How to View Monthly Power Generation in PVSyst｜3 Steps to Check the Report

Table of Contents

• Purpose of checking monthly power generation

• Basics to grasp before checking the report

• Step 1: Run the simulation and open the results screen

• Step 2: Check the monthly power generation in the report

• Step 3: Interpret the reasons for monthly variations

• Key items to look at in monthly power generation

• Common oversights in monthly power generation

• A practical, easy-to-use verification workflow

• Checkpoints when generation differs from expectations

• How to use monthly power generation for design decisions

• Summary

Purpose of checking monthly power generation

In solar PV simulations, the final annual energy output tends to attract the most attention. For business planning, cash-flow calculations, equipment capacity considerations, and assessing the profitability of a power generation project, how many kWh can be generated annually is a major factor in decision-making. However, what is truly important in practice is not only the annual total but also confirming how that generation is distributed throughout the year.

The purpose of looking at monthly power generation is not simply to check the numbers from January to December. It is to interpret seasonal variations in solar irradiance, output changes due to temperature, the effects of shading, the impacts of snow or rainy seasons, the appropriateness of system orientation and tilt, and biases in loss settings. For example, even if annual generation is within the expected range, if winter generation is extremely low, there may be significant shading during periods of low solar altitude. Conversely, if summer generation is not as high as expected, you should review output reductions due to high temperatures, output clipping caused by an oversized design, orientation and tilt settings, and the handling of solar irradiance data.

Monthly power generation is also useful as material for explaining the characteristics of power generation facilities. If you present only the annual generation to clients or internal stakeholders, it is difficult to convey seasonal differences in generation. By showing monthly generation, you can intuitively explain which seasons have higher generation and which have lower. In particular, when considering self-consumption at factories, warehouses, public facilities, commercial facilities, and the like, it is important to compare seasonal fluctuations in power demand with seasonal fluctuations in generation.

Also, monthly generation can be used to check the validity of simulation results. Solar power generation calculations are influenced by the input weather data, location information, module settings, power conditioner settings, wiring losses, shading settings, terrain conditions, and so on. If there are input errors, it can be difficult to notice anything amiss from the annual generation alone, but when viewed monthly you may find that only certain months show unnatural values. Monthly generation also serves as a checklist for detecting input errors in design conditions.

Basics to Keep in Mind Before Reviewing the Report

Before looking at monthly generation, it is important to first organize which values in the simulation results you will check. The report shows multiple values related to generation: the irradiance incident on the solar panel surface, the energy generated on the DC side of the solar panels, the AC-side energy after passing through the power conditioner, the energy exported to the grid, and so on—values differ at each stage. When viewing monthly generation, you need to be conscious of which stage’s generation you are checking.

Generally, in practice the most commonly checked figure is the monthly AC-side generation that is ultimately available or sent to the grid. This number is easy to use for business planning and self-consumption planning. On the other hand, for design verification, DC-side generation and pre- and post-loss figures are also important. For example, if the solar panels themselves are producing adequately but the AC-side shows a large reduction, it is necessary to check for effects such as conversion losses, output limitations, wiring losses, and temperature-related losses.

When checking monthly power generation, pay attention to the units. In reports, monthly generation may be shown in kWh or MWh. For small-scale facilities, kWh is used, while for large power plants MWh is easier to read. There are also indicators that show generation per unit of capacity. These are useful when comparing projects with different capacities. If you only look at simple monthly generation figures, projects with larger capacities will show larger numbers, but comparing on a per-capacity basis makes it easier to see the advantages of design and location.

Furthermore, it is important not to evaluate monthly generation in isolation but to check it together with monthly solar irradiation and losses. Even if there are months with low generation, if those months have low solar irradiation, that is a natural outcome. Conversely, if solar irradiation is sufficient but generation is not increasing, the cause may lie in equipment settings or loss conditions. In other words, monthly generation is the final result, and only by interpreting it together with the underlying solar irradiation, temperature, shading, and losses can you arrive at practical judgments.

Step 1: Run the simulation and open the results screen

The first step to check monthly power generation is to run the simulation for the target project and open the results screen. In photovoltaic simulation software, you create a project, enter the location, weather data, system capacity, modules, power conditioners, layout conditions, loss conditions, and so on, and then run the simulation. Because monthly power generation is displayed as a calculated result based on the input conditions, it is a prerequisite that the calculation has been completed.

