5 Weed Control Measures to Increase Power Generation｜How to Prevent Losses from Shading

Table of Contents

• Weed-control measures to increase power generation should begin with visualizing shadows

• Weed-control measure 1: Check the time periods when shadows appear using power generation data

• Weed-control measure 2: Manage the grass height in front of panels and at their lower edges

• Weed-control measure 3: Reduce the causes of shadows, including trees, vines, and fallen leaves

• Weed-control measure 4: Record locations of regrowth after weeding and use them for the next inspection

• Weed-control measure 5: Organize drainage, pathways, and areas around equipment to make management easier

• Points to check when power generation does not recover with weed control alone

• Summary

Weed Control to Increase Power Output Starts with Visualizing Shadows

When aiming to increase solar power generation, weed control is as important as panel cleaning and equipment inspections. Solar panels generate electricity by receiving sunlight, and even partial shading of a panel can reduce output. Unlike buildings or trees, weeds may seem temporary, but they can grow rapidly from spring to summer, casting shadows on the lower edges and faces of panels and causing reduced generation. The impact of weed shading should not be underestimated, especially at low-voltage solar farms where panels are installed close to the ground, on slopes, on former agricultural land, or at sites near forests.

For practitioners searching "how to increase power generation", it is important not to treat weed control as merely an aesthetic or site-management task. Weeds can lead to multiple problems, including reduced power generation, deterioration of inspection walkways, delays in cable inspections, poor ventilation around equipment, and an increased likelihood of pests and insects. Even if vegetation does not directly touch the panels, shadows lengthen during the morning and evening when the sun's elevation is low, so generation losses can occur to a greater extent than they appear. In other words, weed control is a maintenance task to protect power generation.

To reduce power generation losses caused by weeds, you first need to confirm when, where, and on which equipment shadows are falling. Even if you visit the site at noon and see no shadows and judge there is no problem, long shadows can extend across the front of the panels in the morning or evening. Even if there is no issue in early spring, grass height can suddenly increase around the rainy season and by summer grow to a level that affects power generation. Furthermore, not only grass but also vines, sasa (dwarf bamboo), shrubs, branches of surrounding trees, and accumulations of fallen leaves can combine so that simple mowing alone may not be sufficient to prevent a decrease in power generation.

A common pitfall in weed control aimed at increasing power output is a reactive approach of cutting grass whenever it grows. While this method can temporarily tidy the site, if you haven’t identified the times and locations where output drops, you may end up postponing the areas where work would be most effective. If you tidy the back of the aisles first—areas that have little impact on power generation—and leave the grass in front of the panels that actually cast shadows, it will be hard to achieve improvements in power output.

To increase power generation, weed control should be carried out by linking power generation data, on-site photographs, grass height, times of shading, and work history. If you record which rows have low power generation, at what times it drops, and in which areas grass tends to grow, it will be easier to determine the timing and priorities for future weeding. Below, we explain five weed control measures to implement on-site to prevent losses caused by shading.

Weed Control Measure 1: Check the times when shadows appear using power generation data

The first step in weed management is to review the power generation data before visiting the site. Visually checking whether weeds are growing is also important, but to assess their impact on generation you need to know when output is falling. If you only look at monthly or annual generation figures, you won't be able to tell during which time of day shadows from weeds are occurring. To increase generation, first check the generation curve on clear days and see whether output drops in the morning, at midday, or in the evening.

If the morning power output is low, grass, slopes, low shrubs, or surrounding terrain on the east or southeast side may be casting shadows. If it is low in the evening, check the grass, trees, and overgrown weeds along fences on the west or southwest side. If the midday peak doesn't reach expected levels, candidates include not only shadows from weeds but also dirt on the panel surfaces, equipment-side limitations, and temperature rise. Because shadows from vegetation are more likely to appear in the low sun angles of morning and evening, inspecting the site only during daytime can cause you to miss them.

Comparing installations under the same conditions is also effective. For rows with the same orientation, the same tilt, and a similar number of panels, if only a specific row has lower power generation, check whether grass is growing in front of that row. If the entire plant’s output is low, weather effects may be a factor, but if only some installations are low, on-site causes such as local shadows, dirt, or poor connections are suspected. For weed control, it is important to inspect the site focusing on the rows or installations with low power generation rather than relying on an overall impression.

