7 checks before comparing construction costs of solar power plants

When comparing construction costs for solar power plants, judging only by the total amount on the estimate can cause you to misjudge the final cost, as additional work or changes in conditions may arise later. This is especially true for industrial solar power plants, where many factors affect costs, including land conditions, whether site development is required, the conditions of racking, foundations, and piling, the scope of electrical work, tasks related to grid interconnection, surveying and design, inspection handling, and operation and maintenance after construction.

To appropriately compare construction costs, it is important to first verify not only the total amount but also what is and is not included. Even if work appears to be for the same solar power plant construction, the significance of the cost changes depending on the terms of the estimate. This article explains seven checks practitioners should make before comparing construction costs.

Table of Contents

• For construction costs, confirming the assumptions is more important than the total amount

• Check 1: Verify that the scope of work is consistent under the same conditions

• Check 2: Verify the site conditions and the assumptions for site development and grading

• Check 3: Verify the conditions for mounting structures, foundations, and pile work

• Check 4: Verify the scope of electrical work and grid connection

• Check 5: Confirm how design, surveying, permit applications, and inspection handling are managed

• Check 6: Verify the assumptions for schedule, safety management, and delivery planning

• Check 7: Verify the conditions under which additional costs may occur

• Compare with an eye toward post-construction operation

• Summary

For construction costs, verifying the assumptions is more important than the total amount

When comparing construction costs for solar power plants, many project managers first look at the total amount on the estimate. Of course, the total is important, but when comparing construction costs the total figure alone is not sufficient as a basis for judgment. This is because the scope of work and the assumptions included in estimates can vary from contractor to contractor.

Some estimates include site development and grading, while others treat them as separate items. Even if one estimate covers surveying and responses to design changes, another may require additional billing after on-site verification. The required work for electrical construction also varies depending on whether it is limited to wiring on the generation-equipment side or whether it also includes work on receiving/transforming equipment and grid-connection-related tasks.

Before comparing construction costs, it is important to align each company's estimates so they can be reviewed under the same conditions. Before judging the relative sizes of the estimates, you should first clarify the scope of work, site conditions, whether supplied items are included, design assumptions, schedule conditions, inspection arrangements, and the scope of post-construction responsibilities. If you compare prices when conditions are not aligned, choosing the option that appears cheaper may lead to additional costs or rework.

Also, construction costs for solar power plants are a field where differences by site easily appear. On flat land that is easy to access for deliveries versus land with slopes and mud where heavy machinery cannot operate effectively, the construction difficulty changes even for the same generation capacity. If ground conditions differ, the considerations for piles and foundations also change. Construction planning also varies depending on the width of surrounding roads, securing material storage areas, responses to neighboring residents, and the need for safety measures.

Therefore, before comparing construction costs, you must not simply line up the estimates; it is essential to break down and verify the conditions of each estimate. Rather than focusing only on the lowest bid, it is important to determine how much responsibility will be assumed for that price and to what extent the contractor can address the risks anticipated on site.

Solar power plants are facilities intended for long-term operation after completion. If checks during the initial construction phase are insufficient, this can lead to operational problems such as poor drainage, inaccuracies in mounting structure installation, insufficient cable protection, and reduced ease of inspection. Comparing construction costs is not merely a comparison of initial expenses but also a decision to safeguard stable operation in the future.

Check 1: Verify that the scope of work is consistent under the same conditions

The first thing to check is the scope of work included in the estimate. Installation costs for a solar power plant include various elements such as site development, surveying, foundations, racking, panel installation, electrical wiring, grounding work, substation and transformer equipment, fencing, gates, monitoring equipment, commissioning, and inspection support. What is included in the construction costs depends on how the estimate is prepared.

Before comparing quotes, first review each company's estimate and confirm whether the scope of work is the same. For example, one estimate may include fences and gates while another does not. One estimate may cover material transportation and unloading, while another assumes delivery to the site. If you overlook these differences, you cannot accurately compare bids based on the total amount alone.

