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What is underperformance in solar power plants?

Updated: Jul 11

Solar Modules Underperformance issue not necessaryly, lack of cleaning of solar panels

General statics indicate that solar underperformance results in a loss of 8% to 15% of energy yield in rooftop solar power plants. Different sources such as 'kwtokwh' and 'kWh Analytics' substantiate this solar underperformance with data. In this blog, we will discuss what is solar underperformance, and the different causes of solar underperformance


What is solar underperformance?

Any deviation in the projected performance of a solar power plant is treated as underperformance. In a few cases, this is attributed to the overestimation of solar production or climate change-related lower irradiance values at a location. However, the consensus is now tilting towards attributing the underperformance to solar equipment inefficiency or degradation in the quality of solar components over time.

Why solar losses go unnoticed?

Many solar plants don’t meet their expected performance levels, but this issue often goes unnoticed because plant owners mistake solar generation monitoring for solar performance management. To put it simply, monitoring solar generation is like checking how much fuel is in your car's tank while managing solar performance is like making sure your car is running smoothly and efficiently. Just because you have fuel in the tank and your car is running doesn't mean your car is performing at its best. Similarly, just because a solar panel is generating energy doesn't mean the solar plant is performing optimally. Moreover, solar plant owners attribute underperformance to a lack of solar panel cleaning, which is not true in many cases.

Key causes of solar underperformance

The four primary reasons for solar underperformance or losses in rooftop solar plant are discussed below:

(1) Quality Degradation of Solar Components

The quality of solar components and installation can degrade over time, leading to a reduction in their efficiency. The solar panel, inverter, and other components are exposed to harsh weather conditions, and over time, they can develop faults that affect their performance and increase solar losses. This can be due to manufacturing defects, improper installation, or simply wear and tear over time. In some cases, the use of low-quality or counterfeit components or wrong installation practices can also lead to underperformance.

Some common issues which cause losses in solar panels are listed below:

Common Solar Module Defects
Common Solar Module Defects

Potential Induced Degradation (PID)

PID causes a significant reduction in the performance of PV modules over time, leading to reduced energy output and lower returns on investment. PID occurs when a voltage difference between the PV module's cells and the ground is formed due to the presence of moisture or other pollutants. This voltage difference may induce a flow of electrical current through the PV module's cells, which can lead to a degradation of the cells and a drop in energy output. The severity of PID can depend on several factors, including the quality of the PV modules, the amount of moisture or contaminants present, and the voltage difference between the cells and the ground.

Micro cracks or Cell Cracks

Cell cracks may happen during transportation, installation, or due to environmental factors such as hail, temperature changes, or mechanical stress. Cell cracks can result in a decrease in power output and, in severe cases, complete module failure.


Hotspots are localized spots on the solar module where excessive heat is generated due to a problem with the module's electrical circuitry. This can happen when a cell is shaded, or damaged, or when the module is improperly connected. Hotspots can cause permanent damage to the module, reducing its lifespan and output or solar fires.


Delamination is caused when the layers of the solar module separate due to moisture or other environmental factors. This results in a decrease in power output and, in severe cases, complete module failure. Delamination may also increase the risk of fire.

Snail trails

Snail trails are a discolouration of the solar module's surface that can occur due to moisture or environmental factors. While snail trails need not necessarily impact power output, they can affect appearance and could be a symptom of other issues, such as delamination or corrosion.

Different types of soiling loss
Different types of Soiling

Soiling of solar modules results in losses ranging from 0.5% to 10% based on the region, tilt angle and weather conditions. Periodic cleaning of solar panels can reduce soiling loss.

Mismatch losses

Mismatch losses are caused due to variations in soiling / tilt / temperature / Wp rating / irradiation levels in Solar Modules. For Solar modules connected in a single string of a string inverter, the power output of solar modules is limited to the least performing solar module in that string leading to mismatch loss. Mismatch loss can be reduced to some extent using module-level power electronics such as optimizers or microinverters.


