Frequently Asked Questions (FAQ)

Solar SimulatorsI-V Measurement Systems

Solar Simulators

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Q] What spare parts are needed for the Solar Simulator (SS)?
The Xenon Short Arc Lamp has an average life of 1,000 hours, so it is recommended to buy one or more replacement lamps. The average life of the lamp is defined as the useful life during which the intensity of the lamp goes down to 70% of its original intensity.

Q] Do I need any other replacement parts?
The normal life for Air Mass Filter is 5,000-10,000 hours. Under normal operation a filter would be replaced every 2-4 years. If desired a spare Air Mass filter may be purchased.

Q] How often should the SS intensity be checked / calibrated?
The lamp ages over time. It is expected to deteriorate by 30% over 1,000 hours of operation. The intensity checking / calibration period should be established based on the amount of daily or weekly usage. It is recommended that the calibration be checked and re-calibrated, if necessary, every 200-300 hours of lamp use.

Q] How long does it take to calibrate the intensity?
The intensity can be adjusted in less than one minute using the reference cell. Once the intensity is adjusted this set value is controlled with the light feedback system built into the SS.

Q] How can the uniformity be checked or adjusted?
The intensity of the light is checked at thirty six (36) or sixty four (64) different locations within the specified size of the light filed. Using an appropriate detector (a detector to measure 400-1,100nm wavelengths for Air Mass 1.5) the intensity should be measured at various locations. If desired, contact the factory for testing and non-uniformity calculating procedure. The non-uniformity is a design parameter and does not change as long as the internal optics and external surface of the lamp is kept clean.

Q] How long will it take to change the lamp?
It takes less than one minute to change the lamp and less than five minutes to align the lamp.

Q] How long will it take to change the Air Mass (AM) Filter?
It takes less than one minute to change the filter. The filter does not need to be changed for several years of normal use.

Q] Other than filter and lamp, are there any other spare parts needed?
There are no other spares recommended or needed to continue operating the system.

Q] How is Reference Cell used for light intensity calibration?
A calibrated Reference Cell is created by exposing the cell to a known and calibrated standard one sun light source. The short circuit current (ISC) generated by the Reference Cell is noted under the standard conditions. Once this current value is established, then the Reference Cell is put under the SS light, the current generated is noted and compared to calibration value. If the generated current does not match the calibration value then the light intensity of the SS is adjusted until the generated current matches the calibration value. In general a Reference Cell should be made out of the same material as the cells that are to be tested. If this is not the case, then the spectral mismatch correction factors should be used for more accurate results.

For users that only have Solar Simulators (i.e. no IV Measurement system), a shunted Reference Cell can be used to calibrate the intensity of the Solar Simulator. The shunted Reference Cell has a resistor across the two electrodes of the cell. When the shunted Reference Cell is placed under the light, it generates a signal, typically in mV DC. The value of this resistor is selected such that the output of the Reference Cell is linearly proportional to the intensity of the light.

Q] Do you sell Reference Cells?
Yes, we sell Reference Cells.

Q] Is there any other way of monitoring and adjusting the intensity of the SS?
Another way to adjust the intensity of the light source is to use a radiometer (that measures the intensity between 400-1,100 nm range) to adjust the light intensity so that the radiometer reads a value of one sun. One can either use the Reference Cell or a radiometer to adjust and calibrate the Solar Simulator (light source).

Q] What utilities are needed to operate SS?
The only thing that is needed is a suitable electrical outlet (115V or 220V - single phase) depending on the model. is a vacuum source for holding the cell during testing and operating the probes. In addition, a small water supply may be needed(1 liter/minute). There should be absolutely no problems if the system is not operated in a clean room environment.

Q] Is there a need for any special environmental requirements like temperature or humidity control or clean room for operation of SS?
No special operating environment is required. Only the optics of the SS should be protected from contamination and dirt. This can be done by using lens cleaning cloth and alcohol.

Q] Training: Where is system acceptance?  How much time is provided with system training
If the customer expects a system acceptance then the acceptance criteria should be specified by the customer beforehand. When we deliver a SS it comes with certification and actual values for the test performed to demonstrate that the system meets its class requirements. There will be one day training provided at cost, which includes travel time and per day charge. Typically, this would be approx. $5,000-$6,000.

Q] Comparing pulse and continuous source, what are the advantages or disadv of measurement and maintenance?
Generally, people consider continuous light sources less desirable due to the percieved disadvantages; one being the heating up of the cell. The technical paper provided shows that that is not a true perception. The heating up of the cell during testing is negligible. The other being the lamp life. Once again the same technical paper shows that this is also a false perception.

Q] For Light Source Unit, because the system isn't located in a clean room, how is the Light Source Unit protected?  Does light source unit need to install filterable system?  How much money does it cost if it needs to be installed? How is it to be installed?
There is no need to install any filtration system. The system installation takes about 1/2 day. Installation would be included if the customer requests training. Installation instructions are included in the manual and can generally be performed by a skilled technician.

Q] For shutter lifetime, usually, shutter is used about 20 thousand times in a whole day. How long is the shutter lifetime?
If the system is going to be used 20,000 times a day then it is recommended that the shutter be left open and not used at all.  The only reason to use the shutter is if there is a lot of time between cell testing. In this type production testing rate the shutter should be left open, thus saving on shutter motor life. The shutter motor typically has 5,000,000 duty cycle.