Particular attention should be paid to items listed as "one set" on an estimate. The "one set" notation itself is not necessarily a problem, but if the contents are unclear, it becomes difficult to compare. Even if the estimate says "panel installation — one set," "electrical work — one set," or "support-frame work — one set," you need to confirm which tasks are included. The actual amount of work changes depending on whether it only covers assembly of components, includes layout marking and position setting, covers adjustment work, or even includes site cleanup and tidying.

Also, the division between materials supplied by the owner and materials procured by the contractor is important. Unless it is clearly defined who procures and who stores materials—such as solar panels, mounting racks, cables, junction boxes, and monitoring equipment—and who performs the initial response in case of a defect, responsibilities on site will become unclear. If supplied items arrive late or quantities are insufficient, handling of schedule delays or additional work can also become problematic.

When confirming the scope of work, you must not overlook ancillary tasks that are likely to arise on site. Temporary access roads, temporary fencing, material storage areas, temporary power, temporary toilets, site office space, traffic control, and neighbor briefings or notifications may be required depending on site conditions. Confirming whether these are included in the estimate or require separate negotiation will make unexpected adjustments less likely to occur later.

Before comparing construction costs, it is important to break down estimates by work item and clarify which tasks are included and which are not. Rather than simply choosing the lowest total estimate, check whether any necessary work has been omitted and whether tasks that will be required on site are realistically reflected. An estimate with a clear scope of work reduces misunderstandings after awarding the contract and makes schedule management and quality control easier.

Check 2: Verify site conditions and assumptions for site preparation and grading

Construction costs for solar power plants are determined by site conditions. Even when the scale of the power generation equipment is the same, the work required varies depending on the shape of the land, soil conditions, elevation differences, drainage conditions, access roads, and the surrounding environment. Therefore, before comparing construction costs, you need to confirm what site conditions each estimate is based on.

First, I want to confirm how much site development and grading are included. At solar power plants, to install panels securely and make maintenance and inspections easier, it may be necessary to level surface irregularities, perform tree felling, stump removal, topsoil treatment, drainage work, and slope stabilization measures. Whether these are included in the construction cost or handled as separate site development work will affect the meaning of the estimate.

Even if land appears flat at first glance, there may actually be subtle elevation changes or areas prone to standing water. Locations that tend to become muddy after rain can affect the movement of heavy machinery and the delivery of materials. If the drainage outlet is unclear, the risk of water pooling and soil runoff can remain not only during construction but also after completion. Comparing construction costs without checking these site conditions can lead to additional drainage or ground-improvement measures being required later.

The conditions of the access route are also important. Confirm whether large vehicles or heavy machinery can access the site, whether the road width is sufficient, whether there are problems with turning radii or gradients, and whether deliveries will affect neighboring properties. On sites with poor access conditions, it may be necessary to transport materials in smaller loads, and short transfers from the unloading point to the installation location may increase. Because these relate to construction labor and effort, they should be documented as assumptions for cost comparisons.

When confirming earthworks and grading, it is also necessary to check the design elevations and slopes. At solar power plants, the layout must be determined not only with power generation in mind but also considering drainage, ease of maintenance and inspection, and the stability of the mounting structures. If the site's elevation differences are ignored when deciding the layout, adjustments to racking heights may increase, inspection walkways may become difficult to use, and rainwater may concentrate in specific locations.

Also, confirming site conditions affects the accuracy of the on-site survey. Whether a site check was carried out before preparing the estimate or the estimate was created only from drawings and photos will change the estimate’s reliability. Estimates with insufficient on-site investigation may seem reasonable at the initial stage but are more likely to encounter condition changes after construction begins. If possible, it is reassuring to confirm whether a site check was performed, the scope that was checked, and the assumed soil and drainage conditions.

Before comparing construction costs, confirm that site conditions are correctly reflected in the estimates. Estimates prepared after a careful on-site inspection tend to make the basis for the price clearer and reduce the likelihood of problems after placing the order.

