Solar Energy
Courtesy: Pam Spath, URS
John Jechura – jjechura@mines.edu
Updated: January 4, 2015
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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? • Intensity reaching the surface of the earth strongly dependent upon the latitude (angle to incoming ray of sunlight)
City
Seattle
El Paso
Rio de Janeiro
Glasgow
Tokyo
Naples
Cairo
Johannesburg
Mumbai
Sydney
Insolation
[W/m2]
125
240
200
100
125
200
280
230
240
210
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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
Photons converted directly to electricity using
semiconducting material (without moving parts)
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Phototvoltaic
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%
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Cell Efficiencies
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PV Potential
‐ 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)
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Innovative PV Technology
PV shingles
First full-scale production facility for Dow Powerhouse
solar shingle being built in Midland, Michigan
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Parabolic Trough
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
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Energy Storage
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
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2 Tank Energy Storage System (current technology)
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)
Salt solidifies
below 200°C
Higher temp
for Power
Tower
(550°C)
Heat Transfer Fluid Temperature Range
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Single Tank Thermocline
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
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Other Energy Storage
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
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Current & Future for Parabolic Trough
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
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Parabolic Trough ‐ Plant Size & Cost
‐ 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)
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Compact Linear Fresnel Reflector (CLFR)
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
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Dish/Engine
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
Power
Most efficient solar technology
Conditioning
Unit (PCU)
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Power Tower
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)
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Land Requirement
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
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