28kWh Solar Battery
A 28kWh battery serves large households and premium homes with genuinely high electricity consumption, typically driven by two or more electric vehicles, full electrification, and substantial daily usage across a bigger property. At this capacity, system design becomes the central question: how the battery, inverter, switchboard, and household load profile work together determines the outcome far more than the capacity figure alone.
This guide explains who this capacity suits, how two-EV charging works at this scale, what actually determines backup capability, and why specifications like round-trip efficiency and depth of discharge matter more here than at smaller capacities.
The 28kWh capacity at a glance
- Recommended household size
- 5+ people, all-electric
- Typical daily consumption
- Near self-sufficiency
- Suitable solar system
- 10kW to 13kW
- EV suitability
- Strong EV support
- Expandability
- Yes, confirm platform ceiling
- Typical use case
- Large families, near-independence goals
Who Is a 28kWh Battery Designed For?
A 28kWh battery suits households with daily electricity usage generally exceeding 40 kWh, typically large or premium homes with a 10kW to 13kW solar system.
This capacity is a genuine fit if you:
- Are charging two or more electric vehicles and want stored solar to contribute meaningfully to both.
- Have fully electrified your home, eliminating gas across cooking, hot water, and heating.
- Run a large household with sustained, high daily consumption across multiple zones of the home.
- Are building or already operate a smart home energy ecosystem and want the battery integrated into that system.
- Are approaching your energy system as long-term infrastructure and want meaningful headroom for growth.
If your household sits closer to one EV and 28 to 40 kWh of daily usage, the 20kWh battery is likely the better-matched and more cost-effective capacity. If your consumption or EV fleet exceeds what 28kWh comfortably supports, review the 42kWh battery.
The 28 to 30kWh Capacity Band Explained
As with the 13.5 to 14kWh tier, batteries in the 28 to 30kWh range cluster closely across manufacturers because modular platforms ship in fixed module increments. Depending on the module size a given brand uses, a stacked configuration might land at 28.4kWh usable, 30kWh usable, or a nearby figure. For practical household purposes, these differences are marginal.
What actually differentiates products in this band is not the capacity figure but the surrounding specification: continuous and peak power output (kW), round-trip efficiency, depth of discharge, cycle life warranty, the inverter or inverters the platform pairs with, and whether the platform is genuinely modular or effectively fixed at this size.
When comparing quotes in this range, treat the capacity figure as approximately equivalent across products and focus the comparison on these surrounding specifications instead.
Charging Two or More EVs at This Capacity
At 28kWh, two-EV charging becomes genuinely comfortable in most conditions, though the outcome still depends on more than the battery alone.
The arithmetic. Two vehicles each covering a 40 to 50 km daily commute add roughly 16 to 20 kWh of combined daily charging demand. At 28kWh, this leaves meaningful headroom for household consumption alongside EV charging, particularly when a portion of charging happens directly from solar during the day rather than solely from stored battery capacity overnight.
What still constrains the outcome. The battery's continuous power output (measured in kW, not kWh) determines whether the household and both vehicles can draw simultaneously without contention. A battery with ample stored energy but limited continuous output can still create a bottleneck during periods of concurrent high demand. This is a specification to confirm with your installer for your specific battery and inverter combination, not something that follows automatically from the 28kWh capacity figure.
Charging behaviour matters as much as capacity. Households that schedule EV charging to align with solar generation, or that stagger charging between two vehicles rather than charging both simultaneously overnight, achieve better outcomes from the same battery than households that do not manage charging timing at all.
What Determines Backup Capability at 28kWh
SunRight Solar does not claim or imply whole-home backup at any battery capacity, including 28kWh. Backup capability is the outcome of a system design process, not a specification you can read from a capacity figure. The factors that determine what can be backed up, and for how long, include:
- Battery brand and model, since usable capacity, continuous output, and backup-specific certifications vary between products even at similar nominal capacities.
- Inverter compatibility, as the inverter (or inverters, in some hybrid configurations) manages how power flows between the grid, solar, battery, and your home's circuits.