When you open the results screen, first check the overview of the annual generation. This shows the total annual generation, generation per unit of capacity, performance ratio, the breakdown of major losses, and so on. Before looking at monthly generation, confirm that this overview is not significantly off, as doing so makes subsequent checks easier. For example, if the annual generation is clearly too low, you should review the basic inputs—such as the location and meteorological data, installed capacity, and operating conditions—before proceeding to detailed monthly checks.

Simulation results can often be reviewed on multiple screens or in report formats. Some results can be viewed as graphs on-screen, while others are output as detailed reports for review. In practice, it is common to not only look at the on-screen results but also open the output reports to check monthly tables and graphs. Because reports often organize not only monthly generation but also solar irradiance, temperature, losses, and performance ratio, they are also convenient materials for explaining the results to stakeholders.

At this stage, you should pay attention to whether the simulation's target conditions are correct. In solar power generation simulations, you may create multiple variations within the same project. For example, a variant with a different panel tilt angle, a variant with a different layout, a variant with a different system capacity, or a variant with different loss conditions. When checking monthly power generation, always confirm which condition the currently open results correspond to. Viewing the results of a different variant can lead to incorrect decisions.

Also, before generating a report, check whether the saved conditions are up to date. If you only changed the conditions on the input screen and did not rerun the simulation, the report may still contain results from the old conditions. This is especially true for projects where design studies are repeated many times, since it can become unclear which conditions were used for the calculations; therefore, it is advisable to record the simulation run date and time, variation names, and configuration notes.

Step 2: Check the monthly power generation in the report

The next step is to check the monthly generation shown in the report. In the report, the monthly figures are listed and may also be displayed as bar charts or line graphs. First, look at the flow of generation from January through December and confirm whether it appears natural as a seasonal variation. In many regions, due to sunlight conditions and the sun angle, generation tends to increase from spring to summer and decrease in winter. However, the shape of the monthly profile varies depending on the region’s climate, azimuth, tilt angle, snow, rainy season, and shading conditions.

When looking at monthly power generation, focus on the month with the maximum output and the month with the minimum output. By checking which months are the maximum and minimum, you can understand in which season the installation is designed to perform strongly. For example, installations with a small tilt angle tend to receive more solar radiation in summer, while during periods when the sun's altitude is low in winter their power generation may not increase much. Conversely, installations with a large tilt angle may show relatively improved power generation in winter. In this way, monthly power generation provides clues to the effects of an installation's orientation and tilt angle.

Next, check whether the monthly generation drops off sharply. If a single month is unusually low, it may not be just a seasonal variation but could indicate a problem with the input conditions or the shading settings. For example, if shading losses are much larger in a particular month, it may reflect strong influences from nearby buildings, trees, terrain, racking spacing, or other factors. If there is a significant decline in winter, consider the effects of shading during periods of low solar altitude, snow cover, and reduced solar irradiance.

Monthly generation figures are useful in practice when viewed with an awareness of each month’s contribution to annual generation. Knowing which months account for a large share of the annual generation makes it easier to explain the forecast risk of generation. For example, for installations whose generation is concentrated in a particular season, weather variability during that season will have a large impact on annual generation. Conversely, if the monthly generation is relatively flat, the design can be seen as having little seasonal bias.

In the report, along with monthly power generation, we also check monthly solar radiation. By confirming whether months with high generation also have high solar radiation, or months with low generation also have low solar radiation, it becomes easier to separate whether generation variability is due to meteorological conditions or equipment conditions. If there are months where solar radiation is high yet generation is low, we check whether temperature losses, shading losses, output limitations, wiring losses, etc., are strongly present in those months.

Step 3: Identify the Reasons for Monthly Variations

The final step in checking monthly power generation is to discern the reasons for changes in the figures. Simply looking at a monthly table of generated power does not tell you why a particular month is high or why it is low. In practice, month-to-month increases and decreases in power generation need to be interpreted in connection with irradiance, solar altitude, temperature, shading, losses, and equipment specifications.

