Solar charging for radios and backup batteries in the UK

Solar can replenish a radio or backup battery, but only through a charging system matched to the battery and equipment. Start with the energy you need each day, then check the complete charging path. In a UK winter outage, treat solar as a variable top-up, not a guaranteed daily refill.

Choose the right charging path

• USB-chargeable radio or power bank: use a panel with a suitable regulated USB output and the device's supported charging lead. Check that it resumes charging after cloud or shade interrupts the supply. A bare panel is not a USB charger.
• Portable power station: use its designated solar input and approved compatible panel/cable arrangement. The solar controller is normally built into this path; do not add an unrelated controller or feed a raw panel into an ordinary DC output.
• Separate radio battery: use a correctly configured solar charge controller for the battery's chemistry and voltage, with appropriate protection and a suitable supply path to the radio. For a novice, a documented matched system is safer than assembling unknown components.

A radio's barrel connector may be a power input rather than a battery-charging input. Check the radio and battery manuals: powering the radio does not necessarily charge its pack. Never connect a raw solar panel directly to a lithium pack or assume a lead-acid charging setting is suitable for lithium.

Check compatibility in this order

1. Battery: identify chemistry, nominal voltage, capacity, permitted charge voltage/current and temperature range. Lithium-ion, lithium iron phosphate (LiFePO4), lead-acid and nickel-metal hydride do not share one charging programme.
2. Controller or power-station solar input: check the allowed input-voltage window, maximum open-circuit voltage, current and power. Open-circuit voltage, often labelled Voc, is the panel voltage with no load; it can rise in cold conditions.
3. Panel arrangement: use the manufacturer's supported configuration. Adding panels in series increases voltage; parallel arrangements increase current. Do not assume either is safe just because total watts look acceptable.
4. Cables and protection: check connector type and polarity, cable rating and length, and the required DC-rated fuse/protection arrangement. Protect battery-fed wiring as specified by the equipment documentation. Do not copy a fuse size from a different controller or battery.
5. Radio supply: verify the radio's full permissible input-voltage range, including while the battery is charging. A nominal battery label is not a promise of a fixed regulated output.

The Victron MPPT installation manual explicitly covers battery fusing, guarded terminals, polarity and cold-weather PV voltage. Its component values apply to the named models, not every portable setup. Use a competent installer for exposed-terminal systems or when you cannot confidently establish compatibility; this guide is not a wiring diagram.

Make a daily energy budget

Use watt-hours so that loads and batteries at different voltages can be compared. For a simple nominal battery estimate, Wh = V × Ah: a 12V, 20Ah battery represents 240Wh nominally, not 240Wh guaranteed at your radio. The battery's permitted discharge, conversion losses and operating conditions reduce what you can use.

Illustrative example: a radio system drawing an average 3W for eight hours needs 24Wh at the load. Add any charging and conversion losses when deciding how much solar energy must reach the battery. Include receive/standby consumption, not only transmit time. Our battery-runtime guide explains how to calculate an average radio load.

For a planning scenario, solar energy ≈ panel rated W × equivalent full-output sun hours × a stated delivery allowance. A 100W panel, an assumed 0.5 equivalent hour and a 70% delivery allowance gives 35Wh. With an assumed 0.1 equivalent hour it gives only 7Wh, below the example radio's 24Wh need. These are calculated scenarios, not forecasts, measured results or typical Cumbria winter yields. Equivalent full-output hours are not the same as daylight hours. Define what your allowance includes so you do not subtract the same losses twice.

What changes in a UK winter?

Energy Saving Trust's solar fact check explains that panels can work in cloud and winter but generate less in winter because days are shorter, cloud is more likely and sunlight is less intense. Panel angle, shade, nearby buildings and your actual location matter too. Annual roof-solar generation figures cannot tell you what a small portable panel will provide during a particular storm.

• Start the outage with stored charge rather than expecting sunshine to rescue an empty battery.
• Keep an alternative charging source or a compatible spare battery and reduce non-essential loads.
• Place a portable panel securely where it gets useful light without obstructing paths, exits or others. Do not climb onto a roof or take risks in wind to deploy it.
• Keep batteries and controllers within their specified temperature and moisture limits. A weather-resistant panel does not make its charger or connectors waterproof.
• Never assume all lithium batteries can charge below freezing. Follow the battery's actual limits and verify its protection, including any required temperature sensor or controller setting.

Victron's configuration guidance distinguishes charging algorithms and warns that an incorrect programme can damage the battery or create unsafe conditions. A battery-management system is not a substitute for a compatible charger, and a protection feature mentioned in marketing may require specific equipment or configuration.

Test the whole charging path before relying on it

Follow the manufacturer's connection order, then check indicated charging and a real increase in stored energy under safe conditions. Confirm what happens after temporary shading and whether the radio can operate while charging, if its manual permits that. Chargers can also introduce radio interference: compare reception with charging on and off rather than assuming every MPPT controller is quiet. Record conditions and observations, not just the panel's rated watts.

If you already have roof solar, ask the installer whether it has a supported outage mode: ordinary solar and battery installations do not necessarily power a home during a cut. For an independent portable setup, continue with our power-station sizing guide. Solar power alone does not establish a usable radio path or guarantee access to any local Cumbria network.