Solar power generation simulation is an important task to check “how much power can be generated,” “whether the assumed revenue and self-consumption effects are realistic,” and “whether the design conditions are feasible” before installing equipment. However, because simulation results include many technical terms, if you look at the numbers without fully understanding the terminology, you may overestimate generation or find large discrepancies after operation.

This article narrows down the basic terms you should first grasp to 10 items for practitioners who are researching “solar power generation simulation.” Rather than merely explaining words, it organizes what numbers to focus on in practical work and how to use them in design, proposals, and internal explanations.

# Table of Contents

• Annual generation

• Solar irradiation

• Installed capacity

• Panel azimuth

• Tilt angle

• Conversion efficiency

• System losses

• Shading losses

• Degradation over time

• Self-consumption rate

• Using solar power generation simulation correctly

• Summary

# Annual generation

Annual generation refers to the amount of electrical energy a solar power system is expected to generate in one year. It is generally expressed in kWh and is the most noticed figure when reviewing solar power generation simulation results. For residential, factory, warehouse, store, public facility projects and others, understanding the annual generation first allows you to consider the appropriateness of system size, electricity cost savings, expected power sales, and self-consumption amounts.

However, annual generation alone is not sufficient. For example, systems with the same installed capacity can produce different amounts of power depending on regional irradiation conditions, roof orientation, panel tilt angle, presence of shading, and equipment loss conditions. Therefore, when judging whether annual generation is large or small, you should not only look at the magnitude of the number but also verify the assumptions under which the number was calculated.

In practice, it is important to treat annual generation not as the “maximum achievable” but as a “forecast based on certain assumptions.” Simulations calculate based on meteorological data and installation conditions, but actual yearly sunshine hours and weather vary from year to year. In years with a long rainy season, many typhoons or snowfall, or extreme heat causing higher equipment temperatures, actual generation may fall below simulated values. Conversely, in years with many clear days, generation may exceed the simulation.

When looking at annual generation, it is important to also check monthly generation. Even if the annual total looks sufficient, generation may be lacking at critical times. For example, facilities with increased summer electricity usage need to consider the overlap of summer generation and consumption. Facilities that increase power demand in winter for heating or lighting need careful confirmation of winter irradiation conditions and shading effects.

Also, annual generation tends to be used in internal approvals and investment decisions, but calculating it under overly optimistic conditions increases accountability after installation. At the proposal stage, it is safe to check not only standard conditions but also slightly conservative loss cases and scenarios where generation falls somewhat. Annual generation is a central indicator of solar potential, but it should always be read together with the underlying assumptions.

# Solar irradiation

Solar irradiation refers to the amount of solar energy reaching the ground or a roof surface. Since solar power converts sunlight into electricity, irradiation is one of the most important foundational data for generation simulations. In regions or conditions with higher irradiation, generation tends to increase; under lower irradiation conditions, the same system capacity will generate less.

Irradiation can be considered in several ways: irradiation on a horizontal plane, irradiation on an inclined plane, direct irradiation, diffuse irradiation, and so on. The key point practitioners should first understand is that the irradiation a solar panel receives is not determined solely by regional sunshine hours. The panel’s azimuth, tilt angle, and surrounding objects that cast shadows affect the actual irradiation usable for generation.

Irradiation data used in solar generation simulations are generally averages based on past meteorological data. Therefore, simulation results indicate “this level under average climate conditions.” It is dangerous to judge a simulation as right or wrong by comparing it to actual generation in a single year. You must consider short-term weather variability and view the data as multi-year average tendencies.

When considering irradiation, do not make uniform judgments based only on the region name. Even within the same municipality, irradiation conditions vary due to mountain shadows, clouds from the sea, surrounding buildings, and terrain. Site confirmation is essential, especially for factory or warehouse roofs, facilities in mountainous areas, sloped sites, and urban areas with many adjacent buildings. Even if irradiation data look favorable, long morning or evening shadows on the actual installation surface may reduce generation.

