7 Shadow-Check Tips to Increase Power Generation

When you want to increase the power output of a photovoltaic system, the first thing to check is the effect of shadows. Solar panels generate electricity from solar radiation, so as the duration or area of shading increases, power generation tends to fall below expectations. Moreover, shadows originate from various sources such as buildings, rooftop equipment, trees, utility poles, slopes, and surrounding structures, and their shape and length change with the season and time of day. This article, aimed at practitioners searching for "how to increase power generation", explains seven practical shadow-check tips you should verify in the field to boost power generation.

Table of Contents

• Why start with a shade check if you want to increase power generation

• Tip 1: Suspect shading from monthly and time-of-day generation data

• Tip 2: Focus on shadows in winter and in the morning and evening

• Tip 3: Check shadows from rooftop equipment and surrounding buildings

• Tip 4: Don’t overlook changing shadows from trees, plantings, utility poles, etc.

• Tip 5: Don’t force adding panels in shaded areas

• Tip 6: Also check fallen leaves, snow accumulation, and dirt as temporary shading

• Tip 7: Verify post-mitigation generation with data

• Precautions to avoid mistakes during shade checks

• Summary

Why You Should Start with a Shade Check to Increase Power Generation

When people consider ways to increase the output of solar power generation, many envision adding panels, upgrading equipment, cleaning, and inspections. Of course, those measures are also important. However, when checking the reasons why generation does not improve on-site, the impact of shading is often a major factor. Because shade blocks solar radiation itself, it represents a very direct loss of generation for solar power systems.

The trouble with shadows is that they don't always appear in the same place or in the same shape. The sun's position differs between morning and evening. The solar altitude differs between summer and winter. Even if you visit the site on a clear day and it looks like there are no shadows, long shadows can reach the panels on winter mornings or evenings. Therefore, shadow checks are not something that can be completed with a single site visit; you need to assess them by combining power generation data, season, time of day, and the relative positions of obstacles.

Shadows can also increase after installation. Trees that were small at the time of installation may grow. New equipment or piping may be added to rooftops. Buildings or structures may be erected on adjacent properties. In other words, shading checks for solar power systems are a management task that should be carried out not only before installation but also continuously during operation.

To increase power generation, it is important to first confirm that the existing equipment is receiving the solar radiation it should be receiving. If generation is reduced due to shading, adding panels will have only a limited effect if they are added in locations that are similarly shaded. Conversely, by understanding the effects of shading and reviewing the layout and surrounding management, you may be able to restore generation without increasing installed capacity.

A shading inspection is the first on-site check that should be performed when considering ways to increase power generation. By identifying suspected shading from power generation data, confirming the sources of shading on site, and verifying the effects after countermeasures, improvements in power output can be pursued based on evidence rather than intuition.

Tip 1: Suspect shading from monthly and time-of-day power generation data

The first tip for checking for shading is to look for signs of shading in the monthly and time-of-day power generation data. Visiting the site and performing a visual inspection is important, but because shading changes with the seasons and time of day, an on-site check alone may not be sufficient. By examining the generation data first, you can narrow down the months and times of day when shading is most likely to occur.

In the monthly power generation figures, check whether generation is lower in any particular season. If output drops significantly only in winter, you should suspect not only shorter sunshine hours but also the lengthening of shadows caused by the lower solar altitude. In winter, shadows from surrounding buildings, trees, and rooftop equipment tend to extend farther, and shadows that were not a problem in summer may fall on the panels.

By looking at power generation by time of day, it's easier to estimate the direction of shadows. If morning power generation doesn't reach expected levels, shadows from buildings, trees, utility poles, or rooftop equipment on the east side may be suspected. If power generation falls earlier than expected in the evening, check for obstacles on the west side. If there is an unusual dip around midday, shadows from rooftop structures, piping, railings, or air-conditioning equipment near the panels may be involved.

When looking at power generation data, it is important to consider the effects of weather and the effects of shading separately. On cloudy or rainy days, overall power generation decreases. On the other hand, if power generation drops at similar times each day even on sunny days, the influence of shading or equipment conditions is suspected. By checking whether generation repeatedly drops during specific time periods, the accuracy of shade checks is improved.