- Hybrid or AC-coupled configuration, which affects how the system responds during a grid outage and what switching delay, if any, occurs.
- Backup gateway or EPS (emergency power supply) functionality, a specific hardware and software capability that some products include and others do not; its presence and specification directly determines outage response.
- Single-phase or three-phase electrical supply, which affects both the inverter options available and how backup circuits can be distributed.
- Battery power output in kW, which limits how much can be drawn simultaneously regardless of stored energy in kWh.
- Usable battery capacity in kWh, which limits how long backed-up circuits can run.
- Household load profile, meaning your actual pattern of electricity use, including peak simultaneous demand.
- Critical loads configuration, the specific circuits your household and installer agree should be prioritised during an outage.
- Installation design, including switchboard wiring and how backup circuits are physically separated from non-backup circuits.
- Local electrical regulations, which vary by state and by electricity distributor and affect what configurations are permitted.
Given this number of interdependent factors, any claim about backup capability that is not qualified against your specific system is not a reliable claim. Your installer will work through these factors with you to design a backup configuration matched to your priorities and your property.
Round-Trip Efficiency and Depth of Discharge at Scale
These two specifications matter more at 28kWh than at any smaller capacity in the SunRight Solar range, because the household consumption and cycling volume at this tier are highest.
Round-trip efficiency measures how much of the energy stored in the battery is actually retrieved on discharge. Current LFP batteries range from approximately 90 to 97 per cent depending on the product. At high daily cycling volumes, typical of a household running two EVs and full electrification, a few percentage points of efficiency difference compounds into a materially different quantity of electricity over the battery's operating life.
Depth of discharge describes what proportion of usable capacity can genuinely be drawn down before recharging. Most current LFP products support 90 to 100 per cent depth of discharge. At this capacity, confirm the manufacturer's stated depth of discharge and cycle life warranty together, since these two figures are typically specified as a pair (for example, a warranty to a stated percentage of original capacity retained after a stated number of cycles at a stated depth of discharge).
Ask your installer for the manufacturer's specification sheet for both figures on any product you are considering at this capacity, rather than relying on generic marketing claims.
Modular Expansion: How Close to the Platform Ceiling Is 28kWh?
Most modular battery platforms have a practical maximum capacity, determined by how many modules the inverter or inverter combination can support. At 28kWh, some platforms have meaningful headroom remaining; others are approaching or at their practical ceiling.
This matters for a household weighing 28kWh against 42kWh. If you choose 28kWh on a platform with expansion headroom, you may be able to add capacity later without replacing the inverter. If you choose 28kWh on a platform already near its ceiling, later expansion may require a different inverter or an additional, separate battery system.
Ask your installer directly what the maximum expandable capacity is for the specific battery and inverter combination being quoted, and whether that maximum is above, at, or below 28kWh. This single question meaningfully affects whether 28kWh is a flexible mid-point or effectively your final capacity on that platform.
Is 28kWh Enough, or Should You Plan for 42kWh?
Consider the 42kWh battery instead if any of the following apply:
- Your household runs three or more EVs, or two EVs with very high daily driving distances.
- Your household size or property scale is large enough that daily consumption regularly exceeds what 28kWh comfortably covers alongside EV charging.
- You are specifically prioritising the greatest achievable backup coverage the platform can support and are prepared to invest in the inverter and switchboard configuration this requires.
- You have confirmed with your installer that your preferred platform's practical ceiling sits at or near 28kWh and you want expansion headroom from the outset.
For most large households with two EVs and full electrification, 28kWh paired with a 10kW to 13kW solar system is a well-matched, practical long-term system.
How the Battery Capacities Compare
The table below shows how all six SunRight Solar battery capacities compare, using technically accurate criteria rather than unsupported metrics like guaranteed runtime or appliance counts.
