This paper describes the operation of 570 kW of installed Amonix High Concentration PV systems at various Arizona Public Service (APS) site locations over the last four years. The physical characteristics of the different units in the field are described, including the operating characteristics that make this system applicable for large grid connected, distributed, and off-grid/remote operation. Data is presented showing that the monthly generated energy and annual generated energy over this period of time increased as the technology matured. Discussion and data are also presented on the effects of field shadowing and lens soiling. The latest status of the largest concentrating PV plant in the world is also discussed.

This paper reports work underway in converting a dish-Stirling system to a dish-PV system at UNLV. The existing SAIC dish–Stirling system is being retrofitted with new fixed-focus facets and an Amonix photovoltaic receiver to replace the Stirling engine/generator package. As is the case with photovoltaic systems generally, the Amonix cells being used in this application lose efficiency as their temperatures increase. To combat this effect, cooling is provided by circulating liquid through channels in the backing plate. The liquid is then pumped through an array of automotive type radiators and the excess heat is rejected to the ambient air. Reported here is the development of a numerical model for the cooling system, with specific attention being paid to the transient response. Experimental data is taken to determine the various properties of the individual components to be used in the system and this data is used in a MatLab-based simulation. The cooling system model can then be linked to a similar model for the receiver and cell assembly and the optimization functions included in MatLab can be used to select the input parameters (pump size, number of radiators, fan speed, etc.) that maximize the overall efficiency of the system. The predictions of the model can be used in the selection of the final cooling system design and the validity of the model can be checked against the actual performance of the unit.

A non-imaging (NI) device and thermophotovoltaic (TPV) array for use in a full-spectrum solar energy system has been designed, built, and tested [1,2,3]. This system was designed to utilize the otherwise wasted infrared (IR) energy that is separated from the visible portion of the solar spectrum before the visible light is harvested. The IR energy will be converted to electricity via a gallium antimonide (GaSb) TPV array. The experimental apparatus for the testing of the IR optics and TPV performance is described. Array performance data will be presented, along with a comparison between outdoor experimental tests and laboratory flash tests. An analysis of the flow of the infrared energy through the collection system will be presented, and recommendations will be made for improvements. The TPV array generated a maximum of 26.7 W, demonstrating a conversion efficiency of the IR energy of 12%.

Accurate charge-control and state-of-charge monitoring of lead-acid batteries is an ever-increasing necessity in an industry that demands low-maintenance costs and highly available systems. If the batteries are charged by photovoltaic panels and are installed in remote sites (e.g. Oil sea-platforms, highway emergency bays, autonomous communications systems) and exposed to aggressive environmental conditions (e.g. Extreme temperature, high humidity), the problem of extending the batteries’ useful life becomes a challenge. Most charging algorithms do not perform well when photovoltaic panels are the sole source of energy because energy availability is not guaranteed. A charge algorithm that maximizes the use of energy generated by the panel during daylight hours is needed. This paper presents a microcontroller-based charge-controller suitable for photovoltaic applications. The controller performs temperature compensation on the charge algorithm. It also stores those parameters that provide an indication on batteries’ state-of-charge and state-of-health: Panel voltage, battery’s voltage and current, current demanded by a load and room temperature. The controller has serial communication capabilities that make possible the connection to a personal computer or central station. By using a local industrial network or radio links, multiple controllers can be monitored by a central station running a battery management program. The information collected by all the controllers in the system is analyzed to determine the state-of-charge of individual batteries and, if required, command the appropriate controller to perform special procedures like, for example, thorough diagnostics or equalization. Preliminary field-test results of a controller installed in a high-way emergency bay are presented in this paper. It is shown that protection against deep discharges is achieved, which contributes to extend the battery useful life.

