# Table of Contents

• What it means to compare installation sites using solar power generation simulations

• Step 1 Organize candidate site conditions using the same criteria

• Step 2 Align solar irradiance data and azimuth angles for comparison

• Step 3 Verify shading, surrounding obstacles, and terrain conditions from an on-site perspective

• Step 4 Look at monthly fluctuations and operational risks, not just annual generation

• Step 5 Judge including constructability, maintenance, and future changes

• Common mistakes when comparing installation sites

• How to summarize simulation results for practical use

• Summary

# What it means to compare installation sites using solar power generation simulations

Solar power generation simulations are not just for predicting “how much power can be generated.” In practice, they are used to compare multiple roof surfaces, plots, parking canopies, idle land, factory buildings, warehouse buildings, office buildings, and other options to determine where installation is expected to produce the most stable generation. Even with the same installed capacity, changing the installation site can significantly alter annual generation, seasonal generation trends, shading impacts, ease of construction, and ease of maintenance. Therefore, it is important not to decide solely on generation figures but to carefully interpret the differences in site-specific conditions.

Many practitioners searching for “solar power generation simulation” already have several candidate sites and struggle with which site to prioritize and how to organize materials for internal explanations. Simulation results present many items—annual generation, monthly generation, solar irradiance, loss rates, system capacity, azimuth, tilt angle, shading effects—but if comparison axes are not organized, the numbers alone become difficult to judge. What matters is to standardize conditions for each candidate site, compare under the same assumptions, and be able to explain why numerical differences occur.

The site with the highest generation is not always the optimal choice. For example, a site with high annual generation may suffer large winter declines, have significant morning shading, be likely to receive future shading from adjacent buildings, or have poor inspection access—issues that may cause problems during operation. Conversely, a site with slightly lower generation but with minimal shading, easy construction, and easy maintenance can be the more stable long-term choice.

This article explains five practical steps to compare installation sites using solar power generation simulations. It assumes comparisons among various candidate sites—residential, factory, warehouse, office, public facilities, vacant land—and emphasizes interpretation for decision-making rather than mere number checking.

# Step 1 Organize candidate site conditions using the same criteria

The first thing to do when comparing installation sites is to organize the conditions of each candidate using the same criteria. If input conditions vary before considering simulation accuracy, the resulting outputs cannot be compared. If one candidate assumes the entire roof while another excludes areas around obstacles, you cannot judge superiority by a simple annual generation comparison. First, align items such as installable area, assumed system capacity, panel layout conditions, azimuth, tilt, the meteorological data used, and the approach to loss rates for each candidate.

A common practical situation is that candidate A has detailed drawings, candidate B has only a rough area, and candidate C has only site photos. Running simulations in this state tends to make candidate A’s conditions detailed and strict, while candidates B and C become optimistic. The purpose of comparison is not to produce the most favorable number but to visualize differences among candidates under the same assumptions. Therefore, even if the granularity of information differs, decide the minimum items to align before inputting data.

When organizing installable area, consider not just the roof or site area but the actual area where panels can be placed. For roofs, consider setbacks from edges, equipment, inspection walkways, lightning protection, skylights, exhaust vents, snow guards, guardrails, and planned future renovations. For ground-mounted installations, consider paths, drainage, slopes, trees, existing structures, vehicle circulation, adjacent property boundaries, and maintenance work space. Even if candidate sites have the same nominal area, the actual installable capacity can differ greatly, so pre-simulation organization is essential.

Next, decide the comparison unit. Whether you compare by maximum capacity per site or by placing the same system capacity at each site changes how you interpret results. Comparing by maximum capacity identifies the site’s generation potential. Comparing by the same installed capacity makes it easier to compare site-specific generation efficiency and condition differences. In practice, it’s helpful to first compare generation efficiency with the same capacity and then look at total generation for maximum installation. This avoids automatically favoring larger sites and allows a fair assessment of solar irradiance and shading impacts.

It is also important to record simulation assumptions. If you don’t know which azimuth was entered, which tilt angle was used, how shading was reflected, or what loss rate was set, you cannot explain results later. Internal reviews and client explanations require explaining “why this candidate was prioritized.” With recorded assumptions, you can explain not only differences in generation but also the reasons those differences occurred.

