Backup Power
Keep selected appliances and essential circuits operating when the electrical grid goes down.
SOLAR8 KNOWLEDGE CENTRE
Solar BatteriesMade Simple.
Understand how solar batteries store electricity, how much energy they can provide and how battery storage can keep your home powered when the sun isn't shining or the grid goes down.
THE BASICS
What does a solar battery do?
A solar battery stores electrical energy so that electricity generated by your solar system can be used later.
Solar panels produce the most electricity when there is sunlight. Your household, however, may continue using electricity after the sun has gone down.
A battery allows some of the energy generated during the day to be stored and used later. Depending on the system design, it can also provide backup power when the electrical grid is unavailable.
The important point is that battery size should be matched to your actual electricity usage and the amount of backup you want.
SIMPLE BATTERY ENERGY FLOW
SolarGenerates electricity
→
BatteryStores energy
→
HomeUses electricity
GRID
The grid can supplement the system when solar and stored energy are insufficient.
WHY ADD A BATTERY?
More than just backup power
Battery storage can serve several purposes depending on how your solar system is configured.
Use More Solar
Store excess daytime solar generation and use some of that energy later instead of buying as much electricity from the grid.
Evening Energy
Use stored energy after solar production falls in the late afternoon and evening.
Greater Energy Independence
Combining solar generation with battery storage can reduce your dependence on grid electricity.
UNDERSTANDING CAPACITY
How big should your battery be?
Battery capacity is normally measured in kilowatt-hours, but the number printed on a battery is not necessarily the amount of energy you should plan to use.
01
Battery Capacity
kWh
The battery's rated energy storage capacity. For example, a battery may have a nominal capacity of 5 kWh.
02
Usable Energy
Usable kWh
The amount of stored energy that can realistically be used after considering the battery's operating limits and system configuration.
03
Your Load
kW
Your appliances determine how quickly stored energy is consumed. Higher loads use battery energy faster.
Important:
A larger battery does not automatically mean a longer backup period. Your backup time depends on both the usable battery energy and the electrical load being supplied.
BACKUP TIME
How long will a battery last?
Backup duration depends on how much usable energy is available and how much power your appliances are consuming.
A SIMPLE WAY TO THINK ABOUT IT
Backup Time ≈ Usable Battery Energy ÷ Average Load
More usable energyGenerally increases backup duration.
Higher electrical loadGenerally reduces backup duration.
Lights + Wi-Fi + TV
A relatively small electrical load can allow stored energy to last significantly longer.
Essential Home Loads
Refrigeration, lighting, internet, selected plugs and other essential circuits require more battery energy.
Multiple Large Appliances
High-power appliances can consume stored energy much faster and may require a larger system.
BATTERY TECHNOLOGY
Why lithium batteries are common in modern solar systems
Battery chemistry affects usable capacity, lifespan, operating characteristics, safety requirements and system cost.
Modern residential solar systems commonly use lithium-based batteries because they can provide a useful combination of energy density, cycle life, efficiency and usable capacity.
Different lithium battery technologies exist, and the specifications can vary significantly between manufacturers and models.
When comparing batteries, it is therefore important to look beyond the headline kWh capacity and consider the complete technical specification.
CapacityHow much energy the battery stores
Usable CapacityHow much energy can practically be used
Power RatingHow much power the battery can deliver
Cycle LifeExpected number of charge and discharge cycles
WarrantyManufacturer's coverage and operating conditions
BATTERY TERMINOLOGY
What is Depth of Discharge?
Depth of Discharge, commonly called DoD, describes how much of a battery's available capacity has been used.
20%
Light Use
Only a relatively small portion of the battery's available energy has been used.
50%
Moderate Use
Approximately half of the available battery energy has been consumed.
80%
Deeper Use
A larger portion of the battery's available capacity has been used.
Remember:Battery manufacturers specify operating limits, and the battery management system controls how the battery is charged and discharged.
SIZING YOUR SYSTEM
Battery size should start with your electricity usage
There is no single battery size that is right for every household.
01
Understand Your Loads
Identify the appliances and electrical circuits that need to remain operational.
02
Determine Backup Requirements
Decide how long you want selected appliances to operate during a grid interruption.
03
Match Battery Capacity
Choose a battery system with suitable usable energy and power capability.
04
Match the Inverter
The inverter and battery must be compatible and correctly configured as part of the complete system.
BATTERY TERMINOLOGY
Terms you'll hear when comparing batteries
kWh
A measure of energy. Battery capacity is commonly expressed in kilowatt-hours.
kW
A measure of power. It describes how much electrical power a battery or inverter can deliver at a given time.
Usable Capacity
The portion of the battery's rated capacity that can practically be used by the system.
DoD
Depth of Discharge. The proportion of available battery capacity that has been used.
Cycle
A charge and discharge sequence. Battery specifications commonly refer to expected cycle life.
BMS
Battery Management System. Electronics that monitor and manage battery operation.
NEED HELP CHOOSING?
Let's work out how much battery storage you actually need.
The right battery depends on your electricity usage, backup requirements, inverter and future energy plans. Solar8 can help you understand the options before you invest.