# Table of Contents

• The meaning of checking orientation and tilt in solar power generation simulations

• How to read the impact of orientation on generation

• How to read the impact of tilt on generation

• Basic procedure when comparing orientation and tilt

• How to view simulations without judging by south-facing only

• Notes when evaluating east-west orientations and low-slope roofs

• The importance of including shading and surrounding environment in comparisons

• Check annual generation and monthly generation separately

• How to choose orientation and tilt considering self-consumption and power sales

• Key points when explaining comparison results in practice

• The importance of on-site verification to improve orientation and tilt accuracy

• Summary

# The meaning of checking orientation and tilt in solar power generation simulations

When comparing generation in solar power generation simulations, one of the first conditions to confirm is which orientation the panels face and at what tilt they are installed. Solar power generation varies depending on how efficiently sunlight hits the panel surface. Therefore, even for systems of the same capacity, whether they face south, east, or west, and whether the roof slope is shallow or steep, will change the annual generation and the generation tendencies by time of day.

For practitioners responsible for solar power generation simulations, it is important not just to find the condition that yields the maximum generation. You need to judge which condition is most reasonable among realistically adoptable layouts, taking into account roof shape, building orientation, surrounding shading, constructability, maintenance, the timing of self-consumption, and power demand trends. Especially in residential and small-to-medium buildings, an ideal wide south-facing roof surface is not always available. In factories, warehouses, public facilities, and agricultural facilities, too, roof shape and structural constraints may require designs that combine multiple orientations and tilts.

Comparing orientation and tilt is not only about checking which yields more generation, but also about examining the generation time-of-day and seasonal variations. For example, south-facing tends to increase annual generation, while east-facing tends to favor morning generation and west-facing favors afternoon generation. When emphasizing self-consumption, whether generation aligns with morning and evening power use as well as midday matters. In other words, in simulations it is important not to conclude based only on annual totals but to read how the generation curve changes with orientation and tilt.

Tilt also affects seasonal generation. Because the sun’s altitude changes significantly between summer and winter, the panel inclination determines whether the installation is favorable in summer or helps compensate for lower winter generation. For roof-mounted installations, panels are often aligned with the roof slope and may not allow free choice of tilt, but for racking or ground-mounted installations, tilt selection affects both generation and constructability.

The purpose of comparing orientation and tilt in solar power generation simulations is not to find an ideal desk-calculated value but to compare multiple realistic options that approximate actual installation conditions and balance generation, usability, and explainability. Being able to correctly read differences in orientation and tilt increases the persuasiveness of simulation results and improves the accuracy of adoption and design decisions.

# How to read the impact of orientation on generation

Orientation indicates which direction the solar panels face. Generally, south-facing is considered easiest for obtaining generation, but in practice it is important not to assume south-facing is always correct; include comparisons with east-west directions and southeast, southwest, etc. Roofs are determined by site conditions and architectural plans, so it is not always possible to align all panels to an ideal orientation. Therefore, in simulations you should define the orientation for each realistically installable roof surface and check the generation for each.

South-facing receives sunlight readily during the day and tends to increase annual generation. It particularly tends to produce large generation around midday, making it a promising choice when maximizing annual generation is the priority. However, even south-facing installations may underperform if shaded by neighboring buildings, mountains, trees, or rooftop equipment. It is essential not to judge superiority based on orientation alone but to combine orientation assessment with shading conditions.

East-facing tends to favor morning generation. For buildings that use a lot of power from the morning through before noon, east-facing generation can align well with self-consumption. For example, facilities with large loads at morning startup—lighting, air conditioning, machinery, water heating—may benefit from layouts that generate more in the morning. Even if annual generation appears worse than south-facing, including self-consumption rate and reductions in purchased electricity can change the evaluation.

West-facing tends toward afternoon generation. For buildings whose power demand rises from afternoon to evening, west-facing generation can be useful. Afternoon generation is meaningful particularly in summer when air conditioning loads increase. However, west-facing systems are more susceptible to shading as the evening approaches because the sun’s altitude drops. If adjacent buildings, trees, or rooftop upstands exist, afternoon shading should be reflected in the simulation.

