14 solar energy - today at minesinside.mines.edu/~jjechura/energytech/14_solar_energy.pdf ·...

John Jechura – jjechura@mines.eduUpdated: January 4, 2015

Solar EnergyCourtesy: Pam Spath, URS

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