A block diagram of both heat and electricity production in the pilot project "Solar roof Spansko-Zagreb" is presented in Figure 3. Solar thermal collector with surface area of 10 m2 converts solar energy to heat. The difference between absorbed heat and heat looses is denoted as a useful heat. Working fluid transfers heat into a well-insolated 750-liter storage tank. In this way the useful heat is stored for needs of space heating and hot domestic water preparation. City gas as environmental acceptable fuel is used as a backup source of energy.

Figure 4 presents distribution of measured units in solar thermal — gas system described here for space heating and hot domestic water preparation. The measurement line consists of five transducers:

1. Consumed hot water transducer

2. Solar collectors transducer

3. Backup gas heater transducer

4. Space heating transducer

5. Solar collector used for the space heating transducer

The transducers are integrated with a flow sensor, two temperature sensors and a display. The distribution of the thermal transducers measuring points in the system is shown in Figure 3. Remote supervision and measurements is provided using a PC with
dedicated software on the Windows platform via serial interface and a modem connection. Some parameters are displayed on the outside panel mounted in front of the house (Figure 2).

Thermal energy balance of consumed hot water:

sol cas

Qchw Qchw Qchw

Thermal energy balance of space heating:

Qsh = QT + Qh,

Qchw Consumed hot water thermal energy Qcshowl Solar collector thermal energy QgZ Backup gas heater thermal energy Qsh Space heating thermal energy

Qsghas Backup gas heater used for space heating thermal energy

sol

sh Solar collectors used for space heating thermal energy

According to the power purchase agreement with the local utility, the counters of electric energy register the amount of electric energy delivered to the network and electric energy supplied from the network. There are three additional counters of electric energy connected to the PC. These are counters of produced electricity, consumed electricity and surplus energy delivered to the network when the needs of the loads in the house are satisfied (Figure 2).

Required safety measures are systematically applied, according to Croatian and European regulation for this type of system. When one or more phases in the distribution network switches off, the additional circuit breaker installed in the switchboard disconnects the PV generator from the utility.

Figure 2 External visualization board

Figure 4 Block diagram of solar — gas system for space heating and domestic hot water
preparation in the pilot project “Solar roof Spansko-Zagreb”

By means of the calibrated model the system operation was simulated from June to August using climatic data for a typical year in Milano. The aim was to verify the importance of the progressive temperature increase in the perturbed ground on the system performance.

An on/off control acting on the pumps was introduced in the simulation model, with an air temperature set point T set = 24.5 °C. The mass flow rates had the same values as in the experimental campaign. Simulation results, in terms of discomfort and COP, are reported in Table 1 for each month and for the whole summer. The minimum discomfort is obtained in June but even in July and August it assumes very low values: discomfort values in the cooled room are about ten times lower than in the reference room.

Assuming again typical weather conditions for Milano, a parametric study was carried out investigating the influence of the following parameters:

— the ground loop mass flow rate mg and the room loop mass flow rate mr

— the area of the radiant ceiling surface Ac

— the number of pipes N, the length of each pipe L and the distance between the axes of adjacent pipes d

Variation of any of the above-mentioned parameters affects the pressure drop in the loops. Then for each configuration the power demand of the pumps was calculated by considering the characteristic curve (pressure drop vs mass flow rate) of the system and average values of mechanical efficiencies for commercial pumps.

Mass flow rate. The influence of the mass flow rates was studied by giving the other parameters the current values in the experimental set up i. e. Ac= 10.8 m2, N = 10, L = 6 m and d = 1.5 m. For simplicity we chose mg — mr. The relative discomfort and the COP

dependence on the mass flow rates are plotted in Figure 4, while Qroom and Epjmps are reported in Figure 5. In the explored mass flow rate range, the flow regime remains laminar and so the convective coefficient in the pipes is the same for all mass flow rates. The pumps energy consumption Epumps rapidly grows with the mass flow rate and drives the COP trend. An optimal operating condition can be found minimising the relative discomfort: choosing a mass flow rate value around 100 kg/h gives the lowest discomfort with a still high energy efficiency.

