The biggest expense in an off-grid system

At the heart of an off-grid system are the batteries. It can be tricky to work out what you need when you go off-grid for the first time. There’s a learning phase as you get used to a system’s limits and adapt to more efficient ways of using the power you generate.

If you over-estimate how much energy you use, you may buy expensive batteries that you don’t need. Underestimate it, drain the batteries too low, and you can easily ruin them.

You can hold off on spending large amounts on batteries, but not for too long. Ideally, all batteries are the same size and age. Wire in new batteries to ones that have been used for more than six months, and it immediately reduces the lifespan of the new batteries to that of the older ones.

Older off-grid systems used flooded lead-acid batteries, which are still available to buy. However, they require careful, ongoing maintenance. If used and maintained perfectly, they can last up to eight years, but it can be a bit involved, says Ethan.

“If you’re a bit of a techy person who likes to monitor water levels, top them up, measure the SG (specific gravity, the unit that indicates battery health), they can last a long time.”

Modern lead-acid batteries use gel instead of water, so they’re far more userfriendly and will last five years or more depending on use.

“Gel batteries are also suited to more extreme temperatures and weather conditions – some flooded lead-acid batteries don’t like being too cold or too hot, as it can affect their performance. With gel, so as long as it’s above freezing and below about 50°C, they operate perfectly.”

The newest option is the lithium battery. It’s also the most expensive, costing up to four times more than lead-acid. However, their lifespan is longer (10-15 years) and they’re more forgiving of mistakes.

“Because of the chemistry used in lithium batteries, they don’t degrade when they’re deeply discharged or left in a partially charged state,” says Ethan. “The big thing is to make sure they have a really good management system built into them, so they’re receiving an even charge across the cells.”