7 Conditions for Deciding Whether to Implement Solar Power Using a Solar Power Generation Simulation

When deciding whether to implement solar power generation, it is risky to decide based only on the magnitude of annual power generation. Solar power generation simulations are not only for predicting power output but also serve as decision-making material to check site conditions, on-site consumption, surplus electricity, generation losses, constructability, maintainability, and long-term operational outlook. To determine whether a project is suitable for implementation, whether the design should be revised, or whether on-site investigation should be deepened, it is necessary to check multiple conditions from the same perspective. This article explains seven conditions to judge implementation feasibility for practitioners who search for "solar power generation simulation."

Table of Contents

• Concept for deciding feasibility using a solar power generation simulation

• Condition 1: The basis for annual power generation matches site conditions

• Condition 2: Monthly power generation aligns well with facility demand

• Condition 3: The balance between self-consumption and surplus electricity is appropriate

• Condition 4: Generation reductions due to shading, orientation, and tilt are acceptable

• Condition 5: Generation losses and loss rates are realistically anticipated

• Condition 6: Constructability and grid/equipment conditions are reasonable

• Condition 7: Long-term operation and maintenance are feasible

• Views to avoid when judging feasibility

• Summary

Concept for deciding feasibility using a solar power generation simulation

A solar power generation simulation is a document to check in advance how much power can be generated at a prospective installation site. By checking annual power generation, monthly power generation, system capacity, on-site consumption, and surplus electricity, you can concretely imagine the post-installation effects. However, simulation figures are only predictions based on input conditions. If the input conditions do not match the site, both the expected generation and the judgment of implementation effects will deviate from reality.

What matters when judging feasibility is not only whether the generation is large or small. It is necessary to confirm whether the generated power can be used within the facility, whether surplus is not excessive, whether generation losses from shading, temperature, dirt, snowfall, etc., are reflected, and whether construction and maintenance are feasible. In addition, you should consider not only the first year but whether the system can be maintained over the long term and whether the implementation effect holds if the facility’s power usage changes in the future.

For example, even a proposal with a large annual generation may result in increased surplus power and less-than-expected savings at a facility with low daytime demand. Conversely, a proposal with somewhat modest annual generation can be reasonable if the generation period aligns well with the facility’s demand and self-consumption is stable. Also, a proposal that maximizes installation capacity but obstructs inspection pathways, drainage, or maintenance of existing equipment poses long-term operational risks.

When judging feasibility, it is important to use simulations not as documents to make generation figures look large but as documents to find risks. Proposals with attractive numbers require careful verification of assumptions. Proposals that look modest in generation but realistically reflect shading, generation losses, and maintainability can provide decision-making materials closer to actual operation.

To judge implementation feasibility using a solar power generation simulation, check the following seven conditions in order. Do not draw conclusions based on a single condition; it is important to judge comprehensively by considering generation, usable power, site constraints, and long-term operation.

Condition 1: The basis for annual power generation matches site conditions

The first condition for judging feasibility is that the basis for annual power generation matches site conditions. Annual generation is the most straightforward figure for judging the effect of a solar installation. However, unless you confirm the assumptions used to calculate this figure, it is insufficient as a basis for decision-making.

Annual generation varies depending on system capacity, insolation, orientation, tilt angle, shading, temperature losses, wiring losses, power conversion losses, soiling, snowfall, aging, and other conditions. Even for the same facility or land, annual generation changes if simulation conditions differ. When you see a proposal with high generation, do not simply judge it as good; check why that generation is expected.

First, confirm the system capacity and installable area. For rooftop projects, check whether rooftop equipment, piping, penthouses, guardrails, drains, inspection hatches, waterproofing clearances, and inspection traffic lines are considered. A roof may look spacious on drawings but contain areas where panels cannot actually be installed. For land projects, consider site boundaries, slopes, elevation differences, trees, drainage channels, maintenance paths, candidate connection points, and areas planned for future use.

