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Energy Markets Are Interconnected
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https://publicaffairs.llnl.gov/news/energy/energy.html
How much is available?
• Earth receives 174 PW (petawatts, 1015 ) of incoming solar radiation (insolation) at the upper atmosphere
• 89 PW absorbed by land & oceans
Energy usage in 2002 about the same as solar energy at surface in 1 hour
• Solar energy can be harnessed in different levels around the world. Depending on a geographical location the closer to the equator the more "potential" solar energy is available
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How does location affect available energy?
CityInsolation[W/m2]
Seattle 125El Paso 240Rio de Janeiro 200Glasgow 100Tokyo 125Naples 200Cairo 280Johannesburg 230Mumbai 240Sydney 210
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• Intensity reaching the surface of the earth strongly dependent upon the latitude (angle to incoming ray of sunlight)
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How do we make use of solar energy?
• Photovoltaic
• Solar thermal
Water heating
Space heating & cooling
Process heat generation
• Concentrating solar furnaces
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Solar cooling?
• Based on evaporation carrying heat
• Adsorption chillers driven by hot water rather than large amounts of electricity (like conventional air conditioners)
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What is Driving Growth in Solar?
• Renewable Portfolio Standards
• Tax credits: 30% investment credit until 1/1/2017
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Phototvoltaic
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Photons converted directly to electricity using semiconducting material (without moving parts)
Phototvoltaic
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Cell Types:
Polysilicon - single or multicrystalline (largest percentage)
Thin film – amorphous silicon, cadmium telluride, etc (industry moving towards)
Multi-junction – multiple layers (utilizes multiple parts of the spectrum)
Nanotubes (novel technology)
Cell efficiency = 5 - 40%
Commercial modules = 10-15%
Cell Efficiencies
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PV Potential
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‐Worldwide PV capacity:
- ‐ at end of 2008: 15 GW ‐ by 2012: 26 GW
‐ U.S. PV capacity:
- ‐ at end of 2008: 250 MW ‐ by 2012: 6 GW (3.9 GW in California)
‐Majority are fixed flat plate but can have tracking system (single or dual); also concentrating PV
‐ Residential rooftops (2 – 5 kW)‐ Commercial rooftops (5 – 10 kW)‐ Utility (5 – 54 MW): largest U.S. 22 MW in Florida, largest world 54 MW in Spain
‐ Current cost ≈ $4,000/kW (low price of silicon has decreased PV prices by 50% in last 2 years)
Innovative PV Technology
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PV shingles
First full-scale production facility for Dow Powerhouse solar shingle being built in Midland, Michigan
Parabolic Trough
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Parabolic shaped mirrors concentrate sun to central receiver
Focus light on linear receiver above mirrors
Organic heat transfer fluid (750 ºF – above this fluid breaks down)
Mirrors, receivers, heat exchangers, steam turbine and possibly energy storage
Energy Storage
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Increases capacity factor
8 hours of storage = doubling of solar field
Dispatchable power
Premium power price when demand is high to help pay for additional capital
2 Tank Energy Storage System (current technology)
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Molten salt (60% sodium nitrate / 40% potassium nitrate)
For parabolic trough:Cold storage = 300°C (572°F) Hot storage = 386°C (727°F)
(limited by heat transfer fluid)
Heat Transfer Fluid Temperature Range
Salt solidifies below 200°C
Higher temp for Power Tower (550°C)
Single Tank Thermocline
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Transfer heat to/from inert material (rock/sand)
Hot fluid at top; cold fluid at bottom; in between is thermocline
Must maintain thermocline; will be a zone of unusable energy
Advantages:‐ ‐ 1 tank‐ ‐ storage medium potentially less expensive
Disadvantage:‐ ‐ operation more complex‐ ‐ unusable portion spreads over time‐ ‐ potential for thermal cycling issues;‐ settling of fill material
Other Energy Storage
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Concrete
Advantages: Disadvantages:‐ low cost ‐ low energy density‐ good thermal stability ‐ low thermal conductivity‐ easy to pour/shape
Phase change materials (solid‐liquid)
Advantages: Disadvantages:‐ higher energy density ‐more complex operation‐ lower cost ‐ energy penalty from sensible
heat to latent heat and back
Current & Future for Parabolic Trough
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Total capacity of current operating plants = 625 MW
Total capacity of being constructed plants = 2,270 MW (majority in Spain)
Total capacity of planned plants = 6,615 MW (86% or 5,665 MW in California or Arizona)
Many new plants include energy storage
Parabolic Trough ‐ Plant Size & Cost
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‐Modular but optimal steam turbine size is 100 – 125 MW (economics of pumping heat transfer fluid vs steam turbine located centrally around solar field)
‐ Current largest plant = 100 MW
‐ Constructed plants = 50 MW or 100 MW
‐ Planned plants = many 250+ MW
‐ Current cost ≈ $6,500/kW (levelized cost ≈ $0.18/kWh; compared to $0.11 ‐ $0.07/kWh for residential to industrial)
Compact Linear Fresnel Reflector (CLFR)
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Arrays of optically-shaped reflector mirrors
Focus light on linear receiver above mirrors
Direct steam production (saturated or superheated)
Augment existing plant or stand alone
Prototype in Australia
Dish/Engine
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Power Conditioning Unit (PCU)
No water in power generation
Stable design up to 90 mph wind (“wind still” position)
3 large scale utility projects breaking ground in California & Texas in 2010
Most efficient solar technology
Power Tower
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Tracking mirrors focus sunlight to central receiver (usually mounted on a tower)
Molten salt or direct steam generation
Higher temperatures than parabolic trough (1050ºF vs 750ºF)
3 plants operating in Spain (48 MW)
3 plants being built in Mojave Desert (400 MW)
Land Requirement
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PV = 5 – 10 acres/MW
Compact Linear Fresnel = 3 acres/MW
Solar Trough = 4 acres/MW
Dish/Stirling = 6 acres/MW
Power Tower = 8 acres/MW
