System Application Benefits and Impacts

PV will be use d for many, diverse applications, including utility grid power. The system defined here is for future , grid-connected applications. Since such systems will evolve from today's smaller systems, they have been sized a t 20 kWp-10 MWp in the early years, reaching 20 MW p (as a typical size) in 2010. Actual size will depend on individual, grid-connected applications. However, since PV systems are highly modular (i.e., modules and partial arrays can b e mass produced in the factory), costs are related predominantly to production volume, not to system size.

Two major markets are expected for the kind of multi-use system described in this characterization. In the U.S. , distributed systems delivering electricity at peak demand periods would be the main application [2]. Some intermediate daytime loads would also be met. In developing countries, non-grid-connected systems would provide power to th e hundreds of thousands of villages that have no electricity grid. Both of these markets would take advantage o f significant values that PV electricity can provide. In the U.S., PV output is well-matched to the needs of many utilities for peak power during the daytime for commercial and air-conditioning loads [2]. This is the most costly electricit y for utilities to generate. In addition, PV can be used in distributed locations (i.e., closer to the customer) on a utility grid, reducing the need to add capacity to transmission lines to serve growing suburban communities. Modularit y provides relative ease of siting and rapid installation. In the developing nations, there are few alternatives to PV fo r rural use: diesel generators would be the direct competition. However, diesels require a constant supply of fuel an d substantial maintenance, while PV has no need for on-site labor during operation, and has very low maintenanc e requirements.

PV benefits are numerous. Those described here are in terms of the value of using PV generally, as would result once competitive costs are achieved. PV requires no fuel or water, and is low-maintenance during use. It is an energy source that can be used to 'domesticate' (rather than import) energy, reducing import expenditures. Since sunlight is a loca l fuel that is available globally, national energy security would be enhanced. In addition, since many PV markets ar e international, production and export of these high-tech products would benefit the U.S. economy. For developing countries, the value of rural electrification is substantial, since it helps stabilize rural-to-urban population shifts whil e increasing food supplies, improving food storage, and raising the productivity and living-standard of rural economies . PV use by developing countries would help avoid greater dependence on conventional energy sources and thei r concomitant emissions.

The solar resource base of the Continental U.S. is over 1016 kWh/year. U.S. electricity use is about 2.5 x 1012 kWh/year. Thus, the U.S., an intense user of energy, has about 4,000 times more solar energy than its annual electricity use. This same number is about 10,000 worldwide. Thus PV could in principle provide all the globe's electricity. In particular, if only 1% of land area were used for PV, more than ten times the global energy could be produced (without impacting water and other important resources). The potential of PV to displace major amounts of conventional energy , ultimately depends on the technical viability of cost-competitive PV technologies, storage, and transmission. After cost reductions are achieved, the biggest barriers to the generalized use of PV beyond an estimated 10% daytime level i n developed countries will be the need for electricity storage or advanced transmission schemes that would allow greater dispatchability.

The size of future PV markets will ultimately be determined by the economics of PV systems. Future, lower cost P V systems (such as those based on thin films) have the potential to be used globally on a very large scale. If cost barriers can be overcome, U.S. usage (without storage) of up to 10% of our utility electricity production (more than 200 GWp PV capacity based on projected future U.S. electric capacity) is feasible. Use in developing countries could be as large or larger.

The environmental impacts of thin film PV are minimal and in general, PV is emission-free. Some impacts may b e expected during system manufacture; and issues exist for polycrystalline thin film systems in terms of ultimat e disposal/recycling. These issues are very minor compared to fuel-based energy production and are adequately addressed in References 3-13. (Reference 13 is a bibliography of 94 sources on PV environment, safety, and healt h issues.) There are some issues specific to compound semiconductors such as those found in polycrystalline thin films. Those are also covered in the same references, where 'cradle-to-cradle' recycling schemes have been outlined for ke y materials (see also below). For example, U.S. cadmium telluride (CdTe) companies have announced recycling an d product 'take-back' strategies [14].

In terms of energy use, a PV-based system would radically reduce total fuel-cycle emissions to approximately 5% o f conventional, including full energy payback. Calculations show that thin films require much less energy to manufacture than do other PV alternatives (except perhaps concentrator PV). The amount of CO2 produced during manufacture of thin films is small (about 5%-10% of the amount avoided, [15]). We expect that the mature production of thin films will result in energy paybacks of under three years for the entire system [15]. Since PV systems are expected to hav e useful lives exceeding thirty years, this implies that the reduction of CO 2 due to using PV is about 90% to 95% in comparison with conventional sources. Based on 0.3 million metric tons (MMT) of avoided CO 2/GW of installed PV/yr (assumes 2,000 GWh/GWp-yr and 150 MT avoided CO2/GWh), a scenario in which 230 GW of PV would be installed by 2030 would avoid 70 MMT of CO2/yr (and would have avoided about 800 MMT CO2 over the entire 19952030 timeframe). Since we expect PV to keep expanding in use beyond 2030, these avoided emissions would be only the beginning of a longer term reduction in CO 2.

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