If the installable area is overestimated, both system capacity and annual generation will be exaggerated. At the feasibility judgment stage, it is important to confirm not only the generation in a maximally populated layout but also the generation for a layout that can realistically be constructed and maintained. If the layout changes after on-site surveys, always re-run the simulation to confirm the final annual generation.

Next, confirm the assumptions about insolation and regional conditions. Check whether weather data close to the installation site is used, whether monthly insolation is reflected, and whether impacts from snowfall, cloudy conditions, and extreme heat are considered. Calculations based only on regional average insolation may deviate from reality in mountain areas, coastal areas, basins, snowy regions, or areas with many surrounding buildings.

If the basis for annual generation is clear and matches site conditions, it is easier to proceed with the feasibility judgment. Conversely, if installable area, loss rates, or insolation assumptions are vague, be cautious even if the generation figures look good. The fundamental rule is to judge feasibility not by the size of generation but by whether the basis for the generation can be explained.

Condition 2: Monthly power generation aligns well with facility demand

The second condition is that monthly power generation aligns well with the facility’s demand. Even if annual generation is sufficient, if months with high generation and months with high facility demand are misaligned, the implementation effect may be smaller than expected. In solar power generation simulations, it is important to check not just annual totals but monthly generation.

Solar generation varies by season. Generation tends to increase from spring to summer, while months with reduced generation can result from the rainy season, typhoons, cloudy weather, short winter daylight hours, snowfall, and winter shading. Also, in summer, even with high insolation, panel temperature rises can cause temperature losses.

Facility power demand also varies month by month. At facilities with high air-conditioning demand in summer, summer generation is more likely to be consumed on-site. At facilities with large winter demand for heating, ventilation, production equipment, or hot water, winter generation influences the implementation effect. For facilities with peak and off-peak seasons, if demand is low during high-generation months, surplus may increase.

When judging feasibility, overlay monthly generation and monthly consumption. If high generation months coincide with high demand months, self-consumption effects are easier to expect. If generation-rich months have low demand, surplus electricity will increase, and you will need to consider how to handle surplus—storage, curtailment, or other measures. If months with low generation coincide with high demand, the implementation effect may be weakened.

Winter monthly generation is particularly important. In winter, the solar altitude is low and shadows lengthen. Surrounding buildings, trees, rooftop equipment, guardrails, and penthouses can cause winter generation to fall below expectations. In snowy regions, periods when generation is impossible due to snow may occur. For facilities with high winter demand, do not underestimate these impacts.

If monthly generation and facility demand align well, post-installation effects will be more stable. Even if alignment is poor, you can sometimes improve it by adjusting system capacity, orientation, tilt, adding storage, or load control. To judge feasibility, it is essential to examine not only annual totals but also the monthly overlap of generation and demand.

Condition 3: The balance between self-consumption and surplus electricity is appropriate

The third condition is that the balance between self-consumption and surplus electricity is appropriate. Power generated by solar PV divides into portions used within the facility and portions that remain unused and become surplus. When judging feasibility, you need to look not at total generation but at how much of the generated power can be used.

Self-consumption is the amount of generated power actually consumed within the facility. It is directly linked to reductions in purchased electricity and forms the core of the implementation effect. Surplus electricity is the amount generated but not used within the facility at the same time. Whether surplus is exported, stored in batteries, or curtailed affects the feasibility judgment.

For projects aimed at self-consumption, having sufficient self-consumption is more important than high generation. Factories, warehouses, stores, and offices with large daytime demand tend to overlap well with solar generation. Conversely, facilities that primarily operate at night or have low weekend operation may see increased surplus even if generation is high.

Judging feasibility based solely on self-consumption ratio is risky. Small system capacities tend to show high self-consumption ratios but may have small absolute self-consumption amounts. Large capacities may lower the self-consumption ratio while increasing absolute self-consumption. It is important to view self-consumption ratio, self-consumption amount, and surplus electricity together.

Also check the balance when changing system capacity. Increasing capacity raises generation, but whether the additional generation is consumed on-site or becomes surplus depends on facility demand. Up to a certain capacity, self-consumption increases, but beyond that, only surplus may grow. In such cases, adopting a capacity that matches demand rather than the maximum capacity can reduce investment risk.