Geometric parameters. The influence of the four geometric parameters was investigated by setting mg — mr = 100 kg/h and by varying Ac, N, L and d simultaneously, with the values given below:

— Ac: 3.6, 7.2, 10.8 and 14.4 m2 corresponding to respectively 25, 50, 75 and 100 % of the floor surface of the cooled test room

— N: 5, 10, 15, 20 and 30

— L: 3, 6, 10, 15 and 20 m

— d: 0.75, 1.5 and 3 m

From the simulation outputs it results that the dependence of the relative discomfort on the geometric parameters of the ground heat exchanger can be conveniently represented in terms of an effective heat exchange surface Seff. This quantity is defined as Seff = S • d/D,

where S = N.2nRpL is the total heat exchange surface in the ground and d/D is the ratio between the pipe spacing and a suitable linear dimension of the earth surface occupied by the pipes. The factor d/D weights the actual heat exchange surface taking into account the pipes density in the ground. At high density, i. e. low values of d/D and Seff, the tubes will be in contact with a portion of ground where temperatures might be significantly higher than in the undisturbed soil, hence reducing the effectiveness of the heat exchange. As it is shown in Figure 6, for every value of the radiant ceiling surface AC the relative discomfort is an exponentially decreasing function of Seff. The fitting parameters are reported in Table 2.

The larger AC the lower the horizontal asymptote, i. e. the minimum discomfort achievable. In order to supply the comfort demand the radiant ceiling surface must be larger than 50 % of the ambient surface, but increasing from 75 to 100 % gives marginal advantages.

Design guidelines for the ground heat exchanger can be derived from the decay coefficient Seff. c of the exponential that decreases with AC. Once the effective surface is 4 times Seff, c, any additional increase produces marginal effects on the system performance.

The COP is a decreasing function of the relative discomfort, as shown in Figure 7. In fact the considered variation of the geometric parameters has a significant influence on the delivered thermal energy Qroom but little influence on the system pressure drops and on the electricity consumption Epjmps. Hence the best geometrical configuration from the point of view of comfort is also optimal from the point of view of efficiency.

Conclusions

In this paper the study of a ground cooling system carried out by means of a measurement campaign and dynamic simulations is reported. The experimental results highlight the interesting potentials of the proposed system, looking at the comfort conditions obtained and at the low electricity consumption. A TRNSYS simulation model of the system was developed and calibrated against measured data. A discomfort index and an energy efficiency index were introduced in order to evaluate the system performance. Dynamic simulations on the current system configuration for typical weather conditions in Milano showed that the progressive increase of the ground temperature during summer due to the system operation does not impair the system performance. A parametric study was carried out by changing the water mass flow rates and the main geometric parameters of the radiant ceiling and of the earth-to-water heat exchanger. Increasing the mass flow rate over a certain limit has little effect on the delivered thermal energy but compromises the energy efficiency. An optimal value of about 100 kg/h, giving the lowest discomfort and a rather high COP (around 10), was found. From the point of view of their influence on the relative discomfort index, the parameters of the ground heat exchanger can be grouped together into an effective heat exchange surface in the ground. For every value of the radiant ceiling surface the relative discomfort is an exponentially decreasing function of the effective surface. Design guidelines were extracted from these plots. In order to supply the comfort demand the radiant ceiling surface must be greater than 50 % of the ambient surface and the effective surface must be 3-4 times Seff, c. The COP is a decreasing function of the relative discomfort, so that a geometric configuration which minimises the discomfort maximises the COP at the same time.

The research will prosecute by studying the system behaviour under different climatic conditions and in connection with buildings of different characteristics.

[1]

Figure 2: Operative temperature in test room 1 (cooled) and in test room 2 (free floating),
radiant ceiling surface temperature in test room 1 and outdoor air temperature

SHAPE * MERGEFORMAT

mass flow rate (kg/h)

Mateja Trobec Lah*, Dr. Asist., Ales Krainer*, Dr. Prof.,

University of Ljubljana, Faculty of Civil and Geodetic Engineering, Chair for Buildings and Constructional Complexes

Jamova cesta 2, 1000Ljubljana, P. O. BOX 3422 Slovenia

Tel: +386 01 4768 609 fax: +386 01 4250 688 e-mail: MLah@fag. uni-li. si.

* ISES member

Abstract. The main aim of the paper is to present a progressive strategy in automatic control for a shading device — roller blind, based on the fuzzy logic, to obtain the desired inside illumination according to the available momentary solar radiation. To implement the suitable control system for the movable shading device, the combination of the fuzzy and conventional control algorithm was developed. For this purpose we studied the luminous efficacy of the solar radiant energy in all weather conditions. The developed control algorithm contains a cascade control with fuzzy controller as the main and conventional PID — proportional-integral — derivative controller as the auxiliary controller. The illumination fuzzy controller, which is essential for proper roller blind position, was designed progressively during the experimental procedure. It enables us to use the non-linear knowledge about the optical process and to transfer it to an appropriate control action (roller blind alternation) in a way that is close to human thinking. It was optimized iteratively. A well-designed illumination fuzzy controller means moderate continuous movement of the roller blind. It also assures the inside daylight illumination in the area, where the desired value deviates up to ± 50 lx. Automatic active response of the shading device to the outside weather conditions enables the optimization of internal visual performance together with efficient use of energy, also in the sense of the inside thermal performance.

