How big should your battery be?

Already have solar and thinking about a battery? Learn how to use your overnight electricity usage to work out a sensible starting size, and what to check before accepting a quote.

A practical guide from Andy McMaster, founder of Why Solar, written after his own costly solar mistakes.

32pages, with a sizing worksheet
7questions to ask an installer

Make your next battery conversation more useful.

Find your night-time number.

Understand how much electricity your household uses when your solar isn't covering it.

A 24-hour strip from the guide: from 5pm to 7am is the battery's job, the rest of the day your panels run the house. — From page 8 of the guide

Illustration from the guide: a shed full of batteries at dusk, with a generator running beside it

Why I wrote this guide.

We paid close to $100,000 for an off-grid system that failed us.

The batteries installed weren't the ones we'd paid for, and it took years to put things right.

Today, our home runs on solar and batteries. That experience taught me to look at the household's numbers, understand what the equipment can deliver and check exactly what will be installed.

I wrote this guide to help you ask those questions before you spend your money.

Andy McMaster, Founder, Why Solar

Read it. Use it. Bring your numbers to a quote.

The guide includes a worksheet to organise your figures and a checklist to help you understand an installer's recommendation. About twenty minutes is enough to get started.

CoverHow big should your battery be?
Page 2Inside
Page 8Your night-time number
Page 10The season test
Page 18The number on the box isn't the number you get
Page 23Three households, three right answers
Page 26Seven questions to ask before you sign
Page 28Your numbers: a worksheet

Common questions

Do I need to know my battery size already?: You can start with your electricity usage and work through the guide. An installer will need to assess your home and equipment before making a final recommendation.
Can I use this if I don't have solar yet?: Yes. The guide is particularly useful for people adding a battery to existing solar, and it also explains questions to ask when planning both together.
Does downloading the guide request an installer introduction?: Your signup gives you the guide. An installer introduction is a separate step you can request when you're ready.
What emails will I receive?: We'll email you the guide link. Along with the guide, you'll get five practical follow-up emails from Andy at Why Solar over the next two weeks, including information about our quote-checking and installer-matching services. You can unsubscribe at any time.
How does Why Solar make money?: The guide is free. When homeowners request an introduction, Why Solar works with approved partner installers who pay referral fees. Homeowners do not pay Why Solar for the matching service.

Start with your home's numbers.

Get the free guide, worksheet and questions to ask before accepting a battery quote.

Send me the free guide