THE PHOTOVOLTAIC TECHNOLOGY Ing. S. Castello castello@casaccia.enea.it

1. THE PHOTOVOLTAIC TECHNOLOGY Ing. S. Castello castello@casaccia.enea.it ENEA, Renewable Sources Sector July 2006

2. PV plants features Applications Stand alone plants Grid connected systems and Distributed generation Demonstrative projects Tracking and concentrating systems Market PV industry Plant and kWh costs Diffusion programmes SUMMARY

3. PV TECHNOLOGY • The technology is relatively recent: • Foundation was laid in the early 50’: first modern c-Si cell discovery (Bell Telephone Laboratories) • 1958: first application successful used in space (Vanguard I) • late 70’: starting of terrestrial application and development of market. • From then on the technology has shown a steady progress, the costs have recorded a constant reduction but remain still high in comparison to the other renewable sources

4. Use of an inexhaustible and free fuel Environmentally friendly Good reliability, higher than wind turbines or diesel lasts more than 30 years low maintenance cost Fully automated operation Low risk capital intensive but low O&M costs Modularity the required power is obtained using a number of the same building blocks Exploitation of not utilized surfaces capability PV can be mounted on roofs, integrated in building skin or installed in marginal areas (deserts) PV ENERGY ADVANTAGES

5. Systems able to collect and convert light into useful electricity to be delivered to specific appliances or into the electric grid 2 main categories Stand-alone: to supply isolated users (from consumer to decentralized rural electrification) Grid-connected: to fed power to the electric grid (from small roofs to power stations) plant components PV array and power conditioning unit (PCU) or modules and balance of system (BOS) THE PV PLANTS

6. PV array (Pnom, Vw) A number of PV modules Cables and protection devices Structure (to support and to expose the module for maximum light capture) PCU Stand-alone plants Matches the array output to the load requirements Manages the storage system Grid-connected plants Convert the dc array output to standard ac power Fit the PV array output to the grid (MPPT) Control the quality of the energy supplied to the grid (distortion and power factor correction) THE COMPONENTS

7. PV modules The smallest electrical unit of PV plants, formed with solar cells assembled in series/parallel configuration encapsulated Mechanical and corrosive protection of cells and their interconnection (long operation life) Electrical isolation of the voltages generated material used for encapsulation: glass tempered glass or plastic frame: metal or plastic features required ultraviolet stability tolerance to temperature and heat dissipation ability self cleaning ability THE COMPONENTS

8. BOS Cabling Switching and protection devices Battery Charge controller Dc/ac inverter Module supporting structures Engineering Labour to install a turn-key system THE COMPONENTS

9. When well suited: Remote site far from the grid Maintenance and fuel expensive (transport) Reliability is paramount (tlc, signaling) Simplicity required (remote houses, schools) Transportability (navigation laps, laptop computers) Intermittent power acceptable (fans, pumps) Noise and pollution-sensitive environments (parks) Reducing fuel consumption (small grids) STAND ALONE PLANTS

10. Already competitive with diesel generator for load lower than few kWh/day Preferred option for high value applications Key technology for off-grid application, but further decrease of cost is essential to facilitate their use Costs higher then grid connected systems (batteries) but already with its own nicks market Applications: Domestic Industrial Electrification in Developing Countries STAND ALONE PLANTS

11. Remote users (economic alternative to utility grid at distance > 1 – 2 km) Rural electrification (0,5 – 1,5 kW). light, refrigeration and other low power loads Lighting of isolated areas with PV lamps (100 W) or centralized systems (1-10kW) Consumer Watches, calculators (mW), lamps (10 W) DOMESTIC APPLICATIONS

12. First terrestrial high value applications (PV costs negligible in comparison to the service provided) Competitive with other small generating systems Telecommunication 0,5 – 10 kW Cathodic protection 0,5 – 5 kW Signaling and data acquisition 0,1 – 1 kW Park-meter or Emergency telephones (highway) 10 – 20 W INDUSTRIAL APPLICATIONS

13. 1.7 billion people is aimed to: Basic needs: refrigeration and lighting for sanitary use, potable water Quality of live improvement: lighting in houses streets and schools, telephone, radio and TV services Small scale economic development: water for irrigation and livestock, motorization for small craft and mills ELECTRIFICATION IN DEVELOPING COUNTRIES IEA Source

14. SMALL STAND ALONE PLANTS CHARGE CONTROLLER PV MODULES DC LOADS BATTERY

15. REMOTE DWELLINGS DC LOADS PV GENERATOR GENERATOR CHARGE CONTROLLER DC/AC INVERTER COMMERCIAL AC LOADS BATTERY

16. VILLAGE ELECTRIFICATION PV GENERATORE GENERATOR CHARGE CONTROLLER DC/AC INVERTER LOADS BATTERY RECTIFIER DIESEL

17. WATER PUMPING PV GENERATORE GENERATOR WATER DC PUMP DC/AC INVERTER (FREQUENCY VARIABLE) PUMP (CENTRIFUGAL OR RECIPROCATING) PV GENERATORE GENERATOR TANK CATTLE WATERING TANK SPRINK

