Kathe Hermstad, m. arch,

SINTEF Civil and Environmental Engineering, department of architecture and building technology, 7465 Trondheim, Norway, Web: www. sintef. no Phone: (+47) 40454620

Introduction:

Smartbuild is a six-year strategic research program performed in collaboration by SINTEF and the Norwegian University of Science and Technology, NTNU. This paper is based on the work of sub-task 2.4 — "Building Integrated Photovoltaics". The intention of this sub-task is to strengthen Norwegian research, education, and industry within the BIPV field. The long term aim of the project is developing new BIPV concepts, both for new use of present product lines and for development of new products.

The paper summarizes the first phase of the project. An analysis of trends in office building design and implications for photovoltaics is followed by a presentation of the office building “Pynten” in Oslo. The building forms the platform for evaluating different PV concepts.

Office building design trends and photovoltaics

Successful green buildings have relatively low life-cycle costs, provide healthy, safe, and inspiring work environments and communicate a valuable philosophy. Many companies insist on and pay well for facilities in such buildings, which give the building owners an advantage in the real estate market. Along with all its technological and environmental advantages, photovoltaics (PV) can be one of the most expressive technological solutions in terms of flaunting an environmentally conscious building profile, an asset that helps promoting the buildings to prospective tenants.

In the increasingly competitive and global markets, companies spend much effort on their image. The modern, holistic company profile is comprised by its physical, aesthetical, and cultural capital. The two latter are becoming progressively more important, as they can transform and relate to the market with more ease, and thus better communicate a company’s values. Many companies change locations on a regular basis, as an incentive for corporate culture change or as a part of restructuring. Thus they need a range of facilities that support their environmental profile or technology that can transform the physical profile of new locations with a poor environmental profile. This nomadic corporate culture is likely to embrace technology for retrofitting that has a relatively short payback time or can be transferred to new locations/sold as a second hand product. PV systems still have relatively long payback periods, but increasing production is lowering prices. Simpler systems for retrofitting, with "click-on” features and long lifetimes, make them feasible for moving or reselling.

Today’s companies need facilities that sustain their core activities, and support activities are increasingly outsourced to make the companies more focused and agile.

The shift of companies from building owner to building user is a step in this direction and has given new structures in office buildings in terms of technical infrastructure and the service organisation. Micro-urbanism, with building sectors referred to as neighbourhoods, streets, squares, and public facilities, is one example of the new internal structuring. The common areas are often used to express a building’s “green” profile, and larger installations often appear here. This separation between “public” and “private” is often
elaborated in the fagade. The openness of the public domain is often articulated with large glass surfaces, which again create a need for shading. Photovoltaics (PV) are often used as solar protection in arrays playing with daylight through shadow patterns, colour, and materiality. Although PV is presently a relatively expensive material, its value can extend beyond power production. Building integration and symbiosis with building service is lowering the excessive cost of PV to more acceptable levels. The perception of what building integration comprises, widens constantly.

Although the aesthetics of architecture is interpreted in relation to its use, the exterior and interior of large buildings have complex relations and, to some extent, become separate projects. The built structure and underlying service facilities is designed to adapt to its content and not vice versa, as work methods, users, owners, and the exterior environment is constantly changing. A building may be redefined and restructured several times during its lifetime and modern commercial rental buildings usually maintain their initial internal structure for only 5-10 years. The concept of honest facades thus becomes somewhat hollow in a lifetime perspective. This makes way for new structures that incorporate change as an elementary function and aesthetical ideal. Interactivity, mobility, and layers along with new materials and technology meet in future facades. pV is a natural part of this development, and the material still faces many unexplored conceptual opportunities.

Space planning has evolved from the rigid structural grids and the transformable "typical plan” to modules of complex geometry, often in three dimensions, that create unexpected interior and exterior environments. The move towards more chaotic space structures evolves from aspirations to stimulate creativity and knowledge flow in the organisation through random social interaction. Large structures are necessarily depending on modularity, and the new, more complex modules can introduce natural breaks between work zones for these activities. This can also introduce new aesthetical themes for facades and interiors, as different demands in terms of fagade integrated service for the interiors form new design parameters. The hype towards complex module geometry and three­dimensional surfaces offer many challenges to the PV-industry that mainly produce flat, rectangular modules.