When organizing candidate site conditions, precise design drawings are not always necessary. However, the comparison criteria must be consistent. Use rough assumptions for the preliminary study phase and recompare with detailed conditions during the detailed study phase to avoid excessive rework. Creating a state in which candidates can be compared fairly is the first step in site comparison, rather than trying to achieve a perfect simulation from the start.

# Step 2 Align solar irradiance data and azimuth angles for comparison

Solar irradiance, azimuth, and tilt angle are the most basic comparison items when considering generation differences among sites. Solar PV generates power from solar irradiance, so even within the same region, changing the orientation or tilt of a roof surface alters annual generation and hourly generation patterns. Surfaces closer to due south tend to secure generation throughout the year, but east- or west-facing surfaces can have advantages depending on use. For example, east-facing generation can be beneficial for facilities with high morning power usage, while west-facing generation can match afternoon consumption for facilities with later peaks.

When comparing sites in simulations, first confirm that the same irradiance data are used. Even for candidates on the same property, slight differences in the input location can produce small differences in results. When comparing multiple facilities across a wide area, regional meteorological differences affect generation. Regions with higher solar irradiance look more favorable, but temperature, snowfall, sea breezes, salt damage, mountain fog, and seasonal weather tendencies also affect actual operation. Therefore, evaluate sites not only by irradiance but also by whether stable operation is feasible in that region.

For azimuth comparisons, it is insufficient to simply check whether a surface is south-facing. If a roof surface is slightly southeast or southwest, the annual generation difference may be small, but the generation timing changes. For corporate facilities, it is important not only how much is generated but when the generated power is available. Matching generation timing with lunch hours, operation peaks, air-conditioning loads, production line operation times, and weekend operation yields a more practical evaluation. If high generation is concentrated in times when consumption is low, the expected benefits may not materialize.

Tilt angle also greatly affects comparisons. Roof installations often follow the existing roof slope, while ground installations may allow angle adjustment via racking. Increasing the tilt can improve winter irradiance reception but must be balanced against wind effects, structural constraints, inter-row shading, and constructability. Lower tilt can ease installation and reduce wind effects but affects dirt shedding, generation efficiency, and drainage. Do not adopt the simulation’s optimum angle alone; judge in combination with site conditions.

When comparing candidates, looking at an indicator like generation efficiency—annual generation divided by installed capacity—can be effective. Sites with a large maximum installable capacity tend to show higher total generation, making it hard to tell whether the site conditions are truly good or simply large. Comparing how much is generated for the same installed capacity allows a fairer comparison of azimuth, tilt, and irradiance differences. Also, dispersing installations across east and west faces or multiple roofs can smooth peak generation, which matters not only for maximum generation but also for matching power usage.

In comparing irradiance and azimuth, do not stop at labeling numerical differences as merely “large” or “small.” Be able to explain why the difference occurred, what time-of-day or seasonal characteristics it has, and whether it matches the facility’s power usage. Site comparison is not about winning on generation figures but about judging which site best fits the project objective.

# Step 3 Verify shading, surrounding obstacles, and terrain conditions from an on-site perspective

When using solar power generation simulations to compare installation sites, the most easily overlooked and impactful factor is shading. Even with good irradiance and orientation, surrounding buildings, trees, utility poles, chimneys, HVAC equipment, rooftop structures, guardrails, and mountain ridgelines can cast shade and reduce generation. Especially in mornings, evenings, or winter, when solar altitude is low, obstacles that seem negligible can cast long shadows. How shading is incorporated in site comparisons greatly affects judgment accuracy.

When checking shading in simulations, it is important to grasp its annual variation. A site with little shade in summer may see adjacent building shadows extend greatly in winter. Sites with morning-only shading, afternoon-only shading, or seasonal-only impacts can mask problems if you look only at annual generation. Check monthly generation and hourly generation patterns to determine when and how much shading affects performance.

Rooftop obstacles must not be underestimated. Outdoor HVAC units, ventilation equipment, piping, antennas, lightning protection, inspection walkways, etc., not only reduce installable area but also cause shading. Even small obstacles can affect panel output if they shade part of an array. A roof may look spacious, but a roof with many pieces of equipment allows little layout freedom. In simulations, reflect obstacle positions and heights as much as possible, not just roof area.