Irradiation also varies greatly by season. Summer has longer days and higher solar elevation, so generation tends to increase, though output can decline due to higher temperatures. In winter, shorter daylight hours and lower solar elevation increase the length of surrounding shadows. Therefore, checking not only annual averages but also monthly irradiation and seasonal shadow behavior leads to more realistic simulations.

# Installed capacity

Installed capacity is an indicator of how large a solar panel installation will be. It is generally expressed in kW and is calculated by multiplying the nominal output per panel by the number of panels. In simulations, larger installed capacity generally leads to higher annual generation, but simply increasing capacity is not always beneficial.

When considering installed capacity, you need to examine not only how many panels the roof or land can hold but also electricity usage, incoming power equipment, contract demand, grid connection, future expansion potential, and maintainability. In projects intended mainly for self-consumption, making the system too large can result in excess generation that cannot be consumed. Conversely, if the system is too small, electricity cost savings may be insufficient.

When reviewing simulation results, checking annual generation per installed capacity makes judgment easier. For example, if the same annual generation is achieved only by a very large installed capacity in one case but efficiently by a small system in another, the evaluations differ. If generation per installed capacity is extremely low, verify whether orientation, tilt angle, shading, losses, or overloading conditions are problematic.

Installed capacity can be viewed as panel-side capacity and power conversion equipment capacity. It is common for the total panel capacity to exceed the capacity of the power conversion equipment, but in that case output clipping may occur during high-irradiation periods. This is not inherently bad, but in simulations you should understand to what extent output clipping is expected.

Increasing installed capacity affects not only generation but also weight, wiring, mounting structures, inspection routes, wind loads, and roof waterproofing. Attractive simulated generation can become a project risk if on-site structural or construction conditions cannot accommodate it. Installed capacity is both a basic condition for increasing generation and an important practical term that influences design, construction, and operation.

# Panel azimuth

Panel azimuth indicates which direction solar panels face. Generally, in the northern hemisphere, south-facing installations tend to produce more generation, but in practice south-facing is not always optimal. Roof shape, site conditions, timing of electricity demand, surrounding shadows, and available installation surfaces can make east- or west-facing installations effective.

If panel azimuth is not entered correctly in a simulation, the time-of-day distribution and annual generation will deviate. South-facing systems tend to produce more during midday; east-facing systems tend to peak in the morning; west-facing systems tend to peak in the afternoon. For self-consumption projects, it is important not only to maximize annual generation but also to match generation timing with facility power usage patterns.

For example, factories or stores that operate from the morning may find east-leaning generation valuable. Facilities with higher afternoon power demand may find west-leaning generation better for self-consumption. Even if south-facing is advantageous for annual generation, considering east-west installations can be effective from the perspectives of self-consumption rate and peak power reduction.

Be careful about discrepancies between azimuths on drawings and actual on-site azimuths. Entering data based only on old drawings, simplified layouts, or inaccurate azimuth symbols can affect simulation results. Especially when roof surfaces are divided into multiple planes or the building is rotated relative to the site, verify each surface’s azimuth individually.

Panel azimuth is also closely related to shading assessment. Obstacles on the east have a large effect in the morning, and obstacles on the west in the evening. Even on a south-facing roof, high buildings or trees to the south can significantly reduce generation. Panel azimuth is not just directional information; it is a basic term for interpreting generation timing, seasonal variation, self-consumption effectiveness, and shading risk.

# Tilt angle

Tilt angle is the angle indicating how much a solar panel is tilted relative to a horizontal plane. Panels generate more effectively when installed at an angle that receives sunlight efficiently. However, the optimal tilt angle depends on region, season, installation site, roof shape, wind load, snow, and constructability.