Modern office building envelopes have tasks beyond climatic protection, and provide an increasing number of services to the interior climate. The active envelope changes its properties according to interior preferences and exterior conditions. It supplies fresh air, regulates temperature and lighting, and generates electricity. This organic understanding of the facades is supported by technology increasingly inspired by nature. With a holistic understanding of the service facilities, the bi-products earlier regarded as problems become valuable resources. An example is the excess heat from PV that should be transported away to maintain high power production in the cells.

Safety is becoming increasingly important in office and industry facilities, and buildings are becoming more and more automated with electronic security measures. The buildings are becoming more and more dependant of a minimum access to power to maintain its basic safety operations. The attention on security of basic energy supply is increased through a number of recent electric blackouts in large urban areas several places in the world. In this context, PV stands out as an elegant solution to sustaining security measures.

The presently most successful PV products for office buildings are modules for roof mounting and PV integrated in glazing for atriums, skylights and in double facades. PV has often been given tasks of shading and of enhancing natural air flows through their temperature accumulation. PV has also been successfully integrated in walls, although this
is demanding in the modern more fragmented expressions of office buildings. Some fixed solar shading devices with PV integrated in glazing have become popular for public zones, and some of these products offer certain mobility within the module for better adjustment to the sun. The first mobile elements are out in the market now, and integration with control systems may offer a new control dimension to the work place and dynamical facades. The mobile elements can further become part of the heating and ventilation system and integrate intelligent fagade structures further. In the future, new technology like organic PV opens for a number of new product opportunities.

To constitute a frame, the discrete wavelet transformation generated by sampling the wavelet parameters (time/scale) on a grid or lattice, not necessarily equally spaced, must satisfy the admissibility condition; and, lattice points must be sufficiency close satisfy basic information — theoretic need. The family of basis function {ha, b(t)} with a, b є Z is said to be a frame if it satisfies the property that there exists two frame bounds A>0 and B<<x Where A, B are independent of f(t) such that of all the functions

he L2(R), the sum of square moduli of Wj(a, b) must be between the two positives bounds:

2

(5)

a, b

Recently, a class of frame wavelets has been introduced for its simplicity and availability that suits adaptive processes, particularly in a neural network architecture [15].

The present model was used to solve the analytical problem of specification of the composition of products of photo-decomposition of the operational laser substance generated by solar-pumped laser.

Previous specification of the concrete reaction channels and cross-sections of these channels had been studied insufficiently. To provide the analytical process a computerized facility for chromatic mass spectral analysis of the mixture of photo­organic products was developed on the basis of mass spectrometer and chromatoscope. .

The products generated at photo-chemical reactions accompanying operation of the iodine laser were analyzed. One of the perspective for PDISPL compositions, namely i-C3F7I, was chosen as the operational substance.

Fig. 4 presents the example of identification based on the standard method for one of the chromatographic peaks of the sample taken from CCS of the operating PDISPL using mass spectrometric method. Beside the identified product of photolysis, C3F6, the analysis reveal presence of such the compositions as C2F5I and the like.

Consequently, the products of photo-decomposition of the iodine laser active medium contain the compositions, presence of which can not be explained by the simple kinetic scheme (1 — 6). The reason for this, as we see it, is the ignored in this set distribution of photon energy in the initial photo-dissociation act. The thing is that the fragments formed in the course of process 1, possess the initial energy of ~ 2.5 eV, distributed between them according to different levels of freedom. That is why in the first after the initial act collisions the additional reaction channels are probable:

R+RI ^ products I+ RI ^ products.

The concrete reaction channels and their cross-sections are determined by the construction of the initial radical R. In further studies we plan to specify these dependencies. This job is envisioned as one of the important constituents of the process of specification of usefulness of this or that composition for the concrete PDISPL concept.

The basic idea behind the concept of silicon-heterojunction is the formation of rectifying junctions by deposition of thin-film silicon onto crystalline (monocrystalline, multicrystalline) silicon wafers or ribbons (called substrates in the present paper). The substrate can be either p — or n-type, and the silicon deposition may be applied either to one or to both of its surfaces. An example of an SHJ structure based on an n-type substrate is shown in Fig. 1

In the case of a p-type c-Si substrate, the structure is similar except for the realisation of the back contact. Here, the formation of a p-p+ homojunction for higher-efficiency devices is always achieved by depositing aluminium and subsequently sintering in order to allow the partial diffusion of aluminium atoms into the lattice. In fact the back contact in solar cells based on p-type crystalline silicon, cannot be realised by means of a heterojunction p-type c-Si / p-type a-Si:H. because the high valence band offset between p-type crystalline silicon and the p-type amorphous silicon severely reduces hole collection at the rear metal contact. This is reflected in a lower quantum efficiency and, consequently a lower short circuit current3

