Six Points: High-Temperature Losses to Suspect and Countermeasures in Summers with Low Power Generation

In summer, because solar radiation is greater, people tend to think that the power output of solar power systems will increase significantly. However, in reality, on clear midsummer days you may feel that "generation does not rise as much as expected," "generation efficiency is lower than in spring," or "output plateaus around midday." Low power output is not necessarily due only to malfunctions. Because solar panels and surrounding equipment are affected by high temperatures, in seasons when ambient and equipment temperatures rise it is important to consider high-temperature losses as a potential factor to check.

What is particularly important for operations staff is not to judge solely by the fact that power generation is low, but to separate and examine solar irradiance, air temperature, equipment temperature, past performance, the installation environment, and the operating condition of the equipment. If you can determine whether the decline is a natural reduction due to high temperatures or whether generation is being reduced more than necessary because of insufficient ventilation or heat buildup around the equipment, it becomes easier to prioritize inspections and corrective actions.

Table of Contents

• Summarize the reasons why power generation appears lower in summer

• Align the comparison conditions before suspecting high-temperature loss.

• Check the panel temperature and ventilation conditions

• Check for heat buildup around the power conditioner

• Do not confuse dirt and shadows with high-temperature loss.

• Check for the risk of overheating in wiring and connection points.

• Keep records and assess the effectiveness of improvements.

• Summary In summers with low power generation, consider temperature and on-site conditions separately

Organizing the Reasons Why Power Generation Appears Low in Summer

When you feel that power generation is low in summer, the first thing to understand is that a high amount of solar irradiance does not equal high generation efficiency. Solar power systems generate electricity by receiving sunlight, but as the temperature of the solar panels rises, their conversion efficiency generally tends to decrease. Therefore, even in summer when sunlight is strong, the overall system can appear to be less efficient than in spring or autumn.

On sunny summer days, not only does the air temperature rise, but the temperatures of a panel’s front and back surfaces increase as well. On roofs, around asphalt, on developed sites, on slopes, or in plots enclosed by fences, reflected heat from the ground and surroundings, airflow, and differences in installation height can cause equipment temperatures to vary even within the same area. Even when the air temperature reported by weather services is the same, on-site panel temperatures and the temperatures around equipment need to be considered separately.

Also, although summer is a season when power generation tends to be higher, variations in weather conditions are more noticeable. Even when it looks sunny, thin clouds may pass, cloud cover may increase in the afternoon, and solar irradiance can change due to humidity or atmospheric conditions. If you judge without checking whether a day you felt had low power generation is truly an appropriate comparison, you may confuse high-temperature losses with weather-related differences.

Also, attention must be paid to the operating condition of the equipment. The power conditioner may engage protective control to limit temperature rise when the ambient temperature increases. Even if the unit has not shut down abnormally, its output can be restricted to keep internal temperatures down. If this is dismissed simply as "the panel temperature is high," you may overlook issues such as insufficient ventilation around the equipment or problems with the installation environment.

When checking for low power generation in summer, while keeping high-temperature losses as one possible cause, it is necessary to adopt an approach that breaks down the entire power generation system and examines each part. Organize the temperature effects on the solar panels themselves, the temperature effects on the power conditioner, heat generation in wiring and connection points, soiling and shading, meteorological conditions, and methods for checking measured values, and by inspecting each of these in sequence you can more easily reduce undue concern and unnecessary inspections.

Standardize comparison conditions before suspecting high-temperature loss

To determine that power output is low, you must first make the comparison conditions consistent. Simply comparing summer power output with that of the previous day or the previous month makes it difficult to identify the cause correctly. If solar irradiance, temperature, weather, equipment operating hours, downtime history, whether output control (curtailment) is in effect, or the surrounding shading conditions differ, the generation will also change. Before suspecting high-temperature loss, it is important to compare with past data under similar irradiance conditions.

What you should pay particular attention to is not only the total amount of power generated but also the output trend by time of day. If high-temperature losses are affecting performance, output may ramp up relatively smoothly in the morning, then be less able to increase during the hours when solar irradiance rises, appearing to plateau around midday. However, similar patterns can also be caused by passing clouds, output control, inverter limitations, or grid-side conditions, so it is important not to draw conclusions based solely on the waveform.

Clear days in spring and autumn are also useful for comparisons. In spring and autumn, temperatures are not as high as in summer, yet there can be days with good solar irradiance. When you compare such days with clear summer days, you may sometimes observe that output efficiency does not increase as much despite sufficient irradiation. However, since solar altitude, day length, and the way shadows fall also change with the seasons, you should avoid judging which is better based solely on daily energy generation.