1 Introduction

Using daylighting in buildings is an important and useful strategy in replacing the need for high-grade conventional energy for inside illumination. Energy flows through the building envelope are present all the time. The properties of the building envelope have significant influence on the interaction between the inner and the outer energy conditions in the sense of thermal and lighting flows. The available solar radiation conditioned the response of the building as naturally lit space. The positive aspect of the controlled luminous energy flow through the building envelope is enhanced with the development of the technology, i. e. with the possibility of the automatic active response of the shading elements to the outside conditions. In our case this is realized with a roller blind adaptable to the outside weather conditions. In daylighted spaces the psychological benefit is increased. Also, the lighting energy consumption and the heat gains associated with the electrical lighting are reduced. The main aim of the paper is to present the automatic adaptable roller blind, based on the fuzzy logic control system to obtain the desired inside illumination according to the momentary available solar radiation. A real model of a building, test chamber properly equipped, was built for the development of the fuzzy control system for changeable window geometry. The test chamber allows the investigation and experimentation of illumination control and enables us to study the influences of the movable shade on the luminous efficacy in the interior.

Control system design is a complex procedure usually based on modeling and simulations in the overall iterative approach [1]. In our case the design approach was based only on experimentation. The main focus of the study was on the design and development of the
fuzzy illumination controller. In order to develop an effective illumination control system, sets of preliminary measurements were done, where the daylighting response in the sense of the inside illumination dependent on different sizes of the transparent part of the window and the luminous efficacy was studied. The available daylight inside the building depends on the solar radiation and the building’s geometry. Weather conditions and the level of cloudiness determine the terrestrial total solar radiation and the ratio of diffuse/direct radiation. Actual daylight illuminance in a room is related to the luminance pattern of the sky and also to the window geometry with regard to the room’s dimensions.

Illumination and luminous efficacy correspond to the available solar radiant flux. Spectral distribution of the solar energy is roughly equal to black body spectrum at a temperature of T=5773 K. It is useful to know the impact of the total solar radiation on the optical effect in the interior space. The ratio of the luminous flux Фу [Watt] to the radiant flux Фе [lumen] is defined as luminous efficacy K [lm/W]. Luminous efficacy K of solar radiation is given with the ratio of the luminous flux of the visible light Фу (380 nm < X < 780 nm) and the total solar radiant flux Фу (0 nm <X~ 2500 nm). The maximal value for the solar "overall” luminous efficacy is 93 lm/W. The luminous flux is the part of the radiant power, which is perceived as light by human eye, and the value 683 lm/W is based upon the sensitivity of the eye at 555 nm, which is the peak efficiency of the photopic (daylight) vision curve [2].

In experiments the observed inside luminous efficacy of the solar radiation was the ratio between the measured external available solar radiation (global and reflected) and the measured internal illumination. The observed luminous efficacy K presented in the experiments is:

K [lm/W]: Luminous efficacy = (measured inside illumination)[lx]/(measured external

solar radiation) [W/m2]

Solar luminous efficacy is a quotient, which tells us the real efficacy of the daylight in the sense of internal visual performance taking into account changeable weather conditions. The ratio describes the relationship between the optical and the thermal effect of the available solar energy.

Other sets of experiments were intended to study the relationship between the outside available solar global and reflected radiation and the corresponding inside illumination.

The experiments were done throughout the year using different transparent area sizes to collect and examine the correlation between the solar radiation and the inside illumination. The non-linear mapping between the inside and the outside conditions was used as a basis for defining the fuzzy rules in the illumination fuzzy controllers. For fuzzy rules in the form of if-then statements only the input-output relations are important and not the information about the mechanism, which causes these relations.

The final aim was to create an illumination control algorithm, which enables harmonized variation of the window geometry, i. e. proper positioning of the roller blind in real time conditions. Well designed illumination control algorithm with precise setting of the parameters produces appropriate signals for moderate roller blind alternations according to the outdoor weather conditions and the desired indoor illumination. The result is efficient utilization of the solar energy for the inside harmonized lighting and thermal energy conditions.