Recently, the photovoltaic (PV) power generation system has attracted attention as one of clean energies. Especially, residential roofing PV system connected with power grids has been popularized as a result of increasing concerns over global warming and continuing decline in PV manufacturing costs. The power generated by the PV module increases with irradiance, but it decreases as PV module temperature becomes high. The PV temperature depends on ambient temperature, and becomes more than 60°C in summer. Therefore, the power generated does not necessarily increase even if the irradiance increases in summer. However, if the PV modules were cooled under such a high PV temperature condition, more electrical power would be obtained from PV modules. In this study, a PV power generating system equipped with a cooling device has been developed. The major components of the system are an array of PV modules and cooling panels attached to the backside of the PV modules. The respective PV module is cooled with cooling water flowing through a narrow gap in each cooling panel. Hot water discharged from the cooling panel is delivered to a storage tank and can be reused in anywhere. In order to save energy for introducing cooling water into the panel, a siphonage from an upper level of a building to the ground level is utilized. A siphon tube is connected to a discharge port of the cooling panel, thus the pressure at the discharge port becomes negative. Cooling water enters into the bottom end of the cooling panel at atmospheric pressure and goes up to the top, discharge side. By adopting this cooling water system, we could spread the cooling water evenly over the entire backside of the PV module and thus realized an effective cooling device. In addition, we could make the cooling device light and smaller because no auxiliary pumping system is needed for introducing cooling water. To provide field performance data for the present PV power generation system equipped with the special cooling device mentioned above, long-term monitoring tests in a natural environment were conducted in summer for a test facility constructed at the Yatsushiro National College of Technology (YNCT), Japan. As a result, it was confirmed that the cooling of the PV modules increases the electric power and that the reuse of hot water from the cooling panel contributes very much for saving energy consumed for heating water.

Between April 2001 and September 2002, the Florida Solar Energy Center conducted research to evaluate the performance of several utility-interactive inverters. The major issues to be identified were the efficiency of the inverters and their ability to follow the maximum power point of the photovoltaic (PV) array. Existing PV testing facilities at FSEC were modified to carry out this analysis. This facility, called the Photovoltaic Inverter Test Facility, is capable of providing approximately four kW p of array power to the inverter. Data on inverter performance were collected using a Campbell 10X datalogger. The parameters collected included the following: irradiance, PV array temperature, inverter temperature, PV voltage, PV current, AC voltage, AC current, and AC Power. Because of the voltage windows and power requirements of the different inverters, the array was designed to be easily reconfigured to meet those requirements. Each of the inverters was installed and allowed to run for several weeks under both clear and cloudy conditions. At the end of the test period, inverter efficiencies were calculated from the collected data. The ability of the inverter to follow the maximum power point of the array was evaluated in two ways. In the first method, DC voltage and current were measured while the inverter was operating, then the array was disconnected from the inverter and the maximum power point of the array was immediately taken. By comparing the measured DC voltage and current to the maximum power point of the array, one could determine the effectiveness of the inverter algorithm. Unfortunately this method requires steady-state conditions and does not show the effectiveness of the algorithm in cloudy conditions. To determine its effectiveness in cloudy conditions, DC voltage and current were compared to the expected maximum power. The expected array maximum power point was calculated from IV curves of the array, irradiance measurements, and array temperature measurements. DC to AC efficiency curves were derived from the data as well. Results from the inverters were mixed, but several showed room for improvement.

In developing countries, half of the world’s population lives without electric power. Hybrid power systems, consisting of photovoltaic (PV) modules, battery banks, and backup diesel generators, have the potential to become a cost-effective solution for delivering power to many of these remote villages where grid extension is cost-prohibitive. In this paper, we show that improved dispatch strategies can significantly decrease the cost of a hybrid power system. We propose using a genetic algorithm (GA) in combination with novel load and insolation predictive strategies to reduce the operating costs over the present state-of-the-art methods. Realistic simulations demonstrate that this technique provides an average cost savings of 20.9% over the Set Point Strategy and 13.8% over the Load Following Strategy. We show that this strategy is a viable means of reducing the cost of hybrid power system operation.

