4 Orientation and Tilt Checks to Reassess When Power Output Is Low in the Morning and Evening

If you feel your solar power output is low, immediately suspecting only equipment failure or aging can lead to a longer, more roundabout troubleshooting process. Especially when output is low in the morning or evening, the sun’s position, panel orientation, tilt angle, nearby shading, and the conditions of the mounting surface may be interacting to cause the apparent reduction. In the morning and evening the sun altitude is low, so systems are more susceptible to shading than during midday, and the same installation can produce different output patterns. Therefore, rather than judging solely by feed-in statements or monitoring data numbers, it is important to check the generation curve by time of day together with the actual on-site conditions.

Table of Contents

• In the mornings and evenings when power generation is low, examine the effects of orientation and tilt separately.

• Check 1: Confirm whether it is low only in the mornings and evenings, or also during the daytime

• Check 2: Confirm any deviation between the panel orientation and the sun's position in the morning and evening

• Check 3: Confirm the tilt angle and seasonal solar altitude

• Check 4: Verify long shadows and reflection conditions under a low sun

• Points to consider when reviewing azimuth and inclination

• To continuously manage the causes of low power generation

For mornings and evenings when power generation is low, separate the effects of orientation and tilt

In consultations about low power generation, it is not uncommon for assessments to be made based only on monthly generation or feed-in sales figures. However, the monthly totals alone do not show when generation is falling. Whether the output is low throughout the day from morning to evening, or whether it’s sufficient around midday but underperforms only in the mornings and evenings, the causes to investigate differ. If output is low only in the mornings and evenings, factors such as how sunlight strikes the panels, shading patterns, orientation, and tilt conditions may be involved rather than a decline in the panels’ own performance.

Solar power generation varies depending on the angle at which sunlight strikes the panel surface. The closer the sunlight is to perpendicular to the panel surface, the more solar radiation it receives, and the more obliquely it strikes, the more the amount of light received per unit area tends to decrease. In the morning and evening the sun is low, so even under the same clear-sky conditions it is natural for generation to be lower than around midday. However, if the drop in generation in the morning and evening is noticeably larger compared with facilities of the same scale or the same period in past years, it is worth checking for changes in installation conditions or the surrounding environment.

Orientation and tilt greatly influence the shape of a solar power generation curve. Systems facing close to south generally tend to generate around midday, while those oriented toward the east tend to produce more in the morning and those toward the west tend to produce more in the afternoon. With a steep tilt, seasonal advantages and disadvantages change: there are times when panels receive more sunlight during periods of low solar altitude, whereas conditions can be different under the high sun of summer. Conversely, with a shallow tilt, panels may perform well during daytime in summer, but in the mornings, evenings, and winter sunlight strikes at a shallow angle, which can limit generation.

The important point is not to immediately conclude that low power generation in the morning and evening is an abnormality. You need to distinguish and check whether the decline is a natural decrease given the sun’s movement, a characteristic caused by the design’s orientation or tilt, or a decrease caused by subsequently formed shading or soiling, a tilt in the racking, or changes to surrounding equipment. Drops in generation at morning and evening can be worrying if viewed only as numbers, but combining the generation curve, installation drawings, on-site photos, and historical data makes it easier to anticipate the cause.

In practice, the starting point is to treat low power generation not as a single cause but as phenomena organized by time of day. Especially in the morning and evening, many factors influence generation: fluctuations in solar irradiance, passing clouds, shadows from distant mountains and buildings, shadows from utility poles and fences, and shadows from adjacent rows. Reviewing azimuth and tilt provides the foundation for sorting out these influences. This does not mean immediately retrofitting the equipment; rather, it is important first to understand how the current orientation and angle are reflected in the generation curve.

Check 1: Confirm whether it is low only in the mornings and evenings or also during the daytime

The first thing to check is the time periods when power generation is low. By distinguishing whether output is low only in the morning and evening or low throughout the day including around midday, it becomes easier to decide whether to prioritize the effects of orientation and tilt or to focus on other causes such as equipment or grid issues, soiling, or faults. If it is low only in the morning and evening, effects specific to times of low solar altitude are suspected. On the other hand, if the midday generation peak is clearly low even on sunny days, you should also check factors such as soiling of the panel surface, stoppage of the power conditioner, string faults, output curtailment, temperature rise, and measurement-side problems.

