A poorly written solar tender does more damage than no tender at all. It produces non-comparable bids, invites scope disputes during construction, and routinely ends with the cheapest contractor winning on a specification that allowed them to substitute inferior equipment. A well-structured tender document is the owner's first and most powerful tool for risk allocation — before a contract is signed.
RFQ, RFP, or EPC Tender: Which Do You Need?
The terminology around solar procurement documents is used inconsistently in the market. The table below sets out the four main document types, when each is appropriate, and what response it is designed to elicit from the market.
| Document | Full Name | When to Use | Response Expected |
|---|---|---|---|
| RFI | Request for Information | Early market sounding, no commitment to proceed | Capabilities overview, indicative pricing ranges |
| RFQ | Request for Quotation | Known and fully defined scope, comparing prices on identical spec | Fixed price quote on the defined specification |
| RFP | Request for Proposal | Complex or partly defined scope, inviting contractor design input | Technical proposal plus commercial offer |
| EPC Tender | Engineering, Procurement & Construction | Lump-sum project, contractor takes on design and build responsibility | Full EPC lump-sum price plus detailed design proposal |
For most C&I solar projects in the 100 kW–5 MWp range, an RFP or EPC Tender is appropriate — the owner defines the performance requirements and boundary conditions, and the contractor proposes the technical solution and takes design responsibility. For a straightforward rooftop installation with a fully defined equipment specification and known roof area, an RFQ is sufficient and produces faster, more comparable responses.
Section 1: Project Overview and Scope of Work
The project overview section establishes the boundary conditions that all contractors will bid against. Ambiguity here is the single most common cause of non-comparable bids and post-award scope disputes. Include the following elements:
- Project name and location: Full site address, GPS coordinates, and grid connection point reference if known.
- Installed capacity: State both the DC array capacity (kWp) and the AC export capacity (kW or kVA at the point of connection). If there is a grid export limit, state it explicitly.
- Site conditions summary: For rooftop projects — available roof area by orientation, roof material and structural load rating, existing roof penetrations. For ground-mount — land area available, terrain gradient, access road condition, soil type if known.
- Project timeline: Financial close date (if applicable), target construction start date, and commercial operation date (COD) target. A realistic timeline prevents contractors from padding contingency for schedule uncertainty.
- Scope boundaries — what is in scope and what is not: Clearly state whether design, supply, installation, commissioning, grid connection application, and metering are in scope. Explicitly exclude items the owner retains: land, planning permits, grid upgrade costs, and any owner-supplied equipment. Clear scope boundaries prevent contractor-initiated change order claims that erode fixed-price certainty.
Section 2: Technical Specifications
The technical specification section defines the minimum equipment and performance requirements that all bids must meet. It should be specific enough to produce comparable bids but not so prescriptive that it eliminates competitive design solutions.
Minimum equipment requirements should specify: solar panels (tier-1 manufacturer required, minimum watt-peak per module, cell technology — n-type or PERC as appropriate for the application), inverters (approved brand list or open specification with minimum conversion efficiency and warranty term), mounting systems (certified wind load calculation required, ground mounting rail specification if applicable, roof mounting waterproofing standard), and BESS if applicable (minimum round-trip efficiency, LFP chemistry required, minimum BMS functionality).
Key performance requirements should state: a minimum performance ratio (PR) guarantee — commonly expressed as ≥80% P50 per the owner's energy yield assessment — and a plant availability guarantee of ≥98% as a minimum for a quality O&M contract. Grid export limit compliance and reactive power requirements should be stated explicitly if the grid connection agreement imposes them.
Reference standards applicable to the project should be listed: IEC 61215 and IEC 61730 for PV modules, IEC 62116 for anti-islanding protection, and the applicable national or regional grid code. Listing standards removes the ambiguity of "industry best practice" language that contractors can interpret to their advantage.
Section 3: Commercial Terms
Commercial terms define how the contract will be priced, paid, and enforced. Getting these right at tender stage determines how much leverage the owner retains if the project underdelivers.
