Choosing the Right Panels and Inveters for Your MW Scale Power Plant

All right. So you have obtained that much coveted PPA. You have navigated the stormy, choppy financial waters and convinced your bank to give you a loan at a good rate.

Why, you have even figured out from where to get your equity component and the collateral.

And, after elaborate analyses, you have selected the EPC who you feel could be the best for you.

Now comes the component selection part.

You might counter: Hey, isn’t that something that the EPC will do? Isn’t that his area of expertise?

Yes, to a large extent, your EPC is the best guy to choose the right brands for you. But that does not mean that you, as the developer and owner, needs to be a spectator and observer.

You can play a role too in ensuring you choose the best components for your solar power plant, esp the right solar panels and solar inverters.

How? Read on.

Choosing the Right Solar Panels

With greater awareness among the developer community, choosing the right solar panels is becoming more easy than earlier.

Earlier, we used to hear about how second grade panels, sold at ridiculously low prices, were used in solar farms – and unsurprisingly these panels did not see too many day’s sunshine.

Having seen the almost-immediate damage that happen to power plant owing to the choice of cheaper but lower quality solar panels, most developers today insist that the EPC choose high quality panels.

However, the problem that we have seen most developers face is: They are not sure how to define and characterise “high quality”

Well, at one level, one can ask for the panel efficiency as a key metric of efficiency. But with most panels sporting efficiencies in the range 15-16.5%, it is not easy to fully differentiate one from another

Another metric to choose a module is to use the Tier classification. Many EPCs today mention Tier 1 modules. Well, while there is really no official definition of what is Tier 1 or which module brands belong to Tier 1, there are broad indications for this – see this post

While there might be some ambiguity about Tiers, there is none of that when it comes to grades of modules. Solar panels are graded from A to D, with grade A being the best and grade D modules best avoided. See this post to understand more about what each of these grades means.

So, broadly it is agreed that Tier 1 panels are of high grade. However, there is nothing official about this.

What however is clear is that if you are choosing panels that are either grade A or B, you are safe, regardless of whether these are from Tier 1 companies.

So, our overall recommendation is: Ensure you are choosing Grade A modules, or at least Grade B modules. If your modules are from a Tier 1 supplier, all the better.

Choosing the Right Inverters

The choice of inverter is more intricate than the choice of solar panels because inverters are inherently more complex to understand than solar panels. While solar panels are fairly passive semiconductors, inverters belongs to the category of power electronics, which is anything but passive.

At the inverters, being the brain of the solar power system, is the component for which most attention should be paid during the selection process, even though by cost, it might total only 6-7% of the total while solar panels constitute about 50-55% of the total cost of the solar power system.

Well, one way to use metrics while choosing inverter is to use this checklist we have provided at Solar Mango.

In addition to the checklist provided in the link earlier, you will also need to decide which of the two types – string or central inverter – you would be choosing for your MW scale power plant. Central inverters are so named because they convert the DC into AC from all the panels (or a large portion) at one device. Thus, a 1 MW solar power plant could have just one central inverter.

String inverters, on the other hand, essentially split the entire solar array into multiple strings, and the conversion is done at multiple devices rather than at one single inverter. For instance, for the above 1 MW power plant, we could have also used 10 string inverters of 100 kW each instead of one central inverter of 1 MW.

Both central inverters and string inverters have their pros and cons. See relevant section for more details on inverters, central and string inverters.

So which of the two – string or central – should you choose for your MW solar power plant?

Not an easy call – all we can say is that, in India, central inverters are still the predominant type used in MW-scale grid connected power plants. At the same time, relatively smaller MW power plant (in the 1-5 MW range) have started to experiment with string inverters.

The main grouse against string inverters of course has been their costs, which are significantly higher compared to those for central inverters.

While choosing between a central and string inverter might not be a straightforward decision, what is indeed a straightforward decision is to decide on a reliable and well-known brand when it comes to inverters for MW scale power plants.  Ensure that there are enough installations of the inverter in India or the company is a globally reputed name with inverter installations elsewhere in the world. And also ensure that the company has enough servicing and support personnel in India – because inverter is one component in which you can be sure there will be some need for maintenance regularly.