The basic check is to look at generation trends by time of day, not the daily total generation. If possible, select generation curves from clear-sky days and compare the shapes for morning, late morning/around midday, afternoon, and evening. Days with many clouds or with rain are not suitable for discerning the effects of orientation and tilt, because solar irradiance conditions are unstable. Choose several clear, mostly cloud-free days and check whether the morning ramp-up is slow, the evening drop-off is early, and whether there is a midday peak; doing so makes it easier to organize and interpret the observed phenomena.

If only the morning ramp-up is weak, shadows from the east to the southeast, how open the site is to the east, nearby forests or buildings, roof rises, and shadows from adjacent structures may be involved. If only the evening is weak, check for shadows from the west to the southwest and for any deviation in panel orientation relative to the afternoon sun. If both morning and evening are low while only around midday the output is sharply high, it may be a natural curve caused by a predominantly south-facing layout. However, if the generation period in the morning and evening has become shorter than in the past, you should check for changes in the surrounding environment or shifts in the timing of shadow occurrence.

When making comparisons, it becomes easier to see the actual situation if you compare with clear days from the same month of the previous year or from a similar season. Because the sun’s elevation and the conditions of sunrise and sunset change with the seasons, simply comparing mornings and evenings in summer with those in winter can lead to misunderstandings. In winter, the sun’s altitude is lower and daylight hours are shorter, so morning and evening power generation may not increase easily. Conversely, in summer, even if daylight hours are long, rising panel temperatures can reduce daytime efficiency, making morning and evening generation relatively more noticeable. It is important to compare data that are from the same season, similar weather conditions, and similar equipment conditions.

When monitoring data is available, do not simply look at the total generated energy; also check the peak time, the ramp-up time, and the time when generation approaches cessation. If the peak is shifted toward the morning or afternoon instead of being around noon, this may reflect the characteristics of the panel orientation. If it is biased toward east-facing, it tends to be stronger in the morning; if biased toward west-facing, it tends to be stronger in the afternoon. If the peak timing is significantly shifted despite assuming a near-south orientation, you need to check the actual azimuth, shading, string configuration, and how measurement units are divided.

When investigating low power generation, looking only at the system-wide average can conceal problems. If there are multiple roof surfaces or multiple arrays, orientations such as east, west, south, and north may be mixed. In that case, the system’s overall generation curve is the sum of each surface, so even if it looks smooth at first glance, a specific surface may be dropping significantly in the morning and evening. If you can separate the data by surface, circuit, or power conditioner, checking sections with different orientations separately makes it easier to narrow down where the morning/evening drops are occurring.

Also, when judging morning and evening declines, you need to pay attention to the measurement granularity. Daily or monthly data alone cannot reveal the morning/evening power generation curve. If hourly or finer-resolution data are available, compare the curve shapes across multiple clear-sky days. If short-term dips occur repeatedly, clouds or transient shading are likely; if generation drops at the same time every day, shading from fixed objects or the effects of orientation are suspected. Even simply checking whether the morning/evening decline is regular or irregular can substantially change the direction of the suspected cause.

Check 2: Verify the discrepancy between panel orientation and the sun's positions at sunrise and sunset

Next, check which direction the panels are facing. In solar power generation, the daily power generation curve changes depending on panel orientation. Installations oriented close to south tend to concentrate generation around midday; those oriented toward the east tend to generate more from morning into late morning; and those oriented toward the west tend to generate more from afternoon into evening. Therefore, if you feel generation is low in the morning or evening, first determine which direction the installation is facing and confirm whether the generation curve is natural for that orientation.

When checking orientation, it is important to verify whether the orientation on the drawings matches the actual orientation on site. Even if the design drawings or layout plans state that something is south-facing, in reality it may be oriented slightly southeast or southwest. For rooftop installations, panels are arranged to match the building’s orientation, so they are not necessarily oriented in the direction considered optimal for power generation. Even for ground-mounted installations, the orientation may be adjusted due to site shape, land development conditions, the orientation of racking rows, drainage planning, and the arrangement of surrounding access paths. It is important to confirm orientation on site, not just from the drawings.

