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ME 417 Quiz 5
| Question | Answer |
|---|---|
| What is solar photovoltaic (PV) energy? | Conversion of photons (light energy) into electricity. |
| What are photons? | Packets of electromagnetic energy. |
| What happens to photon energy as frequency increases? | Energy increases, wavelength decreases. |
| What part of the EM spectrum is most relevant to solar PV? | Visible and near-infrared light. |
| What does the spectral irradiance graph show? | Solar energy distribution vs wavelength, with atmospheric losses reducing energy at Earth’s surface. |
| What does the U.S. irradiance map show? | Solar energy potential (kWh/m²/day), highest in the Southwest. |
| Where is solar irradiance highest globally? | The “Sunbelt” regions (near equator and deserts). |
| Why are Sunbelt regions important? | They have the lowest potential cost for solar electricity. |
| What does the global map indicate? | High solar resource regions overlap with developing/emerging markets. |
| Who discovered the photovoltaic effect? | Alexandre Edmond Becquerel (1839). |
| Who installed the first solar panels? | Charles Fritts (1884, NYC rooftop). |
| What material did early solar cells use? | Selenium. |
| What material is used in ~95% of solar modules? | Silicon. |
| Name the three main types of silicon solar cells. | Monocrystalline, polycrystalline, thin-film. |
| What does the silicon material comparison show? | Different panel structures and efficiencies. |
| What type of material is silicon? | Semiconductor. |
| What is a band gap (Egap)? | Energy required for electrons to move to conduction band. |
| When can a photon generate electricity? | When E(photon) > E(gap) |
| What is the bandgap of silicon? | 1.1 eV. |
| What does the photon energy vs absorption graph show? | Only photons above bandgap contribute to electricity; others are lost. |
| What are the main layers in a solar cell? | Semiconductor, transparent electrode, back electrode. |
| What type of power do PV cells produce? | DC power. |
| What does the absorption coefficient graph show? | How different materials absorb light at different wavelengths. |
| What does the efficiency chart show? | Improvements in solar cell efficiency over time. |
| Which technology has the highest efficiencies? | Multijunction (III-V) solar cells. |
| What is a multijunction cell? | A cell using multiple bandgaps to capture more of the spectrum. |
| What advantage do multijunction cells have? | Reduced thermal and spectral losses. |
| What are III-V solar cells? | High-efficiency semiconductor materials (e.g., GaAs). |
| What is a perovskite? | A crystal structure (ABX₃) used in emerging solar cells. |
| Why are perovskites important? | High efficiency + low cost potential. |
| What does the perovskite diagram show? | Crystal structure with A, B, X ions. |
| What is the difference between a cell, module, and array? | Cell → smallest unit; Module → group of cells; Array → multiple modules. |
| What does a DC-DC converter do? | Adjusts voltage levels. |
| What does an inverter do? | Converts DC to AC power. |
| What is a rectifier? | Converts AC to DC. |
| What is an on-grid PV system? | Connected to the electrical grid. |
| Do on-grid systems need batteries? | No (grid acts as backup). |
| What is the difference between centralized and distributed PV? | Centralized = large plants; Distributed = rooftop/local systems. |
| What has happened to solar PV costs over time? | They have significantly decreased. |
| What are “soft costs”? | Permits, labor, overhead, installation. |
| Which system is cheaper per watt? | Utility-scale PV. |
| What is the main cost driver? | Hardware (modules, inverters). |
| What is transparent solar? | Solar cells embedded in windows that generate electricity. |
| What wavelengths does transparent solar use? | UV and infrared (lets visible light pass through). |
| What is spray-on solar? | Coatings that act as solar cells. |
| Who benefits the most from solar installations? | The user (energy savings). |
| How do user benefits compare to manufacturer profits? | 100× greater. |
| What is the long-term benefit of solar panels? | Reduced electricity costs over decades. |
| What are the main types of solar energy systems? | Solar photovoltaics (PV), concentrating solar power (CSP), solar water heating, and passive solar heating. |
| What is solar photovoltaics (PV)? | A technology that converts sunlight directly into electricity. |
| What is concentrating solar power (CSP)? | Uses mirrors to focus sunlight into heat, which produces steam to drive a turbine. |
| What is solar water heating? | Uses solar energy to heat water directly or via a heat-transfer fluid. |
| What is passive solar heating? | Uses building design (windows, materials) to naturally collect and distribute solar heat. |
| What does the solar energy diagram show? | Different solar technologies and their applications from small-scale to utility-scale. |
| How does passive solar heating work in buildings? | South-facing windows collect heat, materials absorb/store it, and heat is distributed inside. |
| What does the solar PV cost graph show over time? | A dramatic decrease in cost per watt since ~1975. |
| What does this trend indicate? | Solar PV is a mature and economically competitive technology. |
| What is the general trend of solar panel prices? | Exponential decrease from ~$100/W to <$1/W. |