Some of the well-known inverter brands for MW scale power plants come from ABB, SMA, Schneider and Bonfiglioli. To some extent, we have also heard of inverters from Toshiba being used as well. Some of the upcoming inverter brands are from ReGen Powertech & Gamesa, both wind turbine OEMs venturing into solar.


21 thoughts on “Choosing the Right Panels and Inveters for Your MW Scale Power Plant

    1. Narasimhan Santhanam Post author

      Hi Mridul

      Good and practical question.

      There are specific conventions and standards using which one can classify a solar panel (actually a solar cell), as belonging to Grade A, B or C

      The specific answer to your question is: No, it will not be written anywhere whether a solar cell/panel is Grade A, B or C, but using the criteria some of which are visual and some of which can be determined from tests, you can determine which grade it belongs to

      You might want to refer to this post I wrote sometime back on what each grade means –

    1. Narasimhan Santhanam Post author

      Hi Avinash

      Thanks for your question

      Well, Tier 1 companies need not necessarily supply only Grade A panels, though you can expect most Grade A panels to come from Tier 1 companies.

      While there is no specific documentation on these, based on my experience I would say that most modules from Tier 1 companies are either Grade A or B. As you know, grades below these are considered poor and Tier 1 companies naturally wish to minimize their supply of Grades C or below into the market.

      Hope my answer is of help

  1. Banu Rao

    For a large solar farm, say 10 MW, using string inverters each of say 50 kW, will mean using 200 inverters! Isn’t that a lot of inverters? Monitoring and maintaining so many inverters over 25 years could be a night mare. Just imagine if the plant size is even bigger – say 50 mw!!

    I think string inverters are more suitable for rooftop solar power plants and grid connected power plants of up to 1 MW.

    What are your thoughts?

    1. Narasimhan Santhanam Post author

      Dear Banu

      Deciding between string and central inverters is not easy, as you have pointed out.

      Eventually, a developer needs to strike a balance between cost, maintenance requirements, increased yield and redundancy benefits.

      Well, for large solar power plants beyond 50 MW, I can safely say that no Indian solar power plant is considering string inverters, but for solar power plants in the range 1-5 MW, I am hearing both string and central inverters being selected by different developers.

      I see string inverters increasingly being used for rooftop solar power plants, of course. Just last week, I was at a hatchery in Karnataka putting up a 600 kW solar power plant, and they have 12×50 kW string inverters.

      If the costs of string inverters drop further to close the gap with central inverters, one will see even relatively larger power plants start using them.

      You might also want to read this –

    1. Narasimhan Santhanam Post author

      Nilesh –

      Thanks for this question, and I know my answer to this is going will stir the proverbial hornet’s nest, because most people simply are not aware of this fact and think what I am about to say is pure baloney.

      Because the answer is: All solar panels, regardless of their efficiency, generate the same amount of electricity per MW for a specified time (a day, month, year…)

      Now, this is confusing and downright counterintuitive and even “un-scientific” isn’t it?

      A solar panel with higher efficiency should be generating more electricity for the same capacity (MW) than a solar panel of lower efficiency, right?

      Well, as it turns out, no.

      Once again: A solar panel of lower efficiency will generate the same amount of electricity per MW as a solar panel of higher efficiency, other things being equal (same region, equally well maintained etc).

      How is this so?

      Let me explain.

      We all agree that efficiency is the ratio of (energy output/energy input).

      Now, let’s consider a solar panel of 300 Wp (watt peak) capacity that has a high efficiency of say, 22% (probably the highest commercially available efficiency as of Jan 2016). Now, let us say this solar panel has a total area of X sqft (the area on which sunlight falls).

      Next, consider another solar panel of 300 Wp capacity that has a more commonplace efficiency of 16% (most solar panels used in large farms today have this efficiency at the panel level). Let us represent the total area of this panel as Y.

      Well, it is simply that Y = X *[1+(22/16)], or about Y=1.38X.

