When homeowners upgrade to a 5 kW rooftop array, the next question is almost always, “How many batteries will keep my house running after sunset?” The answer hinges on three linked factors — daily energy use, desired backup hours, and the usable capacity of each battery.
1. Know Your Daily Consumption
A 5 kW array in good sun typically generates 20–25 kWh per day. Yet production only matters if you know how much you spend. Scan a recent utility bill for “kWh used” and divide by 30 days; many three‑bedroom homes land between 12–18 kWh per day. If your load matches your array’s output, you can think Despre covering 100 % of usage with storage.
2. Decide on Backup Duration
Battery banks are sized for a goal:
- Night‑only autonomy (6–8 hrs). Keeps lights, Wi‑Fi, fridge and fans alive until dawn.
- 24‑hour outage resilience. Common in regions with unstable grids.
- Multi‑day off‑grid. Adds weather buffer but can double or triple cost.
Let’s model the popular overnight scenario. If you consume 15 kWh daily, you may only need half of that — say 7 kWh — between sunset (6 p.m.) and sunrise (6 a.m.).
3. Check Usable Battery Capacity
Lithium‑iron‑phosphate (LiFePO₄) batteries dominate modern solar storage for their deep‑cycle capability. Manufacturers quote “usable capacity” after accounting for safe depth‑of‑discharge (DoD). A 48 V 100 Ah module, for instance, stores 4.8 kWh gross, but with 90 % DoD its usable energy is ≈ 4.3 kWh.
4. Do the Math
Backup energy required ÷ usable capacity per battery = modules needed
Example:
| Item | Value |
| Night‑time demand | 7 kWh |
| Usable energy per 48 V 100 Ah pack | 4.3 kWh |
| Packs required | 7 ÷ 4.3 ≈ 2 packs |
Round up to ensure headroom — three packs (≈ 13 kWh) will power heavier loads like air‑conditioning or cover a cloudy morning.
5. Account for Peak Power
Energy (kWh) keeps appliances running; power (kW) starts motors and handles surges. Check that the battery’s continuous and peak output, plus the hybrid inverter’s rating, equal or exceed the simultaneous loads you expect at night. Two 48 V packs in parallel typically deliver 5–6 kW continuous — ample for most homes.
Why Choose Blue Carbon?
As a leading clean‑energy innovator, Blue Carbon focuses on safe, cost‑effective residential and C&I storage systems. Our modular LiFePO₄ batteries integrate seamlessly with solar PV to create a true “generation‑storage‑application” ecosystem. Deployed in dozens of countries, Blue Carbon solutions bring reliable, sustainable power to remote villages, island resorts and grid‑tied suburbs alike. Ready to Size Your Battery Bank? Talk to our engineers today for a free sizing recommendation and a personalized quote. [Get My Battery Plan]