Check 3: Confirm conditions for racks, foundations, and piling work

The areas of a solar power plant installation where construction costs tend to vary most are the mounting structures, foundations, and piling work. To support solar panels stably over the long term, a structure suited to the ground conditions, approach to wind loads, slope, installation angle, and layout conditions is required. If these aspects are not thoroughly checked and costs are compared alone, it can lead to post-construction defects or the need for repairs.

The first thing to confirm is whether the foundation type and pile specifications are clearly defined. The appropriate approach varies by site—driving piles into the ground, using concrete foundations, or adjusting methods to suit the terrain and conditions. In the estimate, it is important to verify the number of piles, their lengths, the installation method, the support conditions, the approach to pull-out resistance, and whether ground verification has been performed.

What requires particular attention is how ground investigations and trial construction are handled. If piling work proceeds while the condition of the ground and subsurface is unknown, poor placement, tilting, insufficient bearing capacity, and rework during construction can occur. Confirming whether the estimate includes ground checks and trial construction, or whether these will be handled separately as needed, makes it easier to grasp the risks during construction.

In racking installation, not only the assembly of components but also the accuracy of installation positions, tilt adjustments, alignment between rows, the height of the panel surface, and the relationship with inspection walkways are important. If the racks are not arranged according to the drawings, panel installation may require forced adjustments, cable routing can become more complex, and the appearance and ability to inspect after completion can be affected. When comparing construction costs, be sure to check whether the racking installation includes setting-out (positioning) and adjustment work.

On sloped or irregular sites, the difficulty of racking, foundation, and piling work increases. There are factors that increase construction effort, such as pile-driving depth varying by location, increased adjustments to racking heights, restricted working ranges for heavy machinery, and greater difficulty ensuring worker safety. An estimate based on flat land will differ in scope from an estimate that accounts for slopes and elevation differences, even for the same power generation capacity.

Post-installation maintenance is also influenced by the racking conditions. If the height above the ground is insufficient, mowing and inspection work can become difficult. If cables are too close to the ground, they may be more susceptible to weeds, small animals, and drainage. If you prioritize only minimizing construction costs, you may end up with a power plant that is difficult to maintain later.

When comparing estimates for mounting structures, foundations, and piling work, it is important to look not only at the materials and quantities but also at the approach to site conditions, accuracy control, construction inspections, and how rework would be handled. If the contents of the estimate are clear, it becomes easier to compare costs while ensuring construction quality.

Check 4: Confirm the scope of electrical work and grid interconnection

When comparing construction costs for solar power plants, confirming the scope of electrical work is important. A solar power plant is not a facility that is completed merely by arranging panels. Various electrical works are necessary to safely collect and convert the generated electricity and to make it ready for interconnection through the required equipment.

In the quotation, check how far it covers items such as DC-side wiring, AC-side wiring, junction boxes and collection equipment, grounding work, connection to power receiving and transformation equipment, installation of monitoring devices, communication wiring, and testing and commissioning. Even if it says “electrical work (all-inclusive)”, the scope of the work changes depending on whether that covers only the generation-side equipment, extends to the point of interconnection, or includes monitoring and communications.

Particularly easy to overlook are the wiring routes and the approach to cable protection. In solar power plants, cables can run long distances, so it is necessary to properly plan underground conduits, racks, protective conduits, the treatment of riser sections, and methods of securing cables. If the wiring route is unclear in an estimate, route changes may occur on site or additional protective materials may be required.

Grounding work is also important. It relates to safety and equipment protection, and construction methods and verification tasks may vary depending on the site's ground conditions. Checking whether the estimate includes installation of grounding electrodes, measurements, recordkeeping, and any necessary adjustments can help prevent rework during inspections or at handover.

When it comes to grid interconnection, it is necessary to confirm the scope of coordination with general transmission and distribution utility operators and other stakeholders. Actual interconnection conditions, work classifications, whether outage work is required, test schedules, and the scope of on-site attendance vary depending on the project. If it is not clarified how far the contractor will be involved in coordination and which parts the client will handle, project schedule management becomes difficult.

