Damon E. Turney

Life Cycle Greenhouse Gas Emissions of Crystalline Silicon Photovoltaic Electricity Generation

Published scientific literature contains many studies estimating life cycle greenhouse gas (GHG) emissions of residential and utility‐scale solar photovoltaics (PVs). Despite the volume of published work, variability in results hinders generalized conclusions. Most variance between studies can be attributed to differences in methods and assumptions. To clarify the published results for use in decision making and other analyses, we conduct a meta‐analysis of existing studies, harmonizing key performance characteristics to produce more comparable and consistently derived results. Screening 397 life cycle assessments (LCAs) relevant to PVs yielded 13 studies on crystalline silicon (c‐Si) that met minimum standards of quality, transparency, and relevance. Prior to harmonization, the median of 42 estimates of life cycle GHG emissions from those 13 LCAs was 57 grams carbon dioxide equivalent per kilowatt‐hour (g CO‐eq/kWh), with an interquartile range (IQR) of 44 to 73. After harmonizing key performance characteristics (irradiation of 1,700 kilowatt‐hours per square meter per year (kWh/m2/yr); system lifetime of 30 years; module efficiency of 13.2% or 14.0%, depending on module type; and a performance ratio of 0.75 or 0.80, depending on installation, the median estimate decreased to 45 and the IQR tightened to 39 to 49. The median estimate and variability were reduced compared to published estimates mainly because of higher average assumptions for irradiation and system lifetime. For the sample of studies evaluated, harmonization effectively reduced variability, providing a clearer synopsis of the life cycle GHG emissions from c‐Si PVs. The literature used in this harmonization neither covers all possible c‐Si installations nor represents the distribution of deployed or manufactured c‐Si PVs.

Buoyancy flux, turbulence, and the gas transfer coefficient in a stratified lake.

Gas fluxes from lakes and other stratified water bodies, computed using conservative values of the gas transfer coefficient k600, have been shown to be a significant component of the carbon cycle. We present a mechanistic analysis of the dominant physical processes modifying k600 in a stratified lake and resulting new models of k600 whose use will enable improved computation of carbon fluxes. Using eddy covariance results, we demonstrate that i) higher values of k600 occur during low to moderate winds with surface cooling than with surface heating; ii) under overnight low wind conditions k600 depends on buoyancy flux β rather than wind speed; iii) the meteorological conditions at the time of measurement and the inertia within the lake determine k600; and iv) eddy covariance estimates of k600 compare well with predictions of k600 using a surface renewal model based on wind speed and β.

Life Cycle Greenhouse Gas Emissions of Thin‐Film Photovoltaic Electricity Generation

We present the process and the results of harmonization of greenhouse gas (GHG) emissions during the life cycle of commercial thin‐film photovoltaics (PVs), that is, amorphous silicon (a‐Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). We reviewed 109 studies and harmonized the estimates of GHG emissions by aligning the assumptions, parameters, and system boundaries. During the initial screening we eliminated abstracts, short conference papers, presentations without supporting documentation, and unrelated analyses; 91 studies passed this initial screening. In the primary screening we applied rigorous criteria for completeness of reporting, validity of analysis methods, and modern relevance of the PV system studied. Additionally, we examined whether the product is a commercial one, whether the production line still exists, and whether the studys core data are original or secondary. These screenings produced five studies as the best representations of the carbon footprint of modern thin‐film PV technologies. These were harmonized through alignment of efficiency, irradiation, performance ratio, balance of system, and lifetime. The resulting estimates for carbon footprints are 20, 14, and 26 grams carbon dioxide equivalent per kilowatt‐hour (g CO‐eq/kWh), respectively, for a‐Si, CdTe, and CIGS, for ground‐mount application under southwestern United States (US‐SW) irradiation of 2,400 kilowatt‐hours per square meter per year (kWh/m2/yr), a performance ratio of 0.8, and a lifetime of 30 years. Harmonization for the rooftop PV systems with a performance ratio of 0.75 and the same irradiation resulted in carbon footprint estimates of 21, 14, and 27 g CO‐eq/kWh, respectively, for the three technologies. This screening and harmonization rectifies previous incomplete or outdated assessments and clarifies variations in carbon footprints across studies and amongst thin‐film technologies.

A measure of near‐surface fluid motions that predicts air‐water gas transfer in a wide range of conditions

[1] Air-water gas transfer impacts many important biogeochemical processes, yet current understandings involve large uncertainty. This arises because the process depends on a complex interaction between molecular diffusion and fluid motions that has not been adequately characterized. Here we show the first experimental support for a mechanistic model that relates near-surface motions to gas transfer coefficients over a range of wind conditions, including those leading to breaking wavelets. We find that the square root of the root mean square surface-velocity divergence varies linearly with both the gas transfer coefficient, as predicted by theory, as well as with mean square surface slope. Besides advancing the understanding of the mechanisms governing air-water gas transfer, these results suggest easy-to-measure parameters that could, with further investigation, provide gas transfer coefficients in field settings.

