Losses in Solar PV System: Part 1: DC, Mismatch, Wire

As a solar power EPC company, delivering on the promise of efficient energy production and smooth operation of a solar installation for 25 years or more is crucial for customer satisfaction. The energy output of a Solar PV System is influenced by various factors including the quality of components used, the design of the system, the installation process, and Operation & Maintenance practices. External elements such as weather, shading, and soiling also play a significant role.

To maintain optimal performance, regular monitoring of the solar plant is crucial. This article will provide an overview of the common causes of energy production losses in solar PV systems.

What are PV System Losses?

PV system Losses in system simulations refer to effects that are not explicitly modeled by simulation engines. They are calculated as percentage reductions to estimated system production. Here, we will talk about Losses in Solar PV power plants like DC losses Wire loss mismatch loss, availability loss & connection losses.

Types of Losses:

DC Loss

DC losses refer to factors that reduce the amount of direct current (DC) energy produced by solar panels before that energy is converted into alternating current (AC) by the inverter to be used for electrical appliances at home and the current exported to the electrical grid. Most of the DC losses that occur in Solar PV systems are at the module level.

NOTE: We have already discussed in detail the Losses that occur in PV modules in our previous article. In this article, we will be covering only some of the losses at a module level in brief.

Module Nameplate Rating Loss

Nameplate rating loss is the difference between the power stated on the module’s datasheet and how it actually performs at Standard Test Conditions (1000 W/m2 and 25oC).

This type of loss may occur in modules with older technology, particularly those that were not binned into 5W or 10W increments. (As a result of the manufacturing process, modules vary slightly in their power ratings. Binning refers to grouping modules according to their power ratings.)

Mismatch Loss

Mismatch loss is caused by slight differences in the electrical characteristics of the modules installed, and the DC power output is reduced by a fixed percentage.

Mismatch losses in PV systems with a wide error range on rated power, losses will be greater. Depending on the setup of the system and the length of strings, mismatch values range from 0.01% to 3%. Mismatch losses also include losses due to panels installed at different azimuths (in the case of string inverter), partial shading of panels, and mismatch losses in solar PV modules.

Light Induced Degradation

The phenomenon of light-induced degradation (LID) affects a large segment of the crystalline silicon cell market. Light-induced degradation occurs when the solar cell is exposed to sunlight for the first time till the first few days of installation. This can lead to energy production losses of 0.5% – 1.5%.

Note that, LID impacts some module types but not others. The causes of LID, and why certain types of modules are affected, can be explained by understanding two factors: the crystal structure of the solar cell (monocrystalline or multi-crystalline) and its electrical properties (P-type or N-type).

Silicon wafers that make up a solar cell typically form boron-oxygen compounds that cause LID. Monocrystalline solar cells(p-type) with boron will exhibit the most LID, and multi-crystalline solar cells(p-type) with boron will also exhibit LID, but to a lesser extent since oxygen concentrations are lower in multi-crystalline solar cells. The LID process is usually not taken into account in the lab testing of modules, so it won’t be included in the datasheet.

SunPower and LG both use n-type silicon in some of their newer modules, which does not suffer from LID because it contains no boron.

Solar PV System Wiring Loss

There are several components in circuits that can cause a voltage drop, including resistors. There is a small amount of internal resistance in wires, which varies with the thickness and length of the wire. It is up to installers to decide whether to use thicker wire, which reduces resistive losses, or a thinner gauge. A minimum thickness for wires is specified in the National Electric Code in order to prevent electrical fires.

PV Connection Losses

In a PV System, we use PV connectors to connect two modules with each other in a series string. They are also used to connect module level devices to modules such as microinverter.

Causes for PV connection losses:

The connection losses are the resistive losses that occur across diodes and wiring connectors. Most solar panels contain bypass diodes, which let other modules on a string bypass a shaded panel or are poorly performing. Due to the internal resistance of the material and imperfections in the contact surface, these components will have a small voltage drop.

Note that Solar PV Systems with DC optimizers will have to double the number of connections. There are also extra connective losses that are captured in the DC Optimizer component losses.

