The Price of Solar Power Plants and 8 Items to Check During On-site Surveys

When assessing the price of a solar power plant, if you judge it solely based on the documented power generation, gross yield, installed capacity, and terms of power sales, unexpected costs may arise after purchase or acquisition. In particular, when evaluating used solar power plants, completed projects, or projects under development, you need to verify assuming there may be discrepancies between desk materials and on-site conditions.

An on-site inspection is not simply a task of checking whether the equipment is clean. It is an important step to confirm whether the plant is worth the price, how much future repair costs can be expected, whether the assumptions behind power sales revenue are realistic, and whether there are any risks related to the land or surrounding environment. Even power plants that appear to have the same installed capacity can differ greatly in actual value depending on local topography, drainage, shading, racking, wiring, and the condition of maintenance.

This article organizes eight items that practitioners searching for "solar power plant price" should check during on-site surveys. Rather than the price itself, it focuses on the points of verification for judging the reasonableness of a price.

Table of Contents

• The price of a solar power plant can appear very different depending on an on-site survey

• Check the land's shape and development status

• Check drainage and rainwater flow

• Check sources of shading and their seasonal variation

• Check the condition of panels and mounting structures

• Check for degradation of wiring, junction boxes, and electrical equipment

• Check the condition of mowing, weed removal, and weed-prevention measures

• Check fences, access paths, and maintenance routes

• Compare measured data with on-site conditions

• How to incorporate on-site survey results into price assessment

• Summary

The price of a solar power plant can look very different after an on-site survey.

The price of a solar power plant is determined by multiple factors, including generation capacity, the feed-in tariff (selling price of electricity), remaining service life, past generation performance, operation and maintenance costs, equipment condition, and land conditions. Even if the documents make the conditions appear favorable, it is not uncommon for the assessment to change once the site is inspected.

For example, even projects that appear to have stable power generation may, upon on-site inspection, have shadowing on some panel rows, drainage problems that have degraded the ground, or scour around the bases of the mounting racks. Such conditions may not immediately appear as major losses, but they can become factors in future repair costs and reductions in power generation.

Also, seller or broker documentation often focuses on installed capacity and annual power generation, and does not allow the on-site management condition to be fully discerned. Even if photos are attached, because the time they were taken and their coverage are limited, they are insufficient to assess the risks for the entire power plant. In particular, problems that are difficult to see from documentation alone can surface during periods when grass grows, in rainy seasons, or in winter when the sun’s incidence angle is low.

During on-site inspections, rather than nitpicking to lower the price, it is important to concretize the operational risks expected after acquisition. Even if equipment has deteriorated, as long as a repair plan can be drawn up, it can be factored into the investment decision. Conversely, a deal that looks inexpensive on paper may effectively become an expensive purchase if significant renovation risks are confirmed on site.

When assessing the price of a solar power plant, you should evaluate the plant not only as "equipment" but as a business asset that encompasses "land", "electrical equipment", "operation and maintenance", "the surrounding environment", and "future risks". Therefore, during on-site surveys it is essential to assess it from a broad perspective.

1. Confirm the shape and development status of the land

The first thing to check is the site's topography and development status. Solar power plants are outdoor installations, and the condition of the land directly affects power generation, operation and maintenance costs, and disaster risk. Even with the same installed capacity, the long-term operational burden differs greatly between flat, easy-to-manage land and land with many slopes and level differences.

On site, check the overall tilt of the power plant, the stability of the graded surfaces, the condition of fills and cuts, the state of slopes, and whether there is any ground subsidence or cracking. Even if problems are hard to see immediately after grading, rainwater flow and weak ground conditions can become apparent over time. In particular, if there are unnatural steps or offsets beneath panel rows or around racking foundations, the ground may be shifting.

The shape of the land is an aspect that is unlikely to be directly reflected in the price of a power plant. However, because it affects repairs and maintenance after acquisition, it is extremely important in practical evaluations. On sloped land, mowing becomes more labor-intensive, and access by heavy machinery and service vehicles can be restricted. Where there are many slopes, management to prevent collapse and erosion is also necessary. At power plants with poor site development, even if the equipment itself has no problems, land-related repairs may occur continuously.

It is also necessary to check the land boundaries and the elevation differences with adjacent land. If the terrain allows rainwater or sediment to flow in from adjacent land, the power plant may need to take countermeasures. Conversely, if rainwater or sediment is flowing out from the power plant onto neighboring land, it could lead to disputes with neighbors. This is an important risk that cannot be judged from the documented power generation figures alone.