Recent designs in the Solar Decathlon have incorporated solar electric modules with heat capture. Zero Energy Buildings (ZEB) solicitations through the National Renewable Energy Laboratory (NREL) have recently awarded photovoltaic / thermal (PV/T) projects incorporating air and fluid based heat transfer mediums. This paper introduces the PV/T collector with a quick history of four different research and development projects starting with the Massachusetts Institute of Technology (MIT) in 1978. Suggestions for engineering design and performance guidelines are provided. A demonstration of a zero glazed thin film amorphous silicon photovoltaic module with air as the fluid transfer medium, captured off the backside, is presented. The paper provides suggestions on applications and appropriate environments for various PV/T collector types.

A photovoltaic (PV) distributed energy resource (DER) was established to support the Tennessee Valley Authority’s Green Power Switch program, which allows utility customers to purchase blocks of electricity generated by solar resources. The PV DER was also used to study the potential shading benefits of roof-mounted PV systems for commercial buildings. Test data derived by monitoring an offset-mounted PV array shading a built-up low-slope roof system shows that the annual savings per square foot of low-slope roof can be as high as $0.18 ($1.95 per square meter) in Phoenix, AZ.

This analysis uses actual installed system costs from available data to better assess and understand the real installed and life cycle costs for small-scale photovoltaic (PV) installations. Most PV systems are sold on the basis of first cost, but in addition to these first costs, system owners must consider operation and maintenance (O&M) costs and down time, as well as energy savings [1]. The challenge in developing realistic life cycle costs is that most databases have only new data available, and only one database — that maintained by the Florida Solar Energy Center (FSEC) — contains performance information along with cost and maintenance data. The goals of this effort are to: 1. Characterize the actual life cycle costs (LCC) of PV systems installed in Florida and tracked since 1998. 2. Develop a benchmark of PV LCC that will aid in prioritizing cost improvement steps and feed into the U.S. Department of Energy and its subcontractors’ efforts to develop a baseline for grid-connected small residential and larger commercial PV system costs. 3. Develop an easy to use and modify LCC model that allows sensitivity analysis and input of new data as it becomes available. The PV system LCC model developed and used here is based on statistical methods, which provide us with a range of expected outcomes. The Monte Carlo technique allows the use of repeated simulation iterations to mimic a population sample. For inputs, the model relies largely on data from FSEC’s performance and maintenance databases, and where appropriate simplifying assumptions are explained. Beyond establishing an LCC baseline, this project considers the sensitivity of the total LCC to various inputs and thereby provides guidance on the question of where to put valuable resources to substantially reduce PV system costs. Further discussion is offered concerning the additional value of this model in determining the impact of various methods of PV system performance tracking.

Architects, building designers, and building owners presently lack sufficient resources for thoroughly evaluating the economic impact of building integrated photovoltaics (BIPV). The National Institute of Standards and Technology (NIST) is addressing this deficiency by evaluating computer models used to predict the electrical performance of BIPV components. To facilitate this evaluation, NIST is collecting long-term BIPV performance data that can be compared against predicted values. The long-term data, in addition, provides insight into the relative merits of different building integrated applications, helps to identify performance differences between cell technologies, and reveals seasonal variations. This paper adds to the slowly growing database of longterm performance data on BIPV components. Results from monitoring eight different building-integrated panels over a twelve-month period are summarized. The panels are installed vertically, face true-south, and are an integral part of the building’s shell. The eight panels comprise the second set of panels evaluated at the NIST test facility. Cell technologies evaluated as part of this second round of testing include single crystalline silicon, polycrystalline silicon, and two thin film materials: tandem-junction amorphous silicon (2-a-Si) and copper-indium-diselenide (CIS). Two 2-a-Si panels and two CIS panels were monitored. For each pair of BIPV panels, one was insulated on its backside while the backside of the second panel was open to the indoor conditioned space. The panel with the backside thermal insulation experienced higher midday operating temperatures. The higher operating temperatures caused a greater dip in maximum power voltage. The maximum power current increased slightly for the 2-a-Si panel but remained virtually unchanged for the CIS panel. Three of the remaining four test specimens were custom-made panels having the same polycrystalline solar cells but different glazings. Two different polymer materials, Tefzel and Kynar, were tested along with 6 mm-thick, low-iron float glass. The two panels having the much thinner polymer front covers consistently outperformed the panel having the glass front. When compared on an annual basis, the energy production of each polymer-front panel was 8.5% higher than the glass-front panel. Comparison of panels of the same cell technology and comparisons between panels of different cell technologies are made on daily, monthly, and annual bases. Efficiency based on coverage area, which excludes the panel’s inactive border, is used for most “between” panel comparisons. Annual coverage-area conversion efficiencies for the vertically-installed BIPV panels range from a low of 4.6% for the 2-a-Si panels to a high of 12.2% for the two polycrystalline panels having the polymer front covers. The insulated single crystalline panel only slightly outperformed the insulated CIS panel, 10.1% versus 9.7%.

