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January Issue Cover Story- Selecting The Right BOS Systems For Indian Solar Projects

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Selecting The Right Inverters for Indian Solar Projects

Mr. Frank Qiao, Co-founder and Sales Director, Growatt

Solar inverter is the very important part of PV system. Though its main function is to convert the direct current generated by the solar panel into alternating current, nowadays the inverter also undertakes the function of detecting solar panel, the grid and wire running status, data communication, system protection etc. In order to ensure the stable operation of PV system, there are 3 key factors that we should consider when selecting inverters for a solar project:

Quality

To evaluate the quality of an inverter, here are the key factors: the selection of major components, product features, product functionalities, innovation and reliability. Each factor is very important. For inverter manufacturers, the most important thing is establishing a fully comprehensive and controllable product quality system. Then they need to ensure that the inverter could adapt to the harsh working environment and that the inverter lifespan reaches up to 20 years. As a reliable leading inverter brand, Growatt has introduced a comprehensive quality control system with FIVE stages from design to mass production: project kickoff, functional prototype, engineering sample, pilot run and mass production. Its whole product development cycle would last 6 to 18 months depending on the technology requirements. During this process, members from across R&D, QC, marketing, customer service, product testing and manufacturing would work as a whole team and strictly follow the FIVE quality engineering process: design engineering, component engineering, testing engineering, reliability engineering, manufacturing engineering. They bear in mind that quality is the life of the company and do their best to develop the inverter solutions.

Easy Maintenance and Configuration

Inverter configuration and monitoring are critical for a solar system and they can ensure maximum generation and stable operation of the PV system.Traditional ways for configuration and monitoring include RS232, RS485, RF, LAN etc. Now it’s time to see some innovations! Here comes the Growatt’s brand new MAX series inverter. See below chart and check how comprehensive it is. You’ll have multiple options to monitor the system locally or remotely. MAX 50-80KTL3 LV(MV) inverter has powerful Human Machine Interface that can clearly indicate the operating status of inverter as well as easily achieve local and remote communication along with daily maintenance.

Technical Innovation

In a solar system, though inverter takes no more than 5% of the total cost, it takes numerous responsibilities in managing the voltage, current, power capacity and generation, and even the solar panels and DC cables, such as the functions of string monitoring, I/V curve scanning, DC arc detection and panel’s PID recovery.

Keep going beyond the limit, now Growatt MAX series inverters even have the capability to monitor the PV panel status and grid quality with its comprehensive diagnosis functions. With those functions you can easily locate the failure and resolve the problem by doing it remotely on Growatt monitoring cloud, which means you don’t even need to go to site. This is huge cost and time saving!

Environment adaptability

In most part of India, it can be very hot in summer and temperature can reach nearly 50 degree Celsius. This is a great challenge for the inverter performance. Usually in such hot weather inverter will derate its output capacity. However, this is not the case with Growatt Max. With optimized component layout, cooling route and component selection, Growatt Max series inverter is able to output full power at the environment temperature of 50 degree Celsius, while at low temperature it can even output up to 15% extra capacity which can bring much higher yield to the system owner.


Mr. Brijesh Prajapati, Managing Director, Sofar Solar

Solar Inverter is Heart of the Solar PV System. It’s convert DC to AC & Controlling & Monitoring entire SOLAR PV Systems.

There are different types of grid tied solar inverters – micro, string and central.

  1. Micro inverter :- A microinverter consists of a small box located on the back of or situated very close to a solar panel systems . Its role is to convert the DC electricity produced by a single solar Small rating voltage system.
  2. String inverters :- A string inverter is the type most commonly used in home and commercial solar power systems. It is a large-ish box that is often situated some distance away from the solar Depending on the size of the installation, there may be more than one string inverter present. Medium Rating voltage system.
  3. Central inverter:- Central inverters are designed for applications such as large arrays installed on buildings, industrial facilities as well as field installations – they are basically just a very large string Its in high rating voltage systems.

Hybrid Inverter & Storage inverter is now new concept in Solar market. Needed important points of string inverter systems.

  1. Well-designed inverter cases: die-casting housings go through anti-corrosion and anti-rust protection processes
  2. WIDE Display
  3. Support RS485/WiFi/GPRS/Ethernet for data
  4. Built-in SD card with long memories data storage capacity for
  5. Support web portal for online monitoring and APP for mobile
  6. Support zero export solution and PID
  7. Local technical support for whole India
  8. Net metering
  9. Anti-Islanding protection for grid connected
  10. IV Curve
  11. Long Years reliable products warranty (SOFAR SOALR Offering 7 Years warranty in INDIA Market)

Mr. Naveen Jangra, Head – Technical (India), TBEA Xi’an Electric Technology Co. Ltd.

