Off-Grid Solar Systems: How They Work and What You Need

How do off-grid solar systems work? It is built from four parts: panels, a charge controller, a battery bank and an inverter. The panels make the power, the controller manages it, the batteries store it, and the inverter turns it into normal mains electricity. The real skill is sizing it around how you actually live.

The four parts of a solar system

Whether it is powering a narrowboat, a campervan or a cottage, an off-grid solar setup is built from the same four parts.
The panels generate direct current from daylight, the charge controller regulates that power so it fills the batteries safely, the battery bank stores it for the evenings and dull days, and the inverter converts it into the 230V electricity your appliances expect. Getting your system voltage right at the outset is what ties them together neatly.

How big does it need to be?

This is the part people most often get wrong, usually by copying someone else’s numbers instead of working out their own.
There is no standard size. A frugal van or boat can run happily on around 2kW of panels, while a family in a house who want to run everything might need 6kW or more, with anything from a few kWh to 30kWh of battery to match.
Our own setup runs on about 2kW of panels through a pair of 3kVA inverters, which is plenty for the way we live. Work out what you genuinely use, then size to that rather than to someone else’s home.

Sizing it for a British winter

A solar panel in December produces only a fraction of what it makes in June, so you plan around the dark months rather than the bright ones. That usually means a little more panel and battery than the sums suggest, plus a plan for the odd still, grey week when almost nothing charges.

Most off-grid homes keep something in reserve for those spells. For a fixed home that is often a generator, or a small wind turbine where the site suits it, while on a boat or in a van you have the simpler option of topping the batteries up from the engine alternator when you run it or move along.

What it costs

Off-grid solar costs more than a grid-tied system, because you are also paying for the batteries that carry you overnight and through the winter.
A small van system might be a few hundred to a few thousand pounds, while a full home setup with enough winter storage often starts from around £10,000 and climbs from there. Running heavy jobs while the sun is high, and saving energy where you can, keeps the whole system smaller and cheaper.

Frequently asked questions

Can you run a fridge and a washing machine off-grid on solar?

Yes, but big appliances shape your system. A fridge sips power steadily all day, while a washing machine or kettle takes a large gulp in a short burst. Run those while the sun is high, and size your inverter and battery for the peak.

What is the difference between an MPPT and a PWM charge controller?

Both protect your batteries, but an MPPT controller squeezes noticeably more usable power out of your panels, especially in weak winter light. PWM controllers are cheaper and fine for small setups, though most off-grid homes get better value from MPPT over time.

How long do off-grid solar batteries last?

It depends on the type. Lithium (LiFePO4) batteries commonly last ten years or more and cope well with daily deep cycling, while cheaper lead-acid banks often need replacing sooner. Batteries are the part you are most likely to renew, so it is worth budgeting for it.

Can you connect an off-grid solar system to the mains later?

You can, but it is not a simple plug-in. Grid-tied and off-grid systems are wired differently, so adding a grid connection later usually means extra kit and an electrician. If you might connect one day, tell your installer early.