Also, construction work related to monitoring and communications within a power plant is another item where estimates tend to vary. If the installation locations for monitoring devices, preparation of communication lines, wiring methods, ensuring power supply, testing procedures, and so on are ambiguous, it can lead to problems after completion such as unstable monitoring, inability to obtain data, and lengthy investigations into the causes. When comparing construction costs, you need to confirm whether the scope includes not only making the generation equipment operational but also bringing it to a state where the information required for operation can be verified.

Electrical work includes many parts that become difficult to see after completion, so checks at the estimating stage are important. By confirming that no necessary tasks are omitted—from wiring, grounding, protection, and testing to interconnection and monitoring—you can more easily assess the reasonableness of the price and the ease of post-construction management.

Check 5: Confirm how design, surveying, permit applications, and inspection responses are handled

When comparing construction costs for solar power plants, people often focus only on the on-site construction labor costs. However, in reality, pre- and post-construction tasks such as design, surveying, permit applications, and inspection handling also affect the plant’s quality and schedule. If how these items are treated remains unclear in the estimate, additional work may be needed later, causing cost and time forecasts to be off.

First, what I want to confirm is the scope of the design services. Clarify who will prepare and who will check the drawings and documents required for construction, such as layout drawings, single-line wiring diagrams, cable routes, mounting/rack layouts, foundation locations, drainage plans, inspection access ways, and safety measures. It is also important to clarify how design changes will be handled. When it becomes necessary to adjust the layout to suit site conditions, confirm whether those revisions are included in the estimate or treated as separate items.

Surveying is another item that should be checked before comparing construction costs. For solar power plants, it is necessary to accurately determine site boundaries, installation areas, elevation differences, pile locations, racking positions, and equipment layout. Insufficient surveying accuracy can lead to misplacement of installations, interference with boundaries, inconsistencies in drainage planning, insufficient inspection walkways, and other issues. Make sure to confirm whether surveying is included in the estimate, whether existing drawings are being assumed, or whether a recheck will be performed on site.

Tasks related to applications and notifications also vary in scope depending on the project. For solar power plants, confirmations and procedures may be required depending on equipment scale, installation location, interconnection conditions, local ordinances, and how relevant authorities handle matters. It is important to clarify which procedures the contractor will support, which the project owner will handle, and whether engaging a specialist is necessary. If application-related work is not included in the estimate, it may affect the project schedule.

In inspection procedures, items checked include the completion inspection, insulation verification, grounding verification, pre-energization checks, test runs, preparation of record documents, organizing photographs, corrective actions, and so on. If the materials required for inspection are insufficient, handover may be delayed or re-inspection may be necessary. When comparing construction costs, it is important to check not only whether the work is simply completed but whether the price includes bringing the project to a condition that can be handed over after passing inspection.

Organizing as-built drawings and construction records is also important. For maintenance inspections after completion, you need documents that allow you to verify what was installed where, which routes the wiring follows, and what the test results were. If the records from construction are insufficient, additional investigations may be required during future inspections or repairs.

Design, surveying, permit applications, and inspection support are items that may not stand out on an estimate, but they are an important part of supporting the quality and operability of a power plant. Before comparing construction costs, confirm how much of these services are included, whether the scope of responsibility is clear, and what deliverables will remain.

Check 6: Confirm the assumptions for scheduling, safety management, and delivery planning

Construction costs vary not only with the scope of work but also with the schedule and site-management assumptions. In the construction of a solar power plant, many tasks proceed in sequence, such as material delivery, heavy-equipment operations, racking assembly, panel installation, electrical work, inspections, and commissioning. If the schedule is not realistic, waiting times, rework, additional personnel, and re-deliveries can occur, ultimately affecting cost and quality.

Before comparing estimates, confirm the assumptions behind the construction schedule. If a short schedule is proposed, check whether they plan to deploy enough personnel, whether it assumes multiple tasks will be carried out in parallel, and whether there is contingency for bad weather or material delays. If the schedule is long, it is also important to confirm why the time is needed and whether it is the result of considering site conditions and safety measures.