Experts from 19 countries (Australia, Austria, Belgium, Brazil, Canada; Czech Republic, Germany; Finland, Indonesia, Italy, Iran, Japan, Netherlands, New Zealand, Norway, Sweden, Switzerland, United Kingdom, USA) work in four topical areas in this project

• Market — Assessment and Communication

• Design and Analysis

• Demonstration

• Monitoring and Evaluation

The target of this project is to examine in detail residential buildings with exceptional performance in the participating countries. Such successes can be used as models for crafting housing to a very high construction quality, efficient energy production and supply systems and unprecedented thermal comfort by at costs level acceptable in the marketplace. To achieve these goals, the experts are exploring ways to achieve:

• less environmental impact over the life cycle of the building,

• greater reliability for the components, systems and the building as whole,

• increased substitution of renewable for non-renewable energy use,

• lower costs than earlier generations of such housing, and

• more market / occupant oriented design, including special features.

New building components are used, such as high performance windows with overall frame and glass combined U-values less than 0.8 W/m2K, reduced thermal bridges in the building shell, high performance insulation systems and very airtight construction. Energy to supply and temper ventilation air is minimized by using mechanical ventilation systems with high efficiency heat recovery, sometimes coupled with an earth-to air heat exchanger or preheating sunspace. The result is a shortening of the heating season and reduction of the needed heating capacity to such an extent that a conventional heating system is no longer needed. Nor, given the minimal heating energy called for, would a conventional heating system make economic sense. By such small absolute energy quantities to amortize the fixed costs of a conventional system, solar systems become more competitive. They require no chimney sweep, exhaust gas control, meter reader, or service subscription and they have a long lifetime. Finally, given the very small demand on non-renewable energy with the resulting drastic decrease in primary energy demand, detrimental effects on the environment are also reduced. Figure 1 illustrates the path of

energy conversion from primary energy to the end uses of space heating and hot water, taking into consideration the conversion losses outside the building and heat losses inside the building.

In conclusion, new high performance housing shows a way to a new generation of fulfilling domestic needs with drastically reduced primary energy demand and the subsequent impact on the environment. Figure 1 draws, that the primary energy demand can be decrease by extension of renewable energies.

A. Thanachareonkit, M. Andersen and J.-L. Scartezzini

Solar Energy and Building Physics Laboratory (LESO-PB)
Swiss Federal Institute of Technology in Lausanne (EPFL)
CH — 1015 Lausanne (Switzerland)

ABSTRACT

Scale models represent a standard method for the assessment of daylighting performance in buildings. Recent studies however pointed out their general tendency to overestimate work plane illuminances and daylight factors. The cause of this inaccuracy between real buildings and scale models performance is due to several sources of experimental errors, such as modelling of building details, surfaces reflectance, glazing transmittance, as well as photometers features. To analyse the principal sources of errors, the comparison of a 1 : 1 daylighting test module and its 1 : 10 scale model, placed within identical outdoor conditions, were undertaken. Several scale model parameters were modified in order to determine their impact on the performance assessment, comprising the accurate mocking — up of surfaces reflectance, the model outdoor location, as well as the photometric sensors properties. This experimental study showed that large ranges of discrepancies between daylighting performance figures assessed in both ways can occur, some of them being even caused by slight differences of surfaces reflectance and photometers cosine responses. These discrepancies can be curbed down to a 20 % relative divergence, providing that enough time and effort is spent to mock-up the geometrical and photometrical features of the real building.

Keywords : Daylight factors, work plan illuminance, scale models, experimental errors.

INTRODUCTION

Daylighting contributes in essential way to buildings atmosphere and visual amenity of inhabitants. It is generally preferred to electric lighting, offering simultaneously a visual access to outdoor and contributing to sustainable development through displacement and saving of electricity into buildings (IEA, 2000). Scale models represent a standard method for the assessment of daylighting performance in buildings (Schiler, 1987), over passing computer modelling for certain practical daylighting design (Compagnon, 1993). They are usually used to mock-up real buildings and placed within sun and/or sky simulators to proceed to the assessment of their daylighting performance (Michel et al, 1995). Recent studies however pointed out their general tendency to overestimate work plane illuminances and daylight factors in comparison to the figures observed in real buildings.

