Sliver® cells for concentrator systems

One of the fundamental principles of concentrator PV systems is that expensive solar cells can be replaced by less expensive optics. However, the proliferation of concentrator systems has been somewhat held up by the fact that cells remain a significant component of total concentrator system cost. Current research in concentrator PV is focused in the area of high concentration systems which employ a smaller number of high efficiency triple junction cells. Sliver® cells, developed at The Australian National University, utilize a novel method for micromachining narrow, thin cells from conventional silicon wafers. The technology gives rise to a marked increase in active solar cell area per wafer processed. The cells were originally designed for nonconcentrating PV applications, though it is possible to modify the design of the cells such that they are capable of operating at low-medium concentration ratios. Modelling has been used to determine the optimum set of design parameters for concentrator sliver® cells. This forms the basis for cell fabrication. Development of low cost concentrator solar cells can provide a pathway to cost-effective low to medium concentration ratio PV systems

Sliver Solar Cells

Sliver solar cells are thin, mono-crystalline silicon solar cells, fabricated using micro-machining techniques combined with standard solar cell fabrication technology. Sliver solar modules can be efficient, low cost, bifacial, transparent, flexible, shadow-tolerant, and lightweight. Sliver modules require only 5 to 10% of the pure silicon and less than 5% of the wafer starts per MWp of factory output when compared with conventional photovoltaic modules. At ANU, we have produced 20% efficient Sliver solar cells using a robust, optimised cell fabrication process described in this paper. We have devised a rapid, reliable and simple method for extracting Sliver cells from a Sliver wafer, and methods for assembling modularised Sliver cell sub-modules. The method for forming these Sliver sub-modules, along with a low-cost method for rapidly forming reliable electrical interconnections, are presented. Using the sub-module approach, we describe low-cost methods for assembling and encapsulating Sliver cells into a range of module designs

A 40Kw roof mounted PV thermal concentrator system

The Australian National University, Centre for Sustainable Energy Systems (ANU-CSES) has developed a photovoltaic thermal (PV-T) concentrator system. This system is based on its Combined Heat and Power Solar (CHAPS) collector technology. This paper describes a roof mounted 40 kW PV-T concentrator system which was installed during 2003-4. The system comprises eight 24 metre long single axis tracking reflective solar collectors. Mirrors are used to focus light onto high efficiency monocrystalline silicon solar cells. The mirrors are constructed by laminating mirrored glass onto a metal backing, and provide a geometrical concentration ratio of 37x. Heat is removed from the solar cells using a fluid, which flows through a passage in the cell housings. The fluid is then passed through a heat exchanger to provide heat for domestic hot water and room heating. The collector movement is controlled by a microprocessor using an open loop time based algorithm. The annual output of the system is expected to be 50 MWHr of electricity and 100 MWHr of hot water

100% renewable electricity in Australia

An hourly energy balance analysis is presented of the Australian National Electricity Market in a 100% renewable energy scenario, in which wind and photovoltaics (PV) provides about 90% of the annual electricity demand and existing hydroelectricity and biomass provides the balance. Heroic assumptions about future technology development are avoided by only including technology that is being deployed in large quantities (>10 Gigawatts per year), namely PV and wind. Additional energy storage and stronger interconnection between regions was found to be necessary for stability. Pumped hydro energy storage (PHES) constitutes 97% of worldwide electricity storage, and is adopted in this work. Many sites for closed loop PHES storage have been found in Australia. Distribution of PV and wind over 10–100 million hectares, utilising high voltage transmission, accesses different weather systems and reduces storage requirements (and overall cost). The additional cost of balancing renewable energy supply with demand on an hourly rather than annual basis is found to be modest: AU$25–30/MWh (US$19–23/MWh). Using 2016 prices prevailing in Australia, the levelised cost of renewable electricity (LCOE) with hourly balancing is estimated to be AU$93/MWh (US$70/MWh). LCOE is almost certain to decrease due to rapidly falling cost of wind and PVThis work is supported by the Australian Government through the Australian Renewable Energy Agency (ARENA) (G00857

Silicon / Silicon oxide / LPCVD Silicon nitride stacks: The effect of oxide thickness on bulk damage and surface passivation

Silicon / thermally grown silicon dioxide / LPCVD silicon nitride stacks were formed to investigate the influence of the oxide thickness on silicon bulk and surface properties after thermal processing. With no oxide, the LPCVD silicon nitride layer causes serious irreversible bulk damage to silicon wafers after a high temperature treatment. A thin oxide layer (~10nm) helps to substantially reduce the damage. A thick oxide (more than 50nm) can help completely eliminate the bulk damage. An increase of surface states was indicated by an increase of emitter the saturation current density for the stacks with thin oxide layers after high temperature treatments. Even after a re-growth of thick oxide layer and forming gas anneal, the stacks previously without oxide layer shows a much higher emitter saturation current value, which indicates silicon nitride causes a serious Si-SiO2 interface damage. Keywords: LPCVD, Emitter saturation current, Effective lifetim

Geographic information system algorithms to locate prospective sites for pumped hydro energy storage

Pumped hydro energy storage is capable of large-scale energy time shifting and a range of ancillary services, which can facilitate high levels of photovoltaics and wind integration in electricity grids. This study aims to develop a series of advanced Geographic Information System algorithms to locate prospective sites for off-river pumped hydro across a large land area such as a state or a country. Two typical types of sites, dry-gully and turkey’s nest, are modelled and a sequence of Geographic Information System-based procedures are developed for an automated site search. A case study is conducted for South Australia, where 168 dry-gully sites and 22 turkey’s nest sites have been identified with a total water storage capacity of 441 gigalitres, equivalent to 276 gigawatt-hours of energy storage. This demonstrates the site searching algorithms can work efficiently in the identification of off-river pumped hydro sites, allowing high-resolution assessments of pumped hydro energy storage to be quickly conducted on a broad scale. The sensitivity analysis shows the significant influences of maximum dam wall heights on the number of sites and the total storage capacity. It is noted that the novel models developed in this study are also applicable to the deployments of other types of pumped hydro such as the locations of dry-gully and turkey’s nest sites adjacent to existing water bodies, old mining pits and oceans

Boron doping of silicon layers grown by liquid phase epitaxy

This paper presents the results of a study of the incorporation of boron into silicon layers grown from a tin melt by liquid phase epitaxy. Boron was added to the melt through the use of boron-doped silicon source wafers. There is a large discrepancy between the amount of boron incorporated into the epitaxial layer and that available in the source wafer. This mismatch is explained by the gradual removal of boron from our system, most likely as a result of boron precipitation in the tin melt. This situation allows for control of the boron profile by adjusting the cooling rate and adding a dwell time. In this way, we have grown an epitaxial layer with an abrupt and highly doped p-type region at the epitaxial layer/substrate interface. This is useful for thin film solar cell applications as it allows the growth of a back surface field and a lightly doped bulk in a single growth step