LeTID/LID-resistant wafers increase panel power in real-world operation
Doping is an important process in wafer manufacturing.
Most cells throughout the industry utilise some form of
doping to achieve p-type properties in their silicon. Earlier
generations of SunPower Performance panels used boron-
doped silicon, which has been known to be susceptible to
light induced degradation (LID). However, SunPower
Performance 5 panels use an enhanced doping process with
LID-resistant wafers to virtually eliminate the effects of LID.
SunPower Performance panels with cells from the LID-
resistant wafers were sent to Fraunhofer CSE for independent
LID and LeTID (light and elevated temperature induced
degradation) testing (figure 13). The final report delivered
from Fraunhofer CSE states:
• Power changes during LID testing are negligible (50 °C,
1000 W/m
2
, 15 kWh/m
2
, IEC 61215 MQT 19)
• In the LeTID test scenario (75 °C, 1 A, 702 h) no
degradation of panel power (<1 %) is observed
• The tested panels are stable regarding LID and LeTID
Given continued fleet monitoring and extended testing
results, SunPower Performance 5 panels offer a minimum
warranted power output of 98.0% in their first year of
operation, with a maximum annual degradation rate of
0.45% over 30 years.
Figure 13: Fraunhofer LID and LeTID test results for SunPower
Performance panels.
Lower temperature coefficient improves yield in higher temperatures
The temperature of a solar panel has a direct effect on its
ability to generate electricity. This has to do with the laws of
thermodynamics and how heat limits the ability of
electronics to produce power. As a panel heats up, power
output is reduced. This relative change in the panel related
to temperature increase is called its temperature coefficient.
The temperature coefficient is expressed as the percentage
decrease in power output for every 1-degree Celsius (°C)
increase in temperature beyond 25 °C. Improving the
temperature coefficient of the panel will decrease the power
loss experienced from higher temperatures.
SunPower Performance panels have a temperature
coefficient of -0.34 %/°C, which is validated by the
independent PV Evolution Laboratory. This means that for
every 1 °C above 25 °C, SunPower Performance panels
decrease in relative efficiency only by 0.34 %/°C.
This is a significant advantage for SunPower Performance
panels in comparison to conventional panels that exhibit
temperature coefficients in the range of 0.36% - 0.37% W/°C.
When comparing the performance of two panels in a hot
climate where the operating temperature could reach 60 °C,
the lower temperature coefficient of the SunPower
Performance panel offers a 1.1% advantage over the
conventional panel. In a 500W panel, this translates to an
additional 5.5W of power per panel.
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