Solar Charge Time Calculator

Peak Sun Hours (PSH) measure how much usable solar energy hits your panels per day, expressed as equivalent hours of full-strength sunlight (1,000 W/m²). A city might have 14 hours of daylight in summer, but only 6 of those hours deliver meaningful energy because early morning and late evening sun is too weak to count. PSH captures that reality. The data in this calculator comes from the National Renewable Energy Laboratory (NREL) and uses the average at latitude tilt metric, which matches how most people angle portable panels, roughly toward the sun at their latitude. This is more accurate than GHI (flat on the ground) or DNI (direct tracking only) for portable power station use.

Two reasons. First, the sun is lower in the sky during winter, which means light passes through more atmosphere before reaching your panels, reducing intensity. Second, winter days are shorter, which compresses the window of usable solar production. In Seattle, the difference is dramatic: roughly 6.5 PSH in July versus 1.3 in December. Phoenix sees a milder swing: about 9.5 in June versus 4.8 in December, because of its lower latitude and clearer skies. The monthly chart on this page shows the full curve for your selected city, so you can size your setup for the months you actually need.

Usually, yes, but voltage compatibility is the catch. What matters is whether the panel's voltage output (Vmp and Voc) falls within the generator's MPPT input range, and whether the combined wattage stays under the generator's solar input limit. Brand does not matter electrically. Connector type does: most third-party panels use MC4 connectors, while some generators use proprietary ports that require an adapter. This calculator checks all of this automatically and flags adapter requirements or voltage mismatches for your specific combination.

Charge times are estimates, not guarantees. The calculator uses verified OEM specifications for every generator and panel, real NREL irradiance data, and applies a 30% real-world derate that accounts for the gap between lab-rated output and field performance. Actual results still depend on factors no calculator can predict: local shading, cloud cover on a specific day, panel angle precision, ambient temperature, and the non-linear charging curve during the last 10-20% of battery capacity. Treat the result as a planning estimate: realistic enough to size your setup correctly, not precise enough to set a timer.