Category Archives: SonSolar

Photo-electric conversion of PDISPL radiation

Certain problems of PDISPL implementation can be solved in pulsed mode, including :

— Photo-electric transformation of PDISPL radiation;

— Specification of the products generated at PDISPL operation;

To solve these problems a laboratory bench was developed and fabricated featuring the following characteristics:

— duration of the pumping pulse 1.510-3 sec;

— spectral distribution of the energy as in black body spectrum with luminescent temperature 3500 — 5000 K;

— intensity corresponding to ~3105 solar constants (~4-104W/cm2).

V

П

0.1

idli]

fallL

L

J

І ЦІ

E

Г

1

L

0

—0

1

0

.a

ms

t

Fig. 7. Laser pulse form

V

Fig. 8 Volt-Ampere characteristics.

Fig. 7 presents to form of laser pulse and fig. 8 — the Volt-Ampere characteristics of GaSb sample under radiation. The maximum power for both the curves is obtained at 0.45 W power. The photo-electric conversion ratio for both was 39%.

A crystal of GaSb made in the Institute of Physics and Technology by Ioffe (FTI) was used as the conversing element. Duration of laser pulse was 650 ^sec and the energy, after release, was 1.1 mJ or 2.2 mJ. These values were chosen jointly with FTI for obtaining the optimal conversion ratios of laser energy into the electrical one.

Selection of the operating composition for iodine laser pumped by solar light is one of the fundamental problems. All the experience of experimental studies of iodine photo-dissociation lasers offers the conclusion — the only class of compositions suitable for implementation as the operational substances are the saturated fluorine organic compositions with one iodine atom, the so-called perfluoroalkyliodides (PFAI), having the common formulation RFI, where RF are fluorine substituted radicals of different construction (linear, branched, cyclic, with ether groups, etc.) The literature [4-6] cites the data on the following compositions: linear: CF3I — C6 F13I

isomeres: iso-C3F7I, 2- C4 F5I, t-C4F9I, 2 — C6 F13I ethers: C3F7OI, h30-C3F7OI

The available spectral-kinetic data on these compositions are presented in tables 3,4.

The following conclusions can be done on selection of the operational compositions for PDISPL based on the data presented in the tables.

Presently the best choice for PDISPL is t-C4F9I. Firstly, this composition possesses relatively wider absorption band with the maximum shifted to the "red” region as compared to the majority of optional compositions. Secondly, t-C4F9I possesses the unique kinetic characteristics. The constant of recombination velocity into the original state for this composition is twice as higher as for KR+R, withdrawal of radicals in reaction 2R-o — R2. This fact can be possibly explained by the necessity of overcoming

Table 4. PFAI radical reactions constants

R

K1 ■1011cm3s-1

K2 ■1011cm3s-1

CF3

2.5 + 0.7

0.55

C2F5

2.25

0.5

n-C3F7I

1.4

0.2

0.8

0.3

i-C3F7I

1.15

0.07

1.8

0.1

C3F7O

2.9

0.55

t-C4F9

0.63

< 10-13

R + R = R2 — K2 R + I = RI — K1

the conformational energy barrier at formation of (CF3)3 — (CF3)3 as opposed to reaction I+(CF3)3 -o — (CF3)3I, following the normal radical, that is without activation energy mechanism. The drawbacks of t-C4F9I include its aggregate state: within the range of normal temperatures and pressures this composition does not have the liquid state.

Table 3. Ratio of PFAI radical reaction constants

PFAI

FC4F9I

2-C6F13

2-C4F9I

n-C4F9I

FC3F7I

n-C3F7I

C3F7OI

C2F5I

CF3I

K1/K2

160

55

33

9.5

9.0

3.5

2.6

2.25

1.45

Conclusions

The resulting PDISPL model will be implemented in follow-up applied research activities. One of those implies further research aimed at optimization of the effectiveness of laser energy conversion into the electrical one at 1.315 pm wavelength. Above all, the technologies and methods developed will be implemented for creation of more powerful simulators of solar radiation.

