SERIIUS R&D Highlights
Read short descriptions of some recent successes by researchers within the Solar Energy Research Institute for India and the United States (SERIIUS). The highlights cover the areas of photovoltaics (PV), concentrating solar power (CSP), and solar energy integration (SEI).
SERIIUS and the McDonnell Academy Global Energy & Environmental Partnership (MAGEEP), with funds from SunEdison, will support the fourth year of SERIIUS Fellows and Scholars.
SERIIUS and the McDonnell Academy Global Energy & Environmental Partnership (MAGEEP), with funds from SunEdison, will support the third year of SERIIUS Fellows and Scholars.
SERIIUS and the McDonnell Academy Global Energy & Environmental Partnership (MAGEEP), with funds from SunEdison, will support the second year of SERIIUS Fellows and Scholars.
SERIIUS, McDonnell Academy Global Energy & Environmental Partnership (MAGEEP), with SunEdison funding, have initiated our SERIIUS Visiting Fellows and Scholars Program, with seven candidates chosen in this first-year competitive process. (Full text)
PV Activity 1: Earth-Abundant PV & Advanced Processing
Metastable Behavior in Admittance Spectroscopy – CZTSSe September 2016
We clearly demonstrate the impact of a carrier-injection pretreatment on copper zinc tin sulfur-selenium in admittance spectroscopy that has a large impact on the number of defect signatures and their corresponding activation energies.
For the first time, we clearly demonstrate that band-tail defects in CZTSSe result in reduced carrier collection at forward bias and VOC limitations through voltage-dependent external quantum efficiency analyses.
CZTS nano-size particles were coated onto Mo-coated glass to obtain a working photovoltaic device with 6% efficiency. (Full text)
Study of plasmonic effect of silver nanoparticles in pn-heterojunction solar cells comprising Earth-abundant, non-toxic nanocrystals (CZTS and Cu@AgInS2). Optimization of the position of the plasmonic nanoparticles for both direct and inverted structures.
Formation of pn-junction solar cells with a layer of p-type Cu2O and a layer of n-type SnO2 nanoparticles. Band-edges of the materials with respect to their Fermi energy from STS measurements were used to derive the energy band-diagram. The all-oxide inorganic heterojunction solar cells have a photo-conversion efficiency in excess to 1%.
We developed a method to fabricate highly stable perovskite solar cells under high relative humidity (50%), without any encapsulation. A typical solar cell retains 80% of maximum efficiency after 1,200 hours and the material is stable for more than 2,500 hours.
Introduction of cuprous oxide (Cu2O) thin films formed by Successive Ionic Layer Adsorption and Reaction (SILAR) method as a hole-transport layer in perovskite (CH3NH3PbI3) solar cells. Formation of planar p-i-n (direct) structure heterojunction perovskite solar cells positively modifies efficiency and reliability.
We developed single-step, atmospheric pressure synthesis of single-crystal, one-dimensional nanostructured thin films as absorber material. We are also developing a new hybrid donor systems for enhanced photon harvesting and minimizing recombination. (Full text)
PV Activity 2: Advanced Process / Manufacturing Technology
PVCore-1: Selective Carbon Elimination for Kerf Recycling September 2015
We have addressed the challenging issue of carbon contaminant removal from silicon kerf using a scalable gas-phase technology.
We completed the experimental setup to recover silicon from kerf. Carbon content in swarf was reduced (109 ppb to 105 ppb) using oxidation. We are studying the distribution of Ni in Cz and CCz wafers and started the solar cell fabrication process on CCz wafers. We achieved weighted surface reflectance of 3.6% from ARC textured surface and acceptable sheet resistance of 45–55 Ω/□. (Full text)
We proposed a new characterization technique—modulated electroluminescence—for determining lifetime of solar cells. We also developed a diagnostic tool using dark current-voltage measurements. (Full text)
PV Activity 3: Multiscale Modeling & Reliability
Developed an end-to-end modeling framework for silicon heterojunction (HJ) solar cell technology to investigate the implication of fabrication process variability on the cell and ultimately on the module (panel) performance.
PV-4: Selective-Spectral and Radiative Cooling to Improve Performance and Reliability for Solar Modules December 2016
We identified the physical origins of self-heating in solar modules to parasitic sub-bandgap absorption and imperfect thermal radiation and proposed the corresponding cooling schemes—selective-spectral and radiative cooling.
