Indian Solar industry’s love affair with Central Inverters

1 GWp cumulative solar capacity – that is a statistic the Indian solar industry can be proud of. From less than 10MWp of capacity in December 2010, India crossed the 1 GWp milestone in July 2012, at an astonishing pace. During this period, most of the discussions on  solar PV centered around PV module technologies. With the JNNSM guidelines specifying a domestic content requirement(DCR) for PV module technologies, there were debates and questions about which technology  suits Indian conditions the best. Every mainstream PV technology – crystalline silicon(c-Si), Amorphous silicon(a-Si) Thin Film, Cadmium Telluride(CdTe) Thin Film and Copper Indium Gallium (Di)Selinide(CIGS) – has been deployed in India by the various PV project developers and till there is substantial performance data from the field about the performance of each of these technologies, the questions and debates about the suitability of each of these technologies for India will continue.
However, the story of solar inverters is quite different. While there are two options available for inverter configuration(central inverter topology and string inverter topology), almost every utility scale solar PV project in India has opted for central inverters. The only major known exception is the 5 MWp Solar PV project in Khimsar, Rajasthan, developed by Reliance Solar. This plant used 432 units of SMA inverters(11 KVA each). (The project details can be found here). The major reason for the unanimous acceptance of the central inverters is the price per Wp. Typically, string inverters cost about 30-50% more than central inverters. For example, central inverters are available in India today at about $0.12 -$0.14/Wp, string inverters cost about $0.18/Wp. The price difference trumps many other factors like ease of installation, higher likely  inverter uptime, ease in operation and maintenance(O&M), and quick repairs, among others.
Interestingly, central inverters are the favorites in countries like China and USA also. The recently released report on global PV inverter market by IMS researchsays that demand for central inverters has increased, mainly from India, China and the USA. This has had an impact on the inverter pricing, which has fallen by almost 20 % year-on-year in Q2 of 2012. According to the report,  “Shipments of inverters over 500 kW in size are forecast to continue to grow substantially in the second half of the year as high demand for utility scale installations is forecast in markets such as the U.S., India and China”.“This change in market share towards larger inverters with a lower price per watt has also been a factor in the reduction of average PV inverter prices.”
So, which technology is better for India? String Inverters or Central Inverters? There are some good arguments on both sides. Denmark based Danfoss, one of the leading manufacturers of solar inverters, has a pretty good concept paper on the advantages of the string inverters over central inverters. The concept paper can be downloaded here and a related video can be found here.SMA, the market leader in solar inverters,has published a case study of how its central inverters can withstand extreme climatic conditions in the deserts of Rajasthan and Gujarat.(The study can be downloaded here). But the answer to the question about which inverter is better for India is not yet available.
I personally feel that there has not been enough discussion on this topic, and I am curious to find out whether the love affair with Central Inverters will continue if the string inverters are able to narrow the price difference with Central Inverters. My feeling is that string inverters will find more and more acceptance as the PV market moves away from large scale systems to smaller systems like rooftop PV systems.
What do you think?
Nawang Chhetan has shared with us a very interesting discussion on the subject. The video can be viewed below.
[youtube_sc url=a7Py2OKxp5k width=560] PS: An impressive video from Danfoss about a 80 MWp PV project that uses string inverters can be found below.
[youtube_sc url=A0oueZhmTc4 width=560]  

4 thoughts on “Indian Solar industry’s love affair with Central Inverters”

  1. I think acceptance on String inverters is minimal even in western markets. Besides string inverter manufacturers also claim it to be more efficient as claimed in Danfoss Video. Moreover I have a hunch that it depends from project to project , system to system, factors like environmental conditions etc. matter. Please checkout this panel discussion, participants are form Kaco, Enphase, SMA, Schneider & Tigo. Enphase is a micro inverter manufacturer with good presence in the US (California mainly). Enphase is pointing out benefits of microinverters & SMA that of central, checkout thr arguments.

  2. It is May 2014 right now and the love affair with central inverters continues. Most of the companies who have won projects in the JNNSM Phase-II Batch-I bidding are going to use central inverters as per my information.
    This decision is driven mainly by cost concerns. I guess Rs.8 per watt (or lower) for central inverters is simply irresistible for these companies to pass up.
    But I would imagine that string inverters can give a better value for money due to more output, lesser cost of DC cabling, better reliability, etc. If only someone would use string inverters in a utility-scale PV power plant. Then we would have some concrete numbers to compare…

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