Not depending on the selected n — or p-type substrate, the reasons to develop SHJ instead of diffused-emitter cells lie in a number of advantages4 derived from the combination of features of thin-film and wafer technology, i. e.:

v A simple structure. No particularly cumbersome step is involved in the fabrication process.

v A low-temperature process. The process is simple and cost-effective. Since sample temperature does not surpass 200-250°C, the degradation of minority-carrier lifetime in the substrate is negligible, even for low-quality substrates. This feature is essential for the use of new-generation silicon materials.

v Surface passivation is concomitant with junction formation. The insertion of a very thin intrinsic layer in the interface is a very powerful tool for passivation and, therefore, for reducing interface recombination. Experimental data have shown that intrinsic amorphous silicon is more effective than silicon dioxide or iodine methanol in achieving silicon surface passivation4. Surface recombination velocities below 100 cm/s have been reported.

v A BSF (back-surface field) structure is easily created in the fabrication process. This is an additional consequence of the excellent passivating properties of intrinsic amorphous silicon.

v Stable cells. The Staebler-Wronski effect is not seen in SHJ cells5. Since the cell absorber is crystalline or multicrystalline silicon, the mechanisms involved in the Staebler-Wronski effect are not applicable.

v Improved high-temperature performance. The temperature coefficients of SHJ cells are smaller than those of diffused-emitter devices. Since actual operating temperatures (between 35 and 40°C) lie well above the reference ones (25°C) this feature represents an enormous advantage in practical applications.

v Easiness to define emitter thickness very accurately. This allows to use thin new — generation substrates without the risk of unwanted diffusion of dopants into the absorber.

These advantages would be meaningless if the cells were limited in performance, but this is far from being the case. Sanyo has reported SHJ-cell efficiencies of 21% for devices being 100 cm2 in area6.

PV system planning for stand-alone requires the over sizing of the PV field and of the battery pack capacitance in order to guarantee sufficient electrical power for the operation of electrical load in the periods of low solar irradiation, but this leads to an increase of the cost of the kWh as regards the one produced by a grid-connected PV system.

The size of the PV systems for island applications is calculated balancing the electrical power absorbed from loads with solar energy incident on the PV modules converted in electrical power.

(1) Ec = Agmin x H x ng

Ec = daily electrical power absorbed from consumers in Wh/day

Agmin = minimal area of the PV field in m2 H = daily global solar irradiation in Wh/m2/day ng = efficiency of the PV plant

For traditional stand-alone PV plants, a tilt of 60° of the plane module array is the best choice because in this condition the daily solar irradiation is more constant during the year.

Instead, for the hybrid PV-Fuel system, a tilt of 40° of the plane module array is the best compromise in terms of yearly availability of global solar irradiation and of constancy of daily global solar irradiation; in fact we have that:

— yearly availability of global solar irradiation is quite close to the one with the Average monthly of daily global solar irradiation modules array tilted of 30°; in Manfredonia, calculated for different tilt planes

— in autumn and winter the

daily global solar irradiation is quite close to the one with the modules array tilted of 60°.

To determine PV field size for island applications, in (1) it has been placed:

— for classic PV system, H = lowest value, corresponding to the month of December;

— for hybrid PV-Diesel system, H = annual medium value.

The load has been chosen so that the maximum engaged power does not exceed too much the 3 kW and so that the daily medium consumption of energy is of approximately 7 kWh, approximately corresponding to 2500^2600 kWh/year, standard value for typical domestic user.

The capacitance of the battery pack is calculated by the expression:

(2)

Qb = Ecmax x Nga / nbx DOD

Ecmax = maximum daily energy absorbed from electrical load in Wh/day nb = battery efficiency, typical value is 80%;

DOD = Dept Of Discharge, maximum discharge level to avoid battery damaging, typical value is 80%;

Nga = lack of sun irradiation in days.

To determine the battery capacitance, it has been placed in (2):

—

for classic PV system Nga = 5 days;

— for hybrid PV-Fuel system Nga = 1 day.

