Hybrid InverterBattery Sizing

A hybrid inverter and a battery are sold as a pair, but they are sized by three different numbers: the inverter’s kW, the battery’s kWh, and the hours of backup the site actually needs. Choose either one first and the other second, and you can still end up with a system that trips when a pump starts or runs flat at two in the morning.

Every rating below comes from our own product pages, and every calculation is written out so you can repeat it.

Three numbers, three different jobs

kW is a rate: how much power can flow right now. kWh is a quantity: how much energy is stored. Hours are not bought directly; they are what you get when you divide usable energy by the load.

• Inverter kW sets the largest load the system can carry, and the surge it can survive for a few seconds.
• Battery kWh sets how long that load can run, after depth of discharge and conversion losses.
• Backup hours is the result: delivered kWh divided by the critical load in kW.

A 10 kWh battery with a 5 kW inverter shows why the three numbers must be read together. At 90% depth of discharge and an assumed 90% round-trip efficiency, about 8.1 kWh reaches the load: roughly four hours at 2 kW, or 1.6 hours at 5 kW.

The battery has a kW limit of its own

Most sizing conversations stop at kWh. That misses a hard limit inside the battery: the BMS and cells allow only a certain continuous current, and current multiplied by voltage is power. A battery with a large kWh label can still be unable to feed the inverter at full output.

The GWR row makes the point. The 5.12 and 10.24 kWh wall batteries are both rated at 100 A, so both deliver about 5.12 kW continuously: doubling the energy did not double the power. The GVR series repeats it, with 16.08 and 30.72 kWh models both listing 200 A, or 10.24 kW at 51.2 V. The larger cabinet buys hours, not kilowatts.

The high-voltage GHS-100 escapes the limit by raising voltage instead of current: 15 modules give 768 V at 50 A, or 38.4 kW from 76.8 kWh. That is why high-voltage stacks appear once a project needs more than about 10 kW from one enclosure.

Which inverter class fits the load

The inverter side has its own limits: rated AC output, surge, battery voltage and maximum battery current.

Charge current matters twice. On the 8 kW SDPO, 160 A at 51.2 V is about 8.2 kW, so a fully drawn-down 16.08 kWh battery refills in roughly 1.6 hours at the limit, before taper. On the 16 kW unit, the 300 A charge limit and two battery inputs are what let a two-battery bank refill overnight.

Worked example: 8 kW peak, 3 kW for three hours

A house peaks at 8 kW (oven, well pump, air conditioning). Its critical-load panel is 3 kW and must run for three hours during an outage.

Step 1: energy for the backup window

The critical load needs 3 kW × 3 h = 9 kWh at the socket. A GVR 51.2V / 314Ah battery stores 16.08 kWh. At the 80% depth of discharge suggested on its page, 12.86 kWh is usable; at an assumed 90% round-trip efficiency, 11.58 kWh reaches the load — 2.58 kWh, about 29%, above the requirement.

Step 2: power to carry the peak

The same battery is rated at 200 A continuous, which is 10.24 kW at 51.2 V. That covers the 8 kW peak and the 3 kW backup load. The SDPO 8 kW delivers 1.5× its rating for 10 seconds, so a pump start does not trip the output.

Step 3: recharging inside the window

The SDPO 8 kW accepts up to 160 A of charge current, or 8.19 kW at 51.2 V, so the 12.86 kWh drawn from the battery is replaced in about 1.57 hours at the limit.

One GVR 16.08 kWh battery and one SDPO 8 kW inverter therefore satisfy all three numbers. Raise the backup to 3 kW for five hours — 15 kWh — and the same battery falls short on energy while still having enough power.

When the peak doubles: 16 kW and two batteries

Scale the same house to a 16 kW peak with a 10 kW critical load for two hours — 20 kWh. One GVR battery is now power-limited: 10.24 kW is 5.76 kW short of the peak, and 11.58 kWh is short of the 20 kWh the backup needs.

Two GVR units in parallel fix both numbers. Power becomes 20.48 kW, above the 16 kW peak. Energy becomes 32.16 kWh nominal, or 23.16 kWh delivered after the same 80% depth of discharge and 90% efficiency, which leaves 3.16 kWh of margin. At the full 16 kW the pair runs 1.45 hours; hold the load to 11.6 kW and it runs the whole two hours.

The SDPO 16 kW is built for that bank: two battery inputs and a 340 A discharge limit, where a single-input 8 kW unit would be the wrong starting point once the peak passes its rating.

Low-voltage or high-voltage

All four inverters above run a 48 or 51.2 V low-voltage battery platform, easy to expand: the GVR series accepts up to 15 units in parallel, and the wall-mounted GWR range covers 5.12 to 10.24 kWh for smaller loads.

Above roughly 10 to 15 kW of continuous battery output, current becomes the bottleneck. A high-voltage stack solves it by raising volts: the GHS-100 configures 6 to 15 modules for 30.74 to 76.8 kWh at 307.4 to 768 V, and the GHS-200 reaches 42 to 157.44 kWh. These are DC platforms for the high-voltage hybrid inverters listed on their pages, not for the 48 V machines above. The residential LFP storage range is the place to compare wall-mounted and floor-standing formats.

What to send for a sizing proposal

A battery cannot be sized from a monthly bill. The proposal needs the shape of the load and the duration of the outage. Send six items:

• Peak kW and the appliances that create it, especially motors.
• Critical-load list in kW, and the hours it must run.
• Daily kWh, or a 24-hour load curve if one exists.
• Grid supply: single-phase, split-phase or three-phase, and the voltage.
• PV size, and whether the battery charges from solar, grid or both.
• Indoor or outdoor siting, ambient temperature, and space for a wall or floor unit.

With those inputs the inverter class and the battery capacity can be checked against each other in one pass. The home battery sizing guide covers capacity bands, and the split-phase backup guide covers the 120/240 V wiring side. To have the numbers checked against a real configuration, send them through our contact page.

Frequently asked questions