Before buying a panel for a power station, check three things against the station’s solar input rating: the panel’s voltage, its watts, and its connector. The station’s solar input is listed on every power station page, and solar input explained covers the station side.
Open-circuit voltage (Voc)
Voc is the panel’s voltage with nothing connected, the highest it produces. Vmp is its lower working voltage at maximum power. The station’s input range must cover both: Vmp must be above the station’s minimum for it to charge, and Voc must stay below its maximum, always. The panels ranked here have Voc from 20.5 V to 49.3 V.
Series or parallel
One panel on its own almost always fits a power station’s input range. With two or more:
- In series (positive of one panel to negative of the next), the voltages add and the current stays the same. Two panels with a 24 V Voc make 48 V. Series suits stations with a high-voltage input and keeps cable losses down.
- In parallel (positives together, negatives together, usually with a branch connector), the currents add and the voltage stays the same. Parallel suits stations with a low maximum voltage, as long as the combined current stays within the station’s input current limit.
Add up the Voc of every panel in a series string, not the Vmp, and compare it with the station’s maximum input voltage.
Cold weather
A panel’s voltage rises as it gets colder. Spec sheets that publish a Voc temperature coefficient give it as a percentage per degree Celsius, such as −0.3%/°C. Multiply it by how far below 25 °C the panel will be to find how much higher its Voc will run. A series string that sits just under a station’s limit in summer can exceed it on a cold, clear morning, so leave a margin.
Connectors
Portable panels come with one of a few output plugs. MC4, the standard for larger panels and rooftop solar, is used by 20 of the panels here, and XT60, common on power stations, by 1. Others use Anderson or DC barrel plugs. Most makers include an adapter to their own stations; for a different brand of station, check the “Cables included” row on the panel’s page, or budget for an MC4-to-XT60 (or similar) adapter.
Sources
- Wikipedia, Solar cell: open-circuit voltage: Voc and Vmp.
- Solar Permit Solutions, NEC 690.7 solar voltage limits: cold raising panel voltage and the temperature-coefficient calculation.
- Voltages, coefficients and connectors: each product’s manufacturer specifications, linked from its page.