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.