18. Not competitive yet, but potentially able to make a substantial contribution to sustainable electricity production in industrialized countries. Applications: Diffuse generation 1 – 50 kW Power stations > 1 MW Grid support (weak feeder lines) 0,5 – 2 MW Small grid support (islands) 100 – 500 kW GRID CONNECTED SYSTEMS DC/AC INVERTER PV GENERATORE GRID LOADS

19. GRID CONNECTED PLANT PV MODULES GRID INVERTER DOUBLE COUNTER COMMERCIAL AC LOADS

20. Small size plants (1 – 50 kW) connected to the LV grid (without battery) Suited to be installed on buildings or other infrastructures (absence of noise, moving parts, emissions) Huge potential: south oriented roofs covered with PV could supply electricity needs in many countries. PV energy cost: still double with respect to the electricity cost paid by users DISTRIBUTED GENERATION

21. Distributed exploitation of a diffused source Production at the place of utilization (transmission losses avoided) Easy grid connection (battery) User contribution in technology diffusion Promotion of energy saving and more efficient appliance Exploitation of not utilized surfaces Positive architectural valence in the urban contest Possibility to combine energy production with building envelop functions (saving of traditional building components) DISTRIBUTED GENERATION ADVANTAGES

22. First installations realised and monitored by ENEA and ENEL (preliminary actions of the Italian Roof-top Programme) Aims to check how proper the identified technical solution were to test new components and new design criteria set up the monitoring network Site: Major Italian Universities and Municipalities In operation since 1999 Long term performance analysis in progress Typical plant size: 2 - 3 kW Applications: roof integration, façade, sunshade DISTRIBUTED GENERATION IN ITALY

23. Marginal spaces utilization Use of noise barrier as supporting structure Use of PV module as noise barrier element Zig-zag structures to combine noise absorption and production maximization Bifacial modules in north-south highway direction DISTRIBUTED GENERATIONSOUND BARRIERS IEA source

24. Typically from hundreds kW to several MW Based on flat plate, tracking structures or concentration systems To be utilized for electricity feeding into the grid Hydrogen production (in future) Electricity cost still high 20 – 40 c€/kWh with respect to the one of conventional electricity (2 – 6 c€/kWh, depending on externalities) POWER STATIONS

25. Large size distribution grids Medium size systems (0,5 – 2 MW) to strength weak feeder Small grids (few MW) of small islands (33 in Italy) small – medium size plants (100 – 500 kW) to provide a significant contribution (10-30%) to energy production Almost cost effective Fuel saving Respect of environmental constraints GRID SUPPORT

26. Promoted by ENEA, ENEL, PV Industry, Municipalities Major projects PLUG (ENEA) Serre (ENEL) Vasto (ANIT) First prototypes in operation since 1984 (long term performance analysys still ongoing) Typical power: 10 kW – 3 MW Application: Power stations (0.6-3.3 MW), Small grid support (200 kW), Water punping (70 kW), Desalination (100 kW), Cold store (45 kW) DEMONSTRATION PLANTSIN ITALY

27. PLANT LOCATION LOCATION OF SOME DEMO PLANTS Zambelli, 70 kW Water pumping Casaccia, 100 kW Car parking Leonori, 86 kW Car parkig Giglio, 450 kW Cold store Vasto, 1000 kW Power station Delphos, 600 kW Power station Altanurra, 100 kW Grid-connected Serre, 3300 kW Power station Carloforte, 600 kW PV-Wind Mandatoriccio, 216 kW Grid-connected Vulcano, 180 kW Grid support Lamezia, 600 kW PV-Wind

28. PLUGPROJECT • Development of a 100 kW standard plant for medium size applications • Aim: cost minimization • Standardization and preassembling of components • Modular architecture of systems • Civil works absence • Applications • Casaccia (preexisting structures exploitation) • Delphos (modular concept) • Alta Nurra (combined use of PV and wind) • Vulcano (high penetration of PV in small grid)

29. Development of a modular segment to be used in large size plants operated by Utilities Objectives Verify of the projectual criteria adopted Evaluation of scale effects on costs Application Serre plant: 9 fixed units + 1 tracking unit (horizontal north-south axes) SERRE PROJECT

30. Development of large grid connected and hybrid systems Aim gather experience in design, construction and operation on large scale PV plants verify the degree of availability Applications Vasto plant 2 segments of 500 kW Carloforte 2 x 300 kW PV + 3 x 320 kW Wind Lamezia 2 x 300 kW PV + 3 x 320 kW Wind ANIT PROJECT

