Solar Project Cost Calculator Guide: $/W, ROI, LCOE & Payback

PES Supply Technical Team
PES Supply Technical Content · Reviewed 2026-07-31

Resource: Solar Project Cost Calculator Guide: $/W, ROI, LCOE & Payback · About PES Supply

Quoting a solar project right means modeling the full cost stack and the full value stack. This guide breaks down component costs, $/W expectations by system size, ROI methodology, LCOE (levelized cost of energy), payback period by state, and financing options. Use the worked formulas to build defensible quotes for residential and commercial clients.

Two numbers clients care about(1) $/W installed, and (2) payback period in years. Everything else (LCOE, IRR, NPV) supports those two.

Component Cost Breakdown

Component	Share of total cost	Notes
Solar panels (modules)	25–30%	~$0.25–$0.40/W wholesale in 2026
Inverter(s)	10–15%	String $0.12/W, microinverter $0.35/W
Racking / mounting	10–15%	Roof $0.10/W, ground $0.20/W
BOS (wire, conduit, breakers, disconnects, labels)	8–12%	$0.10–$0.15/W
Battery (optional)	15–30% if included	$250–$450/kWh LFP
Labor	15–25%	Varies by region and roof complexity
Permitting, inspection, interconnection	5–10%	$500–$2,000 residential
Overhead, margin, warranty	10–15%	Installer margin

$/W Expectations by System Size (2026)

System size	Turnkey $/W (no battery)	Typical total cost
5 kW residential	$2.80–$3.50	$14,000–$17,500
10 kW residential	$2.50–$3.20	$25,000–$32,000
20 kW commercial	$2.10–$2.80	$42,000–$56,000
100 kW commercial	$1.80–$2.30	$180,000–$230,000
+ battery (10 kWh LFP)	+$6,000–$9,000	Add $0.60–$0.90/W on a 10 kW system

These are pre-incentive, fully installed costs. The federal 30% ITC reduces the net cost by ~30%, and state/utility incentives reduce it further.

ROI Calculation Methodology

Annual energy (kWh) = array kW × PSH × 365 × performance ratio (0.80).
Annual value ($) = kWh × blended retail rate (or TOU-weighted if net billing).
Net cost ($) = installed cost − incentives (ITC, state, utility).
Simple payback (yr) = net cost ÷ annual value.
ROI (%) = (lifetime value − net cost) ÷ net cost × 100.

Worked example (10 kW, Boston)10 kW × 4.2 PSH × 365 × 0.80 = 12,278 kWh/yr. At $0.30/kWh = $3,683/yr. Net cost after 30% ITC = $32,000 × 0.70 = $22,400. Payback = $22,400 ÷ $3,683 ≈ 6.1 years. Add a 14 kWh battery ($8,000 net) and shift $1,200/yr of TOU value → payback ~7.5 years with backup.

LCOE (Levelized Cost of Energy)

LCOE = lifetime cost ÷ lifetime energy, expressed in $/kWh. It's the apples-to-apples metric to compare solar against utility rates and other generation.

Formula: LCOE = (Net cost + O&M × years) ÷ (annual kWh × years × degradation factor)

Net cost: $22,400 (after ITC)
O&M: ~$150/yr (monitoring, inverter check)
Annual kWh: 12,278, derating ~0.5%/yr
Lifetime (25 yr): ~290,000 kWh delivered
LCOE: ($22,400 + $3,750) ÷ 290,000 ≈ $0.090/kWh

Compare to a $0.30/kWh retail rate: solar LCOE is a third of grid power — the economic case is strong in high-rate states.

Payback Period by State (10 kW residential, post-ITC)

State	Avg retail $/kWh	Approx payback (yr)
California	$0.31	5–7
New York	$0.28	6–8
Massachusetts	$0.32	5–7
Texas	$0.15	9–12
Florida	$0.16	8–11
Arizona	$0.15	8–11
Colorado	$0.15	8–11
Oregon	$0.13	10–13

Payback is rate × sun × incentiveLow-rate, low-sun states (Pacific NW, parts of the South) push payback past 10 years — a battery or a state SREC market can flip the economics.

Financing Options

Cash purchase: lowest lifetime cost, captures full ITC, fastest payback.
Solar loan (secured/unsecured): $0-down to 20% down, 5–25 yr terms; rate 5–9% in 2026. Client keeps ITC if loan passes it through.
Lease / PPA: $0-down, no ITC to client (third party owns), lower but predictable savings (~10–25% off utility bill).
PACE financing: repaid via property tax bill; transfers with home sale.
On-bill financing: utility-administered, repaid on the electric bill (CT Green Bank, Hawaii).

Building a Defensible Quote

Itemize components with model numbers and wholesale costs.
Add labor, permitting, interconnection, and overhead at your true burdened rate.
Apply ITC (30%) and state/utility incentives.
Model 25-year production (PVWatts) with degradation.
Present $/W, payback, LCOE, and lifetime savings.

Source Components at PES Supply

PES Supply stocks the panels, inverters, batteries, racking, and BOS that anchor your cost stack — at wholesale pricing for EPCs and contractors. 50,000+ SKUs from 169 authorized brands; standard delivery 7–10 business days. Request a bulk quote for volume pricing.