Concentrating optics and light management for competitive trackless planar photovoltaic modules and installations

Transcription

1 Concentrating optics and light management for competitive trackless planar photovoltaic modules and installations Silvia M. Pietralunga IFN-CNR P.zza Leonardo da Vinci 32, Milano Italy

2 Outline: 2 Ø Light management to increase competitiveness of Photovoltaic Energy conversion solutions, according to targeted applications Ø Competitiveness: a crucial interplay of technical and economical ingredients Ø An economic ( cost ) parameter can be the guideline for concentrating optics technical solutions in a design-forcompetiveness approach Ø The example of trackless planar concentrators for highefficiency silicon cells

3 Rationale 3 Competitiveness of Photovoltaic Modules IS MY SOLUTION COMPETITIVE? It s a multi-variate question The recipe for competitiveness cooks a whole WORLD of ingredients!!

4 Competitiveness key ingredient: the efficiency of solar cells 4

5 Competitiveness key ingredient: the targeted application 5 Big Plants Residential Building Integration Aero-space Fabrics Portable wearable

6 Competitiveness key ingredient: the targeted application 6 Different applications è different technologies ( bulk, thin films, organics, transparent, flexible.) Different markets è Different torelable price è Different market regimes and laws

7 Competitiveness key ingredient: the targeted application 7 Example: semi-transparent photovoltaic windows

8 Competitiveness key law: OPTIMIZING THE YIELD 8 The required amout of delivered electrical power At the lowest production cost To make the most out of the solar cell material è OPTIMIZING YIELD OF THE ACTIVE MATERIAL è OPTIMIZING SPECIFIC YIELD OF THE MODULE

9 Optimizing the yield of the active material : exploiting the sun at best 9

10 Optimizing the yield of the active material : exploiting the sun at best 10 To maximize the spectral width of sunlight collection To maximize in band electrical photogeneration

11 Maximizing spectral width of sunlight collection: 1- Multiple junction Tandem solar cells PHOTON MANAGEMENT in Luminescent concentrators: Photonic up and down conversion Number of cells Efficiency % Currie et al, Science, 2008, vol 321, 226 A.W. Bett, F. Dimroth and G. Siefer In: A. Luque and V. Andreev Eds, Concentrator Photovoltaics, Springer, Berlin (2007). [ Third generation solar cell Nelson J. Imperial College M. Bortoluzzi et al. PMMA samples doped with Sm, Eu, Tb or Dy methyl 3-oxobutanoate complexes, Dalton Trans. 2014, 43, 10120

12 Maximizing in-band carrier 12 photogeneration: optical concentration in the active material 1- The BLACK SILICON idea 2- Plasmonic photon management MUCH WORK HAS BEEN DONE SINCE THE FIRST IDEAS around !.. J. E. Carey and E. Mazur, US pat. N B2 (2208)

13 Maximizing in-band carrier photogeneration: light trapping in dielectrics Increasing photon absorption probability by increasing interaction time of light with active material 13 Diffusive concentrators Photonic Crystal resonators

14 Optimizing the SPECIFIC yield of the SOLAR MODULE : PV optical solar concentrators NOT IMAGING OPTICS 14 Lowering costs related to active material A cell < A in Also increasing energy production? Geometrical gain Concentration efficiency Effective concentration (# SUNS) G = A in / A cell P r = P cell / P in C = I cell / I in = G P r Ultimate optical concentration (étendue theorem) C max = I cella I in = n x sinx (ϑ max,out ) sin x (ϑ max,in ) x = " # $% 1 2D 2 3D

15 Optical PV concentrators: Tracking vs. Trackless Tracking 15 ü Active tracking 1 or 2 axes ( 0,1 deg ) ü High Concentration ( C > 50x) ü Used with high efficiency solar cells ( tandem triple junction) ü Low integrability on buildings ü installed on the ground big solar plants/ fields Trackless ü NO sun tracking/ seasonal adjustments ü Low Concentration ( C < 5x) ü Better Building Integration capabilities ü Small solar plants ü Indoor applications / devices 15

16 Optical PV concentrators: Tracking vs. Trackless Tracking 16 ü Active tracking 1 or 2 axes ( 0,1 deg ) ü High Concentration ( C > 50x) ü Used with high efficiency solar cells ( tandem triple junction) ü Low integrability on buildings ü installed on the ground big solar plants/ fields Trackless ü NO sun tracking/ seasonal adjustments ü Low Concentration ( C < 5x) ü Better Building Photo Integration Voltaic capabilities modules ü Small solar plants ü Indoor applications / devices LCPV- Low Concentration 16

17 Are LCPV solar concentrators competitive? 17 BENEFITS: PAID IN TERMS OF: Ø Reduced volume of active material Ø Potentially reduced module cost due to lowered active material usage Ø Capex reduction for active material manufacturing Ø Balance-Of-the-System (BOS) cost potentially equivalent to that of standard fixed panels Ø Additional optical loss Ø Reduction in module efficiency Ø Reduction in module energy production due to limited acceptance angle for input solar radiation Ø long term reliability issues of the concentrating optics It is questionable

18 The Levelized Cost of Energy (LCoE): can an economic parameter drive technological solutions? 18 The economic competitiveness of a solar installation can be evaluated by referring to the concept of LCoE. The LCoE provides the cost of the energy produced in a specific environment and can be used to rate different technologies C p = IM C S = C Si / G + C r C Si + C BOP ( ) N A + ( C BF W P /1000) "# C S + C BV $ % E[kWh] = P r H N A η cell P sun

