How To Calculate A Performance Ratio Of A Solar Plant?

Solar power is a valuable source of renewable energy. It is an optimistic step towards sustainability. Thus, it is equally important to understand how to calculate the performance ratio of a solar plant. This helps to track the efficiency of the solar modules and prevent any loss. Read more for an elaborate preview of the performance ratio of a solar plant. 

India is progressively leading in solar energy production and application. There are several small-scale and utility-scale solar plants in India. In India, hundreds of housing societies have installed solar panels on the rooftop for household power utilisation. However, to sustain its efficiency, it is necessary to track the performance ratio of solar modules or solar plants. This is done through the calculation of its performance ratio. 

Performance ratio is a pivotal metric that tracks the operational efficiency and output of the solar plant. Performance ratio helps to quantify and compare the actual energy generation of the solar panels with the nominal or theoretical energy output. It is a quantitative indicator of how the solar panels are working. This is analysed in favourable conditions. 

The performance ratio might be hampered by consistent soiling on the solar panels. This can be resolved by occasional or monthly solar module cleaning service. This process removes the dust and grime from the panel surface, enabling seamless sunlight absorption and energy conversion.

What Is Performance Ratio or PR? 

Performance Ratio is an important aspect to determine the efficiency of the solar plant. It helps to understand the need of maintenance and repairs, ensuring prolonged lifespan of the solar modules. 

Performance ratio is generated by dividing the actual energy output with the expected or theoretical energy output. It is as mentioned below:

Performance Ratio (PR) = Actual Energy Output ÷ Expected Energy Output x 100%

The performance ratio is normally generated in percentage. A higher performance ratio denotes maximum efficiency of the solar modules. Whereas, a lower performance ratio denotes declined efficiency of the solar plant. 

The average performance ratio of an expansive utility-scale solar plant ranges between 70% – 80% as estimated by . It is determined by various factors like the location, weather conditions, frequency of maintenance, etc.

The solar plant in sunny areas like Rajasthan is expected to produce more solar energy than the rainy regions of South and South West India. However, the performance ratio of all these regions can be kept the same with efficient maintenance and technological advancements. 

What Are The Vital Components Of Performance Ratio? 

Actual Energy Output – The actual energy output is the total energy generated by the solar plant in a week or a month. It is the total power transferred to the grid after the conversion of sunlight. It is generally expressed in units like kilowatt hour (kWh) or megawatt hour (mWh). 

Theoretical Energy Output – The maximum theoretical energy output is the estimated power generation at optimal conditions or Standard Test Conditions (STC). 

PR= Actual AC Energy generated by plant / Nominal Energy or Theoretical Energy x 100%

Here Nominal Energy = GHI (in kWh/m2 X Rated module efficiency X Total Active PV area (in m2)

The parameters used for calculating theoretical energy are as follows:

Solar irradiation – Solar irradiation is the amount of the radiation received from the sun on the solar panels. It is expressed in (kWh/m2).

Total Active Module Area – It is the total area where solar modules are installed and is expressed in (m2).

Rated Module Efficiency – It is the typical efficiency or the ratio of energy output of the solar plant. It depends on the area and the technology used. 

What Is The Manual Method of Calculating Performance Ratio? 

Manual method of calculating performance ratio of solar panels is beneficial for small-scale and budget-constraint solar plants. It is also useful for academic purposes. Manual calculation of performance ratio requires following points. 

• Period of analysis – Performance ratio of solar plant is monitored and calculated for a year. It can also be calculated for a day, week, and monthly basis. 
• Efficiency of the installed solar modules – The operational efficiency of the installed solar modules can be fetched from the module datasheet. 
• Area of the solar module – The total area on which solar modules are placed. It is normally available in design layouts or EPC (Engineering, Procurement, and Construction) documents.
• Theoretical or nominal energy – This is the expected energy output based on the module performance and total irradiance. 
• Average Solar Irradiance – It is measured using irradiance sensors installed at the solar plant or even pyranometres. 

What Are The Steps For Manual Calculation of Performance Ratio?

Here are the steps involved in the manual method of calculating performance ratio:

• Gather required data including installed capacity, panel efficiency, solar module area, monthly generated energy, and solar irradiation. 
• Calculation of nominal energy output
• Calculation of performance ratio using the formula

It is vital to ensure that the irradiation data is recorded at the Plane of Array. The irradiance data and module efficiency should be accurate and in real time. To get the proper results, one must exclude the maintenance, repairs, and downtime of the solar modules. 

Comparison of Manual and Automatic Method of Performance Ratio Calculation

Manual Method of Calculation

• Beneficial for primary and budget-constraint assessments.
• No requirement of costly tools or advanced software.
• A medium of education for researchers and university students. 
• Manual method compromises accuracy in some cases.
• Being a conventional method, it is time-consuming.
• Not suitable for real-time monitoring. 

Automatic Method of Calculation

• SCADA-based systems allow continuous monitoring of performance.
• Enables real-time or live performance tracking.
• Its integration with weather forecasts prevents downtime or operational loss.
• Provide alerts for poor performance or any defect. 
• Comparatively expensive than the manual method but with assured accuracy.

What Are The Factors Affecting Performance Ratio? 

Soiling – The accumulation of dust and other environmental pollutants on the solar panels is called soiling. It hampers the panel’s ability to absorb sunlight and convert it into power. 

Temperature Loss – The performance ratio of the solar module gets impacted due to the loss of favourable temperature. Heating caused by the high temperature can hamper the overall efficiency of the solar modules. 

Shading – Shading over the solar modules caused by the trees, branches, buildings or any other aspect can disturb the efficiency. This reduces the power output.

Light Reflection – The reflection of the light from the panel’s surface results in the loss of energy output. Reducing the light reflection from the PV cells can uplift the operational efficiency of the solar plant. 

What Are The Best Solutions To Improve The Performance Ratio Of Solar Panels? 

Below are the best solutions applied to tackle the declining performance of the solar modules.  

Solar Panel Cleaning System – Solar panel cleaning is a process of removing accumulated dust using water-based or waterless techniques from the solar panels. This prevents energy loss caused by low absorption of sunlight. The power generation increases by 10% – 15% with consistent solar panel cleaning. 

Ensure Inverter Efficiency – Installing and using highly efficient inverters with the maximum power point tracking will enhance the energy output of the solar panels.

Bifacial Solar Panels – Placement of bifacial solar panels can prevent the loss of energy caused by light reflection. 

Timely Maintenance and Repairs – Consistent monitoring of defects and timely maintenance is necessary to sustain the efficiency of the solar modules. To improve the performance ratio, it is always advantageous to hire an experienced operations and maintenance provider. 

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