E.A. Alsema

Energy pay‐back time and CO2 emissions of PV systems

The energy requirements for the production of PV modules and BOS components are analyzed in order to evaluate the energy pay-back time and the CO2 emissions of grid-connected PV systems. Both c-Si and thin film module technologies are investigated. Assuming an irradiation of 1700 kWh/m2/yr the energy pay-back time was found to be 2·5–3 years for present-day roof-top installations and 3–4 years for multi-megawatt, ground-mounted systems. The specific CO2 emission of the rooftop systems was calculated as 50–60 g/kWh now and possibly 20–30 g/kWh in the future. This leads to the conclusion that in the longer term grid-connected PV systems can contribute significantly to the mitigation of CO2 emissions. Copyright

Environmental Impact of Crystalline Silicon Photovoltaic Module Production

Together with a number of PV companies an extensive effort has been made to collect Life Cycle Inventory data that represents the current status of production technology for crystalline silicon modules. The new data cover all processes from silicon feedstock production to cell and module manufacturing. All commercial wafer technologies are covered, that is multi- and monocrystalline wafers as well as ribbon technology. The presented data should be representative for the technology status in 2004, although for monocrystalline Si crystallisation further improvement of the data quality is recommended. On the basis of the new data a Life Cycle Assessment has been performed, which shows that c-Si PV systems are in a good position to compete with other energy technologies. Energy Pay-Back Times of 1.7-2.7 yr are found for South-European locations, while life-cycle CO 2 emissions are in the 30-45 g/kWh range. Clear perspectives exist for further improvements of roughly 40-50%.

Energy requirements of thin-film solar cell modules--a review

In this paper a number of energy analysis studies for thin-film solar cell modules are compared and reviewed. We start with a short introduction into methodological issues related to energy analysis (of PV systems) such as system boundary definition, treatment of different (secondary) energy types and the choice of functional unit. Subsequently we review results from 6 studies on a-Si modules and 3 studies on CdTe modules. The aim is to present results in a unified format, compare them and try to clarify observed differences. Although significant differences were found, many of these differences could be explained by the choice of materials for the module encapsulation. For categories with large observed differences, like indirect process energy and capital equipment energy, we performed additional analyses in order to gain a better understanding of these aspects. Finally we present best estimates of the energy requirement for present-day a-Si and CdTe thin film modules which are between 600 and 1500 MJ (primary energy) per mfn3 module area, depending on cell and encapsulation type. This means that the energy pay-back time is below two years for a grid-connected module under 1700 kWh[-45 degree rule]m2[-45 degree rule]yr irradiation. In the near future an energy pay-back time below one year seems feasible.

Life Cycle Analysis of Solar Module Recycling Process

Since June 2003 Deutsche Solar AG is operating a recycling plant for modules with crystalline solar silicon cells. The aim of the process is to recover the silicon wafers so that they can be reprocessed and integrated in modules again. The aims of the Life Cycle Analysis of the mentioned process are (i) the verification if the process is beneficial regarding environmental aspects, (ii) the comparison to other end-of-life scenarios, (iii) the ability to include the end-oflife phase of modules in future LCA of photovoltaic modules. The results show that the recycling process makes good ecological sense, because the environmental burden during the production phase of reusable components is higher than the burden due to the recycling process. Moreover the Energy Pay Back Time of modules with recycled cells was determined.

Environmental Life Cycle Inventory of Crystalline Silicon Photovoltaic Module Production

Together with 11 European and US photovoltaic companies an extensive effort has been made to collect Life Cycle Inventory (LCI) data that represents the status of production technology for crystalline silicon modules for the year 2004. These data can be used to evaluate the environmental impacts of photovoltaic solar energy systems. The new data covers all processes from silicon feedstock production via wafer- and cell- to module manufacturing. All commercial wafer technologies are covered, i.e multi- and mono-crystalline wafers as well as ribbon technologies. For monocrystalline silicon wafer production further improvement of the data quality is recommended.

A simple model for PV module reflection losses under field conditions

Abstract PV module power ratings are determined at standard test conditions, which require perpendicular incident light. Under field conditions larger incidence angles occur, resulting in higher reflection losses than accounted for in the nominal power rating. In this article we will present a model to take these losses into account, and discuss some results for practical situations. From our model we conclude that the reflection losses relative to STC are determined mainly by the air glass-interface. Limited validation assuming certain spectral losses showed a rough correspondence between calculated reflection losses and experimental values on a yearly averaged basis (1.2% difference between model and experiment). Model calculations show that for modules faced towards the equator, and with a tilt angle equal to the latitude, yearly reflection losses relative to STC are about 3%. For this tilt and orientation, the losses seem to be only slightly dependent on the geographical latitude of the location. Tilt, orientation and seasonal dependence are significant. For vertically mounted PV modules (facades) near the equator the reflection losses can be quite large (up to 8%)

Towards cleaner solar PV: Environmental and health impacts of crystalline silicon photovoltaics

Recent studies give the impression of photovoltaics having considerable environmental impact. Looking closer at the data however, it is clear that these studies are based on photovoltaic systems of the late eighties, with only minor recalculations. Since the photovoltaic market has increased rapidly, a lot of progress has been made regarding the environmental profile of photovoltaics. In this article Mariska de Wild-Scholten and Erik Alsema report on the improvements already achieved, those expected in the near future and the issues that need to be tackled for the development of crystalline silicon photovoltaics. They focus the discussion on multicrystalline silicon solar cells, the technology with the largest market share at present.

V-2 – Energy Pay-Back Time and CO2 Emissions of PV Systems

Publisher Summary This chapter presents the energy viability of photovoltaic (PV) energy technology. Every new energy technology that is promoted as being renewable or sustainable should be subjected to an analysis of its energy balance to calculate the net energy yield. It is of great importance that such an energy analysis is not only based on data for present generation systems but also considers expected improvements in production and energy system technology. Since energy consumption generally has significant environmental implications, the energy analysis may be considered as a first step towards a more comprehensive environmental life-cycle assessment. Furthermore energy analysis results provide a good indication of the CO2 mitigation potential of the considered energy technology. In an energy analysis, a comprehensive account is given of the energy inputs and outputs involved in products or services. The overall energy performance of such products and services is determined by accounting all energy flows in the life cycle. In the case of solar cells, the gross energy requirement is determined by adding together the energy input during resource winning, production, installation, operation, and decommissioning of the solar cell panels and the other system components.

Using life-cycle assessments for the environmental evaluation of greenhouse gas mitigation options

The complex structure of energy supply systems and the range of environmental issues involved, make decisions regarding the use of new or improved energy resources and energy technologies far from being straightforward. A life-cycle approach is required to reveal the full potential for an option to realize increased energy performance and reduced emissions of greenhouse gases. In addition, the life-cycle assessment reveals possible bottlenecks regarding other environmental issues.

Life cycle assessment of photovoltaics: perceptions, needs, and challenges

High impact publications recently depicted PV technologies as having higher external environmental costs than those of nuclear energy and natural-gas-fueled power plants. These assessments are based on old data and unbalanced assumptions, and they illustrate the need for LCA data describing the continuously improving photovoltaic systems and the inclusion of social benefits in this comparison.