By Sarah Chen · environmental engineer · water, waste and everything that flows downhill
“After my 400-litre off-grid tank froze solid at -2°C, I learned that thermal mass alone cannot survive a Tasmanian winter without backup heating.”
— Sarah. Every litre accounted for.
ArticlesCalculatorsSite PlannerShopA 400L thermal storage tank froze solid at -2C in Tasmania. The fix is sizing, insulation and siting for your climate. This guide shows how Australian off-gridders choose tanks that hold heat through cold nights without diesel backup.
Look, if you're off-grid in Australia and want hot water without burning diesel, you need a thermal storage tank. No tank? No hot water when the sun's not shining. Period. Don't overcomplicate it.
Look, if you're off-grid in Australia and want hot water without burning diesel, you need a thermal storage tank. No tank? No hot water when the sun's not shining. Period. Don't overcomplicate it.
Forget "bigger is better." For a couple: 150-200L tank. For a family of four: 250-300L. If you're thinking 500L because you saw it online? You're wasting space and money. Your solar array can't heat that much anyway.
Calculate: 1 shower = 50-100L. 1 bath = 150L. Multiply by people + days you can go cold (e.g., 2 people × 2 showers × 100L = 400L. But you don't need 400L tank – 200L is enough for 2 days of normal use. Stop overbuying.
If your tank isn't properly insulated, it's a money pit. In Australia, heat loss is brutal. Cheap tanks (under $1000) have 25mm insulation – useless. You need 50mm minimum. R-value 3.0+.
Bad insulation = hot water cools in 6 hours. Good insulation = stays hot for 24+ hours. That's why you pay $1,800-$2,500 for a tank, not $500.
Stratification is when hot water stays at the top and cold at the bottom. If you don't have it, your tank mixes hot/cold and wastes energy. It's not magic – it's physics.
How to get it: Your tank must have a cold water inlet at the bottom and hot outlet at the top. Most modern tanks do this. If you're DIY-ing, check the design. If it's not built for stratification, you're paying for half a tank.
Don't buy a tank because it's "cheap." Buy one that actually works in Australian conditions. Insulation and stratification aren't "nice-to-haves" – they're the difference between hot water and a cold shower when the sun's down.
Get a 200L tank from Solar Hot Water. Pay $1,900. It'll last 10 years. Save $300 now, lose $1,000 later. Your call.
While many off-grid projects are achievable as DIY, certain situations require licensed professionals:
Always check local regulations and obtain necessary permits before commencing work.
Worth a watch: Top 3 Ways to Heat Water Off the Grid · Solar Surge