Path-Q Solar
How does battery round-trip efficiency affect the solar system size needed for evening use?
Answer
Round-trip efficiency means that only part of the energy sent into a battery is available later. To deliver a target amount of evening energy, solar must produce enough extra energy to cover the battery's charging and discharging losses, so lower efficiency generally requires more solar generation or a larger charging window.
Key points
- Required stored energy is approximately the desired delivered energy divided by round-trip efficiency.
- For example, delivering 10 kWh with 80% round-trip efficiency requires about 12.5 kWh to enter the storage cycle, before other system losses.
- Battery sizing must also consider usable capacity, reserve settings, power output, and seasonal solar production.
What it depends on
- Battery round-trip efficiency under the expected operating conditions
- Evening energy demand and desired backup reserve
- Solar production profile and available charging hours
- Battery usable capacity and maximum charge or discharge power
Risks and trade-offs
- Using a nominal efficiency figure may overstate real-world delivered energy.
- Oversizing the battery does not solve inadequate solar production during low-sun periods.
- Higher storage capacity can increase cost and may reduce financial returns if it is rarely used.
Information you may need
- Hourly or interval evening consumption
- Battery's usable capacity and efficiency specification
- Desired reserve and backup requirements
- Seasonal solar production estimate
Your next step
What to do next
Create an hourly energy model that includes battery losses and compare the resulting solar and storage sizes.
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