| Scenario | kWdc | DC/AC | Module $/W | Inverter $/Wac | Racking $/W | Labor $/W | Cont. % | Profit % |
|---|---|---|---|---|---|---|---|---|
| Commercial rooftop | 150 | 1.15 | 0.27 | 0.09 | 0.14 | 0.33 | 6 | 10 |
| Ground mount (standard) | 500 | 1.25 | 0.24 | 0.08 | 0.11 | 0.27 | 5 | 9 |
| Remote site (higher logistics) | 300 | 1.30 | 0.25 | 0.08 | 0.12 | 0.31 | 7 | 11 |
- Wdc = kWdc × 1000
- Wac = Wdc ÷ (DC/AC ratio)
- Equipment subtotal = Σ(per‑W items × W) + Σ(fixed items)
- Shipping = equipment subtotal × shipping %
- Labor = Wdc × labor rate × site multiplier
- Direct costs = equipment + shipping + labor + fixed soft costs + optional storage install
- Construction management = direct costs × CM %
- Adders apply sequentially: escalation → contingency → overhead → profit
- Sales tax = (selected taxable base) × tax %
- Total EPC = direct + CM + escalation + contingency + overhead + profit + sales tax
- Unit cost = Total EPC ÷ kWdc (and ÷ Wdc)
- Enter system size (kWdc) and a realistic DC/AC ratio.
- Set per‑W rates using current supplier and subcontractor quotes.
- Adjust the site multiplier for access, roof height, or remoteness.
- Include fixed items for design, permitting, and interconnection needs.
- Apply escalation, contingency, overhead, and profit to match policy.
- Choose the taxable base items and enter the sales tax rate.
- Click Calculate; review breakdown, then export CSV/PDF.
EPC cost structure by work package
Solar EPC budgets are usually dominated by equipment and installation. A practical split on many projects is modules at 30–45%, inverters at 5–10%, racking and electrical BOS at 15–25%, and field labor at 15–30%. Soft costs such as engineering, permitting, interconnection, and commissioning often add 3–8%. Overhead and profit commonly add 10–20%, shaped by scope and risk.
Scaling effects and unit cost
Unit cost often improves with size because fixed items spread across more watts. A fixed allowance of 40,000 adds about $0.40/W to a 100 kWdc project, but about $0.04/W to a 1,000 kWdc project. Use the fixed fields to reflect these step costs and compare scenarios consistently. This is why unit costs vary between small commercial and utility-scale work.
Site conditions and productivity
The site multiplier represents productivity changes from access, elevation, remoteness, and ground conditions. Constrained rooftops, difficult soils, or long material handling routes can increase labor and install adders. Pair the multiplier with shipping and mobilization to capture travel, laydown limits, temporary power, and safety requirements that frequently drive variance.
Risk allowances and commercial terms
Escalation anticipates price drift, while contingency covers uncertainty. Many budgets use 1–4% escalation and 3–10% contingency, depending on schedule maturity. Profit targets often range from 6–15% and may rise when liquidated damages, performance guarantees, or insurance requirements increase exposure for the EPC contractor.
Example estimate snapshot
Example inputs below illustrate how totals roll up in a mid‑scale ground mount scenario.
| Example inputs | Value |
|---|---|
| System size | 500 kWdc |
| DC/AC ratio | 1.25 |
| Module / Inverter | $0.24/Wdc • $0.08/Wac |
| Racking / Electrical / Labor | $0.11 • $0.10 • $0.27 per Wdc |
| CM / Esc / Cont / OH / Profit | 4% • 2% • 5% • 7% • 9% |
| Example output (approx.) | $605,575 total • $1.211/Wdc |
1) What does “EPC” include in this estimate?
It includes equipment, labor, logistics, fixed soft costs, construction management, escalation, contingency, overhead, profit, and optional sales tax. Optional storage adders are included when battery size is greater than zero.
2) Why does the calculator use both Wdc and Wac?
Some components scale with DC nameplate (modules, racking, labor) while inverters scale with AC capacity. The DC/AC ratio converts DC size to an estimated AC size so each rate is applied to the right basis.
3) How should I choose the site multiplier?
Start at 1.00 for typical access and productivity. Increase it for difficult logistics, roof constraints, long lifts, or remote sites. Decrease it only when you have strong evidence of faster-than-normal installation conditions.
4) What’s the difference between contingency and overhead?
Contingency is a risk buffer for unknowns in scope, quantities, and productivity. Overhead is the contractor’s business burden, including management, compliance, and support functions. Both can be needed in a realistic EPC budget.
5) Can I model partial sales tax or exemptions?
Yes. Select only the items that are taxable in your jurisdiction and set the sales tax rate. This produces a tax base and applies tax only to the selected line items, rather than to the entire EPC total.
6) How do I benchmark the result to $/Wdc?
Use the unit cost outputs ($/kWdc and $/Wdc) and compare across scenarios with the same scope boundaries. Keep fixed items, risk adders, and tax assumptions consistent to avoid misleading comparisons.
7) Does this replace a detailed bid or BoQ?
No. It is a transparent estimating tool for early budgeting and sensitivity checks. Final pricing should be based on drawings, quantities, site investigations, supplier quotes, and contract requirements.