Direct answer: For a large home, 128 kWh can provide substantial whole-home backup, but battery capacity alone does not determine how long the house can operate during an outage.
The real answer depends on the home's daily energy use, simultaneous peak demand, air-conditioning load, inverter capacity, usable state of charge (SOC), solar production, and which high-demand appliances are allowed to operate at the same time.
A recent MERITSUN residential project in Punta Cana, Dominican Republic provides a practical example.
The property uses eight MERITSUN 16 kWh wall-mounted batteries, providing 128 kWh of total nominal storage, together with a 28.8 kWp rooftop solar array and a Schneider Electric inverter platform.
Rather than designing the system around battery capacity alone, the project focused on three questions:
- How much energy does the home use each day?
- How much power must the system deliver at one time?
- Which household loads should remain available during an extended grid outage?
The result is a residential solar-plus-storage system designed to maintain most normal household functions while controlling the highest-demand loads.
Project at a Glance
| Project item | Configuration |
|---|---|
| Application | Large residential solar energy storage and whole-home backup |
| Location | Punta Cana, Dominican Republic |
| Property size | Approx. 520 m² / 5,600 ft² |
| Battery system | 8 × MERITSUN 16 kWh wall-mounted batteries |
| Total nominal capacity | 128 kWh |
| Solar PV | 28.8 kWp |
| Inverter platform | 3 × Schneider Electric XW Pro 6848 |
| Approx. inverter capacity | 20.4 kW |
| Air conditioning | 6 inverter mini-split systems |
| Typical daily consumption | Approx. 55–65 kWh/day |
| High-temperature consumption | Up to approx. 70–75 kWh/day |
| Main design focus | Whole-home backup, cooling, load management and extended outage operation |
Why Did This Home Need a 128 kWh Battery System?
The property is a two-story residence with five bedrooms, multiple living areas, a home office, swimming pool equipment, water pumps, kitchen loads and six air-conditioning systems.
For a home of this size, the backup requirement was not limited to a refrigerator, several lights and internet equipment.
The homeowner wanted to maintain a much broader group of loads during an outage, including:
- refrigeration;
- lighting;
- internet and office equipment;
- security systems;
- water pumps;
- selected kitchen circuits;
- multiple air-conditioning zones; and
- pool circulation on a controlled schedule.
Typical household consumption is approximately 55–65 kWh per day, while hotter days with heavier cooling demand can reach approximately 70–75 kWh.
A smaller battery bank could have supported essential loads.
The reason for moving to 128 kWh was to provide a larger usable-energy reserve while allowing the house to continue operating closer to normal during longer outages.
The battery capacity also provides room for:
- a minimum SOC reserve;
- inverter and system conversion losses;
- changing household demand;
- periods of low solar production; and
- additional operating margin during hot weather.
The design therefore reflects the required backup experience, rather than simply selecting the largest battery available.
What Does 128 kWh Actually Mean?
The battery calculation is straightforward:
8 batteries × 16 kWh = 128 kWh nominal capacity
But 128 kWh answers only one question:
How much energy can the battery bank store at its nameplate rating?
It does not tell the installer:
- how many kilowatts can be supplied at one time;
- whether several air conditioners can start simultaneously;
- how much capacity remains after maintaining an SOC reserve;
- how much energy is lost during conversion;
- how much solar energy will be available during the outage; or
- how long the selected household loads will operate.
That is why battery capacity must always be evaluated together with the home's load profile and inverter architecture.
kW vs. kWh: Why Both Matter in a Whole-Home Backup System
One of the most important design distinctions in residential storage is the difference between power and energy.
| Term | What it measures | Practical question |
|---|---|---|
| kW | Instantaneous power | Can the system operate the connected loads at the same time? |
| kWh | Stored energy | How much energy is available over time? |
| SOC reserve | Energy intentionally kept in reserve | How much battery should remain available during an outage? |
| Usable AC energy | Energy available after operating limits and losses | How much stored energy can actually reach household loads? |
| Runtime | Operating duration | How long can the selected loads continue to run? |
For this project, the 128 kWh battery bank addresses energy capacity.
