4 Points to Calculate Household Solar Power Generation by Month

When calculating the power output of residential solar systems, looking only at annual generation can make practical operational decisions difficult. Solar generation varies month to month even with the same installed capacity. This is because the result is determined by a combination of factors such as solar irradiance, hours of sunlight, temperature, shading, snowfall, soiling, panel orientation, installation angle, and the conversion efficiency of the power conditioner. Especially for households, because it affects seasonal variations in electricity consumption, self-consumption, electricity sold to the grid, combinations with battery storage, and future maintenance decisions, it is important to estimate generation on a monthly basis.

This article explains four key points that practitioners should keep in mind when organizing monthly generation figures from the perspective of "solar power generation calculation." It summarizes, in a format useful for preparing materials before publication and for explaining to clients, not only simple calculation formulas but also commonly overlooked calculation assumptions, the mindset for month-to-month comparisons, and methods for reconciling with actual results.

Table of Contents

• Prerequisites to be established first for monthly calculations

• Incorporate monthly solar radiation and seasonal variations into the calculations

• Adjust power generation for each month according to loss conditions.

• Review calculation conditions while comparing them with actual values.

• Summary for correctly interpreting monthly power generation of residential solar systems

Preconditions to Establish First for Monthly Calculations

When calculating monthly power generation for residential solar, the first thing to do is clearly define and align the assumptions for the calculation. Solar power generation is not determined solely by installed capacity. Even with solar panels of the same capacity installed, monthly generation varies depending on location, orientation, tilt angle, roof shape, surrounding environment, and operating conditions. Therefore, before starting the calculations, you need to organize which conditions you will fix and which you will vary month by month.

The basic concept is to estimate electricity generation by applying monthly solar irradiance conditions and loss factors to the installed capacity of the solar panels. In practice, installed capacity, local solar irradiance, the azimuth and tilt of the mounting surface, the overall system loss rate, and the number of days in each month are combined to estimate monthly generation. However, be careful not to simply divide the annual average conditions evenly by 12. Because solar power generation varies seasonally, dividing the annual generation by 12 tends to deviate from the actual monthly pattern.

For example, from spring through early summer solar irradiance is high, and under conditions where panel temperatures do not rise as much as in midsummer there can be months in which generation tends to increase. On the other hand, in midsummer, although irradiance is high, panel temperatures tend to rise, so it is necessary to account for output reductions caused by temperature increases. In winter, daylight hours are shorter and the sun’s altitude is lower, so in some regions the effects of shading and snowfall become significant. Thus, in monthly calculations it is important to include seasonal characteristics as assumptions rather than relying on a simple average.

The first thing to confirm as a prerequisite is the rated output of the solar panels. For residential use, calculations are based on the total capacity of the rooftop-mounted panels. However, the rated output is a value measured under specific test conditions and does not always correspond to the output in actual outdoor environments. Therefore, when calculating monthly electricity generation, you should not treat the rated output as the actual generation but consider the real generated output taking into account solar irradiation conditions and loss factors.

The next thing to check is the installation site. Solar power generation is greatly affected by the area's solar radiation. Even with the same installed capacity, monthly generation differs between areas with good solar radiation and areas with frequent cloudy weather or heavy snowfall. Moreover, even within the same area, actual generation can vary due to mountain shadows, neighboring houses, trees, utility poles, antennas, roof steps, and other factors. During the calculation stage, it is easier to organize the process by first using the region's solar radiation as the baseline and then applying corrections for site-specific conditions.

Orientation and tilt angle are also important. In general, the more a solar panel is installed in a direction and at an angle that receives sunlight, the more its power generation tends to increase. However, for residential systems, roof shapes often impose constraints, so panels cannot always be installed at the ideal orientation or angle. They may be installed not only on south-facing roofs but also distributed across east- and west-facing roofs. In that case, surfaces that generate more power in the morning and those that do so in the afternoon are separated, so there will be differences not only by month but also by time of day.

In monthly calculations, don't forget the number of days in the month. Even if the average daily power generation is the same, the monthly total will change if the number of days in the month differs. Because February and March, and April and May have different numbers of days, when comparing monthly totals you need to take the difference in days into account. When judging a decline in power generation, converting to a daily average and comparing that rather than using only the monthly total gives a more realistic assessment.

