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silicon to the bottom surface, electrons move to the top n-doped surface, are collected, and then flow through the load to return through the bottom connector where they recombine with the holes, thus completing the circuit. Putting a conducting grid on the surface reduces the light entering the silicon, and hence reduces efficiency. This has led to several other architectures that Gilles summarised briefly. The PERC (passive emitter rear contact) cell developed at UNSW, in now very common, while the IBC (Interdigitated Back Contact) cell, with no contacts on the light-facing surface is another contender. Corrosion of connectors is a
major factor in determining the effective life of solar PV panels. Not all solar PV cells are based on silicon. The CIGS (Copper, Indium Gallium Selenide) cell has much higher light absorption than silicon, and therefore can be used in thin film form, only around 1 μm thick. These cells can be fabricated in several ways including coevaporation, electrodeposition and by printing. There are several technologies based on hydrogenated amorphous silicon, including multi-junction cells that are effective over wide ranges of light wavelengths. Among the alternatives, thin film
hybrid inorganic-organic materials with the perovskite crystal structure have progressed remarkably in just a few years. These are relatively cheap and easy to manufacture but, at first sight these would hardly seem very practical, as they are relatively unstable in oxygen, moisture, heat and light! Nevertheless, Gilles expressed confidence that these issues would be overcome and that the commercial target of a twenty-year useful life would be achieved. Silicon is not necessarily the ultimate material for solar PV cells, but the enormous established manufacturing base means that it is likely to remain dominant for a long time.
Sir Frank Ledger Breakfast Meeting - 29 November 2023 Challenges Associated with Safe and Efficient Operation of Large Scale, Multi‐Emitter Carbon Capture and Storage Projects Source: Stephen Stokes, Global Head of CO2 transport and storage, John Wood Group plc Stephen Stokes is a chemical engineer, and throughout his career he has had a continuing focus on the properties and flow of multiphase phase fluids. Before joining Wood, he had spent more than twenty years in oil & gas operations in the North Sea and in Western Australia, progressing from operations to carbon capture and storage (CCS). Wood is
currently involved in more than half the CCS projects worldwide. Most members of the audience were already familiar with vertically integrated CCS projects, in which producers of natural gas remove and re-inject CO2 to reduce greenhouse gas emissions. In this address, Stephen’s focus was
on multi-emitter projects, involving several diverse and geographically widespread industries including thermal power stations, hydrogen, and ammonia production plants. Liquefied CO2 is transported through branch and trunk pipelines to a collection hub and then transported to, and injected into, depleted petroleum reservoirs. Stephen referred to several such projects, including the European ‘Northern Lights’ project in which CO2 is to be collected and shipped by tanker to an injection platform the North Sea. Another project in Korea involves repurposing existing assets for an endof-life hydrocarbon platform to transport and inject CO2 into the depleted (low pressure) reservoir; this is financially attractive as it reduces abandonment cost (ABEX). Locally, the ExxonMobil SE Australia CCS project will collect CO2 from across the region and re-inject it into depleted Bass Strait formations. In the United States, the Gulf Coast CCS project envisages 400 km of pipeline, collecting 12 Mtpa by 2030. It has been estimated that this CCS market will grow to USD 4 trillion per year by 2050, together with increased
L to R: Stephen Stokes and Ehsan Karaji
16 | DECEMBER 2023
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