Field power calculator

A trip to a summit (SOTA) or a park (POTA) comes down to one thing: how much energy you can carry in your rucksack. Give me your radio’s draw and time on air, and I’ll calculate consumption in Ah/Wh, what battery to take (LiFePO4 or AGM) and how big a solar panel you need so you don’t come back with a dead radio.

RX/TX draw + duty battery [Ah] PV panel [W] off-grid

Calculate power How I calculate it

Portable LiFePO4 battery — powering a radio in the field (SOTA/POTA)

Your trip

// choose the radio profile and operating time — the rest works itself out

Radio profile

Receive current (A)

Transmit current (A)

Duty cycle

30%

Operating time

4 h

Hours of full sun

4 h

PL: summer ~5 h, spring/autumn ~3 h, winter ~1.5 h.

Battery type

Usable capacity: LiFePO4 ~90%, AGM/gel ~50%.

Your kit for the trip

Take a battery — Ah (LiFePO4) · panel — W · you’ll use — Wh over — h

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“Sustaining” vs “recharging” panel. A sustaining panel covers the ongoing draw when the sun is out (the radio runs “off the panel”). A recharging panel is sized to recover all energy used within the given hours of sun — pick the larger of the two if you want to return with a full battery. Add a ~20–30% margin for clouds and cold.

Under the bonnet

How I calculate it

A simple energy balance: average current draw × time = consumption, and from that you size the battery and panel.

Equations

Average draw: I = I_rx · (1 − duty) + I_tx · duty [A]. On transmit the radio draws a lot, on receive little — duty cycle is the fraction of time with key/PTT pressed.
Consumption: Ah = I · time, and energy Wh = Ah · 12.8 V (LiFePO4 nominal voltage).
Battery: Ah_bat = Ah / DoD — you don’t discharge to zero. You can use ~90% of LiFePO4, ~50% of AGM/gel, so for the same consumption you need almost twice as much lead.
Sustaining panel: P = I · 12.8 / 0.72 [W] — covers the draw in sun (0.72 accounts for losses in MPPT, angles, heat).
Recharging panel: P = Wh / (sun_hours · 0.72) — recovers all consumption within the sun window.

SunTrack energy storage — illustration for the technical section

✓

QRP wins in the field. A 5–10 W radio on CW/SSB averages a fraction of an amp — a small LiFePO4 battery and a light, folding ~20–50 W panel will last all day. It’s only at 100 W that power becomes real baggage: the battery and panel grow several-fold.