Advanced Photovoltaics Including New Materials and Approaches; GRID Applications By Zachary Koop, with motivation from Dr. Stan Burns

Outline Silicon and Solar New Developments in PV Grid Integration and Micro-Grids Sources 5 Key Points

Silicon Materials as Solar Devices Si is a semiconductor (bandgap ~ 1.1eV) Si is the second most abundant resource on Earth, 27.7% of Earth’s crust Our economy is adept at processing Si (think “Silicon Valley”). Si is not the most efficient material for absorbing the Sun’s light. The theoretical maximum efficiency of Si solar cells is 30%. Education at Jlab.org

Solar Cells: The Basic Structure Incident photons excite electrons beyond the bandgap caused by the pn-junction. Electrons captured by metal contact, and then complete a circuit, powering a load. The electron are returned to their lowest possible state. *Traditional silicon absorb a relatively small portion of the solar spectrum. NREL NREL

Monocrystalline, Polycrystalline, Amorphous Most Efficient (23%), Most Expensive Efficiency is ~ 15% Least Efficient (<10%), Least Expensive Wikimedia Commons, public domain

High-Concentration III-V Multijunction Solar Cells Layering multiple semiconductor materials to generate more current from Sun’s photons of various wavelengths. Popular materials: Gallium-Indium-Arsenide, Gallium-Indium-Phosphide Law of diminishing returns NREL NREL NREL

Hydride Vapor-Phase Epitaxy (HVPE) Manufacturing Low-cost, ultra-high efficiency. Addresses two major costs of III-V solar devices, epitaxial growth and single-crystalline substrates used for growth (seed). Targets production tandem cells with goal achieving of >30% efficiency. Essentially, takes what used to be a series production process and makes it parallel. The idea is to drive down the marginal cost of production using new manufacturing technologies. National Renewable Energy Lab

Electro-Absorption Modulators and the Quantum Confined Stark Effect Two promising traits: Would allow the absorption spectra of a solar cell to be shifted. By introduces new nanopaticle material, can achieve additional absorption peaks. Koop, Gansen, King, Bailey Koop, Gansen, King, Bailey

Pictures of actual nano-particle layers using Atomic Force Microscopy. Koop, Gansen, King, Bailey

Organic Dye-Sensitized Photovoltaics: “Gratzel Cell” Quasi-Semiconductor that is cheaper to manufacture. Efficiencies theorized to reach 15%. Relatively new, won the 2010 Millennium Technology Prize (aka Nobel Prize) ‘gcell.com’ National Renewable Energy Lab National Renewable Energy Lab

How it works: “Photoelectrochemical System” Incident photons excite electrons in the TiO2 dye-sensitized layer. Transparent Conducting Oxide Glass Substrate Titanium Dioxide Dye-Sensitized Titanium Dioxide Triiodide Electrolyte (Graphite) Carbonized Layer e- Ec Ev Koop, Elliott

How it works: “Photoelectrochemical System” Incident photons excite electrons in the TiO2 dye-sensitized layer. e- absorbed into TiO2 layer and transported to the TCO layer. Transparent Conducting Oxide Glass Substrate Titanium Dioxide Dye-Sensitized Titanium Dioxide Triiodide Electrolyte (Graphite) Carbonized Layer e- Ec Ev Koop, Elliott

How it works: “Photoelectrochemical System” Incident photons excite electrons in the TiO2 dye-sensitized layer. e- absorbed into TiO2 layer and transported to the TCO layer. e- transported to opposite electrode generating a current. Current Transparent Conducting Oxide Glass Substrate Titanium Dioxide Dye-Sensitized Titanium Dioxide Triiodide Electrolyte (Graphite) Carbonized Layer Koop, Elliott

How it works: “Photoelectrochemical System” Incident photons excite electrons in the TiO2 dye-sensitized layer. e- absorbed into TiO2 layer and transported to the TCO layer. e- transported to opposite electrode generating a current. e- are transported back to TiO2 sensitized-dye layer through iodide layer. Current Transparent Conducting Oxide Glass Substrate Titanium Dioxide Dye-Sensitized Titanium Dioxide Triiodide Electrolyte (Graphite) Carbonized Layer Koop, Elliott

Grid-Integration: Solar Energy Grid Integration System American Grid was developed technology a century ago. Used to be as simple as supply and demand. Consumption was predictable, production was static. Today, consumption is still predictable, but production is dynamic. Use software to optimize to generation/load balance. Develop forms of energy storage. Wikipedia

Derivation from Modern Survival Blog, see Appendix Derivation from Modern Survival Blog, see Appendix. Uses data from US Census Report.

Microgrids Allow energy to exist where no expansive energy grid pre-exists. Underdeveloped parts of the world. Decentralizes power generation. Complex, unsophisticated, and expensive. National Renewable Energy Lab

Summation of Sources Education.jlab.org www.rsc.org www.nrel.gov Koop, Gansen, King, Bailey Research on ZnMgO EAM’s Koop, Elliott Research on Organic Gratzel Cells www.rreal.org ModernSurvivalBlog.com w/ data from US Census Report Commons.wikimedia.com: public domain pictures available for educational usage

5 Key Points The maximum efficiency for traditional Si solar cells is projected to be ~30 Si is a popular solar material because it is non-toxic, has a variable bandgap (semiconductor), abundant, and is a traditional material. A majority of solar research is aimed at “fine tuning” solar technology. Organic non-semiconductor solar cells (“Gratzel cells”) are a promising new technology with efficiencies approaching 15%. The United States grid cannot sustain the future projection of renewables (solar energy) without radical innovations to technologies such as energy storage.