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The Charge and Discharge Cycle
A solar battery captures surplus solar electricity during the day and releases it when you need it, converting between DC and AC twice in the process with modern efficiency of 90 to 95 percent.
What is a solar battery, in plain English?
A solar battery is a rechargeable energy store that captures surplus electricity from your solar panels during the day and holds it until you need it. In a typical Melbourne home, panels generate most of their output between 9am and 4pm, while household demand peaks in the evenings. A battery shifts your own generation to match your own demand, reducing what you draw from the grid.
Understanding the charge and discharge cycle helps you set realistic expectations about what a battery can do for your household or business. The cycle is simpler than the spec sheets make it look.
- 1
Panels generate DC electricity
During daylight hours, your solar panels convert sunlight into direct current (DC) electricity. Generation peaks around solar noon and tapers off in the morning and late afternoon.
- 2
Inverter converts DC to AC
A solar inverter converts the DC output to alternating current (AC), which is what your home or business uses for appliances, lighting, and other loads.
- 3
Surplus flows to the battery
When solar generation exceeds what you are consuming at that moment, the surplus would normally export to the grid. A battery intercepts that surplus and stores it. Depending on the system configuration, the battery may store DC (DC-coupled) or AC (AC-coupled).
- 4
Battery holds the energy
The stored electricity sits in lithium cells inside the battery cabinet, ready for use. Modern lithium iron phosphate (LFP) cells hold their charge well and can cycle daily for over a decade.
- 5
Battery discharges when you need it
In the evening, on cloudy days, or during a grid outage, the battery converts its stored DC energy back to AC and powers your home or business automatically. Most systems switch seamlessly, with no action required from you.
The two conversion steps - from AC into DC for storage, and from DC back to AC for discharge - are where round-trip efficiency losses occur. Modern lithium batteries complete this cycle at 90 to 95 percent efficiency, meaning very little energy is lost as heat.
Key Technical Terms Explained
Understanding usable capacity, depth of discharge, round-trip efficiency, and cycle ratings lets you compare batteries honestly rather than being misled by headline nominal capacity figures.
Battery specifications use a consistent set of terms across brands. Knowing what each one means lets you compare products honestly, rather than being misled by the headline number on a spec sheet.
| Term | What it means | Why it matters |
|---|---|---|
| Nominal capacity | The total energy the battery can physically hold, stated in kilowatt-hours (kWh) | This is the headline number you see in marketing, but it is not what you can actually use |
| Usable capacity | The portion of nominal capacity available to you after the depth of discharge limit is applied | Always compare usable capacity between batteries, not nominal - this is what you actually get |
| Depth of discharge (DoD) | The percentage of the battery's total capacity that can be safely drawn down without shortening its life | LFP batteries commonly allow 100% DoD. A higher DoD means more energy per kWh of nominal capacity |
| Round-trip efficiency | The percentage of energy that comes back out as a proportion of what went in | 90% means for every 10 kWh stored, you recover 9 kWh of usable power. Matters over thousands of cycles |
| C-rate | The rate of charge or discharge relative to the battery's capacity. A 1C rate charges or discharges a full battery in one hour | A higher C-rate means the battery can respond faster to peak demand, relevant for commercial demand charge management |
| State of charge (SoC) | The current energy level of the battery, expressed as a percentage of usable capacity | Monitoring apps display this in real time. Most batteries keep a small reserve (5-10%) to protect cell health |
All capacity figures are indicative. Check the manufacturer's current spec sheet for the model being quoted.
Battery Chemistry: LFP vs NMC
Lithium iron phosphate (LFP) chemistry has become the dominant choice for Australian residential solar batteries, offering superior cycle life, deeper usable discharge, and better thermal stability than older NMC types.
Two lithium chemistries dominate the residential and commercial battery market in Australia. Understanding the difference helps you evaluate which battery suits your situation.
LFP (Lithium Iron Phosphate)
- Rated for 4,000 or more cycles to 80% of original capacity
- Tolerates up to 100% depth of discharge in most configurations
- More stable at high temperatures - important in Melbourne summers
- Slightly lower energy density, so physically larger for the same kWh
- Now the dominant chemistry in Australian residential storage
- Used by Tesla Powerwall 3, Enphase IQ Battery, Sigenergy, most Sungrow and AlphaESS models
NMC (Nickel Manganese Cobalt)
- Higher energy density - more compact for the same nominal kWh
- Typically rated for 1,000 to 2,000 cycles before degradation to 80%
- More sensitive to high temperatures over time
- Usually limited to 80-90% depth of discharge to preserve life
- Found in older battery generations and some consumer EV packs
- Less common in new Australian residential installs as LFP has matured
Which chemistry should you choose?
For rooftop solar storage in Melbourne's climate, LFP is the clear choice for most homes and businesses. It cycles more, degrades more slowly, tolerates deeper discharge, and handles warm roof spaces better. Most batteries being installed in Australia today are LFP. If a supplier quotes an NMC unit, ask about the rated cycle count and warranty terms before comparing.
How a Battery Connects to Your Solar System
There are three integration configurations for a home solar battery: AC-coupled retrofit, DC-coupled hybrid, and all-in-one hybrid inverter, and the right choice depends on whether you are adding to existing solar or starting fresh.
There are three main ways a battery can be integrated with an existing or new solar installation. The right approach depends on your existing inverter, your budget, and how you want the system to behave during an outage.
AC-Coupled (Most Common Retrofit)
In an AC-coupled configuration, the battery connects to the AC wiring in your home, after your existing solar inverter. The battery has its own inverter built in (or a separate battery inverter) to handle the DC-to-AC and AC-to-DC conversions. This approach works with almost any existing solar inverter, making it the standard choice for retrofit installs. The Tesla Powerwall and Enphase IQ Battery are both AC-coupled in retrofit configurations.
