5 Steps to Check Roof Orientation to Improve Solar Power Generation

When you want to improve solar power generation, checking the roof orientation is as important as cleaning and equipment inspections. Because solar panels generate electricity by receiving sunlight, the roof's orientation and the times of day when it receives sunlight affect annual power generation and self-consumption. However, roof orientation alone does not determine the amount of power generated. It's important to consider the roof's tilt, shading, seasonal variation, usable installation area, and even the facility's electricity usage hours. This article provides a five-step roof orientation check to improve solar power generation, aimed at practitioners searching for "how to increase power generation".

Table of Contents

• Why roof orientation matters for improving power generation

• Step 1: Accurately identify the orientation of each roof surface

• Step 2: Check generation time windows for each orientation

• Step 3: Assess roof orientation and tilt angle together

• Step 4: Check shadows and obstructions for each roof orientation

• Step 5: Connect to self-consumption and layout improvements

• Decisions to avoid when assessing roof orientation

• Summary

Why Roof Orientation Matters for Improving Power Generation

Roof orientation is a critically important item to check when improving solar power generation. Even with the same installed capacity, solar panels will receive different amounts of sunlight and generate electricity at different times depending on which direction they face. In general, roof surfaces that face closer to the south tend to produce higher annual generation. However, in practical efforts to increase generation, it is not sufficient to consider only whether the roof faces south.

Roof orientation affects not only the total amount of electricity generated but also the times of day when it is produced. East-facing roof surfaces tend to generate electricity in the morning, while west-facing surfaces tend to generate in the afternoon. South-facing surfaces tend to produce larger amounts around midday. In other words, roof orientation changes the times during the day when generation occurs.

This difference in time periods is important when considering self-consumption. For example, for offices or factories that operate from the morning, power generation on east-facing roof surfaces can be effective. For facilities where electricity usage increases in the afternoon, generation on west-facing roof surfaces can be helpful. If a facility has high power demand around midday, prioritizing south-facing roof surfaces becomes more significant.

Roof orientation also affects how shadows fall. If there are tall buildings or trees on the east side, east-facing roof surfaces tend to have reduced power generation in the morning. If there are obstructions on the west side, west-facing roof surfaces tend to have reduced power generation in the evening. If there are obstructions on the south side, they can cast shadows during the times when power generation tends to be higher, so they may have a larger impact on annual power generation.

When you want to increase power generation, it is important not to view the entire roof as a single surface, but to check each roof plane separately for orientation, tilt, shading, and usable installation area. By separating south-facing, east-facing, west-facing, north-leaning surfaces, and flat-roof sections, you can determine which surfaces are effective for improving generation.

Checking roof orientation is useful not only at the time of installation but also when verifying a decrease in power generation of existing equipment. If only a specific roof surface shows low generation, you can narrow down the cause by checking that surface’s azimuth, shading, soiling, tilt, and equipment/system. To improve power generation, it is important to verify roof orientation from both generation data and on-site conditions.

Step 1: Accurately determine the orientation of each roof plane

The first step in checking roof orientation is to accurately determine the orientation of each roof plane. Even if a building appears to face south as a whole, it may actually have multiple roof planes with different orientations. For gable roofs, hip roofs, mono-pitch roofs, flat roofs, and the large roofs of factories or warehouses, the solar exposure varies by roof plane.

To improve solar power generation, first check which roof surfaces face which directions. South-facing, southeast-facing, southwest-facing, east-facing, west-facing, and north-leaning surfaces differ in their expected generation output and in the times of day they generate power. Surfaces closer to south tend to yield higher annual generation, but east- and west-facing surfaces can also be effective depending on the facility's electricity usage hours.

When checking roof orientations, it is important not to rely solely on the orientations shown on the drawings. The orientation on the drawings may be inaccurate, or the building may be positioned slightly askew. By verifying the orientation on site and recording the direction of each roof plane, you make it easier to confirm the assumptions used in energy production simulations and contractor proposals.

Also, we will confirm the installable area for each roof surface. Even on roof surfaces with a favorable orientation, if there are roof-mounted equipment, piping, drains, access hatches, handrails, penthouses, waterproofing clearances, inspection walkways, etc., the area that can actually be used will be limited. Just because a roof surface has a good orientation does not mean you can place panels over the entire surface. It is important to verify the area that can actually be used.

