Reliable methods for PV power plant performance testing

By Evan S. Riley, Renewable Energy Consultant, Black & Veatch

Using a prescribed test protocol to compare the measured performance of a solar PV power plant relative to its expected performance is often a means by which the value of the facility is determined. Performance testing is used contractually to determine matters such as the fee paid to a constructor, the price paid to a seller, and the cost of capital from a lender or investor. To ensure that performance testing produces consistent and independently verifiable results, it is essential that accurate and repeatable test methods be used. This paper outlines critical deficiencies in older solar PV performance testing protocols, and how the methods prescribed in ASTM E2848 and E2939 eliminate these deficiencies and enable test practitioners to produce consistent, verifiable results with a high degree of confidence.

Large-area solar irradiance mapping

By André Nobre, SERIS, National University of Singapore; Dazhai Yang, SERIS, National University of Singapore; Rupesh Baker, PV Systems Engineer, SERIS, National University of Singapore; Thomas Reindl, Deputy CEO and Cluster Director of Solar Energy Systems, SERIS, National University of Singapore

As PV systems proliferate and become an important part of the global energy mix, it is increasingly important to forecast their energy output in order to ensure a safe and reliable integration of their variable output into electric power grids. One of the main prerequisites for that is the detailed recording and interpolation of the actual irradiance in a spatially resolved way. Such 2D irradiance maps would also allow the assessment of the performance of the many PV systems that do not have irradiance sensors installed at the site. The maps are ideally based on a dense network of irradiance sensors; however, in many cases the costs of high-precision pyranometers, real-time monitoring and frequent maintenance are prohibitive for such operational forecasting systems. On the other hand, many PV installations are in fact equipped with reference cells in the plane of array (POA) for evaluating and monitoring the performance of the systems. Adding this network of reference cells to existing pyranometer networks (from meteorological services or research institutes) would substantially help in improving the accuracy of the irradiance maps. This paper introduces an irradiance conversion technique that allows POA irradiance measurements from an on-site reference cell to be converted to global horizontal irradiance data, which can then collectively be used to generate large-area irradiance maps.

Fundamentals of the commissioning tests of large-scale PV power plants

By Jorge Coello, R&D Department, Enertis Solar; Leonardo Perez, Enertis Solar

This paper presents the minimum aspects to consider for the commissioning of large-scale PV plants. This methodology has been successfully implemented in the commissioning of more than 40 PV facilities worldwide and it represents a very useful tool to assure the good performance of the PV project.

PV’s plug-in power plants: How modular design is cutting the cost of solar electricity

By Mark Osborne, Senior News Editor, Photovoltaics International

The pioneers of utility-scale PV construction have drawn on methods used in other industries to make power plants more efficient and more competitive. This paper investigates how cutting-edge techniques in modularndesign are being used to drive down plant costs. The evolution of modular design and its attractiveness to theinvestor community are discussed.

A fast solution for the optimal location of the DC combiner box in a PV array

By Jian Chen, Jiangsu Sainty Machinery Import & Export Corp., Ltd.; JianGuo Chen, PV Engineer, Jiangsu Sainty Machinery Import & Export Corp., Ltd.; XiChen Wang, Jiangsu Sainty Machinery Import & Export Corp., Ltd.

In PV power systems the choice of an appropriate location for the installation of the PV array box (or DC combiner box) is an important undertaking. It is essential that the box be placed so that the amount of DC cabling is minimized in order to not only save cable costs but also reduce voltage losses. This paper presents a fast solution to this problem, based on a mathematical model for the minisum location of the combiner according to the Manhattan metric between the PV array and the DC combiner box. The target function and its optimal solution (i.e. the most economical amount of cabling) for this particular model were obtained, and the optimality of the solution proved by contradiction. The application of this model is illustrated by means of two typical examples, involving an odd and an even number of strings in a PV array. The proposed model is efficient and easy to apply, and as such should be of interest to PV engineers and designers.

In-field performance of a polycrystalline versus a thin-film solar PV plant in Southeast Asia

By Philip Napier-Moore, Heads the Regional Renewable Power Team, Mott MacDonald; Setta Verojporn, Electrical and Renewable Energy Engineer, Mott MacDonald

This paper considers the relative technical and economic performance, for selected sites in Southeast Asia, of PV plants using crystalline and thin-film PV module technology. Technical performance estimates are based on a forensic analysis of in-field data for two grid-connected PV installations in Thailand using polycrystalline and thin-film PV modules. These two case studies help to validate the performance simulation approach for the other considered countries with similar environmental conditions. The case studies show that Mott MacDonald’s yield analysis approach demonstrates acceptable accuracy for energy yield assessment in a grid-connected PV plant, at least under the observed environmental conditions, which are most relevant to Southeast Asia plants with polycrystalline and thin-film PV modules installed. The findings presented in this paper are relevant to project developers and investors who have an interest in selecting solar PV technologies for Southeast Asian regional conditions.