      That is, for the same Wp, a lower efficiency solar panel will require a higher area than one for a higher efficiency, the extra area essentially accounting for the extra sunlight it requires to generate the same amount of electricity as a higher Wp panel.

      For the example considered, the panel with the lower efficiency of 16% will require 38% more space to generate the same amount of electricity as the panel with a 22% efficiency.

      You are perhaps a bit more convinced that this is not so un-scientific! A panel with a lower efficiency generates the same amount of electricity as a panel with a higher efficiency because more light falls on the former than on the latter!

      In the above example, panels with 16% efficiency have 38% more light falling on it, so the amount of electricity it generates is 1.38X*16%= 22%X (the same as what a 22% panel generates) – where X is the amount of light energy falling on a unit area, which is of course the same for both panels.

      Let us say I have convinced you. Your next question is sure to be this: If low efficiency panels generate the same number of units as high efficiency panels, why is everyone super-hyping high efficiency panels?

      There is a reason, and you have probably already guessed it. It is – AMOUNT OF AREA REQUIRED

      If you are planning a large solar farm in a place where land is super cheap, you should not waste your time on higher efficiency panels, because they cost significantly more than panels with 16% efficiency, whereas land cost is very low – you might as well go with lower efficiency panels available at much lower prices and buy lots more land to accommodate them.

      On the other hand, if you are planning to have a solar power plant on your rooftop and wish to have the highest amount of electricity generated from your rooftop, you are sure going to consider having a high efficiency solar panel. Because, well, rooftop space is usually limited and in most cases you cannot “expand” your rooftop.

      And oh by the way, here’s a trivia on high efficiency solar cells: Some of the earliest solar cells that were made in the 1960s and 70s were mainly high efficiency solar cells because they were used in a special place – on the satellites to power them for a long time. As you would have already figured out, space is a premium on satellites, and cost was hardly a consideration!

      Thank you once again for asking the question.

    1. Narasimhan Santhanam Post author

      Dear Mervyn

      Many thanks for your query

      I might not be able to do full justice by trying to answer your question, as the inverter is indeed a fairly sophisticated topic

      I will instead try to point out what have been the key inverter challenges faced by some of the earliest solar developers.

      As you will know, most of these were central inverters, so we are talking about 500 kW or 1 MW inverters.

      The key challenges in the first three years have been:
      ==Inverter malfunctioning owing to the heat and dust (mainly in Rajasthan)
      ==Lack of technically skilled workforce to maintain the inverters
      ==Time required for the inverter vendors to turnaround when there were problems – in some cases, the vendors sent the repaired part to their home country!

      Based on what I have seen in the past 1 year, most of the above issues have been taken care of; in addition, today inverter companies have put up enough support staff on the ground for quick turnarounds.

  2. Raghuram Reddy

    Dear sir

    Is it true that foreign inverters have been made more with conditions in Europe in mind and is it true these might not work well under Indian conditions as our enviironment is hotter and more dusty?

  3. Kalai


    Is it advisable to use monocrystalline solar panels as they have much higher efficiency upto even 23%

    where as polycrystalline panels have only till 17% sir

    please advise

    1. Narasimhan Santhanam Post author

      Dear Kalai

      Many thanks for your question

      I would request you to refer to my detailed response to Nilesh nayak above, whose question was “Will solar panels of higher efficiency generate more electricity per MW? How much more?”

      Thank you

  4. Kiran Mannargudi

    Is it true that a 16% efficiency solar Panel will generate the same amount of electricity Per W as would a 22% solar Panel??

    1. Narasimhan Santhanam Post author

      Dear Kiran

      Many thanks for your question

      The answer is a surprising YES.


      I request you to refer to my detailed response to Nilesh nayak above, whose question was “Will solar panels of higher efficiency generate more electricity per MW? How much more?”

      In fact, I have used the 16% and 22% benchmarks provided by you as the inputs for my calculations for that response.

      Thank you

  5. Dahram Anand

    Dear sir –

    I wish to know about flexible solar cells.

    Are flexible solar panels that can be applied on curved and non-flat surfaces available in India right now?

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India Renewable Energy Expert