the environment for 30 years or more and can then b e recycled), that PV may ultimately play a role as a safe and productive 'sink' for numerous materials that are today without any long-term sequestering strategy.

PV systems do not use water during operation.

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