Photovoltaic modules Session 6 http://pveducation.org/pvcdrom/modules/hot-spot-heating DAMON FYSON

Photovoltaic modules Session 6 PV cells can be arranged in a series configuration to form a module (panel) Modules (panels) can then be connected in parallel-series configurations to form series string and parallel arrays.  When connecting cells or modules in series, they must have the same voltage rating to produce an additive voltage output, and similarly, modules must have the same current rating when connected in parallel to produce larger currents. DAMON FYSON

A number of PV panels in series is termed a string Photovoltaic modules Session 6 A number of PV panels in series is termed a string A number of strings in parallel is termed an array DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON

Photovoltaic modules Session 6 Mismatch losses are caused by the interconnection of solar cells or modules which do not have identical properties Output determined by the solar cell with the lowest output. example, when one solar cell is shaded remainder in the module are not, the power being generated by the "good" solar cells can be dissipated by the lower performance cell rather than powering the load. The comparison of an ideal and a non-ideal solar cell. For mismatch, the greatest difference is when the cell is driven into reverse voltage bias Source http://pveducation.org/pvcdrom/modules/mismatch-effects DAMON FYSON

Theory of I-V Characterization Photovoltaic modules Session 6 Theory of I-V Characterization PV cells can be modeled as a current source in parallel with a diode.  When there is no light present to generate any current, the PV cell behaves like a diode.  As the intensity of incident light increases, current is generated by the PV cell, as illustrated in Figure 1 DAMON FYSON

Photovoltaic modules Session 6 I-V Curves for Modules For a module or array of PV cells, the shape of the I-V curve does not change. However, it is scaled based on the number of cells connected in series and in parallel.  When n is the number of cells connected in series and m is the number of cells connected in parallel and ISC and VOC are values for individual cells, the I-V curve shown in Figure 10 is produced. DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Panels in series (string) Vt = V1+V2…. Photovoltaic modules Session 6 strings in parallel It = I1 +I2…… Panels in series (string) Vt = V1+V2…. DAMON FYSON

Understanding cell connection Photovoltaic modules Session 6 Understanding cell connection Current (A) The PV module is the basic unit in a complete PV system Understanding how the module is designed and assembled provides key understanding to designing a system Towards this end consider the following IV characteristics of a single cell 4 Voltage (V) 0.6 DAMON FYSON

Photovoltaic modules Session 6 Current (A) With three cells connected in series the combined characteristics are shown Connecting the cells in series maintains the same current, only the voltage of each cell is added together 4 Voltage (V) 0.6 1.2 1.8 The combined IV characteristics of three identical cells connected in series DAMON FYSON

Current (A) Current (A) Photovoltaic modules Session 6 Current (A) Current (A) C If two cells with different characteristics (dissilimar) are wired together in series, the result is shown in following figures Series connected dissimilar cells produce an added voltage output, but series current is equal to the lowest value of the two Voltage (V) A B Voltage (V) A B The individual IV characteristics of two dissimilar cells Current (A) C D Voltage (V) A+B The combined IV characteristics of the two dissimilar cells connected in series DAMON FYSON

Fill Factor Photovoltaic modules Session 6 (slide ½) DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Commercial Modules Photovoltaic modules Session 6 Solar module manufacture was 39MWs in 1994 increased to 1900MWs in 1994 PV module production capacity increased by nearly 70% over the course of 2010, reaching nearly 30 GW by the end of the year according to IMS Research source : superhydrophobic-pv-array Some Common standards applied to PV modules IEC61215- Crystalline Silicon Terrestrial photovoltaic (PV ) modules IEC61646- Crystalline Thin-film Terrestrial photovoltaic modules DAMON FYSON

Five common solar panel defects Photovoltaic modules Session 6 Five common solar panel defects The following defects are common when testing solar panels: Scratches on frame / glass Excessive or uneven glue marks / Glue marks on glass Gap between frame and glass due to poor sealing Lower output than stated in data sheet (we require positive tolerance on each solar panel) Lower FF than stated in requirements DAMON FYSON

