Irradiance. Solar Fundamentals Solar power investment decision making

Irradiance

Chilean Solar Resource Assessment Antofagasta and Santiago

December 2010

Edward C. Kern, Jr., Ph.D.

Irradiance, Inc.

Solar Fundamentals

Solar power investment decision making

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Global Solar Radiation

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Solar Power is Changing Rapidly

• Technology, markets, investments, players

• Regulations and Incentives

• Public awareness, pro-activism and potential backlash

• Climate stabilization policies

• Environment protection policies

• Economic development policies

• Energy security policies

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Solar Power Technologies

• Concentrating Solar Power (CSP)

• Flat Plate Photovoltaic (PV)

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Concentrating Solar Power Technologies

Parabolic Trough Power Tower

Dish Sterling Engine Concentrating PV

Linear Fresnel

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Andasol CSP Plants

Guadix, Andalucia

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Andasol CSP

Steam Power Blocks

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Andasol CSP

Linear Parabolic Line Focusing

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Crystalline Silicon (c-Si)

Preferred for rooftop applications

Thin Film (a-Si, Cd-Te, CIGS)

Favored in utility scale applications

Solar Photovoltaic Technologies

Common focus to drive down cost per watt installed

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Crystalline and Thin Film PV Manufacturing

Crystalline PV Module (Evergreen Solar)

Thin Film PV Module

(Moser Baer)

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Rapid Global Growth of Solar PV as Grid-Tied Solar Scales (Historical and Forecast)

• Solar PV is now the fastest growing (in % terms!) power

generation technology

with a 70% increase in

2008 to reach 13 GW

installed

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PV Materials, Cells and Modules

• Crystalline silicon solar cells

 Most widespread use, most field experience

 Preferred for rooftop and remote power (higher efficiency)

 Single and multi-crystalline manufacturing processes

 Mature with limited potential for cost reduction

• Thin-film solar modules

 Silicon and other semiconductor materials

 Preferred for large grid solar power; lower cost, lower efficiency

 More potential for significant cost reduction

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20 MW PV Plant near Valencia

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PV Plants can look like lakes

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PV Design Process

• Terminology used with PV technology and systems development

• Solar energy resources

• Relationships between efficiency and required land/roof area

• Prices for the glass, copper, concrete are needed

• Physics underlying power generation (yield) calculations

• Infrastructure requirements, site constraints and environmental influences (pro and con)

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PV Project Development Stages

Develop Simple Cost/ROI Model

Define system size, location

and solar resources

Estimate land, labor and operation costs Develop design

concept and a performance

model Exercise the cost model to

check investment

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Solar PV Power Plant Operations

• Things that can go badly wrong (rare)

 Power conversion equipment failure

 High temperature failures in electrical junctions/wiring

 High wind-, snow- or ice-caused failures in PV panels or structures

 Electrical fires in modules and wiring (very rare)

• Things that can go a little wrong (common)

 Dirt, dust and pollen soiling, snow and ice shading

 Miscalculated solar energy resources

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Losses in Efficiency

• Depends on PV material type

• Temperature rise reduces output; passive cooling is good

• Spectral impacts

• Shading losses

• Wiring (copper) I²R losses

• Maximum power point tracking losses

• Transformer losses

• Soiling losses (cleaning impacts)

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Terminology

• Peak Watts (rated Watts)

 Power produced in nominal full sunlight of 1000 W/m^2 irradiance with cells operating at 25 C

• Efficiency

 Ratio of input to output; modules: irradiance to dc power (5-20%);

inverters dc to ac power (90-98%)

• Temperature

 Thermal coefficients for thin-films

 Spectral and diffuse light response differs between technologies

• Product differentiation/marketing spin (beware)

 Know how percentage differences translate into absolute performance differences

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Solar Resources

• Irradiance and insolation (power and energy units)

• Beam, diffuse, total and “Plane of Array” irradiances

 Point focus and line focus concentrators

 Flat panel fixed and tracking

• Array peak Watts (PV dc or thermal collector field)

• System rated Watts (PV ac inverter or thermal turbines)

• Fixed, one and two axis tracking yield differences from flat panel systems (approximately ~20% and ~40% more solar radiation enters the collectors; but at increased cost and greater land area requirements)

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Solar Energy (Above Atmosphere)

• Above the atmosphere about 1.4 kW/m

facing the sun (33.6 kWh/m

in 24 hours)

• Earth’s rotation cosine/nighttime losses reduce to 7.6 hours equivalent

 Total is about 10.7 kWh/m² per day parallel to the earth’s surface

• Absorption, reflection and scattering by the

atmosphere; typically 4 to 6 kWh/m

on earth’s

surface (Atacama is NOT typical, range 6 to 8

kWh/m

?)