Furthermore, it is important to clarify the purpose of the calculation. The required level of accuracy and the conditions that need to be checked depend on whether it is a pre-installation power generation forecast, a verification of an existing system’s performance, or an investigation into a decline in generation. If it is a rough estimate before installation, the main objective is to grasp monthly trends. On the other hand, verification of an existing system requires cross-checking actual generation data, weather, outage history, and cleaning and inspection records. If calculations are done without a clear purpose, it becomes difficult to determine whether differences in generation are caused by problems or by differences in calculation conditions.

In residential solar systems, there is the concept of self-consumption—using the electricity generated at home—and selling any surplus. By not only calculating monthly generation but also overlaying it with household electricity usage, you can grasp how much of the generation can be self-consumed in months with high output and, conversely, how much purchased electricity will increase in months with low output. In residential practice, it is important not to stop at calculating generation alone but to link the results to lifestyle and system operation.

Thus, calculating monthly power generation is not simply a matter of plugging numbers into a formula. You need to interpret the calculation results after aligning assumptions about system capacity, location, orientation, tilt, shading, the number of days in the month, purpose, and the approach to self-consumption. If the initial assumptions are ambiguous, no matter how many detailed corrections you make afterward, the results tend to deviate from reality. The first step to improving the accuracy of monthly calculations is to organize and clarify the conditions before calculation.

Incorporate monthly solar radiation and seasonal variations into the calculations

When calculating monthly power generation for residential solar systems, the primary variable factor is solar radiation. Solar power generation tends to increase the more sunlight reaches the solar panels. However, solar radiation is not constant from month to month. Because the sun’s altitude, day length, and typical weather patterns change with the seasons, monthly generation varies. Therefore, it is important to reflect monthly solar conditions rather than calculating based only on the annual average solar radiation.

When considering monthly solar radiation, you first need to understand the differences in solar altitude. During periods of high solar altitude, depending on installation conditions, solar radiation is more likely to reach the panel surface and power generation tends to increase. Conversely, during periods of low solar altitude, even under the same clear sky the amount of solar radiation reaching the panel surface tends to be smaller, and shadows from surrounding buildings and trees extend farther. The reason power generation is lower in winter is not simply because it is cold, but because shorter hours of sunlight, lower solar altitude, and a greater tendency for shadows to lengthen coincide.

Sunshine hours are also an indispensable factor in monthly calculations. In periods close to summer, daytime is longer and the hours available for power generation increase. In periods close to winter, daytime is shorter and the hours during which generation is possible are limited. However, longer daytime does not necessarily mean that the month's power generation will be the highest. Because the effects of weather, air temperature, panel temperature, the rainy season, and typhoons can overlap, one should avoid judging based solely on sunshine hours. In monthly calculations, it is necessary to view solar irradiance and sunshine hours together while taking regional weather tendencies into account.

The reason some regions tend to see higher power generation from early spring through early summer is that solar irradiance is relatively consistent and panel temperatures do not rise as much as in midsummer. Solar panels generate electricity from sunlight, but their output decreases as panel temperature increases. Therefore, even if sunlight is abundant in midsummer, generation may not rise as much as expected due to increases in panel surface temperature. If this is not taken into account and summer generation is overestimated, discrepancies with actual performance are likely to occur.

During the rainy season and other periods with frequent rain, solar irradiance tends to decrease. For residential solar power, generation does not stop completely on cloudy or rainy days, but the output is lower compared to sunny days. Monthly calculations can reflect these weather patterns to some extent by using average monthly irradiance conditions. However, because weather varies from year to year, predicted values and actual results do not always match exactly. It is important to treat calculation results as a guideline based on standard conditions.

In winter calculations, it is necessary to consider not only solar irradiance but also the effects of snowfall and frost. In snowy regions, when snow accumulates on the panel surface, power output can drop significantly. Even with roof pitches or installation angles that allow snow to shed naturally, generation declines during the period when snow remains. Also, in areas where frost forms in the early morning, the start of generation can be delayed until the sun melts the frost. These effects are factors that tend to be overlooked in monthly power generation calculations.

When including solar irradiance in calculations, it is important to pay attention to the difference between irradiance on a horizontal surface and on an inclined surface. Because solar panels are often installed along the slope of a roof, the irradiance actually received by the panels differs from simple horizontal-plane irradiance. Installation angle and orientation can change the amount of irradiance incident on the panel surface even within the same region. To make monthly power generation estimates closer to actual conditions, it is effective, if possible, to use irradiance data that match the conditions of the installation surface.

