Terawatt Challenge

Terawatt Challenge

• Terawatt Challenge

• What is it?
• Photovoltaics for the TW challenges
• Importance of rapid growth
• Recent milestones in PV
• But what about …..
• Myths of photovoltaics: land area; efficiency; energy payback time; materials availability; time to impact; duck curves, etc

• Future prospects

• Education

Terawatt Challenge: Encapsulates the dichotomy surrounding energy– essential for improved quality of life, but also tied among the most serious global challenges.

• Terawatt Challenge: Encapsulates the dichotomy surrounding energy– essential for improved quality of life, but also tied among the most serious global challenges.

Why is compound annual growth rate important?

• Why is compound annual growth rate important?

In the nearly two decades since the TW challenge paper, renewables have reached multiple milestones

• In the nearly two decades since the TW challenge paper, renewables have reached multiple milestones

• In US, renewable compound annual growth rate 4.8% from 2000-2012 (NREL data)

Germany, Spain, Italy have yearly installed PV capacity > yearly increase in electricity demand.

• Germany, Spain, Italy have yearly installed PV capacity > yearly increase in electricity demand.

• In Germany, PV is 50% of summer peak electricity demand

PV learning curves show compound annual growth rate (CAGR) of ~30% over the last several decades

• PV learning curves show compound annual growth rate (CAGR) of ~30% over the last several decades

• Extending the growth rates shows ability of PV (renewables more generally if these are included) to make a substantial impact on electricity generations

ASU – reached 50% of total electricity supplied by PV

• ASU – reached 50% of total electricity supplied by PV

Energy payback time

• Energy payback time

• Land use

• Cost

• What do you do at night for power?

• Materials availability

• For silicon, limitation is silver in grids, which cause a limitation at 2 TW
• Availability subject to efficiency, thickness

Power after sun goes down a concern for utilities.

• Power after sun goes down a concern for utilities.

• Can mitigate by load management.

Optical configuration of photovoltaic systems: One-sun or flat plate; concentrating systems; tracking

• Optical configuration of photovoltaic systems: One-sun or flat plate; concentrating systems; tracking

Concentration or stacking multiple solar cells increases efficiency

• Concentration or stacking multiple solar cells increases efficiency

• To reach >50% efficiency, need ideal bandgap 6-stack tandem, (assuming ~75% of detailed balance limit).

• Hard to get compatible materials with the right bandgaps.

Approaches to high efficiency:

• Approaches to high efficiency:

• Concentrate sunlight. “One sun” = 1kW/m2, max concentration ~46,000.
• No entropy penalty for concentrating sunlight, but etendue limits to acceptance angle and concentration.
• Optically split solar spectrum (i.e. tandem)
• No entropy penalty
• Efficiency controlled by existence of materials
• Beneficially circumvent one of the assumptions in thermodynamics

Key issue for III-Vs: need precisely controlled band gaps which are lattice matched

• Key issue for III-Vs: need precisely controlled band gaps which are lattice matched

• “Missing” low band gap material

• Approaches:

• Lattice matched; Ge-GaAs-GaInP
• Metamorphic;Ge-GaInAs-GaInP
• Metamorphic; GaInAs-GaAs-GaInP

• Band gaps for 4-tandem are poorly lattice matched;5 band gaps and six band-gaps are better matched

• Metamorphic solar cell reached 40.7% at ~200X.

Carrier-selective contacts enable ideal VOC

• Carrier-selective contacts enable ideal VOC

Demonstrated 746 mV on 50 µm wafers

• Demonstrated 746 mV on 50 µm wafers

InAs QDs achieved on GaAsSb material

• InAs QDs achieved on GaAsSb material

• Increasing Sb composition decreases QD size and increases QD density

Monolithic III-V tandem solar cells; Series connected; three junctions

• Monolithic III-V tandem solar cells; Series connected; three junctions

• High efficiency used in high concentration, two-axis tracking systems

• High concentration means small area (and lower cost) needed for solar cells

• Trade balance of systems and solar cell cost.

Ideal solar cell consists of a light-trapped, thin solar cell

• Ideal solar cell consists of a light-trapped, thin solar cell

• Nanostructured surfaces allow light trapping and advanced concepts (e.g., multiple exciton devices)

Silicon pilot line capabilities for interaction among students, industry and researchers

• Silicon pilot line capabilities for interaction among students, industry and researchers

• 10 Fulton Undergraduate Research Initiative Projects

• 2 honors thesis

• 4 capstone projects

• Questions?