For ground-mounted systems, terrain affects both generation and constructability. Even seemingly flat land may have subtle slopes, embankments, poor drainage, nearby trees, adjacent structures, or snowdrift areas that constrain layout or racking plans. Terrain undulations can cause inter-row shading and orientation variance, reducing generation compared to desk-based simulations. On vacant or large sites, do not be reassured by ample area alone; confirm which portions can be used stably.

Don’t overlook future changes in the surrounding environment. A site with little current shading may be at risk if adjacent buildings are likely to be built, trees will grow, or rooftop expansions or equipment renewals are planned. Because solar PV is intended for long-term operation, consider whether irradiance will remain adequate in the future. In comparisons, separate sites with high current generation from those with low future risk.

Do not rely solely on simulations to check shading. Combining site photos, roof drawings, positions of surrounding buildings, obstacle heights, and seasonal solar altitude reduces input errors and oversights. Especially when comparing multiple candidates, avoid modeling shading strictly for some sites and not for others. If you reflect shading, do so for all candidates; if you do not at the preliminary stage, state that assumption explicitly for fairness.

When confirming shading, obstacles, and terrain, consider not only reduced generation but also trouble prevention after installation. Forcing installation in shaded locations can create large discrepancies from expected generation and lead to “the simulation was different” complaints after deployment. If shading is carefully assessed at the comparison stage, generation estimates will be closer to reality and easier to justify.

# Step 4 Look at monthly fluctuations and operational risks, not just annual generation

Annual generation is the most prominent indicator in site comparisons. When listing generation for each candidate, it is tempting to pick the site with the largest number. However, judging by annual generation alone can overlook seasonal fluctuations and operational risks. Sites with the same annual generation may differ in when they generate: some produce strongly from spring to summer, while others generate more stably year-round. When emphasizing self-consumption, not only total generation but also timing matters.

Monthly generation reveals site characteristics more clearly. Sites that drop sharply in winter may be affected by low solar altitude, snow, surrounding building shadows, mountain shadows, or roof orientation. Sites that don’t ramp up in summer may suffer from temperature-related efficiency loss, afternoon shading, orientation impacts, or regional cloudiness. Even when annual generation differences are small, monthly data can reveal weaknesses in specific periods.

For corporate facilities, overlay monthly generation with seasonal power usage to evaluate fit. Sites that can secure generation during summer when air-conditioning load is high align well with self-consumption. Conversely, facilities with high winter power usage may receive less benefit from sites that decline in winter. Confirming whether high-generation seasons match high-usage seasons makes evaluation more practical.

Hourly generation patterns are also important. East-facing sites tend to generate more in the morning; west-facing sites tend to generate more in the afternoon. South-facing sites secure daytime generation, but whether that matches usage peaks depends on the facility. Some factories increase power use immediately after start-up, while others have peak air-conditioning loads in the afternoon. Comparing simulation results with facility operation patterns moves evaluation beyond simple generation figures.

From an operational risk perspective, examine generation variability. Weather-driven fluctuations are unavoidable, but some sites may show unstable generation during specific hours due to shading or terrain. A site with high generation but local shading may show unnatural drops in monthly or hourly views. Such sites may require panel layout or circuit design adjustments. Identifying risks at the comparison stage makes later design adjustments easier.

Also accept that simulation values carry inherent uncertainty. Meteorological conditions vary year to year, and actual generation changes with equipment aging, soiling, environmental changes, and inspection practices. Therefore, do not prioritize minute numerical differences when ranking sites; focus on major trends. When differences are marginal, emphasize constructability, maintainability, and lower future risk.

Combining annual, monthly, and hourly generation views makes site characteristics three-dimensional. One site may excel in annual generation, another in compatibility with self-consumption, and another in low future risk. The goal is not simply to find the highest numeric site but to choose the site that best meets the installation objective.

# Step 5 Judge including constructability, maintenance, and future changes

Simulations are a powerful means of comparing generation, but final site decisions must consider constructability, maintenance, and future changes. Even if a site has the highest generation, it is not optimal if construction is difficult, inspections are hard, the roof is unstable, or renovations are planned. Simulation results should be a central decision input, but in practice, do not draw conclusions from them alone.

