Photovoltaic Systems

Precise and Accurate Testing of Photovoltaic Systems: A Must for Quality Assurance

By: S K Srivastava, M Dutta, Vandana, P Prathap, Subhalaxmi, P Kumar, C M S Rauthan, The authors are from the Department of Physics of Energy Harvesting, CSIR-National Physical, New Delhi
Sunlight being plentiful in India, the country has the potential to meet its energy needs through renewable sources of energy. While India has been slow in adopting solar energy, it is presently catching up.
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Energy sustainability is very important for the development of any country as it drives industrialisation, urbanisation, economic growth and overall improvement of the living standard of the society. Energy demand is increasing significantly all over the world due to rapid industrial and population growth. One of the most important issues of this century is to provide clean energy at affordable prices for domestic and industrial use while maintaining the ecological balance, for which every country has to frame new strategies and policies according to its needs. Conventional non-renewable energy resources of the world are diminishing fast. Moreover, they disturb the ecosystem by emitting carbon dioxide (CO2) and other polluting gases which have reached alarming levels and pose many threats, including climate change and disasters. With the spike in energy demand and the high cost of conventional sources all over the world, it becomes necessary to develop sustainable, non-conventional, eco-friendly alternative energy sources that will keep the environment pollution free (Shafiee and Topal, 2009; Kannan and Vakeesan, 2016).

An alternative source of power is nuclear energy, being clean with low carbon emissions, although there are inherent threats of radioactive hazards. Biomass is a well utilised source of energy and may remain so for thousands of years to come but it also generates harmful gases. Other renewable energy sources like hydropower, wind, geothermal and tidal have immense potential but have several limitations. In case of wind energy, for example, the required tall wind turbines with long blades, spread over large areas may not be possibly practical to meet the energy supply/demand balance. The most plausible alternative to fossil fuel may be solar energy which can be available at almost no cost. It is an infinite, clean, reliable and renewable source that can fulfil the future energy demands of the world. The sun emits energy at the rate of 3.8×1023 kW, out of which  the earth captures approximately 1.8×1014 kW (Panwar et al, 2011). Technological solutions are available to harvest solar energy through two different routes: solar thermal and solar photovoltaic (PV) which are based on conversion of solar radiation energy into thermal and electrical energy respectively. Solar PV devices have much higher potential as they convert solar energy directly into electricity, something obvious from the phenomenal growth of the PV industry with an average increase of more than 40 per cent in last 15 years(Armaroli and Balzani, 2007; Kropp, 2009). The intensity of solar radiation and its distribution are two key factors that contribute to and determine the efficiency of solar PV devices. Solar PV systems do not cause noise pollution and can be used everywhere as standalone systems including remote places, to generate power ranging from milliwatts to several megawatts.

The deployment of PV systems around the world for the effective utilisation of solar energy is going at a rapid pace. However, fast performance degradation of PV modules as compared to normal expected performance is observed and reported in many studies. It brings long term and adverse financial implications as power generation decreases over time. Precise, accurate,reliable measurements and performance testing of PV systems must be assured to avoid piling of degraded modules known as solar waste. Primarily, an infrastructure must exist in the country for testing and quality assurance of PV materials and systems.

Photovoltaic Technology

Photovoltaic technology is used to convert sunlight into electricity directly based on the photovoltaic effect. Photovoltaic effect is the generation of voltage and electric current in a material when light falls on it. Basically photovoltaic devices are p-n junctions made in semiconductor materials. The principle of this device is to activate electrons by giving additional energy (photoenergy). This device works on the principle that the electrons are activated from lower energy state (valence band) to higher energy state (conduction band) due to additional energy from sunlight, thus creating a number of holes and freeing electrons in the semiconductor. The electron-hole pair is separated by an in-built junction field and collected by metal electrodes on the top and bottom of the device, thus producing electricity. Although PV devices are simple in design, the technology needs to be improved for better outputs. (Green, 2002). First generation solar cells and photovoltaic devices use silicon in the form of mono-crystalline, poly-crystalline, multi-crystalline silicon. Second generation PV devices and systems use amorphous and micro-crystalline silicon, copper indium diselenide, copper zinc tin sulphide and cadmium telluride thin films. Nowadays, third generation PV devices based on organic semiconductors and perovskites are also drawing attention. However, these devices are still at the research and developmental level and lack efficiency and stability. Material selection is influenced by a number of factors like cost, availability, complexities in technology, efficiency etc. At present, the global PV industry is driven and dominated by silicon solar cell based flat-plate PV system technology which holds more than 90 per cent of the market share market share (Razykov et al, 2011).

