17th European Photovoltaic Solar Energy Conference, Munich, Germany, 22-26 October 2001. 2736 ... energy management kits which do exhibit for instance.
17th European Photovoltaic Solar Energy Conference, Munich, Germany, 22-26 October 2001 PV LIGHTING SYSTEMS EVALUATION AND RATING METHODS (PLISE) FINAL RESULTS P. BOULANGER 1 , P. MALBRANCHE 1 ,T. BRUTON 2, A. PARSONS 2 , J.C. MARCEL3 G. MOINE 3 F. GARCIA ROSILLO 4 , U. HUPACH 5 , W. VAASSEN 5 , A. PERUJO 6, K. DOUGLAS6 1 : CEA – GENEC - Cadarache, 13108 St-Paul-Lez-durance (FR) 2 : BP Solarex, Chertsey road, Sunbury on thames, Middlesex TW16 7XA (UK) 3 : Transénergie, 3 allée Claude Debussy, 69130 Ecully (FR) 4 : Ciemat, Avda Complutense, 22, 28040 Madrid (ES) 5 : TÜV Rheinland, Am Grauen Stein, D-51105 Cologne (DE) 6 : JRC ESTI, I-21020 Ispra (IT)
Abstract This paper describes the outstanding results of the PLISE project. This project aim at setting up a rating procedure for PV lighting systems, using mainly performance specifications in addition to component specifications. A rating method of the lighting system performance would provide a standardised information to potential customers and allow an objective comparative assessment of different designs. Until now, neither overall specifications nor procedures exist which address the performances of a complete system independently of the performances of the constitutive components. Three tests have to be performed to evaluate the performance of ten European solar home systems : components tests, definition and validation of indoor procedure using both a solar simulator or a programmable DC power supplied and definition and validation of outdoor procedure. Final results are presented and allow to validate the different procedures established, providing a good comparison between all the results obtained in indoor (solar simulator or electronic PV array simulator) and outdoor conditions with data collected in the field. Key words: SHS, Qualification and testing, Performance
1. Introduction The main goal of the PLISE project, partially funded by the European Commission (DG Research), is to set up a rating procedure for PV lighting systems, using mainly performance specifications in addition to component specifications. A rating method of the lighting system performance would provide standardised information to potential customers and allow an objective comparative assessment of different designs. The additional goals of this project are: · To develop a standardised representation of system features and performance, making the procurement process easier. · During the work done for the development of the indoor and outdoor test procedures, several samples coming from different European manufacturers have been be tested. The results will be a by-product of this project. · To assess outdoor test procedures in some test centres located in developing countries, for comparison purposes under real conditions.
2. Methodology The main problem to be solved was to develop an indoor rating procedure, which can fit several system designs and must be representative enough of most weather conditions and end-user needs. The selected approach consisted of three steps: · A review of existing test procedures and standards, and at the same time, the supply of several systems, provided by the most representatives European suppliers. · The performance of three types of tests in parallel: component tests (performance of
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qualification tests for each individual component of the system), indoor system tests (testing of the completely assembled systems in a laboratory under managed conditions) and outdoor system tests (testing of the completely assembled systems in outdoor conditions). the validation of the indoor rating and test procedure and use of this procedure within the appropriate standardisation organisations.
3. System testing The first step of the project was presented in Glasgow [1]) and dealt with components results. This second and final step emphasises the overall “system approach”. Photovoltaic systems considered as a black box, is a system, which depends mainly on two variables : irradiation and load consumption. There is a gap between most of the design methods, which consider only a monthly constant consumption and a monthly averaged solar irradiation while in the field, irradiation and consumption can be considered as almost stochastic inputs. In between these two situations, the analysis of the daily behaviour of a system seems to be a good compromise. From this fact and from a large experimental campaign (issued from laboratory tests and field data), it appeared that it exists a kind of typical signature for a system. The approach we adopted to study this new signature is progressive : · at first to control irradiation and consumption (based on standardised profiles or classification) · then to control only consumption · at last to control nothing
should operate until the battery reaches Vr and then for at least another 3 days. UBC2 – Final Usable Battery Capacity Test This, the final battery capacity test, is conducted the same as UBC0. The purpose of UBC2 is to determine if the battery capacity has changed significantly after running the entire test sequence and to determine the hours of autonomy for the system. The following table summarises the main features of the kits under tests. Test campaigns started in 1999 and lasted till 2001.