The main causes of these inaccuracies were identified by former authors (Love and Navvab, 1991), as due to inappropriate model details construction, such as window frames and surfaces reflectance, leading even to parasitic light into the scale model; the calibration of photometric sensors, as well as their size, levelling and placement in the model, were also mentioned as a source of experimental errors. A more recent study

(Cannon Brookes, 1997), confirmed the former one, pointing out other physical factors, such as building maintenance and dirt, as contributors to these discrepancies.

In order to carry out a detailed analysis of the physical parameters responsible for the overestimation of daylighting performance of buildings in scale models, a comparison of illuminances and daylight factors, monitored within a 20 m2 single office room equipped with side lighting windows (a test module) and its 1:10 scale model placed within identical outdoor daylighting conditions, were undertaken. Moreover, the photometric sensors features, which were used in the test module and in the scale model, were compared. The principal causes of the performance overestimation were identified through this comprehensive experimental study : their understanding should lead to the elaboration of more appropriate roadmaps for architects and lighting designers in their assessment of daylighting performance in buildings.

The error we are interested in is the error in the maximum power absorbed. Figure 7 shows that for a two pane window where the outer pane is a grey 4 mm float glass and the inner pane is a clear 4 mm float glass, the largest values for absorbed power is in the interval 20-30°. In that interval, we have shown that the Angular Variation Model is more accurate than the other two models.

As with the maximum absorbed power analysis (Figure 2), a selection of three panes serves as examples. The three figures 7-9 show that the largest absolute errors are found in the interval 60-80°, depending on what model is used and what pane is examined.

Figure 7 shows the error in the absorptance in the outer pane of a double pane window where the outer pane has a thin silver layer (Ag+) on the inner side of the outer pane.

Figure 7 Absolute error in absorbed power versus angle of incidence for the outer pane in a double pane window where the outer pane has a thin silver layer (Ag+) on the inner side of the outer pane. The errors are shown for all three models and for four orientations for each model.

Figure 8 shows the error in the absorptance in the outer pane of a double pane window where the outer pane has a thin stainless steel and nitride layer (SsTiN) on the inner side of the outer pane.

Figure 8 Absolute error in absorbed power in the outer pane of a double pane window where the outer pane has a thin stainless steel and nitride layer (SsTiN) on the inner side of the outer pane versus angle of incidence. The errors are shown for all three models and for four orientations for each model. Figure 8 shows the error in the absorptance.

Figure 9 shows the error in the absorptance in the inner pane of a triple pane window where both the outer and the inner pane have a thin silver layer (Ag) on the inner and outer side, respectively.

Figure 9 Absolute error in absorbed power absorptance in the inner pane of a triple pane window where both the outer and the inner pane has a thin silver layer (Ag) on the inner and outer side respectively versus angle of incidence. The errors are shown for all three models and for four orientations for each model. Figure 8 shows the error in the absorptance.

Figure 9 shows a pane in a window suited for cold climates, like Stockholm. Most of the power absorbed by the inner pane in a window eventually continues into the room and helps heating it. Figure 9 shows the absolute error in maximum power for different incidence angles in the inner pane of a three pane window where the outer and inner panes have a thin film silver layer and the middle pane is clear. Therefore the absorptance in the inner pane is more interesting for energy balance calculations of the room. Figures 7 and 8 show windows suited for warmer climates, solar control windows. Their coatings are "tuned” so that they not only reflect the radiant heat from the surrounding, but also the near infrared heat in order to minimize the need to use air conditioning [2].

When we went through the 62 tested panes, we noticed that the largest errors in maximum power absorbed generally occurred in the outer glass, a pattern that is also present in Figures 7-9 in this report. When studying the energy balance of the room, though, the amount of irradiation absorbed in the inner pane is more relevant.

All extreme values shown in table 2 occur when the window is facing the west. In eight cases the incidence angle was 30° and in one case 20°.

Conclusions

From the 62 panes in the 27 windows we studied, it can be seen that the largest errors typically occur in the outer panes.

The Angular Variation Model gives smaller errors in absorbed power than with the other models. This is not least the case for the ten worst approximations, as can be seen in Table 1, where the errors with the Angular Variation Model are smaller and more evenly distributed. The errors with the Angular Variation Model is on average 0 for the ten worst cases and the standard deviation of the error for these ten cases is 2 W/m2, whereas the average error for the ten worst cases with the Constant Value Model is -7±4 W/m2 and for the Clear Pane Model 11±3 W/m2.

The main disadvantage with the Angular Variation Model compared to the other two models is that one has to know to which of the 27 window categories the window belongs. When that is known, however, this model is better than the other two presented alternatives.