Southeast and southwest orientations often achieve generation close to south-facing and are frequently compared as realistic designs matched to roof shape. Southeast leans toward the morning and southwest toward the afternoon. Which is better depends not only on simple generation totals but on building usage hours and where demand peaks occur. For homes, consider living patterns; for corporate facilities, consider operating hours and equipment operation times.

North-facing generally suffers a large decline in generation and is difficult to adopt actively. However, in cases with very shallow slopes or limited installable area, you might not completely exclude north-facing surfaces and instead check how much generation they would actually produce. Of course, reflections, shading, snow, soiling, and reflections toward neighbors should also be considered. North-facing requires careful evaluation so that risks beyond generation are clearly explained.

When comparing orientations, it is important not only to use broad categories like south, east, and west, but to input the actual azimuth as accurately as possible. Judging only from roof drawings can lead to thinking a surface faces due south when it is actually south-southeast or south-southwest. Even a small difference can affect estimated generation when comparing multiple surfaces or designing a large-capacity system. To improve simulation accuracy, combine drawings, on-site checks, and positioning information to carefully determine orientation.

# How to read the impact of tilt on generation

Tilt indicates how much the solar panel is inclined relative to the horizontal plane. For roof-mounted installations, panels are often installed to match the roof pitch; for flat roofs or ground-mounted installations, tilt can be set with racks. Tilt affects annual generation, seasonal generation, wind loads, constructability, maintenance, and the extent of shading. Therefore, tilt should be decided by viewing the overall installation environment, not by generation alone.

In solar power generation, panels generate better when sunlight strikes the panel surface as close to perpendicular as possible. However, the sun’s position changes throughout the day and its altitude varies by season. That means an angle optimal at one moment is not necessarily optimal over the whole year. Simulations compare annual and monthly generation for a specific tilt based on annual irradiance conditions.

Increasing tilt can make panels receive light more effectively at the low sun angles of winter. Conversely, in summer when the sun is higher, too much tilt can reduce generation. Reducing tilt can be advantageous in summer or when the sun altitude is high, but winter generation may then be weaker. Thus, tilt differences are reflected not only in annual totals but in seasonal generation balance.

When installing to match a roof pitch, you often cannot freely choose tilt. In practice, input the roof pitch itself as a simulation condition and compare generation for each roof surface. For example, even with the same south-facing orientation, a shallow-pitch roof and a steep-pitch roof will show different monthly generation patterns. Shallow pitches tend to favor summer generation, while steep pitches can be relatively advantageous in winter. However, regional irradiance and surrounding environments change these tendencies, so check each case.

For flat roofs and ground-mounted installations you have freedom to set tilt, but you may not be able to adopt the tilt that maximizes generation in all cases. Increasing tilt makes shading from one row to the next more likely, requiring wider spacing between rows. Increasing spacing can reduce the number of panels installable in the same area. Conversely, lowering tilt can suppress inter-row shading and allow more modules to be installed, but you must consider soiling runoff, drainage, and snow retention in snowy regions.

When comparing tilt, it is important to separate generation per unit capacity from the total generation based on installable capacity. A tilt that yields high efficiency per panel may require large clearances, reducing total installable capacity. Another tilt might slightly reduce per-panel efficiency but allow more panels, increasing total generation. Practitioners must perform comprehensive comparisons including per-tilt efficiency, number of panels that can be placed, row spacing, maintenance aisles, and equipment layout.

# Basic procedure when comparing orientation and tilt

When comparing orientation and tilt, do not simply stare at simulation values; first organize the comparison conditions. Start by separating candidate roof or site surfaces and check each surface’s orientation, tilt, area, and presence of obstacles. Next, decide whether to compare at the same installed capacity, the same usable area, or the maximum number of panels that can actually be installed. If these premises are vague when comparing, you may misinterpret the meaning of the results.

