Rooftop PV – Is a East-West Configuration Better Than The traditional South Facing Configuration?

With the interest in rooftop PV picking up, especially after the call for RfS by the Solar Energy Corporation of India(SECI), and due to the various state policies( KarnatakaGujarat, Kerala and Tamil Nadu ), design and installation of rooftop systems are getting a closer look. The different possibilities to reduce cost and increase yield are also currently being examined by various players.
One such possibility is to go for a East-West configuration of PV modules as against the south facing configuration. CHROSIS, a Germany based firm, has released a white paper which compares the yields of the two configurations and also examines the cost savings for each of these configurations.(Earlier, CHROSIS had released a very relevant whitepaper on Capacity Utilisation Factor(CUF) Vs Performance Ratio(PR) – the details of which can be found here).
As per the whitepaper, the simulated yield generation in Chennai for a classic south facing system is 1565 kWh/kWp and for the E/W is 1525kWh/kWp. Some of the inferences from the whitepaper are given below.
”When looking at the results from a designer’s perspective, the main benefit of a E/W-configuration is less shading and higher installed capacity. Different locations will lead to different results. When looking from a financial perspective, the investment costs are interesting. If substantial savings on the BOS costs can be realized, the lower output per kWp will not be a problem.”
The whitepaper can be downloaded here.
Interestingly, Larsen and Toubro(L&T) has installed PV modules using the both the configurations in the rooftop of their building in Chennai. In an interview that was published two years back, L&T had mentioned that E/W configuration is better than the South configuration because
a. more panels can be installed in the same area(more MW/acre) and
b. more energy is generated per MW installation
L&T had observed that the E-W facing modules’ output was upto 9% higher (in peak summer) than the South facing installations, and on an average, the output was 5% more.
Read the full interview here.
The traditional south facing configuration was optimal when the BOS cost was quite low compared to module cost. But in today’s pricing environment where the share of PV module cost as a percentage of Capex has dropped drastically, reducing the BOS cost becomes utmost important. And E/W configuration promises that BOS cost reduction.
What are your views on the South vs E/W configuration? ___________________________________________________________________________________________
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11 thoughts on “Rooftop PV – Is a East-West Configuration Better Than The traditional South Facing Configuration?”

  1. Jagannadha Raju

    Its very interesting and useful information to me for making many installation in future in East -West facing buildings-Regards
    -Jagannadha Raju

  2. In the UK, an EW rooftop system only seems to get 75% output of a S facing system the same size. I appreciate that on a ground mont system you may get more panels in EW because you can put them back to back, but generally always better S facing if they fit. Maybe further south, difference decreases and on the equator, would be the same.

  3. The technical performance of the plant will depend on geo-location, technology and other frame conditions. It is difficult to compare system in general and I would like to avoid this.
    By the end of the day there will be the question what the definition of performance really is. I see a technical performance, but also a economical performance.
    Since our customers understand solar-PV systems as a investment, they will look for economic performance. I agree that the specific yield form a east-west-system might be lower than the specific yield from a system facing south, but we have to look at the specific investment costs to see the full picture.
    Again, I propose to look at a individual system and compare the individual designs based on given space, location, frame conditions, investment costs and specific yield to prepare a well informed decision on what is the best system for the individual demand or application.

  4. I do not know Sebastian, but I would partly support him. The yield difference is much higher in the higher latitudes, when the employment of SATs too do not give significant yield increase. The specific yield in any case can not exceed the N-S orientation unless there is blockage to the sun light.

  5. If you employ modules faced with Saint Gobain Albarino P textured solar glass you can achieve up to 10% additional yield in an East West orientation in the UK and similar latitudes.
    We have installed Emmvee modules (German-Indian manufacturer using Bosch cells)with this glass on a number of projects with good results and are hoping to secure a very large West facing roof installation very soon. or Google Saint Gobain Albarino P

  6. Very interesting reading. So far I have always considered that the module orientation SHOULD be North-South only. But this reading has impacted by views.
    Ashok Toshniwal

  7. Hi Madhavan
    I’ll run some PVSyst analysis and send you the results. One thing I’d like to mention here is that even though we, as solar professionals, like to do cost/investment analysis (compare system output to investment/costs), the client only cares about the final system output.
    I’ll give you an Off-Grid system’s example. A client can buy and install a 1kWp system for any price ranging from 1.2 lakh to 2.5 lakh (even 3 lakh in some cases). His final assessment of the system will be based on the number of hours his fans, lights, computers, and other appliances run. He will not care whether he could have gotten saved Rs. 5000 if he allowed his appliances to run for 30 mins (just an assumption here) less. The purpose of the off-grid system is then defeated.
    This case may not hold true for an On-Grid system where I will argue that a tracking system is always the best choice. However, for an on-grid system I have doubts that the E-W orientation will save some structural costs and help the yield (increased GCR may pose some isses). But I’ll run some analysis on this as well. I’ll also work on some CAD designs and send them across.

    1. Hi Gayrajan,
      Thanks for the comments.As the article mentions, E-W still may be better only in certain cases, but the point is that this option hasn’t been explored much.
      I look forward to your PVSyst analysis.

  8. Prof. B. Raghavendra Prasad

    Dear Mr. Madhavan Nampoothiri
    We have been looking at installing Solar PV system as part of our clean and sustainable energy initiative. I found that your portal has lot of very useful information. It has been a good learning exercise reading them. However, I could not read much of the white paper “Roof top ideas for India” as the hyperlinks were not opening. Please send me the .pdf or the .doc file of the same.
    Thank you

    With best regards
    B. Raghavendra Prasad
    Dr. B. Raghavendra Prasad
    Indian Institute of Astrophysics
    Department of Science & Technology
    Government of India
    Bangalore – 560 034, INDIA
    Phone : +918022541294 (Office)
    : +918028452197 (Residence)
    Mobile : +919448444001

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