PV-4: Prediction and Management of Point Defects for Improved Performance of PV Semiconductors December 2016
A DFT / SRH model run in collaboration with WUStL identified the most detrimental defects to carrier lifetime in SnS. Carrier lifetimes improved from <100 ps in thin films to >3 ns in bulk crystals with targeted defect engineering.
We hypothesized that extrinsic point defects are a limiting factor in tin sulfide. Our baseline material exhibits about 100 ns minority-carrier lifetime. We grew SnS using 6N pure feedstock and observed luminescence decays > 1 ns—a significant improvement over the baseline.
The design space for further optimizing perovskite-based solar cells and the practical limits of efficiency are not well known. To address these issues, we identify the detailed balance performance limits, identify the physical mechanisms that contribute to sub-optimal performance of current perovskites, and suggest schemes to further improve the performance.
We analyze a novel Si heterojunction-perovskite (HIT-PVK) bifacial tandem cell that uses direct light as well as the albedo. Using state-of-the-art sub-cells, the bifacial tandem yields ~330 W/m2, which is 30% higher compared to a conventional HIT-PVK tandem under standard solar illumination.
We developed a new, first-principles model to directly calculate electronic transport properties (e.g., mobility, conductivity, Seebeck coefficient) of semiconductors. (Full text)
We developed a systematic characterization framework to extract key parameters in HIT solar cells. (Full text)
We characterized i09nversion charge in HIT cells using a multi-probe approach that involves I-V and C-V measurements, and illustrated that many features of dark I-V correlate well with C-V measurements. We also developed a comprehensive modeling framework, well calibrated with experimental results from literature, to understand / interpret perovskite-based solar cells and suggest further optimization schemes. (Full text)
We developed a systematic characterization framework to extract key parameters in HIT solar cells. (Full text)
We correlated power degradation rate of field-aged modules to the module temperature data obtained from infrared (IR) thermography. Modules with higher temperature inhomogeneity (module ΔT) degrade at a faster rate, mainly due to faster degradation in the fill factor.
We correlated inactive areas in an electroluminescence (EL) image to the short-circuit current loss of the solar cells.
Reliability is one of the primary factors dictating the projected PV electricity cost ($/kWh). PV reliability is critical to project developers, to quantify long-term performance and to increase confidence of investors and financial or insurance backers. This work addresses one of the major reliability issues—Potential-Induced Degradation (PID)—of already installed PV modules in the field.1
PV-5: Reliability Survey of PV Modules in India January 2017
A comprehensive field survey of PV modules located in different climatic zones in India was undertaken to obtain degradation rates (% reduction in power per year). The main factors found to affect degradation are: climate, module quality, and installation practice.
In this bi-national project, we have studied and compared the performance and reliability of c-Si PV modules in the field in the USA and India. This provides an important comparison as to what effects are due to climate, and what are due to other "local" considerations.
We performed a survey of over 1,000 modules in the field in different climatic zones of India. This extensive survey yielded performance and reliability data, enabling a scientific analysis of degradation mechanisms.
We developed a method to replicate the natural process of dust deposition on the solar modules in a laboratory environment using deionized water (DI) water as a carrier solvent. DI water is used as a carrier solvent because water, in the natural environment, is present in the form of moisture and dew drops that causes dust deposition and hence leads to cementation of dust over the surface.
We found that the rate of solder thermomechanical fatigue damage varied significantly depending on deployment location. We also determined the number of accelerated thermal cycles to impart an equivalent amount of damage.
We are developing a comprehensive reliability database for the lifetime prediction of PV technologies, especially in the context of the environment of India and the United States.
Our analysis, which predicts the cost- and energy-efficient use of DC solar-power systems in commercial buildings, is being validated in India using rooftop PV for DC-powered buildings.
We identified the most promising n-type ZnS-based TCM as 6.25% Al-doped ZnS, with the optimal combination of physical stability, transparency, and electrical conductivity (3,830 S cm-1 at n=1.0x1021 cm-3 and 300 K). Mobility in this material is limited by ionized impurity scattering at high carrier concentrations.
PV6: VHF Plasma Etching of Patterned PMMA September 2016
We generated large-area regular micro/nano-size patterns in PMMA on flexible ultrathin glass substrates by means of nano imprint lithography and subsequent VHF plasma etching.
