Techno Commercial Analysis of DC Overloading in Solar Photovoltaic Power Projects

Posted on Posted in Knowledge Center

overloading

The concept of overloading is not new. And it has its own pros & cons

Lets walk through the Techno commercial analysis of DC Overloading in Solar Photovoltaic Power Projects

The Inverter has been overloaded on DC side due to the following list of benefits:

  • Inverters are power converting devices which merely convert the energy received by them, hence in order to maximize the generation in a solar power plant, the DC side is generally overloaded to a certain limit. The input energy received by the inverter is dependent on the solar irradiation which varies throughout the day. The morning and evening period generally witness low levels of irradiation. Connecting higher DC  to inverters helps transmit higher energy to inverter, hence increasing the inverter output during these low irradiation conditions leading to significant gain in energy overall.

Screen Shot 2016-01-29 at 2.56.27 PM

  • Inverters are power electronics devices which give maximum efficiency when input power is close to 90-100% of the inverter’s rated power. As we know that the modules in the field are subjected to higher ambient temperatures (as compared to Standard Test Conditions(STC) at which they are tested)  which leads to degradation in output of the modules, we can balance this loss by putting in extra DC power to harvest higher DC energy which also helps inverter work at max efficiency.
  • SPV modules are subjected to annually degradation of 0.7% year on year which again leads to low power input to the inverters and hence lowering its efficiency & corresponding output power. In order to maintain the rated DC power of the plant after years of operations overloading of inverters comes to aid in order to maximize the power been generated throughout the plant life-cycle.

The benefit in terms of Generation and Cost has been analysed and graphically represented below:

The below analysis is based on the assumed capacity of 1MW solar PV plant at Koppal (NE coordinates). The values may vary depending upon the increase/decrease in capacity.

The cost analysis has been prepared on the assumed Tariff rate of INR 5.00/kWh. The values presented here are merely indicative in nature and these does not include any additional O&M cost over and above the standard O&M conditions.

Cost benefit with DC overloading

Analysis of overloading

The above graph shows the energy gain and cost estimation per Watt for 10%, 15% and 20% overloading on DC side. The energy generation considered here is the estimation of annual energy generation for the first year from a typical 1MW solar PV plant for the Koppal location.

The graph shows that increase in overloading on DC side increases the energy generation with increase in cost per Watt which ultimately increases the probability of meeting the AC PLF of 20%.

It is distinct that the cost benefit for the project developer increases with increase in DC capacity.

Long terms Energy Generation trend with considered DC overloading on the Solar Inverter

* Database considered: Meteonorm 7.1

Assumptions

  • Module degradation rate of 0.70% YoY has been taken in to the account
  • Discount factor has not been taken in to account which will impact the time value of money
  • O&M cost does not included in the cost benefit analysis

Energy generation trend in life cycle of Solar PV Project with overloading

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6 thoughts on “Techno Commercial Analysis of DC Overloading in Solar Photovoltaic Power Projects

  1. Dear Sir,

    Your estimate seems to be on higher side. I think you have not taken into consideration the increase in cost of additional structure, cables, String combiner boxes, SCADA system cost as well as additional losses in the system. In addition to the same, due to increase in no of modules the cleaning charge gets increased, since the cleaning charges are linked to the no of modules to be cleaned. No need to say that the O&M cost also increases due to maintenance of higher no of modules.
    This does not seem to give a realistic view.

  2. Nice informative article. May I know how cost per watt increases with increase in DC loading. i.e what other extra components required with increase in DC loading

  3. Pl,explain how to overload on D,C,side ? I am having a small P>V.Panel of 75 Watt and connected through 12 Volt Battery for my Residential power use. Regards, M.D.date

  4. This is very useful. Thank you for sharing. Also it will be interesting to know, what is optimum inverter loading ratio, that way can come to a solution that will have max DC loading on inverter and in turn max cost benefit analysis.

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