As pointed out by Lave et al. (1995), a large-scale introduction of technologies such as EVs that make use of toxic elements such as lead could increase the environmental loading of the metal. However, it is worth noting that this will only be the case if an increased mining of the metal is induced or if recovery and recycling are not more efficient than at present. As shown by Socolow and Thomas (1997) and Karlsson (1999), there is a potential that lead flows can be sufficiently closed within a battery production, use and recycling system. Large batteries and PV systems could be examples of applications where a controlled use of toxic metals is possible. They could then be used as a tech-nospheric 'attractor' for toxic metals. A high demand for the metals would raise metal prices and discourage dissipative uses or even stimulate recovery of hazardous metals from various by-flows, such as cadmium from phosphate fertilizers, vanadium from petroleum refining, lithium from geothermal brines and a number of metals in ore tailings and coal ashes. This sequestration function of technologies has been noted by many, for example Ayres and Ayres (1996) and Kleijn (2000).
However, even if metals can be safely 'stored' in a technological system, one day the technology might be superseded by better performing alternatives. If no other large-scale applications exist that could inherit the metals, the scrap price would fall drastically and we would face the 'riddance problem': who would at that time pay for getting rid of a huge stock of hazardous waste in an environmentally acceptable fashion?
Higher metal demand could also lead to accelerated mining, which could increase sulfur dioxide emissions and metal leakage from waste dumps and cause large-scale land transformations. As shown above, this aspect may also be relevant for metals that currently are recovered as by-products. This gives rise to a 'cadmium paradox'. The presence of the toxic element cadmium is sometimes cited as a major problem for the use of alloys such as cadmium telluride (CdTe). But in line with the argument put forward above, 1GWp of CdTe PV modules could sequester 60Mg of cadmium that otherwise could have been wasted or used in short-lived products. On the other hand, if indium demand became a driver for the mining of zinc ore, 1GWp of CIGS modules could generate 3000-6000Mg of by-product cadmium. In this sense cadmium could become a larger problem for CIGS cells than for CdTe cells.
At present it seems unlikely that the by-product metals considered here would ever become main metals as a result of demand from the PV industry. But if it should happen, this industry could be held responsible for a large share of the environmental effects of mining. The potential PV has to dematerialize the energy system (Ogden and Williams 1989) would be turned into its opposite. As pointed out by Schmidt-Bleek (1994a), rare elements carry heavy 'rucksacks'. To recover 1g of tellurium from copper ore, one needs to mine more than 1t of ore. In the worst case, solar cells could become the 'coal industry' of the 21st century, extracting about as much material from the crust for every kWh of electricity produced.
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