For existing installations, check the power generation for each roof surface. If the south-facing surface is not generating as much as expected, there may be shading, dirt, or equipment malfunctions. If the east- or west-facing surfaces are generating more than expected, they may align well with the facility's demand hours. By looking at orientation together with generation data, you can determine which roof surfaces should be prioritized for improvement.

To increase power generation, the starting point is to accurately identify the orientation of each roof surface rather than leaving it ambiguous. Once you know the orientation, you can determine which times of day are most conducive to generation, where shading is likely to have an impact, and which surfaces should be prioritized for use.

Step 2: Check the power generation time periods by orientation

The second step is to check the power generation time periods for each orientation. Roof orientation affects not only the amount of power generated but also the times of day when generation is most likely. To improve generation, you need to see whether the orientation of the roof surfaces aligns with the facility's electricity usage time periods.

Roof surfaces that face close to south tend to generate more power around midday. In facilities with high daytime electricity demand, making use of south-facing roof surfaces makes it easier to increase self-consumption. In facilities where demand is concentrated around midday—such as air conditioning, lighting, equipment operation, and office work—south-facing generation is more likely to be effective when introduced.

East-facing roof surfaces tend to generate electricity more readily in the morning. For factories, logistics facilities, retail stores, and offices that operate from the morning, east-facing generation can be effective in meeting morning demand. Facilities with high power consumption during the morning start-up period have reason to check the power output from their east-facing side.

West-facing roof surfaces tend to generate electricity more in the afternoon. In facilities where air-conditioning loads increase in the afternoon, facilities that operate until evening, or facilities with high afternoon demand from production equipment or cooling, west-facing generation can help with self-consumption. However, if there are buildings or trees to the west, you need to be aware of evening shading.

To check generation time periods, it is useful to look at time-of-day generation data. If generation is slow to ramp up in the morning, check for shading on the east side and the conditions of east-facing surfaces. If generation drops around midday, check for shading to the south and from nearby equipment. If generation falls off early in the evening, check for shading on the west side and the conditions of west-facing surfaces.

If the purpose of increasing generation is to boost self-consumption, the annual total generation alone is not enough to judge. It is important whether the generated electricity is produced at times when it can be used within the facility. By overlaying the generation time periods for each roof orientation with the facility’s power usage patterns, it becomes easier to assess whether improvements in generation will translate into tangible benefits.

When checking roof orientation, it's important not only to see which roof surface generates the most power, but also which surface matches the facility's demand hours. If you're thinking practically about how to increase power output, be sure to check the generation hours for each orientation.

Step 3: Consider roof orientation and tilt angle together

The third step is to consider roof orientation and tilt angle together. The electricity generation of solar panels is affected not only by orientation but also by the angle at which the panels are installed. Even on south-facing roofs, different tilt angles change how sunlight is received. On east- or west-facing roofs, the tilt angle also alters the times of day when power is generated and the seasonal generation amounts.

When installing along the roof pitch, the tilt angle of the panels is governed by the roof’s own slope. On existing roofs it is often difficult to significantly change the tilt angle, so deciding which roof surface to use and which to prioritize becomes important. Each roof surface needs to be evaluated—for example, a surface with a favorable orientation but a shallow slope that tends to retain dirt, or a surface with a slightly unfavorable orientation but less shading and greater stability.

Tilt angle also affects seasonal power generation. The way sunlight is received differs between summer, when the sun's altitude is high, and winter, when it is low. A steeper tilt can make it easier to receive solar radiation in winter, but considerations such as roof shape, wind effects, ease of installation, and ease of maintenance are necessary. A shallower tilt can make installation easier, but dirt, fallen leaves, and snow may be more likely to remain.

When using mounting racks on a flat roof, you can compare the tilt angles of the racks. However, increasing the angle does not necessarily increase power generation. Increasing the angle lengthens inter-row shading and may require widening the spacing between front and back panels. Widening the spacing can reduce the number of panels that can be placed on the same roof area. It is important to make a decision by considering total energy generation, generation per unit of capacity, inter-row shading, and maintainability.

When checking the roof orientation and tilt angle, we also look at monthly power generation. Even if the annual generation is about the same, generation can differ by season. For facilities with high demand in winter, improving winter generation is important. For facilities with high air-conditioning demand in summer, check the summer generation and temperature losses.

