Characterisation of solar cells and modules under actual operating conditions

A PC-based measuring system is presented for outdoor testing of solar cells and modules under real operating conditions. It consists of a sun-tracked sample holder, different electronic loads (including control), digital multimeters, a PC and a laser printer. Insolation is measured and recorded with pyranometers, pyrheliometers and a reference cell. Current-voltage curves are acquired in the range of irradiance from 10 W/m² to over 1000 W/m². Small single cells of size down to 3 mm by 3 mm as well as large modules and laminates up to 1 m by 1.5 m can be tested. The measurement time for one test can be varied between 5 to 15 seconds. The maximum power point (mpp) is normally detected on-line. However, it can also be determined in a subsequent mathematical analysis, if more precise mpp data are required. The maximum relative uncertainty in the efficiency (determined from mpp data) has been estimated to be less than ± 1 %, depending on type and size of cell or module and on the constancy of the insolation during the testing time. Using a new dynamic method, the temperature coefficient of the efficiency can be determined within a relative uncertainty of about ± 3 %. The coefficient is used to derive standard test condition data. Results are given for two commercial modules.     

Lead Free Ammunition without Toxic Propellant Gases

Environmental and health considerations have encouraged the development of ammunition with substitutes for lead and other heavy metals. In general, the emission products from munitions containing nitro‐based propellants are highly complex mixtures of gases, vapors, and solid particles. The major combustion products are H₂O, CO, CO₂, H₂, and N₂. In addition, compounds including hydrogen cyanide (HCN), ammonia (NH₃), methane (CH₄), nitrogen oxides, benzene, acrylonitrile, toluene, furan, aromatic amines, benzopyrene, and various polycyclic aromatic hydrocarbons are detected in minor concentrations. Many of the identified chemical species have severe toxicological properties, and some of the compounds do even have mutagenic effects. Gun smoke emission is a concern because its exposure to humans may be substantial during military and civilian police training, as respiratory protection equipment is not routinely worn. In this work we study the compositions of some of the main decomposition products, experimentally as well as theoretically. The concept of frozen equilibrium at around 1500–2000 K appears to apply for CO, CO₂, and H₂. However, the trace species in the combustion mixtures appear theoretically to be present in negligible concentrations. Our measured results are many orders of magnitude higher than theoretical results in open space. We forecast that future development of gun powder will focus on reducing the amount of toxic trace species.     

Solar Power 2006, San José, CA

The Solar Power 2006 conference in San José was the largest solar conference event in United States history. This meeting marks a new awakening of the United States to Solar Power, since the peak in interest in it during the 1970s. This editorial reviews the highlights of the meeting, with an emphasis on the companies that participated, and the areas where further research is crucially needed. Primarily, the meeting was focused on a review of the industries currently involved in solar conversion-related manufacturing and development, and the factors that limit market introduction of products. Some of the key outcomes of the meeting include the realization that large-scale concentrating solar thermal installations, rather than photovoltaic (PV) systems, will likely dominate utility-scale energy production (i.e. system outputs of over 100 MWe). It was noted that there has been a steady cost reduction in silicon PV modules, and the goal of a PV module cost near US$1.44/W (in 2002 dollars) is expected around 2013, at which time there will have been a cumulative module production of over 10,000 MW. However, the current shortage of silicon feedstock (polysilicon) will drive PV research directions for many years to come. Many venture-capital funded start-up companies have arisen to develop commercial approaches to thin film solar cells and modules that use less silicon.     

Luminescence and current-voltage characteristics of solar cells and optoelectronic devices

The transduction and conversion of light into work via a quantum process is dependent on the luminescent properties of the materials involved. Materials that can exhibit emission of light upon illumination are likely candidates for solar cells, detectors and optoelectronic devices. This radiative recombination in a material is directly related to the output device parameters, such as the current voltage characteristics. The chemical potential of the incoming light is a function of the photon energy and incident radiance. The maximum amount of work per particle, or voltage, that can be extracted by a solar converter is shown to be equal to chemical potential of the excitation, which can be inferred from the photoluminescence efficiency at ambient temperature. A discussion is made as to the use and optical properties of materials such as Si, GaAs, FeS₂, and organic dyes as efficient solar cell materials. In particular, the silicon I–V curve and luminescence are evaluated using the model, and shown to correspond to measured devices. A discussion is also made as to the extension of the luminescence model to the understanding of the light emitting diode, or LED. By allowing the absorber to remain as thin as possible, lower recombination fluxes and higher voltages are possible in solar cells and detectors.     

Testing of dye sensitized TiO2 solar cells I: Experimental photocurrent output and conversion efficiencies

Recently, a paper was published by the Lausanne Group headed by Dr. M. Graetzel which reported a simple low cost 7% efficient photo electrochemical solar cell made from a trinuclear Ru dye complex adsorbed on the very rough surface of a colloidal TiO₂ film. In the current paper, a verification of this result is presented using procedures described in the literature. Measurements are reported in stimulated and natural sunlight which confirm that the efficiency is indeed in the range previously reported. Predicted Air Mass 1.5 photo currents are compared to those obtained from fabricated dye sensitized cells. Although current densities of 12 mA/cm² and voltages of over 0.6 V are measured,it is found that corresponding fill factors, less than 0.6, limit the performance of the cell under solar illumination. The basic economics of such a device are outlined and it is proposed that cell costs of $ 0.6 per peak watt could be possible if the longevity of the cell is at least 15 years.     

Concentration of solar radiation by white backed photovoltaic panels

In this paper, we present an analysis of the concentration achieved by white backed photovoltaic panels. Concentration is due to the trapping by light scattered in the refractive plate to which the solar cell is bonded. Using the reciprocity relation and assuming the ideal case of a Lambertian distribution, a detailed model is formulated that includes the effects of the thickness and walls of the concentrator. This model converges to the thermodynamic limit and is found to be consistent with experimental results for a wide range of cell sizes. Finally, the model is generalized to multiple-cell photovoltaic panels.