On the basis of the local global solar irradiation and typical daily domestic user power demand, it has been planned and realized a hybrid PV-Fuel system in Manfredonia with:

— two PV systems of 20 PV modules each for a total installed nominal power of 2 x 1024 Wp, angle of tilt 40°, two inverter Sunny Boy 850 of the SMA;

— bi-directional converter Sunny Island 3300 of the SMA;

— battery pack of 30 storage elements with capacitance of 250 Ah/2 V each;

— electrical generator of 5 kVA, one phase, gasoline feeding;

—

data acquisition and plant monitoring with Sunny Boy Control Plus of the SMA.

Using the electrical generator as a backup power supply to balance the difference between electrical consumers demand and monthly average of daily solar irradiation, it has been obtained in comparison with a classic system:

— a reduction of approximately 38% in the size of the PV field;

— a reduction of 80% in the capacitance of the battery pack;

— an increase of the electric power continuity in presence of numerous and uninterrupted low solar irradiation days.

The architecture of the system, represented in the previous figure, allows us to shape it in two ways:

— hybrid PV-Fuel system in stand-alone: the Sunny Island has the task to support and to control the grid for the operation of the PV systems and manages electrical consumers, the battery and the external power supply;

— PV system in grid connect: in lack of mains voltage, the Sunny Island has still the task to support and to control the grid for the operation of the PV systems and behaves also as backup power supply.

All the devices, inverter, power supply and electrical consumers, for the presence of the Sunny Island, interface directly on the stand-alone to industrial voltage and frequency increasing flexibility in comparison with a classical system.

The experimental activities performed on the realized system have produced numerous data useful to optimize the system sizing as a function of fuel cost, and to confirm cost reduction of installation and management estimate in planning.

Using six stress factors for the categorisation process and indexing them according to their intensity makes it easy to assign a RES to a certain category using very simple software. The intensity level for each stress factor has to be given as input and the correct category will be assigned. This, obviously, is a much simpler process than matching a number of time series as regards their similarity. The automatic assignment of a RES to a category is not only possible for RES for which measurements exist, but also for planned RES for which only limited data or the results of simulation software with a sufficient level of detail and time resolution exist.

For each category, recommendations will be given which describe design options, operating strategies and criteria for selecting the most appropriate product for a specific category. The most appropriate product is characterised by the most economic lifetime which, in most cases, is likely to be equivalent to the longest lifetime. Lifetime tests are therefore required, however, some existing lifetime tests for which there are readily available test results have only limited relevance to any of the six categories described above. It is therefore necessary to define those test procedures, which have the highest importance as regards RES, and rank them in their relative importance. Some of the most suitable test procedures are those investigated as part of the Qualibat project /7/.

Conclusions

The results of the project show that it is possible to evaluate measured data of existing RES or simulation data of planned RES automatically and generate detailed recommendations which take the conditions of use into account.

The results of the project will be freely accessible to the international business, technical and scientific community.

• Manufacturers will receive information on the performance requirements that their products have to fulfil for certain categories of use and how best to test them.

• Users and planners of renewable energy system will gain access to a software which will help them to identify the category of use which is most closely related to their own specific installation. They will also obtain recommendations on a wide range of topics, in particular how to select the most suitable components for their application.

Acknowledgement:

The work presented here is the result of the project Benchmarking1".

t „Benchmarking — Development of test procedures for benchmarking components in renewable energy systems applications, in particular energy storage systems". A project carried out by nine major European Research Centres, the Australian Cooperative Research Centre for Renewable Energy and the National Renewable Energy Laboratory in the USA. The project is supported by the EU under the 5lh Framework Programme (ENK6-CT-80576).

Literature

/1/ Standard Evaluation Report; Public deliverable of the Benchmarking project,

deliverable D1.2a by Adolfo Perujo, Joint Resserach Centre Renewable Energy Unit, ISPRA, available at www. benchmarking. eu. org/Publications/Publications. htm or any of the Benchmarking project participants.

/2/ Specification of Minimal Requirement of Measurement Procedures; Public deliverabe of the Benchmarking project, deliverable D1.1 by Ian Baring-Gould, Nationa Renewable Energy Laboratory, USA, available at

www. benchmarking. eu. org/Publications/Publications. htm or any of the Benchmarking project participants.