An important consideration in the practical realization of high-concentration photovoltaic devices is the heat rejection at high power densities to the environment. Recently, optical designs for generating solar flux in excess of 1000 suns on advanced solar cells — while respecting flux homogeneity and system compactness — were suggested with the introduction of solar fiber-optic mini-dish concentrators, tailored specifically to high-flux photovoltaic devices [1]. At the core of the design is the miniaturization of the smallest building block in the system — the concentrator and the cell — permitting low-cost mass production and reliance on passive heat rejection of solar energy that is not converted to electricity. First, this paper proposes a relatively simple 1-D axi-symmetric model for predicting the thermal and electrical performance of such mini-dish high-flux concentrators. Experimental measurements were performed with a real-sun solar simulator, indoors under controllable conditions, a flux levels up to 5,000 suns. A CFD (Computational Fluid Dynamics) model was also developed for model-validation. Both the modeling approaches predict heat sink temperatures within experimental uncertainty of a couple of degrees. Next, the 1-D axi-symmetric model is used to evaluate the sensitivity of different solar cell model assumptions, environmental effects (such as outdoor temperature, and the wind speed), heat sink size and geometry, thermal contact resistance, etc. It was confirmed that the miniaturization of the solar cell module permits passive heat rejection, such that solar cell temperatures should not reach more than 80°C at peak insolation and stagnation conditions. Though the cell rated efficiency degrades by only 1–2% in absolute terms, higher cell temperatures may compromise the integrity of the cell circuitry and of the encapsulation. The 1-D axi-symmetric model also allows optimization of the heat sink geometric dimensions for a given volume. Hour-by-hour performance simulation results for such an optimized design configuration were performed for one month in summer and one month in winter for two locations namely Philadelphia, PA and Phoenix, AZ. The insight gained from this study is important for the proper design of the various components and materials to be used in PV mini-dishes. Equally important is that it allows similar types of analyses to be performed and well-informed design choices to be made for mini-dishes that have to operate under different climatic conditions with cells of different performance and concentration ratios.

Copper indium gallium selenide sulfide, CuIn 1−x Ga x Se 2−y S y (CIGSS) absorber layer was prepared on stainless steel (SS) and SiO 2 -coated titanium substrates. Comparative study was carried out to analyze the variation in the crystal quality depending on the substrate. Identical parameters were used for deposition and selenization/sulfurization of metallic precursors. This paper presents the observations made on the basis of surface morphology using scanning electron microscopy, crystal quality by x-ray diffraction and chemical composition and concentration-depth profiles by x-ray energy dispersive spectroscopy and Auger electron spectroscopy respectively. Film fabricated on both the substrate had chalcopyrite structure with variation of stoichiometry as well as morphology. Selenization/sulfurization cycle must be modified depending upon the substrate to obtain high quality CIGSS film.