During on-site surveys, it is useful not only to walk through the power plant to get a feel for the overall slope, but, if possible, to record location and elevation information so that changes to the graded surface can be tracked. By objectively documenting the condition of the land, it becomes easier later to organize the scope of repairs and the conditions for estimates.

2. Check drainage and rainwater flow

Drainage and rainwater flow are often overlooked during on-site surveys of solar power plants. Even if the site appears problem-free when inspected in fair weather, after rain you may find puddles, mud, soil erosion, and clogged drainage channels. Poor drainage not only causes land degradation but also poses long-term risks to racking and electrical equipment.

What you need to check is where rainwater enters, where it flows through, and where it exits. Inspect the drainage channels, side ditches, catch basins, the base of slopes, and areas near entrances and exits within the power plant to confirm that water flow is being handled naturally. If drainage channels are clogged with sediment or vegetation, even if there is no major short-term problem, heavy rain can cause water to overflow.

Areas beneath panels where puddles readily form lead to excessive vegetation growth and weakening of the ground. If the wet conditions persist, not only does workability deteriorate, but the soil around the mounting foundations may wash away and protection around cables may become insufficient. Also, if only certain parts of the plant are constantly muddy, insufficient compaction during site preparation or flaws in the drainage design should be suspected.

Poor drainage does not necessarily become immediately apparent as a decrease in power generation. Therefore, it tends to be underestimated in price assessments. However, when long-term ownership is assumed, poor drainage becomes a factor that increases operation and maintenance costs. Because it may require reconditioning of drainage channels, sediment removal, slope repairs, and reinforcement of access routes, on-site inspection is indispensable.

Also, the surrounding environment is important. If there are forests, farmland, roads, or developed land upstream of the power plant, the amount of water flowing in from outside can increase. If the land use of neighboring properties changes, the flow of rainwater may also change. During on-site surveys, it is important to check not only the power plant site but also the surrounding topography and drainage outlets.

If possible, being able to check photos not only of sunny conditions but also of the post-rain condition makes it easier to judge whether the price is reasonable. Even if confirming the post-rain condition is difficult, you can infer the flow of water from traces of sediment accumulation, how the grass has been flattened, scouring of the ground, and the amount of mud in the drainage channels.

3. Confirm the sources of shadows and seasonal variations

Shading is a major factor that significantly affects the power generation of a solar power plant. During on-site surveys, it is necessary to anticipate not only the shadows that are currently visible but also those that occur depending on the season and time of day. In particular, because the solar altitude is lower in winter, shadows from trees, utility poles, buildings, slopes, and adjacent equipment that are not a problem in summer can affect power generation.

On site, potential sources of shading are checked, focusing on the east, south, and west sides of the property. If trees are nearby, it is necessary to consider not only their current height but also their future growth. If woodlands or bamboo groves adjoin the site, the extent of shading may expand in a few years. If there is a possibility that buildings or structures could be erected on adjacent land, that should also be considered a future risk.

Shading between panels is also important. In solar power plants with narrow row spacing, shadows from the front row may fall on the rear row during winter mornings and evenings. Even if the layout diagrams look tidy on paper, the way shadows fall can change depending on the site's slope and the racking height. Especially on sloped sites, it is difficult to judge actual shading from drawings alone, so on-site verification is important.

The impact of shading cannot be judged simply by the area that is shaded. Shading on some panels can affect the power generation of other panels connected to the same circuit. Therefore, it is desirable to check both where shading occurs and how the electrical grouping is configured. Even if you cannot fully confirm the circuit configuration on site, recording the locations of shading allows you to cross-check them with documentation later.

When evaluating the price of a solar power plant, it's dangerous to assume shading is not a problem just because there are past generation records. Past records may already include the effects of shading, but tree growth and changes in the surrounding environment could increase shading impacts in the future. Especially for used projects, it is necessary to assess the risk of shading with the remaining service life in mind.

During on-site surveys, it is important to record the sources of shadows, the rows of panels that are shaded, the times of day, and potential seasonal variations so they can be compared with power generation simulations and actual performance data.