If you have data broken down by mounting surface or by system, you can narrow down the cause further. If it’s not the overall power generation that’s low but only a particular roof surface or a specific group of panels, that area may be shaded. If there are trends such as the south-facing surface being normal while only the east-facing surface is low, or only the west-side rows showing a drop in output, it becomes easier to prioritize on-site inspections.

In shadow checks to increase power generation, rather than immediately surveying the entire site, it is effective to narrow down suspicious areas from the data. By identifying when production is low and where it is low before inspecting the site, you can more easily find the source of the shading and make the prioritization of countermeasures clearer.

Tip 2: Pay special attention to shadows in winter and in the morning and evening

When checking for shading, shadows in winter and in the morning and evening are particularly important. During on-site inspections for solar power generation, it's common to look at roofs and land on a clear midday and conclude "there is little shading." However, shadows change with the sun's position, so their shape can vary significantly both within a single day and across seasons. To increase power output, you need to prioritize checking conditions that are likely to produce shadows.

During winter, shadows lengthen because the sun's altitude decreases. Shadows from nearby buildings, trees, and rooftop equipment that did not reach the panels in summer can extend in winter and fall on the panels. If winter power generation is lower than expected, it is important not to simply conclude that daylight hours are shorter, but to check the extent of winter shadows.

Morning and evening shadows are also easily overlooked. In the morning, obstacles on the east side tend to cast shadows, and in the evening, obstacles on the west side do. In systems where generation is concentrated around midday, output in the morning and evening may already be low, but if a facility’s electricity demand is high in the morning or evening, those shadows can affect self-consumption. It is necessary to check not only the total amount of generation but also whether generation occurs during the hours when the facility can use it.

Morning and evening shadows also appear in power generation data. If, even on sunny days, the morning ramp-up is slow, the evening drop-off occurs early, or generation is consistently weak during the same time each day, shading may be the cause. On site, we focus on inspecting surrounding buildings to the east and west, trees, utility poles, signs, and rooftop equipment.

When checking shadows in winter and in the morning and evening, it is important to check not only the shadows observed at the time of the site visit but also to consider the movement of the sun. Even if no shadows are present at the time you visit the site, shadows may appear at different times of day or in other seasons. By combining on-site photos, positional relationships, and power generation data, you can more accurately determine the impact of shadows.

When performing shading checks, it's important not to overlook low solar altitude conditions, not just around midday when power generation is highest. By focusing on shadows in winter and during the morning and evening, you can more quickly detect generation losses that are difficult to notice after installation.

Tip 3: Check shadows from rooftop equipment and surrounding buildings

The third tip is to check the shadows cast by rooftop equipment and nearby buildings. When solar panels are installed on a roof, there are various rooftop installations around the panels. Roof penthouses, air-conditioning units, ventilation equipment, piping, railings, access hatches, antennas, and lightning protection equipment can cast shadows depending on the time of day and the season.

The shadows cast by rooftop equipment can affect power generation even for short periods because the obstacles are close to the panels. In particular, when there is tall equipment near the panels, shadows can extend far in winter and during the morning and evening. Shadows from piping and risers located immediately adjacent to the panels are easily overlooked on drawings alone, so it is necessary to check their heights and positional relationships on site.

Shading from nearby buildings is also important. If adjacent buildings are tall, large shadows can fall at certain times of day even if the roof’s orientation and tilt are favorable. In densely built areas, morning and evening shadows and wintertime shading are particularly likely to cause problems. If shading from surrounding buildings is not adequately reflected in pre-installation simulations, actual power generation can end up lower than expected.

When checking for shadows, confirm not only the presence of obstacles but also their distance from the panels, their height, and their direction. Even low structures can cause shading if they are close to the panels. Even tall buildings may have only a limited shading impact if they are far away. Determine which obstacles are actually affecting power generation by comparing generation data with on-site conditions.

The areas around rooftop equipment affect not only shading but also maintenance. Placing panels without securing the space required for equipment inspection and repair can interfere with building management. Adding panels up to the vicinity of rooftop equipment to increase power output not only makes the panels more susceptible to shading, but can also worsen inspection and maintenance access.

