What is round-trip efficiency and why does it matter?

LG RESU's 95% RTE means for every 100 kWh charged, you get 95 kWh back out. Enphase IQ Battery at 89% RTE loses more than twice as much energy per cycle. Over daily cycling, this translates to hundreds of kWh and tens of dollars per year in difference — meaningful over a 10-year warranty period.

LG Energy Solution Battery Calculator

LG RESU deep-dive — select RESU Prime 16H (16 kWh), RESU FLEX modular (8.6–17.2 kWh), or RESU 10H Prime (9.6 kWh). Get backup hours, round-trip efficiency, cycle life, ITC savings, and inverter compatibility check vs Tesla, Enphase, and SolarEdge.

LG Energy Solution battery inputs

LG ESS model?

Backup capacity needed?

kWh

Backup duration needed?

hours

Existing inverter brand?

RESU Prime 16H — 16 kWh — Whole-home flagship — 16 kWh at 400V DC, works with most string inverters

RTE: 95%Cycles: 6,000 @ 80% DoDWarranty: 10 years$/kWh: $850

LG ESS battery results

Capacity note: Selected configuration provides 14.4 kWh usable — consider stacking more RESU FLEX modules or adding a second unit.

Inverter compatibility: Native SolarEdge compatibility — LG RESU Prime is the reference battery for SolarEdge StorEdge. Seamless integration.

Metric	Result
Total usable capacity	14.4 kWh (16.0 kWh rated)
Units / modules	2 × RESU Prime 16H
Avg load supported	0.67 kW
Actual backup duration	21.6 hours
Round-trip efficiency (RTE)	95%
Energy lost per cycle	0.80 kWh (5% loss)
Cycle life	6,000 cycles at 80% DoD
Expected battery life	16.4 years (daily cycling)
Capacity at year 10 (warranty end)	11.5 kWh (≥80% guarantee)
Estimated system cost	$27,200
Federal ITC (30%)	-$8,160
Net cost after ITC	$19,040
Warranty	10 years — 80% capacity guaranteed

vs. Competitors

Brand	kWh	$/kWh	RTE	Cycles
Tesla Powerwall 3	13.5	$930	97%	3,650
Enphase IQ Battery 5P	5	$1100	89%	4,000
SolarEdge Home Battery	9.7	$880	94%	6,000
LG RESU Prime 16H ★	16	$850	95%	6,000

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How to Use This Calculator

Important: LG Energy Solution vs LG solar panels

LG Electronics discontinued its solar panel line in 2022 — those panels are no longer manufactured. LG Energy Solution (LGES) is a separate company that continues to manufacture RESU home battery systems. LGES is one of the world's largest battery manufacturers (EV batteries for GM, Honda, Hyundai), and their RESU home storage products have industry-leading cycle life and round-trip efficiency. This calculator covers the RESU battery lineup only.

Enter your backup capacity and duration needs

Backup capacity (kWh) is how much energy you need stored. Duration (hours) is how long you need it to last. Essential loads only (fridge, lights, WiFi router, phone chargers) consume approximately 500W–1 kW continuously — about 5–10 kWh overnight. A whole-home backup including HVAC consumes 2–5 kW continuously, needing 20–40 kWh for 12 hours. Use these benchmarks to enter realistic values and let the calculator tell you whether the selected RESU model covers your needs.

Select modules for RESU FLEX

The RESU FLEX is the only modular model in the lineup — you can install 1, 2, or 3 modules and add more later without rewiring. Each module is 8.6 kWh usable (nominal). A 2-module FLEX configuration gives 17.2 kWh nominal. This is the most expandable option if your needs might grow — adding a second battery system later with the RESU Prime or 10H Prime requires a new installation.

The Formula

Total Usable kWh = Model Usable kWh × Module Count (FLEX only) Average Load = Capacity Needed ÷ Backup Hours Actual Backup Duration = Total Usable kWh ÷ Average Load RTE Energy Loss per Cycle = Capacity × (1 − 0.95) Expected Battery Life = 6,000 cycles ÷ 365 cycles/yr Estimated System Cost = Model kWh × $/kWh × Module Count Federal ITC = System Cost × 30% Net Cost = System Cost − ITC Year 10 Capacity = Usable kWh × 80% (warranty minimum)

The 95% round-trip efficiency (RTE) means for every 1 kWh you charge into the battery, you get 0.95 kWh back out. The remaining 5% is lost as heat during charge/discharge cycles. At 6,000 cycles rated for 80% depth of discharge (DoD), daily cycling gives a projected 16+ year battery life — well beyond the 10-year warranty period. Real-world cycle life depends on temperature, charge rate, and average DoD.