When morning generation is low, check whether the panels are oriented to receive sufficient sunlight from the east. For south-facing installations, the morning sun is low and comes in from the east, so the time they receive it directly is limited. Therefore, it is natural for morning generation to be lower than at midday. However, if morning generation is extremely low even on southeast- or east-facing surfaces, you should check the view to the east, shading, soiling, circuit faults, and so on. In particular in the morning, shadows from building edges, trees, slopes, fences, utility poles, and adjacent racking rows tend to stretch long, and even small obstructions can cast shadows over a wide area.

If evening power generation is low, check the conditions on the west side. Installations that are oriented somewhat westward tend to retain generation relatively better from the afternoon into the evening. Nevertheless, if output falls off early, you should check for shading from west-side buildings, mountains, trees, equipment, fences, and similar objects. It is natural for south-facing installations to decline in the evening, but if the drop occurs earlier than in the past, consider changes such as surrounding trees growing, an increase in structures on adjacent land, or shifts in parts of the mounting racks or panels.

Orientation deviations can appear not so much as a reduction in total power generation but as a bias in the times when generation occurs. For example, if generation is strong in the morning and weak in the afternoon, the system may be oriented slightly east. Conversely, if generation is weak in the morning and strong in the afternoon, a westward orientation may be influencing it. If this matches the design intent, it is not necessarily a problem. For installations that prioritize self-consumption, there is also the idea of adjusting orientation to match the times when power demand is high. What’s important is not just the impression that generation is low, but understanding the characteristic generation curve caused by orientation and deciding whether it indicates an abnormality.

Operational staff should be careful not to evaluate roof faces with different orientations as a single installation. When a roof has multiple faces, east-, west-, and south-facing surfaces may be mixed. In that case, the east-facing roof face generates power in the morning, the south-facing face at midday, and the west-facing face in the evening, so looking only at the total for the whole installation can make it difficult to see problems on individual faces. When generation is low in the morning or evening, it is necessary to check which face's generation is low, how large the capacity differences between faces are, and whether each face is connected to the same equipment. Organizing by orientation makes it easier to separate underperforming faces from normal ones.

On-site photos are also useful for orientation checks. If you take photos from the same position on a clear day in the morning, at midday, and in the evening, it becomes easier to see how sunlight falls and how shadows appear. When saving photos, record the shooting time, shooting direction, the panel surface being photographed, and the weather together, as this makes it easier to match them with generation data later. Causes of low generation can be small anomalies that seem insignificant on-site but become clear when combined with the data. Don’t finish the orientation check in a single pass; observing at different seasons and times of day will allow for a judgment closer to actual conditions.

Check 3: Verify the tilt angle and solar altitude for each season

Along with orientation, the panel tilt angle is important. The tilt angle determines the angle at which sunlight strikes the panel surface. The sun’s elevation changes with the seasons—higher in summer and lower in winter. Therefore, even with the same tilt angle, the times of day when generation is easier and the amount of power produced vary by season. If you feel that generation in the morning and evening is low, it is important to check how the tilt angle is affecting the sun’s altitude for the current season and installation location.

Shallowly tilted panels can receive sunlight more easily during periods when the sun is high and around midday, but when the sun is low in the morning and evening or in winter, sunlight tends to enter at a shallow angle. For that reason, you may feel that power generation in the morning and evening is less likely to increase. Conversely, steeply tilted panels can better receive low-angle sunlight in some situations, but they are not necessarily advantageous depending on the season and time of day. Tilt angle should not be judged on its own; it needs to be considered together with orientation, the installation site, surrounding shading, how snow and dirt flow off, wind effects, and mounting conditions.

In roof-mounted installations, the tilt angle is governed by the roof pitch. Even if there is an angle you would like to adjust purely for power generation, in practice there are constraints such as roof shape, building requirements, waterproofing, loads, constructability, and safety. For ground-mounted installations, the tilt angle is determined by the racking design, but site elevation differences, row spacing, wind loads, maintenance aisles, drainage, and ground conditions also play a role. Therefore, low generation in the morning and evening does not necessarily mean you should immediately change the tilt angle. First, it is important to understand how the current tilt is reflected in the power generation curve.