Generally, the suitable angle differs between summer, when solar elevation is high, and winter, when it is low. Prioritizing summer may require a relatively shallow angle to receive sunlight easily; prioritizing winter may require a steeper angle to capture sunlight from a lower sun. The tilt angle that maximizes annual generation is not necessarily the same as the angle that emphasizes generation in a particular season.

In practice, panels are often installed to match roof pitch, and simulations typically input roof pitch as the tilt angle. On flat roofs, racking may add tilt, but increasing tilt often requires spacing between rows to avoid mutual shading, reducing the number of panels. Therefore, tilt angle should be judged in balance with installed capacity, shading, and constructability, not just generation efficiency.

Small tilt angles reduce wind impact and allow efficient use of installation area, but dirt may not be washed off easily by rain. Large tilt angles can increase generation under some irradiation conditions but raise issues of wind load, racking structure, and inter-row shading. Simulations should reflect these practical constraints.

Tilt angle also affects monthly generation profiles. Projects aiming to secure winter generation will see results sensitive to tilt angle differences. Conversely, for projects emphasizing summer generation and self-consumption, shallow tilts may be practically acceptable. Tilt angle is an essential term not only for annual generation but also for assessing seasonal generation balance.

# Conversion efficiency

Conversion efficiency indicates how much of the solar energy received by a panel can be converted into electricity. It is generally expressed as a percentage: the higher the efficiency, the more power can be obtained from the same area. Conversion efficiency is important when you want to generate as much as possible from limited roof area.

However, using high-efficiency panels does not necessarily guarantee a large improvement in simulation results. Actual generation is determined by many factors beyond panel performance: irradiation, azimuth, tilt angle, shading, temperature, wiring, power conversion equipment, soiling, and degradation over time. Conversion efficiency is important but not the sole determinant of generation.

When reviewing conversion efficiency in simulations, separate the panel’s individual performance from overall system performance. Even if a panel has high single-module efficiency, poor installation conditions will limit generation. Conversely, standard-efficiency panels can provide stable generation if orientation and tilt are good, shading is minimal, and loss management is appropriate.

Conversion efficiency relates to generation per area. On residential roofs or small facilities with limited roof area, high-efficiency panels may be advantageous to increase capacity per area. Where ample roof area or land is available, prioritize the overall balance of the installation plan and maintainability, not just efficiency.

In practice, conversion efficiency is often emphasized in proposal materials, but practitioners should not assume “high efficiency equals safety.” Check the loss conditions reflected in the simulation. You must see how much the entire system will generate and how much can be used; otherwise, investment decisions are incomplete. Conversion efficiency is a basic term for understanding panel performance and for avoiding overreliance on a single number.

# System losses

System losses are the collective term for the various losses that occur between the power generated by solar panels and the power actually available for use. In simulations, rather than simply calculating generation from irradiation and installed capacity, losses expected in real systems are subtracted to estimate a more realistic generation figure.

System losses include losses in power conversion, wiring losses, soiling on panel surfaces, output declines due to temperature rise, equipment variability, output controls, and losses from inspections or shutdowns. How much of these losses are assumed significantly affects simulation results. Underestimating losses tends to overstate annual generation.

Pay special attention when system losses are shown as a single aggregated percentage. Although a loss rate is easy to understand, if the breakdown is unclear you cannot judge which factors are the main causes of generation reduction. In practice, confirm which losses and to what extent are assumed, and check whether they match project-specific conditions.

For example, dust-prone factories, sites with bird droppings concerns, coastal salt damage environments, snowy regions, or places with heavy leaf fall should take soiling and maintenance-related losses more conservatively than standard conditions. Roof materials that heat up or poor ventilation conditions can make temperature-related output reductions significant. Facilities with frequent shutdowns or inspections will see operating rate affect generation.

System losses are adjustment items to make simulation results realistic. Anticipating losses is not to make generation look smaller for its own sake, but to reduce the gap between post-installation performance and forecasts. Practitioners should understand system losses not merely as negative factors but as important terms for visualizing risk.

