Solar Panel Output Calculator: Daily, Monthly and Yearly kWh

Estimate how much electricity a solar system produces per day, per month, per year and over 25 years. Enter the system size and your peak sun hours; the tool applies standard system losses and yearly panel aging.

Your state

Fills in typical peak sun hours. Your roof may differ.

System size

DC size in kilowatts, shown on your quote.

Peak sun hours

Daily sunlight expressed as hours of full 1,000 W/m² sun, averaged over the year.

Panel wattage

Most home panels sold in 2026 are about 400–450 W.

More optionsFewer options

System losses

NREL PVWatts uses 14% by default (wiring, dirt, heat, inverter-adjacent losses).

Panel output loss per year

NREL studies put the median near 0.5% a year.

Your result

Yearly output 9,448 kWh

Monthly average: 787 kWh
Daily average: 25.9 kWh
Per panel, per year: 525 kWh
kWh per kW per year: 1,350
25-year output: 222,566 kWh

This system would make about 9,448 kWh a year, or 25.9 kWh on an average day. Summer days produce more and winter days less.

Educational estimate only. Not financial, tax or legal advice.

Yearly output over 25 years

Solar output (kWh)

View as table

Year	Solar output (kWh)
1	9,448 kWh
2	9,401 kWh
3	9,354 kWh
4	9,307 kWh
5	9,261 kWh
6	9,215 kWh
7	9,168 kWh
8	9,123 kWh
9	9,077 kWh
10	9,032 kWh
11	8,986 kWh
12	8,942 kWh
13	8,897 kWh
14	8,852 kWh
15	8,808 kWh
16	8,764 kWh
17	8,720 kWh
18	8,677 kWh
19	8,633 kWh
20	8,590 kWh
21	8,547 kWh
22	8,504 kWh
23	8,462 kWh
24	8,420 kWh
25	8,377 kWh

Output year by year with panel aging

Year	Solar output (kWh)	% of year-1 output
1	9,448	100%
2	9,401	99.5%
3	9,354	99%
4	9,307	98.5%
5	9,261	98%
6	9,215	97.5%
7	9,168	97%
8	9,123	96.6%
9	9,077	96.1%
10	9,032	95.6%
11	8,986	95.1%
12	8,942	94.6%
13	8,897	94.2%
14	8,852	93.7%
15	8,808	93.2%
16	8,764	92.8%
17	8,720	92.3%
18	8,677	91.8%
19	8,633	91.4%
20	8,590	90.9%
21	8,547	90.5%
22	8,504	90%
23	8,462	89.6%
24	8,420	89.1%
25	8,377	88.7%
Total	222,566

Compare system losses

Result	A 10% losses (clean, cool)	B Your inputs	C 20% losses (shade, dust)	Difference (B − A)
Yearly output	9,888 kWh	9,448 kWh	8,789 kWh	-439 kWh
25-year output	232,918 kWh	222,566 kWh	207,038 kWh	-10,352 kWh

Results update as you type. Without JavaScript you see the worked example below.

How to use it

Pick your state to fill typical peak sun hours, or enter your own figure.
Enter the system size in kW from your quote.
Enter the panel wattage to see output per panel.
Under advanced, adjust system losses and the yearly panel output loss if you have better numbers.
Read yearly, monthly and daily output, then check the 25-year schedule and the losses comparison.

On this page

A solar panel output calculator multiplies system size by peak sun hours and subtracts losses. With the defaults, a 7 kW system with 4.3 peak sun hours and 14% losses makes about 25.9 kWh a day, 787 kWh a month and 9,448 kWh a year, or 1,350 kWh per kW. Sunshine is the biggest variable.

How to use the solar panel output calculator

Your state. Fills typical Peak sun hours. Your roof may differ, so overwrite it if you have a better figure.
System size. DC kW from your quote. Default 7 kW.
Peak sun hours. Daily sunlight expressed as hours of full 1,000 W/m² sun, averaged over the year. Default 4.3.
Panel wattage. Used only to show output per panel. Default 400 W.
Advanced fields. System losses (default 14%, the PVWatts default) and Panel output loss per year (default 0.5%).

