Photovoltaic materials abundance limitations literature review/Silicon: Evolution and future of technology

Silicon: Evolution and future of technology^[1][edit | edit source]

Monocrystalline silicon is also used in the manufacturing of high performance solar cells. Since, solar cells are less demanding than microelectronics for as concerns structural imperfections, monocrystaline solar grade (Sog-Si) is often used, single crystal is also often replaced by the cheaper polycrystalline silicon. Monocrystalline solar cells can achieve 21% efficiency. silicon Monocrystalline siicon

The writers of one of the chapters W.Heywang, K.H.Zaininger were the pioneer men who had seen the evolution of the silicon technology over the years. They summarized certain properties of silicon during their study.

1. It is abundant easy to obtain and low cost.
2. It is a single crystal with substrate diameter as large as 12 inches in which defects could be eliminated or selectively utilized.
3. Not brittle and can easily be handled with an excellent mechanical substrate.
4. Adequate thermal conduction to take away electrically generated heat.
5. Thin crystalline films can be grown over substrate having different electrical properties via epitaxy.
6. Thin crystalline films can be grown over insulators to provide improved isolation, speed and lower capacitance.
7. Novel films of III - V compounds containing quantum dots can be grown onto substrate by CVD or MBE.
8. Doping (n type or p type)can improve the conductive properties of silicon using diffusion or ion implantation.\
9. It is not light sensitive and is stable under various light conditions.

Solar cell surface characterization^[2][edit | edit source]

Majority of solar cells are produced using monocrystalline or large grained polycrystalline silicon. To reduce manufacturing cost industries use lower quality siliocon refered as metallurgical grade silicon which has about 98% purity. For this material the light absorbtion efficiency is very low. Increasing the effective optical thickness of the silicon surface is the most reliable way to increase cell efficiency. It is called as surface texturing and depends on the nature of silicon. On the other hand in multicrystalline silicon, texturing is not so effective because most of the grains have dislocated orientation. Surace texturing on this has the disadvantage that different grain etch at different rates giving steps at grain boundaries which proves to be a problem for the subsequent processess.

Producer responsibility and recycling solar photovoltaic modules^[3][edit | edit source]

In this paper Pearce et al have given vital information on the recycling of the photovoltaic materials in 5 major technologies vis polycrystalline silicon, crystalline silicon, amorphous silicon, cadmium telluride and CIGS. From this analysis the postulated formulas for mass of recovered semiconductor and glass, and profit from resale of recovered semiconductor and glass.

Thermodynamic limitations to nuclear energy deployment as a greenhouse gasmitigation technology^[4][edit | edit source]

To both replace fossil-fuel-energy use and meet the future energy demands, nuclear energy production would have to increase by 10.5% per yearfrom 2010 to 2050. Global warming is already occurring, and if combustion of fossil fuels continues, temperatures are projected to rise by between 1.8°C and 4°C in the next 100 years. the US National Energy Policy Development Group stated, "Nuclear power today accounts for 20% of our country's electricity. This paper shows how they could reduce the GHG emission by using efficient methods.

Global electricity production using different sources^[5][edit | edit source]

World electricity generation rose at an average annual rate of 3.6% from 1971 to 2009, greater than the 2.1% growth in total primary energy supply. This increase was largely due to more electrical appliances, the development of electrical heating in several developed countries and of rural electrification programmes in developing countries. The share of electricity production from fossil fuels has gradually fallen, from just under 75% in 1971 to 67% in 2009. This decrease was due to a progressive move away from oil, which fell from 20.9% to 5.1%. Oil for world electricity generation has been displaced in particular by dramatic growth in nuclear electricity generation, which rose from 2.1% in 1971 to 17.7% in 1996. However, the share of nuclear has been falling steadily since then and represented 13.4% in 2009. The share of coal remained stable, at 40-41% while that of natural gas increased from 13.3% to 21.4%. The share of hydro-electricity decreased from 22.9% to 16.2%. Due to large development programmes in several OECD countries, the share of new and renewable energies, such as solar, wind, geothermal, biofuels and waste increased. However, these energy forms remain of limited importance: in 2009, they accounted for only 3.3% of total electricity production for the world as a whole.