The first thing to check is solar irradiance. The output of solar power generation is fundamentally heavily influenced by solar irradiance. Months with high monthly generation are generally months with high solar irradiance. However, the month with the highest solar irradiance does not always coincide with the month with the highest generation. This is because solar panel output can decline during periods of high temperature, and output can be limited by the capacity of the power conditioner. In summer, although solar irradiance is high, temperature losses tend to increase, so generation may not rise as much as expected.

Next, check the impact of shading. Shading is a factor that can cause large differences in monthly power generation. In particular, in winter the solar altitude is lower, so the same obstacles cast longer shadows. Buildings, trees, surrounding equipment, terrain, adjacent racking rows, and similar features can cause shading to occur more easily during winter mornings and evenings. As a result, power generation in winter can drop significantly. If the report displays monthly values of shading losses, verify whether the months with low generation overlap with the months with large shading losses.

Furthermore, temperature losses are also important. Solar panels have the characteristic that their output decreases as temperature rises. Therefore, even in months with high solar irradiance, in regions or installation environments with high ambient temperatures, power generation can be suppressed by temperature losses. In particular, roof-mounted systems with poor ventilation or where the mounting surface tends to become hot are more susceptible to the effects of temperature conditions. When examining monthly generation, it is important to verify whether the summer generation is reasonable relative to the solar irradiance.

Output limitations and the effects of an oversized design should not be overlooked. If the power conditioner (inverter) capacity is designed smaller relative to the solar panel capacity, output can hit its limit during periods of high irradiance and some generation may be curtailed. This effect tends to show up in months with high solar irradiance. Looking only at monthly generation, it may appear that summer generation is somewhat restrained, but that could be due to output limits. It is important to check the loss breakdown in the report and identify in which months which losses are large.

Main items to check in monthly power generation

When checking monthly power generation in practice, you should not simply look at the generation numbers alone; you should check related items as a set. The first thing to check is the finalized monthly generation figures. This is the most important result because it is directly related to commercial viability and self-consumption planning. Examine the monthly values to confirm whether the seasonal variations are natural, whether they are balanced against the annual total, and whether any particular month shows an extreme value.

The next thing to look at is monthly solar radiation. By checking the relationship between solar radiation and power generation, you can determine whether increases or decreases in generation are natural. It's natural for power generation to be low in months with low solar radiation, but if generation doesn't increase in months with high solar radiation, you need to investigate other factors. Viewing solar radiation and power generation side by side makes it easier to separate variations caused by weather conditions from those caused by equipment conditions.

Performance ratio is also an important item to check. The performance ratio is used as an indicator of how efficiently the installation is generating power relative to solar irradiance. By looking at the monthly performance ratio, you can check whether efficiency has dropped in a particular month. For example, if the performance ratio falls significantly in winter, you might suspect shading; if it falls in summer, you might suspect temperature losses or output curtailment. The performance ratio helps to read the condition of the installation that is not easily visible from the amount of energy generated alone.

Also review the loss items on a monthly basis. In photovoltaic power generation simulations, various losses are considered, including temperature loss, shading loss, reflection loss, wiring loss, conversion loss, and output curtailment. By looking at how these losses occur month by month, you can identify the causes of decreased power generation. In particular, shading loss and temperature loss tend to vary greatly with the seasons, so it is worth checking them together with monthly generation.

It is also useful to check the power generation per unit of installed capacity. When comparing multiple projects, differing installed capacities make it difficult to judge by simple generation comparisons. Looking at generation per unit of capacity makes it easier to compare the merits of site conditions and design parameters. If you are evaluating multiple layout options in the same area, or comparing proposals with different tilt angles or orientations, monthly generation per unit of capacity is a valuable decision-making metric.

Common Oversights in Monthly Power Generation

One common oversight when checking monthly generation is assuming that if the annual generation looks reasonable, the monthly figures must be fine as well. Even if the annual total is close to expectations, there can be large imbalances when viewed month by month. For example, if generation is high in summer but extremely low in winter, problems may be hard to spot by looking only at the annual total. When considering self-consumption or seasonal variations in electricity demand, monthly imbalances are an important factor to consider.

Another oversight is attributing all months with low power generation to weather conditions. Indeed, generation tends to be lower in winter or during rainy seasons, but not all declines are due to natural variability. Shading configuration, equipment azimuth, tilt angle, loss conditions, and terrain effects can cause a specific month’s generation to drop significantly. When you find a month with low generation, it is important to check, in order, solar irradiance, shading losses, temperature-related losses, and output curtailment.