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Atmospheric Scattering/Absorption

• Without an atmosphere (e.g. moon) there is just direct (sunlight) irradiance

• On earth scattering creates diffuse (skylight) irradiance

• Typical clear day, bright day:

 800-900 W/m² direct

 200-100 W/m²diffuse

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Practical Solar Insolation

• Direct normal and diffuse irradiance

• Total irradiance nominally 1 kW/m

 800 to 1000 W/m

for direct (beam)

 200 to 100 W/m

from diffuse

• “Hours” of Sunlight

 Effective hours at the nominal 1 kW

 Typically 4 to 6 hours per day annual average, perhaps to 8 in high deserts (Atacama)

 Average, about 5 kWh/m

per day

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Shadowband Radiometer Testing

Colleagues at Plataforma Solar Almeria

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Resource Assessment at University of Jaen

Studying the accuracy of day ahead resource predictions

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Minute to Minute and Hourly Irradiance

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Daily Variations

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Basic Power Yield Modeling

• Really Simple

Spreadsheet model

• PV Watts model from NREL (USA)

• RetScreen model from Natural Resources

Canada

• PVSYST model from Univ. of Geneva

Sunlight PowerDC

Grid AC Power

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NREL’s “PV Watts” Calculator

Component Derate Factors PVWATTS Range Safe PV module nameplate DC rating 0.950 0.80 - 1.05 0.980 Inverter and Transformer 0.920 0.88 - 0.96 0.920

Mismatch 0.980 0.97 - 0.995 0.980

Diodes and connections 0.995 0.99 - 0.997 0.995

DC wiring 0.980 0.97 - 0.99 0.980

AC wiring 0.990 0.98 - 0.993 0.990

Soiling 0.950 0.30 - 0.995 0.950

System availabilty 0.980 0.00 - 0.995 0.990

Shading 1.000 0.00 - 1.00 1.000

Sun-tracking 1.000 0.95 - 1.00 1.000

Age 1.000 0.70 - 1.00 1.000

Overall DC-to-AC Derate Factor 0.770 0.802

http://rredc.nrel.gov/solar/calculators/PVWATTS/

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Project Economics

Negatives Positives

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Simple PV System Cost Model

Design and Construction $/Watt(DC)

PV module unit price $ 2.75

Array structure and wiring $ 0.20

Power inverters $ 0.20

Plant planning costs, fees, permits $ 0.15

System construction $ 0.20

Total Capital Cost $/Watt (DC) $ 3.50

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PV System Performance Model

Finance and Operation

Cost of money (%/yr) 5%

Annual O&M (% of capital cost) 0.5%

Plant module DC to inverter AC efficiency 80%

Generation capacity factor 20.0%

Annual production (kWh/W) 1.40

Annual plant cost ($/Watt DC) $0.28

Average kWh cost ($/kWh) $0.20

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Good Practice

• Avoid novel technology, be conservative



Use proven solar and inverter technology



Stress importance of long-term goals

• Initial projects lay foundations for future



Track and report metrics for multiple stakeholders



Include outreach to policymakers and power

sector

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Summary

Solar Resource

•Solar Resource

•Air temperature

PV Technology

•Modules, inverters and balance of systems

•Maintenance

Production Economics

•Predictable maximum power generation by hour

•Forecasted losses from clouds

•Generation value by hour, day, and season

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Uncertainties: 2010-2011

• Will financial incentives continue with sovereign debt increasing?

• Will progress toward “grid-parity” continue and maintain public support?

• Will new, lower-cost technologies make today’s systems obsolete and/or will prices drop so fast that buyers wait?

• Can more accurate site-specific yield projections increase investment return (ROI) certainty?

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Contact Details

36

Edward Kern Irradiance, Inc.

eckern@irradiance.com