TBEA Xi’an Electric Technology Co. Ltd., is one of the global leaders in Solar Inverter manufacturing having its Global Headquarters in Xi’an, China. Company is a part of TBEA group, and inherits the engineering & manufacturing excellence of

70 years’ experience having a professional R&D team. India being second largest solar market globally focus on Utility scale projects followed by commercial & rooftop scale segment and TBEA proudly supports both having Central inverters and String Inverters in its product basket. TBEA have always focused on product quality and customer services being fruitfully awarded and have more than 2GW Inverters Supplied in India.

Solar projects executed in India are majorly Utility scale having smooth, undulated land surface having same PV module orientation and configuration which reduces the mismatch losses. So, in these conditions we learned from our long time experience that central inverters are the best choice for utility scale projects. However we do have both kind of solutions in our product portfolio – string as well as central inverter solutions. TBEA have 2 types of central inverters – Containerized & Outdoor Solution. Containerized Inverters are ready to plugin solution provided within IP protected container kept in open air without any requirement of separate housing. Rather, Outdoor Solution is most preferred & suitable solutions according to Indian projects. Complete outdoor solutions are smaller in size, easy to maintain, have better IP protection level and reduced cost of foundation & saves time.

Commercial scale projects are increasing with focus on uneven surface, differentiated shadow pattern and different PV module orientation for Rooftops or Hilly areas. TBEA supports with its wide range of multi MPPT string inverter having higher efficiency and easiness to commission and maintenance.

Why to choose TBEA Inverter Solutions!

  • TBEA inherits an engineering experience of 70 years having highly experience & professional R&D team.
  • Inverter solutions manufactured by TBEA are based on 3 level topology to provide maximum efficiency and power generation reducing the switching losses.
  • TBEA is the only brand manufacturing the highest capacity of central inverter of 5MW single unit, which saves the BOS cost of the customer.
  • TBEA manufacturer’s plugin type solution which supports the critical short span project commissioning trends of India.
  • Company have a world-class manufacturing facility in China which meets the globally acceptable quality Company use TIER 1 components in its inverter solution which enhances the life cycle of the inverter providing a sense of peace to the customer.
  • TBEA have always focused on product quality and customer services being fruitfully awarded with more than 2GW of inverter installation base in India serving almost all major Big & Small Project developers & EPCs namely ACME, Renew Power, Adani, L&T, Avaada, Azure Power, BHEL, KEC International, OPG Energy, KC Solar, Enrich Energy, Maheshwari Mines, Rays power expert, Rays Power Infra, etc.
  • TBEA achieved 29% of sales in Q3 2018 against other competitors, according to the report generated by Bridge to India.

The overall performance of inverters is remarkable leading to reliability over the brand & technology capabilities of TBEA.


Selecting The Right Structures for Indian Solar Projects

Ms. Monika Rathi, Head Business Development, Mahindra Susten

 

Mr. Tejvinder Sondhi, Design Manager, Mahindra Susten

2018 has been a roller coaster ride for the Indian solar industry, where the ups included the increase of installed capacity to 25.21 GW as of 31 December 2018, while the downs included the higher GST rate and introduction of safeguard duty. While falling prices and generation of 101.83 billion units of renewable power in 2018 is definitely good news for the industry, it has also put tremendous pressure on the developers and EPC to optimize costs.

With the constant decrease in the tariff prices it becomes more important that the system design must be optimised vis a vis costs, generation, land utilisation and most importantly the asset quality. One of the prime drivers in the asset valuation of a solar power plant is the Module Mounting Structures (MMS) which is a key ingredient in the successful running of a solar power plant. While most of the BoS components such as inverter DC cables junction boxes transformers, etc. are readily bought from the equipment suppliers the workmanship and the expertise of an EPC contractor is reflected mainly through module mounting structures and its design.

The design of module mounting structure depends largely on site location, wind speed and soil type. As a PV plant is expected to last more than 25 years, it is important that the mounting structure remains intact until the lifetime of the project, and also sustains the natural phenomenon which are not prevalent but could happen during its lifetime including storms within design speed, and water logging as per site conditions. Let’s look at some of the salubrious principles which must be adhered to ensure that the plant runs smoothly and efficiently for its desired service life.

