Category Archives: SonSolar

Encouraging the use of Renewable Energy Sources in the implementation of the EU Energy Performance Building Directive[18]

M. Beerepoot, OTB Research Institute for Housing, Urban and Mobility Studies / Delft University of Technology — P. O. Box 5030 — 2600 GA Delft — The Netherlands — m. beerepoot@otb. tudelft. nl

K. Engelund Thomsen, Danish Building and Urban Research — Dr. Neergaards Vej 15 — DK-2970 Horsholm — Denmark — ket@bv-og-bva. dk

The recent EC Directive on the Energy Performance of Buildings (Directive 2002/91/EC, in short: EPBD) will urge member states to develop and design energy performance regulations before 2006. The international EC Fifth Framework Altener research project Build-On-RES[19] was formulated with this objective in mind. The Build-On-RES project aims to develop the methodological and contextual framework to maximise the incorporation of renewable energy sources (RES) in an Energy Performance Method for both new and for existing residential buildings. Build-On-RES started by benchmarking energy regulations in five of the EU member states that have experience of energy performance regulations and scrutinised the extent to which they encourage the use of RES in buildings. In addition to energy regulations, other policy schemes that encourage use of RES techniques like financial incentives and schemes based on communication have been collected and described. On the basis of this collection of existing information, the project is designing a framework to maximise the incorporation of RES in an Energy Performance Method for use by member states that are in the process of (re)designing their (new) energy performance building regulations. This paper describes the results of the Build-on-RES research and presents in short the methodological and contextual framework to maximise the incorporation of RES in an Energy Performance Method.

Risk Management in the Photovoltaic Branch

In Risk Management the questions summarized in figure 3 have to be considered.

— What can be damaged?

— When occur the risks?

— Defensive measurements?

— Who bears the risks?

— Which insurances should be taken out?

— Who should insure?

— How to insure?

What can be damaged? It is not only the photovoltaic cell or the module which can be affected. Injury of persons by accident or through illness is normally covered by the Employer’s Liability Insurance Association or by the sick-fund. Buildings and equipment can be damaged. Property and fortune can be wounded too. Credits must also be repaid when due to a damage no electricity is produced. When as a consequence the financing collapses the personal reputation is affected too.

When occur the risks? During planning, erection and construction or during operation.

Which defensive measurements are possible? These are for example regular revisions. An easy way reducing risk of damage to the electronic power inverter is to place it not in a cellar room which is Figure 3: Risk Management overflowed regularly after heavy rain.

Who bears the risk? The risk of force majeure e. g. natural hazards is borne from the employer. A damage during the warranty phase will be claimed against the contractor. Of course it is an advantage if the producer bears the warranty risk. But this is not really helpful if shortly after putting into operation the producer goes into liquidation. During operation the operator is responsible for failures.

Which insurances should be taken out? In the concept from Marsh it is property, business interruption and as an option, reduced receipts.

Who should take out insurance and which conditions (e. g. which sum insured, which deductibles, which perils)? The erection and construction of a big power plant but also of a photovoltaic system is carried out by several companies. Each party could insure its own risk, but a better solution is to take out collective insurances which include all involved parties. The most important point to observe is the fact that the party with the main interest should take out insurance. During erection this is not the contractor but the initiator of the building project and during service this is the operator who has to make profit with the system.

ESTIMATING THE ECOLOGICAL FOOTPRINT OF THE. HEAT ISLAND EFFECT OVER ATHENS, GREECE

M. Santamouris, K. Paraponiaris and G. Mihalakakpou

University of Athens, Department of Physics, Division of Applied Physics, Laboratory of
Meteorology, University Campus, Build. PHYS-V, Athens, GR 15784. Greece.

