Small Solar Panels: What 10 to 100 Watt Panels Can Charge

A small solar panel of 10 to 100 watts can charge phones and power banks, keep a 12V car or boat battery topped up, run a gate opener or a trail camera, and recharge a small power station. Expect each watt of panel to give about 4 to 6 watt-hours on a clear day, minus 20 to 30% for losses.

What a small solar panel makes in a day

A panel’s watt rating is its maximum output under Standard Test Conditions, a lab setting. Renogy, a panel maker, notes that panels rarely reach that rating in everyday use, because location, weather, angle, shading and heat all cut output. The Department of Energy adds that solar cells generally work best at low temperatures, so a hot summer roof can make less than a cool spring day.

The simple math is: daily watt-hours = panel watts x peak sun hours. One peak sun hour is an hour of sunlight at 1,000 watts per square meter. Renogy gives Phoenix about 6 to 7 peak sun hours a day and Seattle about 3 to 4, so the same panel can make twice as much in one city as in the other.

The losses column uses the middle of Renogy’s 20 to 30% range for heat, wiring and the charge controller. Cloudy days make far less.

Charging phones and power banks with a small panel

A folding panel with USB ports is the simplest small panel: unfold it, face it at the sun and plug in a phone. USB-C ports follow the USB Power Delivery standard, which the USB Implementers Forum says allowed up to 100 W, and up to 240 W under revision 3.1. A 10 to 30 W folding panel delivers far less than either limit, so the panel’s watts and the sun, not the port, set the charging speed.

A phone’s charging can pause each time a cloud passes. Charging a power bank from the panel during the day, then the phone from the power bank, smooths that out.

Keeping a 12V battery charged

A small panel is a good match for a battery that sits unused: a car in storage, a boat, a tractor or an RV between trips. Renogy’s sizing guide lists 75 to 100 W of panel for a 50 Ah 12V battery, recharged in about 6 to 8 hours, and names car battery maintenance and small lighting as typical uses. A 100 Ah battery needs about 150 to 200 W.

To size your own, Renogy uses watts = amp-hours x 12 volts / hours of charging, then adds 20 to 30% for losses. A 100 Ah battery charged over 10 hours works out to 120 W before losses.

Solar panels for gate openers and trail cameras

Gate openers and trail cameras are built around small panels. Mighty Mule’s FM123 kit is a 10 W panel that trickle-charges the opener’s 12V battery and works with its gate openers. The maker’s chart of daily gate cycles assumes 8 hours of sunlight, offers a 30 W option for busier gates, and notes that adding accessories may call for an extra battery. Mighty Mule also tells owners to check the opener’s manual for the most solar watts it can accept, so a bigger panel is not always better.

Trail cameras use even smaller panels. SPYPOINT sells external panels at 5 W (SPLB-10) and 10 W (SPLB-22), and says both are IP66 waterproof for wet weather. Mount the panel where it sees the most sky, even if the camera itself sits in the shade.

For gate posts, fences and poles, our guide to solar panel mounts covers pole and wall brackets that hold a small panel at a steady angle.

Charging a power station from a small panel

A 100 W panel can recharge a small power station, but slowly. Using the table above, it makes about 300 Wh after losses on a day with 4 peak sun hours, so refilling a 1,000 Wh unit takes 1,000 ÷ 300, or about 3.3 such days. That is an estimate, and cloudy or hot days stretch it. For faster charging, use a bigger panel or several panels, within the power station’s solar input limit. Our guide on how to charge a solar generator covers input limits and connectors, and what size solar generator you need helps match battery size to your loads.

Picking a battery for a small solar setup

A panel only makes power while the sun is up. For lights at night or a camera that runs around the clock, pair it with a 12V battery and a controller. If you choose a lithium iron phosphate (LiFePO4) battery, check that the charge controller has a lithium setting. Our LiFePO4 vs NMC comparison explains how the two lithium chemistries differ. If the job is moving air in a greenhouse, shed or coop, a fan kit with its own panel is simpler; see our guide to solar powered fans. Our guide to solar charge controllers covers sizing one, and solar panels for sheds compares the options for an outbuilding.

Bird droppings, pollen and leaves can shade whole cells on a small panel. A gentle rinse clears them; see how to clean solar panels. For every panel guide in one place, start at our solar panels section.