As countermeasures, you can exclude areas around heavily shading equipment from the layout, avoid shaded zones when expanding installations, run simulations that reflect shading conditions after on-site surveys, and secure maintenance space. By accurately assessing the shadows cast by rooftop equipment and surrounding buildings, the roof surfaces that should actually be used to increase power generation become clear.

Tip 4: Don’t overlook changing shadows from trees, plantings, utility poles, etc.

The fourth tip is not to overlook shadows caused by trees, plantings, utility poles, and similar objects. Shadows from buildings and rooftop equipment are relatively easy to identify, whereas trees and plantings can change the extent of their shadows as they grow, which may cause problems after installation. When checking for shading to increase power generation, you need to consider not only the current shadows but also shadows that will increase in the future.

Trees grow year by year, and the way their branches and foliage spread changes. Even trees that did not cast shadows on panels at the time of installation may, a few years later, cast shadows in the mornings, evenings, or during winter. Evergreen trees can create shade year-round, and even deciduous trees produce denser shade during the seasons when they have leaves. In winter, even with fewer leaves, the sun's low angle can cause branches and trunks to cast long shadows.

Trees create not only shade but also impacts from fallen leaves and birds. When leaves accumulate on panels, they block sunlight. In environments that attract birds, soiling from bird droppings is likely to occur. At sites where trees are nearby, it is important to check shade, fallen leaves, and soiling together.

Shadows from utility poles, signs, and narrow structures are also factors that are easily overlooked. Even shadows that cover a small area can lead to reduced power generation if they fall on the same spot at the same time every day. In particular, narrow shadows lengthen in the mornings and evenings and during winter, so if you observe a drop in generation data at specific times, you should investigate.

As a mitigation measure, first distinguish whether the source of the shading is controllable. If it is trees on the property, consider pruning or managing branches. Items that cannot be freely addressed—such as trees on neighboring properties or utility poles—should have their shading effects reflected in the assumptions about expected power generation and be used to inform decisions on panel layout and the scope of any expansion. Ignoring uncontrollable shading in simulations can result in actual post-installation power generation being lower than expected.

Shadows from trees, plantings, and utility poles can be difficult to judge from a single site visit. It is important to verify them by combining power generation data, season, time of day, and relative positions, and to manage them continuously as changing shadows.

Tip 5: Don’t force adding panels to shaded areas

The fifth tip is not to force adding panels in shaded areas. When you want to increase power generation, if there is space on the roof or land, you may be tempted to add panels there. However, an available spot is not necessarily suitable for generation. Adding panels in areas with significant shading may not increase output as much as you expect.

If you increase installed capacity, the simulated annual energy production may appear to rise. However, in areas with long periods of shading, the energy output per unit of capacity becomes lower. Even if the total generation seems to increase, the amount of energy obtained per unit of installed equipment may be smaller. To improve generation efficiency, it is important to look not only at total generation but also at energy output per unit of capacity.

Also, even if generation increases in shaded areas, if the facility is not using electricity during that time, it may only increase surplus. If the goal is self-consumption, you need to check whether the times when generation increases coincide with the facility’s demand periods. For facilities with high morning demand, if there is strong shading on the east side, adding capacity on the east side may not significantly improve self-consumption.

Deciding to completely avoid areas with shade is not the only correct approach. If the shading is brief and has only a small effect on power generation, or if it is limited to certain seasons, it can be acceptable. The important thing is not to increase the number of panels without understanding the impact of shading. Make a decision after confirming at which times of day and to what extent the shading will affect power generation.

During expansions and layout reviews, we prioritize areas with minimal shading. For rooftop projects, we select surfaces that receive little shading from rooftop equipment and surrounding buildings. For land projects, we avoid shading from trees, utility poles, and slopes, and we also consider access roads and drainage. Prioritizing locations with less shading makes it easier to increase actual power generation even with the same installed capacity.

To increase power generation, you need to adopt the mindset of placing panels where they can generate electricity, rather than simply where they can be placed. Rather than trying to force more panels into shaded areas, it is important to accurately identify areas with less shade and use them efficiently.

