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Over-sizing of Solar Arrays

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Over-sizing is become a popular theme in solar power plant design in India as there is an increased pressure to drive down costs in installations. Let us understand the technical benefits and dangers of over-sizing solar arrays.

1. Advantages of Oversizing Solar Arrays

1.1 Higher Yield

As all solar EPCs know, a solar array typically never generates at more than 80% of the nameplate capacity or kWp. Thus a 10 kWp solar array, at any given time in Indian conditions would rarely exceed 8 kWp. Thus if we can connect more than 10 kWp of solar panels to a system with a 10 kVA inverter, the net generation or yield of electricity will ofcourse be higher.

1.2 More Optimal or Lower System Costs

In an industry where Rs/ Wp is the main criteria for vendor selection, everyone is pushed to optimize cost vs generation. Specifically in smaller residential roof top systems, the inverter is sometimes as high as 27 Rs/Wp or more. In such cases, by oversizing within acceptable technical limits it is possible to reduce the cost of the system without impacting system efficiency.

2. Disadvantages of Oversizing Solar Arrays

2.1 Components age faster

When solar inverters are loaded at more than there ratings, the inverter is operating at its peak capacity for more percentage of the time- this can lead to overheating and shorter life-span of the components in the system. Hence the components will age faster. This it is extremely important to ensure that you are not voiding the inverter manufacturer’s warranty by oversizing the solar plant. Most reputed inverter manufacturers like Fronius and Delta will provided a written undertaking on what percentage of oversizing is supported under warranty.

2.2 Lower Efficiency

efficiency-oversizing-inverter

Oversized arrays typically have higher Vdc or string voltages. Refering to an inverter’s efficiency curve, we find that over-sizing an inverter to the higher limits of the MMPT voltage range may cause the system to always run at 0.5-2% lower efficiencies. It is however important to note that an inverter can be oversizing properly up to 20-30% by staying in the optimal voltage range for highest efficiency.

2.3 Power Clipping and Generation Loss

Under-sizing your inverter will mean that the maximum performance of your system will be dictated by the size of your inverter and regardless of how big the output of your solar panels is, the output will be cut-off by the inverter.

Let’s take and example where you oversize a 10 kW solar inverter by 150% with 15 kWp solar panels. In such a condition, at noon, 15 kWp of solar panels may be capable to produce 12 kW of power. However the inverter will only be able to process 10 kVA and 2kW/ 2kVA will be lost or clipped.

Additionaly most good quality inverters derate the inverter output in high ambient temperatures in order to manage temperature and increase the life of the inverter. If a system is over-sized by more than recommended design, then the power may be clipped for more percentage of the time.

3. Conclusion

Inverter and array sizing are one of the most important tools in the hands of a solar system installer to optimize cost and generation.

If the inverter is sized with the ‘average power received on-site’ then some money can be saved by choosing a smaller inverter (‘average power received’ being a calculation based on meteorological data and estimated solar panel efficiency at those conditions).

Sunkalp Energy recommends a 120-130% oversizing with most reputed solar inverter brands for operation in Northern India.

 

Kanika Khanna

Kanika is passionate about data and technology- and writes about how they apply to roof-top solar.

7 thoughts on “Over-sizing of Solar Arrays

  1. Good article, thanks for sharing. Can you share your thoughts for oversizing using single axis tracker.

    I was surprised to see inverter costing 27 INR/Wp, could you give an example?

    1. Dear Siddharth,
      Typically generation increases with use of single axis tracker, but the peak power generated at any given time will still not be more than the design Wp with a fixed installation. So my assessment is that with similar oversizing of 20-30%, you will be safe on accounts of technical parameters such as temperature clipping, power clipping etc. However with tracking, your inverter will operate at the peak capacity for almost 100-200% more time causing ageing. As long as the manufacturer of the equipment will provide you a certificate that warranty will not get voided, it is safe to oversizing with single axis tracking.

      27Rs/ Wp is the cost for very small capacity inverters (1-3 kW) from international brands such as Fronius or Schneider.

  2. I also want to install SOLAR SYSTEM on my house roof-top in Delhi DDA FLATS. My existing load is 5 KW. Can anyone give the details of total installation expenses & the total saved amount comparing to my electricity bills which is presently 9000/- per month in summer & 2500/- in winter.

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