PV6: Encapsulation with Ultralow Permeability September 2016
A single graphene layer embedded in a flexible polymer reduces its water vapor transmission rate (WVTR) by up to a million-fold. We demonstrated large-area, transparent, graphene-embedded polymers with a WVTR as low as 10−6 g/m2/day.
Soil samples collected from the surface photovoltaic modules installed in six locations of India have different current or performance losses, for identical surface soiling density, depending on the mineral composition/color in the respective soil types.
We have done extensive spectral and angular loss characterizations and modeling for soiled photovoltaic modules using naturally and artificially deposited field soil samples collected from various locations in India and the U.S.
We synthesized a new, hybrid barrier material to protect photovoltaic active layers. It comprises block co-polymer (PS-P2VP) and hygroscopic nanoparticles (MgO). The hybrid structure enhances the barrier properties—hydrophobic polystyrene (PS) layers block most water, and what water makes it through is scavenged by hygroscopic MgO nanoparticles in poly-2-vinylpyridine (P2VP) domains. (Full text)
We developed a unique solar PV module soiling test station that is being deployed to collect and analyze dust samples, test commercially developed PV module coatings, and develop and evaluate new coatings based on nanotechnology approaches. (Full text)
We propose disruptive multi-material solar cells with junctionless metal/insulator/semiconductor (MIS) carrier-selective contacts fabricated on a Si substrate with efficiencies approaching ~39% with substantially lower cost of manufacturing. (Full text)
Current conventional encapsulants have several significant problems, and we are developing new materials using polymer and nanocrystals to overcome their shortcomings while also improving their properties. (Full text)
CSP Activity 1: High-Temperature, High-Pressure, Closed-Cycle CO2 Brayton
We characterized convection and radiation heat transfer in simultaneously developing laminar flow of s-CO2 in tubes. This study showed that for certain physical and geometric conditions, neglecting radiative heat transfer—particularly the participation of s-CO2 in thermal transport—can lead to large errors in predicting wall temperature, which affects lifetime and cost.
A new coupling method that combines optical, thermal-fluid, and structural analyses has been developed and implemented for the analysis of high-temperature pressurized receivers. (Full text)
CSP-1: Technoeconomic Study of Solarized s-CO2 Power Cycles September 2015
Performed the first comprehensive technoeconomic analysis of alternative solar-driven supercritical CO2 (s-CO2) power cycles. (Full text)
We developed a framework for the control and regulation aspects of CO2 Brayton cycles for solar and non-solar power plants using a relatively unconventional coordinate system involving two thermodynamic path functions, namely, efficiency and specific work output. (Full text)
CO2-based cycles can be can be used in both Brayton and Rankine cycles. Low-side pressure and expansion ratio are the key parameters in optimizing the cycle efficiency for a given source temperature. (Full text)
We studied the annual field efficiency of a 1-m2 and a 4-m2 receiver with a range of heliostats. (Full text)
CSP Activity 2: Low-Temperature, Organic Rankine Cycle
CSPCore-2: Numerical and Experimental Evaluation of Ceramic Honeycombs for Thermal Energy Storage January 2017
Novel compositions of mullite- and chromite-based ceramic honeycombs were developed for high-temperature thermal storage application. The materials have shown favorable performance for use in high-temperature thermal energy storage. (Full text)
Demonstrated the new alloy design approach involving substitution of Sn by Al in Cu-Sn-based single-phase Cu41Sn11 alloy to enhance the specular reflectance property. In particular, bulk Cu-Sn-Al intermetallic alloy-based solar reflectors with 80%-83% specular reflectance were developed.
CSP-4: PV and CSP: Why Hybrids Make Sense November 2015
Our comparative analysis of the strengths and weaknesses of photovoltaics (PV) and concentrating solar power (CSP) generation shows that a hybridization may be able to merge the best of both worlds by splitting the solar spectrum and sending the optimum wavelengths to PV and CSP.
We developed a design and analysis dynamic simulation tool for optimizing micro-concentrating solar power hybridized with photovoltaics and backup fuel sources in islanded mini-grid applications. (Full text)
We developed a generalized procedure for generating optimum scroll geometries using a genetic algorithm. (Full text)
CSP Activity 3: Thermal Storage & Hybridization
Using numerical simulation, we studied the short- and long-term effects of flow disturbances on the performance of thermocline-based thermal energy storage systems. We observed that the thermocline tank is resilient to flow disturbances for high Atwood number values and oscillation frequencies in the thermocline region are lower than Brunt-Väisälä frequency.