When panels are installed on east- or west-facing roofs, not only the monthly generation totals but also the time-of-day generation patterns change. East-facing roofs tend to generate more in the morning, while west-facing roofs tend to generate more in the afternoon. Compared with south-facing roofs, the monthly total generation may be lower, but if it matches the household’s electricity usage times, it can be advantageous for self-consumption. When performing monthly calculations, it is easier to provide practical explanations if you consider not only the absolute amount of generation but also its relationship to people’s lifestyle.

Also, even when calculating using monthly solar irradiance, it is not possible to predict all abnormal weather events or temporary adverse conditions. If a particular year has unusually high rainfall, an increased number of typhoons, prolonged heat waves, or extended snowfall, actual values may deviate from standard calculated values. Therefore, the calculation results for monthly power generation should not be judged based on a single month alone; it is important to combine multi-month trends with comparisons to the same month of the previous year.

When explaining to customers and stakeholders, it is important for practitioners to share the premise that monthly variations in power generation are not abnormal. In particular, when generation falls in winter or during rainy periods, people may worry about equipment faults. However, taking seasonal differences in solar irradiance and sunshine duration into account, a certain decrease in generation can be explained as a natural fluctuation. Conversely, if a large drop is observed in a month that should have favorable solar conditions, it can prompt suspicion of other factors such as shading, soiling, shutdowns, or equipment malfunctions.

The purpose of handling solar irradiance in monthly calculations is not simply to predict power generation. By having expected values for each month, it becomes easier to judge whether actual values are reasonable. By distinguishing whether generation drops in months with low irradiance or whether generation is underperforming despite sufficient irradiance, you can better prioritize inspections and root-cause investigations. When calculating monthly power generation for residential solar, it is necessary to focus on irradiance and seasonal variation while layering in the effects of temperature, weather, and shading.

Adjust power generation by month for loss conditions

In calculating solar power generation, it is necessary to consider various loss conditions as well as solar irradiance. Even if sunlight reaches photovoltaic panels, not all of it becomes electricity usable in the home. Actual generation is lower than theoretical values due to panel temperature rise, conversion losses in the power conditioner, wiring losses, dirt, shading, degradation over time, equipment downtime, and so on. When calculating monthly generation, it is important not only to aggregate these losses into a single uniform figure but also to separate the factors that vary from month to month.

First, consider the reduction in output caused by temperature. Solar panels tend to lose generation performance as panel temperature increases. Especially in summer, not only the ambient air temperature but also the roof surface temperature rises, leading to higher panel temperatures. Therefore, even in months with high solar irradiance, if temperature losses are not taken into account, the estimated generation can be overstated. In monthly calculations, it is important not to simply estimate midsummer generation based only on irradiance, but to apply a correction for temperature rise.

On the other hand, in winter, because temperatures are low, output loss due to temperature tends to be relatively small. However, winter has shorter sunlight hours, lower solar elevation, and is more susceptible to shading and snowfall. In other words, the loss conditions to emphasize change by month — for example, focusing on temperature losses in summer and on insufficient solar radiation, shading, and snow in winter. Using the same loss rate for the entire year can cause the monthly peaks and troughs in power generation to fail to match actual conditions.

Next, check losses due to shading. In residential solar installations, rooftop antennas, chimneys, neighboring houses, trees, utility poles, and surrounding buildings can cast shadows. The impact of shading varies by season. Even if shadows are short and unlikely to fall on the panels when the sun is high, in winter shadows can lengthen and reach the panels. Also, during morning and evening when the sun is low, the system is more susceptible to shading from nearby obstacles. When calculating monthly generation, you should not treat shading simply as a constant annual loss; you need to consider the possibility that shading will increase in winter and during mornings and evenings.

Losses due to soiling are an easily overlooked factor in month-by-month assessments. Solar panels can accumulate dust, pollen, yellow sand, bird droppings, fallen leaves, tree sap, and other deposits. Rain can wash some of these away, but depending on the type of soiling and how it adheres, residues may remain. Early spring brings pollen and windblown dust, autumn brings fallen leaves, and depending on the surrounding environment there may be bird-related fouling; the pattern of soiling changes with months and seasons. If soiling concentrates on particular panels, the reduction in power generation can become noticeable. In monthly calculations, rather than only including a standard loss, it is advisable to identify months with higher soiling risk based on site conditions.