In a complete PV system, to generate electrical power, PV modules consisting of solar cells are arranged in arrays along with many other components (Fig. 1) like mounting, tracking system, regulating and controlling structures, electronic devices, electrical connections and mechanical devices are used for better operational efficiency. PV systems are rated in peak Kilowatts (kWp), the maximum possible electrical power generated under standard conditions delivered when the sun is directly overhead in a clear day (Parida, 2011). The power delivered by a PV system depends on many factors. Throughout the world, a number of researches have been conducted from the beginning to increase the efficiency of PV devices (Kropp, 2009). The primary focus of research has been to enhance the efficiency of solar cells, modules and panels to achieve consistent efficiency with time. However, many other factors are also important and have been widely studied. They include factors like local conditions, storage and distribution, utilisation of power generated, the nature of the system, i.e., whether it is standalone or grid connected. For better efficiency, the current generated by photovoltaic technology is fed into grid systems. Grid field installations can be of two types,  ground mounted or built on the roof of
the building.

Many countries are cooperating for development of each other in order to develop advanced PV technologies for utilising solar energy. In 2016, our Prime Minister, Narendra Modi and the former French President, François Hollande had initiated the International Solar Alliance (ISA) to promote and develop solar energy and products through mutual cooperation and sharing knowledge resources for wider deployment and cost reduction(PIB, 2016). The international scientific community is focusing on many research activities towards enhancing the efficiency of solar devices and reducing the cost by maintaining long term reliability (Armaroli and Balzani, 2007).

Status of Solar PV in India

India has been consistent in utilising solar energy through the PV route. Most parts of India receive solar radiation of 4-7 kWh/m2/day for about 300 clear and sunny days a year. The total solar energy incidence on India’s land area is about 5,000 trillion kilowatt-hours (kWh) per year and exceeds the possible energy output of all of fossil fuel energy reserves in the country. Solar power in India is a fast developing industry and daily average solar-power-plant generation capacity is 0.20 kWh per m2 of used land area(EAI, 2013). As of now the total solar PV installed capacity has reached 23 GW. The target of 20 GW capacity set for 2022 under the Jawaharlal Nehru Solar Mission was achieved four years ahead of schedule through public and private partnership. The average current price of solar electricity achieved grid parity is 18 per cent lower compared to the average price of its oil cum coal-fired counterpart (McGrath, 2017).

India’s manufacturing capacity for solar cells was 1,212 MW and 5,620 MW for 2016 (Sengupta, 2016). Some of the solar cell manufacturers in India are: Tata solar power, Mundra Solar (Adani group), Bharat Heavy Electrical Limited (BHEL), Central Electronics Limited, Indosolar, Moserbaer, Websol, Udhaya energy photovoltaic, Vikram solar, Maharshi solar etc. There are many PV module manufacturers in India. For utility scale solar projects, top solar module suppliers are Trina Solar, JA Solar, Canadian Solar, Risen, Hanwha and GCL Poly. For rooftop solar projects, international companies with the largest market share in the India were: Trina Solar, Canadian Solar, Renesola, REC Solar and Jinko Solar. Similarly, top Indian suppliers were: Tata Power Solar Systems, Vikram Solar, Waaree, Adani, Emmvee and Jakson (Bridge to India, 2017).

In 2017, India was ranked fifth globally in terms of power generation and third in power consumption (Nagendran, 2018).The Indian government has taken many initiatives for the generation and utilisation of solar energy to reach the poorest of poor individuals. In 2015, India expanded its solar plans by an ambitious target to generate 100 GW of PV power, including 40 GW from rooftop by 2022. As per MNRE reports, apart from grid-connected solar PV initiative, off-grid solar power products were developed for local and rural energy needs. For example, a very large number of solar lanterns, home lighting and street lighting systems were installed and solar cookers and other product were distributed to cut down the uses of kerosene (MNRE, 2015).