4. Check the condition of the panels and mounting structures

When evaluating the price of a solar power plant, the condition of the panels and mounting structures is a basic item to check. The panels are the central equipment of the plant, and the mounting structures support its power-generating performance. If either shows deterioration or defects, it can lead to reduced power output, repair costs, and decreased safety.

For panels, inspect for cracks, chips, surface dirt, discoloration, burn marks, frame distortion, loosened fasteners, and the like. Large surface cracks are easy to spot, but fine hairline cracks and internal deterioration can be difficult to assess by visual inspection alone. Therefore, on site it is practical to first record any visible abnormalities and, if necessary, follow up with more detailed inspections.

Soiling on the panel surface is also important. If sand and dust, bird droppings, fallen leaves, pollen, or dirt originating from agricultural land adhere to the panels, they can affect power generation. It is necessary to determine whether the soiling is temporary or the result of an environment where it occurs continuously. If there are nearby fields, unpaved roads, forests, factories, or places where birds tend to gather, this will also affect cleaning frequency and maintenance costs.

For the mounting structure, inspect the posts, beams, fasteners, bolts, and foundation. The basics are to look for rust, corrosion, deformation, looseness, and tilting. Corrosion is particularly likely to progress in areas close to the ground or where water tends to collect. In coastal areas, snowy regions, and high-wind areas, the loads on the mounting structure are also greater, so inspections should be carried out more carefully than usual.

Tilt or unevenness of the mounting racks is not just a cosmetic issue. Uneven panel angles can affect power output. Also, if there is structural instability, the risks increase during strong winds or heavy snowfall. If obvious tilt is observed on site, it is necessary to determine whether it originated during installation or is due to ground settlement or foundation movement.

The condition of the panels and mounting structures directly affects price negotiations and repair planning at the time of sale. However, rather than judging a site to be a bad deal simply because there is degradation, it is important to separate and organize the extent of the degradation, its causes, the ease of repair, and the impact on power generation. Localized defects may be addressable, but when widespread structural deterioration or installation defects are suspected, careful judgment is required.

5. Check for deterioration of wiring, junction boxes, and electrical equipment

During on-site inspections of solar power plants, attention tends to focus on the panels and the land, but checking wiring and electrical equipment is also extremely important. Deterioration of electrical equipment can lead to power generation stoppages, malfunctions, fire risk, and increased repair costs. Because many issues are difficult to detect from appearance alone, it is important to carefully inspect all areas that can be checked on site.

For wiring, check for damage to cable sheathing, sagging, contact with the ground, damage to protective conduits, and deterioration of fasteners. If a cable is in contact with the ground, there is a risk it will be damaged during grass cutting. If protective conduits are cracked or connections are exposed, they become more susceptible to rainwater and ultraviolet exposure. Even small defects can lead to major failures over the long term.

In junction boxes and collector equipment, check for rust on the outer enclosure, the condition of door closures, deterioration of gaskets, signs of moisture ingress into the interior, and traces of insects or small animals entering. Equipment installed outdoors is exposed to temperature changes, humidity, wind and rain, and ultraviolet light. If watertightness or airtightness is reduced, internal components may deteriorate.

We also inspect conversion and monitoring equipment for exterior condition, installation environment, ventilation status, abnormal noises, display anomalies, and accumulation of grass or dust around the equipment. If grass is overgrown around the equipment, it can lead to poor ventilation or insect intrusion. In environments prone to high temperatures, the equipment’s lifespan may also be affected.

Electrical equipment faults can appear as intermittent declines in power generation performance. However, monthly data alone often cannot identify the cause, so it is necessary to assess the situation together with on-site inspections of equipment condition. If there are past shutdowns or repair records, their details should be checked against the current on-site condition. Even if repairs have been completed, a future risk remains if the environment that allowed the same cause to recur still exists.

When assessing the price of a solar power plant, the condition of the electrical equipment is extremely important. If replacement or repairs become necessary, there may be periods of power generation downtime. You need to consider not only the repair costs but also the opportunity loss during that time. During on-site inspections, even if specialized measurements are not performed, carefully recording any abnormalities that can be confirmed by visual inspection will lead to more detailed investigations later.

6. Check the status of mowing, weeding, and weed-control measures

One of the recurring tasks in the operation and maintenance of solar power plants is mowing and weeding. During on-site inspections, it is necessary to check not only the current condition of the vegetation but also the frequency of maintenance, whether weed-control measures are in place, and how easy the work is to perform. The state of vegetation management affects power generation, equipment degradation, worker safety, and operation and maintenance costs.

