The period of ‘profitless prosperity’ in the PV industry is finally at an end. Throughout 2013, despite continued economic woes, the PV industry has continued to expand and finally become a global industry. Market forecasts indicating that the sector could reach its next 100GW milestone in just the next two years suggest the industry is on the cusp of another period of strong growth. All the signs confirm this is the case, with utilization rates at their highest level since 2010, companies reporting full order books well into next year and the first tentative announcements of factory capacity expansions making the headlines.
Recent advances in cadmium telluride (CdTe) research and development have improved the long-term power output degradation and extended reliability test performance of First Solar’s thin-film CdTe PV modules. This paper reviews the characterization results of the new First Solar cell structure with improved back-contact design that better manages the fundamental power-output degradation mechanism. First Solar's proprietary ‘Black’ series module construction significantly enhances the long-term durability and extended test performance of the modules. The accelerated lab-testing methods, field testing and associated analyses are discussed. These advances in the solar cell performance, coupled with upgraded module materials, further substantiate the long-term power-generating capability of First Solar's CdTe PV modules in harsh operating conditions.
Minimizing the breakage rate of silicon wafers and cells during production has been one of the key issues for reliable and productive solar cell manufacturing. However, the root causes of damage or breakage,
as well as the mechanical characteristics of manufacturing processes, are not completely understood. In the study described in this paper the change in mechanical strength and the damaging of wafers and cells was analyzed in an industrial cell manufacturing line in order to detect critical process steps and handling operations in certain processes such as etching, diffusion, screen printing and firing. An analysis and discussion of damage sources is presented which offers more insight than the conventional study
of breakage rate that is mostly performed by cell manufacturers. In a systematic experimental study, 19 different locations in the production line were investigated. The mechanical strength of 800 wafers or cells at different points in the cell line was subsequently determined using the four-line bending test and the statistical parameters for the Weibull distribution. It was discovered that dramatic changes in strength
occur at different process steps because of the change in defect structure; there were also found to be several positions at which no further damage was detected. This method of investigation can therefore be used as
a fingerprint of a cell line in respect of yield and breakage rates. Individual processes can be identified that indicate high damage potential, although the actual breakage could occur in a subsequent process step.
Beyond lowering energy costs and demand charges, Superstorm Sandy demonstrated the frailty of centralized power generation. Building owners/operators throughout the Northeast in the USA are evaluating distributed power generation options for supporting building-critical loads during future grid outages. Those options (many of which also incorporate commercial-scale grid storage solutions) include on-site diesel generators, micro-turbines, fuel cells and solar PV systems. As electrical vehicle (EV) charging is added to the mix, the grid requirements and demand costs will further increase. This article will discuss specific value streams for integrating energy storage with PV for commercial buildings, and technologies - specifically, advanced power converters – that will enable those benefits to be achieved.
As part of the European FP7 R&D project ‘Cu-PV’, the compatibility of copper-electroplated metal wrapthrough (MWT) cells with conductive adhesives has been investigated. The objectives of this project include to reduce, by the use of copper plating, the amount of silver utilized in cell manufacturing, and to demonstrate the compatibility of high-power n-type back-contact module technology with copper-plated cells. The overall goal is to reduce the impact on the environment of cell and module manufacture. MWT module technology as developed by ECN uses conductive adhesive to make the interconnection between cells and a conductive backsheet foil. These adhesives have been proved to result in very reliable modules in the case of cells with fired silver metallization. To determine the compatibility of conductive adhesive with copper-plated cells, component tests were performed, followed by the manufacture of modules with copperplated cells and conductive adhesive interconnections. Climate chamber testing of these modules showed that the adhesive is compatible with the copper-plated cells. The next steps include further optimization of the plating process and additional testing at the module level.
Electrically conductive adhesives (ECAs) are an alternative interconnection technology especially suited to high-efficiency cell concepts with new contact structures. This paper describes the basic principles of this
emerging interconnection technology and discusses the different material types on the market. Mechanical and electrical characterization methods for conductive adhesives are also presented. Results are included from
peel tests, volume and contact resistivity measurements, metallographic investigations, dynamic mechanical analysis and differential scanning calorimetry. Finally, a novel simulation approach for the cure kinetics of
ECAs and arbitrary temperature profiles is briefly described and demonstrated by an example of an epoxy adhesive cure.
