Calculate cost per watt, solar price per watt after incentives, or electricity running cost from power, hours, rate, and size for quick comparisons.
Related Calculators
Cost Per Watt Formula
The calculator uses three formulas, one for each mode.
Price per watt:
PPW = Total Cost / Watts
Solar quote with incentives:
Net PPW = (Gross Cost * (1 - Tax Credit %) - Rebate) / System Watts
Running electricity cost:
Daily Cost = Watts * Hours per Day / 1000 * Rate
- Total Cost: purchase price in dollars.
- Watts: rated power, converted from W, kW, or MW.
- Gross Cost: solar quote before incentives.
- Tax Credit %: percentage incentive such as the 30% federal credit.
- Rebate: fixed dollar incentive applied after the percentage credit.
- System Watts: either the entered system size or panels times watts per panel.
- Hours per Day: average daily run time, capped at 24.
- Rate: electricity price in dollars per kilowatt-hour.
The Price per watt tab divides any cost by any wattage to give dollars per watt and dollars per kilowatt. The Solar quote tab does the same but adds a percentage credit and fixed rebate, then flags whether the gross figure is low, typical, or high. The Running cost tab converts watts and hours into kWh, then multiplies by your electricity rate to project daily, monthly, and yearly cost.
Reference Tables
Use these as sanity checks against your own inputs.
| Residential Solar PPW (gross) | Interpretation |
|---|---|
| Under $3.00/W | Low, verify equipment and warranty. |
| $3.00 to $4.50/W | Typical US residential range. |
| $4.50 to $5.50/W | High, ask for an itemized quote. |
| Over $5.50/W | Very high, get competing bids. |
| Appliance | Watts | Cost at 4 hrs/day, $0.17/kWh |
|---|---|---|
| LED bulb | 9 | $0.19/month |
| Incandescent bulb | 75 | $1.55/month |
| Laptop | 150 | $3.10/month |
| Microwave | 1,000 | $20.69/month |
| Space heater | 1,500 | $31.04/month |
| Central AC | 3,500 | $72.42/month |
| EV charger | 7,200 | $148.97/month |
Worked Examples
Example 1: Solar quote. A 6 kW system is quoted at $19,800 gross. The federal tax credit is 30% and the utility offers a $500 rebate.
- Gross PPW = 19,800 / 6,000 = $3.30/W
- Net cost = 19,800 × 0.70 − 500 = $13,360
- Net PPW = 13,360 / 6,000 = $2.23/W
Example 2: Running cost. A 1,500 W space heater runs 5 hours per day at $0.17/kWh.
- Energy = 1,500 × 5 / 1,000 = 7.5 kWh/day
- Daily cost = 7.5 × 0.17 = $1.28
- Monthly cost ≈ $38.80
FAQ
Should I compare quotes using gross or net price per watt?
Use gross PPW to compare installers on equal footing. Incentives vary by location and tax situation, so net PPW reflects your wallet but not the installer's pricing.
Does price per watt include the inverter and installation?
For solar, gross system cost should be the full turnkey price: panels, inverter, racking, wiring, permits, and labor. If a quote excludes any of these, the PPW will look artificially low.
Why is monthly cost calculated with 30.4375 days?
That is the average days per month over a year (365 / 12). It avoids the swing between 28 and 31 day months.
What electricity rate should I use?
Check the supply and delivery charges on your utility bill and add them. The default of $0.17/kWh is near the US residential average but varies widely by state.
