Free Energy Storage Cost calculator with clear step-by-step results.
Storage is not judged on its purchase price but on what each stored kilowatt-hour ends up costing. Divide the installed cost by the energy the battery will actually deliver over its life — capacity × cycle life × round-trip efficiency — and you get the levelised cost of storage. Efficiency matters twice over: energy lost on the round trip never reaches the load, so a 90% system delivers only 90% of its nameplate throughput. The result is the figure to compare against your tariff spread.
Lifetime throughput
Throughput = usable capacity × cycle life × round-trip efficiency
Levelised cost
LCOS = installed system cost ÷ lifetime throughput
Cycle life is a warranty figure measured under specified conditions and degrades faster with heat, high charge rates and deep discharge. Battery installation is regulated work — use a qualified installer and follow local electrical codes.
When the levelised cost per kWh is below the difference between your import and export or peak and off-peak prices. If storage costs $0.12/kWh and your peak-to-off-peak spread is $0.20, arbitrage is viable before considering backup value.
Batteries reserve a depth-of-discharge margin to protect cycle life, so nominal capacity overstates what you can actually cycle. Manufacturers quote both — use the usable figure.
Yes. Inverter, wiring, enclosure, permitting and labour are often 30-50% of a residential system, and excluding them makes the levelised cost look far better than it is.