Standard PV Panel testing parameters: Photovoltaic modules Session 6 Standard PV Panel testing parameters: With the use of the flash test, the following parameters are tested. 1. VOC (V), open-circuit voltage, The voltage output of the module is measured with the module disconnected from any load. 2. VMP (V), voltage at maximum power point, the voltage at which the module puts out the most power 3. ISC (A), the short-circuit current, Circuit Current (Isc)” and is the amount of current that the pv module supplies into a dead short. 4. Imp (A), Current at maximum power point (Imp)” and is the number of Amperes delivered by the module at its maximum power point. 5. Pm (W), Maximum Power and Maximum Power Point, power is equal to Amperes times Volts (P=IE, or Watts=Amperes X Volts). Every module has a specific point on its power curve where the product of Amps times Volts yields the greatest Wattage. This is the Maximum Power Point, the flash test takes data over the entire range of voltage and current. This way the wattage for each Current and Voltage data point can be calculated. By doing this we can find the Maximum Power Point in the sea of Current versus Voltage data. 6. FF (%), Fill Factor, the Fill Factor is defined as the maximum power produced (at MPP) divided by the product of Isc and Voc. One can see that the Fill Factor will always be less than 1. DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON

2011 Global Top Ten Solar Cell Manufacturer Photovoltaic modules Session 6 2011 Global Top Ten Solar Cell Manufacturer Company Capacity (MW) Country Suntech 2,400 China JA Solar 2,100 Trina 1,900 Yingli 1,700 Motech Solar 1,500 Taiwan Gintech Canadian Solar 1,300 Neo Solar Power Hanwha Solar One 1,100 JinkoSolar Source EnergyTrend [3] DAMON FYSON

2011 Global Top Ten Solar Module Photovoltaic modules Session 6 2011 Global Top Ten Solar Module Company Capacity (MW) Country Suntech 2,400 China LDK 2,500 Canadian Solar 2,000 Trina 1,900 Yingli 1,700 Hanwha Solarone 1,500 SolarWorld 1,400 Germany Jinko 1,100 Sunneeg 1,000 Sunpower USA Source EnergyTrend [4] DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON                                                                                                                                  Although yearly ranking is as listed above, quarterly ranking can indicate that which company can sustain particular conditions such as sever price adjustment, Government Feed- Photovoltaic modules Session 6 DAMON FYSON

Example of specification on a typical module 188 Watt Photovoltaic modules Session 6 Example of specification on a typical module 188 Watt monocrystalline panel Source: DAMON FYSON

Continue Example of specification on a typical module Photovoltaic modules Session 6 Continue Example of specification on a typical module 188 Watt monocrystalline panel Source: DAMON FYSON

String inverter with one string Photovoltaic modules Session 6 String inverter with one string String inverter grid The PV array is connected as one string and then connected to one inverter DAMON FYSON

Several strings connected in parallel Photovoltaic modules Session 6 Central inverter grid Several strings connected in parallel DAMON FYSON

The output of a single module Vmp = 17V Imp= 4A Photovoltaic modules Session 6 The output of a single module Vmp = 17V Imp= 4A What will be the array output DAMON FYSON

The output of a single module Vmp = 17V Imp= 4A Photovoltaic modules Session 6 The output of a single module Vmp = 17V Imp= 4A What will be the array output DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Electrical Protection Photovoltaic modules Session 6 Electrical Protection The PV module far right will not pass current Because the cells in the module are connected in series and a cell is damaged(or some cells shaded) the current from the whole modules is reduced, and hence the string or array If one cell is damaged the rest of the array can force current through it This phenomenon is known as a Hot –spot, the cell may cause the whole array to go open circuit The following slides shown how a diode may minimize the problem DAMON FYSON

+ _ Photovoltaic modules Session 6 BYPASS DIODES The module will produce less power One or more of the cells is defective One of more of the cells is shaded An operating module will cause a reverse voltage to appear across the defective or shaded cell The diode provides an alternative path for a current when a reverse voltage is present + _ DAMON FYSON