When a possible shading issue is identified from the power generation data, we also adjust the on-site inspection time accordingly. If the drop occurs in the morning, take on-site photos in the morning; if it drops in the evening, check for evening shadows. Looking only at a noon condition with no shadows does not reveal losses in the morning and evening. Especially in summer, grass grows quickly and conditions can change within a few weeks. Even if there was no problem at the previous inspection, if the power generation curve changes on the next sunny day, it is necessary to recheck grass height and shadows.

To link weed control to improved power generation, it is important to keep power generation data and on-site photos together. If you record the time periods when power generation has decreased, the locations where shadows were observed, the height of the vegetation, and the positions of the affected equipment, you can compare how power generation changed before and after weeding. If the morning and evening dips improve after weeding, it becomes highly likely that shadows from the weeds were the main cause of the power loss at that site. Conversely, if there is no improvement after weeding, it is necessary to check for causes other than shadows.

Weed Control 2: Manage weed height in front of and at the lower edge of the panels

The most fundamental aspect of weed control is managing grass height in front of the panels and around their lower edges. When grass grows in front of a solar panel, shadows are more likely to be cast from the panel’s lower edge. Even if the grass does not touch the panel, shadows can extend farther when the sun is low in the sky, reducing power generation. This is especially true for installations where the panel’s lower edge is close to the ground; in such cases, even a small increase in grass height can cause shadowing.

In vegetation height management, it is important not to aim solely at mowing the entire site uniformly. Of course, tidying pathways and the overall site is important, but the areas that have the greatest impact on power generation are the front of the panels, the vicinity of the bottom edge, between rows, around equipment, and inspection walkways. If grass is growing in front of installations with reduced power output, prioritize measures in that area. Even if you tidy locations that are less likely to affect power generation first, improvements will be limited if shadows in front of the panels remain.

During grass-cutting work, care must be taken to avoid contact with cables and connection points. In areas with dense weeds, cables and conduits can be hidden and difficult to see. Working in such conditions increases the risk of accidentally damaging cables. Weed-control measures intended to increase power output must not create other power-generation problems. Before starting work, check the location of cables, the area around equipment, and under the mounting racks, and avoid attempting unsafe or unreasonable tasks.

Keeping vegetation short also relates to ventilation. If grass becomes overgrown under panels and around equipment, airflow can be impeded and heat may become trapped. While solar power generation tends to be easier under strong sunlight, higher temperatures can make it harder for output to increase. Even if weeds are not directly casting shadows, they can still affect power generation by causing poor ventilation and making inspections more difficult.

To continue managing grass height, it is important to record where grass tends to grow. If there are patterns—grass growing in the same spots every year, the same areas becoming dense after rain, or grass height rising mainly below slopes or where water accumulates—you can adjust future inspection timing and weeding areas. Weed control aimed at increasing power generation is not a one-time mowing task, but an operational approach to maintain grass heights that are less likely to cause generation losses.

Weed Control Measure 3: Reduce Sources of Shade, Including Trees, Vines, and Fallen Leaves

When it comes to weed control, attention tends to focus only on grasses growing from the ground, but to prevent a decrease in power generation you need to identify shading causes including trees, vines, bamboo grass, shrubs, and fallen leaves. Even if you cut the grass in front of the panels, if branches of surrounding trees extend they will cast shadows in the morning and evening and during winter. If vines wrap around fences or mounting racks, they become sources of shading that ordinary mowing cannot fully remove. If fallen leaves accumulate at the lower edge of the panels or in drainage flows, they can cause soiling and the regrowth of weeds.

Shading from trees is a factor that tends to become problematic during long-term operation. Even trees that had little effect at the time of installation can grow over several years and reduce power generation. Trees located on the south, east, and west sides, in particular, can cast shadows on solar panels depending on the time of day. At solar power plants near forests or slopes, the height of the terrain combined with tree height can create long shadows in winter. Even if issues are not obvious in summer, sites where power generation drops in winter need to check trees together with the terrain.

Vines are an easily overlooked cause of power generation loss. Because vines climb and spread by entangling fences, mounting racks, posts, and wiring, they can remain after simple mowing. If left unchecked, they can make cables and connection points hard to see during inspections, delaying the detection of abnormalities. Weed-control measures aimed at increasing power output should check not only the height of ground-level vegetation but also the condition of plants entangled in racks and fences.

Fallen leaves may land directly on the panel surface, or accumulate at the panel lower edge or in drainage paths, leading to soiling and the recurrence of weeds. Areas with heavy leaf fall can experience reduced power generation when combined with shading from nearby trees. If leaves stick to the panels or pile up at the lower edge, they can cause local shading or soiling that affects power generation. For rows with nearby trees, check branch overhang, leaf accumulation, wind direction, and rainwater flow together.