| What are the main components of a PV cell? | Semiconductor, transparent electrode, back electrode. |
| What type of current is produced by PV cells? | Direct current (DC). |
| Electron flow through the semiconductor creating what kind of power? | DC power |
| What are the major PV technology categories? | -Crystalline silicon - Thin-film - III-V multijunction - Emerging PV (perovskites, organic, quantum dots) - Hybrid tandems |
| What is a tandem solar cell? | A cell combining multiple materials to capture more of the solar spectrum. |
| What is the key advantage of multijunction cells? | Higher efficiency by capturing different wavelengths. |
| What losses are reduced in multijunction cells? | Thermalization losses and spectral losses. |
| Single-junction: | more energy losses |
| Multi-junction: | better spectral utilization |
| What do “wide-Eg” and “low-Eg” regions represent? | Different bandgap materials absorbing different parts of the spectrum. |
| What is centralized PV? | Large-scale power plants. |
| What is distributed PV? | Rooftop or local systems. |
| Why is visible light transmitted? | To keep windows transparent. |
| What are the main cost components of solar systems? | Module, inverter, hardware, labor, soft costs. |
| What are “soft costs”? | Permits, overhead, installation, etc. |
| Which is cheaper: utility-scale or residential solar? | Utility-scale. |
| What trend is shown for utility-scale solar costs? | Significant decrease over time. |
| How do residential costs compare? | Higher than utility-scale due to installation and soft costs. |
| What dominates residential solar cost? | Soft costs and labor. |
| What is geoengineering? | Large-scale intervention in Earth’s climate system to counteract climate change. |
| Solar radiation management: | reducing incoming sunlight |
| What organisms are shown as inspiration for solar energy concepts? | - Eastern Emerald Elysia (sea slug) - Spotted salamander - Oriental hornet |
| Why are these organisms relevant? | They exhibit natural or bio-assisted energy capture/solar-related processes. |
| What is unique about the sea slug shown? | It can perform photosynthesis-like processes using stolen chloroplasts. |
| what does W(dot) represent? | power output |
| What does ηPV represent? | efficency |
| what does A(col) represent | collector area |
| what does G"(solar) represent? | Solar irradiance (W/m^2) |
| What is η(0)? | Reference efficiency under ideal conditions. |
| What is β(PV)? | Temperature coefficient (how efficiency drops with temperature). |
| What is T(c)? | Cell temperature. |
| What is NOCT? | Nominal Operating Cell Temperature (realistic operating condition). |
| What is the optimal tilt angle equation? | Optimal tilt = Latitude − Declination |
| What is declination angle? | Angle between Earth’s equatorial plane and the sun. |
| Why is tilt important? | Maximizes solar energy absorption. |
| What is T(amb)? | Ambient temperature. |
| What is C(f)? | Tilt correction factor. |
| What does clearness index represent? | Atmospheric clarity affecting solar radiation. |
| What does the diagram combine? | Tilt effects + irradiance + temperature modeling. |
| What is LCOE? | Cost per unit of electricity over a system’s lifetime. |
| What is the full LCOE equation concept? | Discounted total costs divided by discounted total energy produced. |
| What are included costs? | Investment, operation, maintenance. |
| What is the simplified LCOE form? | LCOE ≈ Total Lifetime Energy / Total Lifetime Cost |
| what does I(t) stand for in LCOE equation? | investment cost at t |
| what does O(t) stand for in LCOE equation? | operating cost at t |
| what does M(t) stand for in LCOE equation? | maintenance cost at t |
| what does r stand for in LCOE equation? | discount rate |
| what does t stand for in LCOE equation? | time |
| what does E(t) stand for in LCOE equation? | electricity generated in year t |
| What are solar thermal technologies? | Systems that convert sunlight into heat. |
| Name two types of solar thermal technologies: | - Concentrated Solar Power (CSP) - Solar water/space heating |
| What is the Ivanpah facility? | A large CSP plant in the Mojave Desert using mirrors to focus sunlight. |
| How does CSP generate electricity? | Mirrors focus sunlight → heat → steam → turbine → electricity. |
| What are common CSP types? | - Parabolic trough - Solar tower - Dish/engine systems |
| What is radiation heat transfer? | Energy transfer via electromagnetic waves. |
| Does radiation require a medium? | No. |
| How does radiation occur at atomic level? | Oscillating charges produce electromagnetic waves. |
| What happens when radiation reaches another object? | It excites atoms and increases temperature. |
| What types of radiation exist in the EM spectrum? | Radio, microwave, infrared, visible, UV, X-ray, gamma. |
| How do wavelength and frequency relate? | Inversely proportional. |
| Where does geothermal energy originate? | Heat from Earth’s core and mantle. |
| What does the geyser image represent? | Natural release of geothermal heat through steam and hot water. |
| What drives heat transfer inside Earth? | Convection currents in the mantle. |
| How do convection currents work? | Hot material rises, cools, then sinks, creating circulation. |
| Why are convection currents important? | They drive plate tectonics. |
| what is plate tectonics? | Movement of earths lithospheric plates |