Conversion losses of the power conditioner are also a basic factor that should be included in power generation calculations. The direct current generated by solar panels is converted into alternating current that is convenient for household use. Certain losses occur during this conversion process. These losses are usually treated as part of the overall system loss rate, but in high-temperature summer conditions or depending on the ventilation at the installation site, equipment temperature rise can affect power output. Differences between outdoor and indoor installation, ease of ventilation, and the degree of exposure to direct sunlight are also points to check when comparing with actual measured values.

Wiring losses should also be included in energy production calculations. In residential systems the wiring distances may be shorter than in large-scale installations, but losses occur depending on the dispersion across roof surfaces, the distance to junction boxes and power conditioners, and the conditions of the wiring routes. Wiring losses do not vary greatly from month to month, but during periods of high generation the current is larger and the effect of losses may become more apparent. Rather than treating them as a major variable in monthly calculations, it is important to reliably account for them as part of the baseline losses.

Degradation over time should also be considered in power generation calculations. Solar panels are equipment used for long periods, and their output may gradually decline as years pass. If the purpose of monthly calculations is pre-installation forecasting, it is easier to explain by separating the forecast for the first year from the forecast for long-term operation. When evaluating the generation of existing installations, comparing to initial calculated values without taking the elapsed years since installation into account can make the output appear to have decreased more than it actually has. When comparing monthly generation, keep in mind that the assumptions differ for the same month between the initial installation period and several years later.

Impacts from equipment shutdowns or output curtailment can also cause large differences in monthly power generation. For example, inspections or construction, temporary stoppages, breaker operations, data loss due to communication failures, or output curtailment because of grid-side conditions can all lead to a significant drop in monthly generation. These are causes of decline that cannot be explained by solar irradiance or design conditions alone. When comparing monthly calculated values and actual values, you should first check whether there were any shutdown days or missing-data days in the target month. Even just a few days of shutdown can produce a large difference in the monthly total.

When looking at data for self-consumption and electricity sold to the grid, it is also important not to confuse the generated output itself with the surplus remaining after consumption. In residential solar, part of the electricity generated is used within the home and the excess is sent out. For that reason, looking only at the amount sold to the grid can lead to the mistaken conclusion that generation is low. When calculating monthly generation, you need to separate and organize generation, consumption, surplus, and purchased electricity. Especially in summer and winter, air-conditioning use tends to increase, so even if generation is high, self-consumption can rise and the surplus may appear small.

The advantage of considering loss conditions on a monthly basis is that it makes it easier to explain differences between calculated results and actual values. For example, if actual power generation fails to reach the calculated value in summer, you can check temperature-related losses and the thermal environment of the equipment. If there is a large drop in winter, you can check sunlight hours, shading, snow accumulation, and frost effects. If a noticeable decline occurs in spring, you may check the effects of pollen, dirt, and yellow sand. If generation falls in autumn, consider fallen leaves, post-typhoon soiling, and shading from nearby trees. By linking monthly characteristics with loss conditions in this way, you can move from merely comparing numbers to analyzing the causes.

In practice, it can be difficult to quantify every loss in detail. Even so, separating in the monthly calculations the "losses that are nearly constant throughout the year" and the "losses that tend to vary by month" makes the calculations easier to follow. Treat conversion losses and wiring losses as baseline losses, and treat temperature, shading, snow accumulation, soiling, outages, and missing data as monthly variable factors — this kind of organization is effective. When calculating energy generation, it is important to be able to explain not only the detailed numbers but also which losses tend to impact which months.

Review calculation conditions while comparing with actual results

After calculating the monthly power generation for a residential solar system, the next important step is comparing those calculations with actual results. Calculated values are merely forecasts or estimates and can differ from actual generation. By correctly interpreting those differences, you can not only verify the validity of the calculation assumptions but also detect early signs of equipment faults, changes in shading, soiling, outages, or data gaps. Monthly calculations are not an end in themselves; their value lies in reconciling them with actual results and using that comparison to drive improvements.

