Aaron Sahm

Cleanliness Maintenance for an Amonix Lens System

The Amonix system is a high concentration PV system that utilizes Fresnel lenses to focus the sun’s rays on PV cells. This paper deals with issues related to the cleanliness of the lenses, the impact on performance, and the methods that can be used to clean the lenses. Issues addressed in the paper include the estimation of air-borne dirt accumulation with time. Data found in the course of our study were compared to data given in the literature about loss of transmissivity with acrylic soiling. These data were then modified to account for the two-axis tracking used for the Amonix unit, compared to the fixed orientation of the test. The effects of the loss of transmissivity were used to estimate decreases of the power produced. Costs of cleaning were compared to the lost revenue due to the decrease in sunlight reaching the cell. It is shown that rain is a good cleaning agent for the lenses. Barring precipitation, though, cleaning once a month is recommended.Copyright

Fresnel Lens Soiling Characterization and Effect Upon Performance

The Amonix system is a high concentration PV system that utilizes acrylic Fresnel lenses to focus the sun’s rays onto dispersed PV cells. The Fresnel lenses become soiled with dust over time which decreases power performance. Because of the effect soiling has upon the system performance, Amonix and the University of Nevada, Las Vegas (UNLV) have defined a long term soiling investigation and cleaning methodology. The test and measurement procedure for determining Fresnel lens soiling rate characterization is discussed. Lens soiling rate data is presented for different sites that show the soiling rate is a direct function of the angle of the lens. This paper also discusses the test and measurement procedure of the first phase of an on-going Fresnel lens cleaning investigation. An assessment of the soiling rate upon power production is also presented.Copyright

Initial Testing of the HiTek Solar Tracking Monitor

HiTek Services, Inc. has designed, fabricated, and tested a solar monitoring system that can measure the sun’s position with high accuracy. Sun position data, measured by the University of Nevada, Las Vegas Center for Energy Research, is presented showing that the instrument’s accuracy is better than 0.004 degrees (one σ). A histogram is presented showing that nearly 100 % of the time the measurement error is less than 0.008 degrees. The capability of using multiple sun monitors with synchronized data collection to measure the structural bending of one part of a tracking structure relative to another part of the structure is discussed and data are presented. Other operating features, such as being self-contained, no external cables required, and the ability to record data for a week without recharging the batteries, are discussed.Copyright

Two Types of Calorimeters for Assessing Fresnel Lens Performance in Concentrating Solar Systems

Concentrating solar energy systems can use either refractive or reflective approaches to achieve the desired concentration ratio. However this is done, there is always a question about what the flux might actually be incident on the target of interest after the concentration process. Assessing the losses due to the concentration process is quite important in understanding the overall performance of the solar concentrating system. An issue that impacts this measurement is the type of system being evaluated, as the total flux at the focal point could be quite large. We have been working with concentrating PV units that utilize acrylic Fresnel lenses to achieve the necessary concentration on a single multi-junction cell. The magnitude of the losses associated with these types of lenses was desired. We developed two calorimeters for the purpose of evaluating the optical efficiency of Fresnel lenses utilized in various point focus concentrating systems. The first calorimeter developed utilizes a transient technique whereby a time-measured pulse of the beam is directed to a mass of material in a cavity form. The material has a high conductivity, so the lumped mass approximation can be used for the analysis of the energy absorbed if the temperature rise of the material is measured. The other calorimeter developed was a steady-state type that employs a technique commonly known as flow calorimetry. In this approach, the concentrated flux is beamed into the core of the calorimeter which is cooled to some steady-state value of temperature with a liquid (water near the ambient temperature was used in our tests). Knowing the liquid flow rate and temperature rise of the fluid allows the total heat input to be assessed. This paper discusses the development, testing, and comparison of the two calorimeters. Results are given for the evaluation of several types of commercial acrylic Fresnel lenses having different characteristics such as groove density and focal length.Copyright

The Long-Term Viability of Concentrated Photovoltaic Systems in the Southwestern US