For constructability, check material logistics, workspace, safety measures, interference with existing equipment, roof strength, ground conditions, drainage planning, and wiring routes. On roofs, even if generation is good, if workers cannot move safely, inspection passages cannot be secured after installation, or the roof material is in poor condition, the plan may need revision. For ground installations, a large site does not guarantee easy construction. Ground conditions, drainage, weed control, vehicle access, and relationships with nearby facilities matter.

Ease of maintenance is also an important evaluation axis. Solar installations require long-term inspection, cleaning, anomaly detection, and management of the surrounding environment. Hard-to-inspect locations, areas prone to soiling, leaf or bird fouling, heavy snow, or strong winds can lead to reduced generation and increased management burden. High simulated generation may be offset by difficult maintenance and lower actual operational effectiveness.

Future changes must also be checked. Planned roof renovations, building expansions, equipment updates, changes in site use plans, adjacent development, and tree growth can affect generation and manageability after installation. Because solar installations assume long-term use, confirm whether the site will remain usable in the future. For corporate facilities, installing in locations inconsistent with business plans or building renewal schedules may require relocation or removal later.

When comparing sites, combine multiple evaluation axes while centering on generation. Compare annual generation, monthly stability, shading, constructability, maintainability, future risk, and compatibility with self-consumption to make a comprehensive decision. You do not need a site that is best on every item—real candidates always have trade-offs. The important point is to judge whether a weakness is tolerable relative to the installation objective.

For example, projects aiming to maximize generation may accept complex construction in favor of superior irradiance. Projects prioritizing self-consumption may choose sites that generate during high-usage hours even if annual generation is somewhat lower. For disaster resilience or facility resilience, consider not only generation but also protectability, inspection ease, and lower surrounding risk. Clarify project objectives and reinterpret simulation results accordingly.

Including constructability, maintenance, and future changes requires accurate on-site verification. Level differences, obstacles, roof material conditions, drainage, surrounding shading, and inspection circulation not visible on drawings or maps can be missed without field checks. Correcting simulation results with site information reduces discrepancies between desk studies and real operation. Site comparison becomes practically usable only when simulation and field verification are combined.

# Common mistakes when comparing installation sites

There are several common failure patterns when using solar power generation simulations to compare installation sites. The most common is ranking candidates solely by annual generation figures. Annual generation is important, but without checking the assumptions behind that number—whether shading was incorporated, whether comparisons use the same installed capacity or maximum installable capacity—you cannot make a correct judgment.

Another frequent issue is inconsistent input conditions across candidates. If shading is considered for one candidate but not for another, simulation results are unfair. If one candidate assumes installation to the roof edge while another leaves wider inspection paths, the comparison loses meaning. In practice, differences in input assumptions can manifest directly as differences in generation. Be careful not to compare the roughness of inputs instead of candidate performance.

Overlooking shading is another major mistake. Winter shading, morning/evening shading, rooftop equipment shadows, and future tree growth are easily missed. If site visits are done only on summer afternoons, winter shadows may be missed. Photos alone make it hard to judge obstacle height and distance, so simulations may not reflect them accurately. Underestimating shading leads to actual generation falling short of expectations after deployment.

Overestimating installable area is also common. Treating roof or site area as fully usable can lead to major capacity reductions at the design stage. Considering inspection space, setbacks, existing equipment, structural constraints, wiring routes, drainage, and maintenance circulation typically reduces installable area. Estimating realistic installable areas at the simulation stage reduces the risk of large drops in projected generation later.

Also be cautious about overanalyzing small differences between candidates. Simulations carry uncertainty; actual generation varies with weather and operations. Rather than choosing based on marginal differences, prioritize stability factors like low shading, constructability, maintainability, and future usability. Numbers are important, but they do not replace practical usability on site.

Finally, avoid presenting only conclusions in internal materials. If you simply state “Candidate A is optimal” without explaining why, stakeholders will have difficulty accepting the decision. In site comparisons, be ready to explain how you evaluated generation, shading, constructability, maintenance, and future risks. If the reasoning process is organized, it is easier to revisit decisions when assumptions change.