Units in reports can sometimes be overlooked. If you copy monthly generation figures into documents without confirming whether they are displayed in kWh or MWh, you may misstate the order of magnitude. In particular, caution is required when combining multiple documents or processing figures for internal materials. Errors in units can have a significant impact on the profit-and-loss calculations and presentation materials of a power generation business, so always verify them.

Also, when comparing multiple options, it is often the case that the conditions are not aligned. For example, if option A and option B use different meteorological data, different loss conditions, different equipment capacities, or different simulation execution conditions, you cannot correctly compare monthly power generation. When comparing design options, you need to make the conditions as consistent as possible except for the items you want to compare. If you want to compare differences in orientation, capacity, meteorological data, and loss conditions should be kept the same.

Furthermore, care must be taken not to treat the monthly generation figures directly as actual future generation. Simulation results are forecasts based on the input meteorological data and equipment conditions. Actual generation will vary due to year-to-year weather differences, equipment soiling, maintenance status, failures, output curtailment, changes in the surrounding environment, and other factors. Monthly generation figures are important values that help inform design decisions and planning, but they must be used with the understanding that they are not actual measured performance values.

Practical, easy-to-use verification workflow

When checking monthly power generation in practice, following the same procedure each time reduces mistakes. First, confirm the target project and the simulation conditions. Check that the location, weather data, equipment capacity, azimuth, tilt angle, panel type, power conditioner capacity, and loss conditions are as assumed. If the input conditions are incorrect at this stage, analyzing the monthly generation becomes meaningless.

Next, check the annual energy production and the performance ratio. Confirm whether the annual energy production is within the expected range and whether the performance ratio is not abnormally low. If you notice any significant discrepancy at this stage, review the basic conditions before proceeding to a month-by-month detailed check. If the annual values deviate substantially, there may be a major error in the site settings, the selection of weather data, the system capacity, the loss settings, or similar.

After that, check the table or graph of monthly power generation. Look at the months with the highest and lowest generation, the seasonal trends, and any months with sudden drops. Confirm whether there is a natural pattern of increasing from spring to summer and decreasing from autumn to winter. However, because the pattern can vary depending on the region and installation conditions, it is also important not to judge based solely on general tendencies.

Next, compare this with the monthly solar radiation. Check whether increases and decreases in generation align with increases and decreases in solar radiation. If there are months with high solar radiation but low generation, investigate the losses for those months. If both solar radiation and generation are low, it is more likely a natural variation due to weather conditions. By examining the relationship between solar radiation and generation, you can determine where to investigate in more detail.

Finally, check shading losses, temperature losses, output limits, and other losses. By seeing which losses are larger in months with lower generation, you can identify directions for improvement. If shading losses are large, check the layout and surrounding obstacles; if temperature losses are large, check the installation method and ventilation conditions; if output limits are large, check the capacity ratio and equipment configuration. In this way, monthly generation is not merely a result but can be used as an entry point for design improvements.

Points to Check When Power Generation Differs from Expectations

If the monthly power generation differs from expectations, the first thing to check is the site information. If the site's latitude, longitude, elevation, time zone, or regional settings are incorrect, they will affect calculations of solar irradiance and the sun's position. In particular, even if you think you selected a nearby place name, you may actually be using weather data for a different location. If the monthly power generation is generally too high or too low, first check the site and weather data.

Next, review the types and contents of the meteorological data. In solar power generation simulations, results change depending on the meteorological data used. Average-year data, observed data, estimated data, etc.—monthly solar irradiance varies according to the nature of the data. If power generation is unnaturally high or low in a particular month, check whether the solar irradiance data for that month is biased. Because meteorological data underpins generation forecasts, reliability and suitability for the target site are important.

Also check the system capacity settings. If the number of solar panels, their output, the number in series, the number in parallel, and the power conditioner capacity are not set correctly, the generated power can differ significantly from expectations. In particular, the relationship between DC-side capacity and AC-side capacity affects monthly generation. If output limitation is large in months with high irradiance, you should check the capacity ratio settings.