1. Introduction

The city of Athens is characterised by a strong heat island effect, mainly caused by the accelerated industrialisation and urbanisation during recent years. The urban heat island phenomenon has been investigated in 23 experimental stations located in the Greater Athens Area, (GAA). Hourly values of ambient air temperature and relative humidity were recorded at each station. Based on the above mentioned experiment, the influence of various climatic parameters and of the prevailing synoptic conditions on the heat island effect was studied in (Santamouris et al., 1999; Mihalakakou et al., 2002; Mihalakakou et al., 2003; Livada et al., 2002). In Santamouris et al. (2001) it can be seen the impact of the urban climate in the greater Athens area on the energy consumption of urban buildings during summer 1996. Moreover in Hassid et al. (2000) it can be observed the effect of the Athens heat island cooling energy consumption of another reference building in various stations of the western GaA and for the years 1997 and 1998.

Everybody has an impact on Earth, as they consume the products and services of nature. Their ecological impact corresponds to the amount of nature they occupy to keep them going. The ecological footprint is defined as the the land and water area that is required to support indefinitely the material standard of living of a given human population, using prevailing technology, (Rees, 1992). The ecological footprint is a measurement of the ecological sustainability, illustrating the reality of living in a world with finite resources, (Barett and Scott, 2001). It provides a final figure in land areas, (in hectares), which is necessary to support an individual, city, region, country or the entire world population. It provides a visual picture of the Earth’s carrying capacity. For that reason, the ecological footprint has become recently very popular as it can offer a representative idea of the ecological limits, which is one of the main topics of sustainable development. The ecological footprint can be regarded as a potential aggregated indicator for sustainable development. Each year the ecological footprint becomes more refined, portraying a more and more accurate figure of the appropriated land for humanity, (Wackernagel and Rees, 1996; Simmons and Chambers, 1998; Wackernagel et al., 2000).

Calculation of the additional ecological footprint is performed by simulating the additional energy consumption of buildings caused by the heat island effect. Simulations have been performed using experimental data from various urban climatic stations located in the Athens Urban area, for the summer period of the years 1997 and 1998. The ecological footprint of this energy cost is then calculated in the present study using the globally accepted CO2 sequestration pattern.

Numerical Calculations by Rigorous Coupled Wave Analysis

1.1 A Calculation model

We have performed rigorous coupled wave analysis (RCWA) calculation [8,9] to simulate the optical properties of the periodically microstructured surfaces. RCWA is a method to analyse the general 3D grating diffraction problem by solving the following Maxwell’s equations rigorously,

(i)

‘ V-(*e) = 0 V — H’ = 0 Vx E — — ikoH Vx H’- iko£E

here, E;electric field, H; magnetic field, h = ^eJm0h’ , k =x/2n, s; dielectric constant and X; wavelength. Assuming the Incident electromagnetic wave with wavelength of X, Incident angle 9, azimuthal angle ф and polarization angle ф, the electric and magnetic fields at the grating region is expressed by,

і E2 = ^SP, q (Z)ExP[-i(kx, pX + ку,,У)]

IH 2 = X £ UM (z )Exp[-i(kx, px + kMy)] ^

Here Sp, q^ Up, q is the electric and magnetic amplitude created by the diffracted wave with order of (p, q). The wave vectors and dielectric constant are expressed with the periodicity Лх and Лу,

£2

m n x + y Ax Ay

(4)

nEXP

kx p — k0 {nc sin в cos ф — p(Х/Лх)} I ky q — k0 {nc sin (9 sin ф — q(l/Ay)}

Here, nc is the refractive index of each region, and e’m. n is the (m, n)-th order of Fourier series.

As shown in the above formulation of RCWA, diffraction efficiency for each diffraction order is calculated with inputting the state of incident beam, structural profiles, and optical

constants (n, k) of materials. Any fitting parameters are not used and the accuracy of the solution computed depends solely on the number of terms retained in space harmonic expansion of electromagnetic fields, which corresponds to diffraction order N=(p, q). We have conducted calculations varying N up to 10 and confirmed that spectral feature mostly converge at N > 7. So we consider the diffraction orders up to +7th for x — and y — directions, respectively, and therefore diffraction efficiencies for 225 diffraction orders are calculated for each wavelength in this study. The literature data of optical constants for metals are used in the calculation.

