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Want to buy a solar panel? – Key things to be considered

Article takes a look at the slew of factors that one needs to consider while determining the right solar panel technology and the criticality of the choice in shaping a financially feasible solar project.

In today’s market there are thousands of solar panel manufacturers available. A solar panel buying decision should be based on analysis of factors such as the solar panel technology to be used, selection of an ideal panel manufacturer, certifications of the panel, its operating specifications, effect of variance in its performance and efficiency of the panel.

Critical parameters to be considered for solar panel evaluation

1. Selecting the right technology: It is not just about the price
Based on the cell structure, solar panels can be classified into two categories: crystalline silicon and amorphous silicon or thin-film.The crystalline silicon solar panels can be further classified as mono-crystalline and poly crystalline.  Below is the comparison between different types of solar cell technologies:

Table 1: Different type of solar cell technology

There is no fixed rule for selecting one technology over the other. The selection of solar panel technology generally depends on space available for installation and the overall plant cost. Use of crystalline silicon panels can increase panel cost but reduce Balance of System (BOS) cost, which comprises all components of a solar power plant apart from the solar panels, such as land, panel mounting structures, cables, power conditioning units etc.The thin-film variant is cheaper and will reduce panel cost but increasesthe BOS cost.Following are the sample calculations for 1MW solar power plant using crystalline silicon and amorphous silicon solar panels.
 

Table 2: Comparative capital required for a crystalline and amorphous solar panel plant.

As calculated above, the per MW capital cost of a crystalline silicon solar power plant is approximately Rs. 12.05 Cr., whereas the capital required for amorphous silicon solar power plant is around Rs.1.18 Cr lower than crystalline variant. This is a marginal cost saving and varies from plant to plant, depending on BOS cost. Hence, overall plant economics play a significant role in selecting the right technology.

    
India’sJNNSM is neutral to the type of technology to be used for the solar power plant. Both crystalline and amorphous silicon technology panels can be used to claim financial benefits under the mission.
 

2. Selecting the right manufacturer: Warranty represents value only as long as the manufacturer is able to support the same
It’s always best to select a financially sound manufacturer to ensure the company can withstand the fluctuations encountered in a highly dynamic solar panel market. On this front, a publicly listed company may represent a preferred choice as they are expected to have the resources to enable them to absorb the after-effects or fallouts from catastrophic manufacturing defects, e.g. REC Solar had recalled its 420,000 solar panels to repair manufacturing defect. The whole exercise cost REC SolarUS$56 Million. A small manufacturer is unlikely to have the resources to offer such service if faced with a similar challenge. In India, some of the key solar panel manufacturers are listed below along with their panel manufacturing capacity:

Table 3: India's key solar panel manufacturers.


 

In India, to claim the financial incentives under JNNSM’s Phase I Batch II bidding, it is mandatory for projects based on crystalline silicon technology to use both cells and panels manufactured in India. This is true irrespective of whether the project is an Off-grid / stand-alone system or a grid connected solar   rooftop / smaller plant connected directly to distribution network at voltage levels below 33 kV. During the first batch of projects under Phase 1 of JNNSM, this rule was applicable only on the panels and solar cells were exempted. There is no mandatory domestic content requirement for projects based on other technologies.

3. Certification Requirements: Tap into the Subsidies Available
To avail the financial incentives under JNNSM, the plant needs to adhere to certain certification requirements for off-grid or stand-alone solar systems and grid connected rooftop PV or other small solar power plants.For state level benefits, Rajasthan has same certification requirements for solar panels as JNNSM, while Gujarat’s Solar Policy of 2009 specifies technical requirements of power plants in terms of experience of power plant developer but no specific requirements are mentioned for solar panels. West Bengal requires the solar system components to be tested and certified by Government of India accredited test centre – all these are similar requirements in nature to those defined for the JNNSM.
 