The scientific results obtained on different spheres of interest cannot be named final. The authors have highlighted the ways for upgrading the effectiveness of PDISPL model together with updating the methods pre-developed.

INTELLIGENT PERFORMANCE CHECK OF PV SYSTEM OPERATION BASED ON SATELLITE DATA

A. Drews* J. Betcke, E. Lorenz, D. Heinemann; Energy and Semiconductor Research Laboratory, Carl von Ossietzky University, Oldenburg, Germany P. Toggweiler, S. Stettler, J. Rasmussen; Enecolo AG, Moenchaltdorf, Switzerland W. van Sark; Dept. of Science, Technology, and Society, Utrecht University; Netherlands

G. Heilscher, M. Schneider; Meteocontrol GmbH, Augsburg, Germany

E. Wiemken, W. Heydenreich; Fraunhofer Institute for Solar Energy Systems, Freiburg, Germany

H. G. Beyer; Dept. of Electrical Engineering, FH Magdeburg-Stendal, Magdeburg, Germany

The PVSAT-2 project, supported by the European Union (EU), aims at the assembling of a fully automated service for performance check and error detection for photovoltaic (PV) systems.

This procedure will reduce the operators running costs by helping optimizing energy yields and system maintenance by daily surveillance.

Malfunctions of a grid-connected PV system, e. g. drop out of single module strings, shading by surrounding objects, or inverter errors lead to energy losses that can be high and costly if they remain undetected for a longer period of time.

PVSAT-2 provides a user-friendly, accurate, and reliable method to avoid unnecessary energy losses and therefore prevents operators from decisive financial losses.

PVSAT-2 is the successor of the EU project PVSAT that already helps PV system operators to detect system faults by providing monthly a system specific reference yield calculated from satellite measured irradiance data and a PV system simulation. PVSAT-2 takes up here with newly added components like error detection, further improvement of the irradiance calculation and PV simulation, and the fully automation of the whole procedure:

• A local hardware device will automate yield measurements and will communicate daily with a central server.

• Software on this server will analyse the performance of the PV system on a daily basis and automatically detect system failures and their causes.

• Combining satellite data with ground data of irradiance will improve the accuracy of the horizontal global irradiance.

• An enhanced model for diffuse radiation will improve the accuracy of the array plane irradiance.

• The PV system model that carries out the PV simulation will be improved to allow the simulation of non c-Si modules.

This paper will present the overall structure of the PVSAT-2 performance check and and some first results. The main focus will be on the error detection routine and its central footprint algorithm. The improvements made at the irradiance calculation scheme and its relevance for the error detection will be touched. Further details on the irradiance calculation will be presented in detail in a separate paper as well as the enhanced PV system model.

corresponding author: anja. drews@uni-oldenburg. de

Determination of the influence of encapsulation methods on the magnitude of Thermal Interfacial Resistances in Photovoltaic modules

Gibbons C. J. B. Sc. M. Phil.1, Murphy D. B. Eng.1

1Energy Engineering Group, Department of Mechanical and Manufacturing Engineering, Cork Institute of Technology, Cork, Ireland. Tel 00353-21-4326224, Fax 00353-21 4326627, email cgibbons@cit. ie

Introduction

The conversion efficiency of Photovoltaic cells is influenced by a large number of diverse factors, ranging from the material properties of the semiconducting materials, the environmental conditions under which the cell is operating, and the thermal properties of the encapsulants. The work presented in this paper examined the influence of the Thermal Interface Resistance (TIR) between the layers of the composite encapsulated cell, and more specifically the interrelationships between aspects of the encapsulation process, and the operating TIR of the module.

Objectives

The main objective was to quantify the significance of the stages of the manufacturing process, and specifically the thermal curing cycle, on the TIRs which occur between each pair of composite layers of the PV Laminates. The TIR acts as additional resistance to heat flow away from the cells, and hence an increase in TIR induces a higher cell temperature. The highe r cell temperature leads to a significant reduction in the conversion efficiency of the cells, with less electrical output being produced.

