Photovoltaics International Papers

The cost of PV modules manufactured and sold in 2012 is highly reliant on the materials used in the construction. A significant part of the market price is driven by the bill of materials, while other direct costs and depreciation form a small proportion of the total cost. Changes within the supply chain, and in the cost of the materials needed and used, are extremely important influences on the module cost and the end market price. In 2012 we have seen a slowdown in growth in the installation of both commercial and residential PV, despite dramatic falls in module costs. Some of the trends and effects of these changes on the materials supply chain for PV modules will be examined in this paper.

Production equipment is the backbone of the PV industry, but the equipment sector is suffering because of overcapacity. The 2012 global capacity utilization is at 55% for crystalline silicon (x-Si) module production, 70% for cadmium telluride (CdTe) and 80% for copper indium gallium (di)selenide (CIGS). Under these market conditions, there are almost no expected capacity expansions in the near term. The overcapacity has driven the average selling price (ASP) for modules significantly lower, resulting in hyper-competition in the PV industry, where almost all PV companies recognize the importance of product differentiation while still reducing costs. These market conditions present an opportunity for equipment manufacturers to differentiate their offerings through enabling lower production costs and higher efficiency of cells and modules.

This paper provides an overview of reducing the ‘soft costs’ of solar, with a focus on driving down the cost of balance of system (BOS) and operations, primarily in commercial-scale installations. Attention is drawn to the internal data and information on specific case studies/best practices that can be replicated by other companies. Mainstream Energy (which supports three business units – REC Solar, AEE Solar and SnapNRack) aims to simplify system design and configuration by utilizing new technologies and streamlining internal processes to reduce total system cost – and take solar to the mainstream.

This paper provides an overview of reducing the ‘soft costs’ of solar, with a focus on driving down the cost of balance of system (BOS) and operations, primarily in commercial-scale installations. Attention is drawn to the internal data and information on specific case studies/best practices that can be replicated by other companies. Mainstream Energy (which supports three business units – REC Solar, AEE Solar and SnapNRack) aims to simplify system design and configuration by utilizing new technologies and streamlining internal processes to reduce total system cost – and take solar to the mainstream.

Economic success in operating PV systems depends essentially on the likelihood of their long-term operation and their delivery of the expected energy yield. These requirements, for which a lifetime of 20–25 years is often assumed, are demanding and cannot be met without preparation. Preconditions are the acceptable quality and long-term stability of the products employed (particularly the PV modules, but also all other components and materials) and the absence of damage to these items during transport and handling. Moreover, PV systems must be professionally planned and properly implemented. This includes considering energy yield assessments not only in the initial estimation of the energy yield, but also in the subsequent planning for concrete implementation. In addition, professional operational management and appropriate maintenance measures will ensure operation with maximum availability. Yield insurance policies can safeguard profitability and render the risks calculable; various models exist for this purpose and these must be carefully tested. It is important that the insurances services also cover the possible insolvency of the responsible system and component suppliers.

Electroluminescence (EL) imaging for photovoltaic applications has been widely discussed over the last few years. This paper presents the results of a thorough evaluation of this technique in regard to defect detection in photovoltaic modules, as well as for quality assessment. The ability of an EL system to detect failures and deficiencies in both crystalline Si and thin-film PV modules (CdTe and CIGS) is thoroughly analyzed, and a comprehensive catalogue of defects is established. For crystalline silicon devices, cell breakages resulting from micro-cracks were shown to pose the main problem and to significantly affect the module performance. A linear correlation between the size of the breakages and the power drop in the module was established. Moreover, mechanical stress and temperature change were identified as the major causes of the proliferation of cracks and breakages. For thin-film modules, EL imaging proved the existence of an impressive reduction in the size of localized shunts under the effect of light-soaking (together with a performance improvement of up to 8%). Aside from that, the system voltage was applied in order to monitor transparent conductive oxide (TCO) corrosion effects and laser-scribing-induced failures, as well as several problems related to the module junction box in respect of its sealing and the quality of its electric connectors.

In this paper an assessment is made of the impact of causal peer effects found in a recent paper by Bollinger and Gillingham, simulating solar adoption over many markets in the presence of a causal peer effect. Heterogeneity in both the peer effect and the baseline adoption rate is introduced and their interaction assessed. The nature of the heterogeneity and the size of the peer effect both have implications for the resulting diffusion process. Causal peer effects have implications for firms and policymakers, who have the ability to utilize social spillover effects in their marketing activities in order to increase and expedite solar adoption.

Like all semiconductor photovoltaic devices, cadmium telluride (CdTe) modules have a characteristic response to temperature changes. This paper describes the effects of the temperature coefficient of power, using operational system data to quantify the First Solar CdTe technology energy-yield advantage over typical crystalline silicon technology in high-temperature conditions. This paper also describes the underlying mechanisms of initial stabilization and longterm degradation that influence module efficiency. The processes used to characterize and rate module power output, given these effects, are further discussed. First Solar’s significant experience in building and operating power plants in high-temperature conditions, along with associated system performance data and accelerated lab test data, is reviewed to substantiate the warranty considerations and long-term capability of power plants using CdTe PV modules.

There has been recent interest in the use of thermoplastic encapsulant materials in photovoltaic modules to replace chemically cross-linked materials, for example ethylene-vinyl acetate. The related motivations include the desire to reduce lamination time or temperature, to use less moisture-permeable materials, and to use materials with better corrosion characteristics or improved electrical resistance. However, the use of any thermoplastic material in a hightemperature environment raises safety and performance concerns, as the standardized tests do not currently include exposure of the modules to temperatures in excess of 85°C, even though fielded modules may experience temperatures above 100°C. Eight pairs of crystalline silicon modules and eight pairs of glass/encapsulation/glass thin-film mock modules were constructed using different encapsulant materials, of which only two were designed to chemically cross-link. One module set with insulation on the back side was exposed outdoors in Arizona in the summer, and an identical set was exposed in environmental chambers. High-precision creep measurements (±20μm) and performance measurements indicated that, despite many of these polymeric materials being in the melt state during outdoor deployment, there was very little creep because of the high viscosity of the materials, the temperature heterogeneity across the modules, and the formation of chemical cross-links in many of the encapsulants as they aged. In the case of the crystalline silicon modules, the physical restraint of the backsheet reduced the creep further.

Apart from aesthetics, the gain in electrical performance of back-contact solar cells and modules is particularly attractive compared to conventional PV modules. This major benefit results from getting rid of (the majority of ) the metallization at the front, and providing all the cell contacts at the back. An overview is presented here of the different concepts put forward by different institutes and companies around the world for such back-contact modules. The different types of state-of-the-art back-contact cell are first introduced, together with their corresponding contacting and interconnection schemes. Keeping in mind the reference module technology for two-side-contacted cells as a starting point, each module concept is then briefly discussed in terms of technology and level of maturity. Finally, the main technological differences are summarized.