Solar Electric Power Systems

1. Solar Electric Power Systems ELEG 620 Electrical and Computer Engineering University of Delaware February 25, 2010 ELEG 620 Solar Electric Power Systems February 25, 2010

2. ELEG 620 Outcomes • Understanding the nature of Solar Radiation • 2. Design of a solar cell from first principles • 3. Design of a top contact system • 4. Design, construction and test of a solar power system ELEG 620 Solar Electric Power Systems February 25, 2010

3. ELEG 620 Solar Electric Power Systems February 25, 2010

4. ELEG 620 Outcomes • Understanding the nature of Solar Radiation • 2. Design of a solar cell from first principles • 3. Design of a top contact system • 4. Design, construction and test of a solar power system ELEG 620 Solar Electric Power Systems February 25, 2010

5. Solar Cell Design Silicon Solar Cell Design Homework Due: March 9, 2010 Design a silicon solar cell. Calculate the following: Light generated current at short circuit Open circuit voltage Maximum power (show voltage and current at maximum power) Efficiency Thickness and doping of each layer Show key equations ELEG 620 Solar Electric Power Systems February 25, 2010

6. Solar Cell Design • Silicon Solar Cell Design Homework Due: March 9, 2010 • Design a silicon solar cell. • Following assumptions can be used • Structure is N on P • There is no surface recombination • There is no surface reflection • Series resistance = 0 ohms • Shunt resistance is infinite (shunt conductance = 0) • Sunlight = AM 1.5 global ELEG 620 Solar Electric Power Systems February 25, 2010

7. I-V Curve of a Well Behaved Solar Cell I + ILight 60 Current (mA) IDiode V 40 20 _ Voc -1 -0.5 0.5 1 Voltage(V) -20 -40 Isc -60 (Vmp,Imp) I-V curve of a well behaved solar cell ELEG 620 Solar Electric Power Systems February 25, 2010

8. Solar Cell Operation • Key aim is to generate power by: • (1) Generating a large short circuit current, Isc • (2) Generate a large open-circuit voltage, Voc • (3) Minimise parasitic power loss mechanisms (particularly series and shunt resistance). ELEG 620 Solar Electric Power Systems February 25, 2010

9. Design rules for high performance • For a high solar cell efficiency, simultaneously need high absorption, collection, open circuit voltage and fill factor. • Absorption and collection are typically achievable by “clever” engineering & innovation. • Voltage is controlled by worst, localized region, NOT the same region which absorbs the light – this is fundamentally why single crystal solar cells are highest efficiency. • Predictive models and design rules for all characteristics are necessary for the device parameters. ELEG 620 Solar Electric Power Systems February 25, 2010

10. I Front contact Emitter Voc Pmax Base 0 V Back contact Isc Structure, Equivalent circuit and IV curve of solar cell + Ilight V I-V Characteristic of Solar Cell Equivalent circuit of solar cell ELEG 620 Solar Electric Power Systems February 25, 2010

11. Theoretical Analysis of Solar Cell ELEG 620 Solar Electric Power Systems February 25, 2010

12. The maximum theoretical limit of single junction solar cell depends on the incident spectrum. It is 29.2% for AM1.5G Spectrum Irradiance AM1.5G Single junction solar cell efficiency for AM1.5G ELEG 620 Solar Electric Power Systems February 25, 2010

13. Single junction solar cell Voc for AM1.5G Single junction solar cell Jsc for AM1.5G At one sun ELEG 620 Solar Electric Power Systems February 25, 2010

14. Maximizing efficiency h = Isc Voc FF Pin •  Isc • EG •  Reflection • Surface • Metal •  Ln, Lp •  Sr • xj optimum •  Voc • EG •  doping •  Ln, Lp •  Sr •  FF • Series R • Metal • Emitter •  doping • Thick emitter Doping and diffusion length are related ELEG 620 Solar Electric Power Systems February 25, 2010