Figure 2 shows schematic diagram of the calculation model in this study. For the ease of calculation, we restrict the grating shape to a simple 2D binary grating with rectangular cavities. Here we define some parameters to describe surface microstructures and the state of incident wave as periodicity Л, aperture size a and depth d. In this study, we set Ax = Лу = Aand ax = ay = a. Incident angle 9 and azimuthal angle ф are also defined as shown in the figure, and polarization angle is defined as у = tan^As/Ap), where As and Ap denote the amplitudes of the s — and p — polarization components of the incident wave, respectively.

HYBRID POWER GENERATING SYSTEM COMPONET MODELING

Wind Generator

Inverter

A5

DC

Charge

Regulator

To Load

Control

Unit

PV Array

Fig. 1. PV-wind hybrid energy system components.

The hybrid power generating system consists of wind turbine generator, PV array, storage batteries, and control unit. A typical autonomous wind-PV HPGS generating system is shown in Fig. 1.

PV Module Performance Model

Fig.2 PV modul I-V curve.

Tc = Ta + 0.03 • Ga (1)

The electrical characteristics of a PV module are short circuit current, open-circuit voltage and maximum power point. A typical PV module I-V curve is shown in fig. 2. Current and voltage depend on temperature and irradiance. The temperature coefficient for the open circuit voltage is negative and large, which is approximately equal to -2,3 mV/°C for an individual cell. On the other hand, the current coefficient is positive and small, that is approximately +6 pA/°C for a square centimeter of the module area (Markvart, 1994). The operating temperature of the cell, which differs from the ambient temperature, determines the open-circuit voltage. Operating temperature can be calculated using equation 1 for a given ambient temperature (Lorenzo, 1994).

— exp

(2)

PV module short-circuit current is proportional to the number of parallel connected PV cells and irradiance. PV module open-circuit voltage is a logarithmic function of current and proportional to the number of serial connected PV cells. The PV module’s current IM under arbitrary operating condition can be described as;

The necessary number of PV modules to be connected in series is derived by the number of modules needed to match the bus operating voltage.

V =Vм ■ N

PV OC SM (3)

The current output of a PV array at time t, Iм (t), is related to the number of parallel strings as follows:

Ipv (t) = Iм (t) • Npm ■ fMM (4)

Wind Turbine Performance Model

Manufacturers give the characteristic curves for wind turbines as power output versus wind speed at the hub height. The design parameters of a wind turbine generator (WTG)
determine the amount of energy it can harvest from the wind. A power curve, which is a plot of output power against the average wind speed, can be constructed for a WTG design as shown in Fig. 3.

WTG are designed to start generating at the cut-in wind speed, vci Fig. 3 shows that the power output increases nonlinearly as the wind speed increases from to the rated wind speed (vr) . The rated power is produced when the wind speed varies from to the cut out wind speed (vco), at which the WTG will be shut down for safety reasons. The electrical power generated hourly can be calculated from the wind speed data using the power curve of the wind turbine specified ratio, always dispatching wind energy to allow a maximum of its share. In this way, the useful capacity of the wind turbine can be calculated.

Fig. 3. Manufacturers give the characteristic curves for wind turbine.

Wind turbines are usually only connected in parallel, not in series. Several wind turbines can be connected in parallel to match the system current requirements. This can be done with parallel strings of the same wind turbine type or with strings of a different wind turbine type. It is assumed here that at most two different turbine types are used at the same time in one system. Energy densities for wind are calculated using equation 5.

