This page lists some of the projects I've been a part of over the course of my research career. Here you can find short descriptions of the projects, as well as links to publications, presentations and other resources that go into further detail. If your expertise is in similar areas as mine, you may be better served by my Google Scholar or ResearchGate profiles. If you don't have institutional access to any of my publications, most should be available on DSpace@MIT.
Much of my graduate research can fit broadly under the umbrella of "Concentrating Solar Power" or CSP. Perhaps a more apt name is "Solar-Thermal," as in CSP systems sunlight is converted to heat and then subsequently converted to electricity (as opposed to photovoltaics, which convert sunlight directly to electricity). CSP is so called because typically concentration of sunlight is required in order to reach high enough temperatures for the heat to be converted to electricity at reasonable efficiency. CSP is an important piece of our renewable energy portfolio because it is much cheaper to store heat than electricity. This means that if we want solar energy to be able to provide electricity at night, CSP with thermal storage has significant advantages over photovoltaics with batteries.
Photograph of the Solana Generating Station, a CSP plant which uses parabolic trough mirrors to focus sunlight onto vacuum receiver tubes. Photograph by Dr. James Loomis.
Concentrating Solar Power in Chemical Reviews
Limit to the spectral selectivity of a passive radiative surface based on the Kramers-Kronig relations at the 2017 ASME Summer Heat Transfer Conference
Limit on the Performance of Spectrally Selective Surfaces for Solar Applications at the 2016 MRS Fall Meeting
Directional Selectrivity as an Alternative to Concentration for High Efficiency Solar Thermal Systems in the proceedings of the 2015 ASTFE Thermal and Fluids Engineering Summer Conference
I am helping to develop a solar-thermal receiver which uses transparent silica aerogel as the insulating material. Silica aerogel has very low thermal conductivity and can be made transparent in the solar spectrum. If this aerogel is used to cover a solar absorber, sunlight can transmit through the aerogel and be absorbed, but the aerogel traps the heat in the absorber, reducing thermal losses. This receiver could achieve efficient conversion of sunlight to high temperature heat more reliably and inexpensively than the vacuum tube receivers which are currently used.
Aerogel-based solar thermal receivers in Nano Energy
A Solar-Thermal Aerogel Receiver (STAR) for Cost-Effective Electricity Generation at the 2016 MRS Spring Meeting
I helped design a spectrum-splitting hybrid PV and thermal solar receiver. This receiver was conceived to address the ARPA-E FOCUS program goals of optimizing the use of the entire solar spectrum. In this receiver, photons converted most efficiently by PV are directed to a PV cell, while the rest of the solar spectrum is absorbed as thermal energy. Such a receiver takes advantage of cheap and efficient PV cells, while also collecting high temperature heat that can be stored inexpensively and converted to electricity on demand.
Hybrid PV and Thermal Solar Receiver Using Silica Aerogel and Thin-Film Multi-Layer Spectral Splitting at the 2015 MRS Fall Meeting
I designed an optical cavity to reduce radiative losses from solar receivers. The cavity takes a near hemi-spherical shape, with the solar absorber surface being placed at the center. An aperture in the cavity allows sunlight in, but radiation leaving the surface at large angles which would normally be lost are reflected back to the absorber and reabsorbed. This cavity can also improve the effective absorptance of PV cells, as photons which reflect off the cell the first time can become trapped in the cavity, yielding multiple chances for absorption.
Photographs of the experimental set up used to demonstrate the optical cavity concept.
Enhanced absorption of thin-film photovoltaic cells using an optical cavity in Journal of Optics - this paper was also recognized in a lab talk and named a highlight of 2015
Angularly dependent emissivity using optical cavities at ASME IMECE 2013 (in session 7-9-1)
External Cavity for Enhanced Absorption in Thin-Film Photovoltaics at ASME Energy Sustainability 2014
Thermoelectric (TE) materials are materials which generate a voltage gradient when subjected to a temperature gradient. TE materials can thus be used to convert waste heat to electricity without any moving parts, which makes them promising as scalable, reliable heat engines. TE materials can also generate electricity from sunlight in a solar thermoelectric generator (STEG) arrangement, where the heat input comes from a solar absorber. I have been involved in improving STEG performance through the integration of optical concentration to reach higher temperatures, exploring alternate STEG configurations, and coupling STEGs with thermal storage.
Concentrating solar thermoelectric generators witha peak efficiency of 7.4% in Nature Energy - this paper received a fair amount of media coverage
Modeling of thin-film solar thermoelectric generators in Journal of Applied Physics
Demonstrated high efficiency of concentrating solar thermoeletric generators at the MRS 2014 Fall Meeting (talk CC8.01)
While at UC Berkeley, I worked on a project developing a flow energy harvester to power wireless sensor nodes in HVAC ducts. The device used a bluff obstacle to create periodic vortices which excite a piezoelectric bender (piezoelectric materials can generate electricity when they vibrate). Throughout my involvement in the project we were able to increase power output of the device by about three orders of magnitude.
Diagram of working principle of the flow energy harvester and a photograph of a device prototype.
Vortex shedding induced energy harvesting from piezoelectric materials in heating, ventilation and air conditioning flows in Smart Materials and Structures
I had the good fortune to work at The Buck Institute for Age Research the summer after I graduated high school as a research intern. While I was there, I worked on a project examining the effect of curcumin (a primary component of turmeric) on melanoma cells (skin cancer). While my research career has moved in a very different direction than where I started, I am still happy I was exposed to research at The Buck Institute and that I had a positive experience there.