For instance, when comparing orientation A and orientation B, if A allows a larger installable capacity and B allows a smaller capacity, comparing only annual generation can confuse whether differences are due to orientation or capacity. If you want to see the performance difference due to orientation itself, align the compared scenarios to the same capacity. Conversely, if you want to see realistic introduction effects, compare using the realistic capacity that can be placed on each surface. It is important to change comparison conditions according to the objective.

As a basic procedure, first create a baseline plan. The baseline chooses the roof surface that can most naturally be used or the orientation and tilt that generally yield higher generation. Then create alternatives that change orientation, change tilt, increase surfaces used, or include shading, and observe generation differences. Because having too many comparison cases makes decision-making difficult, in practice it is also necessary to narrow options to a few according to the purpose.

In comparisons, check annual generation, monthly generation, and time-of-day generation tendencies. Annual generation is useful to grasp overall scale, but orientation and tilt differences appear more clearly in monthly and time-of-day results. East-facing and west-facing may have similar annual values but generate at different times of day. Tilt differences change summer-winter variations. For self-consumption-focused projects, whether generation aligns with demand timing is especially important.

It is also effective to view comparison results as percentages. Showing how much a given alternative generates relative to the baseline makes it easier to explain to stakeholders. However, judging by percentage alone can obscure the absolute magnitude of real generation differences. A few percent difference in a large system equates to a large annual energy difference. Conversely, in small systems, if differences are minor, prioritizing constructability and roof usability may be better.

Record simulation comparison conditions so they remain understandable later. Organize azimuth, tilt angle, capacity, number of panels, shading conditions, loss rates, meteorological data used, and treatment of surrounding obstacles. Solar generation simulations are not a one-time calculation but an iterative process where conditions are updated with design changes and on-site checks. Clarifying comparison premises from the start reduces rework downstream.

# How to view simulations without judging by south-facing only

It is often explained that south-facing is advantageous in solar power generation and it does tend to increase annual generation. However, in practice it is important not to treat south-facing as the absolute. Depending on roof shape, the timing of power usage, shading conditions, and installable area, combining orientations other than south-facing can sometimes improve introduction effects.

For example, if the south-facing roof area is small and wide east-west roof surfaces are available, limiting yourself to south-facing will result in a small system capacity. In such cases, utilizing east-west surfaces can potentially increase total annual generation. Even if south-facing is advantageous per unit capacity, limited installable capacity means the building’s total generation will not grow. In simulations, separate generation efficiency per orientation from installable capacity.

Also, south-facing tends to produce more around midday, so buildings with low daytime demand may experience surplus. For projects prioritizing self-consumption, maximizing midday peak is not necessarily the right objective. Facilities operating from morning may benefit from east-facing, while those with large afternoon loads may benefit from west-facing generation. Even if annual generation is slightly lower, these layouts can better reduce purchased electricity.

Be cautious if south-facing roofs are shaded. Even if south-facing appears advantageous as an orientation, if long-duration shading occurs in the morning or afternoon, a less-shaded alternative orientation may provide more stable generation. Rooftops often have parapets, ventilation equipment, piping, railings, or lightning protection that cast shadows at certain times. South-facing superiority assumes sufficient irradiance; if shading exists, that advantage can be offset.

When comparing orientations, use the south-facing option as a baseline and compare southeast, southwest, east-west, and multi-surface combined alternatives to make judgment easier. Do not simply rank by generation quantity; read which times of day generate, which seasons are strong, and what level of shading risk is present. South-facing is a strong candidate, but the optimal solution for a project depends on installation conditions and power use objectives.

# Notes when evaluating east-west orientations and low-slope roofs

East-west roofs and low-slope roofs are common in practice. Whether residential or industrial, roofs are not always widely south-facing. Therefore, correctly evaluating east-west and low-slope conditions in solar power generation simulations is indispensable.