/3/ ThEsA (Technical Hybrid Energy System Analysis); Public deliverable of the Benchmarking project, deliverable D1.2 by Fraunhofer Institute for Solar Energy Systems, available at www. solar-monitoring. de/ithesa/ Password and Username ITHESA

/4/ Sauer D.-U., Bachler M., Bopp G., Hohe W., Mittermeier J., Sprau P., Willer B., Wollny M.: What happens to batteries in PV-systems? Costs, lifetime, Strains; Paper presented at LaBAT 96, Varna, Bulgaria, 1996

/5/ Categorisation of batteries in RES applications; Public deliverable of the Benchmarking project, deliverable D2 by Vojtech Svoboda, Zentrum fur Solartechnik und Wasserstoffforschung, Ulm, available at

www. benchmarking. eu. org/Publications/Publications. htm or any of the Benchmarking project participants.

/6/ Svoboda V.: The influence of fast charging on the performance of VRLA batteries;

Ph. D. dissertation thesis, Brno University of Technology, 2002

/7/ Qualibat, Investigations for a Quicker Assessment of Liefetime and other key

characteristics of photovoltaic BATteries; Publishable final report by GENEC, project funded in part by the European commission in the framework of the Non-Nuclear Emergy Programme JOuLe III, contract no. JOE3-CT97-0161

In the first configuration 6 modules distributed inverters were parallel connected. Figure 1 shows the measurements points A and B, where the background level have been determined, before making the measurements. The AC module inverters marked with letter A are referred in table 2 while those indicated with B refer to table 3.

The measurement at the cable LISN (point A, power delivery), refers to the open circuit test without the PV plant connected, figure 2.

Figure 2. Spectrum revealed at point A in figurel.

The signals in figure 2 around the marker between 10 and 30 MHz are found to be radio stations with the peak set at 21.3 MHz

The measure at point B with the PV plant connected to the DC part defines the background threshold, to be used as reference for the successive measurements. Figure 3 shows the optimal situation for the background threshold after making some adjustments to improve the layout of measurement.

Considering all the uncertainties of a measurement in a pre compliance procedure, we can assume the following considerations.

From the examination of figure 3 it seems that the background noise overcomes the limit line of the average value. The spectrum of the analyzer reports the behavior of the peak values and average. The EMC standard refers to the conducted limits in terms of quasi­peak and average value. The measurements are to be compared with the corresponding detectors.

In practice at first a fast measurement is performed, with the detector in the all range of frequency and then the points in which there was recorded the overflow are analyzed more carefully; only for those signals the measurements with the quasi peak detector and average values are made for the comparison.

As results from the table 9, reporting also the highest values, the quasi-peak values and the average values of the measurements are below the levels set by the standard EN 55011 (the signal at 7.199 MHz is very close to its limit value of 46 dB p. V), respectively listed in tables 7 and 8. Anyway demoduling the same signals we found they were radio station signals, so unavoidable during the measurements.

So we can conclude that the electromagnetic background interferes with the PV system but with values below the referring standard.

Figure 4 reports the measurements of noises with the facade plant in operation. Each module is connected to its own inverter.

The plant presents 3 modules connected to the 3 type A module inverters and other 3 ones connected to the type B ones. All inverters were parallel connected. The power was of 206 W AC side.

Examining more carefully the figure 4 it results that the limit lines are both overcome by the peak values when the waiting time was set at 3 minute in several frequency ranges. During the measurement the max hold function reports only the maximum values during a preset interval.

By looking in the ranges of frequency were there were the highest values, 4 more representative values are selected, so obtaining the table 10. In correspondence of the

frequencies 4.66743 MHz and 6.93344 MHz, even if just a bit, there is the overcoming of the limit values in term of quasi peak and average values.

Successively conducted emissions related to other configurations have been measured; in particular the inverter type A and the type B have been analyzed.

Configurations with 3 and 1 inverters have been compared and figures 5 and 6 refer to the case with the AC module inverter type В respectively.

These configurations comply with the Standard within all the frequency range from 150 kHz to 30 MHz, where all the signals present values of quasi-peak and average below the maximum, and even for those whose values overcome the average curve, as reported in table 11.

Figures 7 and 8 refer to the case of type A module inverters.

In these cases the limit values are just a bit lower. That happened for the signal at 4.2925 MHz in the case of 3 inverters and for the signal at 6.78 MHz for the one inverter, as shown in tabs 12 and 13.

From the comparison it results that the type B module inverter complies just a little more with the standard, respect to the type A, even if the differences are not so impressive.

The last case refers to the configuration where all the modules are series connected and connected to only one inverter, referred at table 1, as results from figure 9.