If combining batteries, check results both without and with batteries. Batteries store surplus for use at other times but have charge/discharge losses and capacity constraints. Viewing only battery-included results can obscure surplus risk inherent to solar alone. When judging feasibility, confirm how much surplus occurs without batteries and how much self-consumption increases with batteries.

If the balance between self-consumption and surplus is good, generated power is easier to use efficiently. If surplus is too large, reassess system capacity, operation methods, batteries, and load control before deciding on implementation.

Condition 4: Generation reductions due to shading, orientation, and tilt are acceptable

The fourth condition is that generation reductions due to shading, orientation, and tilt are acceptable. In solar power simulations, the orientation and tilt of installation surfaces and surrounding shading greatly influence generation. If these conditions are unfavorable, generation will decrease and implementation benefits may be weakened.

Sources of shading include surrounding buildings, rooftop equipment, penthouses, guardrails, piping, trees, utility poles, signs, slopes, and terrain elevation differences. Shadows change by time of day and season. Even if shading is minor in summer, shadows can lengthen in winter when solar altitude is low. Simulations that do not sufficiently reflect shading may overestimate generation.

When judging feasibility, check the difference between generation with and without shading. If shading impact is small and its effect on generation and self-consumption is within an acceptable range, implementation is easier to proceed with. If shading has a large impact, measures such as reconfiguring panel layout, excluding shaded surfaces, adjusting system capacity, or adding on-site surveys are necessary.

Orientation is also important. South-facing surfaces tend to achieve higher annual generation, but east- or west-facing surfaces may be useful depending on facility demand timing. East-facing generation can help facilities with high morning demand, and west-facing generation can help those with high afternoon demand. The optimal orientation is not the one that maximizes annual generation but the one that matches facility demand and generation timing.

Tilt angle also affects generation. For rooftop projects, panels often follow the existing roof slope and you cannot freely choose the ideal angle. For flat roofs or land projects, you can set mounting angles, but increasing angle can cause row-to-row shading, wind and load issues, and impact maintainability. Reducing angle can allow more system capacity but may affect seasonal generation efficiency and snow/dirt shedding behavior.

It may be difficult to completely eliminate generation reductions from shading, orientation, and tilt. The important point is to reflect those reductions in the simulation and judge whether they are acceptable for the intended implementation. If reductions are too large, the solution may not be to cancel the project but to improve layout or capacity. Judging based on effective generation that reflects site conditions improves the accuracy of feasibility decisions.

Condition 5: Generation losses and loss rates are realistically anticipated

The fifth condition is that generation losses and loss rates are realistically anticipated. Solar PV systems do not always generate at peak under ideal conditions. In practice, generation decreases due to temperature, wiring, power conversion, soiling, snowfall, shading, equipment outages, aging, and more. Simulations that do not sufficiently account for these factors may overstate implementation benefits.

Temperature loss is the reduction in output due to panel temperature rise. Pay particular attention in summer and for rooftop installations. Even with high insolation, elevated panel temperatures can prevent generation from increasing as much as expected. For proposals that show very high summer generation, verify whether temperature losses are included.

Soiling loss is also important. Dust, pollen, leaves, bird droppings, exhaust-related grime, and particulates on panel surfaces reduce generation. In environments with many trees nearby, unpaved land nearby, frequent dust generation, or bird congregation, standard loss rates may be insufficient. Check the ease of cleaning and inspection.

In snowy regions, verify generation reductions due to snow. When snow accumulates on panels, there will be periods without generation. Consider snow shedding angles, snow storage space, ease of snow removal and inspection, and snow load resistance when judging feasibility. If winter generation looks high, confirm whether snow and residual snow effects are reflected.

Check wiring losses and power conversion losses too. Power generated at panels flows through wiring and equipment before it can be used within the facility, incurring losses along the way. Confirm whether the simulation’s generation figure refers to panel-side generation or usable energy after conversion.