The triple play: Achieving commercial benefits of PV and energy storage

By John Merritt, Director of Applications Engineering, Ideal Power

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.

Using satellite insolation data to calculate PV power output variability

By Thomas E. Hoff, Founder and President of Research and Consulting Group, Clean Power Research; Richard Perez, Research Professor, ASRC, University at Albany

As the PV capacity of utility systems increases, utility planners and operators are becoming more and more concerned about the potential impacts of power supply variability caused by transient clouds. Utilities and control system operators need to adapt their planning, scheduling and operating strategies to accommodate this variability while at the same time maintaining existing standards of reliability. Effective management of these systems, however, requires a clear understanding of PV output variability and the methods to quantify it. The present objective is to develop analytical methods and tools to quantify PV fleet output variability. This paper presents a method using location-specific inputs for estimating correlation coefficients, and discusses the key findings that resulted from applying the method to three separate geographical regions in the USA. The approach has potential financial benefits for systems that are concerned about PV power output variability, ranging from individual distribution feeders to state-wide balancing regions.

Modelling for PV plant optimization

By Joshua S. Stein, Distinguished Member of the Technical Staff, Sandia National Laboratories; Bruce H. King, Principal Member of the Technical Staff, Sandia National Laboratories

Because most of the costs of developing a PV power plant are paid before any energy is generated, optimizing the energy production from the plant is critical during plant design. Lost energy and increased operations costs due to non-optimal site characterization, technology choice, plant design, installation and other factors result in lower energy production and a higher levelized cost of energy (LCOE). Many design decisions are based on results from PV performance models. Current PV performance models can represent only some of the differences between sites, technologies, designs and operations choices. This paper provides a description of what is currently known about some of the performance tradeoffs faced by PV plant designers and operators. It presents a vision for improving PV performance models so that in the near future a full optimization can be carried out to improve the performance and lower the costs of PV plants. This will hasten the adoption of clean energy production from the sun.

The next big step - Optimizing the performance of PV power assets

By Steve Hanawalt, Founding Partner, Power Factors, LLC

To achieve project cash flow expectations, it is necessary to operate, maintain and optimize the performance of a PV power asset to meet or exceed the pro forma operating assumptions. To assume as given the achievement of these model assumptions is both naive and risky. Experience in operating the largest fleet of solar PV power plants in the world has demonstrated that project financial hurdle rates can be missed by as much as 25% if the plant is not well maintained and its performance is not optimized. Conversely, an optimized PV asset can generate cash flows 2–10% higher than expected if the optimization approach described in this paper is implemented.

Driving down BOS costs in commercial installations

By Alexander Griffiths, Project Development Engineering Manager, Mainstream Energy; Ethan Miller, Vice President of Operations, Mainstream Energy

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.

Project assessment for bankability: Quality assurance from the PV module through system planning to sustainable operational management

By Ingo Baumann, Senior Expert in Innovative Services, TÜV Rheinland; Willi Vaassen, Business Field Manager, TÜV Rheinland

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.

Performance characterization and superior energy yield of First Solar PV power plants in high-temperature conditions

By N. Strevel, Technical Sales Engineer, First Solar; L. Trippel, Module Product Line Director, First Solar; M. Gloeckler, Vice President of Advanced Research, First Solar

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.

The myth of PV module manufacturers’ bankability in project financing

By Felix Holz, Vice President / Head of Industry Expert Team Greentech, Deutsche Bank AG

A typical financial structure for a utility-scale (i.e. larger than a few MW) PV project is the so-called ‘non-recourse project financing’. Experience shows that lenders may occasionally refuse financing because they dislike a technology or even a certain supplier. This past behaviour has created the ‘myth of bankability’ and the perceived necessity of manufacturers to get onto the banks’ ‘bankability lists’. But there is no strictly defined process for doing this, and many of the experienced banks do not even work with such lists for good reason. Moreover, ‘bankability’ is not a feature that a manufacturer or a product can achieve or maintain forever.

Reduced solar capital costs in India

By Mohit Anand, Senior Consultant, BRIDGE TO INDIA

India is a unique market. As part of an India-specific strategy on the part of the players, solar capital costs in India have significantly fallen in relation to the global average. This paper describes the trend for lower cost modules and services to be offered by module suppliers and EPC companies in order to capture the greatest share of the Indian market. In this context, more importance is being given to gaining a greater market share than earning a higher return.