To assess the effect of tilt angle, comparisons across seasons are indispensable. If generation is low in the mornings and evenings during winter, the sun’s altitude is low and shadows extend longer, so a natural decline may be included. Spring and autumn have intermediate sun angles, making them relatively easy periods in which to discern the characteristics of orientation and tilt. In summer, daylight hours are longer, but higher midday panel temperatures can reduce generation efficiency. If you compare only a single day’s generation without understanding seasonal characteristics, you may misjudge the influence of the tilt angle.

When checking whether morning and evening declines are related to tilt angle, it's easier to judge if you look not only at just after sunrise or just before sunset, but also at the times when generation practically ramps up and when it begins to drop. Even when the sun is up, if the angle is too shallow or shadows are present, output won't increase much. On systems with a shallow tilt, the morning ramp-up can be slow and the evening drop may be felt earlier. If this appears the same way in the same season every year, it can be considered a characteristic of the installation conditions, but if it changes suddenly, other factors should be suspected.

When checking tilt angles, we also check whether the panel surfaces are kept uniform. Due to long-term use, ground conditions, settling of the mounting structure, or loosening of fastenings, the angle of only some rows may change. Even a slight difference that is hard to see can affect how shadows and reflections appear when the sun is low in the morning and evening. Especially for ground-mounted installations, if the height or tilt varies between rows front to back, the front row’s shadow is more likely to fall on the rear row. If power generation is low not only in the morning and evening but also in specific sections, you need to check for tilt variability and the condition of the racking.

The relationship between tilt and row spacing should not be overlooked. When panels are arranged in multiple rows, the low solar altitude in the morning and evening or during winter makes it easy for shadows from the front row to fall on the rear rows. Even if shading was accounted for under certain conditions during design, the way shadows fall can change because of actual terrain, construction errors, or changes in the surroundings. If output is low in the morning and evening, it is important to check not only the panel tilt angle but also the distance between rows, elevation differences, ground slope, and the orientation of the racking. Even if only part of some panels is shaded, depending on the electrical configuration that can affect power generation more than expected.

Check 4: Confirm shadows and reflection conditions when the sun is low

One cause to check in particular for low power generation in the morning and evening is shading. At times of low solar elevation, shadows from buildings, trees, fences, utility poles, nearby equipment, and adjacent rows of panels extend long. Small obstacles that are not noticeable at all during the day can cast long shadows onto the panel surface in the morning and evening. Therefore, if you judge there is no shading based only on on-site checks during daytime, you may overlook the cause of the reductions in the morning and evening.

For checking shadows, it is ideal to inspect the site at the times when power generation is dropping. If generation is low in the morning, check during the morning hours; if it is low in the evening, check during the evening hours. Visiting the site at midday will not reproduce the morning or evening shadows. If possible, first identify the times of the dips in the generation data, and then observe the shadow positions on site at those times. If generation drops at the same time every day, shadows from fixed objects may be involved. If the drops vary with the weather, consider the influence of clouds or fluctuations in solar irradiance.

Shading requires attention not only when it broadly covers the entire panel surface, but also when it falls narrowly on part of it. Thin shadows from power lines, handrails, fences, antennas, racking members, or tree branches can affect power generation depending on their position and the connection configuration. Especially in the morning and evening, shadows lengthen, so even narrow shadows can cross multiple panels. When generation is low, it is important to check not only whether there is shading, but also which panels are shaded, in what direction, and from what time to what time.

At ground-mounted solar power plants, shadows from surrounding vegetation and slopes are elements that are easy to overlook. As grass height increases, shadows can reach the lower parts of the panels in the morning and evening even if they are not noticeable during the day. Trees vary in foliage with the seasons, and their growth can cause shading to increase year by year. Even installations that had no issues at the time of commissioning should have surrounding vegetation checked if generation in the morning and evening declines after several years. Pay particular attention to boundaries on the east and west sides, as these are more likely to align with the sun in the morning and evening.