Judging a roof surface as "good" or "bad" based solely on its orientation is insufficient. By considering the combination of slope angle, shading, soiling, snow accumulation, and maintainability, you can correctly determine which roof surfaces are suitable for improving energy output.

Step 4: Check shadows and obstacles for each roof orientation

The fourth step is to check shadows and obstacles for each roof orientation. Even with the same roof orientation, energy output can vary greatly depending on what obstacles are nearby. Even a south-facing roof surface may have reduced output if there are buildings or trees on the south side. Morning shadows are particularly important for east-facing roof surfaces, and evening shadows are particularly important for west-facing roof surfaces.

Sources of shadows include surrounding buildings, rooftop equipment, roof structures (penthouses), handrails, piping, air-conditioning equipment, ventilation equipment, utility poles, signboards, trees, slopes, and changes in terrain elevation. On roofs, even small pieces of equipment located close to the panels can cast shadows. Piping, upstands, and handrails that are difficult to notice from the ground can cast shadows on the panels depending on the time of day.

To check shadows for each roof orientation, it is important to view them together with the power generation hours. For east-facing roof surfaces, since they receive sunlight more readily in the morning, check for shadows from trees, buildings, and equipment on the east side. For west-facing roof surfaces, check for shadows from the afternoon through the evening. For south-facing roof surfaces, because shadows around midday have a large impact on power generation, focus particularly on obstacles and nearby equipment on the south side.

Don't overlook winter shadows. In winter, the sun's altitude is low, and shadows become much longer. Even roof surfaces that are not shaded in summer can receive shadows from surrounding buildings, trees, or rooftop equipment in winter. For roof surfaces where power generation drops significantly only in winter, check winter shadows as well as orientation.

In existing installations, we compare the power generation data for each roof surface with shading conditions. If the east-facing side is lower in the morning, the west-facing side falls off earlier in the evening, or the south-facing side shows an abnormal dip around midday, we check for obstacles corresponding to each orientation. If the shading is caused by trees, we determine whether they can be managed; if it is caused by rooftop equipment or nearby buildings, we use the information to inform decisions on layout changes or additional installations.

When assessing roof orientation, do not rely solely on compass direction; you need to verify whether that orientation can actually receive sunlight. By checking shadows and obstructions for each roof surface, you can identify which surfaces should be prioritized to increase power generation and which should be treated with caution.

Step 5: Connect roof orientation checks to self-consumption and layout improvements

The fifth step is to connect checking roof orientation to self-consumption and layout improvements. If the purpose of improving solar power generation is not simply to increase generation but to increase the amount of electricity available for use at the facility, you must always confirm the relationship between roof orientation and self-consumption.

Prioritizing roof surfaces with higher generation is important, but if that generation does not match the facility’s demand hours, surplus energy may increase. For example, south-facing surfaces, which concentrate generation around midday, tend to yield higher annual generation, but if the facility’s demand is low at midday, excess can become more likely. For facilities with high demand in the morning, east-facing generation can be effective, while for facilities with high demand in the afternoon, west-facing generation can be effective.

When prioritizing self-consumption, check generation, facility demand, and surplus electricity by time of day. Even if generation increases, if the additional output merely becomes surplus, the improvement in the benefits from the installation will be limited. Conversely, even if the annual increase in generation is small, if generation rises during the times when the facility uses power, the practical impact can be significant.

In layout optimization, consider the role of each roof orientation. South-facing surfaces support daytime generation, east-facing surfaces supplement morning generation, and west-facing surfaces supplement afternoon generation. Of course, it isn’t always best to use every surface. Take into account shading, soiling, tilt, maintainability, and available installation area, and prioritize the surfaces with higher effective energy production.

Also, using the entire roof surface is not always optimal. Forcing installations on heavily shaded areas, north-facing surfaces, sections that are difficult to inspect, or places that would interfere with drainage or waterproofing management can not only prevent power generation from reaching expected levels but also degrade maintainability. When improving the layout, we check not only the power output but also whether the system can be managed over the long term.

Checking roof orientation is most effective when combined with on-site surveys and power generation simulations. By running simulations that reflect orientation, tilt, the presence or absence of shading, and the timing of self-consumption, it becomes easier to determine which roof surfaces to use and which to avoid.