CSP-5: Numerical Analysis of Latent Heat Thermal Energy Storage using Encapsulated Phase Change Material for Solar Thermal Power Plant May 2016
We investigated transient response of a packed-bed latent heat thermal energy storage system (LHTES) in removing fluctuations in the heat transfer fluid (HTF) temperature during the charging and discharging period. To evaluate the system performance, we computed the overall effectiveness and transient temperature difference in HTF temperature in a cycle for different geometrical and operational parameters.
We studied the interaction of coherent structures with the thermocline and analyzed the coherent structures associated with R-T instability.
CSP-5: Stability of Poiseuille Flow Over a Porous Layer November 2015
We found that the following key factors stabilize a system that has Poiseuille flow over a porous layer: decrease in Darcy number, increase in depth ratio, increase in anisotropy parameter, and decrease in inhomogeneity factor.
CSP-5: Mixing Dynamics Across a Stratified Interface November 2015
This work re-examines the underlying physical processes and the factors controlling the interface mixing dynamics across a stratified interface.
CSP-5: Comparative Analysis of Dual- and Single- Media Thermocline Tanks for Energy Storage September 2015
Using numerical simulation, we performed a detailed thermal analysis of thermocline tanks with molten salt and quartzite rock (dual-media), and with only molten salt (single-media). Both tank designs have high thermal performance: we observed greater flow disturbance in the single-media tank, and diffusive thermal losses inside the dual-media tank. (Full text)
We designed and developed a research (laboratory) molten-salt-loop system for storage for Brayton cycles in concentrating solar power. (Full text)
An efficient reduced-order numerical model of thermocline energy storage with phase-change materials (PCMs) is integrated to system-level model of a concentrating solar power plant. A cascaded distribution of PCMs with different melting temperatures can yield to significant improvement in plant performance. (Full text)
CSP-5: Simulation of Thermocline Formation in an Experimental Molten-Salt Energy Storage System for CSP Applications
Purdue University conducted thermal analysis of the experimental thermocline tank at IISc Bangalore; simulations are performed at flow velocities below and above a flow rate that induces instability in the thermocline region to identify a stability criterion. (Full text)
We use numerical simulation to perform a detailed thermal analysis of thermocline tanks with molten solt and quartzite rock (dual media), and with only molten salt (single media). Both tank designs have high thermal performance: greater flow disturbance is observed in the single-media tank, and diffusive thermal losses inside the dual-media tank. (Full text)
An efficient reduced-order numerical model of thermocline energy storage with phase-change materials is integrated to a system-level model of a CSP plant. A cascaded distribution of PCMs with different melting temperatures can yield significant improvement in plant performance.
Thermocline tanks are a potential low-cost storage concept for next-generation CSP plants. We developed a new model for thermocline energy storage that is 100x faster than conventional CFD models. Low computing cost enable an advanced system-level simulation of a CSP plant with thermocline storage. (Full text)
SEI Activity 1: Roadmapping & Assessment
We developed a comprehensive model to determine the annual efficiency of a heliostat field, considering various factors such as shadowing, blocking effects, and cosine effects. (Full text)
We developed a comprehensive financial model showing that if lower-interest-rate loans with longer tenures are available to developers using Indian modules, then comparable equity internal rates of return (IRRs) can be achieved, compared to developers using imported modules. (Full text)
CSTEP conducted an invited training session for senior government officers in the Energy Department (Government of Karnataka) on Public-Private Partnership (PPP) Financial Models in the Energy Sector. (Full text)
SEI Activity 2: Solar Energy Integration and Storage Analysis
SEI-2: Preliminary Design of Heliostat Field and Performance Analysis of Solar Tower Plants January 2017
We developed a methodology to estimate the preliminary design of a heliostat field and performance of a tower plant with storage and hybridization using an external cylindrical receiver.
We developed a detailed procedure to arrive at the critical parameters of solar tower technology (e.g., tower height, mirror area, receiver sizing) for a chosen capacity, storage conditions, and location of tower. (Full text)
SEI-3: Quantifying the Reduction in Solar Generation Variability through Interconnected PV November 2015
Collection and analysis of over 1 year of observed power production data from 50 utility-scale solar plants in the state of Gujarat shows that interconnecting as few as 12 photovoltaic plants achieves the majority of the reduction of variability.