High temperatures affect far more than the instantaneous output of solar PV modules. They can reduce PV string voltage, trigger inverter thermal derating, accelerate battery aging, increase cable losses, and create localized hot spots at electrical connections.
This technical white paper explains how elevated temperatures affect the main components of a solar energy system, including PV modules, solar inverters, batteries, cables, connectors, and protection devices.
It also presents practical methods for evaluating thermal losses and reducing temperature-related risks through proper system design, installation, monitoring, and preventive maintenance.
What This White Paper Covers
- The difference between ambient temperature and solar cell temperature
- The effect of temperature on PV module voltage and output power
- How to calculate temperature-related power losses using module datasheet values
- The effect of high temperatures on PV string voltage and MPPT operation
- Inverter thermal derating and its effect on energy production
- The impact of installation location and ventilation on inverter performance
- Battery aging under high-temperature operating conditions
- Cable derating, voltage drop, and increased electrical losses
- Hot spots caused by loose or high-resistance electrical connections
- Practical inspection and maintenance recommendations for hot climates
Why High Temperature Matters
Solar PV modules are rated under Standard Test Conditions, where the cell temperature is assumed to be 25°C. However, during real operation, module cell temperature can rise significantly above ambient temperature, especially during periods of high solar irradiance and limited airflow.
As cell temperature increases, module voltage decreases. Although current may increase slightly, the reduction in voltage normally causes the module’s maximum output power to fall.
The actual power output can be estimated using the module temperature coefficient:
PT = PSTC × [1 + γP × (Tcell − 25)]
Where:
- PT is the estimated module power at the actual cell temperature
- PSTC is the rated power under Standard Test Conditions
- γP is the module maximum-power temperature coefficient
- Tcell is the actual solar cell temperature
For example, a PV module rated at 550 W with a maximum-power temperature coefficient of −0.35%/°C may experience a noticeable reduction in output when the cell temperature reaches 65°C.
The temperature difference from Standard Test Conditions is 40°C:
Estimated power loss = 40 × 0.35% = 14%
The module may therefore produce approximately:
550 W × 0.86 = 473 W
This calculation represents the temperature effect only. Other losses, including soiling, mismatch, cable losses, inverter losses, shading, and degradation, must be assessed separately.
Effect on PV Strings and MPPT Operation
High temperature reduces both the open-circuit voltage and the maximum-power-point voltage of PV modules. Because modules are connected in series within a PV string, the voltage reduction is multiplied across the complete string.
If the string operating voltage falls close to or below the inverter’s minimum MPPT voltage, the inverter may be unable to track the maximum power point efficiently.
This can result in:
- Reduced energy production
- Unstable MPPT operation
- Delayed inverter startup
- Early inverter shutdown
- Reduced performance during the hottest operating periods
PV string design should therefore be checked at both low and high temperature conditions. Low temperatures determine the maximum possible string voltage, while high temperatures determine the minimum operating voltage.
Effect on Solar Inverters
Solar inverters generate internal heat during operation. When ambient temperature is high or ventilation is insufficient, internal component temperatures may rise beyond the inverter’s normal operating range.
To protect its internal components, the inverter may automatically reduce its output power. This is known as thermal derating.
Thermal derating can be caused by:
- Direct exposure to sunlight
- Installation inside an unventilated enclosure
- Insufficient clearance around the inverter
- Blocked ventilation openings
- Dust accumulation on cooling surfaces
- Fan deterioration or failure
- High electrical loading during peak temperature periods
Thermal derating should not be confused with inverter clipping. Clipping occurs when available DC power exceeds the inverter’s rated AC output. Thermal derating occurs when the inverter reduces output because of high internal temperature.
Inverter temperature, output power, alarm history, and derating events should be reviewed together to determine whether production losses are thermally related.
Effect on Batteries
High operating temperatures accelerate the chemical and electrochemical processes responsible for battery aging.
The result may include:
- Faster capacity degradation
- Increased corrosion in lead-acid batteries
- Higher water loss in flooded batteries
- Increased risk of cell imbalance
- Reduced expected service life
- Activation of battery management system protection limits
- Restrictions on charging or discharging current
Battery rooms and enclosures should be designed to maintain the manufacturer’s recommended temperature range.
Charging settings should also consider battery temperature. Where supported, temperature-compensated charging should be used to prevent overcharging or undercharging under changing thermal conditions.
Battery temperature should be measured at cell or module level whenever possible. Room temperature alone may not accurately represent the temperature of the battery during charging and discharging.
Effect on Cables and Connections
Higher conductor temperature increases electrical resistance and therefore increases power loss and voltage drop.
Cable current-carrying capacity must be corrected according to:
- Ambient temperature
- Installation method
- Cable grouping
- Enclosure temperature
- Exposure to direct sunlight
- Ventilation conditions
- Manufacturer correction factors
High-resistance electrical connections can create localized heating. These conditions may occur at:
- PV connectors
- Fuse holders
- DC isolators
- Circuit breakers
- Terminal blocks
- Cable lugs
- Combiner boxes
- Inverter terminals
Possible causes include poor crimping, loose terminals, contamination, corrosion, incompatible connectors, and incorrect installation torque.
Thermal imaging is a valuable inspection method for identifying abnormal temperature differences between similar electrical connections operating under comparable load.
Thermal Design Recommendations
To reduce the effect of high temperatures on solar PV systems:
- Provide adequate airflow behind PV modules
- Avoid installing modules directly against hot surfaces without ventilation
- Install inverters in shaded and well-ventilated locations
- Maintain the manufacturer’s required clearance around inverters
- Review inverter thermal derating curves during equipment selection
- Apply cable correction factors for high ambient temperatures
- Minimize excessive voltage drop on DC and AC circuits
- Use compatible and properly installed PV connectors
- Apply the correct tightening torque to electrical terminals
- Monitor module, inverter, battery, and enclosure temperatures
- Clean inverter filters, fans, and ventilation openings periodically
- Include thermal imaging in preventive maintenance programs
- Investigate repeated thermal alarms rather than resetting equipment without diagnosis
Practical Site Assessment
When a solar PV system shows reduced output during hot periods, the following data should be reviewed:
- Solar irradiance
- Ambient temperature
- PV module temperature
- DC string voltage and current
- Inverter internal or heat-sink temperature
- Inverter output power
- Inverter alarm and derating logs
- AC and DC voltage drop
- Battery temperature and state of charge
- Thermal images of connectors and protection devices
- Comparison between similar PV strings
The objective is to separate temperature-related module losses from inverter derating, cable losses, connection faults, shading, soiling, or other system problems.
Conclusion
High temperature affects the complete solar energy system, not only the PV modules.
A system may have adequate installed capacity and still underperform because its actual operating temperatures were not fully considered during design and equipment selection.
Reliable performance in hot climates requires:
- Temperature-aware PV string design
- Suitable inverter selection and installation
- Correct battery thermal management
- Proper cable derating
- High-quality electrical connections
- Continuous monitoring and preventive inspection
The correct design approach should be based on real site conditions rather than nameplate ratings alone.