Wind Loading: Wind loading in India is governed by the provisions of the IS 875 Part III – 1987 revised in 2015. The main factors pertaining to an MMS are as follows.

A). Basic wind speed – The basic wind speed data is contained in the wind map of India which specifies the wind speed inn m/s for a 3s gust at a height of 10m from the ground level for 50 years return It is different for different regions based on the Latitude and Longitude of the location.

  • k1 - probability factor- While the basic wind speed accounts for 50 years return period, k1 factors out this basic speed into design life of 5, 25, 50 or 100 Generally, for an MMS k1 is considered for a 25 years life.
  • k2 - terrain roughness and height factor is how closely spaced are the obstruction around the structure for which this factor is being Generally, MMS category lies in between category 2 & category 3.
  • k3 - topography factor considers the general level of site above sea level
  • k4 - importance factor for the cyclonic region is applicable only if the site is situated within a fetch distance of 60kms from the nearest
  • Kd – Is 875 P III-2015 allows for consideration on directionality factors which is considered as 9 since generally the MMS is made up of lattice structures.

Other coefficients that depend on the tilt of the module is calculated from Table 8 of IS. While the latest version of IS 875 allows for a reduction in the wind pressure up to 20 % it also demands that the coefficients considered in calculation of wind loads normal to the module plane considers the eccentricity effect also as suggested in the foot note to Table 8. Hence any reduction in wind pressure must be backed by considering the most critical effect on eccentricity.

For example, basic wind speed in Rajasthan is 47 m/s. For a design life of 25 years k1 = 0.9, k2=1, k3=1 & k4=1. This implies Vz=47x0.9 = 42.3 m/s. Pz = 1.073 kN/m2. With kd =0.9, ka=1 & kc =1, Pd= 0.966 kN/m2. However further 20 percent reduction would mean the design wind pressure (pd) = 0.772 kN/m2. So any optimisation in tonnage from 0.966 to 0.772 kN/ m2 is on account of applying a reduced wind pressure and not by way of any better design.

IS 875 also has laid down coefficients in table 29 which are to be used for force calculation on individual exposed width of the members of an MMS. Many a times these forces are not considered leading to under design of the structures. These forces are to be considered acting in combination with the pressure & suction forces normal to the surface of the module.

The coefficients mentioned in table 8 are calculated from wind tunnel tests, some designers insists on conducting site specific wind tunnel test to study the laminar flow of wind on closely spaced rows with variations resulting from row spacing and the collector width. More important wind tunnel test results are valid only if the ground slope is less than 3 degrees. For ground slopes more than 3 degrees the factor k3 must be increased suitably.

B). Structure design: Structure design for steel structures is governed by IS 800-2007 for HR members while IS 801-1975 for cold formed In earlier days, structures were two- poled and were not strong enough to bear various loads, however, soon were the days, when industry moved toward single pole structure for topographic modularity, reduction of foundations and subsequent efforts, labour and energy associated with it. It is extremely important to consider the correct effective length of buckling in calculation of actual stresses in vertical post.

With markets flooding with high strength steel, and in the race to reduce the consumption of steel/MW many a times the designers are tempted to increase the permissible yield strength to arrive at a lower weight section. However, it is a well-known fact from the inherent nature of material steel, any increase in yield strength will invariably lower the ductility of the material. Ductility ensures the structure remains flexible under effect of cyclic loading under wind. Hence in considering use of high strength steel a proper account of the stress strain curve is a must to ensure that the material remains below its permissible yield strength.

C). Corrosion Protection: Mounting structure life is highly affected by corrosion and it is important that structure galvanization should be sufficient to protect it from The typical structure galvanization thickness is kept of the order of 80 Microns HDG for Horizontal Rails and 550 GSM Pre-galvanized for Cold Form Rails. In case of purlin the structure can be cold formed steel with a lesser galvanization thickness of the order of 80 microns. As the solar penetration is increasing, more and more solar parks are coming in tougher terrains where water logging is expected. In such scenarios, the corrosion protection of the structure needs to be suitably increased to ensure life cycle of >25 years for the structure.

To summarize, a good structure design can significantly reduce structure weight per MW, however this should be done considering proper design criteria and safety margins. Moreover structure with an integrated wiring management system can be developed so that cables can run through perforated sections, which will help save the overall BoS cost.