31. Negligible pollution during plant operation: Chemical: total absence of fumes or emissions (COx, SOx NOx) Thermal: maximum temperatures < 60°C Acoustic and electromagnetic : acceptable (if inverter within norm limits are adopted) Complete absence of: moving parts waste (components can be recycled) radiation or scories circulation of high temperature or pressure fluids Emission comparison PV 30 gCO2 /kWh Gas 400 gCO2 /kWh Oil 800 gCO2 /kWh CO2 emission avoided = emission avoided for electricity production – emissions related to the construction of the PV plant ENVIRONMENTAL IMPACT

32. ENERGY PAY BACK TIME

33. FUEL SAVING • Plant life time 30 years • Energy pay back time 5 years • Plant useful life 25 years • Yearly energy production 1 300 kWh/kW • Energy produced in 25 years 32 500 kWh/kW • 1 kg of fuel 4 kWhe • Fuel saving 8 000 kg/kW • CO2/kWh 0.77 kg • Emissions avoided 25 000 kg/kW

34. MODULE EFFICIENCY DEGRADATION Experience conducted by ENEA on 80 modules installed in 1980 Results: Declared efficiency 10,6% Measured efficiency - at acceptance tests: 9,54%, (-10%) - after 11 years: 9,14%. - after 25 years: 8,6%. Efficiency degradation: 10% in 25 years Mean degradation rate: 0,4% /year

35. Tedlar leak Grid oxidation MODULE FAILURES Defects detected after 25 years don’t have caused further efficiency degradation with respect to the natural degradation (0,4%/year) This experience demonstrate that the life time of “old generation”, “glass-tedlar” can be considered around 30 years. Tedlar detachment or delamination module browning

36. Array degradation factors Natural degradation power degradation life-limiting wear-out BOS component failures Accidental degradation due to single-module failure (which does not involve failures of entire strings) data on efficiency and module failures have been collected for many years from 2 arrays (at ENEA research centre) the influence of module failure on efficiency degradation was found to be very low if module failure occurs at rate <0.1 %/year In this case module replacing could be not urgent especially in BIPV or remote systems unless the module failure (such as low-insulation loss) cause chained failure of entire strings ARRAY DEGRADATION

37. PLANT EFFICIENCY DEGRADATION Efficiency degradation Inverter failure Inverter failure string failure

38. TIPICAL SEQUECE OF EVENTS Module efficiency degradation (0,4%/a) Module failure (infiltration, ossidation, delamination) System tuning failure (PVgen or inverter) Inverter substitution

39. Land occupation Plant power 1 MW Yearly energy production 1.300 MWh Domestic users supplied 600 (in Italy) Land required 1.5 hectares Energy consumption in Italy 300 millions of MWh (land required: 3.000 km2) Possibility of using marginal lands or not utilzed areas (20.000 km2 in Italy) Integration into existing structures IMPACT ON LAND

40. Total amount of solar energy on earth surface: 15 thousand times the world energy consumption Technical potential: 4 times the world energy consumption Unrealistic due the mismatch generation/demand Unless PV energy utilized for H2 production (in future) South oriented roofs in Europe: electricity needs in Europe PV POTENTIAL

41. Typologies integrated into architectural structures Roofs (sloped, horizontal, curved) Facades Sun shadings (fixed and mobile) Glass roofs and curtains Covering elements Balustrade Typologies integrate into urban infrastructures shelters (car, bus stop, train station) Industrial buildings Noise barriers PV AND ARCHITECTURE

42. BIFACIAL MODULES • applications with architectural constraints • solar radiation exploitation on both sides of module • larger energy production (>10-20%) with respect to standard modules • ease maintenance against snow, dust and bird dropping

43. TRACKING SYSTEMS ONE AXIS TRACKING FLAT PLATE

44. ONE AXIS TRACKING Incident energy > 20%- 25% with respect to fixed plated Fixed flat plate (tilt = latitude) north-south axis tracking flat plate Tilt=latitude

45. TWO AXIS TRACKING

46. TWO AXIS TRACKING Sistema piano ad inseguimento su due assi Incident energy > 30%- 35% with respect to fixed plated Fixed flat plate (tilt = latitude) Tilt = latitudine 2 axis tracking flat plate

47. FIXED No maintenance Simple mounting and transport content cost Modest foundations Less energy collected modest aesthetical result TRACKING Maintenance necessity Exacting transport and installation Higher costs Larger areas required More energy collected Harmonious aesthetical result STRUCTURES COMPARISON

48. The efficiency of cells is higher (30% - 40%) high concentration factors: 100X – 1.000X (Irr*logIrr) smaller cells Solar radiation Solar radiation Lens PV cell PV cell CONCENTRATING PV • PV material (high cost), is partially substituted with mirrors or lenses (lower cost)

49. CONCENTRATING PV The incident energy is almost the same with respect to fixed plates systems: only the direct component of light is exploited Concentrating system Fixed flat plate (tilt = latitude)

50. CONCENTRATOR MODULES • - Concentration factor: 100X – 400X • - Lens efficiency: 80% - 85% • - cell cooling difficulty • - Inexpensive polymer lens • lifetime not verified