If grass grows up to the front of the panels, a reduction in power generation due to shading may occur. This is especially true for panels installed at low positions, where even a small amount of grass growth can cause shading. Even if the reported generation looks good on paper, if it cannot be maintained without increasing the frequency of mowing, the management burden will be large.

Ease of mowing is also important. Conditions such as narrow spacing between panel rows, steep slopes, ground that easily becomes muddy, many rocks or obstacles, or difficulty accessing under the racks reduce work efficiency. If working time increases, maintenance costs and safety risks also rise. On site, check whether there is sufficient room for workers to move, whether mowers can be used easily, and whether work under the racks can be performed.

Even when measures such as weed-control sheets or crushed stone are in place, it is necessary to check their condition. If the weed-control sheet is torn, lifted, not properly secured, or grass is growing through gaps in the sheet, repairs are necessary. Even if weed-prevention measures have been implemented, if the treated area is limited, regular mowing will still be required.

Also, it is useful to check the types of grass. If there are many fast-growing grasses, climbing plants, woody weeds, or plants with bamboo-like characteristics, the maintenance burden can become heavier. If, in addition to grass, tree seedlings are increasing, this may lead to shade and root problems in a few years.

The condition of mowing and weed control tends to be overlooked when assessing the price of a power plant. However, because these are recurring annual maintenance items over the long term, they affect actual profitability. During on-site inspections, it is important not only to check whether the site looks tidy now but also to consider how much effort will be required to maintain that condition.

7. Check fences, pathways, and maintenance access routes

Solar power plants are facilities that require ongoing maintenance and inspections over the long term. Therefore, the condition of fences, entry points, pathways, and maintenance access routes is an important item to verify when assessing price. Even if the power generation equipment itself is in good condition, a site that is difficult to maintain can lead to reduced inspection quality or increased labor costs.

For fences, check for damage, leaning, rust, gaps, and whether gates are locked. If a fence is damaged, there is a risk of people or animals entering. Animal intrusion can lead to cable damage, digging up of the ground, and dirt around equipment. Also, in areas at risk of intrusion by suspicious persons, there are concerns about theft and vandalism.

The condition of the entrances and exits is also important. Check whether vehicles can enter safely, whether the ground becomes muddy in rainy weather, and whether there are any problems with the opening and closing of gates. At power plants where inspection and repair vehicles cannot enter, extra effort is required for each operation. If replacement of large components becomes necessary, restricted delivery routes can make the repair plan itself difficult.

Walkways within a power plant are involved in patrol inspections, mowing, equipment replacement, and emergency response. If walkways are narrow, have many steps, are prone to becoming muddy, or are overgrown with vegetation, inspection efficiency decreases. In particularly large power plants, poor maintenance routing makes missed inspections more likely. If abnormalities are not detected early, failures can persist longer and may lead to generation losses.

When assessing maintenance access routes, it is important to consider not only routine inspections but also responses during failures and after disasters. Consider which routes will be used for on-site inspections and which pieces of equipment will be difficult to approach after typhoons, heavy rain, snowfall, or earthquakes. Even if there are no problems under normal conditions, a power plant that cannot be accessed after severe weather is assessed as having a low ability to respond to risks.

The price of a solar power plant may not fully reflect how easy it is to manage. By checking not only the apparent condition of the equipment but also whether the site is easy to use as a location for ongoing operation and maintenance, you can make a more realistic assessment.

8. Cross-check measured data with on-site conditions

It is important to always cross-check what was confirmed during a site survey with measured data and past records. Judging only by impressions seen on site tends to lead to a subjective evaluation. Conversely, judging solely by data can result in overlooking on-site risks. To appropriately assess the price of a solar power plant, you need to consider the site conditions together with the data.

The data to be checked include historical power generation, solar irradiance, equipment outage history, inspection reports, repair history, and anomaly notification history. If there is a month with low generation, it is necessary to distinguish whether this is due to weather, equipment outages, or the effects of shading or vegetation. If on-site inspections confirm overgrown vegetation or shading, check whether there is a downward trend in power generation during that period.

Variation in power generation is also important. Even if the annual generation appears to be fine, there can be unnatural drops when viewed on a monthly or daily basis. If generation falls only during specific time periods, shading or faults in some equipment may be involved. Confirming the sources of shading during an on-site survey makes it easier to link observed declines in the data and make a judgment.

