Solar panel output calculator: how much power per day?
A panel’s watt rating is what it makes in perfect full sun. Multiply by your peak sun hours and take off system losses to get what it really produces in a day.
Enter your measurements
More options: Losses · Battery V
- Per month (30 days)
- 11.6 kWh
- Per year
- 141 kWh
- Into a battery per day
- 30 Ah
- In one hour of full sun
- 86 Wh
- Peak charging current (MPPT)
- 7.8 A
100 W × (1 − 14% losses) = 86 Wh per peak sun hour
× 4.5 peak sun hours = 387 Wh a day (30 Ah at 12.8 V)
Quick answers for common sizes
| Example | Answer |
|---|---|
| How much power a 100W solar panel produces per day | 387 Wh a day at 4.5 sun hours |
| How much power a 200W solar panel produces per day | 774 Wh a day at 4.5 sun hours |
| How much power a 400W solar panel produces per day | 1.55 kWh a day at 4.5 sun hours |
Output at other peak sun hours
| Peak sun hours per day | Output per day | Per month (30 days) | Into a battery per day |
|---|---|---|---|
| 2 | 172 Wh | 5.2 kWh | 13 Ah |
| 3 | 258 Wh | 7.7 kWh | 20 Ah |
| 4 | 344 Wh | 10.3 kWh | 27 Ah |
| 5 | 430 Wh | 12.9 kWh | 34 Ah |
| 6 | 516 Wh | 15.5 kWh | 40 Ah |
| 7 | 602 Wh | 18.1 kWh | 47 Ah |
Worked examples: how much power a 100W solar panel produces per day, how much power a 200W solar panel produces per day and how much power a 400W solar panel produces per day.
How panel output is worked out
Wh per day = panel watts × peak sun hours × (1 − system losses) kWh per year = Wh per day × 365 ÷ 1,000 amp-hours per day = Wh per day ÷ battery volts
The watt rating on a panel is measured at standard test conditions: 1,000 W/m² of sunlight at a 25 °C cell temperature. Real days rarely look like that, so solar is planned in peak sun hours — the day’s total sunlight expressed as hours of that full sun. System losses (heat, dirt, wiring, mismatch, conversion) then take a share; PVWatts’ default is 14%.
Peak sun hours by city
| City | Peak sun hours (year) | 100 W panel, Wh/day | 400 W panel, kWh/year |
|---|---|---|---|
| Phoenix, AZ | 6.57 | 565 | 715 |
| Los Angeles, CA | 6.09 | 524 | 680 |
| Denver, CO | 5.74 | 494 | 654 |
| Miami, FL | 5.57 | 479 | 621 |
| Dallas, TX | 5.41 | 465 | 605 |
| Chicago, IL | 4.46 | 384 | 523 |
| New York, NY | 4.45 | 383 | 517 |
| Seattle, WA | 3.83 | 329 | 428 |
Per hour: the question people ask
A 100 W panel makes at most about 100 W in the brightest midday sun on a cool day — and typically less, because panels get hot. Averaged over the day, it is far lower. That is why “watts per hour” is the wrong question: ask for watt-hours per day, which is what fills a battery.
Things that cut output
- Heat. Victron’s example panel loses about 0.45% of its power for every °C above 25 °C; at a 75 °C cell temperature, a 100 W panel makes about 77.5 W.
- Flat mounting. A panel lying flat on a van roof misses a lot of winter sun; see the best angle for solar panels in winter.
- Shade and dirt. Partial shade on one cell can drag down a whole panel.
- PWM controllers. A PWM controller pulls a 12 V panel down to battery voltage; Victron measured 81 W from a 100 W panel at 25 °C versus 100 W with MPPT.
What you’ll need
- 100 W solar panelMid-range price
The building block of most van, boat and RV systems. Check the data-sheet Voc and Isc before you decide how to wire several of them.
See options on Amazon (opens in a new tab) - MPPT solar charge controllerMid-range price
Converts a higher panel voltage into charging current, so you can wire panels in series and lose less in the cables. Size it on output amps and maximum PV voltage.
See options on Amazon (opens in a new tab) - Adjustable tilt mount bracketsBudget price
Lets you change a ground- or roof-mounted panel’s angle with the seasons instead of leaving it flat.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much power does a 100W solar panel produce per day?
About 387 Wh on a 4.5-peak-sun-hour day after 14% losses — roughly 30 Ah into a 12.8 V battery. In Phoenix’s yearly average of about 6.6 peak sun hours it is about 565 Wh. See how much power a 100W solar panel produces per day.
How much power does a 100W solar panel produce per hour?
Up to about 100 W in perfect full sun, and less on a hot panel; after typical 14% system losses, about 86 Wh in an hour of full sun. Over a whole day the average is much lower.
How many kWh does a 400W solar panel produce per year?
PVWatts gives about 715 kWh a year in Phoenix and about 428 kWh in Seattle for a tilted, south-facing 400 W panel. See how much power a 400W solar panel produces per day.
Why does my panel never reach its rated watts?
The rating is at 1,000 W/m² and 25 °C. In real sun the panel heats up — Victron’s example loses 0.45% per °C above 25 °C — and dirt, wiring and the controller take their share.
Related guides
Sources
- National Laboratory of the Rockies (formerly NREL) — PVWatts® Calculator (opens in a new tab) — Look up the solar resource (peak sun hours) and yearly output for your own address; default system losses 14%.
- NLR (formerly NREL) — PVWatts® v8 API, NSRDB PSM V3 TMY data (opens in a new tab) — City figures on this site: fixed open-rack array facing due south, tilted at the site’s latitude, 14% system losses, queried October 2026.
- Victron Energy — Which solar charge controller: PWM or MPPT? (2020) (opens in a new tab) — MPPT output current = panel watts ÷ battery voltage (100 W ÷ 13 V = 7.7 A); a PWM controller pulls the panel down to battery voltage (81 W from a 100 W panel at 25 °C, about the same as MPPT at 75 °C); temperature-coefficient method; example panel Voc 21.6 V, −0.35 %/°C.