When reducing causes of shading, prioritize locations that have the greatest impact on power generation. Rather than perfectly tidying the entire site, prioritizing in front of and around equipment with low output, directions that cast shadows in the morning and evening, and rows where fallen leaves tend to accumulate is more likely to lead to improvements in power generation. After the work, record whether the shading has been eliminated, whether inspections have become easier, and where fallen leaves or vines are likely to recur.

Weed Control Measure 4: Record Locations of Regrowth After Weeding and Use Them for the Next Inspection

To increase power generation through weed control, it's important not to simply weed and be done, but to record locations that are prone to regrowth. Weeds will grow back even after being cut. In particular, areas where rainwater tends to accumulate, locations with good sunlight exposure, spots with soft soil, below slopes, along fences, in front of panels, and around equipment can repeatedly become overgrown in the same areas. To prevent reductions in power generation, rather than searching for the same problems from scratch each time, you need to identify these recurrence-prone locations as areas to be managed.

The items you should record are the locations where grass had grown, the times when shadows appeared, the equipment that was shaded, the extent of weeding, photos after weeding, and the period when reinspection is needed. If you link power generation data with on-site photos, it becomes easier to determine whether weeding improved power generation. If morning and evening power generation improves, it is more likely that shadows from grass or trees in that area were contributing to generation losses.

At sites with no records, every time the person in charge changes, the same locations have to be checked from scratch. In large power plants, because similar rows and equipment are lined up, it can be difficult to identify locations from photos alone. If equipment numbers, location information, photos, and work history are recorded together, it becomes easier to check the same location during the next inspection. Weed-control measures to increase power generation should not rely solely on experience; it is important to shift to reproducible record management.

Records kept after weeding also help determine the timing of maintenance. If grass grows in the same place at the same time every year, inspections can be scheduled before power output declines. If you can identify locations that grow rapidly around the rainy season, sites that repeatedly become overgrown in summer, and spots that tend to grow after rain, you can take proactive measures. Rather than scrambling to respond after power output has declined, it is more efficient in practice to manage before generation losses occur.

Recording is also useful when power generation does not improve after weeding. If the generation curve does not change after weeding, the main cause of the drop in output may not be weeds but other factors such as dirt, poor connections, shutdown of conversion equipment, temperature conditions, or output curtailment. By recording the results of the work, it becomes easier to narrow down which causes to check next. Weed control is both an initial step toward improving power generation and a basis for distinguishing other causes.

Weed Control Measure 5: Arrange drainage, walkways, and areas around equipment to make management easier

To prevent reductions in power generation caused by weeds, it is important not only to cut the weeds themselves but also to review environments where weeds easily grow and site conditions that make inspection difficult. Areas where water tends to accumulate, where sediment flows in, mud-prone pathways, at the base of slopes, along fences, and around equipment tend to be places where weeds recur. On sites with poor drainage or access, inspections and weeding work themselves tend to be delayed, and as a result power generation losses can be prolonged.

In areas where puddles remain after rain, grass tends to grow more easily. In spots where moisture lingers, weeds may regrow and become dense again in a short time after weeding. Furthermore, where sediment flows in, soil can accumulate under panels and around cables, causing dirt and damage. For weed control aimed at increasing power generation, it is important not only to cut the grass but also to check where water flows in, where it gathers, and where it drains out.

Keeping inspection pathways clear is also important. If grass grows and pathways become hard to distinguish, the efficiency of inspections and cleaning declines. In areas with mud or uneven ground, workers find it difficult to approach, which can delay the detection of abnormalities. Even if low-performing equipment is identified through data, if it is hard to reach the corresponding location on site, corrective measures will be delayed. Weed control is necessary not only for power generation but also to create sites that are easy to inspect.

Grass around equipment must not be overlooked. When grass grows densely around power conversion equipment and junction boxes, visual inspections can become difficult and ventilation may be impaired. If heat tends to build up around equipment, it can affect operating conditions. When weeds hide cables and connection points, detection of damage or abnormalities is delayed. From the perspectives of both improving power generation and safety management, it is important to keep the area around equipment clear, accessible, and well ventilated.

Measures to tidy drainage, walkways, and areas around equipment may not immediately appear as increases in power generation when implemented. However, in the long term they help reduce weed regrowth, the occurrence of shadows, delayed inspections, poor ventilation, and overlooked cable damage. To achieve stable increases in power generation, it is essential not only to cut grass but also to create a site environment where grass is less likely to grow and inspections are easier.