# Shading losses

Shading losses refer to generation reductions caused when buildings, trees, utility poles, equipment, surrounding structures, or shadows from panels themselves prevent sufficient solar irradiation from reaching the panels. Among simulation inputs, shading losses are highly influenced by site conditions, and inadequate input or verification can lead to large gaps between predictions and actual performance.

Shadows do not necessarily reduce generation only in proportion to the shaded area. Solar panels consist of multiple cells and circuits; partial shading can cause output to drop more than expected. The impact also varies depending on panel layout and electrical connections. Therefore, lightly dismissing small shadows on site can lead to overestimated simulation results.

Shading impacts vary by time of day and season. In winter, lower solar elevation causes the same obstacle to cast longer shadows. Morning and evening shadows tend to be longer, making east and west obstacles influential. Locations that seem problem-free in summer can experience significant shading in winter. If a site survey is conducted only at one time, simulation should compensate for seasonal differences in solar elevation.

In practice, categorize shading causes into fixed and variable objects to organize assessment. Buildings, rooftop structures, fences, and mountain ridgelines are fixed and unlikely to change. In contrast, tree growth, new construction on adjacent lots, rooftop equipment additions, and temporary structures may change over time. Even if shading is minor at the time of simulation, conditions may change over the years, so view risks with long-term operation in mind.

When confirming shading losses, don’t rely solely on roof drawings or aerial photos; if possible, verify on-site height relationships and surrounding conditions. Small protrusions, piping, handrails, or air-conditioning units on the roof can cast shadows at certain times. Shading losses affect not only generation but also panel layout and circuit design, making this a basic term you must understand in solar generation simulation.

# Degradation over time

Degradation over time refers to the gradual decline in generation performance of solar power equipment over time. Since panels and related equipment are used for long periods, it is important to estimate not only first-year generation but also generation several years or decades later. Ignoring degradation in simulations can make long-term financial projections and investment decisions overly optimistic.

Solar panels are exposed to outdoor environments over long periods. They are affected by UV rays, temperature fluctuations, wind and rain, humidity, snow, salts, soiling, and other factors, so performance does not remain perfectly constant. The degree of degradation depends on product specifications, installation environment, construction quality, and maintenance, but long-term simulations typically assume some decline.

When considering degradation, separate first-year annual generation from long-term average generation. Judging profitability based only on first-year generation can lead to underperformance over the long term. For corporate projects or self-consumption systems, confirming generation trends that reflect degradation is important to evaluate multi-year electricity cost savings.

Degradation is not only about panels. Power conversion equipment, wiring, connections, racking, and monitoring devices may require inspection or replacement during long-term operation. Simulations usually treat this as a decline in generation performance, but in practice it relates to maintenance planning and equipment replacement considerations.

Underestimating degradation yields higher long-term generation. Conversely, overestimating it will undervalue the installation benefits. The important thing is to set assumptions that match the project’s environment and operation period. Degradation is a necessary term for treating a solar installation as a long-term asset rather than a short-term generation device.

# Self-consumption rate

Self-consumption rate is the proportion of the power generated by solar that is actually used on-site in a company facility or home. In self-consumption projects, it is important not only how much is generated but how effectively the generated power can be used. Even with high generation, if consumption timing does not match and excess is large, expected electricity cost savings may be harder to achieve.

To understand self-consumption rate, overlay generation timing and power usage timing. Solar generates during daytime; if a facility’s power use is mainly at night, the share of generation that can be self-consumed decreases. Conversely, facilities with significant daytime usage for air conditioning, lighting, production equipment, refrigeration, or office equipment can increase self-consumption rate.

Annual generation alone cannot determine self-consumption rate in simulations. You need to combine monthly, daily, and hourly generation profiles with facility load data. For corporate projects, differences in weekday vs. holiday operation, seasonal operation, long vacations, lunch breaks, and operating hours can change the self-consumption rate.

