Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Photovoltaics in the UK Climatic Influence on Performance Dr. Christian N. Jardine Environmental Change Institute University of Oxford

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Overview PV technologies Influences on performance The PV-Compare project System level effects Conclusions

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Energy of Sunlight Average power of 102,000 TW strikes earth 10,000 times global power demand In the UK, kWh/m 2 per year Average household kWh per year for lights and appliances More energy during long summer days Even on a cloudy day we receive 1/3 the energy of a clear day

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine What are Photovoltaics? Photovoltaics are made out of materials called semiconductors Photovoltaics can absorb the energy of light to generate electric current Most commonly made from silicon Silicon is the second most abundant element in the earth’s crust Supplies of silicon are truly sustainable CdTe and CuInSe 2 also available Other novel semiconductors being developed (dye-sensitised cells, organic semiconductors)

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Why Photovoltaics? Available resource much larger than other renewables No climate altering CO 2 emissions No NO x, SO x, mercury or dioxin emissions during operating lifetime No moving parts - Silent & maintenance free Lifetime > 25 years Suitable for use within an urban environment Modular technology; can be sized to suit needs Secure supply of energy; distributed generation Avoids reliance on fuel imports Added ‘green image’

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Monocrystalline Silicon A single crystal is grown from a melt The crystal is sawn into wafers Contacts are added Black or blue with rounded corners High efficiency cells (ca. 15%) are produced Efficiency = Electrical energy out / Solar energy in

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Multi-crystalline Silicon Multi-crystalline silicon is cast from a melt, then sawn into wafers It can also be drawn from the melt as sheets Not as efficient as mono-crystalline silicon (8-12%) Very attractive product

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Amorphous Silicon No long range crystal structure; low efficiency (4-6%) Very low material input (1/1000 mm thick) Low production temperatures Highly suited for mass production Range of substrates (plastic,glass) Semi-transparent or flexible modules available

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine CdTe and CIS Other semiconductors can be deposited as thin films Suited for mass production Higher efficiencies than amorphous silicon (CdTe 7%, CIS 9%) But worries about toxicity of cadmium Supplies of indium are limited. A renewable energy source that is unsustainable!!

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine I-V Curves Voltage and current variable Inverter finds maximum power point (MPP) Voltage Current BatteryPV MPP

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Influence of Insolation No of incoming photons affects current produced Voltage Current 1000 Wm Wm -2

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Influence of temperature Voltage decreases with increasing temperature Voltage Current 25 ºC 30 ºC

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Influence of spectral effects Different technologies absorb different colour photons Colour of sunlight varies with solar elevation (Rayleigh Scattering) Direct component – red, diffuse – blue Cloudy conditions = more blue

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Summary of Response Mono crystalline Multi Crystalline Amorphou s CIS EfficiencyHighMediumLowMedium Temperat ure coefficient Large -ve Small -veLarge -ve Spectral response Green-IR uv-reduv -IR

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Influences on System Performance Insolation Temperature Spectral effects Inverter tracking (finding and holding the MPP) Inverter efficiency Wiring losses Shading Component failures

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Correlation of effects DullBright ColdHot Red (clear) Blue (high elevation) or blue (cloudy)

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Peak Power Each module designated with rated peak power (kWp) Power produced under light of 1000 Wm -2 intensity, AM 1.5 spectrum, at 25 ºC Peak power is not produced at all times. Customers purchase on the basis of kWp

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine The PV-Compare Project Lab standard conditions (1000 Wm -2, AM1.5, 25 ºC) not related to the real world We are interested in energy produced Different technologies respond differently to environmental factors Insolation, temperature, spectral effects Performance will be location dependant

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine The PV-Compare Project Two identical arrays of 11 products established in Mallorca, Spain and Oxfordshire, UK Covers range of technologies Total array size 6.2 kWp. 0.3% of UK Solar capacity in 1999!

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Monitoring Power measured every 1/2 hour by DC to AC inverters Insolation, ambient temperature, module temperatures also recorded Elevation, AM number & cloudiness are derived 32 channels every 1/2 hour for 2 years at two sites

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Daily Profiles ClearIntermittent Cloudy

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Mallorca vs. Oxford Mallorca produces 8050 kWh per year Oxford produces 4880 kWh per year Oxford array is more efficient (5 ºC cooler in UK) UK can outperform Mallorca on a daily basis

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Seasonal efficiency

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Available fraction for amorphous Si

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Power vs Insolation

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Efficiency vs. insolation

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Two types of low light level Clear = red Cloudy = blue

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Influence of cloud cover Cloudy Clear

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Energy Production Wide range of energies per peak power Best modules give 50% more energy than worst - important consumer issue Amorphous Si & CIS perform better than crystalline Si & CdTe. Good response to overcast lighting.

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Mallorca Performance Amorphous better because of high temperature performance Bright light also bluer

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Oxford Performance Amorphous and CIS better in UK due to blue light response CIS also like cold

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine System level effects West Oxfordshire District Council Offices, Witney

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Inverter tracking

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Inverter sizing

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Conclusions of PV-Compare UK climate suitable for PV production UK produces 60% electricity of Mallorca Wide range of kWh/kWp values Insolation, temperature and spectral effects all important Performance under cloudy conditions is critical in the UK Performance under high temperatures is most important in Mallorca. Demonstrated potential of PV in the UK

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Modules Modules can be simply roof mounted

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Innovative Solar Architecture Increased use of Building-integrated Photovoltaics (BIPV) Use of PV materials as the building fabric Performs the function of conventional building materials (waterproofing, insulation, soundproofing) But generates clean, green energy Cost of conventional material can be offset Cheaper than prestige cladding materials

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Architectural Possibilities Roofs Facades Louvres Glazed-sunspaces Etc.

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Solar Roof Tiles Simple to install Can be installed by a conventional roofer

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Glass-glass Laminates Semi-transparent PV laminates Very attractive architectural material

Royal Statistical Society12th June 2007 Dr. Christian N. Jardine Standing Seams Quick, easy method of installing large areas of PV