Hot-Spot Heating and Bypass Diodes Photovoltaic modules Session 6 Hot-Spot Heating and Bypass Diodes Dissipation of power in poor cells leads to breakdown in localized regions of the cell p-n junction. An enormous power dissipation can occur in a small area, leading to local overheating, or "hot spots", which in turn leads to destructive effects, such as cell or glass cracking or melting of solder http://www.southalabama.edu/engineering/ece/faculty/akhan/Courses/EE590- Renewable/supporting%20meterial/PVDevices/pvcdrom/Ch06/Hotspot.Htm DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Example of Non-Uniform Soiling Photovoltaic modules Session 6 Example of Non-Uniform Soiling DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

The next 3 slides show what may happen with blocking diodes Photovoltaic modules Session 6 The next 3 slides show what may happen with blocking diodes source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Bypass diodes fit a potential catastrophic event. Photovoltaic modules Session 6 Bypass diodes fit a potential catastrophic event. source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 Bypass diodes allow current to pass around shaded cells and thereby reduce the voltage losses through the module. When a module becomes shaded its bypass diode becomes “forward biased” and begins to conduct current through itself. All the current greater than the shaded cell’s new short circuit current is “bypassed” through the diode, thus reducing drastically the amount of local heating at the shaded area. Source: http://www.civicsolar.com/forum/9824/what-bypass-diode DAMON FYSON

Photovoltaic modules Session 6 bypass diodes are integrated into the solar cell structure during cell fabrication. The main conclusion is that the present integral bypass diode approach automatically protects against thermal instability in both small and large arrays without the need for any other protective measures. Source: http://wenrunopto.com/product/Diode.htm DAMON FYSON

Source: Paul Hernday so Photovoltaic modules Session 6 Source: Paul Hernday so DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON

Bypass diodes do cause other problems Photovoltaic modules Session 6 Bypass diodes do cause other problems source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 DAMON FYSON source: http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf DAMON FYSON

Photovoltaic modules Session 6 One potential problem arises from an open-circuit in one of the series strings. The current from the parallel connected string (often called a "block") will then have a lower current than the remaining blocks in the module. This is electrically identical to the case of one shaded solar cell in series with several good cells, and the power from the entire block of solar cells is lost. The figure below shows this effect. Potential mismatch effects in larger PV arrays. Although all modules may be identical and the array does not experience any shading, mismatch and hot spot effects may still occur sorce: http://pvcdrom.pveducation.org/MODULE/Array.htm DAMON FYSON

Photovoltaic modules Session 6 The current may now flow through the by-pass diodes associated with each module, but must also pass through the one string of by-pass diodes. These by-pass diodes then become even hotter, further reducing their resistance and increasing the current flow. If the diodes are not rated to handle the current from the parallel combination of modules, they will burn out and allows damage to the PV modules to occur. Bypass diodes in paralleled modules. There are typically two bypass diodes in each 36 cell module. Source: http://pvcdrom.pveducation.org/MODULE/Array.htm DAMON FYSON

Photovoltaic modules Session 6 In addition to the use of by-pass diodes to prevent mismatch losses, an additional diode, called a blocking diode, may be used to minimize mismatch losses. With parallel connected modules, each string to be connected in parallel should have its own blocking diode. This not only reduces the required current carrying capability of the blocking diode, but also prevents current flowing from one parallel string into a lower-current string and therefore helps to minimise mismatch losses arising in parallel connected arrays. Impact of blocking diodes in parallel connected modules DAMON FYSON

Junction box with integrated bypass diodes Photovoltaic modules Session 6 If an inactive cell (e.g. due to shading) is fed current by the other, active cells, it converts this energy into heat. The worst case scenario is that a hot spot builds up in the inactive cell that can destroy the module. To avoid this, bypass diodes are used that duct the current past the cell string containing the inactive cell. Junction box with integrated bypass diodes Source: http://www.solarfassade.info/en/construction/planning_factors/bypass_diodes.php DAMON FYSON