Towards sustainable photovoltaics: the search for new materials^[6][edit | edit source]

This paper talks about the material scarcity that are used in PV systems and to find alternative to them and says if PVs is to make a significant contribution to satisfy global energy requirements, issues of sustainability and cost will need to be addressed with increased urgency. In terms of primary (thermal) power rather than energy, the corresponding 2008 figure is 13.2 TW, of which less than 0.8 TW was generated by non-nuclear renewable resources (primarily hydroelectric). The total power of the Sun's radiation that is incident on the Earth can be calculated from the solar constant (1.366 kW m−2) and the cross-sectional area of the Earth. The result is 1.4×1017W, i.e. around 5000 times the estimated primary power requirement for 2050. If we assume that we could cover 1 per cent of the Earth's land surface with solar arrays operating at a power efficiency of 10 per cent, a rough calculation based on the land area illuminated by the Sun and losses owing to weather and seasons indicates that photovoltaics (PVs) could generate around 25 TW. The current contribution of PVs to the total world energy requirement is still very small, with total worldwide installed capacity just over 20 GWp.

The bandgaps of different materials are compared and the bandgap of the CIGS system can be tuned by controlling the In/Ga ratio. CdTe thin film solar cells CdTe-based solar panels are currently the most rapidly expanding thin-film PV technology, with module sales from First Solar reportedly passing the 1 GWp mark in 2009. This paper therefore attempted to show that thin-film PVs are having an increasing impact on renewable energy strategies. Existing technologies based on well-known semiconducting materials are driving down cost and carbon footprint, and novel technologies are moving towards the market.

Materials availability for thin film (TF) PV technologies development: A real concern?^[7][edit | edit source]

The authors have compared 6 different papers (Andersson et al, 1998; B A Anderson, 2000; Keshner and Arya, (report), 2004; Feltrin and Freundlich, 2008; V Fthenakis, 2009; Wadia et al., 2009) which have all talked about material availability for thin film solar cells. It shows the different assumptions on which all these papers have postulated their theory. Assumptions with respect to cell efficiencies, material thickness, material utilization for solar industry, recycled material useage etc. which all results in different numbers related to power production. It states that PV generation will play a major role in the future global energy mix up to 11% of global electricity by 2050. In 2009, c-Si had a 82% market domination and thin film (TF) technologies had 17%. CdTe TF modules are currently the least expensive to manufacture with a module cost production of $0.76/W. They suggest that the implications of rising material costs as a result of relative scarcity may be more significant to the future development of CdTe and CIGS technologies than any fundamental limit on material supply.

This paper compares certain different papers on material availability of indium and tellurium and says that the estimates of future availability of indium and tellurium used in the literature present several uncertainties, both in the data and in the methodologies adopted. Regarding the availability of material data shown by USGS every year, to collect this data would require a significant international co-operation which they assume to be unlikely. It states that In and Te could be extracted from Iron and Lead respectively which have not been estimated by USGS. Therefore they argue that there is more In and Te than that is estimated. These three factors (marginal reserves, improving geological knowledge and technological advance) are collectively referred to as 'reserve growth'. Reserves, reserve growth, and 'yet to find' (YTF) can be collectively referred to as Ultimately Recoverable Resources (URR). To increase the power, one or all the 3 points could be implemented. 1) Increasing cell and module efficiencies. 2) Reducing the active layer thickness. and/or 3) Higher material utilisation during production.

