Battery tariff arbitrage: charge cheap, discharge expensive

A home battery does not have to be solar-only. On a time-of-use tariff, tariff arbitrage means charging during a low-cost grid period and using that stored energy during a higher-cost period.

Australian Government guidance explicitly recognises this use. The Australian Energy Market Commission also finds that households with substantial evening usage can benefit strongly because the battery can displace expensive evening grid imports.

Australian Government battery bill-savings guidance → · AEMC residential battery analysis →

Solar arbitrage versus tariff arbitrage

Solar arbitrage: store your own excess daytime PV and use it later.

Tariff arbitrage: buy electricity when the grid rate is cheap, store it, then avoid buying at a more expensive time.

A battery can use both strategies, but filling it cheaply from the grid can reduce the room available for free excess solar later. Good control logic therefore balances both.

Why evening peak matters

Many Australian TOU plans have their most expensive residential period in the late afternoon or evening. Exact periods vary by network and retailer, so the schedule must use the tariff on your actual plan rather than a generic “peak starts at 4pm” assumption.

What a useful strategy needs

The battery platform must support the operating mode you want; grid charging must be permitted; charge and discharge windows need to align with the tariff; reserve SOC must leave enough usable energy; and external VPP/EMS controls must be understood.

Do not optimise from tariff alone

Round-trip losses, solar expected the following day, household load, battery power and cycle economics all matter. This page explains the control concept; it does not claim every price spread is profitable.