You get yearly, monthly and daily output, output per panel, kWh per kW per year and 25-year output. A bar chart shows each year's output over 25 years, and a schedule lists every year's kWh and its percent of year-one output, with a CSV download. The scenario table reruns your system at 10% losses (clean, cool panels), your own losses, and 20% losses (shade or dust).

How the calculation works

Daily kWh        = system kW × peak sun hours × (1 − losses)
Yearly kWh       = daily kWh × 365
Monthly average  = yearly kWh ÷ 12
Panels           = system watts ÷ panel watts (rounded)
Per panel/year   = yearly kWh ÷ panels
kWh per kW       = yearly kWh ÷ system kW
Year-n output    = yearly kWh × (1 − degradation)^(n−1)
25-year output   = sum of years 1 to 25

Assumptions that match the code:

One yearly average for sun hours; no month-by-month weather.
14% losses by default, matching PVWatts (opens in a new tab): soiling 2%, shading 1%, mismatch 2%, wiring 2%, connections 0.5%, light-induced degradation 1.5%, nameplate 1%, availability 3%.
0.5% yearly degradation, the median in NREL's field-data review (Jordan and Kurtz, 2012 (opens in a new tab)).
When you pick a state, peak sun hours are derived from the state's yearly output per kW divided by 365 and by 0.86, so the two tools agree.

Worked example

Default inputs: 7 kW, 4.3 peak sun hours, 14% losses, 400 W panels, 0.5% degradation.

Daily: 7 × 4.3 × 0.86 = 25.9 kWh.
Yearly: 9,448 kWh; monthly average: 787 kWh.
Panels: 7,000 ÷ 400 = 17.5, shown as 18, so 525 kWh per panel per year.
1,350 kWh per kW per year; 25-year output: 222,566 kWh.

Second example, a sunny Southwest roof: 8 kW, 5.6 peak sun hours (close to the PVWatts yield for Phoenix of 1,755 kWh per kW), 430 W panels, other inputs at default.

Daily: 38.5 kWh; monthly: 1,172 kWh; yearly: 14,063 kWh (1,758 kWh per kW).
19 panels, about 740 kWh each per year; 25-year output: 331,261 kWh.

How losses change output

Scenario	Default 7 kW system, yearly	Default, 25 years	Phoenix 8 kW, yearly
10% losses (clean, cool)	9,888 kWh	232,918 kWh	14,717 kWh
14% losses (PVWatts default)	9,448 kWh	222,566 kWh	14,063 kWh
20% losses (shade, dust)	8,789 kWh	207,038 kWh	13,082 kWh

What your result means

Compare the yearly figure with the production estimate on your quote. If a proposal claims much more than this tool or PVWatts shows for the same size and location, ask what assumptions it uses. Then compare output with your use in the how many solar panels do I need tool, and turn kWh into dollars with the solar savings calculator.

Yearly output is also the denominator in cost per kWh. Our guide to how much solar panels cost explains why a cheaper system with poor output can be a worse deal.

Rules that change the answer

Orientation and tilt. DOE says south-facing roofs with a 15 to 40 degree slope generally perform best (DOE (opens in a new tab)). Check your angle with the solar panel angle calculator.
Climate. Heat lowers panel efficiency, while clear skies raise output. Phoenix and Tampa both get strong sun but different weather; see solar panels in Arizona and solar panels in Florida.
Shading and soiling. A tree or chimney shading part of the array can push losses past 20%.
Inverter clipping. PVWatts assumes a DC-to-AC ratio of 1.2 and 96% inverter efficiency by default (PVWatts API (opens in a new tab)); a much smaller inverter can clip peak output.