The Schneider inverter system addresses power delivery.
Three Schneider Electric XW Pro 6848 inverter/chargers provide approximately 20.4 kW of combined inverter capacity.
This distinction matters because a house can contain enough stored energy for an overnight outage and still exceed the inverter's power limit if several high-demand appliances start at the same time.
The reverse is also possible: an inverter may be capable of handling a short peak while the battery does not contain enough usable energy to sustain that load for many hours.
A useful way to think about the difference is:
Battery capacity helps answer “how long?” Inverter and battery discharge limits help answer “how much at once?”
Which Loads Matter Most in This Home?
The system was not designed around unrestricted operation of every appliance.
Instead, household loads were divided into three operating groups.
Essential Loads
These receive the highest backup priority:
- refrigerators and freezers;
- lighting;
- internet and network equipment;
- security systems;
- home-office equipment;
- control circuits; and
- selected receptacles.
These loads generally have moderate power demand but need predictable access to stored energy throughout an outage.
Managed Comfort Loads
Cooling is one of the most important loads in a Caribbean home.
The property uses six inverter mini-split air-conditioning systems:
- four 12,000 BTU units;
- two 24,000 BTU units.
The objective is not to operate all six continuously at maximum output.
During backup operation, occupied rooms receive priority while unused zones can be switched off or cycled.
This allows the home to maintain reasonable indoor comfort without unnecessarily shortening backup duration.
Scheduled High-Demand Loads
Other high-demand equipment includes:
- pool circulation;
- water pumps;
- cooking appliances;
- laundry equipment; and
- selected water-heating loads.
These loads can be scheduled rather than operated simultaneously.
For example, pool circulation does not need to run while multiple cooking appliances, water pumps and cooling systems are already creating a high household load.
Load scheduling reduces coincident peaks and preserves stored energy.
How Much Usable Energy Can 128 kWh Provide?
Nominal battery capacity is not the same as usable AC energy.
For preliminary planning, installers can use:
Estimated usable AC energy = nominal capacity × usable SOC window × system efficiency
For example, assuming:
- 128 kWh nominal capacity;
- an 80% usable SOC window; and
- 90% overall delivery efficiency,
the preliminary usable-energy estimate would be:
128 kWh × 0.80 × 0.90 = 92.16 kWh
Runtime then depends on the average supported household load.
| Average supported load | Illustrative runtime |
|---|---|
| 3 kW | 30.7 hours |
| 4 kW | 23.0 hours |
| 5 kW | 18.4 hours |
| 6 kW | 15.4 hours |
| 8 kW | 11.5 hours |
| 10 kW | 9.2 hours |
These figures are planning examples rather than guaranteed runtime.
Actual performance changes with:
- temperature;
- SOC settings;
- inverter efficiency;
- auxiliary consumption;
- cooling demand;
- changing household behavior; and
- solar production during the outage.
What Happened During an Extended Grid Outage?
A useful test of the system came during an overnight grid outage lasting approximately 14 hours.
Grid power was lost during the evening and returned the following morning.
During the outage, the household continued operating:
- refrigeration;
- lighting;
- internet and security equipment;
- water-pump loads;
- selected kitchen circuits; and
- two to three air-conditioning zones as required.
High-demand appliances were not all operated simultaneously.
The battery bank entered the outage at approximately 94% SOC and remained around the mid-40% SOC range by the time grid service returned.
Early-morning solar production had also begun contributing to household demand before utility power was restored.
The important result was not simply that the system operated for 14 hours.
It was that the house maintained most of its normal essential and comfort functions without treating every appliance as an unrestricted load.
That is the difference between a large battery installation and a properly managed whole-home backup system.
How Does the 28.8 kWp Solar Array Change Backup Duration?
Battery runtime should not always be evaluated as if the battery were the only energy source.
This project includes approximately 28.8 kWp of rooftop solar PV.
During daylight backup operation, solar production can first support household demand.