| what are the three main plate boundaries | - convergent - divergent - transform |
| where is geothermal activity most common? | near plate boundaries |
| what is the "ring of fire"? | a region around the pacific with high volcanic and seismic actiivty |
| why is the ring of fire important for geothermal energy? | high heat flow makes it ideal for geothermal resources |
| what does the U.S. groundwater temperature map show? | surface temperatures vary geographically |
| what happens to temperature as depth increases | it increases (geothermal gradient) |
| what does the 3.5 km map show? | moderate subsurface temperatures |
| what changes at 5.5 km depth? | higher temperatures, especially in the western U.S. |
| what happens at 6.5 km? | even higher temperatures |
| what is observed at 10 km? | very high temperatures, especially in geothermal hotspots |
| where is geothermal potential highest in the U.S.? | western states |
| what is hydrothermal geothermal energy? | uses naturally occurring hot water/steam near the surface |
| what are the two main uses of geothermal energy? | - direct use (heating) - power generation |
| what is a binary power plant? | Uses geothermal heat to vaporize a secondary fluid |
| what are flash/dry steam plants? | use geothermal water/steam directly to drive turbines |
| what is an Enhanced Geothermal System? (EGS) | artificially created reservoirs by drilling deep into hot rock |
| what determines how geothermal energy is used? | temperature of the resource |
| what temperature range is needed for power generation? | 150°C to 370°C (300–700°F) |
| what can high-temperature geothermal produce? | electricity and hydrogen |
| what are medium-temperature applications? | industrial processes (drying, processing) |
| what are low-temperature uses? | - building heating - greenhouses - aquaculture |
| what is direct use geothermal? | using geothermal heat directly without electricity generation |
| what are examples of direct use? | - heating buildings - food processing - fish farming |
| are lower temperatures sufficient for many practical uses? | yes |
| why does geothermal power generation require deeper wells? | higher temperatures are needed |
| what is the trade-off with depth? | deeper wells = higher cost but more energy potential |
| why is geothermal energy location-dependant? | it depends on underground heat availability and tectonic activity |
| why is the western U.S. ideal for geothermal? | plate boundaries and higher heat flow |
| what is the biggest advantage of geothermal energy? | reliable, constant (baseload) energy |
| What is a major limitation? | High upfront drilling cost and geographic constraints |
| What is the key takeaway about temperature vs application? | Higher temperatures → power generation lower temperatures → direct use. |
| what is a new insight about geothermal use? | it can support multiple sectors simultaneously (electricity, industry, agriculture) |
| What is a ground heat exchanger? | a system that transfers heat between the ground and a building |
| What are closed-loop horizontal systems? | pipes buried horizontally: cheaper but require more land |
| what are closed-loop vertical sysetms? | pipes drilled deep: more efficient but more expensive |
| what are pond/lake systems? | use nearby water bodies for heat exchange |
| what are open-loop systems? | use groundwater directly (least expensive but risk fouling) |
| what is the first step in EGS? | measure underground temperature gradient |
| what does the temperature gradient graph show? | temperatures increase with depth; geothermal regions have steeper gradients |
| what is a typical gradient? | normal temperature increase vs enhanced geothermal regions (higher) |
| what is the next step after profiling? | drill production-scale wells |
| what is a key challenge of drilling? | high cost |
| what is done after drilling? | install valves and control systems |
| what does the surface equipment show? | control of high pressure steam/ water flow |
| how does EGS extract heat? | Water is injected → heated by hot rock → returns as hot fluid/steam. |
| what role do turbines play in geothermal plants? | Convert steam energy into mechanical energy → electricity. |
| who produced the first geothermal electricity? | Piero Ginori Conti (Italy, 1904) |
| what is an Organic Rankine Cycle? (ORC) | a cycle using a low-boiling-point fluid instead of water |
| why use ORC in geothermal systems? | works with lower temperature heat sources |
| what is a dry steam plant? | uses steam directly from underground resrvoirs |
| where is the largest geothermal field in the world? | The Geysers, California |
| what are the main components of a geothermal power system? | - production well - turbine - generator - cooling system - injection well |
| what happens during operation? | Hot water rises → pressure drops → steam forms → drives turbine → water reinjected |
| how do binary cycle plants work? | - use geothermal water to heat a secondary fluid - secondary fluid vapor drives turbine |
| which country has the highest geothermal capacity? | U.S. |
| where is innovation happening in geothermal? | - enhanced geothermal systems (EGS) - advanced drilling technolgies |
| is geothermal energy renewable? | Yes, long term - but can be locally depleted short-term |
| what is a key advantage of geothermal? | clean, reliable baseload energy |
| what is a limiation? | location-specific and high upfront cost |
Created by:
mccurdyo