Round trip efficiency (RTE) is a measure of how efficiently a battery can store and discharge energy. Find out why it’s crucial in the world of BESS.
Terminology in the world of battery storage can seem daunting to the average Joe.
Luckily, we’re here to help.
Round trip efficiency (RTE) is something you may have come across in relation to batteries.
In a nutshell, RTE measures how efficiently a battery can store and discharge energy.
How is RTE calculated? Why are there no batteries with 100% RTE? How has RTE in storage batteries improved in recent years?
Read on to find the answers to these questions.
How to calculate the RTE of a battery?
The RTE of a battery can be calculated as a percentage using a simple formula shown below:
Energy output ÷ energy input x 100 = RTE
Let’s demonstrate what this means in practical terms with an example.
Mrs Jones installs a storage battery for her home. As she and her family typically use 10 kWh of electricity per day, she opts for a 10 kWh storage battery.
As someone who is both eco-conscious and has an above-average income, Mrs Jones installs both solar panels and a wind turbine to power her battery storage system. This means she can charge her 10 kWh battery from renewable sources.
However, Mrs Jones soon realises that she isn’t getting 10 kWh per day from her storage battery.
In reality, she gets 8 kWh per day. That’s because her 10 kWh battery has 80% round trip efficiency.
If she had opted for a 10 kWh battery with 90% round trip efficiency, she would get… yep… 9 kWh per day.
For her remaining 2 kWh per day of electricity needs, she draws energy from the grid.
Why do batteries lose energy?
Unfortunately, batteries always lose a small amount of energy during operation.
This is usually because of heat loss, self-discharge, high internal cell resistance or other factors.
Are there any batteries with 100% RTE?
You can think of it like this: if anyone ever tries to sell you a 100% RTE battery, run a mile because they’re almost certainly lying.
What is the RTE of a typical battery?
RTE varies among different types of storage batteries.
For older battery systems, 80% round trip efficiency would have been considered a good standard. Some evidence suggests the typical lithium-ion battery – a popular choice for modern battery energy storage systems and electric vehicles – has round trip efficiency of around 83%.
GivEnergy’s own batteries – using LiFePO4 (lithium iron phosphate) – have achieved 93% round trip efficiency.
RTE – not to be ignored
Grid-level battery storage is becoming increasingly common to accommodate the growth in renewables, especially solar and wind.
Round trip efficiency is a factor that decision-makers need to take into account when assessing the overall efficiency of an energy storage system.
And it’s something YOU also need to bear in mind when installing your own battery storage system for your home or business.
Remember: 100% round trip efficiency is a lie! However, 93% round trip efficiency with a GivEnergy battery using LiFePO4 technology is not a lie.
Looking to play your part in the energy storage revolution? Get started by finding an approved GivEnergy installer today.