If PV output exceeds the active loads, surplus energy can then be used to recharge the battery.
This creates a different operating pattern from a battery-only backup system:
Solar → Household Loads
and when sufficient solar energy is available:
Solar → Household Loads + Battery Charging
For an extended multi-day outage, this solar contribution can be more important than simply adding additional battery capacity.
A system that reaches sunrise with sufficient reserve may begin another charging cycle instead of continuing to discharge throughout the following day.
What Had to Be Checked With the Schneider Electric Inverter Platform?
Matching a lithium battery bank with an inverter involves more than confirming that both systems operate around the same nominal voltage.
For an eight-battery system, the project configuration needed to consider:
- battery and inverter operating-voltage windows;
- maximum continuous charge current;
- maximum discharge current;
- inverter continuous output;
- surge capability;
- approved battery grouping;
- BMS communication;
- firmware and operating settings;
- DC protection;
- isolation;
- conductor sizing;
- grounding;
- minimum SOC behavior; and
- source priority between grid, solar and battery.
Three Schneider Electric XW Pro 6848 units provide approximately 20.4 kW of combined inverter capacity.
However, that does not mean 20.4 kW should be treated as a target continuous household load during an outage.
Power availability and energy conservation are separate decisions.
The system may technically support a high short-term load while still using load management to preserve battery runtime.
What Was the Main Engineering Challenge?
The project did not have one single technical problem.
The challenge was balancing whole-home expectations with real electrical limits.
High Cooling Demand
Air conditioning represents a large part of electricity consumption in Punta Cana.
Running demand changes continuously as compressors cycle, temperatures change and different rooms are occupied.
The system therefore had to accommodate cooling without allowing every air-conditioning zone to operate without restriction.
Simultaneous High-Demand Loads
Water pumps, cooking appliances, pool equipment and air conditioning can create substantial coincident demand.
Load prioritization and scheduling were therefore part of the system design.
Multi-Battery Integration
Eight battery units must operate as one coordinated battery bank.
SOC alignment, communication, charge/discharge limits and inverter configuration must remain consistent across the system.
Tropical Coastal Environment
The installation also had to account for:
- high ambient temperature;
- high humidity;
- salt-bearing coastal air;
- heavy rainfall;
- potential flooding;
- severe-weather exposure; and
- equipment service access.
These are not secondary installation details.
In tropical markets, environmental exposure is part of system engineering.
How Were the Batteries Installed for Caribbean Conditions?
For a large wall-mounted battery installation, site selection matters.
The installation area should reduce direct exposure to sun and rain while still maintaining the clearances required by the approved product manuals.
The site review should address:
- direct solar heating;
- ventilation;
- salt-air exposure;
- corrosion control;
- flood level;
- drainage;
- wall structure;
- battery weight;
- cable routing;
- bend radius;
- mechanical protection;
- access to disconnects;
- access to displays; and
- maintenance clearance.
The final installation must always follow local electrical, grounding, bonding and permitting requirements.
How Was the Eight-Battery System Commissioned?
A multi-battery installation should be commissioned in stages rather than immediately connecting the entire house.
1. Battery-Level Checks
Each unit should be checked for:
- identification;
- battery voltage;
- SOC alignment;
- communication status;
- alarms;
- isolation; and
- connection integrity.
2. Inverter and BMS Configuration
Charge and discharge limits must remain within the approved battery operating range.
The installer should also confirm:
- communication mode;
- inverter settings;
- source priorities;
- SOC reserve;
- low-energy response; and
- recovery behavior.
3. Controlled Charge and Discharge
Before introducing full household loads, the system should be observed through a controlled operating cycle.
Important parameters include:
- current direction;
- voltage behavior;
- SOC tracking;
- communication status; and
- active alarms.
4. Staged Load Testing
Essential loads are introduced first.
Cooling and other managed loads are then added progressively.
High-demand motor and compressor starts should be observed separately from normal steady-state operation.
5. Grid-Loss Testing
The installer should verify how the system responds when the utility source is removed.