With over 3.2 GW of Solar projects, Mahindra Susten ensures provision of a structure that could last for the lifetime of a plant, a structure which does not sag due to thermal expansion and a structure whose resilient design and integrated wiring management depicts its strength and durability.

 


 Selecting The Right Electrical Components for Indian Solar Projects

 


Mr. Chandan Singh Managing Director Stäubli Tec Systems India Pvt. Lt

 

Minimizing risk, maximizing return.

Bankability is today critically important in the PV business and has become an essential benchmark with substantial influence

on investors, banks and other financing institutions. In order to ensure the deciding factors for the long-term success of a PV system, bankable project partners must be acquired. Careful selection of bankable products and components to be built into the system is also a core topic, as these have considerable impact on the bankability of the PV project.

I would say, “A minimal investment in high-quality components can have a big impact on a project’s bankability, improving the safety and efficiency of an installation and protecting its long-term health.”

The components for cabling (connectors, junction boxes, cables) often play only a minor role in the calculation as they amount to less than 1% of the total initial costs, for connectors an even tinier percentage (approx. 0.003 %). In sum, potential savings are small – but choosing low-end over quality products may have serious consequences for the profitability of a PV system.

Those apparently minor components can have an ultimately decisive influence on the risks and on the return on investment respectively the LCOE of a PV project. Saving a few dollars in the short-term could greatly increase a project’s operations and maintenance costs. Furthermore, the risk for power losses, a (partial) system failure/downtime, or even a fire may increase significantly during the operation phase.

As a pioneer and global market leader for connectors, Stäubli Electrical Connectors has amassed over 20 years of experience in the photovoltaics industry. To date, we have more than 230 GW of installed photovoltaic capacity, amounting to approx. 50 % of the global cumulative PV capacity that had been successfully connected using our original MC4 connectors. This figure demonstrates the reliability and highest quality of our products.

The core of all Stäubli products is the innovative MULTILAM advanced contact technology. Thanks to their constant spring pressure, MULTILAM louvers ensure continuous contact with the contact surface and constantly low contact resistance. This provides for safe and long-life operation whilst reducing downtime and service cost significantly. Furthermore, risks for power loss and hotspots or fire that may lead to enormous reconstruction costs are reduced to a minimum.

By choosing Stäubli, you benefit from profound expertise, extensive support by a global network of trained staff and experts as well as long-life components that keep your PV installation up and running efficiently and safely. Stäubli therefore is your reliable partner when it comes to fulfilling the requirements of bankability and guaranteeing a sustainable return on investment in the long term.

 


Mr. Amit Thussu, Vice President, Power-One Micro Systems Pvt. Ltd.

 

The first thing to know about inverters is that NOT all inverters are created equal.

In a solar system, inverter is the only component that has the capability to talk back.

In order to choose the right kind of inverter, we need to first understand what kind /type of Inverter would suit our requirement and at the same time check for its operational and economic feasibility.There are however, a few points that we need to pay a special attention to while choosing the inverter for Indian market. India is a country with different climatic conditions; so in our case, we cannot have one size fits all. Therefore, whenever we choose an inverter, the following points must be considered based on the location and the design of the project:

  1. SHELF LIFE: Solar panel manufacturers give a promise of 25 years for the working of the panels, so the inverter should be able to keep up as well; therefore, we have to first look at the SHELF LIFE of the YES, it is the SHELF LIFE and not the warranty I am talking about. Inverter manufacturers give a warranty in the range of 5 to 12 years.

The questions we need to ask are:

  1. At what efficiency will the inverter perform after 5, 10, 15, and 20 years of operation?
  2. What kind of service is available after warranty is over?
  3. Also, ask for original certificate of warranty document, specifically if the inverter is being billed by a distributor or a channel partner and
  4. Get in writing the conditions under which warranty is void from the
  1. HEAT MANAGEMENT: The inverter converts DC to AC and in the process generates heat. As per the international standards, the output of an inverter is the power it can generate at 500C The point to note here is that the ambient temperature of the city is not usually the ambient temperature of the inverter. As the inverter generates its own heat, the ambient temperature of the inverter is relatively higher as compared to the surroundings. So the questions to ask are:
    1. At what temperature does the inverter derate?
    2. Ask for the temperature deration curve, preferably certified by a third party as a proof.
    3. While comparing inverters make sure that the capacities are compared at the same temperature.
  2. EFFICIENCY: There are two efficiencies mentioned on an inverter catalogue – Max efficiency and European The main questions to ask here are:

a. What is the efficiency deration of the inverter year by year?

b. At what efficiency will the inverter perform after 5, 10, 15, and 20 years of operation?