Loss rates are sometimes presented as a single comprehensive number. In such cases, check how much of temperature, shading, wiring, conversion, soiling, snowfall, and aging are included. Proposals with unrealistically low loss rates show inflated generation and may be overly optimistic about site conditions. When judging feasibility, confirm that loss rates are appropriate for the site environment.

Condition 6: Constructability and grid/equipment conditions are reasonable

The sixth condition is that constructability and grid/equipment conditions are reasonable. Even if a simulation shows favorable generation, implementation cannot proceed if actual construction is infeasible. Moreover, to use generated power within the facility, inverters, wiring, connection equipment, and grid conditions must be realistic.

For rooftop projects, verify structure, waterproofing, loading, rooftop equipment, drains, inspection hatches, and access to existing equipment. Filling a roof with panels may make generation look large but can hinder waterproofing repairs or equipment inspections. Check whether there are unreasonable placements near roof edges, guardrails, or drains.

For land projects, check site boundaries, slopes, elevation differences, ground conditions, drainage, maintenance paths, weed control, and candidate connection points. Filling the entire site may increase system capacity but leave insufficient maintenance paths, drainage, or service space. Terrain and ground conditions may necessitate changes to the initial simulation layout.

Also confirm the balance between inverter capacity and panel capacity. Even if panel capacity increases, inverter capacity or connection conditions may cap output. Output capping is not necessarily bad in itself, but you must check how much annual generation loss will result and whether it affects self-consumption.

Grid constraints and handling of surplus power also affect feasibility. Generated power cannot always be fully used within the facility. Whether surplus can be exported externally, whether exporting is not assumed, whether output must be curtailed, or whether batteries will be used changes system capacity and financial considerations. If grid conditions are unclear, you may not be able to fully utilize generation after installation.

Check equipment installation locations and wiring routes. Ensure equipment is accessible, inspection space exists, wiring distances are not excessive, and locations are protected from rain, high temperatures, snow, and strong winds. If constructability and equipment conditions are proper, it is easier to realize the simulation figures.

When judging feasibility, confirm not only desk-calculated generation figures but also whether construction, connection, and maintenance are feasible. If constructability or grid/equipment conditions are unrealistic, revise the design before making a decision.

Condition 7: Long-term operation and maintenance are feasible

The seventh condition is that long-term operation and maintenance are feasible. Solar power is equipment used for long periods, and feasibility should not be judged solely on immediate post-installation generation. It is necessary to confirm whether generation can be maintained over time, whether inspection and cleaning are possible, and whether the system can respond to equipment degradation and changes in the surrounding environment.

In long-term operation, accounting for aging is important. Solar panels, inverters, wiring, connections, and mounting structures may require inspection, repair, or replacement after long-term use. Even if first-year generation is high, that state may not continue long-term. When simulating long-term revenue, confirm whether aging, equipment outages, and replacements are considered.

Maintainability is also important. Check whether inspection paths are secured, whether rooftop equipment and drains are accessible, whether weed control and cleaning are possible on land projects, and whether personnel can approach equipment. Layouts that maximize generation can become difficult to maintain. Over the long term, a slightly reduced-generation but easier-to-maintain layout may lead to more stable operation.

Anticipate changes in the surrounding environment. Trees may grow and increase shading, new buildings may be erected nearby, rooftop equipment may be added, dust may increase from previously unpaved land, or snowfall and wind impacts may increase—these changes affect generation. While it is difficult to predict everything, it is important to identify risks during on-site surveys and to establish a system for post-installation checks.

Post-installation performance management should also be part of feasibility assessment. If you record monthly generation, hourly generation, generation per installation surface, self-consumption, and surplus electricity and compare them to the simulation, you can more quickly identify causes of generation decline. Plans without performance management risk delayed response if problems arise.

If long-term operation and maintenance are feasible, post-installation risks are easier to mitigate. Conversely, if there are no maintenance routes, equipment is inaccessible, or it is difficult to check dirt and shading, or the plan does not consider long-term demand changes, then even proposals with good generation figures should be judged cautiously.

