//250 kWp Solar Roof-Top System-Engineering Case Study

250 kWp Solar Roof-Top System-Engineering Case Study

Designing a roof-top system is not easy. There are many challenges associated with it. The project that I am going to talk about is an on-going project in TamilNadu on an industrial roof-top. According to my understanding there are several stages of a solar rooftop project.

Let’s talk a little about the engineering aspect of it.

The first step is to do a preliminary site-survey and try to get a feel of the place. We can ask for the existing roof-top drawings, Structural drawings, Electrical Drawings and other relevant drawings. Their drawings have to be studied and the preliminary site drawings can be drafted based on the site-visit and drawings provided by the client. We can gauge the number of panels which can be accommodated on the roof-top and come to a conclusion of the system size.

The first thing I learnt from this project was that, we can not assume the drawings provided by the customer to be the final drawing and draft our final drawings out of the same. The existing drawings would have been revised several times and the same changes would not have been incorporated in the drawing. To avoid problems make sure the team that has done the site survey has collected as much information as possible so that the process is smooth and drawings are as accurate as possible.

Pictures from the first site survey.

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First Site Visit

The preliminary drawing was made based on first site visit and CAD drawings provided by the client. As you can see proper walk-ways can be provided which will help the maintenance person to clean the panels easily. The roof-top is a trapezoidal metal sheet profile which is east west facing and has a slope of 5 degrees approximately.

Other things which can be decided on the first site visit are – the solar termination point, Earthing pit location, Lighting arrestor is required or not, cable routing etc.

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Technical Site Visit

Once the site visit report and preliminary drawings were submitted and accepted by the client, next step was to do a detailed site survey. For this particular case, it was very crucial as there are lot of skylights on the rooftop which has to be avoided and checking the rooftop dimensions so that the chances of error were minimum. In technical site visit a lot of things can be studied such as the sheet profile, so that the mounting structure which is to be used can be decided, distances between each skylights, whether the sheet profile is same throughout, etc. This is crucial as the industrial structure might have been built in different phases & at different time period, and chances are that the structure & the sheets may vary for different phases. Other aspects such as earthing down conductor to the pit, cable routing, anchorage of the bolts for the safety line and other crucial parts have to be checked.

Working on drawings

Once we were back from the site survey, it was time to start making the final drawings. First a 3-D model was made and validated in SketchUp. Several revisions were made before the drawings were finalized. I would like to give you a glimpse and few insights of the project.

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Mounting structures were to be riveted on to the sheet profile, so the placement of the structures were away from the purlin as riveting on the I Section would require different type of solution all together, as the I-Sections used for these Sheds looked quite heavy.

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Avoiding the Air-Vents area so that fumes coming out of vents does not affect the generation of the panels.

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A Structure is being fabricated out L-Angles and C-Channels for mounting the Inverters, DC Distribution Board, AC Distribution Board, Cable Trays etc. The inverters usually are quite heavy. So a fabricated structure, if needed for mounting the Electrical accessories should be strong enough to take on the weight it will be subjected to. The gap between each inverter has be maintained as per manufactures recommendation for proper dissipation of heat from the inverter.

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It’s not just random placement of panels which you see on the roof here, each roof is accommodated with panels in such a manner that the strings are not divided between two roofs and thus we have less cables running from rooftop to the inverter location. Try to keep it as simple as possible, the more complex design you give to the site engineer, the more time it would take him to execute the project.

Once the placement of the panels were decided it was time to start making the electrical drawings. For this project there were 10 drawings which were made some of them were, Structure Drawings, Wiring Diagram, String Layout, Earthing Layout and others.

Once all the drawings were reviewed and validated by the Technical Head, it was time to start the project. Project management team had allocated the resources and the project is being executed.

The main challenge while doing the structure work faced by the site engineer was alignment of the structure as the sheet is not properly overlapped on each other due to the long running distance of the sheds which is around 70 meters. The site engineer had to make sure the structure is aligned properly. Safety is also one of the most important aspect of any project so a lot of precautions were taken.

Some of the pictures from the third site visit.

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A project takes a lot of effort and a team which is up for the challenges. It is very tiring but exciting, it is very laborious but tangible, long hours of work but rewarding and the list goes on. There were so many things which I have learnt from this project, I would like to thank our most experienced team member Mr. Ranganath for his endless support and experience and his ways of teaching me designing a system, Mr. Sayooj for his support and teaching me all the electrical engineering, Mr. Venkat for all his knowledge and experiences which he shares with us all the time, our Engineering team, Mr.Sriram and Mr.Vineeth for making so many drawings and revising it countless times and delivering all the drawings on time.

My Manager in EcoSoch Mr. Santosh and Mr. Nishay, for giving me an opportunity to work on the project.

And at last I have some pictures for you guys directly from the site. The system is expected to be up and running by 20th of this month.

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Written by Samanth, Project Engineer, EcoSoch Solar Pvt. Ltd.

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