Tip 6: Treat fallen leaves, snow, and dirt as temporary shade

The sixth tip is to treat fallen leaves, snow, and dirt as temporary shade. When you think of shade, you tend to imagine shadows cast by buildings or trees, but anything that covers the panel surface can also block sunlight and thus cause a reduction in power generation. In particular, fallen leaves, snow, and dust that recur seasonally should not be overlooked when trying to increase power output.

Fallen leaves are a common issue at sites surrounded by trees. Dry leaves can be blown away by the wind, but when they become wet from rain they may stick to panel surfaces. When they accumulate at the lower edge of panels or around frames, they not only block sunlight but can also lead to dirt buildup. On rooftop projects, fallen leaves that collect in drains can also affect building maintenance.

Snow accumulation is a major factor that significantly reduces power generation in winter. While snow sits on the panels they cannot receive sunlight, and power output falls sharply. Not only the time it is snowing but also the duration that snow remains after a snowfall is important. When the panel tilt is small or in locations where snow does not shed easily, the downtime of power generation can be extended. Fallen snow that builds up at the lower or front parts of the panels can also create additional shading.

Dirt also blocks sunlight. When sand and dust, pollen, yellow sand, bird droppings, exhaust-derived grime, or particulate matter adhere to the surface, power output decreases. Dirt often accumulates gradually and may not be visible as a sudden anomaly. If only a specific surface has lower power output, if output does not recover after rain, or if it is slow to increase in spring or autumn, check for dirt.

As a countermeasure, it is effective to set inspection timings for each season. During periods with many fallen leaves, after snowfall, when pollen and dust are abundant, and when birds are likely to cause issues, check the power generation data and the on-site conditions. If cleaning or removal is necessary, prioritize safety above all and choose methods that will not damage the panels or the roof.

By including not only fixed shadows but also temporary factors that block sunlight in shading checks, you can more accurately identify the causes of reduced power generation. To increase power generation, the basic principle is to keep the panel surface exposed to sunlight.

Tip 7: Verify energy production after shading mitigation with data

The seventh tip is to verify energy production after shading mitigation using data. Even if you identify the sources of shading and manage trees, revise the layout, or perform cleaning, you cannot judge the effectiveness of the measures unless you confirm whether energy production actually improved. To increase energy production, it is important to examine the changes in the data before and after the measures.

When validating, simply comparing power generation before and after the countermeasures is insufficient. Power output naturally fluctuates with weather and season. If possible, compare similar clear-sky days, the same month of the previous year, generation for the same season, power generation curves by time of day, and power generation by installation surface. It is important to confirm whether there is an improvement in power generation during the times and areas where shading countermeasures were implemented.

For example, if you managed trees on the east side, check whether morning power generation has improved. If you reduced shadows caused by obstacles on the west side, look at evening power generation. If you arranged the layout to avoid shadows around rooftop equipment, check whether the unnatural dip around midday has improved. When evaluating shadow countermeasures, focusing on the time periods when the shadows occurred makes the effects easier to see.

Also check self-consumption as well as generation. Even if generation increases due to shading countermeasures, if that increase occurs during times when the facility is not using the power, the impact on the effectiveness of the installation may be small. It is important to confirm whether the improvement in generation leads to an increase in self-consumption or merely to an increase in surplus.

It is also important to record the results of countermeasures. If you keep the cause of the shading, the measures taken, power generation before and after the measures, on-site photos, inspection date and time, and location information, you can use them for the next inspection, internal reporting, and consultations with contractors. Improving power generation is not a one-time task; it should be carried out continuously in response to changes in site conditions. Having records makes it easier to respond if the same problem recurs.

Measures against shading should not be left to intuition; only when you verify their effectiveness with data do they become practical improvements. To increase power generation, it is important to establish a process of mitigation, recording, and verification.

Precautions to Avoid Failing Shade Checks

To avoid failing a shade check, it is important not to make a judgment based on a single site visit. Shadows change depending on the time of day and the season, so their appearance can vary greatly depending on the timing of the on-site inspection. Even if there are no shadows during the daytime in summer, shadows may appear in the mornings and evenings in winter. On-site inspections need to be conducted in combination with power generation data.