(5)

PwT-0,5. Cp. pair. V

The power output of the wind turbine array at time t,

pwt (t) — !wt (t) ‘vwt 0)- Npwt (6)

Battery Performance Model

Batteries in a hybrid system are connected in series to obtain the appropriate nominal DC bus voltage. Therefore the number of batteries connected in series for the same type of battery in a battery bank is calculated as follows;

N S Bat=VP V/VBat (7)

The hybrid system can have several battery banks, which typically consist of different battery types. The battery state of charge of a battery bank at time t is calculated based on adding the charge current (positive sign) or discharge current (negative sign) to the battery bank state of charge at the previous time instant. When adding the battery current to the battery state of charge, self discharge losses and battery charging losses need to be taken into account. (Seeling-Hochmuth, 1997)

BatB

SOC(t +1)

(8)

XiSOCi(t) ‘ Qi + ^Bat(t) ‘ ^t ‘ ^i(Ikolbat(t)) J’ NPBat i=0

The inverter characteristics can be described by the inverter input-output relationship. Some of the power going into the inverter will be lost due to transformation losses that are named inverter efficiency losses. Efficiency losses of inverter depend non-linearly on the AC output power, and therefore non-linearly on the AC load current.

PIIP ‘Vi = PIOP, Vim = f (PIOP) (9)

Control Unit performance Model

The control unit provides an interface between all components of hybrid energy system, giving protection and control. The most frequently encountered components of control unit are blocking diodes, charge regulators, energy routing switches, measurement sensors and the controller. In fact charge regulators can be modeled as a switch which connects and disconnects generator to battery or load according to battery state of charge, temperature or load demand (Engin, 2002). The output power, PBCOP of the battery charger equals the input power PBCIP multiplied with the efficiency losses during the energy conversion. Efficiency losses depend non-linearly on the DC output power, and therefore non-linearly on the DC output current of the battery charger.

Pbcip -Vbc ~ Pbcop, Vbc ~ f (PBCOP) (10)

Efficiency losses can be calculated from efficiency losses versus output power curves that are given manufacturers. Energy routing switches position is defined by controller that was defined operation strategy. Efficiency losses of energy routing switches are small and can be neglected.

Costing Model of Hybrid System

The hybrid system life-cycle costs are sum of initial investment costs and discounted operation costs. Using equation 11, LCC can be calculated. The hybrid system operation costs are in general non-linear, and depend on component size and type. It also depends on how system is operated (Engin et al., 2002).

NumberofConpenents

LCC

(11)

Cc + / DiscountedCnp,

m

Selection of the factor level settings

Selecting the settings at which the levels are to be set also needs to be addressed. The range of the settings needs to be broad enough to accurately represent the operating process. However if the level settings are outside the feasible range to produce sufficient products then the results will be confined.

The level settings carefully chosen for the experiment factors are shown below in table 1.

Factor

Level 1

Level 2

Level 3

Tpc

4 mins.

8 mins.

—1

m

§

4 mins.

6 mins.

8 mins.

Temperature

1350C

1550C

1750C

Table 1: Factor Levels

The Solar Powered Recharge Backpack

Figure: 7

Prototype “Solar Tergo” mounted on Boblbee

In the framework of a master thesis project, an existing backpack (Boblbee) was equipped with a click-on unit comprises of a solar panel to generate electrical power and a compartment with electrical energy buffer storage unit including electronic charge- recharge control electronics [Weitjens, 2003]. In this design a flexible PV panel is used to accommodate the shape and a convenient utilisation of the backpack. In addition this curved PV panel enhances the appearance. Mobile products that could be recharged are for example a cellular phone, a PDA, ect. They were placed either in a special compartment outside or just inside the backpack. The recharge process could be done all the time the mobile products were carried around in the backpack both outdoors and indoors.

2.4.2 The Solar Cell White-board

A whiteboard will be used at places where there is sufficient light. A whiteboard usually constitutes of a large area (1 m2 or more) surface. Covering a metal plate with white enamel usually makes a whiteboard. So combining these three facts could result in a practical example of application of the Solar Cell Enamel techniques.