The effect of the curing cycle was evaluated experimentally using a Guarded Heat Flow Meter that was designed and constructed to the required international standard. The meter allowed accurate measurement of the TIR under controlled conditions.

A Taguchi methodology (Peace, 1993) was employed to determine the sequence and production factor levels for the three parameters thought to be likely to effect the TIR. These manufacturing parameters were; the thermal cycle duration, and the temperature levels during the bonding and curing phase. The results were analysed statistically to determine the significance of each parameter and combinations of parameters.

Theoretical analysis of the behaviour of materials at interfaces was also completed, and used to try and predict TIR values for selected situations, these results compared well with experimental results and some general agreement was established. However this aspect of the research is not presented in this paper due to spatial constraints.

Considerations towards a mature design of sustainable PV powered products

1.1 General system design considerations

In general one can say that in designing PV powered Products; a good balance has to be found between its sustainability, its functions and user context including ergonomics, and its overall design quality. Taking for granted that the use of PV powered products contribute eventually towards a more sustainable energy consumption concept, one could concentrate on the remaining subjects.

To answer what ‘mature and sustainable design’ is all about, one should focus on the following consideration:

a) Design Quality:

• Users become aware of ‘quality only in depth’, they will not judge a product for its pure surface beauty. As a result one of the considerations in sustainable product design will be that the appearance of PV cells for the long term should not the prominent factor of design. The PV cells simply have to perform well in the intended application but they should neither be allowed to interfere with the design freedom of shape nor with the user friendliness. An example in architecture, PV tiles with colour of normal tiles. It will not be obvious at first glance that the roof is something special. In other words a virtually invisible PV application. Of course if the purpose is to show the use of PV on the roof, this example will not be applicable.

• To get rid of the predicate ‘just a gadget’ the added value of the additional use of PV cell must be apparent.

b) User friendliness or Ergonomical Design Quality:

• The use and integration of PV cells in products must not introduce additional inconveniences such as for example in PV torch where the flat PV cells hamper a good grip.

• By introducing PV energy, the battery will work for a longer time. The common approach could then be to integrate more functions into the products, nullifying the energy gain. In maturely and sustainable designed products, all these additional functions must be implemented in such a way that the user can select which function is needed at that moment and be able to shut down the other functions.

c) Sustainable energy matching:

• To be able to claim sustainability at least there must be proper matching between the energy and cost payback time of the used PV cells and the economical time of the product concerned. As a consequence fancy, sexy and trendy designs are by definition not sustainable. Most today trendy designs will be outdated tomorrow ready for disposal. Quite often in these cases the incorporated PV cells still need years to function to meet their payback target.

• Proper sustainable energy matching means a systematic approach towards energy efficiency improvement. For instance reducing the energy loss introduced by ‘stand-by’ [Kan, 2002].

• Battery powered products with sustainability in mind must facilitate the use of rechargeable batteries. There is however a discrepancy between primary non rechargeable batteries on one side and rechargeable secondary batteries on the other side with respect to the voltage delivered namely 1.5 V versus 1.2 V. This consideration therefore has two aspects namely: environmental and ease of use of the products. . Historically the primary non-rechargeable penlight batteries for example were designed to deliver voltages at multiples of 1.5V, while the rechargeable penlight batteries deliver only a voltage at multiples of 1.2V. Products that can only function in a voltage range limited by multiples of 1.5 V and which are not designed flexible enough to be able to function also at the lower voltages as usually delivered by rechargeable batteries are therefore by design not sustainable. Parallel to this observation, to promote sustainable design, there must be a growing awareness at the battery manufactures that somehow there must be some international standardization. A logical step would be to have the rechargeable batteries also at multiples of this 1.5 V.

