A 10kWh Solar Retrofit Design: Worked Example from Load Profile to Equipment Scope

The Battery Size Is the Last Number I Trust

A 10kWh home battery retrofit should be designed from the household load profile, existing solar production, evening energy demand, inverter power requirement, and backup objective—not from the fact that “10kWh” is a popular battery size. In the worked example below, a 10kWh-class battery is a reasonable fit because the household regularly has enough daytime solar surplus to charge it and enough evening demand to use most of that stored energy.

Dawnice's current HZEB-LCT-10 provides a useful real product reference: 10.54kWh nominal energy and approximately 9.49kWh usable DC energy at 90% DoD under its stated test conditions .

But I would not start the design there.

I would start with Tuesday.

Tuesday Tells Us More Than the Annual Electricity Bill

Consider an illustrative home with an existing 6.6kWp rooftop PV system .

A typical weekday looks roughly like this:

The annual bill might simply tell us that the household imports electricity.

This profile tells us when .

There is substantial daytime solar surplus, while approximately 8kWh is consumed after 18:00 when PV production has disappeared.

That is the battery opportunity.

Would 10kWh Actually Be Used?

Suppose the battery provides around 9.5kWh usable DC energy .

Not all of that becomes usable AC energy at the household loads because the inverter and system have conversion losses.

So I would not sell this as:

10kWh battery = 10kWh of evening electricity.

Instead, I compare the battery's usable energy with the household's actual evening requirement.

Here:

Evening demand ≈ 8kWh

Usable battery energy ≈ 9.5kWh DC before system conversion losses

That is a sensible relationship.

A 20kWh battery might store more electricity, but this household may not regularly have enough nighttime demand—or enough winter solar surplus—to cycle it economically.

The correct question is not:

How much battery can the homeowner afford?

It is:

How much battery can this home regularly use?

Now Check kW, Because kWh Cannot Run an Appliance

At 19:00 the homeowner might have:

Heat pump: 2.2kW

Cooking load: 1.8kW

Refrigerator/lights/electronics: 0.6kW

Simultaneous demand:

4.6kW

A battery containing 10kWh of energy is useless for this moment if the battery–inverter combination can deliver only 3kW.

For a low-voltage Dawnice retrofit, the HZEB-LCT-10 is rated at 51.2V / 206Ah , while Dawnice currently offers 8kW and 10kW single-phase hybrid inverters with a 45–58V battery window and 51.2V rated battery voltage.

That makes the Products electrically interesting for the same system class.

It does not automatically prove the exact retrofit configuration is approved.

I would still verify:

battery–inverter communication

maximum battery current

firmware

existing PV string voltage/current

local grid requirements

and the actual backup configuration.

Dawnice also publishes dedicated communication tutorials for its 10kWh batteries with several inverter configurations, which is useful evidence that communication compatibility is an integration task rather than merely matching voltage.

Retrofit Architecture Comes Before the Shopping List

Now inspect the existing solar inverter.

If it is a conventional grid-tied PV inverter, the installer has two broad paths.

AC-coupled retrofit: keep the existing PV inverter and add a compatible battery inverter.

Hybrid/DC-side redesign: replace or reconfigure the existing inverter so PV and battery operate through a hybrid inverter.

The second approach might create a cleaner integrated architecture, but replacing a perfectly functional PV inverter has a cost.

The first can preserve existing hardware, but creates another conversion/control layer.

So the quotation should state which architecture is being supplied.

“10kWh solar battery retrofit” is not an equipment scope.

Backup Changes the Design Again

The homeowner now says:

“I also want the battery to run the house during an outage.”

Which house loads?

Suppose essential circuits are:

Refrigeration: 150W average

Internet/security: 50W

Lighting: 150W

Heat pump average: 1.8kW

Other essential loads: 350W

Approximate simultaneous/average design load:

2.5kW

If the system provides, illustratively, around 8.7kWh usable AC energy after the assumed operating and conversion boundaries:

8.7 ÷ 2.5 ≈ 3.5 hours

That is a worked estimate, not a guaranteed runtime.

Heat-pump cycling, startup power, outdoor temperature, starting SoC, other appliances, and whether PV remains available during the outage can change the result substantially.

Backup also requires the installer to define which circuits are actually connected to the protected-load output.

What Would I Put in the Equipment Scope?

For this home, the preliminary scope might be:

Existing 6.6kWp PV array — retain if electrically suitable

10.54kWh Dawnice HZEB-LCT-10 LiFePO4 battery

Compatible hybrid/battery inverter sized from simultaneous load and PV requirements

Battery–inverter communication cable/interface

Battery protection and isolation required by the system design

Meter/CT for import-export measurement

Backup/essential-load arrangement if required

Monitoring

Cables, connectors and installation hardware

Commissioning and operating-mode configuration

Dawnice lists the HZEB-LCT-10 at 83.5kg, IP54, RS485/RS232 communication, and scalability up to 15 parallel units , so future expansion can be considered during the initial installation rather than discovered later.

For a Ruibit/Dawnice distributor, this is also a better quotation structure than:

1 × 10kWh battery
1 × inverter

The buyer can see what problem each component solves.

The Design Has One Final Test

Before ordering equipment, I would replay several representative days—not only sunny Tuesday.

A winter day.

A cloudy day.

A high-load weekend.

A day with unusually low evening demand.

Then ask:

Does the battery regularly charge?

Does it regularly discharge enough to justify its capacity?

Can the inverter support the household's simultaneous loads?

Does the backup scope match what the homeowner expects?

Can the existing PV system actually be integrated without creating another compatibility problem?

If those answers hold across representative conditions, the 10kWh number has earned its place in the quotation.

A good solar retrofit does not begin with a 10kWh battery and search for a reason to install it. It begins with the home's energy flows—and discovers whether 10kWh is the right answer.

FAQs

1. Is a 10kWh battery suitable for an existing rooftop solar system?

It can be if the household has enough daytime solar surplus to charge the battery and sufficient evening or nighttime demand to use the stored energy . Battery size should be based on the home's actual load and solar-generation profile.

2. Is 10kWh battery capacity enough to determine the correct inverter size?

No. kWh determines stored energy, while kW determines how much power can be supplied at one time. Inverter sizing should consider simultaneous household loads, battery discharge limits, PV requirements, and backup loads.

3. Should an existing solar retrofit use AC coupling or a hybrid inverter?

It depends on the existing PV equipment. AC coupling may allow the existing solar inverter to remain, while a hybrid/DC-coupled design may require inverter replacement or system reconfiguration. Compatibility and project cost should be compared before selection.

4. What should a 10kWh solar battery retrofit quote include?

A complete scope should identify the battery, compatible inverter, communication interface, metering/CT, protection and isolation, backup arrangement if required, monitoring, cables, installation hardware, commissioning, and operating-mode configuration .