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Interview with Dr Sanjay Kumar Srivastava and Dr Pathi Prathap



Interview with Dr Sanjay Kumar Srivastava and Dr Pathi Prathap, CSIR-NPL, New Delhi

[Braunschweig, 4 November 2022]

Dr Srivastava and Dr Prathap work at India’s National Metrology Institute (CSIR-NPL) that cooperates with PTB for the development of a facility for reference solar cell calibration. Both scientists came to PTB for a 4 month-training on this special measurement set-up.

Photo: Prathap Pathi, Ingo Kröger, Sanjay Kumara Srivastava

Prior to our interview, we had the opportunity to visit PTB’s working group 4.52 to have a look at the measurement station our guest researchers are working on to get an idea as to what this is all about. In this context, we would also like to thank Dr Ingo Kröger who - together with our guest researchers – provided a short introduction on how this measurement station for solar reference cells works.


PTB: To start, could you tell us something about your work at home in India?

Sanjay Kumar: Well, we both work at the National Physical Laboratory which is the NMI of India. NPL’s structure is similar to that of PTB – there are also different metrological divisions and departments.


PTB: Ok, I see… just to get an idea, how many employees work for the NPL?

Pathi Prathap: In total, around 800 to 900. And there are about 200 persons working on a contractual basis for NPL.


PTB: And the division you are working for…

Sanjay Kumar: … is the Division of Advanced Materials and Device Metrology, which covers different areas from mechanics to optics. Particularly, we are responsible for research activities and measurements in the field of photovoltaic metrology.


PTB: OK. Well, from what we already learned you have come here for a special purpose…

Pathi Prathap: Exactly…

Sanjay Kumar: Yes, indeed… the reason for our stay here at PTB is to receive training for the solar cell device calibration facility, which will later be set up at NPL India.


PTB: And this facility for solar cell reference device has been explicitly built for NPL. What exactly is behind that?

Sanjay Kumar: The construction and set-up of the device as well as our training here at PTB is part of a project financed by the Indian government. So far, we did not have such a facility at the NPL.


PTB: Thus, the measurement station will be shipped to India to be mounted at the NPL?

Pathi Prathap: Right, setting up the measurement station is planned for the beginning of next year.

Sanjay Kumar: We are almost done, we have already completed the site in India with all the necessary requirements regarding ambient conditions (humidity, cooling water, etc.); to set up the measurement station, we have prepared a cleanroom which is completely blackened, because a dark room is needed for the measurements.


PTB: Shipping of the measurement station will certainly be a challenge… considering its size…

Pathi Prathap: Yes, indeed… the total length of the instrument is 8 metres and is has many components… so in total, there will be 5 tons to be shipped.


PTB: And how many people will be engaged in this project in India?

Sanjay Kumar: The team consists of 4 scientists and a technical support staff consisting of 2 persons.


PTB: After having received your training here at PTB you will then train your colleagues in India?

Sanjay Kumar: Exactly, we will share what we have learned during our training here at PTB. And we will also take care of the mounting of the measurement facility together with staff from PTB.


PTB: Well, I suppose this project with all its activities, including the set-up of this reference device at NPL will have an enormous impact, also financially…

Sanjay Kumar: Oh yes, the impact is reasonably high, and our country will surely benefit from it.


PTB: What are your development plans for photovoltaic power?

Pathi Prathap: Up to now, we are working in the range of 40 GW and our current target is to increase it to 120 GW, and to 200 GW until 2030.

Sanjay Kumar: And against the background of a growing solar energy sector, it is very important to have such a facility in India. The calibration facility enables us to offer the corresponding services to industry and laboratories. And it is important for the export/import of solar modules.

Pathi Prathap: And, of course, such a facility is also needed to verify that imported PV panels really do have the efficiency that the manufacturer claims.


PTB: I understand that in India there is a well-established industry for producing solar panels. What about the manufacturing of solar cells?

Pathi Prathap: Well, there is also production of solar cells in India, but the majority of the cells are not manufactured in India, they are imported. But the Government of India has put strong efforts for indigenous development of raw materials required for cells.

Sanjay Kumar: Yes, in the past there was a larger production in India, but due to global competition this has decreased... nowadays it's more about manufacturing solar panels...


PTB: So, it’s more about making solar panels… but maybe this will change in the future.