Points to Check When Power Output Does Not Recover with Weed Control Alone

If power generation does not sufficiently recover after weed control, you need to check for causes other than shading. The cause of reduced power output is not necessarily just weeds. Dirt on the panel surface, bird droppings and fallen leaves, faults at connection points, cable damage, inverter shutdowns, output curtailment, temperature increases, and poor drainage may be occurring simultaneously. Even if power output does not improve after weeding, do not assume that weed control was unnecessary; it is important to check for the possibility that other sources of generation loss remain.

The first thing to check is soiling on the panel surface. Even after cutting weeds and removing shadows, if a band of dirt remains along the bottom edge of the panels or bird droppings and fallen leaves are attached, power generation is unlikely to improve. In rows close to trees in particular, fallen leaves, sap, and bird droppings tend to accumulate, so weed control and cleaning need to be considered together. If the daytime peak in the power generation data does not increase, soiling or equipment-side factors should also be considered.

Next to check are abnormalities in the strings and connection points. If a particular string is underperforming compared with equipment under the same conditions, not only dirt or shading but also poor connections or cable damage may be involved. If power output becomes unstable after rain, suspect moisture ingress or the environment around the connections. When inspecting electrical equipment, prioritize safety: organize the affected equipment, the time the issue occurred, changes in power output, on-site photos, and the surrounding environment, and, if necessary, connect to a professional inspection.

It is also necessary to check for stoppages or output curtailment of conversion equipment. If the power generation curve suddenly drops midway, the upper part of the curve flattens out even on sunny days, or only the range connected to a particular device is low, check the equipment history. Even if weeds are controlled, if stoppages or restrictions remain on the equipment side, power output will not recover. Matching the time of the power drop with the equipment history makes it easier to isolate the cause.

Also, improving airflow by removing weeds alone may not fully eliminate temperature-related effects. If power output does not increase as expected on sunny summer days, check the panel temperature, the temperature around equipment, and the ventilation conditions. Weed control is important, but to raise power output you need to consider soiling, shading, connections, equipment, temperature, and drainage comprehensively.

Summary

In weed-control measures to increase power generation, the objective is not simply to cut the grass itself but to reduce generation losses caused by shading. In solar power generation, you cannot increase the incident solar radiation at the site itself. However, you can bring the system closer to a state in which the received sunlight is converted into electricity without waste. To do this, it is important to check generation data to identify the times when shading occurs, manage grass height in front of and at the lower edge of the panels, and reduce causes of shading including trees, vines, and fallen leaves.

To avoid failures in weed control, it's important not to judge based only on the site's appearance. Even if there are no shadows at noon, grass and tree shadows can extend long in the morning and evening. Even if there are no problems in early spring, grass can grow rapidly around the rainy season and by summer it may affect power output. Record installations with low power output, the times when shadows appear, and locations where grass tends to grow, and by comparing power output after weeding you can more easily assess the effectiveness of your measures.

Weed control is not something that can be completed with a single operation. Even if you remove weeds, grass will grow back, trees will continue to grow, and fallen leaves will accumulate seasonally. In places with poor drainage or where water tends to pool, weeds are more likely to recur. If inspection paths or areas around equipment become overgrown with vegetation, it also affects the detection of abnormalities and ventilation. To consistently increase power generation, operations must include not only mowing but also drainage, pathways, areas around equipment, and record management.

Especially at large power plants, a system for accurately sharing problem locations is important. If inspection photos are saved with location information for rows where grass grows easily, spots where shadows occur, weed-control areas, places where water accumulates, spots prone to vine entanglement, and areas where fallen leaves remain, stakeholders can more easily confirm the same locations. By combining power generation data with on-site location information, it becomes easier to explain the prioritization of weed control, pruning, cleaning, and repairs, and it also streamlines follow-up checks in subsequent inspections.

If you want to continue weed-control measures to increase power generation based on field data, using LRTK is also effective. LRTK, as an iPhone-mounted high-precision GNSS positioning device, is useful for recording, together with high-precision location information, areas within a solar power plant where weeds tend to grow, locations where shadows occur, weed-control coverage, poor drainage spots, areas around equipment, and on-site photographs. By keeping the results of weed-control measures with location information, you can continuously reduce losses due to shading and make it easier to improve power generation based on field data rather than on intuition.