The characteristic of east-west orientation is that its generation peak differs from south-facing. East-facing favors morning generation and west-facing favors afternoon. Installing on both east and west faces may not achieve as high a midday peak as south-facing, but it often creates a relatively gentle generation curve from morning through evening. This can be advantageous when considering self-consumption. For buildings that consume power over a wide time span during the day, continuous generation over many hours can be more useful than a sharp instantaneous peak.

On low-slope roofs, the impact of orientation differences may appear smaller. When panel surfaces are close to horizontal, the effect of directional tilt weakens. However, it is risky to assume any orientation is the same on low-slope roofs. Even slight slope differences affect drainage direction, soiling retention, shadow length, and construction methods. Low-slope roofs may also retain dirt more easily, so consider long-term generation degradation and maintenance.

When evaluating east-west or low-slope roofs, check not only annual generation but also how effectively you can utilize the entire roof area. For instance, using low-angle racks can reduce row spacing and increase installable capacity. Conversely, adding tilt introduces row shadows and requires spacing. Compare options that increase installable capacity with options that increase per-unit efficiency to determine which better suits project objectives.

For east-west orientation, consider distributing modules across both faces rather than just one. This disperses generation between morning and afternoon. However, when spanning multiple orientations you must pay attention to grid connection configuration and differences in generation characteristics. Treating panels with different orientations or tilts under the same conditions can lead to discrepancies with actual behavior. In simulations, input conditions separately for each roof surface and check both aggregated and per-surface results.

East-west and low-slope roofs are often judged simply as inferior to south-facing, but in real projects they can be perfectly valid options. The important thing is to compare orientation and tilt practically, including building conditions, installable capacity, power usage, shading, and maintainability rather than relying on theoretical ideals.

# The importance of including shading and surrounding environment in comparisons

A frequently overlooked aspect when comparing orientation and tilt is the impact of shading and the surrounding environment. Even if a south-facing surface with an appropriate tilt looks good in simulation, in reality adjacent buildings, trees, rooftop equipment, mountains, utility poles, railings, or parapets can cast shadows and reduce generation more than expected. Orientation and tilt are important conditions, but they do not alone determine generation.

Shading impacts vary by time of day and season. In winter the sun altitude is low so shadows from the same obstacle extend farther. In summer the sun altitude is higher and shadows may be shorter. An obstacle on the east side affects morning generation; an obstacle on the west side affects afternoon generation. Tall buildings or trees to the south can greatly impact midday generation. Combining the generation tendency by orientation with the time-of-day shading pattern produces a more realistic judgment.

When comparing shading effects, confirm whether shading occurs during the time of day when the most generation is expected. For example, if south-facing panels are shaded around midday, the impact on generation tends to be large. Conversely, brief shading only in the morning or evening may have a relatively small effect on annual generation. However, if shading concentrates on specific panels, depending on system configuration the generation loss can spread. Therefore, consider shading not just by area but by which positions, at what times, and in which seasons shading occurs.

Changing tilt alters shading behavior. Adding tilt on a flat roof makes shadows fall onto rear rows more easily. Sufficient row spacing avoids shading but may reduce installable panel counts. Lower tilts suppress inter-row shadows but affect seasonal generation patterns and soiling runoff. When comparing tilt, consider not only the irradiance the panel surface receives but also the shadow created by the panels themselves.

The surrounding environment can change in the future. Even if shading is minor now, neighboring land may be developed, trees may grow, rooftop equipment may be added, and so on. You cannot predict everything, but where development likelihood is high or where trees near the site will grow, design margins and explanations should account for that. Generation simulation is a prediction based on current conditions; if conditions change, results will change, so communicate this to stakeholders.

Including shading and surrounding environment in comparisons makes orientation and tilt evaluations more practical. Reflecting site shape and obstacles, not just simple irradiance conditions, prevents overestimation and increases post-installation satisfaction.