Figures 10 and 11 show the measurements respectively with the plant not in operation (open circuit), and in operation at power of 216 W.

From the figure 10 it results a threshold background more than acceptable, namely the 6 dB of attenuation are respected within all the measurements, since the highest values refer to the broadcasting radio stations.

From the figure 11 it results that the plant complies with the limit curve of the quasi-peak values while for the average level some doubts arise in the low frequency part between 150 kHz and 400 kHz.

Table 14 shows the measurements of two of the more representative signals within the remaining interval, highlighting that they are largely below the considered limits.

Conclusions

Considering the not ideal conditions the measurements have been performed and the precompliance nature of them, it should be said that the revealed conducted emissions could reasonably comply with the Standard EN 55011, and so in all the configurations. So the supply of power from the PV facade to the grid happens in respect with the standard rule.

The configuration with only one inverter is more conservative respect to the diffused inverters case. For those the module inverter type B revealed just a bit less interfering of the inverter type A.

The measurements have showed that if there is an important background level, some signals can be captured from the PV plant, specially if long cables are present and particularly if they are put inside the buildings.

Those signals can travel along the cables of the electric wires in the buildings and acting as noises on appliance sensitive to the same frequencies.

From that it follows that the PV plant should be carefully designed in term of geometry and the frequencies of the transmitted frequencies should be analyzed.

This has been the first analysis and new surveys on existing BIPV applications are needed to be performed so to give answers to the following questions:

— what about the power size?

— what about the different responsiveness to the irradiance levels?

— what about the inverter types and configurations?

— what about the geometry?

Genetic algorithm has been used to optimize the MIS/IL solar cell parameters by changing the device physical parameters namely, doping concentration NA, oxide thickness dox, metal work function external back bias on the inversion grid V, mobile charge density Nm and fixed oxide charge density Nf [12]. Binary encoding scheme is used in this algorithm to encode the MIS/IL solar cell parameter [13-14]. The chromosome contains all parameters as shown in Fig.3. Each gene parameter encoded as 4-bit to include sixteen quantized values, as shown in Fig.4, and eight populations are selected to be greater than the number of genes per chromosome. Elitism is used to save the best solutions to improve the performance of the genetic algorithm [14].

The algorithm is started with a set of solutions (represented by chromosomes) called population. Solutions from one population are used to form a new population. This is motivated by a hope, that the new population will be better than the old one. Solutions which are selected to form new solutions (offspring) are selected according to their fitness. The more suitable they are the more chances they have to be reproduced. This is repeated until some conditions (for example number of populations or improvement of the best solution) is satisfied. The genetic algorithm proceed as follows, [13]

(1) Create a population of random individuals which represents a possible solution to the problem at hand.

(2) Evaluate each individual fitness i. e. its ability to solve the specified problems.

(3) Select individual population members to be parents.

(4) Produce children by recombining parent’s material via crossover and mutation and add them to the population.

(5) Evaluate the children fitness.

(6) Repeat steps (3-5) until a solution with the desired fitness goal is obtained [15-16]. The genetic algorithm flow chart of the optimization problem is shown in Fig.5.

Beside the definition of the system properties and system planning, modeling was carried out to investigate the planned system. As because basically two different subsystems were planned, the simulation was carried out for each of them. The simulations study of was elaborated using the Nsol simulations software.

The principal elements of the process are:

— indication of the applications site,

— selection from the database the principal insolation data,

— and the produced energy data.

The next steep is to set the hardware properties and the indication of the electrical system parameters like system voltage DC or AC and the used inverter type. As because of the software the equipment database is elaborated mainly for USA use but the data base of the program was possible to extend with the properties of the planned panels, as well.

After the simulations process information can be obtained about the system behaviour, and the energy balance. All the data can be evaluated in graphically and table form, as well. The simulations results for the ASE-100 and the DS40 subsystems are presented.

First the insolation analysis of the proposed site was modelled, the results are shown in Fig. 5.

From the insolation data the power generated by one panel and by the subsystem was estimated first by use of the software. The results for the ASE-100 subsystem are presented in Fig. 6. and 7.

Finally, the energy production of the whole system was calculated in monthly distribution. The results of this calculation can be seen in Fig. 10.

Conclusions

In the paper the planned 10 kWp grid-connected PV system set-up, the hardware configuration and the modelling of the energy production of the subsystems are presented.

In the first part a detailed analysis of the selection of the location is presented with the pros and contras of the selected sites.