Ways to increase self-consumption include sizing the system to match demand, scheduling energy-consuming tasks during generation hours, combining storage systems, and analyzing peak usage. However, simply maximizing self-consumption rate is not always correct. Reducing installed capacity tends to increase self-consumption rate but may reduce total generation and savings. Therefore, balance self-consumption rate with annual generation, surplus energy, and investment returns.

Practitioners should avoid treating generation simulations and load analyses separately. You must confirm not only how much is generated, but when, where, and how much of that power can be used to understand post-installation effects. Self-consumption rate is a basic term for evaluating solar not only as a generation asset but as a mechanism to improve facility power operations.

# Using solar power generation simulation correctly

The terms introduced above may seem independent, but in actual simulations they are strongly interrelated. Annual generation is calculated from irradiation, installed capacity, azimuth, tilt angle, and loss conditions. Self-consumption rate relates not only to generation but also to facility power usage patterns. Shading losses and degradation help temper attractive first-year figures to more realistic long-term expectations.

When using simulations in practice, first check the validity of input conditions. If the installation location, roof area, azimuth, tilt angle, installed capacity, surrounding obstacles, power usage, operating days, loss rates, and so on do not match reality, the output generation will diverge from actual performance. Simulations perform advanced calculations, but inaccurate inputs produce inaccurate results.

Next, do not judge results by a single number. Annual generation alone does not reveal seasonal biases, hourly generation, ease of self-consumption, shading impact, or long-term degradation. By checking monthly generation, hourly generation trends, loss breakdowns, and differences between first year and long-term averages, you can use simulation results more effectively for practical decisions.

Simulation results are often used as materials for internal or customer presentations. In such cases, be prepared to explain not just the technical terms but also the assumptions behind the generation figures, which risks are accounted for, and which values have uncertainty. Especially, prepare for possible underperformance by arranging factors such as weather variability, shading, soiling, shutdowns, and degradation in advance to facilitate post-installation verification.

Solar power generation simulation is not meant to produce attractive numbers to sell equipment. It is a process for comparing design conditions, identifying risks, and creating standards for verifying post-installation generation. Understanding basic terms allows practitioners not just to accept simulation results but to verify input validity and request recalculation or additional surveys when necessary. This is a major differentiator for practitioners.

# Summary

To read solar power generation simulations correctly, you need to understand basic terms such as annual generation, solar irradiation, installed capacity, panel azimuth, tilt angle, conversion efficiency, system losses, shading losses, degradation over time, and self-consumption rate. These terms are not mere jargon in documents; they are practical decision-making factors directly linked to the validity of generation figures, system sizing, comparison of design conditions, explanation of investment effects, and post-installation verification.

Especially important is not to accept simulation results as “the correct number.” Generation varies with irradiation conditions, installation conditions, shading, losses, degradation, and power usage patterns. Therefore, when reviewing results, check not only annual generation but also monthly generation, loss breakdowns, self-consumption rate, and long-term generation trends.

Moreover, since solar systems are intended for long-term operation, do not conclude with pre-installation simulation only; adopt an attitude of improving operations by comparing actual generation after installation. If generation is lower than expected, determine whether it is a temporary weather-related fluctuation or due to shading, soiling, equipment stoppage, or input errors so you can drive operational improvements.

Finally, improving simulation accuracy requires accurately grasping site conditions. If roof or site position, azimuth, elevation differences, surrounding obstacles, or installable areas remain vague, even meticulous calculations will likely produce deviations. Therefore, obtain accurate on-site position information and align design and simulation assumptions beforehand.

LRTK, which can obtain high-precision position information by attaching to an iPhone, can be used in site surveys and installation planning for solar systems to efficiently record roof surroundings, site boundaries, obstacle positions, and survey point data. The accuracy of simulation depends greatly on the accuracy of on-site conditions entered. By understanding the basic terms and accurately capturing site position information, you can better connect desk calculations with actual construction and operation.