It should also be pointed out that that recycled indium and tellurium are not fully accounted for by the literature in estimating materials' future availability. Indium is increasingly reclaimed from deposition process of indium tin oxide (ITO) in liquid crystal displays (LCDs) manufacturing, which accounts for more than 50% of primary indium demand. This number could be increased to 92% based on the research. Also Average recovery rates of around 90–95% are possible for Te from CdTe end-of-life cells. Materials constrained potential of CdTe and CIGS technologies has to be assessed while acknowledging that future market size and cumulative installed capacity are to be satisfied by a mix of PV technologies. Thus, it is possible to conclude that absolute availability of indium and tellurium is not a constraint to future development and deployment of CIGS and CdTe PV technologies per se. More than 50% of refine Indium is used by ITO industry and only 2% in the solar industry. Thus ITO has been held accountable for the price increase in indium. However, 11% of tellurium was used in the solar industry in 2009 which might have a significant role in driving the prices. However, as some contributions in the literature have suggested, it is the price of indium and tellurium that could have a negative impact on cost reduction ambitions and future developments of CdTe and CIGS technologies. Ultimately the author says that there is more amount of indium and tellurium available that can be discovered which can be used in the solar cells. In conclusion, they have said that there is plenty of reserves available for In and Te, but the factor that posses a threat to the development of these technologies is the price hike in the near future.

Can solar power deliver?^[8][edit | edit source]

Until 2013, mono crystalline and multi crystalline silicon modules have contributed to 90 % of installed PV capacity. It clearly states with number that even if we harvest just over 1% of solar energy available in a year, we exceed the annual power and electricity requirement. (Useable land area and whether conditions have been considered). Assuming if 15% efficiency cell were modules deployed in London, only 5% of its land area would be required to power the whole city. This shows that there is plenty of land available for solar installation. It quotes solar power as intermittent energy source, and need to be cascaded with other renewable energy source like wind to provide the energy needs. In projections of future energy supply, PVs are expected to play a significant role, delivering up to 16 per cent of global electricity by 2050. It states that the cost could be reduced using the new technological milestones. BOS has an important contribution in the cost of the module and new technologies are ensuring that BOS is reduced. In the growth of the PV industry every year, carbon emission play an important role. Its states for short term that higher growth of low carbon intensive technology will reduce the carbon effects and for longer term, with R&D, high efficiency cell would help in utilizing higher device area which will ultimately mitigate the carbon issue drastically.

Technology Roadmap: Solar Photovoltaic Energy^[9][edit | edit source]

This technology roadmap estimates that: 1. By 2050, PV could provide 11% of global electricity production and avoid 2.3 gigatonnes (Gt) of CO2 emissions per year. 2. By 2020, PV is expected to reduce system and generation costs by more than 50%. PV residential and commercial systems will achieve the first level of grid parity. 3. Towards 2030, typical large-scale utility PV system generation costs are expected to decrease to USD 7 to USD 13 cents/kWh.

Assessing the dynamic material criticality of infrastructure transitions: A case of low carbon electricity^[10][edit | edit source]

Criticality is currently defined as the combination of the potential for supply disruption and the exposure of a system of interest to that disruption. The European Commission defines critical materials as those at risk of supply disruption and which are difficult to substitute. The criticality assessment has been done in particular for Neodymium. Fig 2 shows the criticality of two scenarios of transition to low carbon electricity generation in the UK from 2012–2050. The results show that criticality in the Core Pathway increases more than threefold over the period from 2012 to 2050, with a step-change occurring in 2030, as shown with reference to 2012 values. This trend is even more dramatic in the Renewables scenario with a ninefold increase. The results of the case study demonstrate the importance of considering the dynamic analysis of the risk of material criticality.

Photovoltaic material resources^[11][edit | edit source]

This chapter refers to materials critical in the thin film photovoltaic industry like Gallium, Indium and Tellurium and makes an analysis regarding it. Referring to different sources it says that Te ranges from critical to not critical material. Projections for 2050 vary by nearly 2 orders of magnitude with the lower end stating 100GW and upper end 10TW. This difference is due to the different assumptions made by the sources. The lower end of the projection for 2050 represents less than 2% per annum compounded growth suggesting little difficulty in increasing material suppy rates. The higher end of the range represents a growth rate of 20% per annum.

