Solar Energy Technologies

These are notes from Renewable Energy Futures Study.

• Introduction
• US population uses about 4,000 TWh of electrical energy each year
• about the amount of solar energy that falls on US every few hours
• fraction of generation is small but rapidly growing 3,400 MW in 2011
• generating technologies began in 1970s, 80s
• solar deployment initially dominated by CSP(Concentrating Solar Power) until PV became more popular around 2005
• Resource Availability Estimates
• Solar energy contains both a direct and diffuse component
• direct accounts for 60-80% of surface solar insolation and is needed for high efficiencies for solar technologies
• CSP is more reliant on direct components than PV or passive heating
• Solar resource greatest in southwestern united states but generally high in most parts of the united states except alaska and pacific northwest
• i.e. Germany is world leader in PV but has less than 40% efficiency as systems in LA

• Technology Characterization
• Solar Photovoltaics
• PV convert sunlight into electricity through excitation from ground state
• several technologies deployed at gigawatt scale
• Emerging tech
• Copper indium gallium diselenide thin films
• concentrating PV
• organic PV cells

• Concentrating Solar Power
• CSP uses lenses or mirrors to focus sunlight onto receiver to heat fluid
• Parabolic trough systems, first commercialized in 1984, 96% of global deployment
• 1 axis track linear receiver to focus sunlight
• Dish uses 2 axis tracking
• Other Solar Technlogies
• water heating, space heating, cooling, and lighting, displace end use electricity
• Technologies included in RE Future Scenario Analysis
• PV Markets
• grid connected residential rooftop PV
• grid-connected commercial rooftop PV
• distributed utility scale PV
• central utility scale PV
• CSP technologies
• trough systems no storage
• trough with thermal energy storage
• tower systems with thermal energy storage
• Technology Cost and Performance
• steady trend of improvement
• RE technology costs RE-ETI (renewable electricity evolutionary technology improvement)
• represents more complete implementation of renewables
• RE-ITI (renewable electricity incremental technology improvement)
• represents only a partial achievement of potential technologies
• Solar costs refer to bottom up estimates of materials, manufacturing, installation
• Solar prices refer to market price of PV
• Solar Photovoltaics Cost and Performance

• since 1980s, factory gate module prices have decreased

• Engineering Analysis of Advancement Potential for Solar Photovoltaics
• PV Prices will improve from increasing module efficiencies, manufacturing throughput, reducing wafer thickness
• PV market dominated by multi crystalline and mono crystalline PV dominates about 85% of global market
• thin film cadmium telluride represents a significant other portion

• Balance of systems costs for solar photovoltaics
• BOS includes cost of inverters, transformers, support structures, mounting hardware, electrical protection devices, wiring, monitoring equipment, shipping, land, installation labor, permitting, and fees $1-4 per watt
• Hard BOS
• increase module efficiency, reduce size of installation
• developing racking systems to enhance energy production and integrate them into modules
• create standardized package systems and supply chains
• improve inverter price/performance
• Soft BOS
• reduce supply chain margins
• create standardized practices
• expand financing plans
• Solar cost projections in the SunShot vision study
• in 2011 the Department of Energy launched the SunShot Initiative
• push solar energy to become competitive with retail tech
• PV target to reach $1 per watt for utility scale systems, and 1.25 for commercial rooftop scale PV, and $1.50 for residential rooftop
• CSP targeted to reach $3.60 for systems with 14 hour storage
• RE futures modeling scenarios do not reach these price and performance targets
• Resource Cost Curves
• curves developed for rooftop PV, distributed PV, central utility PV, and CSP
• derived using solar resource characteristics from NREL's National Solar Radiation Database and the National Land Cover Data
• The following table describes the supply curves for PV

• Rooftop PV has technical potential of 700 GW in US
• Distributed Utility PV has about 2,000 GW
• Technical potential of central utility PV about 80,000 GW
• land availability not likely to limit PV deployment
• Output Characteristics and Grid Service Possibilities
• Solar Electricity consists of 2 distinct technologies with different generation characteristics
• PV provides DC in the range from 100-200W, then converted into utility grade power with 60 Hz frequency
• PV fluctuation in production varies, even more than wind generation
• Depends on cloud variability, short time variations
• CSP systems have much less short term variability due to thermal inertia of system
• CSP with storage viable to improve power quality, voltage, frequency stability
• Advantages
• PV generation curve does match peak load which occurs during the day
• PV reduces line losses due to distributed generation
• Technology Options for Power System Services
• Utilize inverter's power electronics
• reactive power, voltage control, and low voltage ride through
• Large Scale Production and Deployment Issues
• Environmental and social impacts
• land area required for PV and CSP is very large
• PV is modular, can be sited virtually anywhere, CSP has more specified locations
• Water Use
• CSP consumes water through evaporation, PV requires only maintenance water
• Life cycle Greenhouse Gases
• life cycle greenhouse gas emissions insignificant in comparison to power generation
• 45.5g carbon dioxide for PV, 19.0g carbon dioxide for CSP 
• Other Impacts
• CSP often use oil or salt heat transfer fluid, which is not risk free
• glare from PV can cause risk to nearby persons
• Manufacturing and Deployment Challenges
• scale up capital is necessary
• availability of raw materials shouldn't be an issue, byproducts of electrolytic copper refining can be used for PV, cadmium telluride
• Indium is byproduct of zinc refining
• Material for silicon PV virtually unlimited
• High up front costs, low operating costs
• Human resources needed for design, manufacture, installation, and maintanence
• Conclusions
• fraction of solar usage is currently small but growing rapidly
• it faces mainly the issues of high upfront cost, and regulations especially for rooftop pv, local legislature can limit growth
• large scale deployment may cause landscape change

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