A method for three-dimensional interfacial particle image velocimetry (3D-IPIV) of an air–water interface

A new stereoscopic method for collecting particle image velocimetry (PIV) measurements within ~1 mm of a wavy air–water interface with simultaneous measurements of the morphology of the interface is described. The method, termed three-dimensional interfacial particle image velocimetry (3D-IPIV), is tested in a wind wave channel with a wind speed of 5.8 m s−1, water depth of 10 cm and a fetch of ~9 m. Microscale breaking waves populate the interface and their flow patterns are clearly visible in the velocimetry results. The associated capillary waves and surface divergence patterns are observed. Several statistical measurements of the flow are compared with independent measurements and good agreement is found. The method shows great promise for investigating the transfer of momentum, heat and gases across an air–water interface, both in the laboratory and in field settings. Additional methods are described for manufacturing the flow tracers needed for the 3D-IPIV method. These tracers are likely to be useful for other researchers, and have the characteristics of being fluorescent, neutrally buoyant, non-toxic, monodisperse, inexpensive and easy to manufacture.

Real-time materials evolution visualized within intact cycling alkaline batteries

The scientific community has focused on the problem of inexpensive, safe, and sustainable large-scale electrical energy storage, which is needed for a number of emerging societal reasons such as stabilizing intermittent renewables-based generation like solar and wind power. The materials used for large-scale storage will need to be low cost, earth-abundant, and safe at the desired scale. The Zn–MnO2 “alkaline” battery chemistry is associated with one-time use, despite being rechargeable. This is due to material irreversibilities that can be triggered in either the anode or cathode. However, as Zn and MnO2 have high energy density and low cost, they are economically attractive even at limited depth of discharge. As received, a standard bobbin-type alkaline cell costs roughly

Regenerable Cu-intercalated MnO2 layered cathode for highly cyclable energy dense batteries.

20 per kW h. The U.S. Department of Energy ARPA-E

A conversion-based highly energy dense Cu2+ intercalated Bi-birnessite/Zn alkaline battery

100 per kW h cost target for grid storage is thus close to the cost of alkaline consumer primary cells if re-engineered and/or cycled at 5–20% nominal capacity. Herein we use a deeply-penetrating in situ technique to observe ZnO precipitation near the separator in an alkaline cell anode cycled at 5% DOD, which is consistent with cell failures observed at high cycle life. Alkaline cells designed to avoid such causes of cell failure could serve as a low-cost baseload for large-scale storage.

Large photovoltaic power plants: Wildlife impacts and benefits

Manganese dioxide cathodes are inexpensive and have high theoretical capacity (based on two electrons) of 617u2009mAhu2009g−1, making them attractive for low-cost, energy-dense batteries. They are used in non-rechargeable batteries with anodes like zinc. Only ∼10% of the theoretical capacity is currently accessible in rechargeable alkaline systems. Attempts to access the full capacity using additives have been unsuccessful. We report a class of Bi-birnessite (a layered manganese oxide polymorph mixed with bismuth oxide (Bi2O3)) cathodes intercalated with Cu2+ that deliver near-full two-electron capacity reversibly for >6,000 cycles. The key to rechargeability lies in exploiting the redox potentials of Cu to reversibly intercalate into the Bi-birnessite-layered structure during its dissolution and precipitation process for stabilizing and enhancing its charge transfer characteristics. This process holds promise for other applications like catalysis and intercalation of metal ions into layered structures. A large prismatic rechargeable Zn-birnessite cell delivering ∼140u2009Whu2009l−1 is shown.

A micro-jet array for economic intensification of gas transfer in bioreactors

Manganese dioxide (MnO2)–zinc (Zn) batteries are cheap and environmentally benign and have sufficient theoretical energy density to be used as an energy storage device for the grid; however, they have been relegated to primary systems, where the complete energy is delivered in a single discharge, due to the irreversibility of their active materials. Until recently, rechargeable MnO2–Zn batteries have only been able to cycle ∼10% of MnO2s theoretical 2-electron capacity (617 mA h g−1), thus delivering significantly reduced energy density. In a recent paper from our group, we reversibly accessed the full theoretical 2-electron capacity of MnO2 for >6000 cycles by using a layered polymorph of MnO2 mixed with bismuth oxide (Bi2O3) called Bi-birnessite (Bi–δ-MnO2) intercalated with Cu2+ ions. This discovery highlighted the possibility of achieving very high energy densities from inexpensive aqueous batteries; however, a full-cell demonstration with Zn as the anode was not studied. Here we report for the first time the effect of Zn anodes on the cycle life and energy density of a full cell, where we observe that 15% depth-of-discharge (DOD) of the Zns theoretical capacity (820 mA h g−1) creates a cell energy density of ∼160 W h L−1; however, this causes a drastic shape change and formation of irreversible zinc oxide (ZnO) at the anode, which ultimately causes cell failure after ∼100 cycles. A drop in energy density is also observed as a result of the interaction of dissolved Zn ions with the cathode, which forms a resistive Zn-birnessite compound in the early cycles, and then forms a highly resistive haeterolite (ZnMn2O4) in the later cycles, and ultimately causes cathode failure. A possible solution using a calcium hydroxide layer as a separator is presented, where the layer blocks the interaction of zinc ions through a complexing mechanism to obtain >900 cycles with >80% retention of MnO2 DOD.