Also, when looking at equipment monitoring data, you need to pay attention to the measurement units and the aggregation period. Instantaneous output, daily generation, monthly generation, and generation per unit of installed capacity all mean different things. Even when a report comes from the field that generation is low, simply confirming which value was used to judge it as low can help narrow down the cause.

In practice, aligning ambient temperature, weather, solar irradiance, site photos, generation graphs, and shutdown history by the same date makes assessment easier. For example, when comparing daily totals, a day that was clear in the morning but became cloudier in the afternoon can appear to have lower generation. Conversely, if it was sunny throughout the day yet daytime output clearly fails to rise, it is worth considering high-temperature losses or the impact of equipment temperature.

High-temperature loss is a natural phenomenon and does not necessarily indicate equipment failure. However, if you conclude “it’s unavoidable because it’s summer” without aligning the comparison conditions, you may overlook heat buildup or poor ventilation that could actually be remedied. Conversely, if you conclude “it’s a malfunction” without aligning the comparison conditions, it can lead to unnecessary emergency responses. The first step is to organize the observed drop in power generation so it can be viewed separately under solar irradiance conditions and temperature conditions.

Check panel temperature and ventilation conditions

At the center of considering high-temperature losses is the temperature of the solar panels. Panels generate electricity by receiving solar radiation, but they also hold heat. On hot days, when winds are weak, or in locations with poor ventilation behind the panels, panel temperatures tend to rise. When inspecting a site in summer—when generation is low—it is important to first check the panels’ installation environment and the pathways for heat to escape.

With roof-mounted installations, if the space between the roofing material and the panels is narrow, heat can become trapped. For ground-mounted installations, wind flow is affected by the racking height, tilt, surrounding grass, fences, adjacent objects, and the type of ground surface. If grass has grown and is obstructing airflow under the panels or around the racking, it may not only cause shading issues but also create conditions where heat cannot easily dissipate.

However, improvements to the ventilation environment should not be decided on-site and carried out arbitrarily. Mounting structures and panel layouts are related to wind loads, installation conditions, maintainability, and safety. You should avoid removing components or changing fastening methods just to improve ventilation. What the person in charge should do first is record the current situation and identify any factors that could lead to heat buildup.

When checking, it is useful to look for differences by location within the same power plant. Check whether there are differences in generation between windward and leeward sides, edges and the center, upper and lower parts of slopes, and areas near buildings or embankments. If only specific rows or sections tend to have lower output, it may be due not to simple seasonal factors but to location-specific ventilation, shading, soiling, or connection conditions.

Also, avoid touching the panel surface carelessly during periods when it is extremely hot. Prioritize safety; if temperature confirmation is required, appropriate measuring instruments and inspection procedures should be used. Rather than having on-site personnel attempt to check by touch, it is more realistic to record photos, the time of day, weather, wind conditions, and power generation graphs so the situation can be communicated to a specialist.

As countermeasures against losses from high temperatures, the basics are vegetation management around the site, clearing items that obstruct ventilation, ensuring inspection access routes around panels, and checking drainage and sediment accumulation. These affect not only power generation efficiency but also ease of inspection and safety. Even if generation appears low only in summer, if poor ventilation conditions persist it can become a long-term equipment-management issue.

Check for heat buildup around the power conditioner

When power generation drops in summer, attention should be paid not only to the solar panels but also to the temperature around the power conditioner. The power conditioner is an important device that converts the generated direct current into alternating current, and it heats up during operation. If it is installed in a location with a high ambient temperature and poor ventilation, a rise in the device's internal temperature can make it harder for its output to increase.

When power generation is low, the monitoring screen may not show any significant anomalies. You may be tempted to assume there is no problem because the system hasn't stopped, but in reality the equipment may be engaging in protective control to limit its temperature. In particular, if output is reduced only during the hot daytime hours and returns to near-normal behavior in the evening, it's worth checking the temperature environment around the equipment.

What you should check are whether the installation site receives direct sunlight, whether there are nearby obstructions, the condition of ventilation openings, whether objects are placed around the equipment, and whether airflow is being impeded by weeds or dust. Even for outdoor installations, locations near walls or enclosures, places where wind does not pass through easily, or areas prone to reflected heat can see ambient temperatures rise more than expected. If installed indoors or inside an enclosure, it is also important to check ventilation systems, filters, and intake and exhaust pathways.

However, internal inspection or electrical testing of the power conditioner requires specialized knowledge and safety procedures. Even if power generation is low, on-site personnel should avoid opening the cover or approaching live components. It is safest to limit on-site checks to the exterior, surrounding environment, any abnormal noises or odors, warning indicators, operation history, and generation graphs.