Considerations of resource availability in technology development strategies: The case study of photovoltaics^[12][edit | edit source]

World electricity demand is continuously growing and is expected to be 28 000 TWh by 2030 and range between 50 000 TWh and 60 000 TWh in 2050. The pay back times of different PV technologies have been mentioned in this paper. The theoretical limit for energy production by solar based technology is the global irradiation which accounts to 1 083 000 000 TWh and the (state-of-the-art) technical limit is 444 000 TWh which takes into account issues like available land, electricity net configuration, conversion efficiency, etc. As the technical limit (444 000 TWh) is about 9–7.5 times the expected demand in 2050 as mentioned above (50 000–60 000 TWh), irradiation and technology should not be a limiting factor. As an example of material thickness, 3 micon of a CdTe absorber layer are only around 9 g of Cd and 9 g of Te per square meter. For c-Si, losses due to sawing and losses at ingot growing are in the range of 45–51%. In the case of CdTe and CIGS the material utilization is currently around 40% and 90% foe a-Si. In this scenario 25% of worlds electricity demand is supposed to be produced through PV installations by 2040. In absolute numbers this accounts for 10000 TWh of the produced electricity by 2040. For material availability specifically for tellurium, Even in the optimistic scenario cumulative tellurium demand is around 2.5 times the known reserves for 2040.

Sustainability of photovoltaics: The case for thin-film solar cells^[13][edit | edit source]

This paper talks about the availability of material for solar applications, in particular, tellurium and indium. To ensure photovoltaics become a major sustainable player in a competitive power-generation market, they must provide abundant, affordable electricity, with environmental impacts drastically lower than those from conventional power generation. The recent reduction in the cost of 2nd generation thin-film PV is remarkable, meeting the production milestone of $1 per watt in the fourth quarter of 2008. This achievement holds great promise for the future. However, the questions remaining are whether the expense of PV modules can be lowered further, and if there are resource- and environmental-impact constraints to growth. The potential of thin-films in a prospective life-cycle analysis has been examined, focusing on direct costs, resource availability, and environmental impacts. These three aspects are closely related; developing thinner solar cells and recycling spent modules will become increasingly important in resolving cost, resource, and environmental constraints to large scales of sustainable growth. In conclusion he say that there is huge potential in solar power generation, and future R&D should concentrated on reducing the thickness of the material used in the thin film solar cells.

Considerations of resource availability in technology development strategies: The case study of photovoltaics^[14][edit | edit source]

This paper has done an analysis on the tellurium and indium availability. Photovoltaic (PV) technologies have experienced considerable growth rates of up to 70% in the last years. This has been possible because of low total CO2 emissions and a positive overall energy balance for PV. Several institutions have developed future scenarios which show an increase in global electricity demand from 17 000 TWh in 2005 to some 60 000 TWh by 2050. A significant part of this amount should be supplied by PV installations. Based on selected scenarios material demand is calculated for four different PV technologies: crystalline silicon (c-Si), amorphous silicon (a-Si) in tandem configuration, cadmium tellurium (CdTe) and copper indium gallium diselenide (CIGS). As these technologies use rare metals it is shown, that particular scenarios are unlikely to be realized because of supply constraints and scarcity phenomena. Critical materials are silver, tellurium and indium. We consider photovoltaics as an appropriate example for the implementation of resource availability considerations into technology development strategies.

They have conducted sensitivy analysis on different solar cell technologies. Only a-Si in tandem configuration with μc-Si has, from today's point of view, the potential to be installed on a several terawatt level. They say that recycling of material would become a huge aspect when larger capacity power installations are done in the future.