Contract type: A lump-sum turnkey contract transfers design and construction risk to the contractor and is the preferred structure for owners who want budget certainty and maximum risk transfer. A cost-plus structure is appropriate only where scope is genuinely impossible to define upfront — for example, a phased ground-mount development on a complex brownfield site. Using cost-plus on a well-defined C&I rooftop project simply transfers financial risk to the owner without benefit.
Payment milestones: A typical lump-sum payment structure distributes financial exposure across the construction period. A standard structure for C&I projects is: 10% on contract signing, 30% on equipment delivery to site (against delivery receipts and inspection), 40% on mechanical completion (all equipment installed, pre-energisation checks complete), 15% on commissioning and grid connection, and 5% at completion of the performance test. The final 5% retained until performance test completion gives the owner leverage to enforce the PR guarantee before making the final payment.
Liquidated damages (LDs): Set an LD rate for PR shortfall below the guarantee — a typical rate is 1% of contract value for each 1% of PR below the guaranteed level, subject to a cap (commonly 10–15% of contract value). Set separate delay LDs for late achievement of COD — commonly 0.1% of contract value per calendar day, subject to a cap of 10%. LDs must be genuine pre-estimates of loss, not penalties, to be enforceable in most jurisdictions.
Warranty: Require a minimum 12-month workmanship warranty post-COD, covering all installation defects. For BESS projects, 24 months post-COD is the market standard given the longer commissioning and stabilisation period for battery systems.
Section 4: Evaluation Criteria
Publishing evaluation criteria in the tender document serves two purposes: it guides contractor responses toward the information that matters to the owner's decision, and it protects the owner from legal challenge if a disappointed bidder questions the award. Multi-criteria scoring consistently produces better outcomes than lowest-price-wins evaluation.
| Criterion | Weight | What to Assess |
|---|---|---|
| Technical compliance | 30% | Specification compliance, equipment brand and quality, design methodology, compliance with reference standards |
| Commercial price | 40% | Total EPC lump-sum price, payment milestone structure, warranty terms, LD exposure clarity |
| Track record | 20% | Reference projects of similar scale and geography, client references, defect history on completed projects |
| Financial capacity | 10% | Ability to provide performance and warranty bonds from a rated bank, company financial statements, parent company guarantee if applicable |
Weight commercial price at no more than 40–50% of the total score. An evaluation heavily weighted toward price invites bids that sacrifice equipment quality, warranty coverage, or schedule certainty to win on headline number — precisely the outcome a well-structured tender is designed to prevent.
Common Mistakes in Solar Tenders
The following errors appear consistently in poorly performing solar tenders. Each can be avoided with careful document preparation:
- Vague scope of work: "Supply and install a solar system" with no stated capacity, equipment requirements, or warranty — this produces bids that cannot be compared and contractors who will interpret scope in their favour at every dispute.
- No performance guarantee: Without a PR guarantee and enforcement mechanism, the owner has no contractual remedy for an underperforming plant.
- Open brand lists without minimum specifications: "Any tier-1 panel" is not a specification. Without a minimum watt-peak, efficiency, and warranty term, contractors substitute the cheapest available module that claims tier-1 status.
- Unrealistic timeline: Requiring COD within 8 weeks of contract award for a 1 MWp rooftop project is not achievable. Contractors either decline to bid or inflate contingency to cover the risk of LD exposure they expect to incur.
- No site visit organised for bidders: Contractors who cannot inspect the site cannot price accurately. The result is either inflated bids covering unknowns or change order claims after award when conditions differ from assumptions.
- Missing grid connection clarity: The tender must state explicitly who is responsible for the DNO application, who bears the cost of any required network upgrades, and what happens if the connection is delayed beyond the owner's control. Grid connection ambiguity is the most common source of post-award commercial disputes on C&I solar projects.
A well-structured EPC tender is not a bureaucratic exercise — it is the document that determines whether the owner receives the plant they intended, at the price they agreed, on the schedule they planned. Investing a week in a thorough tender document consistently saves months of dispute and rework on the other side of financial close. For owners procuring equipment independently ahead of EPC award, Econo Solar can provide panel, inverter, and mounting specifications aligned to tender requirements, reducing the risk of contractor substitution during procurement.