Figure 1 : Principle of the procedure The procedure is divided into seven steps that aim at reproducing the complete behaviour of a lighting kit in outdoor condition, as illustrated in figure 1. This procedure is directly applicable for system with LVD (Low Voltage Disconnection) and Vr (Voltage regulation) thresholds but can be applied for advanced energy management kits which do exhibit for instance variable LVD (L “SOC” D). UBC0 - Initial Usable Battery Capacity Test The UBC0 test establishes a baseline battery capacity. With the load disconnected, the battery is charged up to regulation voltage (Vr) by the array and held there for an accumulated 12 hours. Next, with the array disconnected, the battery is discharged by operating the load continuously until the system reaches low-voltage disconnect (LVD). By knowing the UBC and the load current, the load run time, or hours of autonomy, can be predicted. CB – Charge Battery With the load disconnected, the battery is charged up to Vr by the array and held there for at least 12 hours before beginning the FT. FT – Functional Test The FT is run at least 7 days to determine if the system and load work properly under normal system operation. The load is set to operate 4 hours per night. For at least 2 consecutive days, the array should receive “low” solar insolation, £ 2 sun hours per day (1 sun hour = 1kWh/m2), to verify the load can operate from the battery with minimal array contribution. For at least 2 (not necessarily consecutive) days, the array should receive “high” solar insolation, ³ 5 sun hours per day, to verify the controller regulates the battery charge properly.
PV Kits Wp Ah Volt nb lights 2*55 2*80 24 X Siemens AC 2x12 72 12 2 Free Energy 50 105 12 4 Total Energie 100 2*105 12 4 Total Energie 45 60 12 4 BP solarex 70 140 12 4 BP solarex 50 100 12 3 Shell Solar 100 105 12 X Fortum Table 1 : Outline of systems tested For each test, a procedure was defined, measurements and results were compared to the same calculation and representation [2].
4. Indoor testing A global experimental approach on several typical manufactured products has been conducted in several conditions and leads to the same results. tests have been performed : · indoors with a solar simulator or an electronic programmable dc power supply with standardised insolation and consumption profiles, · outdoors in controlled conditions with standardised consumption profiles in several laboratories around the world, · outdoors directly in the filed in two different locations. In order to define typical weather sequence, IEC 61725 “Analytical expression of reference solar day”, has been adopted, then approximated with several stages, according to the possibilities offered by either the solar simulator or the DC controlled power supply.
UBC1 – Second Usable Battery Capacity Test This, the second battery capacity test, is conducted the same as UBC0. The purpose of UBC1 is to determine if the battery capacity has changed significantly after the FT. RT – Recovery Test The purpose of the RT is to determine how many sun hours are required for the array to charge the battery from LVD to Vr with the load enabled. After reaching LVD in the UBC1 test, the system is set for normal operation with the load set to operate 4 hours per night. The system
Figure 2 : Solar profiles (IEC 61725)
Then, in order to be able to plot the P-Chart with a sufficient accuracy, a sequence of ten consecutive days has been defined. The following figures
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illustrate the consecutive stages of the definition of the procedure.
5. Outdoor testing Outdoor tests were performed at different locations, in order to evaluate the effect of the daily or seasonal effect on the results, effect which dramatically reduce the use of another performance indicator called Performance Ratio (PR). Test at GENEC
Figure 3 : Meteorological sequences
Genec performed three test campaigns (1999, 2000, 2001), two campaigns were conducted during summertime, the lat one during wintertime. This intermediate approach consist of only controlling the load according to a defined level of service.
Tests using a solar simulator (JRC Ispra) Tests have been performed at JRC Ispra. The following photograph illustrates the inside view of the indoor test equipment. This solution offers certainly the most satisfactory in terms of completeness, but uses certainly the most expensive apparatus.