DC-Coupled (New Installs or Inverter Replacement)
In a DC-coupled setup, the battery connects before the main inverter, on the DC side of the system. This avoids one of the AC-to-DC conversion steps and can achieve marginally higher round-trip efficiency. DC-coupled systems require a compatible hybrid inverter, so this approach is most practical when installing a new solar system or replacing an existing inverter as part of a battery upgrade.
All-in-One Hybrid Inverter Systems
A hybrid inverter handles solar input, battery charging and discharging, and grid management in a single unit. This is the cleanest installation for new builds or full system replacements - one unit, one set of settings, one monitoring interface. Sigenergy SigenStor, Sungrow SH series, and AlphaESS SMILE models use this approach.
Not all configurations include backup power by default
Backup capability requires a specific transfer switch or gateway unit in the installation. In an AC-coupled system without a gateway, a grid outage will cause the battery to shut down alongside the grid for safety reasons. If backup power is important to you, make sure you ask for it explicitly in your free quote - it changes the hardware and wiring involved.
What Affects How Much Energy You Can Store and Use
Your battery's nameplate capacity is only a starting point, because array size, seasonal variation, daytime usage patterns, and round-trip efficiency losses all shape how much stored energy you actually benefit from each day.
A battery's nameplate capacity is only one factor in how much energy you actually benefit from in practice. Several variables affect whether a given battery size suits your household or business load.
- Solar array size and orientation: a larger array charges the battery more fully, more quickly. A 6.6 kW array will fill a 10 kWh battery by mid-morning on a clear summer day. A 3 kW array may not fully charge the same battery.
- Season and weather: shorter winter days in Melbourne produce less daily solar generation, meaning the battery may not reach full charge every day in June and July.
- Your daytime vs evening usage split: if you run appliances during the day (dishwasher, washing machine, pool pump), there is less surplus for the battery. Shifting daytime loads to solar hours is the complementary strategy.
- Battery capacity and depth of discharge: two batteries with the same nominal kWh can have different usable capacities depending on their DoD settings.
- Round-trip efficiency losses: every charge-discharge cycle loses some energy to heat. At 90 percent efficiency, 10 kWh of stored solar yields 9 kWh of evening power.
- Number of cycles per day: some commercial and VPP configurations cycle a battery twice per day (once on solar, once on off-peak grid). This increases total throughput but also affects long-term degradation if the battery is not rated for high-cycle use.
The battery is not the whole picture. How you use energy during the day shapes how much the battery can actually do for you at night.
Battery Backup Power: What it Can and Cannot Do
Not every solar battery system can keep your home running during a grid outage, because backup capability requires specific transfer switch hardware that is only included in systems configured for backup mode.
Backup power is one of the most misunderstood aspects of home battery storage. Whether a battery can keep your home running during a grid outage depends entirely on how the system is configured - and whether you have paid for the backup hardware.
What a Properly Configured Backup Battery Can Do
- Power essential circuits - lights, fridge, Wi-Fi router, phone charging, and small appliances - automatically during an outage
- Transition to backup mode in milliseconds, so clocks and computers typically do not reset
- Recharge from solar panels during the day, extending backup indefinitely in good conditions
- Power a whole-home load if the system is sized large enough and the loads are within the battery's continuous output rating
What a Standard Battery Cannot Do
- Run without a specific backup configuration installed at the time of the job - standard installs without a gateway or transfer switch shut down with the grid
- Power high-draw appliances like electric ovens, electric water heaters, or ducted reverse-cycle air conditioning on a typical residential battery without careful load management
- Provide backup if the battery is empty and there is no solar generation to recharge it
- Substitute for a generator in situations requiring three-phase power for industrial equipment, without specific three-phase battery hardware
Designing a backup system
If backup power is a priority for you, mention it in your free quote request. We design the system around your critical loads - the appliances and circuits that must stay on during an outage - and quote for the hardware that makes it happen reliably. A well-designed backup system is a distinct configuration, not a standard battery with an extra feature switched on.
Common Questions About How Solar Batteries Work
These are the most frequently asked technical questions from Melbourne homeowners considering solar battery storage.
Can a solar battery charge from the grid as well as from solar?+
Yes. Most battery systems can be configured to charge from the grid during off-peak rate periods, then discharge during evening peak-rate hours. This is called time-of-use arbitrage. Combined with solar charging during the day, it maximises the hours the battery is working. The right strategy depends on your tariff structure, which we review in your free quote.
Will a battery still work if my internet goes down?+
Yes. The internet connection is used for monitoring and remote access via the manufacturer's app, but it is not required for the battery to charge and discharge automatically. A loss of Wi-Fi does not affect the core charge-discharge function. Monitoring data may not sync until the connection is restored.
How does a battery interact with a time-of-use electricity tariff?+
On a time-of-use tariff, import rates vary across the day - lower during off-peak periods (typically overnight) and higher during peak periods (evenings and sometimes early mornings). A smart battery system learns your tariff schedule and prioritises solar charging, then grid charging at off-peak rates, then discharges during your peak periods. This can significantly reduce evening import costs.
What happens to the battery when I export surplus solar?+
The battery charges first, up to its usable capacity limit. Once full, any additional solar surplus flows to the grid as a normal feed-in export, earning the applicable feed-in tariff. The battery does not prevent feed-in - it just captures the surplus before export, so you export less and use more of your own generation.
Can I add more battery capacity later if I need it?+
This depends on the battery brand. Some models, like the Enphase IQ Battery and Sigenergy SigenStor, are highly modular and designed to expand in increments. Others, like the Tesla Powerwall, allow you to add complete additional units up to a system maximum. A few battery models are standalone only. We factor future expansion plans into our recommendations during your free quote.