Round-Trip Efficiency: What It Means for Your Solar Battery Performance

Maria Suerte
Oct 24
2 min read

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When you charge and discharge a solar battery, not all the energy that goes in comes back out. That’s where Round-Trip Efficiency (RTE) comes in — it measures how much stored energy your battery can actually give back when you need it.

In simple terms: Round-Trip Efficiency = Energy Out ÷ Energy In

Example: If your battery stores 10 kWh of energy but only delivers 9 kWh back to your home, the efficiency is: 9 ÷ 10 = 0.9, or 90%

That means you lose about 10% in the charge–discharge process.

Why Energy Loss Happens

Every battery system experiences small energy losses — it’s completely normal. Losses can come from:

Battery chemistry: Some energy converts to heat during charging or discharging.
Inverter conversion: DC to AC and back conversions reduce total efficiency.
Temperature: Extreme heat or cold slightly affects battery performance.

The goal is to choose a system that minimizes these losses so you get the most usable power possible.

What’s a Good Round-Trip Efficiency?

Most high-quality lithium-ion solar batteries have an efficiency of 90% to 95%. Older or lower-cost battery types (like lead-acid) can be much lower — around 70–85%.

Battery Type	Average Round-Trip Efficiency
Lithium-ion (e.g., Tesla, Sungrow, BYD)	90–95%
Lead-acid	70–85%
Flow battery	75–85%

When you see “90% round-trip efficiency” on a spec sheet, it means you’ll get about 9 kWh back for every 10 kWh stored — a strong performance rating.

Why It Matters for Your Solar Savings

Even a small difference in efficiency adds up over time. A more efficient battery gives you:

More usable energy per charge
Better return on investment
Longer system lifespan (less wasted energy means less wear)

At SolarMatch AU, we help you compare batteries side by side — including round-trip efficiency, usable kWh, and backup capability — so you can see which one offers the best value for your home.

Real-World Example

Let’s say you store 20 kWh of solar energy per day:

A 90% efficient battery gives you 18 kWh usable
A 95% efficient battery gives you 19 kWh usable

That 1 kWh daily difference can add up to over 350 kWh per year — enough to power a typical Australian home for several days.

Final Thoughts

Round-trip efficiency tells you how well your solar battery stores and returns energy. The higher the percentage, the less energy you lose — and the more savings you keep.

In short: 90% efficiency = 10% energy lost during the charge–discharge cycle.

When comparing solar batteries, always check round-trip efficiency — and let SolarMatch AU help you find the one that delivers the best performance for your budget and home.