The simulations results of the PV grid-connected system provided data series which can be used of the evaluation of the real behaviour of the system. The simulated data can be compared with the measured ones, collected by the data acquisition system.

Acknowledgement

The research was carried out in the framework of the PV Enlargement (EC, NNE5-2001- 00736), the TET RO-11/2002, the OTKA T-042520 and the KAC F-17-03-00011 projects.

a. Analog Input Unit. Is constituted by two different types of devices. One of them consists of FP analogue input modules, which filter, digitalize, calibrate and scale raw sensor signals to engineering units.

The second one is a high-speed analogue-to-digital (ADC) conversion card. The FP modules are used for measuring signals at low sampling rate whereas the card is used for measuring signals which require to be captured at high rates. The analog input unit includes the following devices:

■ Module FP-TC-120: Filters the input signal by removing 60 Hz noise. A high-accuracy, 16 bit resolution ADC, with an ultra-stable voltage reference and built-in calibration circuit digitalizes input signals. It also provides cold-junction compensation.

Additionally, the device has the following technical features.

S Eight thermocouples or milivolt inputs.

S Four voltage ranges: ±25mV, ±50mV, ±100mV,-20 to +80mV S Update rate: 0.8 s.

у Offset error: 3|jV (in the minimum used range)

The FP-TC-120 module is used to measure the signals coming from the radiation/temperature sensor and from the DC current transducer.

■ Module FP-AI-100: This module is suitable to monitor milivolt and volt inputs from a variety of sensors and transducers. This module has the following technical features:

S Eight analog voltage input channels.

S 11 input ranges: ±15V, ±5V, ±1V, 0-15V, 0-5V, 0-1V.

S 12-bit resolution

S Update rate: 2.8 ms

S Offset error: 1.1mV (in the used range)

■ NI6024E Card: Is used to monitor the signals coming from the IAC and VAC transducer and the IDC and VDC signals coming from the I-V characteristic Unit. This board is also used for harmonic analysis of the AC signal generated by the DC/AC inverter. The board has the following technical features:

S 16 analog input channels.

S Voltage ranges: ±50mV, ±500mV, ±5V, ±10V.

S Sampling rate: 200KS/s S Update rate: 10 KHz. f Output voltage range: -10 to 10V.

b. Interface unit: Is constituted by the network communication FP-1000 module, which connects the Field Point I/O modules directly to the PC RS-232 port, and the NI-6024E Board which connects its analog input directly to the PCI port.

The FP-1000 module manages communication between the host PC and the I/O modules at a maximum rate of 115.2Kb/s via local bus formed by Field Point terminal bases.

The configuration of all hardware of the Field Point modular distributed I/O system and of the NI-6024E data acquisition board is made by software. The Field Point Explorer and NI — DAQ software are used to configure the FP-1000 system and the NI-6024E board respectively.

c. Unit for I-V Measurements. The monitoring system includes a unit by which the I-V characteristics of the PV-Generator can be obtained through a special design of the measuring circuits. The current and voltage measurements can be made at high sampling rates, allowing the achievement of the entire I-V curve in a short time (less than 5 sec); the fast achievement of the I-V characteristic is convenient to prevent cloud interference during outdoor measurements.

The PV current-voltage measurements are made varying the load of the PV generator, keeping it under illumination. During the time in which the load is varied, the operating point of the PV generator changes, allowing the current and voltage points to be captured along the I-V curve.

The principle of operation is an electronic load connected in parallel to the combination of the PV-generator in series with the battery bank. The electronic load is constituted by several transistors in cascade (Darlington combination), which are connected to the parallel combination of a resistor and a capacitor.

If the transistor conducts, the battery compensates the generator current, taking the generator close to the short circuit point. Reducing gradually the transistor base current, the generator moves from its short circuit point to the open circuit voltage status. It is required from the battery to supply current of several amps (sufficient to compensate the current generated by the PV-generator) at low voltages (<12V).

The variation rate of the base current is given by the time constant of the RC circuit. The scan of the I-V curve is automatically achieved through a relay which is driven through the virtual instrument, controlling the I-V measuring process. In order to achieve a uniform sweeping through the I-V curve, the base current was linearly varied. The linearization is

achieved by changing the time constant of the RC circuit during the I-V measurement, with the help of a tool included in the Virtual Instrument and implemented with LabVIEW. The entire measurement process is controlled by computer.