Checking roof orientation to improve power generation doesn't end with simply determining the azimuth. To increase the amount of electricity usable by the facility, it's important to evaluate roof orientation together with generation time periods, demand time periods, and maintainability.

Judgments to avoid when checking roof orientation

What you should avoid when checking roof orientation is simply judging south-facing roofs as good and east- or west-facing or north-leaning roofs as bad. Roof surfaces that are close to south-facing tend to yield higher annual energy production, but east- or west-facing roofs can also be effective depending on a facility's demand hours. Conversely, a south-facing roof will not generate much power if it is heavily shaded. Roof orientation needs to be considered together with shading, tilt, available installation area, and demand hours.

Also, you should avoid treating the entire roof as a single orientation. On buildings with multiple roof planes, each plane can have a different orientation and tilt. An average view of the whole roof will not show which planes are contributing to power generation and which are reducing output. It is important to check each roof plane separately.

Caution is needed when determining roof orientation from drawings alone. The orientation shown on the drawings may be misaligned with the actual building, and obstacles or shading may be observed on site. Roof orientation should be determined by combining the drawings, on-site verification, and power generation data.

You should avoid judging the suitability of a roof’s orientation solely by total power generation. Even if generation is high, if it occurs at times when the facility cannot use it, it may only increase surplus. If you prioritize self-consumption, you need to check the relationship between generation times and the facility’s demand.

Furthermore, you should avoid decisions to fully utilize the roof surface at the expense of maintainability. Even if the roof orientation is favorable, a layout that interferes with inspection walkways, drains, rooftop equipment, or waterproofing management will pose challenges for long-term operation. To increase power generation, it is important not only to choose surfaces that are favorable for generation but also to arrange them in a maintainable layout.

Confirming roof orientation is not just a simple determination of direction. By assessing power generation, self-consumption, shading, tilt, and maintainability together, you can identify practical improvements that are useful in real-world work.

Summary

When checking roof orientation to improve solar power generation, it is important to accurately identify the orientation of each roof surface, understand generation time periods by orientation, and make judgments together with tilt angle, shading, and self-consumption. Roof orientation has a large impact on generation, but the amount of generation is not determined by orientation alone. By looking at site-specific conditions and facility usage together, you can choose more effective improvement measures.

In Step 1, accurately determine the orientation of each roof surface. Rather than viewing the building as a whole, it is important to separate and examine south-facing, east-facing, west-facing, north-leaning surfaces, and sections of flat roof. In Step 2, confirm the power-generation time windows by orientation. Because south-facing surfaces tend to generate around midday, east-facing in the morning, and west-facing in the afternoon, assess these in conjunction with the facility's power usage hours.

In Step 3, we consider roof orientation and tilt angle together. The tilt angle affects seasonal power generation, soiling, and how likely snow is to remain. In Step 4, we check shadows and obstacles for each roof orientation. Morning shadows are important on east-facing roofs, evening shadows on west-facing roofs, and shadows around midday on south-facing roofs. In Step 5, we connect this to self-consumption and layout improvements. If increased generation only produces more surplus, the practical benefit is limited.

When checking roof orientation, things to avoid are assuming that only south-facing is good, treating the entire roof as a single orientation, judging based only on drawings, and deciding the layout while ignoring maintainability. Roof orientation is important when considering how to increase power generation, but it must be judged together with shading, tilt, installable area, facility demand, and maintainability.

Moreover, accurate on-site information is essential to improve the accuracy of roof-orientation assessments. If the orientation and slope of each roof surface, rooftop equipment, obstacles, trees, drains, inspection routes, and potential connection points can be accurately identified, it becomes easier to determine which roof surfaces should be prioritized and which will be problematic due to shading or soiling.

If you want to efficiently carry out roof orientation checks to improve solar power generation—accurately recording on-site roof surface orientation, pitch, obstructions, trees, rooftop equipment, inspection/maintenance routes, and candidate connection points—the use of LRTK, an iPhone‑mounted GNSS high‑precision positioning device, is effective. If high‑precision positional information can be obtained on site, it becomes easier to organize the orientation of each roof surface, the causes of shading, feasible installation areas, and maintenance access routes, making it straightforward to proceed consistently from on-site verification for power improvement to simulation comparisons and post‑installation performance management. To improve solar power generation through roof orientation, it is important not only to make desk‑based orientation judgments but also to accurately grasp the site and translate that into layouts that improve both power output and self‑consumption.