Cross-checking with the repair history is also essential. If the same equipment has experienced multiple failures in the past, the issue may not be a one-off malfunction but could be caused by design, construction, or environmental conditions. If insufficient wiring protection or poor drainage is found on-site, it is necessary to verify the connection to the failure history.

Even if there is an inspection report, it is important to reconfirm the situation through an on-site survey. If the report was produced a long time ago, conditions may have changed since then. In particular, vegetation, drainage, fences, corrosion of mounting racks, and growth of surrounding trees change over time. If you do not grasp the latest on-site conditions, the assumptions behind price assessments will be off.

It is useful to organize the results of on-site inspections with photos, location information, notes, and simple drawings. If you record where and what kind of abnormalities are present, it will be easier to discuss them later with the seller, the management company, the contractor, and internal stakeholders. It is important not to leave the survey results with a vague impression, but to organize them as information that can be used for pricing decisions.

How to Reflect On-Site Survey Results in Pricing Decisions

When problems are found during an on-site survey, how to reflect them in pricing decisions is a crucial practical point. Rather than simply deciding "avoid it because there's a problem," you need to separately classify and organize the type of problem, its scope, urgency, repairability, impact on power generation, and future management burden.

First, issues that could immediately cause power generation to stop or affect safety are high-priority items. Damage to electrical equipment, major deformation of mounting structures, significant damage to fences, and impacts on equipment due to poor drainage should have the response policy confirmed before acquisition. If repairs are necessary, it is important to clarify who will be responsible, whether they will be corrected before acquisition, or whether the buyer will address them after acquisition.

Next, we organize the issues that affect power generation. Shading, vegetation, dirt, partial panel malfunctions, and records of equipment downtime directly affect profitability. We separate whether these effects are already included in past generation performance and whether they may worsen going forward. Even if past performance has been good, care should be taken if growth of surrounding trees or deterioration in maintenance could cause generation to decline in the future.

Additionally, evaluate items that affect maintenance costs. Difficult-to-mow terrain, the propensity of drainage channels to clog, poor pathways, and inconvenient access all add to the annual maintenance burden. Because these factors squeeze revenue over the long term rather than representing a single large expense, it is important not to overlook them when judging the reasonableness of a price.

It is more practical for day-to-day work to organize the results of on-site surveys, as much as possible, into "items to confirm", "anticipated risks", "additional investigations required", and "conditions to verify before signing the contract". You do not need to reach final conclusions on everything on the spot. What is important is to clarify points that were not apparent from the documents alone and to incorporate them into the assumptions underlying pricing decisions.

Solar power plants are assets intended for long-term operation. Even if they appear slightly cheaper at the time of purchase, they can become more expensive when future repair costs and declines in power generation are taken into account. Conversely, even if minor issues are found on site, a project may still be worth considering if the management condition is understood and a repair plan can be easily developed. On-site inspections are conducted not to make subjective judgments of good or bad, but to visualize the actual risks relative to the price.

Summary

When assessing the price of a solar power plant, it is essential not only to consider the generation capacity and past performance shown in the documents, but also to verify the actual conditions through an on-site survey. By checking the land shape, drainage, shading, panels, mounting structures, wiring, weed control, fencing, maintenance access routes, and cross-checking against measured data, you can identify which risks are included in the price and which are not.

What matters in an on-site survey is not simply finding problems, but judging how much those problems will affect power generation, repair costs, operation and maintenance costs, safety, and future operations. Even a power plant that looks visually clean may have issues with drainage or shading. Conversely, if some deterioration is observed but its scope is limited and a management plan can be developed, it may still be possible to assess it reasonably.

In practical operations, it is important not to leave on-site observations as just photos and notes, but to record them together with location information so they can later be cross-checked against documents and power generation data. If you can accurately record which panel rows are shaded, where water tends to accumulate, and which walkways are difficult to use, that information can be used for internal briefings, pre-contract checks, repair estimates, and maintenance planning.

To improve the accuracy of on-site surveys, a positioning environment that can accurately record inspection points within a power plant is helpful. LRTK, as a GNSS high-precision positioning device that can be attached to and used with a smartphone, makes it easier to record on-site inspection locations with high accuracy. In on-site surveys to determine the price of a solar power plant, linking photos, inspection notes, and location information allows the survey results to serve as more objective grounds for judgment.