Common mistakes

Treating peak sun hours as hours of daylight.
Using a summer-day reading as the yearly average.
Forgetting losses and quoting system kW × sun hours as AC output.
Ignoring panel aging when estimating 25-year totals.
Assuming more panel watts means more total output for the same kW.

Limits of this calculator

This is an educational estimate, not a production guarantee. It uses one yearly sunshine figure and a flat loss factor, so it cannot show seasonal swings, partial shading or weather years. For a site-specific estimate, run PVWatts for your address and roof angle, and compare it with your installer's production report.

Frequently asked questions

How many kWh does a solar panel produce per day?

A 400 W panel getting 4.3 peak sun hours, after 14 percent losses, makes about 1.5 kWh a day, or roughly 525 kWh a year. The same panel in a sunnier place with 5.6 peak sun hours makes about 1.9 kWh a day. Output is higher in summer and lower in winter.

What are peak sun hours?

Peak sun hours express a day's sunlight as the number of hours of full-strength sun, 1,000 watts per square meter, that would deliver the same energy. Four peak sun hours does not mean four hours of daylight; it is a yearly average energy figure. PVWatts gives the most reliable estimate for an address.

Why does the calculator subtract 14 percent?

Fourteen percent is the default total loss in PVWatts. It covers soiling (2 percent), shading (1 percent), mismatch (2 percent), wiring (2 percent), connections (0.5 percent), light-induced degradation (1.5 percent), nameplate rating (1 percent) and availability (3 percent). Inverter conversion is handled separately in PVWatts.

How much less will my panels produce over time?

The default is 0.5 percent a year, the median rate found in NREL's 2012 review of about 2,000 field measurements. At that rate, year-25 output is about 88.7 percent of year one. The year-by-year schedule shows the decline and can be downloaded as CSV.

Why is my real production different from this estimate?

Weather varies year to year, and your roof's direction, tilt and shading matter. This tool uses a single yearly sun-hours figure and a flat loss percentage. PVWatts models your exact location, tilt and azimuth with typical-year weather data, so use it to check a quote's production promise.

How much does a 7 kW solar system produce?

With the defaults, 4.3 peak sun hours and 14 percent losses, a 7 kW system makes about 9,448 kWh a year, 787 kWh a month and 25.9 kWh a day. In a sunnier location with 5.6 peak sun hours, an 8 kW system makes about 14,063 kWh a year.

Does panel wattage change total output?

Not for a given system size. Output depends on total kW, sunshine and losses. Panel wattage only changes how many panels make up that kW, and therefore the output per panel.

Sources

Checked against these sources. Dates show when each was last reviewed.

PVWatts Calculator (opens in a new tab), National Laboratory of the Rockies (formerly NREL) (as ofOctober 2026)
PVWatts V8 API documentation (opens in a new tab), National Laboratory of the Rockies (formerly NREL) (as ofOctober 2026)
Photovoltaic Degradation Rates: An Analytical Review (opens in a new tab), National Renewable Energy Laboratory (Jordan and Kurtz, 2012) (as ofOctober 2026)
Homeowner's Guide to Going Solar (opens in a new tab), U.S. Department of Energy (as ofOctober 2026)
U.S. Distributed Solar and Storage: 2026 Data Update (opens in a new tab), Lawrence Berkeley National Laboratory (as ofOctober 2026)