Challenges and issues

India has pledged to deploy 100 GW of solar PV installations by 2022 to meet its enhanced energy demand through renewable energy route and to reduce carbon emission intensity by 33–35 per cent by 2030. Almost 23 GW installations have already been achieved and the deployment of PV modules is increasing at a rapid pace.In general, durability (lifetime) of PV system varies according to the maintenance conditions, load and local environmental conditions. In principle, a well-developed PV panel can operate satisfactorily for up to 10 years at 90 per cent performance capacity and 25 years at 80 per cent performance capacity with respect to initial capacity (Devabhaktuni, 2013).

Solar modules are made from solar cells which are fabricated in solar grade silicon.Most PV devices are imported. To enhance the PV power share, the manufacturing base for solar cells and module production needs to be strengthened. 80 per cent weight in solar module is of flat glass and 100 to 150 tons of flat glass is used to manufacture a 1 MW solar panel (ibid). The production capabilities of raw materials like silicon, flat glass, EVA should be expanded and fabrication infrastructure to produce solar cells and modules should be created manifold in order to eliminate supply constraints or reduce imports in future (ibid). Facilities for evaluation of materials and testing should also be developed.

The PV market is hampered by under performing, unreliable and failing products that create barriers to the development and enhancement of this renewable technology and its adoption. The majority of imported solar panels imported come with a warranty of 25 years (Fig. 2). The stability of PV modules for 25 years (with 80 per cent of peak power requirement) demands the degradation rate of less than 0.8 per cent per year. In the US and Japan, the stability even manages to approach 50 years with 90-95 per cent peak power, demanding a degradation rate of less than 0.4 per cent per year. However, the performance results of the installed PV modules/panels across different parts in India are surprisingly dismal and are of major national concern. A national survey conducted by MNRE-NISE and IIT Bombay for the year 2016 shows a frighteningly high rate of 2-5 per cent, indicating that the life of panels is less than 10 years. This will not only make achieving 100 GW net solar capacity a far-off dream, but also create a huge waste in the immediate future that will be difficult to dispose of (MNRE, 2015).

The basic reasons for the fast degradation of the PV modules are as below:

  • Existing testing facilities for PV modules in the country are inadequate and often provide non-reliable test results. The poor test results arise mainly due to the non-calibration of test equipment to traceable national/primary standards. Manufacturers send their PV modules to foreign countries, which is not only expensive and time consuming but is also not tested as per Indian climatic conditions
  • Mostly, long term performance evaluation test results are non-reliable and inaccurate making it difficult to estimate the life of modules. The higher degradation much before time is indeed a matter of worry in achieving the set target. Also, the expected huge waste arising due to degraded panels will be an issue
  • The testing standards as well as the testing facilities are based on European conditions which are quite different from Indian conditions that have high humidity, high temperature, high level of saline content and larger amounts of dust and ammonia in the environment. A recent report by IRENA too highlighted that the cause of underperformance of PV modules made in India is due to the lack of accurate and
    precise testing
  • Improper training of manpower has also contributed to the underperformance of PV modules in India

Precise PV measurements are critical in enhancing its value chain; otherwise it leads to inefficient estimation of the product value, leading to sale/purchase the products at a different price than required. This results in negative financial implications on the user or manufacturer. A measurement uncertainty of one per cent, and with an average price of INR 25/Wp, leads to the financial uncertainty of ~ INR 250 million/GW. These factors reveal a high demand for precise measurements on solar cell/module for sustainable growth of solar PV sector and hence its value chain. In view of the above, there is an urgent need for setting up a national testing centre for the traceable, precise and accurate measurements on PV modules in the interest of the nation. R&D should also be done to upgrade the testing facilities to suite the Indian conditions.

Creation of a National Centre for PV Module Testing at CSIR-NPL

The rate of installed module failures in fields, low performance and poor reliability is high. In view of this MNRE, GoI has taken the initiative on quality regulation for the solar photovoltaic systems/devices/components. CSIR-NPL being the National Metrology Institute (NMI) of the country has a great role to play in order to achieve the objectives of improving the total value chain of PV products. With a grant from MNRE, CSIR-NPL has already initiated work to establish the primary standard for solar cell calibration using laser based differential spectral response system (L-DSR), aimed to achieve the lowest uncertainty in the world. Recently, it has also established efficiency validation with higher possible accuracy for different kinds of cells. These facilities will help to save foreign exchange in expensive calibration being done outside India and will also save time.