19 The Levelized Cost of Energy (LCoE): can an economic parameter drive technological solutions? 19 E[kWh] = P r H N A η cell P sun Ø H is the equivalent number of sunny hours at maximum power in one year (depending on the geographical position of the plant) Ø Psun [kw] is the nominal solar power density at sea level (AM 1.5) Ø ηcell is the cell efficiency at nominal conditions Ø Pr is the Performance Ratio, defined as (IEC61724) P r Energy produced (in time T) Nominal Power delivered by the panel / Incident sunlight Energy(in time T) 1 kw/m 2 P r does not depend on η cell and summarizes all suorces of reduction in energy production efficiency of the panel in the plant, caused by the optics and the electrical system.

20 The Levelized Cost of Energy (LCoE): An economic parameter to drive technological solutions 20 We distinguish between OPTICAL and ELECTRICAL sources of losses by DEFINING P ro-eff < 1 So that: η sys is the electrical efficiency of the system And P ro-eff is the Effective Optical Performance Ratio The target is to MAXIMIZE P ro-eff for the specific concentrator geometry and installation environment while choosing G C MAX, and C MAX compatible with trackless condition

21 1- Maximizing P ro-eff 21 The case of planar trackless LCPV Generally: P ro = P ro (θ NS,θ EW ) TRACKING CONCENTRATORS: operated at maximized P ro MAX (θ EW = θ NS = 0) TRACKLESS CONCENTRATORS: P ro eff = E c E o = 1year P "# ro θ NS ( t),θ EW ( t) $ % P "# t,θ ( t ),θ Ai NS EW ( t) $ % dt P "# Ai t,θ NS ( t),θ EW ( t) $ % dt 1year P ro-eff evaluated once known: the specific location where the panel is installed the relative fractions of direct and diffused light since all these elements affect the P Ai,distribution

22 2- Comparing to the LCoE of other 22 possible solutions to the same application WHICH SUITS THE BEST?

23 2- Comparing to the LCoE of other possible solutions to the same application A design rule for trackless LCPV concentrators of absolute validity in itself 23 To maximize P ro-eff, while choosing G C MAX,, with C MAX compatible with trackless condition Competitiveness of the concentrating solution is THEN set by the condition : ΔLCoE = (LCoE) s (LCoE) c 0 By expressing the ΔLCoE 0 in the {G, P ro-eff C r } space the domain of existence of competitive LCPV solutions can be retrieved and mapped.

24 Competitiveness of a luminescent diffusive concentrator 24 Spectralon/WR 6080 Planar concentrator Segmented cell (d=h/2, G = 2.4): Variation of P r for non-ideal conditions: - loss - No lateral mirrors - NO AR coating

25 Competitiveness of a luminescent diffusive concentrator 25

26 A trackless LCPV concentrator: MPCCP ( Modified Prism Coupled Compound Parabola) Designed to maximize Effective Optical Performance Ratio P r,o eff = E c /E o Yearly averaged over the evolution of solar position 26 Primary optics: Modified parabolic mirrors MPCCP Patent n. WO 2013/ A1 ( 07/03/2013) LCPV at high optical efficiency (> 85 %) and Geometrical Gain up to G=5 Secondary optics: High-refractive-index dielectric prism 26

27 A trackless LCPV concentrator: MPCCP 27 ( Modified Prism Coupled Compound Parabola) Optimization Variables: 1. Height parabolic mirrors: h 2. Curvature of the parabola 3. Axis angle: Ф 4. Prism height: h prism Constraints: 1. Solar cell dimension: L cell = 5 mm 2. Height parabolic mirrors: h < 40 mm Parameters: 1. Geometric gain: G geo = (3 5) 2. Prism Refractive index: n = ( ) Optimization: Maximize P ro,eff (Effective Optical Performance Ratio)

28 A trackless LCPV concentrator: MPCCP ( Modified Prism Coupled Compound Parabola) 28 INDOOR and OUTDOOR TESTS Numerical simulations

29 Comparing LCoEs of possible solutions to the same application 29 Competitiveness of the concentrating solution is set by the condition : ΔLCoE = (LCoE) s (LCoE) c 0

30 Conclusions 30 Ø A design-for-competitiveness approach has been introduced as a guideline for concentrating optics for photovoltaics Ø The key concept is the LCoE, which is a commonly employed parameter to evaluate the economical competitiveness of photovoltaic solutions, and used it to issue PV panels design rules. Ø The aggregate structure of LCoE well expresses the interplay among various elements, composing the concentrated panel, which contribute to energy production and cost. By making the LCoE expression explicit, the domains of acceptance for the different contributing elements can be highlighted, so that the condition for competitiveness is turned into a set of design rules. Ø Example: The success case of the design of a trackless LCPV module to become economically competitive with PV systems based on standard panels.

31 Acknowledgments: 31 Giuseppe Monteleone Erminio Greco Giorgio Grasso Aldo Righetti Maria Chiara Ubaldi Francesco Morichetti Marco Bortoluzzi Progetto TIMES "Tecnologie e materiali per l utilizzo efficiente dell energia solare". Accordo Quadro tra Regione Lombardia e CNR 16/07/2012, Decr. Reg. n /04/2013