Battery Capacity Comparison
| Specification | 5kWh | 10kWh | 14kWh | 20kWh | 28kWh This capacity | 42kWh |
|---|---|---|---|---|---|---|
| Recommended household size | 1 to 2 people | 2 to 4 people | 3 to 5 people | 4 to 6 people | 5+ people, all-electric | Large homes, maximum independence |
| Typical daily consumption | 8 to 14 kWh | 10 to 15 kWh | 12 to 20 kWh | High consumption | Near self-sufficiency | Maximum residential capacity |
| Typical backup scope see the note on backup scope below the table | Essential circuits, few hours | Selected circuits, several hours | Selected circuits, overnight | Selected circuits, overnight+ | Selected circuits, extended | Selected circuits, longest duration |
| Suitable solar system | 6.6kW | 6.6kW to 10kW | 6.6kW to 10kW | 10kW | 10kW to 13kW | 13kW |
| EV suitability | Not suitable | Limited | Partial (with daytime charging) | Supports EV charging | Strong EV support | Multi-EV support |
| Expandability | Yes (modular systems) | Yes | Yes | Yes | Yes, confirm platform ceiling | Often at platform maximum |
| Typical use case | Apartments, small households, budget entry point | Standard family homes | The "sweet spot" for most Australian households | Higher-consumption or all-electric homes | Large families, near-independence goals | Maximum energy independence |
Backup scope is not determined by battery capacity alone. Which circuits can be backed up depends on battery and inverter specification, hybrid or AC-coupled configuration, backup gateway/EPS functionality, phase supply, continuous power output, household load profile, critical loads configuration, installation design, and local electrical regulations. Your installer will confirm the achievable scope for your home.
If your household matches the 28kWh column, this capacity is built for large-scale, multi-EV energy demand. If your platform's expansion ceiling sits near this figure and you anticipate further growth, review the 42kWh guide before committing.
Frequently Asked Questions
Can a 28kWh battery charge two electric vehicles at the same time as running the household?
In most conditions, yes, with meaningful headroom for two vehicles covering typical daily commutes. The outcome also depends on the battery and inverter's continuous power output in kW, not just the stored kWh, and on whether EV charging is scheduled to align with solar generation. Confirm continuous output specifications with your installer for your specific system.
Does a 28kWh battery provide whole-home backup?
No claim of whole-home backup is made at any capacity, including 28kWh. Backup capability depends on battery brand and model, inverter compatibility, hybrid or AC-coupled configuration, backup gateway or EPS functionality, phase supply, power output in kW, usable capacity in kWh, household load profile, critical loads configuration, installation design, and local electrical regulations. Your installer will design a backup configuration matched to your priorities based on these factors.
Why does round-trip efficiency matter more at 28kWh than at smaller capacities?
Because household consumption and cycling volume are highest at this tier, typically driven by two EVs and full electrification. A few percentage points of efficiency difference compounds into a materially larger quantity of electricity over the battery's operating life at this level of daily use than at smaller capacities.
Is 28kWh close to a modular platform's maximum expandable capacity?
It depends on the specific platform. Some modular systems have meaningful headroom above 28kWh; others are near or at their practical ceiling, determined by how many modules the paired inverter can support. Ask your installer directly what the maximum expandable capacity is for the specific product being quoted.
What is the practical difference between 20kWh and 28kWh?
20kWh is typically matched to one EV as a primary driver alongside high household consumption. 28kWh is typically matched to two or more EVs, full electrification, and larger households. If you are on the boundary, the deciding factors are usually your EV count, whether you have eliminated gas, and your household size.
Compare With the 20kWh BatteryWhat solar system size should pair with a 28kWh battery?
A 10kW to 13kW solar system is the typical pairing, sized to generate sufficient daily surplus to substantially charge a battery of this capacity. The right choice within that range depends on your specific consumption, location, and roof area, which your installer will assess.
Design Your 28kWh Battery System
Two-EV charging, backup capability, and expansion headroom all depend on how the battery, inverter, switchboard, and household load profile work together. Request a free, no-obligation quote and we will design the complete system around your property.