Transfer behavior, battery operation, inverter status, alarms and SOC reserve logic should all be checked before handover.
6. Customer Handover
The homeowner should understand:
- which loads have priority;
- which loads should be scheduled;
- normal system status;
- SOC reserve;
- alarm behavior; and
- what information is needed if remote support is required.
What Changed After the Installation?
The value of the project is not simply that eight batteries were mounted on a wall.
Before storage was added, a grid outage meant that household electricity availability depended directly on the utility supply or a secondary backup source.
After installation, the property gained a structured energy system capable of maintaining most everyday household functions under controlled load conditions.
During an outage:
- refrigeration remains available;
- lighting remains available;
- internet and security equipment remain online;
- water pumping can continue;
- selected air-conditioning zones can operate;
- essential kitchen circuits remain available; and
- solar production can begin supporting the home again once daylight returns.
The homeowner does not need to choose between only two extremes:
normal grid operation or almost no electricity.
Instead, the house can continue operating in a managed backup mode.
This is the practical value of combining:
Solar + Battery Storage + Schneider Inverter Capacity + Load Management
into one residential energy architecture.
What Installers and EPCs Can Learn From This Project
The project illustrates several principles that apply to other large residential energy-storage systems.
128 kWh does not mean 128 kW. Energy capacity and output power must be sized separately.
Whole-home backup does not necessarily mean unrestricted load operation. Large loads still need priorities and operating rules.
Cooling must be included in the design from the beginning. In hot climates, air conditioning can materially change both peak demand and backup duration.
Solar generation matters during long outages. A battery should not always be evaluated as an isolated energy source.
Third-party inverter integration must be verified as a complete system. Model, firmware, current limits, communication, protection and battery grouping all matter.
Tropical conditions are part of the electrical design. Heat, humidity, salt air, rain and service access can affect long-term installation quality.
Commissioning matters as much as battery capacity. A large battery bank only becomes a successful residential backup system after its behavior under real household loads has been tested.
Frequently Asked Questions
Is 128 kWh enough for whole-home backup?
For many homes, 128 kWh represents a very large residential battery bank.
Whether it is enough depends on average household demand, simultaneous peak load, air-conditioning use, usable SOC, solar production, inverter capacity and target backup duration.
A circuit-level load assessment is still required.
How long can a 128 kWh battery run a house?
There is no single runtime.
Runtime depends on usable battery energy and average supported load.
For example, approximately 92.16 kWh of usable AC energy at a 5 kW average load represents roughly 18.4 hours in a simplified planning calculation.
Actual runtime may be shorter or longer.
Can a 128 kWh battery run air conditioning?
Yes, if the air-conditioning demand remains within the inverter and battery limits.
However, multiple AC units can significantly increase both instantaneous power demand and energy consumption.
Load management may therefore be necessary.
Is all 128 kWh available to the household?
No.
Usable energy is lower than nominal capacity after accounting for SOC reserve, conversion losses, temperature, auxiliary consumption and battery operating limits.
Does a 128 kWh battery determine system output power?
No.
Battery capacity is measured in kWh.
The inverter's continuous and surge ratings, together with battery discharge limits, determine how much AC power can be supplied at one time.
Can a lithium battery system work with a Schneider Electric inverter?
Potentially, but compatibility must be verified at the system level.
Operating-voltage range, charge and discharge limits, communication protocol, firmware, protection and approved battery grouping must all be checked.
Planning a Large Residential Energy Storage Project?
A successful whole-home backup system begins with the load profile—not the battery quantity.
For a project review, prepare:
- installation country;
- utility service type;
- inverter model;
- solar-array capacity;
- average daily energy consumption;
- major household loads;
- air-conditioning configuration;
- motor-starting requirements;
- target backup duration;
- minimum SOC reserve; and
- installation environment.
MERITSUN can use these inputs to review a battery configuration around the actual electrical architecture and operating priorities of the project.
For installers, EPCs, distributors and residential energy partners, this creates a more useful starting point than asking only:
“How many kWh of battery do I need?”
