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