The first thing to do is compare the total monthly power generation. Place the calculated monthly generation side by side with the actually recorded monthly generation and identify months with large discrepancies. However, looking only at monthly totals can overlook the effects of differing numbers of days or missing-data days. Therefore, in addition to the monthly totals, it is advisable to check the average daily generation. Even if February’s generation appears lower than other months, that may be due to having fewer days. Normalizing by the number of days makes it easier to determine whether there is an anomaly.

Next, check the impact of the weather. Even if there is a month in which power generation is lower than the calculated value, if that month had many rainy or cloudy days, it does not necessarily indicate an equipment fault. Conversely, if the month had many clear days yet generation has fallen significantly, you should suspect other factors. When comparing actual values with calculations, it is important not simply to look at the difference from the calculated value, but to assess it together with the month's weather trends. If possible, check daily power generation to see whether the decline is spread evenly across the whole month or is concentrated on specific days.

Viewing daily data makes it easier to isolate causes. If low power generation persists even on clear days, dirt, shading, equipment malfunction, or poor connections may be suspected. On the other hand, if output is extremely low on only certain days, possibilities include temporary shutdowns, inspections, power outages, communication errors, or sudden weather changes. Factors that are not visible from monthly totals alone become easier to identify by breaking the data down by day. In practical monthly calculations, it is important to review totals, daily averages, and daily trends in stages.

When comparing against actual values, pay attention to the type of generation data. In a solar power generation system, multiple figures may be displayed, such as generation, consumption, amount sold, and amount purchased. If you calculate monthly generation but use the amount sold as the comparison target, the portion consumed within the household will not be reflected and generation may appear low. Especially in months when people are at home more, when heating or cooling use is high, or when hot water and appliance use increases, self-consumption can rise and surplus decrease. Always confirm whether the number you are comparing is generation or amount sold.

When comparing calculated values and actual results, it is important not to judge based on a single month alone. Because solar power generation is affected by the weather, judging system performance from a difference in only one month can be misleading. Looking at trends over multiple months makes it easier to determine whether the variation is within normal seasonal fluctuations or represents a sustained decline. For example, if output drops sharply in a single month but returns the following month, that could indicate temporary weather conditions or a short-term shutdown. On the other hand, if actual values remain below the calculated values over several months, a review of calculation assumptions and an on-site inspection will be necessary.

Comparing with the same month of the previous year is also useful. Monthly power generation has large seasonal variations, so comparing only with the previous month can make it difficult to judge. An increase in generation from winter to spring is a natural change, and generation may decrease from summer to autumn. Therefore, comparing with the same month of the previous year, which has similar seasonal conditions, makes it easier to detect abnormal declines. However, because weather can differ between the previous year and this year, comparison with the same month of the previous year should not be used as an absolute judgment but only for confirming trends.

If the actual measured values are consistently lower than the calculated values, review the initial assumptions. Check whether the equipment capacity is incorrect, whether the installation orientation (azimuth) and tilt angle match the actual conditions, whether shading conditions have been underestimated, or whether loss rates have been set too optimistically. If calculations were performed only from the drawings and specification documents at the time of installation, there may be differences from the actual rooftop installation conditions and the surrounding environment. In particular, changes such as buildings being constructed later, trees growing, or antennas and equipment being added can affect power generation.

Even when actual values are higher than calculated values, it is worth checking the reasons. Possible causes include conservative calculation assumptions, favorable solar irradiance conditions, shading effects being smaller than assumed, or the equipment being in good condition. However, the data aggregation range or units may also be incorrect. For example, if the target period is not from the first to the last day of the month, data from multiple systems have been combined, or the displayed value is a cumulative total, the result can appear higher than the actual situation. Even with high results, verification of the calculation conditions is necessary.

Also, when a drop in power generation is detected, it is important not to immediately proceed to parts replacement or large-scale construction, but to check the calculation conditions and actual performance data step by step. First check the weather, the number of days, shutdown history, missing data, shading, and soiling, and then consider the possibility of equipment malfunction. In residential solar, low generation is not necessarily due to a simple equipment failure. Using monthly calculations to separate natural seasonal variations from anomalies that require inspection is effective in reducing unnecessary measures.

Keeping a record of the comparison between calculated and actual values is also important. Recording, on a monthly basis, the calculated values, actual values, differences, weather notes, outage history, and cleaning and inspection histories makes it easier to make decisions in subsequent years. In particular, when power generation declines gradually, changes that are hard to notice in a single month become visible by accumulating records. For operational staff, monthly power generation calculations serve not only as forecasting materials but also as standards for operation and management.