# How to summarize simulation results for practical use

Simulation results comparing sites can be hard to use in practice if you merely list numbers. To communicate with stakeholders, organize each candidate’s characteristics, strengths, weaknesses, and caveats into an easy-to-decide format. Beyond generation magnitude, clarify why a site is advantageous, what risks to anticipate, and what to check next.

First, concisely summarize the assumptions for each candidate: installable area, assumed system capacity, azimuth, tilt angle, whether shading was reflected, main obstacles, and on-site verification status. Clear assumptions help stakeholders understand generation differences. Conversely, showing results with ambiguous assumptions leads to follow-up questions about “why these numbers,” causing rework.

Next, explain annual generation together with monthly trends. High annual generation is attractive, but monthly data may show seasonal weaknesses. When monthly declines exist, relate their causes to shading, azimuth, weather tendencies, snow, or obstacles. In practice, saying not just “low in winter” but “low in winter because of low solar altitude and susceptibility to adjacent structure shading” makes the result more actionable.

If self-consumption is prioritized, describe compatibility between generation timing and facility power usage. Confirm whether a candidate’s generation peak aligns with facility load peaks to evaluate benefits realistically. Facilities with high morning use, large afternoon AC loads, or low weekend operation change the value of the same annual generation. Supplement generation data with notes on operational compatibility.

Also list the next items to confirm for each candidate to facilitate further study. For example: Candidate A has high generation but needs detailed verification of rooftop equipment shadows; Candidate B has moderate generation but good constructability and maintenance access; Candidate C has ample area but requires confirmation of terrain and drainage conditions. This format helps stakeholders see not just rankings but what decisions or checks should follow.

When summarizing simulation results, avoid rushing to conclusions. Use the preliminary stage for narrowing candidates and the detailed stage for locking design conditions. In the initial stage, narrow candidates to a few with remaining uncertainty, then finalize after field verification and detailed design. Trying to decide everything in a single simulation invites mistakes due to insufficient assumptions.

When explaining to stakeholders, avoid absolute rankings—organize conditionally. For example: “If prioritizing generation, choose this site; if prioritizing self-consumption, choose this site; if prioritizing constructability and maintenance, choose this site.” Presenting options by objective facilitates consensus. Solar power generation simulation is not an automatic single correct answer tool but a tool to organize multiple decision axes. Understanding and using that characteristic greatly improves comparison accuracy.

# Summary

To compare installation sites using solar power generation simulations, first organize candidate conditions with the same criteria, then sequentially check solar irradiance, azimuth, tilt angle, shading, obstacles, terrain, monthly fluctuations, constructability, maintenance, and future changes. Annual generation is an easy-to-understand indicator, but it alone cannot determine the optimal site. Interpret why generation differences occur, whether generation timing matches facility power usage, and whether long-term stable operation is feasible.

In practice, simulations are sometimes run before comparison conditions are aligned. If input conditions differ, output numbers cannot be fairly compared. Align installable area, system capacity, azimuth, tilt, shading treatment, and loss rate assumptions, and record each candidate’s premises to improve explanatory power. Internal reviews and client explanations require showing not just which site generates more but the basis for that judgment.

Confirming shading and surrounding obstacles is especially important in site comparisons. Locations that look good in irradiance may lose generation in winter or in morning/evening due to shading. Considering rooftop equipment, adjacent buildings, trees, terrain, and future development or renovation plans reduces post-installation discrepancies. Combining simulation with on-site verification leads to decisions closer to reality.

In the final decision, do not choose solely the site with the highest generation; choose the site that matches the project objective. If self-consumption is important, check timing compatibility with power usage; if long-term operation is important, prioritize ease of maintenance; if stability is important, prioritize low shading and low future risk. Solar power generation simulation is a practical tool for organizing candidate strengths and weaknesses and making a justified installation decision.

Improving comparison accuracy also requires accurately capturing on-site location information, obstacles, roof surfaces, site boundaries, and terrain conditions. The higher the accuracy of position information collected on-site, the easier it is to refine installable area, shading checks, drawing verification, and simulation assumptions. Using LRTK—a GNSS device that can be attached to an iPhone to acquire high-precision location information—allows practitioners to efficiently record candidate locations and checkpoints on-site and more reliably organize the field information needed for solar power generation simulations. If you want to move from desk-based numbers to decisions based on field information, LRTK is a powerful option for practitioners.