Because construction of solar power plants mainly involves outdoor work, it is subject to weather conditions. During rain, site formation, pile driving, electrical work, and delivery operations may be constrained. In strong winds, panel handling and work at heights require caution. Confirming how weather risks are accounted for at the estimation stage makes it easier to discuss responses in the event of schedule delays.

It is also necessary to confirm the assumptions for safety management. At power plant construction sites there are various risks such as contact with heavy machinery, materials toppling over, falls on slopes, electric shock, heat stroke, and debris scattering in strong winds. Check whether the estimate reflects the personnel, morning briefings, work area zoning, protective equipment, traffic controllers/signallers, emergency response, and the establishment of site rules required for safety management. An estimate with insufficient safety measures may look low on the surface but can result in overlooking the risk of accidents or work stoppages.

Delivery planning also affects cost comparisons. Solar panels and racking components are numerous, so on-site storage locations and delivery sequences are important. If materials are stored in unsuitable locations, they will need to be moved every time work is carried out, reducing efficiency. On sites with narrow access or sloping terrain, there may be restrictions on delivery vehicles and an increase in the amount of small-scale handling required. Check how delivery conditions are treated in the estimate.

Also, the placement of site managers and the communication framework are items you should review. At sites where multiple work crews are present, schedule coordination, quality checks, responses to design changes, and communication with the client become important. If the management system is inadequate, work duplication, omissions, and poor information sharing are more likely to occur. When comparing construction costs, you need to verify not only the number of workers but also how the site will be managed.

Construction schedule, safety management, and delivery planning are aspects that are difficult to discern from the quotation price alone. However, on an actual site they are critical factors that determine construction quality and the project timeline. By confirming these assumptions before making comparisons, it becomes easier to assess not only the price but also the systems and arrangements in place to complete the work as planned.

Check 7: Confirm the conditions under which additional charges will apply

What you must always confirm before comparing construction costs is the conditions under which additional charges will occur. In solar power plant construction, underground obstacles that were not visible during site surveys, unexpected ground conditions, design changes, changes in material specifications, schedule changes, weather-related impacts, and changes in stakeholder coordination can all arise. When these occur, it is important to clarify the extent to which they are included in the estimate and from what point they will be treated as additional.

What you should check in an estimate are the exclusions and items quoted separately. Exclusions may list work that is not included in the quoted amount. For example, removal of underground obstructions, unforeseen drainage measures, additional site development, design changes, additional consultations with relevant authorities, night work, holiday work, and extra safety measures may be treated as separate items. If you compare only the total without reading these, you may be left unsure when later presented with explanations of additional costs.

When confirming additional costs, not only the conditions under which they arise but also how they are determined are important. Confirm under what circumstances something will be judged as additional, whether this will be discussed in advance, whether costs will be settled after emergency responses on site, and whether photos or records will be kept. If the method of judgment is unclear, misunderstandings are likely to occur during construction.

Another point to confirm is how design changes will be handled. At solar power plants, panel layout, racking locations, wiring routes, and equipment placement may be adjusted to suit site conditions. Sometimes only minor adjustments are needed, while other times drawing revisions or additional materials may be required. Confirming how much change is included in the estimate and what approval procedures will be used when changes occur can prevent confusion during construction.

Additional costs resulting from schedule changes are also items that are easy to overlook. Delays in material deliveries, delays in stakeholders’ preparations, changes to coordination schedules, adverse weather, and coordination with other construction work can cause workers and heavy machinery to be placed on standby. Confirming in advance how standby or rearrangements will be handled makes it easier to clarify the scope of responsibility.

Also, it is necessary to confirm how corrective action will be handled after completion. Defects caused by construction, changes in design conditions, owner-requested changes, or defects in supplied items are handled differently depending on the contract and warranty terms. If a defect is discovered after handover, it is advisable to confirm for what period and to what extent it will be addressed, and who the contact point will be.

A quote with clear conditions for additional charges is easier for the client to manage. Conversely, a quote that appears low in total but contains many separate line items and has ambiguous rules for deciding on extras makes the final financial burden difficult to predict. Before comparing construction costs, always check not only the quoted amount itself but also the likelihood of additional charges and the rules for determining them.