In calculating power generation for residential solar PV systems, it is more important to keep revising the assumptions to match actual results than to produce a perfect forecast from the outset. By comparing calculated values with actual results and checking which assumptions were off, which losses were underestimated, and which months have characteristic factors, you can improve the accuracy of your next calculation. Monthly generation calculations can be used as a practical tool that links pre-installation estimates, post-installation inspections, customer explanations, and improvement proposals.

Summary for correctly interpreting monthly electricity generation of residential solar systems

To calculate the monthly electricity generation of a residential solar PV system, you need to organize not only the system capacity but also the local solar irradiance, installation orientation (azimuth), tilt angle, number of days in each month, seasonal variations, temperature losses, shading, soiling, snow, conversion losses, outage history, and the type of data. Simply dividing the annual generation by 12 does not adequately represent actual monthly variations. By reflecting the monthly solar irradiance conditions and loss factors, you can create a more realistic estimate of generation.

The first point is to ensure the preconditions are aligned before performing calculations. If you do not clarify the solar panel capacity, installation location, roof orientation, tilt angle, whether shading is present, and the purpose of the calculation, the meaning of the calculation results becomes ambiguous. The items that need to be checked vary depending on whether it is a pre-installation prediction, verification of existing equipment, or an investigation into the causes of reduced power generation. By clarifying the purpose of the calculation, you can separate parts that need to be examined in detail from those for which a rough estimate is sufficient.

The following point is to reflect monthly solar radiation and seasonal differences. While power generation often increases from spring through early summer, midsummer can see reduced output due to higher temperatures, and in winter you need to take into account shorter daylight hours, shading, and the effects of snowfall. Monthly generation figures include natural seasonal variations. If generation is lower in some months, do not immediately conclude there is an anomaly; it is important to compare the figures with the monthly solar radiation conditions.

The third point is to consider loss conditions separately by month. Some losses, such as conversion loss and wiring loss, are relatively constant and easy to treat throughout the year, while others—temperature, shading, soiling, snow accumulation, frost, shutdowns, and missing data—vary in their impact from month to month. In particular for residential systems, shading from nearby buildings and trees, partial soiling on the roof, and seasonal changes in household electricity use affect the way generation appears. In monthly calculations, rather than compressing these into a single loss rate, organizing them as factors for months when output is likely to be lower makes the approach more practical for real-world use.

The fourth point is to review the calculation conditions by comparing them with actual results. Calculated values are estimates based on standard conditions and may differ due to actual weather and on-site conditions. By checking not only the monthly total but also the daily average, day-by-day trends, the same month of the previous year, outage history, data gaps, and differences between self-consumption and electricity sold, it becomes easier to distinguish whether a reduction in generation is a natural variation or an anomaly that requires inspection. By reconciling calculations with actual performance every month, you can continuously monitor the condition of a residential solar system.

Monthly generation figures for residential solar power systems are useful not only for pre-installation estimates but also for post-installation operation and management. By knowing the expected generation for each month, when you feel output is low you can calmly check whether it’s due to weather, shading or dirt, or an equipment outage. Also, by looking at this alongside household electricity use, you can assess self-consumption and reconsider electricity usage. Calculating generation is not just number-crunching; it’s about creating benchmarks to keep the system operating stably and for a long time.

When practitioners explain monthly power generation, it is important to convey that "the calculated values are not fixed answers but a reference for verifying conditions." Solar power systems are influenced by natural conditions and will not produce the same output every month. For that reason, it is necessary to calculate on a monthly basis, compare with actual performance, and review the assumptions as needed. Even if generation is lower than expected, carefully breaking down the calculation assumptions will reveal the points that need to be checked.

Calculating residential solar power generation on a monthly basis makes it easier to understand seasonal generation trends, equipment condition, and the relationship with household lifestyles. If you want to continuously organize projected and actual generation or to conduct on-site inspections more efficiently, it is helpful to manage calculation results, actual data, site photographs, and inspection histories according to the same standards. By continuing to record monthly generation, you can more easily separate short-term weather-related fluctuations from ongoing declines, which in turn makes it easier to decide on inspections and improvements.