Q] Will the reference cell of test system have aging situation as lamp ages?  How to solve this problem?  If calibration is needed, will it be included with test system?
The Reference Cell is separate from the Solar System. Reference Cell is not affected by the lamp aging of the light source. It is also recommended that the Reference Cell be made out of the same cells as the one's that are to be tested using the system. For example, if the system is to be used for testing Silicon cells then the reference cell should also be made from a silicon cell. The reference cell is calibrated and the calibration is recommended every twelve months. For frequent use, calibration is recommended every six months. If the calibration history shows little or no change then switch to annual calibration.

I-V Measurement Systems

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Q] What kind of temperature control is used with Cell Characterization System (CCS)?
The CCS uses Peltier cells to control the temperature. The temperature is usually controlled within 0.1 degree.

Q] Is the system equipped with temperature sensor?
The standard system is not equipped with temperature sensor.

Q] Is there any software compensation for temperature differences?
Yes the system has temperature compensation, whereby the measurement results can be normalized to 25°C.

Q] Can the system process cells with temperatures higher than 25°C.
There is no problem to make I-V corrections to Standard temperature using software procedures. The problem is to know cell's true temperature. In such situation the only way is to use remote IR temperature sensor which is not too fast (usually it needs 1 or 2 sec for measurement).

Q] Does the characterization system need to be calibrated, if so, how often and what is involved?
The electronic circuitry should be calibrated periodically. Although the system maintains its calibration for a long period of time, those who are concerned should calibrate annually. The calibration involves using a calibrated voltage and current source. The value of the current-sensing resistor is determined and incorporated into the software as a conversion factor. Also, the value of the voltage division ratio is similarly determined and recorded.

The light intensity should be calibrated frequently. This is performed by measuring the electrical output of a reference cell and comparing the measurement result to the reference calibration value for the test conditions of interest. The lamp power should be adjusted until the reference cell measurement is matches its calibration value.

Q] Regarding data storage, can we compare different cell data in computer?
Data storage and data format is really minor problem - it can be adjusted to almost any user requirements.

Q] Do we use CD's to backup data and does the system need to be shut down to do the data backup?
Data back up can be done many different ways – back up to a CD or transfer by Intranet to another computer. There is no need to shut down the system for data backup.

Q] What type of signals are available for interface with automation equipment?
Usually there are binary signals (TTL standard) that can be used for automation interface and sorting purposes. Number of signals depends on user requirements concerning number of sorting groups.

Q] Is demo software available for reference?
Currently it is not available. We plan to make it available in the future.

Q] If a cell is repeatedly measured, will the measured values have any kind of variations or tolerance?
When measuring cells, there are several sources that may introduce variations in the measurements. First, the light source will have some variation, no matter how small, over time. Second, the cell characterization system will also have some variation over time. Third, the cell itself will have a variation in its performance even when there is no variation in the light source and cell characterization, and finally there may be some variation due to environmental factors, such as temperature etc. Despite all these factors, the variation in measured values are extremely small. See the paper titled “Advanced system for calibration and characterization of Solar Cells” by F. Granek and T. Zdanowicz.

Q] What kind of data is provided with the cell characterization system?
All common data such as Isc, Voc, Im, Vm, Pm , FF, Eff, Rs and Rsh is provided. The system may include optionally procedures for extraction cell's internal parameters corresponding to cell's equivalent model to either so called single, double diode or variable diode model (i.e. SEM, DEM and VDEM, respectively).

Q] Is a computer provided with the cell characterization system? Is this PC just a regular PC?
A computer is supplied with the CCS. For lab and research environment we supply a regular PC. For production applications, we recommend an Industrial PC at a slightly higher cost.

Q] What kind of probe is used with CC?  How about spare probe cost?
The probes used are spring loaded “pogo stick” style probes. Some spare probes are included with the system as standard. The cost of replacement probes is nominal.

Q] What type of utilities are needed: gas, water or electrical outlet?  Any special environmental requirements like temperature or humidity?
No special requirements; to start measurements a low vacuum source is needed. If thermal coefficients of cell need to be determined then a water source will be needed (this is rather lab and research option rather than production option). A single phase electrical outlet is required (can be either 115V/60 Hz or 230V/50 Hz as specified by customer). No special operating environment is needed.

Q] Are there any problems expected if the system is not operated in a clean room environment?
The system does not need to be operated in a clean room environment. However, it should be operated in a clean environment.

Q] How much time is needed for system installation and training?
One day for installation and training should be enough.

Q] Other than regular data, can the software be modified to production data, such as yield etc.?
Yes the software can be customized to include production data in the data files.

Q] In regular production system, do customers choose Class A or B for any special reason?
The purpose of using the Solar Simulator is to predict the cell performance when the cells will be exposed to actual sun light. So if the Solar Simulator used exactly matches the sun light, then the prediction of the cell performance will be accurate. If however, the Solar Simulator is not an exact match with the sun light then there will be a difference in the predicted and actual cell performance. Class A system is not an exact match with the sun light, but it is a much closer match than Class B. In the end the decision on which system to use is based on the cost of the Solar Simulator and cost of any problems resulting from a mismatch between predicted and actual preformance of the cell. 

Q] Is the cell characterization automatic?
Yes the cell characterization is automated. The testing is initiated by pressing a key on the computer keyboard. The testing can be initiated externally as well. However, the loading and unloading of the sample is manual. The cell characterization system is capable of being interfaced with a cell transfer automation system and sort the cells in to nine (9) different categories.

Q] Does the system include the probes for making contact for measurements?
Yes the system includes four probes for making the electrical contact with the cell for testing. For production use, a different probing would be recommended based on customer’s needs.

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