Solar Ham Radio Calculator
Duty cycle matters more than TX power. Enter your radio, accessories, and operating hours — get panels, battery Ah, POTA pack weight, and EmComm 72-hour battery sizing.
How to Use This Calculator
Set your radio type and — crucially — duty cycle
The most important input is duty cycle, not TX power. A 100W HF radio at 15% duty cycle draws an average of only ~36W — comparable to a QRP radio at high duty cycle. Most casual ham operating (ragchewing, DXing, POTA activations) is 10-25% TX; CW contesting reaches 40-50%; digital modes like FT8 can run 50%+ but at lower power. SSB voice is typically 15-20%. Getting duty cycle right determines whether your solar system works or runs the battery flat.
Add your accessories honestly
A laptop for logging adds 60W — nearly as much as the radio itself at low duty. Antenna tuners draw 15-25W continuously. A rotator controller draws 100W during antenna movement. These accessories often double the system's actual power requirement. For portable POTA/SOTA use, drop everything you can: phone for logging (5W), simple wire antenna (no tuner needed), no rotator.
Read the EmComm 72-hour battery estimate
Emergency communications operations need to sustain operation for 72 hours (3 days) without reliable solar charging. The calculator sizes the battery needed to run your station for 72 hours without any solar input. This is the worst-case battery sizing for emergency preparedness and is often much larger than the solar-optimized battery.
The Formula
The battery is sized at 1.5x daily Wh — roughly 1.5 days of autonomy. For POTA portable activations, this is conservative (you'll likely charge every day); for EmComm go-kits, the separate 72-hour figure is more relevant. LiFePO4 batteries have 90% usable depth of discharge (DoD) vs. 50% for AGM lead-acid, so an LiFePO4 battery can be roughly half the Ah of an AGM for the same usable energy.
Example
Dave (KD9XYZ) — POTA portable QRP activation
Dave is setting up a portable POTA activation kit. He'll use a QRP radio (5W TX), a manual antenna tuner, and his phone for logging — keeping weight minimal. He operates about 3 hours at each activation, transmitting about 20% of the time.
Result
Dave's ultra-light POTA kit fits in a daypack. A single 100W flexible panel (4 lbs), a 14Ah LiFePO4 battery (3 lbs), and a small MPPT controller (0.5 lbs) give him a self-sufficient station for all-day activations. The key insight: QRP + low duty cycle + no laptop means the power budget is tiny, and the system is cheap and light.
FAQ
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