Views to avoid when judging feasibility

When judging feasibility with a solar power generation simulation, avoid assuming that a proposal with large annual generation is automatically a good proposal. Annual generation is an important metric, but increasing system capacity can make it appear large. Overstating the installable area or understating shading or loss rates also inflates generation. Focus on the validity of assumptions, not on the size of the numbers.

Also avoid judging based solely on self-consumption ratio. A high self-consumption ratio may look good but can simply mean the system capacity is small. To evaluate implementation effects, check not only self-consumption ratio but also absolute self-consumption, surplus electricity, system capacity, and overlap with facility demand.

Do not use initial simulations as the final judgment. After on-site surveys reveal rooftop equipment, obstacles, shading, drains, inspection routes, site boundaries, maintenance paths, and candidate connection points, layouts and generation can change. Use revised simulations after on-site surveys for the final decision.

Be cautious about relying only on battery-included results. Batteries can increase self-consumption, but you must separately confirm how much surplus occurs without batteries and how much improvement batteries provide; otherwise, you cannot judge the feasibility of solar alone.

Ignoring long-term operation is also risky. Even if first-year generation and implementation effects are good, if you do not consider equipment degradation, maintainability, changes in the surrounding environment, and shifts in facility demand, long-term benefits may decline.

When judging feasibility, adopt an attitude of finding conditions that would worsen outcomes rather than seeking good numbers. Check whether generation could fall below expectations, surplus could increase, maintenance could be difficult, or demand could change—and then determine whether the implementation objectives can still be met. This approach reduces practical failures.

Summary

To judge feasibility using a solar power generation simulation, you must comprehensively check not only annual generation but also monthly generation, self-consumption, surplus electricity, shading, orientation, tilt, generation losses, constructability, grid conditions, equipment conditions, long-term operation, and maintainability. A simulation is not a document to push implementation but a document to determine whether conditions are suitable for implementation.

Condition 1 checks the basis for annual generation, including system capacity, installable area, insolation, shading, and loss rates against site conditions. Condition 2 checks the alignment of monthly generation with facility demand and whether seasonal generation reductions affect implementation. Condition 3 checks the balance between self-consumption and surplus electricity, focusing on usable energy rather than possible generation. Condition 4 verifies whether generation reductions from shading, orientation, and tilt are acceptable, using effective generation that reflects site conditions rather than ideal conditions. Condition 5 checks whether loss rates for temperature, soiling, snowfall, wiring, conversion, and aging are realistic.

Condition 6 verifies whether constructability and grid/equipment conditions are feasible. If you cannot construct, connect, or maintain equipment in practice, implementation risks remain even if generation looks good. Condition 7 verifies whether long-term operation and maintenance are feasible; it is important to consider not only first-year effects but also whether generation can be maintained long-term and whether performance management is possible.

When deciding feasibility, do not automatically select proposals with large annual generation, high self-consumption ratios, or attractive battery-included results. Align assumptions, use revised simulations after on-site surveys, and judge including long-term operation to reduce post-installation gaps.

Accurate on-site information forms the foundation for improving the accuracy of feasibility judgments. If you can accurately grasp installable ranges, rooftop equipment, obstacles, trees, site boundaries, orientation, tilt, inspection routes, and candidate connection points, the assumptions of the solar power generation simulation become clear and it becomes easier to judge whether a project is suitable for implementation or whether its design should be revised.

If you want to accurately record installable ranges, rooftop equipment, obstacles, trees, site boundaries, orientation, tilt, inspection routes, and candidate connection points on site and improve the accuracy of feasibility judgments using solar power generation simulations, using LRTK, an iPhone-mounted GNSS high-precision positioning device, is effective. By obtaining high-precision positional information on site, you can more easily organize shading and obstacles, installable ranges, wiring routes, and maintenance routes, facilitating consistent progress from vendor proposal comparison and pre-construction checks to post-installation performance management. To correctly judge feasibility using solar power generation simulations, it is important not only to rely on desk-calculated generation figures but also to accurately grasp the site and establish a system for long-term management.