A solar panel lets you stay on the air long after a battery would have run flat, and it is a large part of what makes Field Day, park activations and emergency practice possible without a generator. It is also easy to get wrong. A panel that is too small, a controller that is mismatched, or a wiring order that damages equipment can turn a good day outdoors into a frustrating one. This guide walks through sizing, pairing and wiring a simple system. Remember that transmitting requires the correct licence, and that rules differ between Canada and the USA, so follow the regulations where you operate.
Start with your load, not the panel
Every solar plan begins with how much energy your station uses. Check your radio's manual for its current draw on receive and on transmit at the power you plan to run. Many modern HF radios draw an amp or two on receive, while a 100-watt transmitter can pull well over 20 amps at peak. Low-power (QRP) setups draw far less. Because most operating time is spent listening, your average draw is much lower than the peak, especially in SSB and CW where the transmitter only works part of the time.
Add anything else on the same battery: a laptop, an audio interface, a tuner, lights. If you are unsure, measure with an inline power meter during a practice session. Actual numbers beat guesses.
Turn amp-hours into panel watts
Here is a simple, illustrative example. Suppose your setup averages about 3 amps over 4 hours. That is 12 amp-hours, or roughly 150 watt-hours at about 13 volts. Sunlight is not constant, so divide by the number of good "peak sun hours" for your location and season. This is often somewhere around 3 to 6 hours a day, but it varies widely, so use a cautious figure. Panels also rarely deliver their label rating, because heat, angle, haze and wiring losses take a share. Planning on well under the rated output is sensible.
With 4 sun hours and a generous allowance for losses, 150 watt-hours suggests a panel in the range of 50 to 60 watts. Round up. Those figures are only an example, so run the same maths with your own numbers.
The three-part system: panel, controller, battery
Do not connect a panel directly to your radio. A panel's voltage swings with light and temperature and can be well above what a radio tolerates. A charge controller sits between the panel and the battery and regulates charging. The battery then powers the radio, smoothing out clouds and shade. For choosing and caring for the battery itself, see our comparison of LiFePO4 and AGM batteries.
Set the controller to your battery's chemistry. Lead-acid and lithium iron phosphate batteries need different charging profiles, and the wrong one can undercharge or damage the battery. Also avoid charging lithium batteries in freezing weather unless the battery is designed for it.
PWM or MPPT?
A PWM controller is a simple, low-cost design that works best when the panel is built for the battery's voltage. An MPPT controller tracks the panel's best operating point and accepts higher input voltages, which gives more flexibility and often more energy in cold or weak light. For one small panel and short outings, PWM can be plenty. For larger arrays or mixed conditions, MPPT is often worth it.
Match voltage and current to the controller
Read the controller's specifications. Two limits matter most: the maximum input voltage and the maximum charge current. A panel's open-circuit voltage is higher than its working voltage, and it rises in cold weather, so a cold, bright morning is the moment a mismatched controller is most at risk. Keep the panel's open-circuit voltage safely below the controller's input limit.
If you connect panels in series, voltages add. In parallel, currents add. Series strings lose more output when one panel is shaded, while parallel wiring needs thicker cable and fusing.
Wire it in the right order
Most controllers want the battery connected first, then the panel, then the load, and the reverse order when disconnecting. This lets the controller detect the battery voltage before it sees panel power. Cover the panel with a cloth while connecting it, so you are not handling live cables in full sun. Confirm polarity with a multimeter before every connection. Reversed polarity is one of the most common ways to destroy electronics.
Place a fuse or breaker in the positive lead close to the battery, and size it for the cable, not just the radio. Fuse the panel side too if your controller's manual recommends it.
- Battery to controller first, with a fuse near the battery
- Panel to controller second, ideally covered while connecting
- Radio to the battery or load terminals, also fused
Choose sensible wire and connectors
Thin wire drops voltage, wastes power and can overheat. Keep runs short and use wire rated for the current. A radio transmitting at full power needs heavy, short leads, so run it from the battery rather than through a long, thin cable. Use connectors that only mate one way, such as Anderson Powerpole-style connectors, which are a common ham standard, and keep the polarity convention consistent across all your gear. Strain relief matters outdoors, because cables get tripped over.
Keep the noise floor down
Some charge controllers and cheap power electronics generate radio noise that raises the receive noise floor, especially on HF. Test with the controller running and your antenna connected. If noise appears, move the controller farther from the antenna and radio, shorten and separate cables, add clamp-on ferrite chokes to the panel and battery leads, or try a different controller. In an emergency you can also disconnect the panel briefly while receiving a weak signal, then reconnect it. Noise is a reason to test at home before the event. The ham radio quick reference is handy on the day for band and mode reminders, and the live HF propagation page helps you decide which bands are worth your stored energy.
Field checklist
- Panel, controller and battery rated for each other's voltage and current
- Controller set to the correct battery type
- Fuses fitted and spare fuses packed
- Multimeter to check polarity and voltage
- Panel tilted toward the sun and not shaded by trees, masts or tents
- Cables secured and connectors weather-protected
- Antenna set up away from people, with everyone kept clear while transmitting
For broader planning, our 72-hour emergency power plan covers what to do when the sun does not cooperate.
Common mistakes
- Connecting the panel directly to the radio. Always regulate through a controller and battery.
- Ignoring open-circuit voltage. The label's working voltage is not the maximum.
- Wrong battery setting. Chemistry profiles matter.
- No fuse. A short circuit on a battery can start a fire.
- Undersizing for the season. Winter and cloudy days give far less energy.
- Skipping a test. Noise and wiring faults are easier to fix in the driveway than in the field.
Wrap-up
Solar power for portable operation comes down to a few steps: estimate your load, size the panel with margin, pair it with a suitable controller and battery, wire it safely in the right order, and test for noise beforehand. Once it works, you can operate for hours without worrying about the battery. Afterward, record what you worked in the free online logbook so your portable contacts are organised and ready for awards and confirmations. If you would like to size your supply from the other direction, our guide to a 13.8V power supply is a good companion read.
How HamRadioList can help
Before you head out with your panel, check the live HF propagation page so you know which bands are worth the battery power. When you get home, log your portable contacts in the free HamRadioList logbook and send friendly QSO cards to the stations you worked.
- Live HF propagation - see current band conditions before you call CQ.
- Free online ham radio logbook - log every contact, import and export ADIF, sync with QRZ.com and keep your awards organised.
- QSL and QSO cards - create shareable QSO and QSL cards from your logged contacts.
- Ham radio quick reference - bands, modes, phonetics and Q-codes on one page.
- Live broadcasting guide - share your own station live on the air.
New here, or getting back on the air? Create your free HamRadioList account to log contacts, check band conditions and practise for your exam, or browse more guides from the blog. HamRadioList is built by amateur radio operators in Nova Scotia for operators everywhere.