2.4.3 Lawn mower robot

Another example is a solar powered lawn mower [Husqvarna, 2004] see Figure 8. When

there is much sunlight, on sunny days, the grass is growing rapidly. The Solar Cells will convert enough sunlight into electricity to power the solar mower. On cloudy days the grass is growing less rapidly, coinciding with a longer period of recharging the batteries. Intelligence is built into the lawnmower Robot, which controls its mow velocity and path. The synergy by introducing intelligence is apparent.

Figure: 8: Lawn mower robot

2.4.4 Solar car Roof

Figure 9:

Solar Car-roof

Solar cells placed on the roof of a car can recharge additionally the batteries [Sunovation, 2004]. The car roofs have usually not flat but curved surfaces.

2.4.5 Solar Sunscreen

Placing solar cells on the box of a sunscreen [Poelman, 2000] is exactly an example in which integration of a function and energy conversion is demonstrated in a practical way. This integration can be pushed even further by making the sunscreen also part of the solar cell. The sunscreen will be used if and only if there is sunlight. On the other side, the solar cell to be functional will also be in need of the sun to shine. Therefore, this example is a clear demonstration of synergy.

ANTIREFLECTIVE COATING ZnO/ZnS FOR SOLAR. CELL OBTAINED BY CHEMICAL SPRAY PYROLYSIS.. INFLUENCE OF THE PRECURSORS

M. C Lopez, D. Leinen, F. Martin and J. R. Ramos-Barrado

Laboratorio de Materiales y Superficie. Departamentos de Fisica Aplicada & ingenieria

Quimica. Universidad de Malaga. E29071 Malaga. SPAIN.

Abstract:

ZnO/ZnS bilayers to antireflection coatings for solar cells have been prepared by spray pyrolysis using mixed aqueous solutions of zinc acetate dehydrated and thiourea or zinc chloride and thiourea. The structure, surface morphology, chemical composition and optical properties of the bilayer are investigated as a function of the initial solution. X-Ray photoelectron spectroscopy (XPS) analysis and Ar ion-beam sputter etching was carried out to obtain XPS depth profile of bilayer. Neither carbon nor others by-products which could change the refractive index of the bilayer have been found in the interface. Some differences between the bilayer with the ZnS film obtained from ZnCl2 or Zn acetate can be observed.

1. Introduction:

The efficiency of solar cells dramatically depends on light that can arrive to the active layer. Due to reflection losses, the photogenerated current density (and consequently, the efficiency) reaches a level much lower than he maximum for the standard terrestrial spectrums of light coming from the sun [1-3]. To reduce the reflection of incident light at the surface of the cell, an antireflecting coating (ARC) can be used over the cell [2-6]. This coating can range from a simple layer to a multilayer system of many layers having almost zero reflectance over a wide range of wavelengths [2].

In general, the design of solar cells, follows a step-down interference coating structure: ns>n1>n2>nm, where ns and nm are the substrate and incident medium refractive indices, respectively [4,6]. This choice is based on the spectral stability of the coating and for low reflectance. Stability means that the low-reflectance spectrum changes very slightly with thickness and refractive index variation [4,6].

Zinc oxide and sulphide can be used to form a bilayer because both compounds have appropriate electrical and optical properties.

Zinc sulphide (ZnS) is an n-type semiconducting. ZnS thin film is a promising material for its use in various application devices due to its wide band gap of 3.7eV at

room temperature, its high refractive index (2.35) [7-11], and its low absortion over a broad wavelength range, from 400 to 1400nm [11].

Zinc oxide (ZnO), is and n-type semiconducting [12]. It is a widebandgap (3.24eV) semiconductor material with high optical transparency in the visible and near-infrarred region of electromagnetic spectrum and high refractive index (1.9). Due to these properties, ZnO is a promising material for solar cell applications such as antireflection coating [13].

