How Do I Calculate How Big My Home Battery Needs To Be?

Home > Blog > Advice > How Do I Calculate How Big My Home Battery Needs To Be?

It is important that you get the right-sized solar battery for your Perth home. A battery too small may force you to rely on the grid, and a battery too large means you are paying for storage you will never use.

Formula For Calculating Home Battery Size

Step 1: What Is Your Overnight Consumption “Battery Load”?

Formula: Daily usage x 0.65 = your target storage size.

Your home battery’s main job is to power your home from 5 pm to 7 am. Most working families use 60%-70% of their daily energy during this period.

First, look at your smart meter data and find your average daily usage in kilowatt-hours (kWh). This data can be found through your energy retailer.

Then, estimate your average evening usage. As mentioned, most families use 60%-70% of their daily energy during the evening.

Calculation	Result
Average daily usage	20 kWh
Estimated evening usage	65%
Battery load	20 × 0.65
Target storage	13 kWh

Important note: There is a difference between usable capacity and total capacity. Some manufacturers advertise a 10kWh battery that only lets you safely use 9kWh to protect the chemistry’s lifespan. Ensure you always check the usable capacity specification.

Step 2: How Much Excess Solar Does Your Home Produce?

Check your energy bill for your solar export amount. This export amount is the amount of power you send back to the grid. This export amount must be larger than your target battery size.

Example: If you export 15kWh of solar a day, you can fill an 11kWh or 13kWh battery. However, if you only export 5kWh per day, a battery with a large storage capacity will sit half-empty all winter.

Step 3: Account For The Efficiency Loss

About 10% of the energy is lost as heat in solar batteries during charging or discharging. To compensate for this loss, it is recommended that you multiply your target storage by 1.1.

Example: If you need 10kWh of power overnight, look for a battery with at least 11kWh of usable battery.

Which Battery Is Likely To Suit You?

Battery Size	Household Profile
5kVA – 7kWh	Small households (1 – 2 people) Gas cooking & hot water Low evening heating/cooling
10 kWh – 14kWh	Average suburban families (3 – 5 people) Fully electric homes Moderate air-con use
15 kWh+	Large homes Large pools with overnight pumps EV owners who charge at night

How Clean NRG Solar Can Help

Clean NRG Solar is a local, family-run company that has been operating in Perth’s solar industry for over 15 years. Experts in all things solar, Clean NRG Solar specialises in the installation and repair of solar panels, solar batteries and even off-grid solar systems.