PV System Availability Loss

PV system availability losses are those losses that disconnect the PV system and prevent it from producing electricity for the home. This loss occurs when the inverter shuts down or a failure occurs. Due to grid outages or any other unusual circumstances due to which solar PV system stops generating. These types of losses are unpredictable thus, the amount of generation loss cannot be estimated that they will cause.

What are PV System Losses?

PV system Losses in system simulations refer to effects that are not explicitly modelled by simulation engines. They are calculated as percentage reductions to estimated system production. Here, we will talk about Losses in Solar PV power plants like DC losses Wire loss mismatch losses, availability loss & connection losses.

Types of Losses:

DC Loss

DC losses refer to factors that reduce the amount of direct current (DC) energy produced by solar panels before that energy is converted into alternating current (AC) by the inverter to be used for electrical appliances at home and the current exported to the electrical grid. Most of the DC losses that occur in Solar PV systems are at the module level.

NOTE: We have already discussed in detail the Losses that occur in PV modules in our previous article. In this article, we will be covering only some of the losses at a module level in brief.

Module Nameplate Rating Loss

Nameplate rating loss is the difference between the power stated on the module’s datasheet and how it actually performs at Standard Test Conditions (1000 W/m2 and 25oC).

This type of loss may occur in modules with older technology, particularly those that were not binned into 5W or 10W increments. (As a result of the manufacturing process, modules vary slightly in their power ratings. Binning refers to grouping modules according to their power ratings.)

Mismatch Loss

Mismatch loss is caused by slight differences in the electrical characteristics of the modules installed, and the DC power output is reduced by a fixed percentage.

Mismatch losses in PV systems with a wide error range on rated power, losses will be greater. Depending on the setup of the system and the length of strings, mismatch values range from 0.01% to 3%. Mismatch losses also include losses due to panels installed at different azimuths (in the case of string inverter), partial shading of panels, and mismatch losses in solar PV modules.

Light Induced Degradation

The phenomenon of light-induced degradation (LID) affects a large segment of the crystalline silicon cell market. Light-induced degradation occurs when the solar cell is exposed to sunlight for the first time till the first few days of installation. This can lead to energy production losses of 0.5% – 1.5%.

Note that, LID impacts some module types but not others. The causes of LID, and why certain types of modules are affected, can be explained by understanding two factors: the crystal structure of the solar cell (monocrystalline or multi-crystalline) and its electrical properties (P-type or N-type).

Silicon wafers that make up a solar cell typically form boron-oxygen compounds that cause LID. Monocrystalline solar cells(p-type) with boron will exhibit the most LID, and multi-crystalline solar cells(p-type) with boron will also exhibit LID, but to a lesser extent since oxygen concentrations are lower in multi-crystalline solar cells. The LID process is usually not taken into account in the lab testing of modules, so it won’t be included in the datasheet.

SunPower and LG both use n-type silicon in some of their newer modules, which does not suffer from LID because it contains no boron.

Solar PV System Wiring Loss

Several components in circuits can cause a voltage drop, including resistors. There is a small amount of internal resistance in wires, which varies with the thickness and length of the wire. It is up to installers to decide whether to use thicker wire, which reduces resistive losses, or a thinner gauge. A minimum thickness for wires is specified in the National Electric Code to prevent electrical fires.

PV Connection Losses

In a PV System, we use PV connectors to connect two modules in a series string. They are also used to connect module-level devices to modules such as microinverter.

Causes for PV connection losses:

The connection losses are the resistive losses that occur across diodes and wiring connectors. Most solar panels contain bypass diodes, which let other modules on a string bypass a shaded panel or are poorly performing. Due to the internal resistance of the material and imperfections in the contact surface, these components will have a small voltage drop.

Note that Solar PV Systems with DC optimizers will have to double the number of connections. There are also extra connective losses that are captured in the DC Optimizer component losses.

PV System Availability Loss

PV system availability losses are those losses that disconnect the PV system and prevent it from producing electricity for the home. This loss occurs when the inverter shuts down or a failure occurs. Due to grid outages or any other unusual circumstances due to which solar PV system stops generating. These types of losses are unpredictable thus, the amount of generation loss cannot be estimated that they will cause.

Originally published at futr.energy/knowledge