Solar glasses with industrial antireflection coatings: evaluation of photovoltaic yearly energy yield gain and market perspectives

Christophe Ballif, Swiss Federal Laboratories for Materials Testing and Research, Feuerwerkerstrasse 39, CH-3602 Thun, E-mail: christophe. ballif@empa. ch Jochen Dicker, Fraunhofer ISE, Heidenhofstr. 2, D-79110 Freiburg,

Dietmar Borchert, Fraunhofer ISE, Auf der Reihe 2, D-45884 Gelsenkirchen,, Thomas Hofmann, FLABEG GmbH & Co. KG, SiemensstraRe 3, D-90766 Furth

The deposition of a thin porous SiO2 antireflection (AR) layer on glass leads to an enhanced light transmittance by reducing the reflection at the air-glass interface. Such a layer can be used to increase the performance of glasses for photovoltaic modules or for solar collectors.

This contribution describes first an industrial sol-gel process established at Flabeg for the preparation of large area AR panels and addresses the issue of the layer stability. All laboratory tests, as well as outdoor tests are successfully passed and no degradation of the layer is observed even after prolonged outdoor exposure.

The base results of our study are obtained on sets of commercial multicrystalline silicon solar cells encapsulated with low-iron glasses, with or without an AR coating. The measurements performed under standard test conditions (STC) show a current gain of 2.65% with the AR glass, when compared to glass without aR layer. An additional current gain is obtained at higher light incidence angles. Based on the results obtained on mini-modules and on the outdoor monitoring of test modules to evaluate temperature effects, simulations are performed to asses the yearly photovoltaic energy yield gain at different geographical locations. An energy yield increase of 3.4%-3.7 % is expected depending on the location.

In the last part, we briefly summarise the market situation for AR glasses. Based on the current production capacity increase and on the significant improvement given by the AR layer, we think that AR glasses are likely to play an important role for a more efficient photovoltaic energy production.

1. Introduction

Because of the refractive index mismatch between air and glass (n ~ 1.5), around 4% of the light hitting a glass surface is reflected by the outer face of a glass panel. As several authors have already shown [1-3], porous SiO2 thin films can be prepared with a refractive index varying between 1.1 and 1.5. This allows hence the deposition of single or multilayer antireflection (AR) coatings even on materials with a low refractive index such as glass. These layers can, therefore, be used to increase the performance of glasses for photovoltaic modules (referred to as PV glasses in the text) [3, 4] or for thermal collectors. Various techniques for the proportion of porous SiO2 layers have been reported in the past, including sol-gel deposition [1, 5], acid etching of the glass [6], or plasma enhanced chemical vapor deposition (PECVD) [7]. For mass production and for long-term outdoor application however, low production costs of the order of a few Euros per square meter as well as long-term stability of the layers are decisive factors. The development of processes filling these two criteria have only been achieved recently and two companies (Flabeg in Germany and Sunarc in Denmark) propose now commercial AR coating of glass for solar applications (thermal collectors or photovoltaic modules).

The purpose of the present contribution is threefold: first we want to present the industrial process developed at Flabeg and address the important issue of layer stability. Second we will show in detail which effects such an AR coating can be expected to have when used to
encapsulate standard multicrystalline silicon solar cells. To achieve this goal, we have prepared 22 mini-modules composed of a single solar cell, and for each cell the efficiency, the spectral and the angular response have been determined before and after embedding. Besides, we tested modules in outdoor conditions to evaluate the effect of the AR layer on the module temperature: in particular we will show that besides providing an efficiency increase of around 2.65% in standard test conditions (STC), the improved angular response leads to an additional yearly energy increase of around 3.5% when compared to a glass without the AR layer. Third we will briefly consider the market situation for AR glasses, which are already implemented by a number a PV module manufacturers, and describe future market perspectives.

Annual solar irradiance curve and annual global irradiation

The annual diagrams of solar irradiance and the annual sum of global irradiation energy are the results of climatic and meteorological matters that depend on local and seasonal conditions. The principal climate database used in the simulation software’s come from Meteonorm program, which has an extensive world-wide database and time series data of adequate quality, are simply to use. For the present application in this case study the solar irradiance date come from IAMEST. — Joint Research Centre GIS based solar radiation database which used the r. sun solar radiation models. In this model we can obtain the solar irradiance curves using the geographical latitude of the site.