Figure 6 : Out door test equipment (Genec) Test in DC Laboratories
Figure 4 : Inside view of the indoor test equipment (JRC solar simulator) Test using a DC power supply (TÜV Rheinland) The use of a PV array electronic power supply leads to a more complex algorithm which is briefly described in the following figure. The main objective of the control algorithm is to act as a PV array would have acted, in real time. It is then necessary to develop a operating point research algorithm , which operates at a frequency higher than the highest frequency of any PWM regulator for instance. 11.1 V
14.6 V
Line of voltage drop due to ohmic losses
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example: 5 m cable 2.5² resistance = 0.034 Ohms Voltage drop at 3 A = 0.1 V
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Figure 7 : Test in Cuba (Ciemat + Cuba university)
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L2 Voltage drop caused by blocking diode (approx. 0.7 V)
Test were performed in more realistic conditions in three DC laboratories. In case of the Cuba university, systems were not equipped with a relay to manage the load, the lights being switch on/off manually (at 10 in the evening !). Thus the load profiles was not overlapping the system recharge, but it was not constant. This simple difficulty was in fact a real change for us in the sense that it allows a simple validation of the methodology to calculate PChart from a non constant load profile, and to generalise the calculation.
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Figure 5 : Principle of the programmable DC power supply (TÜV Rheinland) Figure 8 : Test in Indonesia (LSDE and TÜV Rheinland)
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The last figure enforce the validation of the procedure that bring the comparison of the daily points in a single P-Chart for three similar kits tested at JRC, TÜV and GENEC. 30
Battery Input current (A.h)
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Figure 9 : Test in India (TaTa BP Solar)
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System Balance Point
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TUV JRC GENEC
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6. Field Data (Transénergie)
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Last but not least, field data were collected at different locations, mainly within a project leaded by Transénergie in Brazil. Data collection was performed by ENERPAC®, the data logger developed by Transénergie, as illustrated in figure 10. Five systems were equipped and gave fruitful data to validate the methodology. Time series acquisition is made on a 5 minutes average basis, erasing all information concerning voltage thresholds. But data allow to calculate a equivalent P-Chart and SBP.
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Figure 11 : Comparison of the results indoor/outdoor Finally, a methodology has been proposed and validated to the manufacturer, to present its product performances and to the end user, to verify that the performances claimed by a manufacturer are valid.
7. Conclusion
Figure 10 : Field data (collected by ENERPAC®)
6. Comparison of the results The results are presented in the paper as global results. They demonstrate that all the tests performed at different locations, using different test equipment and methodology, but the same test procedure conduct to a maximum discrepancy in the results less than 10 % (except for one kit to be explain).
System JRC(1) JRC(2) TÜV GENEC GENEC Average STDEV delta max (%)
SHS1 3,80 3,80 4,00 4,40 4,20 4,04 0,26
System Balance Point (kWh/m2/day) SHS2 SHS3 SHS4 SHS5 3,20 3,10 3,20 3,50 3,60 3,40 3,10 3,10 3,20 3,80 2,80 3,80 2,60 3,80 3,30 3,50 3,50 3,25 3,50 3,00 0,33 0,13 0,30 0,39
This work had direct impact on international standard (namely IEC project 62124: “Photovoltaic PV standalone system : design qualification and type approval” and also IEEE P1526). It gives a tool to help quality assurance of solar home systems to be increased and to enforce their market penetration. This work is fully innovative in the sense that it is the first “system approach” which issue such procedure and standard. It seems that the direct follow up of this work is to promote this approach in future call for tenders. Nevertheless, this project was focus on a specific topic and outline three urgent needs: · This approach has to be extended to the reliability of the overall system (which means a lot of test on batteries) · This approach has to be more widely validated (especially with a larger number of field data, for the system, the lamps and the batteries) · This approach can be extended to a complete project, emphasising the socio – technico economical performance indicators lake.
References [1]
SHS7 4,40 4,20 3,80 4,00 4,10 0,26
8,91 8,57 4,62 8,57 16,67 7,32 Table 2 : Final comparison
[2]
PLISE : Photovoltaic lighting system evaluation and rating methods 16th ESPVEC, Glasgow, May 2000 Determining the performance of small SAPV systems P. Mc Nutt, B. Kroposki, R Hansen & C° 28th IEEE – Anchorage, September 2000
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Acknowledgement : this work is funded by the European commission (JOULE Project JOR3-CT98-0.258) and the French photovoltaic research centre CEA-GENEC. The authors prize to thanks all the other persons who participated for a while: Class Helmke, Lucy Southgate, Sidonie Salvat, Mike Patterson, Volkmar Gerhold. At last, this work profited from accurate review of Ben Kroposki, P. Mac Nutt (NREL).
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