Example

David — RESU Prime 16H, whole-home backup, SolarEdge system

David has a 10 kW SolarEdge solar system and wants whole-home backup for 24-hour outages. He needs to power a fridge (150W), HVAC (1,500W cycling), lights and devices (500W), and critical medical equipment (200W).

Model selectedRESU Prime 16H (16 kWh rated)

Backup capacity needed16 kWh

Backup duration needed24 hours

Existing inverterSolarEdge (native compatible)

Results

Total usable capacity14.4 kWh (16 kWh rated @ 90% DoD)

Average load supported0.67 kW

Actual backup duration~21.5 hours

RTE per cycle95% — 0.72 kWh lost

Estimated cost$13,600 ($850/kWh × 16 kWh)

Federal ITC (30%)-$4,080

Net cost$9,520

Expected battery life~16.4 years at daily cycling

David's SolarEdge system integrates natively with the RESU Prime 16H — no additional hybrid inverter needed, reducing installation cost and complexity. The 16 kWh provides ~21 hours at his average load. For true 24-hour coverage, stacking two RESU FLEX modules at 17.2 kWh total would give him a comfortable buffer even if his HVAC runs more than expected.

LG RESU vs Competitors

Spec	LG RESU Prime 16H	Tesla Powerwall 3	Enphase IQ 5P	SolarEdge Home 9.7
Capacity (kWh)	16 kWh	13.5 kWh	5 kWh	9.7 kWh
Round-trip efficiency	95%	97%	89%	94%
Cycle life	6,000	3,650	4,000	6,000
Warranty	10 years	10 years	15 years	10 years
Stackable	2 units	4 units	Unlimited	3 units

FAQ

Does LG still make solar products? ▼

LG Electronics exited the solar panel business in June 2022 and no longer manufactures photovoltaic panels. However, LG Energy Solution (LGES) is a fully separate subsidiary that continues to manufacture RESU home energy storage systems. LGES is publicly traded on the Korean Stock Exchange (KRX: 373220) and is one of the world's largest EV battery suppliers — providing batteries to General Motors (Ultium), Honda, Hyundai, and others. The RESU product line is actively manufactured and warranted through LG Energy Solution North America.

What inverters are compatible with LG RESU batteries? ▼

The RESU Prime 16H and 10H Prime are DC-coupled batteries working natively with SolarEdge StorEdge inverters (most common pairing), SMA Sunny Boy Storage, and several other hybrid inverters. The RESU FLEX is an AC-coupled system — it works with any grid-tied inverter (including Enphase) but requires a separate hybrid inverter (RESU FLEX Hybrid Inverter) included in the system. Generac PWRcell, Enphase IQ Battery, and Franklin Electric batteries use proprietary battery interfaces — not compatible with RESU. Always confirm compatibility with your specific inverter model and firmware version before purchasing.

What is round-trip efficiency (RTE) and why does it matter? ▼

Round-trip efficiency measures how much energy you get out relative to what you put in. LG RESU's 95% RTE means for every 100 kWh your solar panels send to the battery, you get 95 kWh back when discharging. The 5% is lost as heat. Over a year of daily cycling with a 10 kWh battery: 365 × 10 kWh × 5% = 182 kWh lost per year — roughly $20-40 in electricity cost depending on your rate. Enphase IQ Battery's 89% RTE loses 397 kWh/year on the same usage pattern — about 2× the losses of RESU. Higher RTE means more solar energy reaches your loads and less is wasted.

Do home batteries qualify for the 30% federal tax credit? ▼

Yes — the Inflation Reduction Act extended and expanded the 30% Investment Tax Credit (ITC) to include standalone battery storage systems with capacity of 3 kWh or more. As of 2023, you no longer need to pair the battery with new solar to claim the ITC — a standalone battery installation qualifies. The credit applies to the full installed cost of the battery system including hardware, wiring, and installation labor. For a $13,600 RESU Prime 16H system, this means a $4,080 federal tax credit — reducing your out-of-pocket cost to approximately $9,520.

What is the difference between RESU Prime 16H and RESU FLEX? ▼

The RESU Prime 16H is a single DC-coupled 16 kWh unit at 400V — it integrates directly with SolarEdge and SMA inverters without a separate inverter, keeping costs and complexity lower. The RESU FLEX is an AC-coupled modular system — each module is 8.6 kWh nominal and you can stack 1 to 3 modules. The FLEX requires a dedicated hybrid inverter (included) and can be retrofitted to any existing solar system regardless of inverter brand. FLEX is better for expansion plans (you can add a module years later). Prime 16H is better for SolarEdge/SMA systems where native DC coupling reduces losses and installation cost.

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