Future high efficiency silicon solar cells are expected to be based on n-type monocrystalline wafers. Cell and module photovoltaic conversion efficiency increases are required to contribute to lower cost per watt peak and to reduce balance of systems cost. Past barriers to adoption of n-type silicon cells by a broad base of cell and module suppliers include the higher cost to manufacture a p-type emitter junction and the higher cost of the n-type mono silicon crystal. Technologies to reduce the cost of manufacturing the p-type emitter by diffusion or implantation of boron are being developed in the industry. To reduce the cost and improve further the quality of n-type mono silicon crystal, SunEdison has developed a continuous Czochralski (CCZ) crystal pulling process, based on the technology of Solaicx, acquired in 2010. This CCZ technique allows production of a crystal with much greater resistivity uniformity, with a lower incorporation rate of lifetimereducing metals impurities, and allows crystal oxygen to be selected independent of production batch size. CCZ is expected to reduce n-type crystal cost below that of current p-type mono crystal.
This paper presents the status of imec’s work on the use of copper for the main conductor as an alternative to screen-printed silver front contacts in solar cells. This work is motivated not only by the limitations that Ag screen-printed contacts have regarding solar cell efficiency (high contact shading, limited line conductivity, and poor contact resistance to moderately doped emitters), but also by the PV industry's desire to reduce Ag usage for reasons of cost. Despite the potential advantages of Ni/Cu contacts, their commercialization has been limited because of increased process complexity and doubts over the €/Wp advantage and long-term reliability. These three factors all depend on the specific process and toolset and are discussed in this paper. A relatively simple process sequence is described that uses industrial pilot-line tools and consists of: 1) defining the front-contact pattern by ps-UV laser ablation; 2) self-aligned plating of the contacts using Ni/Cu/Ag; and, finally, 3) sintering in N2 for nickel silicidation. The process sequence is applied to 15.6 x 15.6cm2 p-type CZ-Si PERC (passivated emitter and rear cell) solar cells with 120Ω/sq. homogeneous emitters; average cell efficiencies of 20.5% are achieved over more than 100 cells. Cost analysis results are then discussed, indicating that this Ni/Cu process sequence has a lower cost/piece than equivalent screen-printed PERC cells while also providing ~0.5% abs. higher cell efficiency. Thermal-cycling and damp-heat reliability data that meet extended (1.5 x) IEC 61215 criteria for singlecell laminates and small modules are reported. The improved efficiency potential of applying this metallization sequence to rear-junction n-type PERT (passivated emitter and rear totally diffused) cells is discussed and preliminary results are given.
For more than a decade, the growth in PV markets surpassed expectations. Then, in 2012, the European market declined for the first time compared with the previous year. As policymakers’ support for PV hesitates over the costs to society of this technology, it is timely to take an overview of the social costs and benefits, also referred to as the ‘external costs’, of PV electricity. In this article, these costs are put into perspective visà- vis those associated with conventional electricity-generating technologies. The external costs of electricity can be broken down into: 1) the environmental and health costs; 2) the costs of subsidies and energy security; and 3) the costs for grid expansion and reliability. Included in these costs are the increased insurance, health, social and environmental costs associated with damages to health, infrastructure and environment,
as well as tax payments that subsidize producers of electricity or fuels, their markets and the electricity infrastructure. A life cycle assessment (LCA) of the environmental impact is used in the quantification of the associated environmental and health costs. Because the environmental footprint of PV electricity is highly dependent on the electricity mix used in PV module fabrication, the environmental indicators are calculated for PV electricity manufactured using different electricity mixes, and compared with those for the European electricity mix (UCTE), and electricity generated by burning 100% coal or 100% natural gas. In 2012$, coal electricity requires 19–29¢/kWh above the market price, compared with 1–1.6¢/kWh for PV manufactured with 100% coal electricity. The sum of the subsidies, avoided fossil-fuel imports and energy security, and the economic stimulation associated with PV electricity deployment, amounts to net external benefits. Integrating high penetrations of renewables, with the same reliability as we have today, appears to be fully feasible and within the cost horizons of the current activities of system operators.
Economic issues are the driving forces behind PV adoption. Even technological advances are measured against their impacts on cost per watt, levelized cost of energy (LCOE), and total cost of ownership for energy (TCOe™). This sixth paper in a series covering business analysis for PV processes looks at two approaches to manufacturing thin-film copper-indium-gallium-diselenide (CIGS) PV – sputtering and co-evaporation – and their potential areas for cost improvement.
