Photovoltaic SystemsPhotovoltaic SystemsCameron JohnstoneCameron Johnstone

Department of Mechanical EngineeringDepartment of Mechanical Engineering

Room M6:12Room M6:12

cameron@esru.strath.ac.uk

Direct conversion of solar radiation into electricity.Semi-conducting material Silicon - Mono crystalline

$800/m2 or $5.5/ Wp

- Poly crystalline $650/m2 or $5.4/ Wp

- Amorphous (thin film) $450/m2 or $7.5/ Wp

Output/cm2 - Voc = 0.6 V- Isc = 20 - 30 mA

Photovoltaics: IntroductionPhotovoltaics: Introduction

Silicon responsive to: 0.3Silicon responsive to: 0.3m < m < < 1.1 < 1.1mm

Absorb 80% solar flux but respond to 55% of Absorb 80% solar flux but respond to 55% of the spectral intensitythe spectral intensity

Photovoltaics: Spectral responsePhotovoltaics: Spectral response

Photovoltaics: Performance enhancement Photovoltaics: Performance enhancement

Prevent recombination (Barrier creation)

Performance enhancementDoping 1 part per 1000000

Phosphorus -> N type SiBoron -> P type Si

Maximise photon absorptionAnti reflective coatingsGrooving of Si

Photovoltaics: Performance quantificationPhotovoltaics: Performance quantificationPerformance characterisation at Standard Test Conditions (STC)

G = 1000 W/m2 Tcell = 25°CRecord:

Isc Voc Imax & Vmax

Maximum Power (Pmax)

Pmax = Imax * Vmax

 Fill Factor (FF)

FF = Imax * Vmax

Isc * Voc

(for C-Si 0.75 – 0.85)

Photovoltaics: Effects of temperaturePhotovoltaics: Effects of temperature

Effects of TemperatureVoc 1/T  Isc T

Voc = Voc(Tref) [ 1 - v(T - Tref) ] 

Isc = A[Isc(Tref) + c(T - Tref) ]where:

v = Voc temperature coefficient (V/C)

A = constant independent of temperature c = Isc temperature coefficient (A/C) VVmaxmax

Photovoltaics: Effects of temperaturePhotovoltaics: Effects of temperature

Effects of TemperaturePout 1/T

  Pmax = Pmax(Tref) [ 1 - Pp(T - Tref) ]

where:Pp = Pmax temperature coefficient (%/C)

(for C-Si 0.3 – 0.45)

Impact of IrradianceI G

(doubling irradiance (G) doubles Imax)

Small ΔV

Large Δ

I

Photovoltaics: Maximum power point Photovoltaics: Maximum power point trackingtracking

Maximises Efficiency of power delivery from PV: - Provide load control optimisation by tracking Vmax for variations in G and T- Load resistance varied via DC-DC converter

(maintains output voltage but limit supply current)- Integrated within inverter systems- Unit costs from £400

ΔΔVV

Photovoltaics: Grid integrationPhotovoltaics: Grid integration

Converts PV output to grid voltage (DC-AC inverter)- Sinusoidal Inverter (12V, 24V or 48V DC to 240V AC/ 415V 3)- Self synchronising (50Hz UK - 60Hz USA)- Enables Islanded operation- Costs from £1200 (approx)

Issues- Power Quality- Harmonics (transistor switching)- DC injections from frequency synchronisation (heat dissipation at substation)- Must isolate in the event of loss of network

(safety) - Potential for poor part load efficiency performance

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Photovoltaics: Building integrated Photovoltaics: Building integrated Hybrid Photovoltaics (PV-Hybrid)

Utilises both thermal and electrical powerTreated as a flat plate collector with the following format:

i) Power entering the system GA

 ii) Electricity generated by the pv component

GAE

 iii) Power lost from component

UA(Tc-Ta) 

PPmaxmax/ GA/ GA

Photovoltaics: Photovoltaics: Hybrid Photovoltaics

  iv) Thermal power supplied to systemQh = [GA - GAE] - UA(Tc-Ta)

= [GA ( - - ESTC(1 - Pp(Tc - Tref)))] - UA(Tc-Ta)

Typical heat to power ratios of hybrid systems up to 4:1

Typical system efficiencies up to 75%

Photovoltaics: Photovoltaics: Hybrid Photovoltaics

Passive cooling applications

South

Hybrid PV

North

Research based: addressing control and power transfer issues via demonstration

Photovoltaics: Photovoltaics: Solar cars