Sanjay Kumar: Yes, I think manufacturing of solar cells in India will increase. Left: A reference solar cell


PTB: There has been a long-standing cooperation between PTB and NPL. Why exactly did you choose PTB for this project?

Sanjay Kumar: PTB has 30 years of experience regarding these calibration facilities…

Pathi Prathap: … and most important, PTB offers the smallest measurement uncertainty worldwide. The measurement uncertainty achieved by PTB is 0.4%.

Sanjay Kumar: Exactly. We also contacted other NMIs and some of them also told us that PTB has the best expertise for reference solar cell calibration. View inside the measuring station


PTB: It’s quite interesting to understand the background of your visit to PTB. But, of course, we also have some questions regarding your stay as such. For example, was this your first visit to PTB?

Sanjay Kumar: For both of us it’s the first time at PTB. I stayed in Germany before from 2011 to 2012 at the Max Planck Institute for the Science of the Light in Erlangen, so it is my second visit to Germany.

Pathi Prathap: It is my first stay here in Germany, but I have already spent 4 years in France before joining NPL.


PTB: What about the working conditions – is there a great difference working at PTB compared to working at NPL?

Pathi Prathap: The work itself is very similar... same operating procedures, same protocols, so there is not much difference regarding the work environment; at least, we didn’t see much difference.

Sanjay Kumar: I totally agree; we had a good and wonderful experience, everyone’s very helpful here at PTB. And we also visited various other labs linked to our activities.

Pathi Prathap: And we also had the opportunity to get in contact with some companies and establish contacts there required for our facilities upgradation and supporting tools.


PTB: We are glad to hear that… and outside PTB? Maybe you can share some of your impressions or experiences with us?

Sanjay Kumar: Everything worked fine, and we felt comfortable here.

Pathi Prathap: Yes, Braunschweig is a nice city, nice surroundings, with lots of green… basically, there is all you need…

Sanjay Kumar: Compared to New Delhi Braunschweig is small but it has a pleasant size and we have explored many things by bike.


PTB: And what about the communication with people outside PTB? Did you have any difficulties due to cultural or language barriers, for example?

Sanjay Kumar: That was no big deal… people are kind enough and very helpful, even if they don’t always speak English.

Pathi Prathap: For example, one day we lost ourselves .... so, we asked for the way to the city centre. The lady we asked had some difficulties explaining it and so she just said: “follow me” and went all the way with us to the city centre.

Sanjay Kumar: Generally, we have the impression that outside PTB 95% of the people understand and/or speak English – and, at least to our experience, people are very helpful.


PTB: That sounds all very positive… but maybe there was also something that did not go so well…

Sanjay Kumar: No, not really... there was only one experience that was a little bit... well not negative, but which kept us worried for some days… but in the end it all worked out well. Prathap, maybe you can tell the story?

Pathi Prathap: At the beginning of our stay, we took a bus to go to the city centre because we wanted to buy some things. And on the bus, you always have to show your ticket... so we showed our tickets, took a seat and for some reason I didn't put the ticket back in my wallet that was lying beside me, but kept it in my hand and... well, in the end we got off the bus and I accidentally left my wallet on the seat and ...


PTB: Oh my goodness …

Pathi Prathap: Shortly afterwards, in a shop, I noticed that it was missing and of course it was quite a shock, because there was a lot of money in the wallet and of course the personal documents, cards, etc. …

Sanjay Kumar: All in all, not such a nice experience but, as I already said, everything turned out well. We went to the lost and found office of the transportation company and to the police and really everyone was very helpful.

Pathi Prathap: Luckily, after a few days I got everything back, nothing was missing. A lady had found the wallet and handed it in at the police station... She had even tried to contact me via Facebook in the meantime, but I didn't notice it right away. A short time afterwards, we met up with her to thank her personally and had coffee together.


PTB: Glad to hear that this “adventure” turned out so well! And now one last question – Is there anything you would like to add? Maybe some advice for other scientist considering a stay abroad as guest scientist?

Sanjay Kumar: From a professional point of view, I would say that PTB is one of the best places to learn and improve the metrological quality. So, we can clearly recommend coming here as a guest scientist. It was a great experience for us, and we would also like to point out that we had a good support by the staff of PTB. And especially our host Ingo helped a lot. For us everything is perfect... scientifically as well as all the rest.


PTB: Thank you very much for this interview! 

Initiates file downloadInterview Sanjay Kumar Srivastava_Pathi Prathap.pdf