How Many Watts Do You Need to Charge a Phone with Solar?
If you're heading off-grid and wondering how many watts you need to charge a phone with solar, the short answer is: a typical smartphone draws roughly 5 to 10 watts while charging, so a solar panel rated around 15 watts in direct sunlight comfortably keeps a phone topped up. If you want faster charging or the ability to fill a power bank at the same time, step up to 25 watts. Below we break down exactly how solar wattage maps to real-world charge time and which SunJack panel fits your needs.
How Many Watts Does a Phone Actually Need?
Most modern smartphones charge at somewhere between 5W and 10W over a standard USB connection, and fast-charging phones can briefly pull 15W to 25W early in the charge cycle. A full phone battery holds roughly 10 to 20 watt-hours of energy, which is why a phone can usually go from empty to full in one to two hours on a good charger.
The key thing to understand with solar is that a panel's wattage rating is its peak output in direct, overhead sunlight. Real-world output is almost always lower, so you want a panel rated higher than your phone's draw to leave headroom. That's why we recommend matching a 5-10W phone with a 15W or larger panel rather than a 5W panel that barely keeps pace.
Solar Wattage vs. Phone Charge Time
Here's a rough guide to how different panel sizes perform in good, direct sunlight. Treat these as approximate ballpark figures, since actual results depend heavily on sun angle, weather, and your phone's battery size.
| Panel Wattage | What It Can Do | Approx. Phone Charge Speed |
|---|---|---|
| 5W | Trickle charge only | Slow — barely keeps a phone topped up while idle |
| 10W | Charges one phone steadily | Moderate — noticeably slower than a wall outlet |
| 15W | Charges one phone comfortably | Roughly wall-charger speed in full sun |
| 25W | Charges a phone plus a power bank | Faster — tops a phone quickly with energy to spare |
As the table shows, more watts doesn't just mean a faster phone — it means you can charge a phone and bank extra energy for later. Browse the full lineup of portable solar panels to compare sizes side by side.
Why Sunlight Quality Matters More Than the Rating
Solar panels only produce meaningful power in direct sunlight. Point a panel at the open sky on a clear day and a 15W panel performs like a 15W panel. Move into shade, haze, or heavy cloud cover and output can drop to just 10% to 25% of the rating — meaning that same 15W panel might only deliver 2-4W on an overcast afternoon.
A few practical tips to get the most out of any panel:
- Lay the panel flat or angle it directly toward the sun, not toward the horizon.
- Keep the entire surface unshaded — even a small shadow can cut output sharply.
- Reposition every hour or two as the sun moves across the sky.
- Avoid charging through a window; glass blocks a large share of usable light.
Charging at Night: Why You Need a Power Bank
A solar panel produces nothing after sunset, so charging directly from a panel only works during daylight. The smarter approach is to use the panel to fill a power bank during the day, then charge your phone from that battery whenever you need it — including overnight.
This is exactly why our solar panel kits pair a panel with a high-capacity battery. A 10,000mAh power bank holds enough energy for roughly two to three full phone charges, so you bank sunlight while it's available and draw on it whenever. If you already own a panel, you can add a standalone 18W 10,000mAh power bank, or browse all of our power banks.
Which SunJack Panel Should You Choose?
For most people charging a phone, the decision comes down to two panels:
- SunJack 15W panel — the sweet spot for keeping a single phone charged at near wall-outlet speed in direct sun. Lightweight and ideal for day hikes, camping, and everyday emergency backup.
- SunJack 25W panel — the better pick if you want faster charging, plan to charge a phone and a power bank at once, or share power with a travel companion.
If you want a complete grab-and-go solution, the 15W + 10,000mAh kit bundles a panel with a battery so you can capture sunlight by day and charge by night with no guesswork. It's the most popular choice for travelers who want a single, ready-to-use system.
Frequently Asked Questions
Can a 5W solar panel charge a phone?
Yes, but slowly. A 5W panel can trickle-charge a phone in strong direct sunlight, roughly keeping pace with the battery rather than filling it quickly. For a noticeable charge, a 15W or 25W panel is a much better fit.
How long does it take to charge a phone with a 15W solar panel?
In good, direct sunlight a 15W panel charges a typical phone at close to wall-charger speed — roughly one to two hours for a full charge. Clouds, shade, or a low sun angle will extend that time.
Will a solar panel charge my phone on a cloudy day?
It can, but expect far less power. On overcast days, output often drops to just 10-25% of the panel's rating, so charging is slow. This is another reason to bank energy in a power bank when the sun is out.
Can I charge my phone with solar at night?
Not directly — panels need sunlight. Instead, charge a power bank during the day and use that battery to charge your phone after dark. Our kits include a power bank for exactly this reason.
Should I get the 15W or 25W panel?
Choose the 15W panel if you mainly charge one phone and want a light, compact option. Choose the 25W panel if you want faster charging or need to power a phone and a power bank (or a second device) at the same time.