www.ecn.nlwww.ecn.nl 1

Confidential

Desert Proof ModulesWilma Eerenstein

Morocco, Rabat16 November 2015

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Contents• Potential of PV in Morocco• Challenges for PV• Solutions (incl expertise ECN and Dutch Chemical Companies)

– Bifacial, vertical– Application of coatings– Testing on inverters, effect on lifetime and annual yield

• Requirements – Test facilities to test beyond IEC for materials, components and coatings– Outdoor test facilities

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IRENA forecast 2013 MENA renewable• Solar in MENA 2030: 60 GW• MENA solar market worth $50bn by 2020• Plans for PV in Marocco 2020: 2 GW

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Potential of PV in Morocco• Land Area: 446.550 km²

– 1/3 suitable : 148.850 km2

– 10% covered with PV plants– no competition with agriculture

– For PV: 14.885 km2

• Solar Power: 2233 GW• Solar Annual Electricity production with PV

– 4 1012 kWh– 14.700 PJ

• Moroccan electricity consumption (2013): 115 PJ• With 1/30 of land use: 127 x more electricity can be produced than currently

used• 0.8% of land use needed to cover current electricity demand

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Challenges for PV1: Higher operating temperatures

– Reduced PV efficiency (typically -0.45%/°C for mc-Si )– More stress on components in module (Encapsulants, backsheets etc.), reduced lifetime– More stress on BOS components

2: Higher UV exposure– More stress on components in module (Encapsulants, backsheets etc.), reduced lifetime– More stress on BOS components

3: Dust– Lower electricity production– Higher maintenance costs– Possible damage to modules / or coatings– Damage to BOS components

• Lower yield + reduced lifetime and higher maintenance costs Higher LCOE, lower ROI

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Challenges for Desert PV• Reversible:

– Temperature effects follow ambient temperature: temperature coefficient– PV components are soiled and cleaned: O&M strategies

• Non-reversible– Abrasion of coating and glass cover by sand/pebbles in sand storms or cleaning cycle

– Less light capture: performance degradation– UV radiation causes degradation of plastic encapsulant of element

– Lifetime decreases as well as minor performance degradation– High temperature causes degradation of plastic encapsulant of element

Power output:- Can operating temperature of modules stay low at high ambient T?- Does sytem need to be cleaned and how often?System lifetime:- Does system degrade faster than expected?

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Ambient temperature averages

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1: higher operating temperatures – reduced output

10 higher operating temperature, 4.5% less output

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• Thermo-mechanical properties depend on temperature– Change in elastic properties of encapsulant and

backsheet• Can lead to cell movement and

delamination– Particularly with temperature cycles (day-night)

1: higher operating temperatures – stress

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• Inverter Derating: automatic lowering of power when inverter becomes too hot - internal protection– Reduced power output. Presence of dust can block cooling fans on inverters

• Inverter lifetime: condensor sensitive to high temperatures

1: higher operating temperatures – BOS components

PV inverter station

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2: UV exposure• Chemical reaction in encapsulant or backsheet

– Yellowing less light, lower power– Brittleness of materials delamination or moisture ingress (corrosion)

• BOS Components: cables also sensitive to UV light and sand blasting

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3: Dust or Soiling of PV panels

• Many different kinds of sand and dust• Different other conditions such as humidity level and presence of salt/ammonia

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Dust and cementation

• A PV oriented standard concerning impact of dust on power output is lacking (focus only on electronic parts in general)

• To make things worse: humidity levels can be high at night time causing condensation and dew formation: “cementation”, mud cake

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3: Effect of soiling on power output• Depends on location, type of dust and installation angle• Establish for each location before design of plant

• KSA, KAUST (Jeddah location): 8-15% per month• Amman, Jordan: 0.3% per day (40% in 140 days)• Madar, Abu Dhabi: 25% per months

• 10-20% annual loss, for 500 MW power plant• = 5.5-11 Mdollar loss (at 6 ct/kWh)

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Solutions• Improving product lifetime and yield, at low maintenance costs

1. Reduction/prevention of dust:– Dry and wet cleaning– Anti-soiling coatings

2. Bifacial, vertical: reducing dust accumilation, improving yield 3. Improving module lifetime: materials for high UV exposure and higher operating temperatures4. Reducing operating temperatures

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1. Reduction/prevention of dust• Wet cleaning

– Adapted from window cleaning methods, these are often manual, using long (extendable) poles.