This database can estimate the photovoltaic potential of the regions we can obtain PV maps about the yearly electricity generation. The application site radiation date come from this database what presents the annual total yield.

The yearly variation of the date indicate that the average radiation value fluctuates from year to year, the deviation from the long term average are generally about 15%, but extremely values up to 40% have been observed. In the following figures the solar radiation date of the applications sites are presented (Figure 1). In different inclination degree.

Figure 1. Monthly average for daily solar radiation at application site

Figure 2. 1 kWp PV system performance

Using the expression E=365*Pk rpGP to compute the annual total electricity output from the PV system where the Pk, is a peak power installed rp is the efficiency, analogous to the performance ratio, the typical value is 0.75,and Gi is the annual of daily global radiation on the horizontal and inclined solar panel facing, oriented to South. Figure 2 shows the variation of the monthly PV potential of a 1 kWp PV system

Spatial distribution of light absorption in organic. photovoltaic devices

D. P. Gruber1, G. Meinhardt,2 W. Papousek3

1 Polymer Competence Center Leoben GmbH, Parkstrasse 11, 8700, Leoben,

Austria

gruber@pccl. at

2AustriaMikroSystems AG, Premstatten, Austria 3Institute of Nanostructured Materials and Photonics JOANNEUM RESEARCH

GmbH, Weiz, Austria

In case of an organic photovoltaic device the incident sunlight must be absorbed in a very thin area within the photovoltaic device, which can be assured by a proper choice of material parameters and layer thicknesses. In a recent paper it was shown that the dependence on the absorption within the active layer is not a trivial function of its thickness, but follows a rather complicated behavior [6]. In this paper we carried out methods for the specific optimization of light absorption of an organic photovoltaic device. Numerical simulations of multilayered structures on the nanometer scale show interesting spatial distributions of light absorption depending on the thicknesses and the optical constants of the individual layers. Parameter studies were carried out, in which we varied the coefficient of extinction and the refractive index of each layer. That gave us a suggestion for the optical constants of a photovoltaic device with optimal power conversion efficie ncies. In this paper we also present methods which permit to dispose the maxima of absorption density to the area near the pn-junction. According to our calculations photovoltaic devices were built, which show decisively improved power conversion efficiencies. Furthermore we analyzed the correlation between photo current and absorption density in a given area around the pn-junction, which lead to better understanding of the diffusion range of dissociated charge carriers.

1. Introduction

There are two essential limiting factors for the efficiency of photoelectric devices like solar cells and photo detectors: The absorption of the incident light energy and the transport of the built charge carriers. In this paper we present a method for the optimization of the light absorption efficiency of bilayer pn-junction devices which are built up as a stack of four layers on a glass substrate with two separate homogeneous layers building a pn-junction (active area) and a PEDOT layer between an ITO and an aluminium electrode. At the interface between those materials, a fast electron

transfer from the p-conducting layer to the n-conducting layer occurs upon light excitation [6] and the respective charge carriers are transported to the electrical contacts of the photovoltaic device. To optimize the energy absorption in a bilayer pn-junction solar cell one has to take care that the maximum of the density of light absorption matches the region near the pn-junction. Different publications reported
electroabsorption studies of electric fields in bilayer molecular organic photovoltaic devices made of zinc-phthalocyanine (ZnPC), perylene pigment (MPP) and other materials [11,12,13]. It was figured out that the interface field has a different spectral signature as that of the bulk of the two layers [11] but they accounted the square of the electric field as the deciding value for the optimization of energy conversion which turned out to be not the full truth. Investigations in the behavior of the spatial distribution of energy density inside the devices showed that there is a mismatch between the square of the electric field |E|2 and the absorption density in dependence on the position vector through the photovoltaic device. [1,2,3,4]. Later papers reported modeling of light absorption of organic solar cells emphasizing the great potential which still rests in today’s construction of organic photovoltaic devices [6,7]. Our paper leads to improvements in the proper use of current solar cell materials on the one hand and gives an indication about the optical behavior of new materials providing optimal energy conversion for future device setups on the other hand.