Towards real energy economics: Energy policy driven by life-cycle carbon emission^[15][edit | edit source]

This paper focusses on the policy required to have a good future in solar sector. It has done a comparison chart of the CO2 emission occuring due different energy sources. In the table it is mentioned that 1 kWH of energy generated due to combustion of coal produces 881.6 grams of CO2 in the atmosphere. However for solar PV, its in the range of 21-59 g/kWh. Also the energy payback time has been compared to fossil fuel and solar has been proved to be far more superior than any other source of energy used. Thus in conclusion they say, the challenges involved in meeting increasing electricity demand while simultaneously reducing carbon dioxide emissions can be met by the large-scale deployment of alternative energy technologies. However, deployment must be dependent on the life-cycle carbon emissions of each viable technology. Currently employed static life-cycle assessments incorrectly trivialize subtleties associated with rapid growth; this disparity enables the development of a global carbon Ponzi Scheme wherein the carbon mitigation potential of technologies is hindered by large-scale deployment. Dynamic life-cycle analyses offer a superior tool to evaluate deployment strategies for energy technologies. While there remains a need for rigorous simulation of carbon-neutral growth rates on both global and local scales, carbon-neutral growth rates paired with dynamic life-cycle assessments arm policy makers with standardized information needed to optimize electricity generation technology deployment for effective climate change mitigation.

Effect of packing factor on the performance of a building integrated semitransparent photovoltaic thermal (BISPVT) system with air duct^[16][edit | edit source]

In this paper, an attempt has been made to study the effect of packing factor of semitransparent photovoltaic (PV) module integrated to the roof of a building, on the module and room air temperature, and electrical efficiency of PV module. Energy and exergy analysis have been carried out by considering different packing factors (0.42, 0.62, and 0.83) of PV module namely mono crystalline silicon (m-Si), poly crystalline silicon (p-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and a heterojunction with thin layer (HIT). It is observed that the decrease in the temperature of PV module due to decrease in packing factor, increases its electrical efficiency. It is also found that the decrease in packing factor increases the room temperature. Maximum annual electrical and thermal energy is found to be 813 kWh in HIT and 79 kWh in a-Si PV module respectively with packing factor of 0.62

Technology Roadmap: Solar photovoltaic energy^[17][edit | edit source]

1. Solar PV power is a commercially available and reliable technology with a significant potential for long-term growth in nearly all world regions. This roadmap estimates that by 2050, PV will provide around 11% of global electricity production and avoid 2.3 gigatonnes (Gt) of CO2 emissions per year. 2. Achieving this roadmap's vision will require an effective, long-term and balanced policy effort in the next decade to allow for optimal technology progress, cost reduction and ramp-up of industrial manufacturing for mass deployment. Governments will need to provide long-term targets and supporting policies to build confidence for investments in manufacturing capacity and deployment of PV systems. 3. PV will achieve grid parity – i.e. competitiveness with electricity grid retail prices – by 2020 in many regions. As grid parity is achieved, the policy framework should evolve towards fostering self-sustained markets, with the progressive phase-out of economic incentives, but maintaining grid access guarantees and sustained R&D support.

Energy Technology Perspective^[18][edit | edit source]

This report focuses on the stats related to energy and considers the scenarios and strategies to 2050. ETP 2010 presents updated scenarios from the present to 2050 that show which new technologies will be most important in key sectors and in different regions of the world. It highlights the importance of finance to achieve change, examines the implications of the scenarios for energy security and looks at how to accelerate the deployment of low-carbon technologies in major developing countries. It presents roadmaps and transition pathways for spurring deployment of the most important clean technologies and for overcoming existing barriers. With extensive data, projections and analysis, Energy Technology Perspectives 2010 provides decision makers with the detailed information and insights needed to accelerate the switch to a more secure, low-carbon energy future.

References[edit | edit source]

See also[edit | edit source]

• Evolution of microstructure and phase in amorphous, protocrystalline, and microcrystalline silicon studied by real time spectroscopic ellipsometry
• Improvement of solar cells performance by boron doped amorphous silicon carbide/nanocrystalline silicon hybrid window layers
• General Temperature Dependence of Solar Cell Performance and Implications for Device Modelling
• Potential of solar electricity generation in the European Union member states and candidate countries