Last updated: October 18, 2026How we build our calculators

On this page

25D credit (Residential Clean Energy Credit): A 30% federal tax credit homeowners could claim for solar and batteries they paid for. It ended for expenditures made after December 31, 2025; the IRS counts the expense when installation is completed.
48E credit: A federal business tax credit for clean electricity property. Companies that own leased or PPA systems on homes may claim it, subject to construction deadlines and sourcing rules. The homeowner does not claim it.
Avoided cost: What it would cost a utility to produce or buy the same power elsewhere. Some states pay rooftop exports at an avoided-cost rate, which is far below retail.
Dealer fee: A charge a solar lender takes from the loan, usually built into the amount you borrow so the advertised interest rate looks low. The CFPB has warned these fees can add tens of percent to the price.
Degradation: The slow loss of a panel’s output over time. NREL research puts the median around 0.5% per year, and most panel warranties guarantee roughly 80–90% of original output after 25 years.
Escalator: A yearly percentage increase written into a lease or PPA, often 0–3%. A 2.9% escalator raises the payment by about 100% over 25 years.
FEOC rules: Federal “foreign entity of concern” sourcing limits added in 2025 that a business must meet to claim 48E credits on projects starting construction in 2026 or later.
Interconnection: Your utility’s approval to connect a solar system to the grid. Most utilities require an application before installation and a final permission to operate (PTO) before you turn it on.
Inverter: The device that turns the direct current (DC) from panels or batteries into the alternating current (AC) your home uses. Types include string inverters, microinverters and hybrid inverters that also manage a battery.
Islanding (backup mode): When a solar-plus-battery system disconnects from the grid during an outage and keeps powering your home. Ordinary grid-tied solar without a battery shuts off in an outage for line-worker safety.
kW (kilowatt): A unit of power: how fast electricity is made or used at one moment. Solar system size is quoted in kW of panel capacity (DC). A 7 kW system has panels rated 7,000 watts in total.
kWh (kilowatt-hour): A unit of energy: using 1 kW for one hour. Your electric bill charges you per kWh, and solar output and battery capacity are measured in kWh.
Microinverter: A small inverter mounted under each panel. Shade on one panel affects only that panel, and each panel can be monitored separately. Usually costs a little more than one central string inverter.
NABCEP certification: A voluntary professional certification for solar installers from the North American Board of Certified Energy Practitioners. It is a useful signal, but you should also check state contractor licensing.
NEM 3.0: The common name for California’s Net Billing Tariff, which applies to new rooftop solar customers of PG&E, SCE and SDG&E who applied on or after April 15, 2023. Exports earn hourly values far below retail rates.
Net billing: A billing rule where exported solar earns a credit set by a separate, usually lower, export rate rather than the full retail price. California’s Net Billing Tariff (often called NEM 3.0) is the best-known example.
Net metering: A billing rule where each kWh your panels send to the grid earns a credit equal (or close) to the retail price you pay. Credits offset power you buy later, often rolling over month to month.
Offset: The share of your yearly electricity use that solar is designed to produce. A 100% offset aims to match a year of use; under low export credits a smaller offset can pay back faster.
Payback period: How many years of bill savings it takes to recover what you paid for a system. A shorter payback means a better investment, all else equal.
Peak sun hours: Daily sunlight expressed as the number of hours at full-strength sun (1,000 watts per square meter). Five peak sun hours means the day’s sunlight equals five hours of full sun.
PPA (power purchase agreement): A contract where a company owns the system and you pay for the electricity it produces at a set price per kWh, often rising each year.
PTO (permission to operate): The utility’s final go-ahead to switch on a grid-connected system. Running a system before PTO can violate your utility agreement.
Round-trip efficiency: The share of energy you get back out of a battery compared with what went in. About 90% is typical for home lithium batteries.
Solar lease: A contract where a company owns the panels on your roof and you pay a fixed monthly amount, often with a yearly increase (escalator), usually for 20–25 years.
Specific yield: Yearly energy a solar system produces per kW of capacity, in kWh/kW. It depends on sunshine, tilt, direction and shade. Sunny Southwest roofs often reach 1,600–1,800; cloudier northern roofs 1,100–1,300.
Time-of-use (TOU) rate: An electricity plan where the price per kWh changes by time of day, with the highest prices in late afternoon and evening. Batteries save money by covering those peak hours.
True-up: The annual settlement on a net metering or net billing account. Charges and credits from the past 12 months are totaled, and you pay any balance owed. Leftover credits may be paid out at a low rate or lost.
Usable capacity: The share of a battery’s energy you can actually draw. Spec sheets list it in kWh; compare usable, not total, capacity between batteries.

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