No rooftop PV? You can still run a battery as a quiet, automatic backup. Enter your essential load and hours of backup — see the right capacity in kWh, the cost, and the payback from peak/off-peak arbitrage. No email required to use it.
Usable kWh = load (kW) x hours. Nameplate = usable / depth of discharge. Daily arbitrage saving = (peak - off-peak) x usable x 0.9 efficiency x cycles. Without solar the bank lasts only as long as you size it — for multi-day outages add a generator or PV. Figures are indicative; a tailored quote confirms exact sizing and inverter compatibility.
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A home battery does not need rooftop panels to protect you from blackouts. It charges from the grid like a phone when power is normal, then islands your home the instant the grid drops — your lights, fridge and internet keep running with no click, no fuel, no warm-up. Solar only adds one thing: free recharge during a long outage. Without it, the bank runs for exactly the hours you sized it for, then a generator or the returning grid takes over.
The honest trade-off: a no-solar battery earns its keep two ways — peace of mind (avoided food spoilage, lost work, discomfort) and tariff arbitrage (charging off-peak and discharging peak). The calculator above shows both.
Size a no-solar backup by one rule: essential load (kW) x hours you can't be without power = usable kWh, then divide by depth of discharge. Because nothing recharges the bank, be realistic about the hours. Rough starting points:
| What you keep on | Load | Hours | Usable kWh | NovaBESS fit |
|---|---|---|---|---|
| Fridge, lights, internet, phones | ~400 W | 12 | 4.8 | HomeWall 5.1 kWh |
| + a small AC / heater (essentials) | ~1,500 W | 8 | 12 | HomeStack 15 kWh |
| Whole-essentials (well pump, freezer) | ~2,500 W | 24 | 60 | Multiple HomeStack (parallel 60 kWh+) |
If your outages tend to last more than a day, pair the battery with a generator rather than oversizing the bank — a smaller battery plus a generator is usually cheaper than a giant battery you only need once a year.
Cost. Equipment for a LiFePO4 home battery runs about $400-900 per usable kWh (installed typically $800-1,500/kWh). A 13 kWh bank lands around $8,000 equipment. LiFePO4 lasts 5,000+ cycles, so lifetime cost per kWh-cycle is roughly $0.12 — far below lead-acid.
Payback without solar. There is no self-consumption saving, so the only financial payback is time-of-use arbitrage:
Annual saving = (peak - off-peak) x usable kWh x 0.9 x cycles/day x 365
Payback (yrs) = system cost / annual saving
With a $0.23/kWh spread and one cycle a day, a 13 kWh bank saves about $900/year and pays back in roughly 9 years — while also covering 8 hours of backup every time the grid fails. If your tariff is flat (no peak/off-peak gap), the battery has no energy payback; its return is the value of outages you no longer suffer. Compare the math side by side in our cost per kWh calculator.
These three calculators cover the home-battery word group:
For grid-tied self-consumption and off-grid sizing with both tariff and solar inputs.
Same load-based sizing, plus PV recharge during multi-day outages. Use this if you have (or plan) rooftop solar.
Pure grid backup: sizing plus peak/off-peak arbitrage payback, no solar required.
Yes. A battery charges from the grid when power is normal and supplies your home automatically during an outage (islanding). No rooftop PV is required — solar only adds free recharge during extended blackouts. Use the calculator above to size one by your essential load and hours of backup.
Multiply your essential backup load in watts by the hours you want to ride one charge, then divide by depth of discharge. A 1,500 W load for 8 hours needs 12 kWh usable; at 90% DoD that is about 13.3 kWh nameplate. Because there is no solar to recharge it, the bank only lasts as long as you size it.
Only if you use time-of-use arbitrage: charge off-peak (cheap) overnight and discharge during peak hours. That daily spread is the real payback. Used purely for backup, the battery has no energy-bill savings — its value is avoided outage losses and lower generator cost.
Annual saving = (peak rate - off-peak rate) x usable kWh x round-trip efficiency x arbitrage cycles per day x 365. Payback years = system cost / annual saving. A 13 kWh bank with a $0.23/kWh spread and one cycle/day saves about $900/year, paying back a ~$8,000 system in roughly 9 years.
For short, frequent outages a battery is quieter, instant and maintenance-free, and it also earns from arbitrage. A generator is cheaper per kWh stored and better for open-ended, multi-day blackouts. Many homes pair a smaller battery with a generator for the worst cases.
Tell us your essential loads, country and tariff — we'll configure a HomeWall or HomeStack system and quote distributor or OEM pricing.
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