Source: pv_verband 2009 Photovoltaic modules Session 6 Minimising power loss Without a bypass diode, a single shaded cell would reduce power production of the entire series connection to a minimum. Thanks to the bypass diode, the total power yield only decreases by the lost yield of the bypassed cell string. Shading with and without bypass diode Source: http://www.solarfassade.info/en/construction/planning_factors/bypass_diodes.php DAMON FYSON

Source: pv_verband 2009 Photovoltaic modules Session 6 http://ask.metafilter.com/144073/Help-Connecting-A-Solar-Junction-Box DAMON FYSON

Source: pv_verband 2009 Photovoltaic modules Session 6 AS/NZS 5033:2005 1.4.4 Bypass diode A diode that is connected in parallel with a PV module, or a group of PV cells within a PV module, and prevents the PV module or group of cells from being reverse biased (see Figures 1.1 and 1.2). DAMON FYSON

(b) Have a current rating of at least 1.25 × ISC MOD. Source: pv_verband 2009 Photovoltaic modules Session 6 AS/NZS 5033:2005 2.2 BYPASS DIODES Bypass diodes may be used to prevent PV modules from being reverse biased and consequent hot spots occurring. If bypass diodes are added by the installer, they shall comply with all the following requirements: (a) Have a voltage rating of at least 2 × VOC MOD of the protected module. (b) Have a current rating of at least 1.25 × ISC MOD. (c) Be installed so no live parts are exposed. (d) Be protected from degradation due to environmental factors. DAMON FYSON

(a) Have a voltage rating of at least 2 × VOC ARRAY. Source: pv_verband 2009 Photovoltaic modules Session 6 AS/NZS 5033:2005 2.3 BLOCKING DIODES Blocking diodes may be used but they are not a substitute for fault current protection. One of their purposes is to prevent reverse currents from battery systems leaking into a PV array at night, when this protection is not an integral part of the battery charge controller. If used, blocking diodes shall comply with all the following requirements: (a) Have a voltage rating of at least 2 × VOC ARRAY. (b) Have a current rating of at least 1.3 times the short circuit current at STC of the circuit that they are intended to protect. That is— (i) 1.25 × ISC MOD for PV strings; (ii) 1.25 × ISC S-ARRAY for PV sub-arrays; or (iii) 1.25 × ISC ARRAY for PV arrays. (c) Be installed so no live parts are exposed. (d) Be protected from degradation due to environmental factors. DAMON FYSON

The shape of modules are restricted to rectanglar Photovoltaic modules Session 6 The shape of modules are restricted to rectanglar DAMON FYSON

PV Panel Warranties and guarantees Photovoltaic modules Session 6 PV Panel Warranties and guarantees Australian Standards Accredited installer to provide proof that panels meet Australian standards. The Clean Energy Council has a frequently updated list of all solar panel and inverter models that meet Australian standards.. Solar PV systems must also comply with The CEC Design and Installation Guidelines. Warranties and guarantees Solar PV panels generally come with a performance warranty that can last up to 25 years and a guarantee lasting five to ten years. Additionally, panel material warranties and workmanship guarantees generally span 5-10 years. DAMON FYSON

Warranties and guarantees cont…………….. Photovoltaic modules Session 6 Warranties and guarantees cont…………….. It is important to know who is providing the warranty – the manufacturer or the importer. In the absence of a manufacturer, the importer is responsible for the warranty. However, if the importer changes their business name or sells their business, their warranty obligations towards the customer cease. Installer must state who is providing the warranty. A system manual that provides operation, maintenance and safety information should be provided by your installer. This must also include a system energy output (kWh) estimate. It is important for you to provide written confirmation of statements including performance claims, guarantees and warranties. DAMON FYSON

Great web site for pv understanding Source: pv_verband 2009 Photovoltaic modules Session 6 Great source http://www.nwsolarexpo.com/2011-Presentations/NW_Solar_Expo_Hernday_4.29.pdf http://www.pveducation.org/pvcdrom/pn-junction/absorption-of-light Great web site for pv understanding http://pveducation.org/pvcdrom/modules/bypass-diodes DAMON FYSON