As countermeasures, consider removing objects that obstruct air intake and exhaust, cleaning the surrounding area, weed control, ensuring clearance for inspection around the equipment, and checking the effects of direct sunlight and reflected heat. As necessary, consider improvements to heat shielding or ventilation that conform to the design conditions, but it is important not to choose methods that contradict the equipment specifications or installation standards. Simply creating shade can be counterproductive if it impedes airflow.

Also, when there are multiple power conditioners within the same power plant, it becomes easier to make judgments by comparing each device’s power generation and operating history. If only a specific device shows a noticeable output drop in summer, you can separately check the condition of that device itself, the strings connected to it, the surrounding ventilation conditions, and the temperature conditions at its installation location. Differences that are not visible from the plant’s overall power generation can become apparent through device-by-device comparisons.

Do not confuse dirt and shadows with high-temperature losses

When power output is low in summer, focusing too much only on high-temperature losses can cause you to overlook the effects of dirt or shading. Efficiency reductions caused by high temperatures tend to affect the entire system relatively broadly, while dirt and shading can be concentrated in specific locations. To correctly isolate the causes of low power output, you need to check the panel surfaces and the surrounding environment along with the temperature conditions.

In summer, grass grows quickly and surrounding vegetation can extend more than expected. For ground-mounted systems, grass beneath the racks or in front of the panels can cast shadows. Shadows may occur only in the morning and evening, or may affect only part of a row or just the lower edge of the panels. Even short periods of shading can lead to reduced power generation and variability in monitoring data.

There are also summer-specific considerations when it comes to soiling. People tend to think that rain will wash dirt away, but soil dust, bird droppings, pollen, sand, and dust from nearby construction can remain. Sometimes after rain, streaks of dirt are left at the bottom edge of the panels. These are factors separate from thermal losses caused by high temperatures, but they can become apparent at the same time as the summer decline in power generation.

In inspections, we not only view the site from a distance but also compare monitoring data to check for any sections or rows with low power output. If you observe patterns such as only certain rows underperforming, underperformance limited to particular times of day, or changes after rain or around mowing, you should suspect not only high-temperature loss but also the effects of shading or soiling. High-temperature loss tends to appear as a season-wide trend, whereas soiling and shading tend to show location- and time-specific characteristics.

As countermeasures, the basics are regular weeding, checking for obstacles around the panels, checking drainage and mud splashing, and recording areas where dirt tends to remain. When considering cleaning, choose methods that will not damage the panel surface, follow safety procedures to avoid electric shock and falls, and use methods that comply with equipment warranties and management standards. Do not, simply because power output is low, undertake excessive cleaning or use inappropriate tools based on on-site judgment.

Declines in summer power generation can result from a combination of high temperature, soiling, shading, equipment temperature, and wiring conditions. Trying to explain it by a single cause can make the effects of improvements hard to see. Even when suspecting losses due to high temperatures, checking for soiling and shading at the same time and comparing the generation trends after countermeasures makes it easier in practice to determine which factor was most significant.

Check for overheating risks in wiring and connection points

When power generation falls in summer, attention must also be paid to the condition of wiring and connections. In high-temperature environments, connections that already have problems or degraded areas can become more susceptible to heat. Poor connections, loose terminals, damaged cables, and abnormalities around connectors are related not only to reduced power output but also to safety risks.

Problems with wiring and connections can be difficult to determine from power generation graphs alone. They may appear as a single string producing low output, sudden drops at certain times of day, or instability confined to circuits connected to particular equipment. However, because these symptoms can also be caused by shading, soiling, or equipment-side control, it is important to organize the investigation on the assumption that an electrical inspection will be carried out by a specialist.

The items on-site personnel can check include the cable’s appearance, sagging, damage to the cable jacket, bite marks from animals, detached fasteners, abnormalities around junction boxes, a burnt-like odor, discoloration, and unusual noises. When checking these, do not touch energized equipment carelessly. If an abnormality is suspected, do not attempt to deal with it on site; record photos and location information and share them with a specialized contractor.

Especially in summer, in addition to the rise in equipment temperature caused by solar radiation, the connectors themselves may also generate heat. Behind reports of low power generation, there may be abnormalities at the connections rather than merely high‑temperature losses. Therefore, it is important to confirm whether the decrease in power generation is temporary or persistent, and whether it is biased toward specific circuits.

As countermeasures, have the condition of connection points checked during regular inspections, photograph and record any abnormal locations, prevent cable damage caused by weeds or animals, and keep track of wiring routes. Inspections that involve measurements may require specialized checks, such as checking insulation condition and verifying output for each circuit. From the standpoint of safety and equipment preservation, avoid unplugging or reconnecting connection points or re‑tightening terminals based on your own judgment.