– Brushes – manual systems, and robotic systems• Dry cleaning

– Robotic systems with brushes– Electrostatic cleaning

• Prevention – anti-soiling coatings– Hydrophobic– Protection against sand damage– Preventing dust build up

– Prove: coating performance and reliability

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1. Anti-soiling coatings• Several commercial coatings on offer

– E.g. Azur, 3M, c-voltaic, …..• In Netherlands: products from DSM, Vindico

– Reduce cleaning cycles and/or lower the speed of soiling– Maximize module output combining

– anti-reflective properties with anti-soiling– Durability matching module lifetime– Coating able to withstand cleaning methods

• Claims: Prevent dust build up, no transmission loss in visible, passed abrasion testing and outdoor testing

• Independent verification required, ECN has set up test protocol

1. Assessment of anti-soiling coatings at ECN

• Fast method for artificial (accelerated) soiling/cementation developed

• Performance study of anti-soiling coatings from several suppliers

• Durability: abrasion resistance test

• Pass criteria based on standard (EN 1096-2)

References

Travis Sarver, Ali Al-Qaraghuli, Lawrence L. Kazmerski, Renewable and Sustainable Energy Reviews Volume 22, June 2013, Pages 698–733

Thomas Weber et al., Proceedings 29th European Photovoltaic Solar Energy Conference and Exhibition (2014), Page 2499

1. Assessment of AS coatings: approach and results

•Local abrasion of glass sample with anti-soiling coating

•Artificial soiling (white) within and outside the abrasion zone

•Removal of soiling by pulling off using adhesive tape

•Visual inspection

Good AS properties after abrasion AS properties destroyed

1. Assessment of anti-soiling coatings

• Fast method for laboratory evaluation of AS coatings

• Abrasion resistance - vary substantially (by factor >20)

• High and low performing AS coatings distinghuished

• also the initial AS performance varies significantly

• Passing standard EN 1096-2 : sufficient for desert applications?

• Validation by field testing of coatings is important

• Ranking of 3 different AS coatings: effectiveness and abrasion resistance• Pass criteria EN 1096-2 standard (500 strokes). Large variety!

2: bifacial modules

glassglass

opaque back sheet transparent panel

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2. Bifacial module: installing options

Change Albedo- Concrete- White reflective surface

2. Bifacial vs monofacial module

• Concrete floor: 5% higher output for bifacial

• White background: 20% higher output for bifacial

• All trends are linear with irradiance

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Bifacial n-Pasha module: 20% extra power output

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2. Bifacial: vertical• In MENA: Vertical installation: lower output due to angle of incidence• But: with high reflection (albedo), increased output possible

• Bifacial, vertical can result in higher yield, expected to reduce soiling efffects• ECN can execute calculation for Morocco, incl soiling effects

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3. Improving lifetime• Weakest components PV module: backsheet, encapsulant

– Glass glass modules– Improved lifetime by a factor of 2?– Reduces LCOE

– UV stable encapsulant

• BOS - Cables: protection, Inverter: lifetime ventilators and condensors

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4. Reducing operating temperatures• Modules can get rid of heat by 3 mechanisms• Radiation

– Dominant mechanism– But difficult to increase

• Convection– Active cooling

• Conductive heat loss– With heat transfer material behind module?– Eg Phase Change Materials. Effect and lifetime still unclear

• Conclusion: not very likely to be economic. Only when combined with heat storage solutions

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Requirements: Testing• IEC – to gain insight into effect of environmental influences on module

lifetime– Certification bodies

• Beyond IEC– IEC: one size fits all– Not so suitable for MENA– No tests for coatings

• Outdoor and field performance– Proof of the pudding– Including effects of rain, soiling

Irradiance: sun, sky

Temperature:heat, frost,night-day

cycles Mechanical stress:wind-,snow load

hail impacts

Humidity

Moisture:rain, dew, frost

Atmosphere:Salt mist, dust,sand, pollution

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Beyond IEC

• IEC designed for relatively moderate conditions• Need:

– Tests for soiling– Sand abrasion test– Higher UV dose– PID testing– Higher irradiance (now only 1000 W/m2)– Other temperaure ranges (now -45-85C)

– Better understanding of results stress-test and actual field performance

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Field Testing• Very important to test annual performance in real life conditions

– Relation accelerated stress test and field performance– Actual electricity production– Confirm annual electricity calculation

• Preferably at several locations– Near coast: influence salt– Mountains: higher UV, higher temperature differences– Dry, dusty region: influence dust and higher average temperatues

Test site IRESEN

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Conclusions• Morocco has significant potential for solar PV• Challenges with PV in desert like regions

– Dust– Lifetime– Higher operating temperatures

• Solutions– PV materials suitable for desert – high UV, sand storm, temperature– Vertial, Bifacial– Anti-soiling strategies

• Field test and accelerated stress testing required