International Electro-technical Commission (IEC), the leading global organization that publishes consensus-based International Standards for electric and electronic products, systems and services has well established standards for the solar plant components. Most of the Indian requirements established by Bureau of Indian Standards (BIS) are based on these IEC norms.

Requirements for off-grid or stand-alone solar systems:
For Indian and imported panels, following are the certification requirements according to their type:

Crystalline Silicon Solar Panels: IEC 61215 / IS14286

  • The IEC61215 certification tests a panel for parameters which are responsible for its ageing such as sunlight, climate (changing of climate, coldness, warmth, and humidity etc.), and mechanical load (hail, wind suction, wind pressure, snow parameters etc).
  • IS 14286 is the Indian certification covering the same parameters as IEC 61215.

Thin Film Terrestrial Solar Panels: IEC 61646

  • The IEC 61646 certification is for Thin-Film solar panels and is in many aspects identical to the international standard IEC 61215 for crystalline panels.  An additional test records the degradation behavior of amorphous silicon due to temperature and irradiance exposure.

In case of a solar panel used in the solar lanterns and home lights systems, while the IEC/BIS certification for the specific models is not essential, a solar panel manufacturer needs to obtainIEC/BIS certification for any of the panels manufactured by them to be eligible for subsidy.

Requirements for grid connected,rooftop solar systems or other small solar power plants:
The solar panels used in the grid connected solar power projects need to adhere to the  qualityrequirements defined in the latest edition of any of the following IEC solar panel qualification tests or equivalent BIS standards.
 

Crystalline Silicon solar panels: IEC 61215 Edition II

  • All parameters in this certification are same as IEC 61215 and it includes an increased load capacity of 5400Pa for solar panels.

Thin Film solar panels: IEC 61646

  • The IEC 61646 certification is for Thin-Film solar panels and is in many aspects identical to the international standard IEC 61215 for crystalline panels.  An additional test records the degradation behavior of amorphous silicon due to temperature and irradiance exposure.
     

Common requirements:
In addition to the above requirements, the panels must conform to IEC 61730 Part 1 &2. The 1st part covers all the requirements for construction and states the mandatory design characteristics of the panel. The 2nd part consists of the requirements for testing. Part 2 of the IEC61730 defines 3 different application classes for a panel design, specifying the type of use, the related qualification tests and the resulting safety class modifications.
 

Solar panels to be used in a highly corrosive atmosphere (coastal areas, etc.) must qualify SaltMist Corrosion Testing as per IEC 61701 which checks the resistance of PV panels against the corrosive effects.
 

Also, each solar panel must have a RFID tag containing the following information:

  • Name of the manufacturer of solar panel
  • Name of the Manufacturer of solar cells
  • Month and year of the manufacture (separately for solar cells and panel)
  • Country of origin (separately for solar cells and panel)
  • I-V curve for the panel
  • Peak Wattage, Im, Vm and FF for the panel
  • Unique Serial No and Model No of the panel
  • Date and year of obtaining IEC solar panel qualification certificate
  • Name of the test lab issuing IEC certificate
  • Other relevant information on traceability of solar cells and panel as per ISO 9000 series.

MNRE has authorized Solar Energy Centre (SEC), Gurgaon,Haryana and ETDC, Bangalore for testing of the solar panels as per IEC and IS standards.In addition, certificates issued by any laboratories accredited by IEC are also acceptable.
 

4. Operating Specifications: Look BeyondSTC Ratings especially in India
STC is Standard Test Conditions which are used as global standard for quoting solar panel’s specifications. These conditions are 1,000 Watts per square metersolar irradiance, 25 degrees C cell temperature and air mass equal to 1.5. This test is performed by the manufacturer to know true wattage of the panel under these conditions.
 