Spray pyrolysis is a useful alternative to the traditional methods to obtain antireflection coatings for solar cells. It is particular interesting because of its simplicity, low cost and minimum waste production. The spray pyrolysis allows coat big surfaces and it is easy to insert in an industrial line of production. This method of deposition allows obtain thin films with different chemical, physical and morphological properties; the characteristics of the films depend on the spray rate, temperature of the substrate and high of the nozzle values. ZnO/ZnS bilayer obtained by spray pyrolysis technique shows a smooth and homogeneous surface without by-products.

Angular dependency

The measurements of the angular dependence were performed under the solar simulator, on a cooled rotating measurement block. The change in current was determined for the incidence angle varying between -75° and +75°. The main bus bars were perpendicular to the rotation axes during the measurement. The values for positive and negative angles were always averaged. In Fig. 3a, the angular dependency of the normalised short-circuit current /sc(e)/[/sc(0) cos(e)] is plotted as a function of the incidence angle в. The curves are obtained by averaging the results obtained on 6 modules with AR layer and 6 without and show the departure from the ideal cosine law at angles higher than 45°. A significant improvement is given at high incidence angle by the AR layer, where the angular losses remain minimum. In Fig. 3b, the total current gain in % given by the AR layer is shown.

The average gain can be fitted with a single exponential growth curve. Starting from 2.65% at 0° it reaches 3% at 45°, 6% at 60° and 12% at 75°.

Fig. 3. a) Normalised current as a function of the light incidence angle for the glass without and with AR layer (The data points at 80° and 90° have been extrapolated). b) Gain in current given by the AR layer as a function of the incidence angle.

3.4 Outdoor modules

The nominal operating cell temperature (NOCT) of the modules has been determined by analysing 200 values of the module temperatures, for illuminations between 700-900 W/m2 and air temperatures between 20°-25°C. In average, the module with the AR layer was found to be 1.2°C warmer than the module with the normal glass, with an average backskin temperature of 43.4° and 42.2°C respectively (temperature at the backside of the module measured on the Tedlar foil).

ADVANTAGES BY UTILIZING ANTIREFLECTION. TREATED GLASS COVERS FOR PV MODULES

Simon Furbo, Louise Jivan Shah and Louise Overvad Jensen
Department of Civil Engineering
Technical University of Denmark
Building 118, DK-2800 Kgs. Lyngby
Denmark

Email: sf@bvg. dtu. dk
Fax: +45 45 93 17 55

Esben Larsen
0rsted. DTU

Technical University of Denmark
Building 348, DK-2800 Kgs. Lyngby
Denmark

Email: ela@.oersted. dtu. dk

Goran Olsson
Sunarc A/S

Gronlandsvej 14, DK-4681 Herfolge
Denmark

Email: olsson@sunarc. net

1 INTRODUCTION

Experiments have shown that an antireflection surface of a glass cover can increase the transmittance by reducing the normal 4 % reflection at the air-glass interface [1]. Different techniques of the antireflection treatments are sol-gel deposition [2], direct plasma enhanced chemical vapor deposition [3] and acid etching of the glass [4].

The company SunArc A/S applies an antireflection surface to the glass by a special etching process.

Investigations have shown that for incidence angles between 0° and 70° the solar transmittance of a glass cover is increased by 5-9 %-points and the efficiency of a flat plate solar collector is increased by 4-6 %-points by using a glass cover equipped with antireflection surfaces by the company SunArc A/S, [5].

In this paper measurements of the efficiency for a marketed PV module with the normally used glass cover and with the same glass cover after an antireflection treatment of the outer surface of the glass by SunArc A/S are presented.

The efficiency of the PV module was measured outdoors under different weather
conditions: For sunny periods with a small part of the radiation being diffuse
radiation and with incidence angles for the direct radiation of 0°, 15°, 30°, 45°, 60°

and 75°, and for cloudy periods with a small part of the radiation being direct radiation.