Compare with post-construction operations in mind

When comparing construction costs for solar power plants, it's important to consider not only the cost at completion but also the post-construction operation. A solar power plant is not finished when construction ends. It requires checking power output, mowing and cleaning, ongoing inspections, and investigating and addressing any faults. Decisions made during the construction stage affect operating costs and ease of management after completion.

For example, if inspection walkways are narrow, workspace beneath the mounting racks is insufficient, cable routes are unclear, drainage is poor, or the layout makes mowing difficult, operation and maintenance after completion will require more effort. Even if initial construction costs can be reduced, if inspections and repairs are inefficient each time, the long-term burden may increase.

The management of power generation is also related to construction quality. The orientation and tilt of the panels, the effects of shading, the organization of wiring, the condition of monitoring equipment installation, and the reliability of connections are all important for verifying generation performance after completion. If construction records are well organized, it becomes easier to trace the cause when output is lower than expected. Conversely, if records are insufficient, problems may require redoing on-site inspections.

When evaluating with operations in mind, we also review the contents of the handover documentation. If as-built drawings, equipment lists, wiring routes, test records, construction photos, and points to note during inspections are well organized, it becomes easier to hand over to maintenance personnel. If documentation is lacking, additional verification will be required for future repairs or renovations.

Also, you should check the response system for initial defects after installation. The period immediately after completion is important for confirming monitoring data, checking communication status, verifying whether there are connection faults, assessing drainage conditions, and inspecting the condition of mounting structures and cables. Confirming how far the installer will be involved in initial checks and what the contact system will be after handover can reduce worries once operations begin.

Construction costs for a solar power plant are not simply better the lower they are. Of course, unnecessary expenses should be avoided, but if you cut necessary inspections and quality control, it will affect the long-term stability of power generation operations. The purpose of comparison is not to find the lowest estimate, but to choose acceptable terms after ensuring the required quality and scope of responsibility are met.

Considering operation after installation changes how you view estimates. By evaluating whether inspections are easy, records are kept, causes can be traced in the event of a problem, and whether the system can operate stably over the long term, comparisons of construction costs become more practical.

Summary

Before comparing construction costs for a solar power plant, it is important not to judge by the total amount alone but to carefully review the assumptions behind the estimates. By clarifying the scope of work, site conditions, land development and grading, racking, foundations and piling work, electrical work, grid interconnection, design, surveying, permitting and inspection handling, schedule, safety management, logistics and delivery plans, and the terms for additional costs, you can more easily and accurately compare the contents of the estimates.

In particular, it is essential to confirm which tasks are included in the estimate and which are not. Even for the construction of the same solar power plant, the meaning of the price changes if the scope of work and responsibilities differ between contractors. An estimate that looks low at first glance can ultimately result in a much larger burden if site development, drainage, surveying, inspection coordination, or additional work are billed separately.

Also, when comparing construction costs, it is important to verify whether the estimate reflects the site conditions. Site topography, ground conditions, drainage, access routes, the surrounding environment, and safety measures vary from site to site. Estimates that have not sufficiently verified site conditions are more likely to require changes or additional work after construction begins.

Solar power plants are facilities designed for long-term operation. Decisions made during construction affect the plant's post-completion power generation, ease of inspection, reparability, and ease of operation and maintenance. When comparing construction costs, you need to consider not only the initial outlay but also whether the facility can be managed reliably after it begins operation.

When comparing estimates, it is important not to simply list prices but to align the conditions, check for omissions, and clarify the terms for additional costs. In addition, establishing a system that can consistently verify site surveys, design, construction, record-keeping, and operations management will improve the accuracy of your decisions.

Before comparing construction costs for a solar power plant, if you want to accurately understand the on-site conditions and design requirements, it is helpful to organize pre-construction surveys, photographs, drawings, and inspection records so that all stakeholders can confirm the same information. By visualizing site information and aligning the estimating conditions, it becomes easier to carry out checks before and after construction.