Since actual climatic conditions may be different from STC, I-V curve can give the right specification of the panel under specific climatic conditions. For example, using the I-V curve below, we can interpret that at 50 degree C cell temperature and 600W/m2 irradiance, the solar cell will product 4A current at 18V. Hence the power output of the solar cell at these climatic conditions will be approximately 72W. Similarly at same cell temperature and 800W/m2 solar irradiance, the same solar cell will generate approximately 5.8A at 16V or 92.8W power.
 
Figure 2: Sample I-V Curve for a solar cell

5. Negative Tolerance: Can Lead to a Lower System Performance and Reduced Capacity
Negative tolerance rating of solar panel is its deviation from the labeled specification. For example a 5% negative rating panel with 100W label is warranted for 95W power generation. This parameter is very important in case of large power systems where many panels are connected in series to each other to generate high power and performance of one panel can pull down the performance of the whole system. For example, a 500W system in which 5 panels with 100W rating and 5% negative tolerance are connected in series will generate minimum 475W. But if one of the panels is having 10% negative tolerance, that panel will generate 90W minimum. Assuming output voltage of each panel to be 20V, in the mismatch system, 4 panels will be generating 4.75A current to give 95W output from each, whereas 1 panel will be generating 4.5A current to give 90W output. Since all the panels are connected in series, the total output voltage will be 100V and the output current will be the least current generated in the series, which is 4.5A. Hence the overall power output of the system will be 450W. Hence one high negative tolerance panel in the system can pull down performance of other high performance panels.

6. Solar Panel Efficiency Under Different Conditions and Over Time
Solar panel’s efficiency helps you to understand the size of the solar panel. Higher the efficiency, smaller the panel will be as compared to the same wattage panel with low efficiency. Other advantage of high efficiency solar panels is their marginally better performance under low light conditions.If you have enough installation space, then you can consider low efficiency panels, given that other performance parameters are comparable to the higher efficiency panel.

In India under JNNSM, to claim financial incentives, the solar panel used must be warranted for their output peak wattcapacity, which should not be less than 90% at the end of 10 yearsand 80% at the end of 25 years.

On considering the above mentioned points, a solar panel buyer can make an informed decision regarding which solar panel is the best suited for his or her application.

Future of solar panel technologies
As a result of huge research and development work across the world, $/W for solar cells has come down and has also resulted in improvements in almost all aspects of solar cell manufacturing starting from material selection to the manufacturing process. There have been numerous new techniques in solar cell design and manufacturing which seemingly have led to improved efficiency. For example ‘Solar 3D Inc.’ claims the creation of 3-D nanocone-based solar cell technology which has increased the efficiency of solar cells by around 80%. Still in R & D stage, these technologies are yet to be proven at the commercial scale.
 

Solar bidding – why price of solar power is falling in JNNSM?:
Falling of solar power price bid to Rs.7.49/KwHr in JNNSM Batch II of Phase 1, by the French company – Solairedirect has brought solar power very close to grid parity with coal based power plants. JNNSM has forced companies to compete on prices. As per Bloomberg New Energy Finance, till date, Solairedirect's offer is the third-cheapest on record globally. It is behind $110/MWHror Rs.5.50/KWHr bid in China and $120/MWHr or Rs.6.00/KWHr bid in Peru. To succeed in such a competitive environment, companies are focused at cost cutting at every step. Solairedirect seems to have been able to achieve these seemingly aggressive levels (almost 30% lower than average price worldwide) due to its vertically integrated business model as also the extremely competitive prices and deferred payment terms it enjoys from its suppliers.

With unsuccessfulbidders in JNNSM claiming that it will be impossible to supply the electricity at such low prices, it’s a wait and watch situation in the global solar market. The successful completion of projects by low bidders such as Solairedirect will set an example for the entire solar market to reduce the cost of production of solar electricity and make solar more affordableand widely available as an alternative to traditional energy sources.
 

The author, Navdeep Gupta is a Senior Associate at a sustainability consulting firm cKinetics.

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Montgomery Cty Division of Solid Waste Services

Dave Dugdale