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A budget for a 100 kW commercial solar PV system covers equipment, site preparation, design, installation, electrical integration and checks before handover. The price of modules and an inverter answers only part of the question. To compare quotations, establish what capacity each one describes, where the contractor's work ends and which costs your business must cover separately.
This guide considers a grid-connected rooftop system without batteries. It explains how to review an estimate rather than offering a system price. A current quotation requires a defined configuration, site information and dated supplier offers. The useful outcome is a list of priced work, unresolved items and documents still needed for a purchasing decision.
Establish what 100 kW means
Start with two separate entries: the combined nameplate capacity of the modules on the direct current side (DC), and the rated output of the inverters on the alternating current side (AC). A quotation headed simply “100 kW solar system” can describe different equipment quantities. Neither capacity figure is a prediction of annual electricity production.
For a basic arithmetic example, 200 modules rated at 500 W add up to 100,000 W, or 100 kW of module capacity. The inverter capacity in that hypothetical system could be different and requires a designer's assessment. This calculation is not a recommended sizing ratio or confirmation that arbitrary components work together.
Ask for exact models, quantities, the intended operating arrangement and the connection point. If one offer means 100 kW of modules and another means 100 kW of inverter output, align the specification before comparing cost per kilowatt. The grid-connected solar solution for businesses is the commercial starting point for discussing a configuration.
Define the end point of the quoted work
Write down the result your business expects: a delivered equipment package, installed hardware, or a tested system with documentation and monitoring access. Terms such as “installation included” and “turnkey” need a specific schedule of work. Assign a contractor, payer and completion record to each stage.
Give every item one of four statuses: included at a stated price, provisionally estimated, supplied by the customer, or awaiting clarification. “Not required” should have an explanation. For example, a cable to the existing distribution board may be included while alterations to that board remain unpriced.
Include the customer's own work in the project budget. Clearing access, moving warehouse stock or providing lifting equipment can disappear from view when these activities are absent from the supplier's invoice. They still require resources, even under a separate contract. State which existing materials may be reused after their condition and suitability have been checked.
Check the equipment schedule
The module entry should show the model, rated capacity, quantity and unit price. For inverters, request the number of devices and their precise package contents. A vague promise of an “equivalent inverter” is difficult to control during procurement. Agree how a model substitution and its technical differences will be approved before signing.
Next review mounting equipment, electrical components and monitoring. Check rails, clamps, fasteners, cables, connectors, containment, switching and protection against the design. List export control equipment, measurement devices and communications separately where the intended operating arrangement requires them. A headline inverter specification does not establish the complete system scope.
Ask which accessories are already supplied with the inverter or distribution cabinet to avoid duplicate charges. Do not remove a protection item solely because the inverter mentions a similarly named feature. An engineer should confirm its purpose and limits. Procurement needs an agreed equipment schedule, rather than having to design an electrical circuit from invoice descriptions.
Identify costs driven by the roof
The same number of modules does not imply the same installation cost. Roof construction and condition, the mounting method, working access and the means of lifting materials all affect the scope. A rooftop project needs an assessment of the structure under the additional loads. Photographs alone cannot establish whether strengthening is required.
Separate mounting-system installation from roof repairs, waterproofing around penetrations, structural strengthening and access provision. If the roof will need refurbishment soon, agree the sequence. Installing modules first could create a later requirement to remove and reinstall them. Do not assume that such future work is part of the initial quotation.
A solar site assessment helps clarify quantities and constraints. Where a structural survey requires a separate specialist, confirm that specialist's task and fee. A contingency allowance should not replace a known activity that has simply not yet been commissioned. Keep its status visible until the investigation is complete.
Measure the electrical integration work
Identify the starting and finishing point of each main cable route. A cable rate per meter does not establish the total without a measured length, installation method and supporting materials. Routing across the roof, descending to a switchroom and crossing between buildings can involve different work and access requirements.
Review alterations to the existing distribution board, metering, earthing, protective devices and settings as distinct parts of the quotation. If the design affects a transformer or other site infrastructure, define that work separately. Do not assume it is necessary for every 100 kW system or automatically included in a standard package.
Before accepting a final price, distinguish confirmed connection requirements from unresolved questions. Separate work within the customer's installation, services from other contractors and any applicable network charges. There is no universal connection fee in this guide. Each such cost needs evidence relating to the actual site and its proposed arrangement.
Specify what completes the installation
Read the estimate alongside the delivery programme. Transport to the premises, unloading, roof lifting, storage and security may have different responsible parties. Agree crew access, working hours and any shutdowns of the business's electrical equipment. If a shutdown affects production, record that consequence separately in the implementation plan.
When reviewing commercial solar installation, check that commissioning, testing and document handover are addressed. Agree the test records, as-built drawings, operating instructions and monitoring access to be supplied. The final payment milestone should refer to a defined result, rather than merely confirming that modules have reached the roof.
Keep equipment warranties, workmanship commitments and ongoing maintenance terms distinct. Ask how fault reporting, site attendance, diagnosis and replacement will work. A warranty does not automatically answer every question about labor or transport charges. Review the conditions that will actually form part of the contract, including any exclusions.
Bring quotations onto a common basis
Consider two hypothetical offers for the same agreed configuration. All numbers below are invented budget units. They are not market prices, typical cost percentages or ONG quotations. Both options use the same assumed tax basis and comparison date. The exercise only demonstrates how omissions can change the apparent ranking.
| Item | Option A | Option B |
|---|---|---|
| Quoted amount | 100 | 111 |
| Material lifting excluded from the quotation | 6 | 0, already included |
| Additional cable route excluded from the quotation | 9 | 0, already included |
| Total for the equivalent scope | 115 | 111 |
For A, the calculation is 100 + 6 + 9 = 115. For B, it is 111 + 0 + 0 = 111. An initial difference of 11 units favoring A becomes a difference of 4 units favoring B. Zero means the activity is included in the quoted amount, not that it is free.
This result does not select a contractor. Compare models, warranties, delivery dates and acceptance terms separately. If unpriced roof strengthening emerges, both totals are still incomplete. Add an open item and a person responsible for resolving it, rather than inserting an arbitrary zero and presenting the estimate as final.
Record price validity and payment timing
The estimate needs a date, validity period, currency, tax basis and any contractual conversion or price-adjustment method. Do not combine an old equipment price with a revised installation scope. Keep each updated specification as a separately agreed version so that changes remain traceable.
For provisional work, define how the price will be finalized: measured quantities, confirmed equipment counts or a further quotation after inspection. Use an agreed change procedure for additional costs. The record should show the reason, scope, price and schedule effect before work proceeds. This gives the business an opportunity to assess the consequence.
Prepare a schedule of deposits and stage payments separately from the construction total. When considering solar project financing, match funding availability to the dates payments are due. A down payment is not the entire project budget. Interest, fees and operating costs belong in their relevant calculations, without counting the same expenditure twice.
Prepare a useful request for quotation
Give every participant the same version of the information pack. This reduces inconsistent assumptions and identifies questions that still require a site visit.
- The address, roof plan, available drawings and information on roof condition.
- Consumption data, operating hours and the intended use of solar generation.
- Connection information and details of the existing electrical infrastructure.
- Access rules, unloading space and restrictions on production shutdowns.
- The expected work package, target commissioning date and handover document requirements.
Ask ONG Solar for an offer with an equipment schedule, clear installation boundaries and a list of unresolved items. A useful 100 kW solar budget lets you trace each cost to a specific result. An assessment of future savings and payback follows once the initial investment scope is clear.