# Check annual generation and monthly generation separately

When comparing orientation and tilt, always check monthly generation as well as annual generation. Annual generation is an easy-to-understand indicator of introduction effects, but it does not fully show seasonal generation tendencies. Tilt differences especially appear in summer and winter generation, so judging without looking at monthly variation can lead to errors.

Proposals with similar annual generation can have different monthly generation patterns. One option may be strong from spring to summer, while another may show a smaller winter decline. Power demand also varies seasonally. For buildings with heavy summer air conditioning loads, summer generation is important; for buildings with substantial winter heating or hot water loads, winter generation matters. Annual totals alone make it hard to judge compatibility with demand.

Orientation differences appear in time-of-day generation. Tilt differences appear in seasonal generation. Because both factors overlap and influence results, simulations are best understood from three perspectives: annual, monthly, and time-of-day. Practitioners do not need to explain every detail to stakeholders, but those making design decisions should grasp the generation tendencies behind the numbers.

When looking at monthly generation, focus not only on high-generation months but also on low months. Solar generation is affected by weather and irradiance, so there will be months with reduced generation. Consider how much decline is acceptable, whether changing tilt could improve it, or whether increasing capacity is better. However, making tilt excessively steep to slightly increase winter generation can worsen installable counts, wind loads, and constructability. Monthly generation should be interpreted alongside design conditions.

Monthly generation data is also useful for explaining to stakeholders. Presenting only annual generation can give the impression that generation is evenly distributed year-round. In reality, generation fluctuates with seasons and weather. Showing monthly trends makes it easier to explain periods of high and low generation and how they match demand, reducing unrealistic expectations or misunderstandings about simulation results.

# How to choose orientation and tilt considering self-consumption and power sales

When comparing orientation and tilt in simulations, aiming solely to maximize generation can diverge from actual economics and operational effects. For projects prioritizing self-consumption, when generation occurs is important. Configurations that generate more power during times when the building can use it may be advantageous even if annual generation is not maximal.

For buildings prioritizing self-consumption, overlay the power usage profile with the generation curve. Facilities that operate from morning may find east or southeast orientations match demand well. Facilities with heavy afternoon loads may benefit from west or southwest orientations. Rather than a large generation spike for a short midday period, continuous generation from morning through afternoon can better suppress surplus.

Even when considering selling power, more annual generation is not always the sole criterion. Grid connection conditions, output control, contract terms, and operational policies affect how surplus is handled. Without going into specific prices here, in practice you must organize how generated power will be used and how surplus will be treated before comparing orientation and tilt. Simulation results should be evaluated together with assumptions about power usage.

Using storage systems or energy management changes the evaluation of orientation and tilt. If midday-generated power can be stored and used later, generation timing constraints are partially relaxed. But batteries have capacity and control considerations, so rather than only increasing generation, consider the times that are easy to charge, desired discharge times, and the building’s load pattern. Evaluate orientation and tilt within the broader context of building energy operation.

Configurations that maximize generation, increase self-consumption rate, increase installable capacity, and are easy to construct are not always the same. Practitioners should organize which objective to prioritize based on simulation results. In early stages, compare multiple scenarios and finally choose by integrating generation, power usage, constructability, maintainability, and site constraints.

# Key points when explaining comparison results in practice

Comparison results for orientation and tilt must be explained to many stakeholders—owners, facility managers, designers, constructors, and decision-makers. Therefore, simply listing simulation numbers is insufficient. You need to clearly communicate why the results occurred, which conditions are influential, and which option should be chosen.

Begin explanations by clarifying comparison conditions. State whether results are compared for the same capacity or for realistic installable capacity, whether shading is included, and whether orientations and tilts are split by roof surface. Without clear premises, stakeholders cannot correctly interpret the numbers. Especially for projects using multiple roof surfaces, explaining which surface contributes how much generation increases acceptance.

Next, present annual generation differences in an easy-to-grasp form. Showing how much an alternative differs from the baseline helps convey the impact of orientation and tilt. But avoid assigning excessive significance to minute differences. Simulations are forecasts; actual generation varies with weather, soiling, equipment condition, and changes in surrounding environment. When differences are slight, it may be rational to prioritize constructability and maintainability over marginal generation gains.