CSIR-NPL has a rich history in silicon based photovoltaic solar cells over the last four decades. It was the first laboratory in the country to demonstrate the complete process ‘from metallurgical grade silicon to solar grade poly-silicon and fabrication of solar cells’ in the mid ‘70s. The current R&D activities at CSIR-NPL are depicted in Figure 3 and described below:

  • Photovoltaic Metrology—setting national primary standard for solar cell calibration, secondary cell standard and validation of solar cell efficiency
  • PV Module testing—performance analysis, energy yield and degradation related investigations specific to Indian climatic conditions
  • Develop protocols for precise and accurate measurements of PV cells and modules and creation of a national centre for photovoltaic module testing
  • Basic and applied R&D activities to develop efficient and cost effective technology for silicon photovoltaic technology by developing unit process to address optical, electronic and electrical losses, thin-film PV and organic perovskites photovoltaic devices
  • Training programmes to generate skilled manpower to support the Indian PV sector in fundamentals, design and metrology of PV systems

Only a few test centres currently provide module testing services in India. The measured quantity/value must be related to reference through a documented unbroken traceability chain. The aim of testing is to determine the characteristics of a given object and express them in qualitative and quantitative means, including adequately estimated uncertainties. For the testing methodology, metrology delivers the basis for the comparability of test results, for example, by defining the units of the measurement and the associated uncertainty of the measurement results. CSIR-NPL is the custodian of National Standards with the responsibility of providing apex level calibration and dissemination of standards for maintaining traceability of measurement as per quality system IS/ISO/IEC/17025: 2017. CSIR-NPL can be the best authorised body which can be entrusted to take up the challenge and responsibility for setting up national testing centre for the traceable, precise and accurate measurements on photovoltaic modules(CSIR-NTC-PV) for the testing and evaluation of quality, performance and safety of the product along with assurance and reliability for all kind of PV modules as per BIS/International Standards.

The establishment of the test centre at CSIR-NPL for performance evaluation of PV modules will have accessibility to in-house apex calibration facilities, required expertise and trained manpower. The primary standards traceable to SI units are available for all the parameters required to determine the electrical performance of a PV module. The various parameters required for testing and performance evaluation of PV modules are current/voltage, temperature, active area of devices, mechanical strength, force/load, area, radiation etc. Therefore, the test centres providing solar panel/module testing facilities would be traceable to SI units by utilising apex level facilities established and maintained at CSIR-NPL.

Once testing facilities are established and functional, CSIR-NPL will extend the expertise to establish more such test centres across the country. It can also provide traceability to existing test centres in the country for reliable module tests. In addition, country specific standards will be explored through consistent R&D on various testing parameters. At present, India imports solar cells and modules owing to a lack of adequate manufacturing and testing facilities and the high rate of failure. The Centre will ensure that the quality and performance of installed modules is as desired and investments do not go waste. This is essential for achieving the goals of the National Solar Mission and will help India in its long term sustainable green energy sources. It will also help India with foreign exchange deficit due to in-house testing and calibration capabilities. The process of power generation also requires a huge number of skilled PV professionals at different stages of PV deployment and management. In this direction, CSIR-NPL is well equipped for providing comprehensive hands-on training on PV systems including the fundamentals of PV cells and modules manufacturing, its integration in PV systems and deployment for practical uses, precision measurements of required parameters and its impact on estimation of product value (quality as well as financial implications). CSIR-NPL is providing training courses on full cycle of solar PV, raw material, cell fabrication and testing, module fabrication and testing, traceable measurements and analyses, to disposal of solar cells. The role of CSIR-NPL towards achieving the goals of National Solar Mission and sustainable growth of the PV sector in the country is schematically shown in Figure 4.

The Centre will be a great help to Indian manufactures to test PV modules’ reliability in the country and save lots of foreign exchange. In addition, this facility would be open for the International Solar Alliance (ISA) countries. The specific objective is to improve the quality of testing services provided to PV industries to meet International Standardisation Organisation (ISO)/Indian standards (IS) and International Electrotechnical Commission (IEC) PV standards. NPL’s role will be to support the industry and regulators by providing testing, traceability and calibration.


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