  1. OVERLOADING (DC side): this is one of the most misunderstood concepts of solar PV installation. It is not just about how many additional panels can be added over and above the inverter capacity, but at the same time, we also need to acknowledge that if an inverter offers 30% to 50% overloading, it has the capacity to take that So it will most probably have a higher shelf life as the components used would be of a higher grade. Questions to ask here:
    1. What is the maximum DC overloading allowed?
    2. Does the DC overloading give any additional AC side generation benefit?
    3. Is my warranty void if something happens to the inverter in case the inverter is overloaded?
  2. MPPT: Yet another misunderstood concept in world of Today, we have inverters with single to about 12 MPPTs depending upon the capacity of the inverter.

Both single and multiple MPPT options have their benefits and drawbacks. It is very important to know which system suits our requirements best and would make more economical sense. For example, a single MPPT system would give a higher generation on a flat roof without shadows. A multiple MPPT system would be more effective in case of different orientations and shadow zones, but it does not mean that more the MPPTs better the inverter. We need to choose the inverter wisely depending on the site location and orientation.

Some of the other points to consider while choosing an inverter in India are:

  1. Service availability (replacement or repair).
  2. How is the monitoring (level and ease of access)?
  3. OEM or Original.
  4. Certifications.
  5. Installation Base
  6. Display (what information can be accessed).
  7. Regional inverter stock availability (when can inverter be delivered after placing the order)
  8. Remember that any extra warranty claims from the dealer or sub dealer or channel partner are not valid at all unless or until there is a written proof from the OEM.

 

Mr. Girish Vaze CEO & MD, Elcom International Pvt Ltd

In India, most of the Solar Power plants are preferred to be installed in remote areas in order to avail the land at cheap rates.

In that case, the reliability of power plant totally depends upon the accessibility and availability of quality Solar BoS (Balance of Systems) including solar connectors. The failure of the same can lead to a prolonged downtime of the system. Additionally, poor quality connectors can lead to increased O&M work load and hence more time and money would be spent on repairs or encounter frequent breakdowns.

It is imperative to select your system components, PV Cable connectors, in particular, carefully, keeping in mind the long term performance of the system and to ensure fast and easy replacement of the same without causing any downtime.

The most preferred solar connectors offer TUV approved connectors with low contact resistance thus maximizing total system performance. Additionally, it should be easy to assemble using the standard tools available in the market, and which are suitable for

  • Crystalline panel manufacturers
  • Thin-film panel manufacturers
  • System installers Other preferred features of a good solar connector are:
  • IP68 complied, lower contact resistance ≤0.35 mΩ
  • Silver plated pure grade copper terminals
  • “snap-in” safety locking tabs to lock two mating connectors
  • quick, easy, robust and weather-proof
  • excellent housing material
  • complying with UL94-V0 fire safety
  • long term outdoor application
  • resistance against age and UV endurance
  • Minimal heat generation and hence avoiding any accidental fire
  • Engineering plastic, UV-compliant and flame-resistant

Even though, a number of suppliers are available in the market, selling imported Solar Cable connectors at a very cheap prices, but having the TUV approved connectors, along with the customization capability on cable assembly front makes the manufacturers the most sought after supplier in the Indian market. An ideal connectors supplier should be able to offer efficient and durable products with a 25 year guarantee of performance.

There are vendors in India, such as Elcom, who have developed solar connector with TUV certificate for 1500 VDC - as per the latest version of IEC 62852:2014 standard. While selecting the vendor for solar components, such as PV cable connectors, Branch connectors, and cable assembly, one should keep in mind that the manufacturer should be having the required infrastructure and scale capabilities to meet any volume of requirement with minimum lead time to avoid any delays in the projects. Its always preferable to select local vendors (domestic) instead of imported ones who have standardised the manufacturing process over a period of time and are in compliance with Integrated Management Systems (IMS) certifications including ISO - 9001:2015 - Quality Management System and ISO -14001:2015 - Environmental Management.

Thus, even though, the solar connectors make a very small portion of the overall system, it plays a very critical role in providing sustainability to the solar systems installed in those remote areas. Hence, select your component vendor very carefully,keeping the above factors in mind.

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