High-temperature losses are often treated as an issue of power generation efficiency, but on-site in summer you need to consider all heat-related abnormalities. By separating panel temperature, equipment temperature, and heating of wiring, you can more realistically organize the causes of low power output. Viewing power output issues from a safety-management perspective is also important for facility operation in summer.

Keep Records and Evaluate the Effectiveness of Improvements

When you feel that power generation is low in summer, it is important not only to take immediate countermeasures but also to keep records. Because losses due to high temperatures are influenced by weather conditions, it can be difficult to compare before-and-after measures. Even if you perform weeding, cleaning, ventilation improvements, or tidying around equipment, power output will change if the weather is different the next day. To judge the effectiveness of improvements, you need records that allow you to compare days with similar conditions.

As items to record, the basics are date, weather, an estimate of temperature, generated power, output by time period, operating status of the power conditioner, presence of warnings or shutdowns, site photos, conditions of grass and shadows, condition of dirt/soiling, and the date countermeasures were implemented. By keeping these in a single flow, it becomes easier to look back later to identify the causes of low power generation.

What is particularly effective is taking before-and-after photos from the same angle. The way grass grows, the ventilation conditions under the panels, the presence or absence of items around equipment, and how shadows fall can be difficult to convey with text alone. If photos are paired with power generation data, internal briefings and consultations with specialists will go more smoothly. A major advantage is that it makes it easier for stakeholders to share the sense of something being off that the on-site personnel noticed.

Also, it is important not to base the judgment that power generation is low solely on intuition. If you set comparison criteria — such as the same period in past years, similarly sunny days, days with comparable temperatures, or generation per unit of installed capacity — it becomes easier to explain whether an anomaly exists. Simply looking at it as "lower than last year" may overlook differences in weather or operating conditions.

When evaluating the effect of improvements, it's important not to draw conclusions based solely on short-term changes. Even if power generation appears to increase immediately after cleaning or weeding, it may simply be due to better weather. Conversely, if output does not rise right after a measure is taken, it may be affected by cloud cover or output curtailment. Looking at trends over several days and selecting days with similar conditions for comparison will improve the accuracy of your judgment.

Keeping records is useful not only when trouble occurs but also during normal times. If you know the typical power generation trends in normal conditions, you can check how much the output in summer differs from usual when you feel it is low. If you suspect high-temperature loss, having past temperature conditions and generation trends makes it easier to determine whether the change is a natural seasonal variation or something that requires additional inspection.

Summary: In summers with low power generation, view temperature and site conditions separately.

When you feel power generation is low in summer, the mismatch of not seeing higher output despite abundant sunlight may make you suspect equipment failure. However, in solar power generation systems, rising panel temperatures and temperatures around equipment can reduce generation efficiency. Therefore, when investigating reduced summer output, it is necessary to treat high-temperature loss as an important item to check.

However, it is dangerous to attribute the cause solely to high-temperature losses. There are multiple factors that affect power generation, such as solar irradiance conditions, ambient temperature, passing clouds, shading, dirt, grass growth, heat buildup in the power conditioner, and the condition of wiring and connections. When you see results showing low power generation, first standardize the comparison conditions, check the output trends by time of day, and compare them against the site environment.

As measures against high-temperature loss, the basics are removing factors that impede ventilation, checking for heat buildup around equipment, managing vegetation and dirt, securing inspection space, and recording any abnormal locations. None of these should be carried out in disregard of the equipment’s safety or design conditions. In particular, electrical inspections and internal checks of equipment should be carried out on the assumption that they will be entrusted to specialist contractors.

The role of operational staff is to accurately record on-site conditions, link them with power generation data, and compile the information needed for decision-making. If photos, date and time, weather, power generation, the condition of each piece of equipment, and the history of countermeasures are retained, it becomes easier to isolate causes. This allows unnecessary responses to be reduced while quickly enabling necessary inspections and improvements.

Summer reductions in power generation may be caused by natural temperature effects combined with on-site conditions that can be improved. If you notice low power output, start by considering the possibility of temperature-related losses and inspect the panels, equipment, wiring, and surrounding environment separately. Continuously monitoring the site's power generation and organizing inspection records and photos will make equipment management decisions more consistent.

If you want to detect drops in power output early and manage them together with site conditions, it helps to establish a system that can organize inspection records, location information, photos, and generation data within the same workflow. Recording summer high-temperature losses and changes in site environment in a visible form and making them easy to share among stakeholders helps prevent recurrence and improves the accuracy of the next inspection.