Temperature Coefficient and Solar Panels: 2023 Guide

· Maysun Solar News,PV Industry News,PV Technology News

Bright, sunny days are ideal for producing solar energy, yet it's important to note that solar panels experience a decline in efficiency when exposed to excessive heat along with sunlight. This factor should be considered when selecting solar panels and estimating long-term energy savings. Solar manufacturers measure a solar panel's performance under high temperatures using a metric known as the "temperature coefficient". A lower temperature coefficient indicates superior performance of the solar panel in warm conditions. This article delves into what the temperature coefficient is, its various forms, and its significance for solar panels.

Contents:

  1. What is the Temperature Coefficient?
  2. What are the Main Types of Temperature Coefficients? (PMAX, VOC, ISC)
  3. How to Calculate the Temperature Coefficient?
  4. Why is Temperature Coefficient Important for Solar Panels?

What is the Temperature Coefficient?

Within the scope of solar panel efficiency, the temperature coefficient stands as a crucial, yet often overlooked aspect. This parameter is more than a mere technical specification; it reveals how well solar panels can adapt to different temperature conditions. It precisely measures the decrease in energy output when the temperature of a solar panel exceeds the 25°C (77°F) standard established in Standard Test Conditions (STC). The temperature coefficient is usually expressed as a percentage loss per degree Celsius (%/°C) or per degree Fahrenheit (%/°F).

Take, for instance, a solar panel with a temperature coefficient of -0.35%/°C. This means for every degree Celsius increase beyond the STC benchmark of 25°C, there's a 0.35% reduction in the panel's peak power output.

Understanding that the temperature coefficient is assessed under STC is essential. These conditions include a panel temperature of 25°C, solar irradiance of 1000 W/m², and an air mass of 1.5. This coefficient is a key measure of a solar panel’s performance stability across different temperatures. In practical terms, it affects the power output of the panel in environments where the temperature greatly differs from the 25°C norm.

What is the Temperature Coefficient

What are the Main Types of Temperature Coefficients?

The temperature coefficient is a key factor in determining the efficiency of solar panels in generating power. It's vital to have a deep understanding of temperature coefficients, especially those related to Voc (Open-Circuit Voltage), Isc (Short-Circuit Current), and Pmax (Maximum Power), to optimize energy production. This exploration will focus on these three specific temperature coefficients and their effects:

Open-Circuit Voltage (Voc) Temperature Coefficient:

Variable Direction: The Voc temperature coefficient can be either positive, indicating an increase in open-circuit voltage with higher temperatures, which is less common, or negative, the more typical scenario where open-circuit voltage drops as temperature increases.

Significance: With a usual span of -0.3% to -0.5% per degree Celsius, the negative temperature coefficient for Voc highlights the importance of considering and addressing the impact of temperature on open-circuit voltage during both the design and operation stages of solar panels.

Short-Circuit Current (Isc) Temperature Coefficient:

Common Decline: Similar to the Voc, the Isc temperature coefficient predominantly shows a negative trend, indicating a decrease in short-circuit current as the temperature rises.

Quantitative Spectrum: Typically ranging from -0.04% to -0.5% per degree Celsius, the Isc temperature coefficient underscores the essentiality of taking into account the influence of temperature variations on short-circuit current.

Maximum Power (Pmax) Temperature Coefficient:

Integrated Approach: The Pmax coefficient merges the influences of both Voc and Isc coefficients, providing a comprehensive view of how temperature fluctuations affect the maximum power output. It is often the primary indicator used to assess the impact of temperature on the efficiency of solar panels.

Negative Range: Generally falling between -0.2% and -0.5% per degree Celsius, this coefficient is crucial for evaluating the overall effect of temperature on solar panel performance.

How to Calculate the Temperature Coefficient?

The process of calculating the temperature coefficient for solar panels involves several steps. Here is a comprehensive guide:

Apply Formulas:

Utilize the following formulas for each coefficient:

Voc Temperature Coefficient (αVoc):

αVoc = [(Voc – Vocref) / Vocref] / (T – Tref)

Isc Temperature Coefficient (αIsc):

αIsc = [(Isc – Iscref) / Iscref] / (T – Tref)

Pmax Temperature Coefficient (αPmax):

αPmax = [(Pmax – Pmaxref) / Pmaxref] / (T – Tref)

Note:

T represents the current temperature.

Tref is the reference temperature (typically 25°C).

Vocref, Iscref, and Pmaxref are the respective reference values at Tref.

We can usually look for this indicator on the product detail page or datasheet of the solar panel. The graph below shows the temperature coefficient of Maysun Solar IBC full black solar panels:

How to Calculate the Temperature Coefficient

Why is Temperature Coefficient Important for Solar Panels? 

When evaluating the power reduction of IBC solar panels with a temperature coefficient of 0.29%/°C and PERC solar panels with a temperature coefficient of 0.34%/°C in environments with high ambient temperatures (40°C), it's crucial to consider several factors that influence the increase in operational temperature of solar panels. These include:

  1. Elevated Ambient Temperature: Directly increases the panels' starting temperature.
  2. Strong Solar Radiation: Leads to higher heat absorption by the panels, thus elevating their temperature.
  3. Limited Cooling: Poor cooling mechanisms can result in increased panel temperatures.
  4. Compact Installation or Blockages: These factors can create localized temperature spikes in the panels.

With these considerations, we can predict the operational temperatures of both panel types in a 40°C ambient setting and then determine their power degradation.

1. Calculating Operational Temperature:

Ambient temperature is 40°C.

The operational temperature might surpass the typical rise of 25°C, possibly reaching an increase of 40°C or more.

Thus, the operational temperature could be 80°C or higher.

To accurately gauge the effect of high temperatures on solar panel efficiency, we can apply a straightforward formula to calculate power degradation:

Power Degradation = (Actual Working Temperature – STC Temperature) × Temperature Coefficient

2. IBC Solar Panels (Temperature Coefficient of 0.29%/°C):

Increase in operational temperature: 80°C – 25°C = 55°C.

Power Degradation = 55°C × 0.29%/°C = 15.95%.

3. PERC Solar Panels (Temperature Coefficient of 0.34%/°C):

Increase in operational temperature: 55°C.

Power Degradation = 55°C × 0.34%/°C = 18.7%.

Under such elevated temperature conditions, the power degradation for IBC and PERC solar panels is 15.95% and 18.7%, respectively. This shows that IBC solar panels experience less performance reduction in high temperatures. Additionally, the disparity in power degradation between these two panel types grows with increasing operational temperatures. Hence, the temperature coefficient is a vital factor in considering energy efficiency and sustained performance in high-temperature environments.

In this scenario, Maysun Solar's IBC solar panels, boasting an impressive temperature coefficient of -0.29%/°C, present a significant edge. This advantageous temperature coefficient lessens the impact of high temperatures on the panels' functionality, thereby mitigating power generation losses. Opting for Maysun Solar's IBC panels could be a pr