2.

Fig. 1: Electromagnetic wave incident on a multilayer

Theory

Figure 1 shows the electrodynamic setup of an organic solar cell. We assume perpendicular incoming light in counter ‘z’ direction. In the classical model at any interface between two layers the incident light is divided into a transmitted part in ‘ z’ direction and a reflected part in counter ‘z ‘ direction. At l, l +1 reflected parts fall back at l-1,l where they are divided again into a transmitted and a reflected part. Consequently it comes to multiple reflections in every layer. In the model one can substitute multiple reflections by an electric field Em+ in ‘z’ direction and an electric filed in counter ‘ z ‘ direction Em- [1].

incident wave (given): E (r) = Ae

-ik r

(1)

Based on MAXWELL’s equations and the conditions of continuity one gets for the partial waves in the multilayer:

07 — PV Systems and PV Cells

reflected wave: E (r) = Ae-k r

(2)

—■l — — — l — kl-~

wave l — (counter z-direction): E (r) = A e r

(3)

—l + ■» — l + :7l+ r

wave l + (z-direction): E (r) = A e

(4)

transmitted wave: E (r) = Ae ~,k r

(5)

(l = 0,1,2,….. m -1)

e

One can set the coordinate system without loss of generality so that k is parallel to the xz-plane what ensures key = 0. Consequently one gets simpler expressions for the wave vectors of the incident, reflected and transmitted wave. From the conditions of continuity

at z = D1, Dm one gets the amplitude vectors of the reflected and the transmitted

waves as well as for the waves l — and l + within the layers. Furthermore one can choose Ay = 0 without loss of generality. With the wave vectors and the amplitude

incident wave:

Ee (z) = e-i(kXx+kzz) Ax

(6)

reflected wave:

Erx (z) = — r0me-2ikeeDle-i{kXx-kzz ] Aex

(7)

wave l -: Elx- (z)

= kz tom eikzDl+1 e^ik‘.D1 e~i(keex+kzz) Ae

kez tm x

(8)

wave l +: Elx+ (z)

= _ K-lsmr e-ik‘zDi+ie-iktDi Aee-i(kexx-klzz) Ae

e lm x x

kz tlm

(9)

transmitted wave:

k t

Et ( z) = ~^t e~ik‘tDme — ik‘zD1e-i(k‘ex+k‘zz) Ae x e 0m x

<

(10)

vectors and by the use of the Fresnel coefficients [1] one can calculate the electric field of the incident, reflected and transmitted waves as well as for the wave components within the layers:

a

a(z) =T

E

(11)

2

According to the definition of the absorption density in MAXWELL’s electrodynamics

al

kl

2

о

S

2

2

ke

tlm

e 2Im( kl)(Di+i-z)

— 2 Re

+ r 2 e~2Im(kl)(Dl +1+ z) + lm

(Ae )2

r e 2i Re(kl )(Di+i-z) ‘lmc

ai (z)

the absorption density in the layer l turned out as:

(12)

(l = 0,1,2,….. m) where tlm and rlm are the Fresnel coefficients of the part of the layer indicated by the indices.

SHAPE * MERGEFORMAT

Different scenarios study

In this study the direction facing of PV module have to be considered in order to achieve the maximum electricity production of the PV system (Fig. 3). Six different conditions of PV module installation as follow:

• Scenarios 1:

— Module azimuth 16 degree (along the roof orientation)

— Module inclines 0 degree (along the roof incline)

— Pitch 3 degree

• Scenarios 2:

— Module azimuth 16 degree (along the roof orientation)

— Module inclines 14 degree

— Pitch 3 degree

• Scenarios 3:

— Module azimuth 0 degree (South orientation)

— Module inclines 14 degree

Side view

Fig. 3 Module orientation

Fig. 4 Computer simulation view of scenario 1

Pitch 3 degree

Fig. 5 Computer simulation view of scenario 2

Fig. 6 Computer simulation view of scenario 3