PV modules have a problem that the power generated decreases with the rise of the PV module temperature. In order to solve the problem, we recently developed a new PV cooling device utilizing siphonage. In the first report [1] of this series, we presented the experimental results on the PV mounted on an open rack and that the cooling system is effective in both the improvement of the PV efficiency and the reduction of fuel consumption by reusing hot water from the system. In this study, we conducted long-term monitoring tests on the open rack-mount PV system with a cooling panel behind the PV module and with an insulation board (made of foam polystyrene) behind the cooling panel, simulating the residential rooftop PV system. The data obtained in the experiment have been compared with those obtained for the previous system with the cooling panel but without the insulation board. The comparison shows that the increment in energy production after equipping the cooling panel is much more for the present system with the insulation board irrespective of the cooling start temperature, being the PV temperature when cooling water was started to flow. This result suggests that the installation of the cooling system is more useful for the residential rooftop PV system than the open rack-mount system.

The aim of this study is to review issues related to the requirement of thin CIGSS absorber layers, prepare and characterize thin CIGSS films on molybdenum coated glass, improve understanding of material properties, and further enhance solar cell performance. This paper presents the preparation and properties of thin (∼1 μm thick) CuIn 1−x Ga x Se 2−y S y (CIGSS) solar cells on molybdenum coated glass substrate. CIGSS films of thickness ∼1 μm were prepared in two steps. Step one involved the deposition of Cu-In-Ga metallic precursors on molybdenum coated glass substrate and step two involves the selenization/sulfurization of these metallic precursors using diluted diethylselenide (DESe) as selenium source and diluted H 2 S as sulfur source respectively. Thin film solar cells were completed by the deposition of n-type CdS layer by chemical bath deposition, ZnO/ZnO:Al transparent conducting window bilayer by RF magnetron sputtering and Ni-Al front contact fingers by e-beam evaporation technique through a metal mask. This paper presents the preliminary results obtained on very thin (∼ 1 μm) absorber layer.

Hurricanes, floods, tornados and earthquakes create natural disasters that can destroy homes, businesses and the natural environment. Such disasters can happen with little or no warning, leaving hundreds or even thousands of people without medical services, potable water, sanitation, communications and electrical services for up to several weeks. The 2004 hurricane season ravaged the State of Florida, U.S.A., with four major hurricanes within a 6-week timeframe. Over nine million people evacuated their homes and damage to property was extensive. One proactive strategy to minimize this type of destruction and disruption to lives is the implementation of disaster-resistant buildings that are functional and operational. This approach uses the best energy-efficient buildings, fortified to the latest codes, and incorporates renewable energy systems. Businesses, government facilities and homes benefit from using photovoltaics to power critical items. This concept is a mitigation tool to reduce damage and cost of the destructive forces of hurricanes and other disasters. This past season’s experience showed that buildings designed and built to the latest standards with photovoltaic and solar thermal systems survived with little damage and continued to perform after the storm passed. Even following a disaster, energy conservation and use of renewables promotes energy assurance while allowing occupants to maintain some resemblance of a normal life.

BIPV (Building Integrated Photovoltaics) has progressed in the past years and become an element to be considered in city planning. BIPV has influence on microclimate in urban environments and the performance of BIPV is also affected by urban climate. The effect of BIPV on urban microclimate can be summarized under the following four aspects. The change of absorptivity and emissivity from original building surface to PV will change urban radiation balance. After installation of PV, building cooling load will be reduced because of PV shading effect, so urban anthropogenic heat also decreases to some extent. Because PV can reduce carbon dioxide emissions which is one of the reasons for urban heat island, BIPV is useful to mitigate this phenomena. The anthropogenic heat will alter after using BIPV, because partial replacement of fossil fuel means to change sensible heat from fossil fuel to solar energy. Different urban microclimate may have various effects on BIPV performance that can be analyzed from two perspectives. Firstly, BIPV performance may decline with the increase of air temperature in densely built areas because many factors in urban areas cause higher temperature than that of the surrounding countryside. Secondly, the change of solar irradiance at the ground level under urban air pollution will lead to the variation of BIPV performance because total solar irradiance usually is reduced and each solar cell has a different spectral response characteristic. The thermal model and performance model of ventilated BIPV according to actual meteorologic data in Tianjin (China) are combined to predict PV temperature and power output in the city of Tianjin. Then, using dynamic building energy model, cooling load is calculated after BIPV installation. The calculation made based in Tianjin shows that it is necessary to pay attention to and further analyze interactions between them to decrease urban pollution, improve BIPV performance and reduce cooling load.