Input errors in azimuth and tilt angle are also a common cause. If the azimuth is reversed, the tilt angle differs from what was assumed, or the roof surface orientation is entered incorrectly, the monthly power generation trend can change significantly. Azimuth and tilt affect not only the annual energy output but also which seasons produce more power. If the monthly pattern differs from expectations, always recheck the azimuth and tilt.

Shadow settings are also important. If you set shadows from nearby obstructions or between mounting racks, check in which months and to what extent those shadows are affecting output. If generation drops significantly only in winter, shadows during periods of low solar altitude may be responsible. If shadow settings are excessive, the estimated generation will be shown lower; if shadow settings are insufficient, it may be shown higher than actual. How accurately site conditions are reflected directly affects the reliability of the monthly generation figures.

Approach to Utilizing Monthly Power Generation in Design Decisions

Monthly generation figures are not something to just check in a report and be done with. In practice, it is important to apply those results to design decisions and explanatory materials. For example, if generation drops significantly in winter, it may be possible to improve it by reviewing the system’s tilt angle and layout. If shading has a large impact, consider changing the panel layout, increasing clearance from obstacles, or adjusting row spacing.

For self-consumption solar power systems, it is important to compare monthly generation with the facility’s monthly electricity demand. If months with high generation also have high demand, it is easier to increase the self-consumption rate. Conversely, if periods of high generation and low demand are misaligned, it is necessary to consider how to handle surplus power and how to operate the system. Checking monthly generation makes it easier to determine whether the system capacity is oversized and whether the seasonal balance of generation matches demand.

In planning power generation projects, monthly generation figures can be used for revenue forecasts and risk explanations. Using only annual generation obscures seasonal generation variations. With monthly generation data, you can explain when generation revenue will be higher and when it will be lower. It can also be used for maintenance and inspection planning. Because prolonged outages during periods of high generation have a greater impact, monthly generation figures are also useful when considering the timing of inspections and construction work.

Monthly generation is useful even when comparing designs. When you compare multiple proposals with different orientations or tilt angles, the differences in annual generation may be small, but the monthly generation patterns can differ. For example, even if annual generation is nearly the same, one option may be stronger in summer and another stronger in winter. Depending on self-consumption demand or business objectives, it may be more appropriate to choose the option with a monthly balance that matches demand rather than the one with the maximum annual generation.

Furthermore, monthly power generation figures are well suited for explanations both inside and outside the company. Presenting generation by month makes it easier for stakeholders without technical expertise to understand the facility’s generation characteristics. Information that may seem abstract when expressed only as annual generation can be explained as seasonal variation by breaking it down by month. Practitioners should use monthly generation figures not merely as a table of numbers, but as material to convey design intent and operational policy.

Summary

When viewing monthly energy production in PVSyst, the basic procedure is to run the simulation, open the results screen, check the monthly energy production in the report, and interpret the reasons for its variations together with irradiance and loss items. Monthly energy production is not a table for checking the breakdown of annual generation; rather, it is important information for interpreting the validity of design conditions, the effects of shading, temperature losses, output limitations, and the characteristics of the meteorological data.

In practice, rather than judging solely by annual energy production, checking monthly generation trends enables design decisions that are closer to reality. If there are months with low generation, check in order whether it is due to lower irradiance, significant shading, or the effects of temperature or output limitations. When comparing multiple proposals, it is important to run simulations under the same conditions and compare monthly generation, irradiance, performance ratio, and losses.

To improve the accuracy of monthly generation estimates, it is essential not only to set simulation parameters but also to accurately understand the on-site conditions. In designing solar power generation systems, factors such as the site location, elevation, topography, surrounding obstructions, existing structures, and the ground profile after development affect estimates of power generation. Accurately determining the site's coordinates and topography also aids in shadow analysis, layout planning, and verification during construction.

As a way to streamline such on-site verification, you can utilize LRTK, a GNSS high-precision positioning device that attaches to and is used with an iPhone. If you obtain high-precision location information on site and record the positions of survey points and site features, it becomes easier to handle everything consistently—from candidate site surveys for solar power installations, layout planning, and construction inspections to post-completion management. Not only can you check monthly power generation with simulation software, but by accurately capturing on-site location and topographic information you can reduce discrepancies between desk-based assessments and actual site conditions, leading to more reliable solar power planning.