For roof-mounted installations, shadows can be caused by neighboring houses, differences in roof levels, chimney-like protrusions, railings, HVAC equipment, lightning protection equipment, and so on. On the roof, small components that are hard to see from eye level may cast shadows on the panel surface. If power generation is low in the morning and evening, check the overall layout of the roof and the direction of incoming sunlight, and record the times when shadows occur. Around the building, shadows that were not present at the start of generation can appear when new nearby buildings are constructed or signs and equipment are added.

Reflection conditions are also important in the morning and evening. When sunlight strikes solar panels at a shallow angle, it is more likely to be reflected off the panel surface, and power output can be lower compared with when light is received head-on. This is not a fault of the panels but a natural phenomenon caused by the angle of incidence. However, if the panel surface has dirt, dust, pollen, bird droppings, fallen leaves, or water marks, the effects of low-angle light can become more pronounced. Even if you feel generation is only reduced in the morning and evening, you should still check the surface condition.

The relationship between soiling and tilt is another point worth checking. Panels with a shallow tilt may not shed dirt easily in the rain. Dirt can accumulate at the lower edge of the panels, which can cause partial shading or worsen reflection conditions when the sun is low in the morning and evening. This does not occur at every installation, but when tilt is shallow and the surroundings have a lot of dust, farmland, unpaved roads, trees, or bird activity, it is safer to check the condition of the panel surfaces regularly. Don’t limit the cause of low power output to orientation or tilt alone; looking at surface condition together will improve the accuracy of your assessment.

When checking shadows and reflections, it is important to link power generation data with on-site photographs. Recording what position was shaded at what time (hour and minute) and how the power output changed at that moment makes it easier to explain the cause. When sharing the situation among managers, contractors, maintenance personnel, and owners, having photos and timestamps aligned reduces misunderstandings. Drops in the morning and evening are phenomena that are difficult to convey with words alone. Retaining the on-site appearance together with the data provides practical material for decision-making.

Considerations when Reviewing Orientation and Tilt

When reviewing orientation and tilt, it is important not to look only at a low power output result and immediately try to change the equipment’s orientation or angle. For existing installations, changing orientation or tilt involves many factors such as mounting structures, wiring, foundations, roof attachments, waterproofing, loads, and safety. If you make hasty changes solely aimed at improving power generation, other risks may arise. First, you should isolate whether orientation or tilt is truly the primary cause in the current installation, or whether shading, soiling, equipment, measurement, or operational conditions are involved.

Even if morning and evening output is low, it is necessary to confirm how much that affects the installation's annual generation. Because morning and evening are time periods when solar irradiance tends to be weaker, what looks worrying on the generation curve may have only a limited impact on the annual total. On the other hand, for installations that emphasize east- or west-facing surfaces, systems that want to align self-consumption periods with generation times, or installations where morning and evening operation has high value, reductions in morning and evening generation can become a significant issue. Depending on the objective, the extent to which improvements should be considered will vary.

When evaluating azimuth and tilt, it is important not to chase only the ideal values. In solar power generation, there are generally orientations and angles considered favorable for generation, but on actual sites there are constraints such as the site, roof, surrounding shading, regulations, safety walkways, maintainability, drainage, snowfall, wind, and interfaces with existing equipment. Even if the orientation and tilt are not ideal, the overall optimum may be achieved by adapting to site conditions. If you feel the power output is low, check the design intent and site constraints to see whether the current condition has deviated from the original assumptions.

Multiple causes often overlap. For example, if a southwest-facing installation should generate relatively well in the evening but generation in the evening is low, shadows on the west side, dirt on the panel surfaces, and a fault in a specific circuit may be occurring together. Even when installations with a shallow tilt have low output in the morning and evening, shadows from vegetation and the accumulation of dirt can also be factors. Before narrowing the cause of low generation to a single factor, it is important to check, in order, the time of day, orientation, tilt, shadows, dirt, equipment condition, and measurement condition.

