How much solar do you need for a 10, 20, or 30 kWh home battery? Size your panels with our kW-per-kWh table, worked examples, and free solar calculator.
A battery is not only as good as the solar that fills it. Fit too few panels and your battery limps into the evening half-charged, topping up from the grid and quietly eroding your savings. Fit the right amount and it charges fully on an average day and carries you through the night on your own sunshine. This guide shows you how to match solar capacity to battery size.
Understanding Your Home Battery System
A home battery stores excess solar generated during the day so you can use it at night or during peak tariff hours. The specifications that matter are capacity (kWh), power output (kW), depth of discharge (DoD), and cycle life.
Modern lithium iron phosphate (LiFePO4 or LFP) batteries—the chemistry in most quality systems today—offer higher efficiency, longer life, and near-full usable capacity compared with older lead-acid alternatives. VoltX Energy’s battery storage solutions are built to get the most out of every kWh your panels produce.
Assessing Your Home’s Energy Consumption
Sizing solar starts with two numbers from your electricity bills: your average daily use in kWh, and how much of it you use in daylight versus after dark. For most homes, only about 30–40% of consumption happens while solar is generating; the rest is the evening and overnight gap your battery is there to fill. For a full walk-through of calculating your usage and matching it to storage, see our guide to choosing the right battery size.
Evaluating Your Solar Potential
How much your panels actually produce depends on location, roof orientation, shading, and available sunlight. Most Australian regions receive about 4–6 peak sun hours per day—higher in Brisbane, lower in a Melbourne winter—so around 4.5–5 is a safe working figure for sizing.
Panels ideally face north at a pitch that maximises exposure, and you’ll want to account for shading from trees or neighbouring buildings. As a rule of thumb, every 1 kW of solar generates roughly 4–5 kWh per day, averaged across the year.
How Much Solar Per kWh of Battery
Your solar array has two jobs: cover your home’s daytime use in real time and generate enough surplus to refill the battery before sunset.
A quick way to size the charging portion is the five-hour rule. Divide your usable battery capacity by 5 peak sun hours to get the minimum solar needed just to refill it. Add your daytime household load and a buffer for conversion losses, cloudy days, and future growth, and you have your total array.
Here’s how that works out for common battery sizes (north-facing panels, ~4.5–5 peak sun hours):
| Battery Capacity (Usable) | Solar Output to Refill Battery | Suggested Total Array* |
|---|---|---|
| 10 kWh | ~2– 2.5 kW | ~5 kW |
| 20 kWh | ~4– 5 kW | ~6.6 kW |
| 30 kWh | ~6–7 kW | ~9–10 kW |
*The total array also covers typical daytime household use, with roughly 20 – 25% buffer for losses and weather. Location and season shift these figures. A battery that refills reliably every day in Brisbane may finish a cloudy Melbourne winter day only part-charged. Use the solar calculator for a number matched to your postcode and roof.
Worked Examples: 10, 20, 30 kWh Systems
10 kWh Battery – Smaller Home or Unit
A 10 kWh battery suits a smaller home or unit using around 15 kWh of electricity a day—roughly ~6 kWh in daylight and ~9 kWh in the evening and overnight, which the battery covers. Refilling 10 kWh of usable storage needs about 2–2.5 kW of surplus solar. Once you add the daytime load and a weather buffer, a 5 kW array fills the battery comfortably on an average day and still exports it a little.
20 kWh Battery – Average Family Home
A home using around 20 kWh a day, with ~7 kWh in daylight and ~13 kWh after dark, needs roughly 4–5 kW of surplus solar to refill 20 kWh. With daytime use and a buffer included, a 6.6 kW system is the sweet spot. In winter or across a run of cloudy days it may not fully refill, so sizing toward the top of the range pays off.
30 kWh Battery – Large Home
A large home using around 30 kWh or more a day needs about 6–7 kW of surplus solar to refill a 30 kWh battery. Once you include the higher daytime load and buffer, that points to 9–10 kW. This is where a bigger array earns its keep. A 6.6 kW system simply can’t refill 30 kWh and run the house on a short winter day. If your needs are growing, it’s often easier to plan for expansion from the start.
VoltX Energy Solutions
Our scalable battery storage solutions let you expand capacity as your energy needs grow. They're also engineered for Australian conditions with online monitoring and seamless solar integration.
The AlphaESS Solar Battery, for example, is an all-in-one system that pairs a hybrid inverter with modular LiFePO4 storage. It supports up to 200% PV input, so you can oversize your array and still refill the battery on cloudy days. The system is also VPP and Fast FCAS ready, letting you take part in grid services and smart energy management.
Get the Most Out of Solar
Matching your solar to your battery turns storage into real savings. Work out your daily use, split it into daytime and overnight, then size an array that covers the day and refills the battery with room to spare. Get it right and you lean on your own solar instead of the grid—night after night.
The fastest way to get an answer is by using our solar calculator or talking to a VoltX Energy advisor for expert guidance.
Frequently Asked Questions
Around 2–2.5 kW of solar is enough to refill a 10 kWh battery on an average Australian day (using roughly 4.5–5 peak sun hours). Once you also cover daytime household use, a 5 kW solar system is a comfortable match.
Refilling a 20 kWh battery takes about 4–5 kW of surplus solar, and a 30 kWh battery about 6–7 kW. Including daytime use and a buffer for cloudy days, that usually means a ~6.6 kW array for 20 kWh and a ~9–10 kW array for 30 kWh.
Most Australian regions get about 4–6 peak sun hours a day, varying by location and season; higher in Brisbane, lower in a Melbourne winter. Around 4.5–5 kW is a safe working figure for sizing. The solar calculator uses your postcode for a precise number.
Not really. Surplus daytime generation runs your home and exports the rest, and a slightly larger array helps your battery still fill on cloudy days. The bigger risk is the reverse: a battery too large for your solar never fills without drawing from the grid, which erodes your savings. Size the array to refill the battery and cover daytime use, then let any extra export.
Sometimes not. Output can drop sharply on overcast days and in winter, so a battery that fills easily in summer may finish a short winter day partially charged. Sizing your array toward the top of the suggested range gives it the best chance of refilling year-round, and on the shortest days the grid tops up any shortfall.