Total lifetime costs of photovoltaic (PV) systems are important determinants of profitability. But such costs are not always accurately measured and compared against fluctuating electricity costs, which can be an important contributor to long-term profitability. In this paper, we consider the economics of concentrated photovoltaics (CPV), which offer significantly higher efficiency and greater energy production over traditional fixed flat-plate PV installations in high-irradiance regions, but are perceived to be risky investments.Working with two models, one a simple annual model that uses only direct normal solar insolation; the other a more complex hourly model that uses direct normal solar insolation, ambient temperature, and wind speed to predict energy yield, we calculated the energy production and corresponding revenue generation for a 28 kW CPV unit and a comparable single-axis tracker field in Nevada. Our resulting cost matrix shows how much revenue a CPV system can reasonably be expected to generate under different pricing schemes and time periods. While the values vary depending on the assumptions made, the matrix provides an index of profitability, enabling prospective buyers to compare the costs of purchasing, installing and maintaining a system against likely revenue.As a result of our calculations, we anticipate that CPV systems will still be viable in high flux areas because they offer the promise of profitability now and continued or increased profitability as cell costs decrease and/or overall efficiency increases. Nonetheless, other factors, such as long-term reliability and O&M costs, must be addressed if CPV is to compete with other simpler technologies, such as single-axis PV trackers, which have lower upfront costs and are therefore becoming more attractive to potential customers.Copyright

Performance and Operation of the Southern Nevada Water Authority High Concentration Photovoltaic Plant for the Last 800 Days

The Southern Nevada Water Authority (SNWA) obtained six of the Amonix, Inc. multi-junction Concentrating Photovoltaic (CPV) systems in 2009. A description of the CPV systems, plant layout, and operating description is given. Data showing the power and that the systems have generated over 1,200 MWh of grid energy during the last 33 months are presented in the paper. An estimate is given of the net annual energy generated based upon the last 33 months of daily energy performance. Data is also presented showing the daily peak power divided by peak DNI and the energy performance during this period. The effect of shading is discussed and data are presented showing its effects on the annual field performance. Data are also given on the operating reliability and the long-term performance of the plant. A discussion and pictures are given of how the terrain is returning to its natural state and how the habitat has accepted the CPV systems.Copyright

Performance of the Southern Nevada Water Authority of Amonix’s High Concentration Multi-Junction System

The Southern Nevada Water Authority contracted with Amonix, Inc. in 2008 to procure 220 kWdc of their latest generation multi-junction cell High Concentration Photovoltaic systems (HCPV). This paper discusses the performance of the six HCPV systems that started operating in mid 2009. Data sets included show: a. Daily power performance; b. Power performance compared to the specified performance; c. Effect of field shading upon the daily power performance. What is demonstrated is the system power performance has not degraded during this initial period of operation and continues to meet or exceed the specified performance levels.© 2011 ASME

Installation and Operation of Southern Nevada Water Authority High Concentration Amonix Multi-Junction System

The Southern Nevada Water Authority contracted with Amonix, Inc. in 2008 to procure 220 kWdc of their latest generation multi-junction cell High Concentration Photovoltaic system. This paper describes the installation of the six HCPV systems including the design layout of the field, installation of the foundations, the PV modules, and tracking control systems. In addition, the basic operation and features of the Amonix HCPV system are discussed, along with data showing the performance of each system since the start of operation.Copyright

Southern Nevada Renewable Resource Assessment

University of Nevada, Las Vegas Renewable Energy Center (UNLV-REC) currently monitors three meteorological stations in southern Nevada under the direction of the National Renewable Energy Laboratory (NREL) and is funded by the Nevada Southwest Energy Partnership (NSWEP). The three station locations are Eldorado Valley, UNLV-REC Solar Site, and Nevada Power Company Clark Station. The installation dates for each of the locations were October of 2004 for Eldorado Valley station, August of 2003 for the UNLV-REC Solar Site, and March of 2006 for the Nevada Power Clark Station. Publicly available data from each site have been archived since installation completion. This paper discusses the installation of the equipment for each site and images of the setup. The data that is being collected between the sites is also compared. Data comparisons between the sites include net monthly solar energy; monthly peak direct normal irradiance (DNI), average daily wind speed, monthly wind roses, and average monthly dry bulb temperatures. The recently measured data is also compared to resource maps developed by NREL and to TMY data. With these meteorological resources, microclimatic variations can be studied for the area and used as a renewable energy resource for renewable installations in southern Nevada.Copyright

Wet or Dry Cooling

Two major aspects related to water use in solar power plants are examined. First we compare the water used in various approaches to power generation. These include water requirements for cooling (where applicable) and other needs within the plant. Included is attention to water requirements for makeup in Rankine cycles, as well as for cleaning of concentrating solar systems. In the second thrust, we examine the impacts of using dry cooling for Rankine cycles. It is generally established that this approach requires premiums in both capital and operating costs (the latter is dependent upon the cost of water), as well as a penalty in performance when compared to wet systems. We examine the trends associated with this technology and outline some for the current performance issues with various cooling approaches.Copyright