CuInS 2 thin films were fabricated by sulphurization of S/In/Cu Stacked elemental layers (SEL) on slide glass substrates by annealing in vacuum of 10 −3 Torr at temperature of 50 °C ∼ 350 °C. Some S/In/Cu SEL were vacuum annealed under a sulfur atmosphere. The thin films thus annealed were analyzed by measuring structural, electrical and optical properties. When CuInS 2 thin films were made under a sulfur atmosphere, lattice constant of a and grain size of the thin film were a little larger than those in only vacuum annealing. The largest lattice constant of a and grain size was 5.63 Å and 1.2 μm respectively. Also, when the thin films were made under a sulfur atmosphere, conduction types were all p-type with resistivities of around 10 −1 Ωcm and optical energy band gaps of the films were a little larger than those in only vacuum and the largest optical energy band gap of CuInS 2 thin film was 1.53 eV.

This paper describes the Photovoltaic solar electricity generating capacity in Nepal. Although Nepal is rich in hydropower, currently only about 17% of the total population has access of electricity. The majority of the population who are living in the rural mountainous parts of Nepal is still deprived of electricity. The relatively high insulation throughout the year and geographical situation encourage for the development of PV energy in the country. The monthly mean solar radiation analysis shows that April and January receive the highest and the lowest solar radiation respectively. The PV installation rate has increased dramatically in the last five years due to relative decrease in PV module cost and government subsidy. PV technology is reliable because of its simplicity, extremely low maintenance cost and point-of-use installation possibility. The widespread use of PV will help to reduce CO 2 emission and consequently contributes towards better environment.

This analysis expands the photovoltaic (PV) life cycle cost (LCC) results presented at ASES 2004. That paper presented the model and concept used to develop PV LCC, and it showed the results of the analysis of over one hundred systems monitored by the Florida Solar Energy Center (FSEC). FSEC began tracking cost, performance and reliability data for systems installed in Florida in 1998, with data now available through a web-accessible database. For the majority of the 124 systems, installed cost information was collected as part of the state’s PV rebate and PV for schools programs. Results presented previously [1] indicated that over an assumed 20–30 system life time a PV system will have a positive life cycle cost. That is, a negative total return on investment. These results were based on actual cost, performance, maintenance, and reliability data. In the baseline case, average total system costs over the lifetime were 32.4¢/kWh while electricity savings totaled 3.7¢/kWh netting a life cycle cost of 28.7¢/kWh. While based on actual data from over 100 installed systems — some installed for over 6 years — a number of conservative assumptions also drove the analysis, such as the exclusion of the state’s rebate programs (varying from $2 to $5 per DC Watt) which impacted nearly all of the systems in the analysis. Since the first presentation of these results the PV LCC model has been further developed to incorporate additional performance information and expands the sample of systems incorporated. This paper will thus provide further insight into the relative importance of various up-front and on-going costs to the overall lifetime economics of a system. The paper will also address additional sensitivity analysis performed. Particular attention is paid to inverter mean time between failure (MTBF), the impact of incentives, and basic financial assumptions used in the model such as the discount rate and electricity rates. Various scenarios are considered in asking the question of what is necessary for the system LCC to break-even.