When explaining orientation and tilt, communicate not only why some options generate more but also why others generate less. Explaining why east or west orientations produce less than south, why tilt changes seasonal generation, and how shading reduces generation builds trust in the results. Avoid excessive technical jargon and use familiar explanations such as the sun’s movement, roof direction, and how shadows fall.

In final proposals, do not simply push the option with the highest generation; present the option suited to the project’s objectives. Whether the priority is maximizing annual generation, emphasizing self-consumption, making effective use of roof surface, or prioritizing safety and maintenance, recommended alternatives change. Comparison results are decision-making materials and only make sense when tied to design objectives.

# The importance of on-site verification to improve orientation and tilt accuracy

Improving the accuracy of solar generation simulations requires accurate input conditions. Orientation and tilt can be read from drawings, but drawings alone may not sufficiently capture site reality. Building orientation, roof pitch, surrounding obstacles, rooftop equipment, existing piping, maintenance space, and snow/drainage conditions are often discerned only through on-site verification.

Pay particular attention to orientation, since the treatment of north on drawings and actual orientation can differ. Differences arise from drawing notation, building placement, site tilt, and measurement methods. For tilt, roof pitch may not be uniform or may have changed partially due to renovations. Overlooking such differences causes a mismatch between simulation inputs and site conditions, reducing prediction accuracy.

During on-site verification, record not only orientation and tilt but also elements that cause shading. Confirm the height and position of surrounding buildings, tree locations, rooftop equipment placement, and the presence of railings or upstands. Organize photos and notes with positional and height information to aid later simulation and explanations. For large roofs or multi-building facilities, it is easy to become unclear about which position and direction were checked, so how you record matters.

After performing simulations during the design phase, check again before construction to confirm conditions have not changed. It is not uncommon for rooftop equipment to be added, maintenance aisles to shift, nearby construction to begin, or parts of a roof to become unusable. Do not overtrust simulation results; update on-site information and review comparison conditions to reduce post-installation gaps.

The more accurate the on-site verification, the closer orientation and tilt comparisons become to practical reality. Solar generation simulations return results based on entered conditions. Thus, the ability to correctly grasp on-site conditions determines result reliability. Combine drawings, on-site measurements, photo records, and positioning data to perform evidence-based comparisons.

# Summary

Comparing orientation and tilt in solar power generation simulations is not simply a matter of finding the direction or inclination with the highest generation. Orientation affects the time of day when power is generated, and tilt affects seasonal generation tendencies. South-facing is a strong condition that tends to boost annual generation, but east, west, southeast, southwest, and low-slope roofs all have practical value. When emphasizing self-consumption, it is essential to check not only total generation but also whether generation timing aligns with the building’s electricity demand.

When comparing, clarify whether you are looking at orientation differences for the same capacity or the introduction effect for realistically installable capacity. Separate checks of annual generation, monthly generation, and time-of-day generation tendencies, and judge including shading, surrounding environment, constructability, and maintainability to reach more realistic design decisions. Avoid deciding based solely on slight generation differences; select the configuration that is most reasonable for the project objectives.

Simulation accuracy is greatly influenced by the accuracy of on-site information. If you do not accurately grasp roof orientation, pitch, surrounding obstacles, rooftop equipment, and maintenance space, the comparison results will diverge from reality. Correctly comparing orientation and tilt requires not only desk calculations but accurate on-site measurement, recording, and reflection in design conditions.

If you organize simulation conditions for solar generation while accurately capturing roof and site positions, orientations, and measurement points on-site, using high-precision positioning such as an LRTK (iPhone-mounted high-precision GNSS positioning device) can make the flow from site verification to design review more reliable. Comparing orientation and tilt is the foundation of generation prediction. Accurately acquiring on-site positional information and performing simulations based on evidence-based conditions is the first step to improving the accuracy of introduction decisions.