A solar EPC project schedule is not just a project management tool — it is a contractual deliverable that determines lender drawdown milestones, liquidated damages (LD) exposure, and subcontractor payment triggers. Whether you are an EPC contractor managing a 5 MW commercial rooftop or a 100 MW ground-mount utility project, understanding the full schedule from Notice to Proceed (NTP) to Commercial Operation Date (COD) is essential to delivering on time and within budget. This guide walks through every major milestone phase, common schedule risks, and how early procurement optimisation compresses overall timelines.
A solar EPC project passes through four broad phases between contract execution and revenue commencement:
For a typical 10 MW ground-mount project in a jurisdiction with an established permitting framework, total duration from NTP to COD is 9–14 months. For utility-scale projects above 50 MW, 14–24 months is typical. The single greatest driver of schedule extension is equipment procurement lead time — particularly for modules and medium-voltage (MV) transformers, which carry 12–20 week lead times from Chinese factories.
The pre-construction phase typically runs 6–14 weeks and is the most coordination-intensive period, where design, permitting, and procurement decisions cascade into every downstream phase.
Immediately after NTP, the EPC contractor initiates detailed engineering deliverables:
Detailed engineering drives the equipment specifications that govern procurement purchase orders. Issuing purchase orders before engineering is complete risks specification mismatches and costly change orders; delaying purchase orders extends lead times. The optimal approach is to issue "intent to purchase" letters to key suppliers at NTP while engineering progresses in parallel, locking pricing and queue positions without committing to final specifications.
Construction permits run in parallel with detailed engineering. The critical path item is typically the grid connection application (if not already completed in the development phase) and the building or development permit. Permit durations vary enormously by jurisdiction — 4 weeks in some Southeast Asian markets, 16+ weeks in parts of Europe and North America. The EPC contractor should maintain a permit tracker with submission dates, statutory decision periods, and escalation contacts.
Major equipment categories and their lead times (from factory order confirmation to site delivery):
Civil works typically run from Week 6 to Week 16 for a 10 MW ground-mount project, and are largely independent of equipment deliveries (making this phase an excellent opportunity for parallel-track scheduling with procurement).
The eBOS phase — installation of all electrical equipment from module to point of interconnection — is typically the most labour-intensive and schedule-sensitive phase.
Commissioning is governed by the IEC 62446-1 standard for PV systems and the utility's specific interconnection commissioning requirements. Key activities:
| Risk | Likelihood | Schedule Impact | Mitigation |
|---|---|---|---|
| MV transformer delivery delay | High (30–40%) | 4–12 weeks | Order at NTP; dual-source from two factories |
| Permit delay (building/grid connection) | Medium (20–35%) | 2–16 weeks | Submit early; engage permit expeditor |
| Unexpected rock during pile installation | Medium (15–25%) | 1–4 weeks | GPR survey before NTP; contract for rock removal |
| Module manufacturing defect at delivery | Low–Medium (5–15%) | 1–6 weeks (replacement) | Third-party factory inspection; EL test at QC hold point |
| Inverter firmware incompatibility with utility SCADA | Low (5–10%) | 1–4 weeks | Confirm firmware version with utility before order |
| Grid connection energisation delay | Medium (25–40%) | 2–12 weeks | Engage utility liaison from NTP; file applications early |
| Adverse weather during civil works | Medium (varies) | 1–6 weeks | Schedule civil works in dry season; include weather float |
The following timeline assumes a jurisdiction with 8-week building permit processing and no unexpected site conditions. All weeks are measured from NTP.
The single most effective schedule lever available to the EPC contractor is early equipment procurement. Projects that place module and inverter purchase orders during the development phase (pre-NTP, with appropriate cancellation provisions) can compress the total schedule by 4–10 weeks compared to post-NTP ordering.
Econo Solar works with EPC contractors and project developers to lock pricing and production slots at LOI stage, with flexible delivery windows and phased payment terms that align with EPC contract structures. We ship directly from Chinese factories with full documentation (CE, IEC, TÜV, INMETRO, and local certifications as required) to minimise customs clearance delays.
To get a delivery timeline and logistics plan for your next project, contact Econo Solar with your project capacity, location, and target COD date.
Provisional Acceptance Certificate (PAC) is issued when the plant has completed commissioning and passes the performance test defined in the EPC contract — typically a 5–10 day measured performance ratio test against the PVsyst baseline. COD (Commercial Operation Date) is the date on which the plant begins commercial operations and the power purchase agreement (PPA) or feed-in tariff payments commence. COD may be defined contractually as identical to PAC, or it may be a separate milestone triggered by grid authority sign-off, revenue meter certification, or insurer approval. EPC contracts should define both milestones precisely and specify the liquidated damages rate per day of delay against each.
For ground-mount fixed-tilt systems using standard 400–600 Wp bifacial modules, an experienced installation crew of 10–15 workers can typically install 0.7–1.2 MW of modules per day, depending on module weight, mounting system design, and site terrain. For a 10 MW project, module installation takes approximately 9–14 working days. Tracker-mounted systems are 10–20% slower due to tracker assembly complexity. Commercial rooftop installation is 20–30% slower than ground-mount due to roof access constraints, fall arrest requirements, and limited crane access.
Based on aggregated EPC project data, the top three causes of COD delay are: (1) MV transformer delivery delay (the #1 cause globally — typically 4–12 weeks of delay when orders are placed late); (2) utility energisation and grid connection delays, which are outside the EPC contractor's control and frequently slip by 4–8 weeks; and (3) unexpected civil conditions — buried utilities, underground water, or uncharted rock — during pile installation, typically causing 2–4 weeks of delay. EPC contracts should include appropriate delay event provisions (force majeure, utility delay, and differing site conditions clauses) with specific LDs only for contractor-controllable delays.
Econo Solar ships modules, inverters, and MV equipment to your project site with guaranteed delivery windows — designed to match your EPC project schedule.
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