Also, it is important not to assume a single cause for shading. Low power output is not necessarily due only to shading. Shading can coincide with soiling, snow accumulation, equipment faults, or temperature-related losses. If you implement shade countermeasures but the power output does not increase as much as expected, check other factors such as soiling, wiring, equipment, temperature, and snow.

Avoid forcibly adding panels in shaded areas to increase power output. Increasing installed capacity may make the apparent power output look higher. However, in locations with significant shading, the energy produced per unit of capacity is lower and may not lead to the expected improvement. Before adding panels, it is necessary to accurately identify the areas with minimal shading.

When checking for shading, you must not forget about safety. Inspections on roofs or at heights involve risks. Even if you want to increase power generation, you should avoid forcing yourself onto the roof, getting too close to equipment, or checking in areas with unstable footing. Separate what can be checked safely from what requires professional inspection.

Furthermore, not recording the results of shadow checks is another thing to avoid. If you don't record the shadow locations, times of day, seasons, and the impact on power output, you won't be able to compare when the same problem occurs next time. By keeping photos, location, date and time, and power generation data, you can continuously verify the effectiveness of shadow countermeasures.

Shading checks are extremely important as the entry point for improving power generation, but a simple visual inspection alone is insufficient. Making judgments by combining data, on-site conditions, seasonality, time of day, and records leads to shading countermeasures that do not fail.

Summary

When checking shading to increase power generation, it is important to review in sequence the monthly and time-of-day generation data, shading in winter and at dawn and dusk, rooftop equipment and surrounding buildings, trees and plantings, decisions about expanding installations into shaded areas, temporary obstructions such as fallen leaves and snow accumulation, and verification of data after countermeasures. Shadows are a direct factor that reduces photovoltaic power generation, yet they are easily overlooked because they change with the seasons and time of day.

Tip 1: Use power generation data to detect suspected shading. Check for trends such as being low only in the morning, dropping early in the evening, or being significantly lower only in winter. Tip 2: Focus especially on shading in winter and during mornings and evenings. When the solar altitude is low, shadows tend to extend longer. Tip 3: Inspect shadows cast by rooftop equipment and surrounding buildings. Roof towers, piping, HVAC equipment, and adjacent buildings can affect power output.

Tip 4 emphasizes the importance of not overlooking changing shadows from trees, plantings, utility poles, and the like. Trees grow and produce not only shade but also effects from fallen leaves and birds. Tip 5 advises confirming that you do not forcefully add panels into shaded areas. Placing panels where they can generate power is the basic principle for improving energy output. Tip 6 treats fallen leaves, snow accumulation, and dirt as temporary shading; any factor that obstructs the panel surface directly leads to reduced power generation. Tip 7 recommends verifying post-countermeasure power output with data: compare before and after the measures and record the improvement effects.

To avoid failing a shade check, it is important not to make a judgment based on a single site visit, not to focus too narrowly on shade as the only cause, not to neglect safety, and to keep records. To increase power generation, it is necessary to accurately identify the sources of shading and implement measures starting with the areas that have the greatest impact on generation.

And to improve the accuracy of shading checks, accurate on-site information is indispensable. If the installation area, rooftop equipment, obstructions, trees, site boundaries, orientation, slope, and inspection access routes can be accurately identified, it becomes easier to sort out the causes of shading and their impact on power generation.

If you want to accurately record on-site installation ranges, obstacles, trees, rooftop equipment, site boundaries, orientation, slope, inspection routes, etc., and efficiently carry out shading checks to increase power generation, utilizing LRTK, an iPhone-mounted GNSS high-precision positioning device, is effective. If high-precision local position information can be obtained, it becomes easier to organize the causes of shading, feasible installation ranges, surrounding obstacles, and maintenance routes, and to proceed consistently from considering shading countermeasures and comparing simulations to post-installation performance management. To increase power generation, it is important not only to rely on desk-based assumptions but to accurately understand the site and precisely address the causes of shading that reduce power generation.