Home Battery Backup Calculator
Is a home battery worth it? Enter your daily electricity usage, battery specs, electricity tariffs and solar output to see how long the battery can power your home, how much you can save through peak shaving and solar self-consumption, and whether the investment pays off.
Quick Start
Tip: Check your electricity bill for daily kWh usage. Your peak and off-peak tariffs will be shown if you are on a time-of-use plan. Battery specs (capacity, DoD, cycles) are on the manufacturer datasheet.
Settings
Home Consumption
Solar PV (optional)
If you have or plan to install solar panels, the battery can store surplus generation for evening use.
Electricity Tariffs
If you are on a flat tariff, enter the same price for peak and off-peak. Time-of-use tariffs give the best peak-shaving savings.
Battery System
Multi-year Projection
Home battery storage explained: backup, savings and payback
Is a home battery worth the investment?
A home battery is most financially attractive in three scenarios: you have solar panels and export a large proportion of generation at a low feed-in tariff; your utility offers time-of-use pricing with a large gap between peak and off-peak rates; or you need resilience against grid outages. Without at least one of these, payback periods often exceed 15–20 years at current battery prices.
How to calculate backup duration
Backup duration depends on your battery's usable capacity (capacity multiplied by depth of discharge) and your home's average power draw. A 13.5 kWh battery with 90% DoD gives 12.15 kWh of usable energy. A home using 20 kWh per day draws an average of 0.83 kW per hour, so the battery would last approximately 14.6 hours under normal load. Running only essential loads (fridge, lights, phone charging) can extend this to 48 hours or more.
Peak shaving: storing cheap power for expensive hours
If your utility offers time-of-use tariffs, a battery can charge overnight at 0.08–0.15/kWh and discharge during peak hours priced at 0.30–0.50/kWh. The difference, multiplied by the daily kWh shifted, is your annual peak-shaving saving. A 10 kWh battery shifting 8 kWh per day at a 0.18/kWh tariff difference saves around €525 per year.
Solar self-consumption: the strongest financial case
Without a battery, a typical home with solar self-consumes 30–50% of generation and exports the rest at a low feed-in tariff (often 0.04–0.12/kWh). A battery can store midday solar surplus and use it in the evening, boosting self-consumption to 70–90%. The saving is the difference between your import tariff and the export tariff, multiplied by the extra kWh self-consumed.
Battery chemistry: LFP vs NMC
Lithium iron phosphate (LFP) batteries are the preferred chemistry for home storage. They are safer (no thermal runaway), last longer (3,000–6,000 cycles) and tolerate high DoD without significant degradation. NMC (nickel manganese cobalt) batteries are more energy-dense but have shorter cycle life and are more temperature-sensitive. Tesla Powerwall 2 uses NMC; BYD, Sonnen and many newer products use LFP.
What does a home battery cost per kWh stored?
The true cost of battery storage is best measured as cost per kWh delivered over the battery's lifetime. A €10,000 system (including install) with a 10 kWh usable capacity rated for 4,000 cycles stores a total of 40,000 kWh over its life, giving a cost of €0.25/kWh. This is below typical daytime grid tariffs in most markets, meaning the battery delivers cheaper electricity than buying from the grid — the question is whether the timing of savings matches your usage patterns.