What does "100W" mean on a solar panel?
It is the panel's rated power. Panels are often rated at a standard light level of 1,000 watts per square meter. Real sunlight changes from moment to moment, so output changes too.
What are peak sun hours?
Peak sun hours are a day's sunlight counted as hours of full, 1,000 W per square meter sun.
They depend on where you are and the time of year, so a basic estimate uses your area's average for the month. One textbook example: a place that gets 8 kWh per square meter in a day has 8 peak sun hours.
Our solar recharge estimator lets you try your own numbers.
What takes a share of a panel's output?
Output can be lower than the rating times the sun hours, because several things take a share:
- Dirt and dust on the panel's surface take some of the light before it gets into the panel.
- Wiring loses some power to the resistance of the cables.
- Shading, snow, mismatch and connections are among the losses NREL's PVWatts calculator counts.
NREL's PVWatts calculator counts losses from dirt, shading, snow, mismatch, wiring, connections, light-induced degradation, nameplate rating, system age and availability, and uses 14% for them as a default. The examples below use 14% only because it is a published default, not a measurement of any panel. Your real losses can be higher or lower.
The list above does not include heat: solar cells generally work best at low temperatures.
How much energy does a 100W panel make in a day?
Watt-hours a day = 100 W × peak sun hours × (1 − losses)
Example (illustrative): with a made-up 5 peak sun hours, the panel's rating gives 100 × 5 = 500 Wh. Taking off 14% leaves 500 × 0.86 = 430 Wh.
With a made-up 3 peak sun hours, it is 100 × 3 × 0.86 = 258 Wh.
| Peak sun hours | Before losses | After 14% losses |
|---|---|---|
| 3 | 300 Wh | 258 Wh |
| 4 | 400 Wh | 344 Wh |
| 5 | 500 Wh | 430 Wh |
| 6 | 600 Wh | 516 Wh |
What can that run? Device run times, by their makers' figures.
These divide the 430 Wh example day by each device's power, before any battery or conversion losses. The power figures come from each maker's own spec sheet or manual.
- A CPAP. ResMed lists the AirSense 11's typical power use as 56.1 W. That is about 430 ÷ 56.1 = 7.7 hours. On the 258 Wh day it is about 258 ÷ 56.1 = 4.6 hours.
- A Starlink kit. Starlink lists the Standard kit's average power use as 75 to 100 W. That is about 430 ÷ 100 = 4.3 to 430 ÷ 75 = 5.7 hours.
- A refrigerator. Frigidaire lists 410 kWh a year for its 18.3 cubic foot FFTR1835V, or about 410 ÷ 365 = 1.12 kWh (1,120 Wh) a day by that rating. LG lists 417 kWh a year for its 23.8 cubic foot LHTNS2403S. A 430 Wh day covers about 430 ÷ 1,120 = 0.38, a bit over a third, of the Frigidaire's day.
These examples stop at the panel. One inverter maker's manual we hold lists a conversion efficiency greater than 90% at continuous rated output, so some energy is lost when it is converted.
How long does a 100W panel take to charge a power station?
About 2.3 days in the example below, before charging losses. Divide the station's watt-hours by the panel's watt-hours a day.
Example (illustrative): a made-up 1,000 Wh power station and the 430 Wh day: 1,000 ÷ 430 = 2.3 days of that sun.
Check the station's solar input limits before you connect a panel. The solar input limits guide shows how to read them.
Which 100W panels does Solar Gear Scout track?
The table below is live: it is filled in each time this page loads. It lists the panels rated about 100 W that we track, best value first, with the type and weight their makers state.
You can browse every tracked panel on the solar panels page.
A 100W panel checklist.
- Find your peak sun hours for the month you care about.
- Work out watt-hours a day: 100 × peak sun hours × (1 − your losses), or × 0.86 if you use the 14% default.
- Find each device's power use on its own spec sheet or label.
- Divide the day's watt-hours by the device's watts for hours of use.
- Check your power station's solar input limits before you connect.
Related tools and pages.
- Solar recharge estimator
- What a power station's solar input limits mean
- How to size a portable power station
- Solar panel efficiency
- Solar panels
100W solar panel FAQ.
How many watt-hours does a 100W solar panel make a day?
About 100 × your peak sun hours, minus losses. With a made-up 5 peak sun hours and the 14% default, about 430 Wh.
Can a 100W solar panel run a CPAP?
On paper, about 7.7 hours on the 430 Wh example day, by ResMed's figure for the AirSense 11 (56.1 W typical), before any battery or conversion losses.
Can a 100W solar panel run a refrigerator?
On the 430 Wh example day, no. A refrigerator rated at 410 kWh a year is rated at about 1,120 Wh a day; a 430 Wh day covers a bit over a third of that.
Can a 100W solar panel run Starlink?
On paper, about 4.3 to 5.7 hours on the 430 Wh example day, by Starlink's figure for the Standard kit (75 to 100 W on average), before any battery or conversion losses.
How long does a 100W panel take to charge a 1,000 Wh power station?
About 2.3 days in the example, before charging losses.
The general statements on this page rest on published sources, each quoted in our facts file: PVEducation, the online photovoltaics textbook by Christiana Honsberg and Stuart Bowden; Vaisala's solar resource notes; NREL's PVWatts Version 5 Manual (2014); Sandia National Laboratories' PV Performance Modeling Collaborative; and the U.S. Department of Energy's Solar Energy Technologies Office. Device power figures come from each maker's own spec sheet or manual, read and checked by Solar Gear Scout. Solar Gear Scout has not tested any solar panel or device.
The sun hours and the 1,000 Wh power station in the examples are made up, with round numbers chosen to show the math. Panel facts in the live table are filled in from Solar Gear Scout's data each time the page loads.