Also, when comparing power generation you need to take solar irradiance conditions into account. Even with the same installation, the morning and evening appearance can differ greatly between a clear day and a partly cloudy day. On days that are clear in the morning but cloud over by noon, or clear at noon but get cloudier toward the evening, the generation curve can easily change with changing weather. If you have a pyranometer, check irradiance together with generation; even without one, keeping weather records and notes on the local sky conditions makes assessment easier. Avoid assuming orientation or tilt problems based solely on generation, as this helps prevent misjudgments.

Safety should also be considered. Inspections on roofs, at heights, on steep slopes, on embankments, and around electrical equipment can be dangerous. In the early morning and evening it can be difficult to see your footing, and condensation, frost, or wet surfaces after rain can make areas slippery. Even when confirming the cause of low power generation, avoid forcing an on-site inspection; when necessary, take photographs from a safe position or carry out inspections with an appropriate team. In particular, internal inspections of electrical equipment and checks of wiring must be performed by personnel with specialized knowledge following safety procedures.

Reviewing azimuth and tilt is more reliable when judged by accumulating data rather than drawing conclusions from a single inspection. Check the morning and evening power generation curves across different seasons, keep site photos, record the times when shadows occur, and, if necessary, cross-check with drawings. By turning the impression that generation is low into information about which time of day, which face, and under what conditions output is low, the priority of countermeasures becomes clear. Even when measures are required, it becomes easier to consider options other than major equipment changes—such as vegetation management, cleaning, identifying the causes of shading, operational improvements, and reviewing monitoring settings.

To continuously manage the causes of low power output

When generation is low in the morning and evening, checking the orientation and tilt makes it easier to identify likely causes. However, the morning and evening decline also includes natural factors. When the sun’s altitude is low, the incidence conditions on the panel surface tend to worsen, shadows are longer, and light strikes at a steep angle, so it is not uncommon for output to be lower than around midday. The important thing is to distinguish natural declines from those caused by changes in site conditions. To do this, you need to check time-of-day generation data, panel orientation, tilt angle, shadow positions, and seasonal differences together.

In this four-check process, we first confirmed whether output was low only in the morning and evening or also during the daytime, and then examined the relationship between panel orientation and the sun’s position. Based on that, we checked the tilt angle and the sun’s altitude for each season, and finally verified the shadows cast and reflection conditions when the sun is low. Looking at things in this order lets you organize the causes of reduced power generation as phenomena rather than by intuition. In practical work, it is especially important not only to consider the total generation amount but also to see at what times and in what way the output is declining.

An effective approach for ongoing management is linking power generation data with on-site records. Keeping sunny-day generation curves, on-site photos taken in the morning and evening, the times when shadows occur, dirt on panel surfaces, the condition of vegetation, and changes in the surrounding environment makes later comparisons easier. By checking whether generation in the mornings and evenings has fallen compared with the same period last year, whether it is low only in a particular season, or whether it is low only on a specific surface, you can more easily decide the priority of countermeasures. The way you record information becomes especially important when you feel power generation is low.

Solar power generation systems are not finished once installed; their condition changes along with the surrounding environment. Trees grow, grass lengthens, more buildings and equipment are added, and the way dirt accumulates also changes with the seasons. The condition of racking and the ground also needs to be checked over the long term. Power output in the morning and evening is a time when these small changes tend to become apparent. If you can detect anomalies early from morning and evening changes—before daytime generation drops significantly—you can more easily bring inspections and countermeasures forward.

To accurately identify the causes of low generation output, you should not view the entire facility as a single number but adopt an approach that separates by time of day, surface, orientation, tilt, shading, and season. Declines in the morning and evening are especially difficult to distinguish between faults and natural phenomena, so it is essential to assess both data and on-site observations. By combining daily monitoring with regular on-site checks and record-keeping, you can detect generation declines early and be in a position to explain them.

When power generation is low in the morning and evening, the practical approach is to first look at the generation curve, then check orientation and tilt, and verify shading and reflection conditions on site. Based on that, determine whether the decline should be accepted as a characteristic of the equipment or whether it can be improved through maintenance or site/environmental work. By continuously visualizing declines in generation and linking them to on-site conditions so they can be managed, it becomes easier to move from daily checks to decisions on improvements.