Solar panels and charge controllers

Solar is the most effortless of the charging options. Once the panels are fitted and the controller is connected, they quietly top up your battery whenever there is daylight, with no action needed on your part.

What to expect from solar

Solar is brilliant at extending your time off-grid and reducing your daily energy deficit. It offsets what you use each day, so you start each morning with more battery than you would have had without it. For many setups, that makes the difference between running out of power mid-trip and having comfortable headroom.

It is not, however, a guaranteed standalone power source. Output varies with the time of year, cloud cover, and shading, a UK winter day produces a fraction of what a clear summer day does. For full-time off-grid living, solar works best as part of a system alongside a DC-DC charger and mains charging, rather than as the only source of energy. The practical response is to size your panels generously rather than minimally, and not to rely on solar alone to cover everything.

MPPT or PWM controller

Every solar panel needs a charge controller between it and the battery. Its job is to regulate the panel's output into a safe, correct charge. There are two types.

A PWM controller is the basic option. It clips the panel's excess voltage to match the battery, which means a portion of the available energy is wasted. It is adequate for a very small single-panel setup with a lead-acid battery, but it is not the most efficient use of what your panels can produce.

An MPPT controller is the right choice for virtually any build worth investing in. Rather than clipping the excess voltage, it converts it into additional charging current, extracting more energy from the same panels. It works with all battery types including lithium, handles arrays of any size, and delivers power using a multi-stage charging process, the same bulk, absorption, and float stages as a good mains or DC-DC charger.

Key benefits of MPPT:

• Extracts more energy from the same panels than PWM
• Compatible with all battery types including lithium
• Handles arrays of any size
• Multi-stage charging — bulk, absorption, and float
• Adjusts automatically to changing light conditions throughout the day

How much solar do you need

• Weekend and short trips: 100 to 160W is enough to top up the battery between uses and extend a trip by a day or two without worrying about running low.
• A week off-grid comfortably: 200 to 300W gives you enough daily input to run a compressor fridge and general appliances without eating into your reserves.
• Extended or full-time off-grid use: 400W or more, giving you the headroom to manage across varying weather and heavier daily use.

More panels give you more buffer. Sizing generously costs relatively little more in the context of a full build and makes the whole system significantly more resilient.