[1] A. Werner, A. Roos, Trying to find an approximation of the angle dependence of the solar absorptance of a window pane, in proceeding from the conference CIB, Toronto, May 2-5 2004.

The implementation of the commercial buildings programme has so far resulted in a number of innovative new commercial buildings, including among others, the following:

"Supermarkt Pfeiffer":

First passive house supermarket with a 7 kWp facade integrated and a 20 kWp roof mounted PV system. The energy efficient cooling appliances consume 30% less energy.

"Christophorus Building":

Innovative 3 floor passive house office building in timber construction using only environmentally friendly building materials and including a 10 kWp PV plant.

Company Building "SchloBgangl":

First certified passive house company building which consumes only 10% of the energy of comparable buildings. PV and solar thermal installations are included, for transport biofuel is used.

Company Building "Einfinger":

New building for a locksmith’s including 180 m2 facade integrated solar thermal collectors, 47,700 l buffer storage, a 5 kWp PV plant, a PV foil at the flat roof and a biofuel CHP plant.

Sebastian Herkel, Jens Pfafferott

Fraunhofer ISE, Abt. TOS, HeidenhofstraKe 2, D-79110 Freiburg, (0761) 4588-5117 sebastian. herkel @ise. fhg. de

Due to high internal and solar heat gains, office buildings are at the borderline between active and passive cooling. If the heat gains are minimised, they can be counterbalanced by passive cooling during the nights. Due to the building’s thermal inertia, heat gains and heat dissipation can be decoupled and the building provides comfortable room temperatures without an energy demand for active cooling. This paper focuses on the data analyses in three low-energy office buildings, gives hints on the building design and shows limits of passive cooling concepts.

Introduction

In the framework of the German funding Programme "Solar Optimised Buildings” [1] of the German Ministry for Economics and Labour, the Lamparter building [2], the Pollmeier building [3] and the Fraunhofer ISE building [4] have been monitored for 2 years. These long-term monitoring campaigns were complemented with short-term measurements. In summer 2002 and 2003, experiments were carried out to determine the thermal behaviour. During the experiments, meteorological data, air change rates, air temperatures, surface temperatures, and operative room temperatures were measured.

Fraunhofer ISE Pollmeier Massivholz GmbH Hans Lamparter GBR

Freiburg, 2001. Creuzburg, 2001. Weilheim a. d. Teck, 2000.

The studied building is an energy efficient monozone building, used for experimental works, recently constructed at the Plataforma Solar de Almeria, located in a sub arid Mediterranean climate in South Spain (latitude 37° 03, longitude -2° 23, altitude 404 m) (see Figure 1). The house is free of nearly obstacles and with a clear view in all directions. Its plant area is 32 m2 and its volume is І16 m3. Figure 2 shows the building plant and its orientation.

Figurel: Photograph of the building.

Implemented techniques to reduce the energy demand both in hot and cold seasons are: appropriate orientation, door and windows shading devices designed to obtain shading that reduce solar gain in summer and increase it in winter, double glazed windows, diagonally faced window for natural cross ventilation, ceiling and external walls well insulated, internal thermal inertia with exterior insulation, high ceiling, white outside surface, protection of main wind directions, possibility to use roof surface evaporative cooling system.

The building walls composition are presented in Table 1. The floor and ceiling are described in Figure 3 and 4 respectively

Windows north and south area is 2.25 m2, they have double glass 4/6/4 and aluminium frame. Door, 0.6 пП area, is made from aluminium with a 75 x 75 cm2 double glazed window 4/6/4.

The value of the optical transmittance in the range of the visible light 380-780 nm has been performed on different types of modules.

Due to the inhomogeneous nature and the presence of different materials, e. g. glass, EVA, the cell itself, it has been not very simple to get the value of transmittance. We prepared a methodology of measurements that has proved to be useful within the error given by the lighting project, that is less than 5 %. Details of the methodology can be found on a paper presented at the PVSEC conference in Paris 2004 in June.

Different kind of modules were considered and the figures shows the corresponding measured transparencies, depending on the bulk transparency of the materials used for the sandwich glass/EVA/glass, the density of the cells, that means the spacing, and the kind of module ( a double glazing module was also considered). The transmittance values for the transparent part of the modules is just a bit lower 90 %, a part the double glazed modules where it falls at 73 % due to a not very transparent encapsulant layers, fortunately not effective on the cells. Depending on the density of the cells, the ratio of the active area divided the module area, the transmittance of the components can change consequently.

The table 1 below shows some values of the optical transmittance