Vegetation growth or new constructions causing shade on solar modules is also a common issue which caused underperformance in solar modules

Solar inverters may develop 20+ faults during their operation. A few common issues in Solar Inverters are listed below:

Inverter deration

Deration is due to an increase in the internal temperature of the solar inverter. Solar inverter's efficiency goes down when the inverter temperature exceeds a certain threshold. Most solar inverters are equipped with temperature sensors to monitor the inverter's internal temperature the electronic components from overheating and degrading. When the internal temperature exceeds a certain threshold, the inverter automatically reduces its output power or switches to a lower power mode, known as deration. Issues with inverter fans or objects blocking heat dissipation of the solar inverter or direct exposure to sunlight can cause the deration of the solar inverter.

Inverter clipping loss

Clipping occurs, when the solar module's potential power output capacity becomes higher than the inverter's output power, thus limiting the solar plant output to the inverter's maximum rated power. During clipping, the excess power from the solar panels is lost, and the overall generation of the system is reduced. Inverter clipping typically occurs, when the DC capacity of the power plant is significantly higher than the AC capacity of the inverter.

Insulation fault

Insulation fault is caused due to insulation failure in cables, solar connectors or junction boxes or inverters. Insulation faults could be triggered by moisture ingress, physical damage to the insulation, and manufacturing defects. Insulation faults and ground faults can be dangerous, as they can lead to electrical shock, damage to the inverter and other electrical equipment or even cause a fire.

Arc faults

Arc faults happen in the DC circuit due to an unintentional electrical discharge in the form of an arc. An arc fault occurs due to a connection break in dc cables or junction boxes or connectors or a damaged component. Most of the good quality inverters come with built-in Arc Fault Protection devices to prevent the intensity of DC arcs and related fire incidents.

Some common issues in the Solar Balance of system components are listed below:

  • Weak DC Junction Box or MCBs or DC wiring causing arcing

  • Failed SPD (Surge Protection Devices) or MCB causing ground fault or leakage current

  • Tripped MCB or blown fuses or SPD due to surges

  • Loose or very tight clamps may cause module glass breakage

  • Failed earthing due to galvanic corrosion

  • Inter-row seasonal shading due to improper installation of structure

(2) Extreme Climate

Extreme weather events such as storms, snow, hurricanes, hail, heat waves, and heavy rains can damage solar panels and other components, leading to reduced performance. Prolonged exposure to pollution and soiling can also affect the performance of solar panels by reducing the amount of sunlight that can be absorbed by the cells. Some of the common issues which we find after extreme climate events are listed below:

  • SPD tripping MCB due to surges

  • Solar Connector damage due to loose cable ties

  • Solar structure or solar module damage due to wind load exceeding design threshold

  • Water ingress in DC/AC junction boxes or Solar module junction boxes due to flooding or heavy rains

  • Module glass breakage due to hail storm or heavy snow load or objects falling on solar module glass

  • Lightening damage in case of sites with damaged/or no lightening arrestor

Damages to Solar Modules due to climate change
Damages to Solar Modules due to climate change

(3) Unstable Grid

Solar power systems are connected to the electrical grid, which can be subject to surges and variations in voltage supply. These fluctuations can affect the performance of the solar plant, leading to reduced output or even damage to the components. The common issues which we see on the grid side are listed below:

  • Power outage: An outage in power will disrupt the operation of a grid-tied solar power plant leading to downtime and underperformance

  • Surges: secondary surges in the grid may cause the SPD to function and trip MCB or affect the life of inverters. These surges may be due to trees falling on electric posts or repair work done by the utility on the grid side or direct lightning impacting the grid

  • High voltage error: High voltage error occurs when the grid voltage goes above a set threshold (In India, 264 to 270 V), and the solar inverter shuts down. The increase in voltage is attributed to either a voltage rise in the cable due to wrong sizing or an issue from the electricity distribution company.

  • Low voltage error: Low voltage error as the name indicates occurs when the voltage falls below the set threshold (In India, 190 to 184 V)

The thresholds for high voltage and low voltage errors are decided by the utility and configured by Installer as per the compliance requirements of the electricity distribution company

(4) Improper Maintenance

Failure to perform regular maintenance may lead to a buildup of dust, debris, or soil on the solar panels, reducing their efficiency. It may also lead to the development of faults in solar inverters or cause connector/cable damage resulting in safety risks. Improper maintenance, such as cleaning the solar panels with hard water or harsh chemicals or high-pressure water, can also damage the components and reduce performance.


At SolYield, we are focused on improving lifetime performance of solar power plants using digital technologies. Do leave a comment, if you have any queries on this blog. You can also reach us at

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