BESS calculator (residential battery storage)
Size a residential battery storage system for solar self-consumption, backup power, or time-of-use arbitrage. Currently supports the United States, Germany, India, and the United Kingdom. Numbers are 2026 indicative ranges; use them as a starting point, not a final quote.
Your inputs
You have or plan solar; size the battery to store midday production for evening use, avoiding low-rate export.
Typical: US 25–40 · Germany / UK 8–15 · India 10–25
What your utility pays for solar export (NEM 3.0 in CA: low; Germany EEG ~8 ct/kWh)
$970–$1,430 per kWh installed (2026 typical range)
No federal credit for batteries you own installed after Dec 31, 2025 (IRS, 25D ended)
Estimated results
- Recommended battery capacity
- 12.5 kWh
- Recommended power rating
- 6.3 kW
- Gross installed cost
- $14,500
- Net cost after incentive
- $14,500
- Expected annual cycles
- 320 per year
- Annual savings
- $504
- Simple payback
- 28.8 years
- 10-yr loan payment (7.5% APR)
- $172/month
- vs. avg monthly savings
- $42/month
- 15-yr net savings (after net cost)
- $0
Estimates assume 90% round-trip efficiency (typical LFP) and 15-year battery life. Actual prices and savings vary by installer, tariff, state/region, and weather. Get three independent quotes before any commitment.
US defaults and sources
- Residential electricity price
- State average when you pick a state; US average 18.19 cents/kWhEIA Electric Power Monthly, Table 5.6.B (year-to-date through August 2026, preliminary) · checked Oct 27, 2026
- Installed home battery price
- $15,647 for a typical 13.5 kWh battery (about $1,159/kWh); top brands $967-$1,429/kWhEnergySage, solar battery cost (first half of 2026 quotes) · checked Oct 27, 2026
- Federal credit for buying solar or a battery (25D)
- None for systems installed after December 31, 2025IRS FAQs on Public Law 119-21 · checked Oct 27, 2026
How this calculator works
The calculator sizes a residential battery based on your primary use case. For solar self-consumption, it recommends ~40% of daily consumption — enough to shift midday solar production to evening use. For backup power, it sizes to cover your critical load for the desired backup hours, with a 1.25× safety factor. For time-of-use arbitrage, it sizes for ~50% of daily consumption — enough for one full charge/discharge cycle per day. Power rating is set at 2-hour discharge (kW = kWh / 2), which is standard for residential batteries.
The three use cases explained
- Solar self-consumption — your solar generates midday, you use most of your electricity in the evening. Battery stores the surplus so you don't pay retail rates in the evening. Most valuable when retail rate (€0.30+/kWh) is much higher than export rate (€0.04–€0.08/kWh) — Germany, California NEM 3.0, parts of UK.
- Backup power — for outage-prone areas (US Texas/Florida, parts of UK, most of India). Battery sized to cover refrigerator, lights, internet, and possibly one AC zone for the desired hours. Savings here are mostly insurance value — quantify by outage frequency × duration × critical load × premium over normal rate.
- Time-of-use arbitrage — for customers on dynamic tariffs (Octopus Agile UK, Tibber DE, real-time pricing in some US states). Battery charges during cheap hours (often nighttime) and discharges during peak hours. Best economics when peak-offpeak spread is > €0.15/kWh.
Important caveats
- Estimates only — actual installer pricing varies 20–35% on identical hardware.
- Annual cycles assumed: 320 for solar self-consumption, 4 for backup, 360 for arbitrage. Your actual cycles depend on weather, tariff structure, and discipline.
- Round-trip efficiency assumed 90% (typical LFP). Actual efficiency depends on inverter, depth of discharge, and ambient temperature.
- 15-year savings assume electricity rates stay flat. Real-rate inflation of 2–5%/year (typical in US, EU, India) makes actual savings higher.
- India incentive treatment varies by state — Tamil Nadu, Karnataka, and Gujarat have limited residential battery grants but the federal subsidy structure prioritizes solar PV via PM Surya Ghar, not standalone batteries.
Frequently asked questions
How much battery storage do I need for my home?
Depends on use case. Solar self-consumption: ~40% of daily kWh consumption. Backup power: critical load (kW) × backup hours × 1.25 safety factor. Time-of-use arbitrage: ~50% of daily kWh consumption. Typical US/EU residential battery: 10-15 kWh.
How much does a residential battery cost in 2026?
Installed cost per kWh in 2026: US about $970-$1,430 (EnergySage first-half 2026 quotes); Germany €650-€950; India ₹45,000-₹70,000; UK £700-£1,000. EnergySage puts a typical 13.5 kWh US battery at $15,647 before incentives, and US homeowners who buy now get no federal credit.
Is there a federal tax credit for home batteries in 2026?
Not for batteries you buy. The 30% residential clean energy credit (25D), which covered batteries of 3 kWh or more, does not apply to expenditures after December 31, 2025, and the IRS counts the expenditure when installation is completed. A leased battery can still earn the provider a commercial credit under section 48E. In Germany the 0% VAT applies to batteries paired with residential solar up to 30 kWp. UK has 0% VAT on residential batteries since 2024.
How long does a residential battery last?
Modern LFP batteries (Tesla Powerwall 3, Enphase IQ Battery, BYD Battery-Box) are warrantied for 10-15 years with ~70% capacity retention. Practical operating life is typically 15-20 years. Plan for one battery replacement during a 25-year solar system life.
Should I get a battery if I'm on net metering?
If your utility offers full retail-rate net metering, the economics of battery for solar self-consumption are weak — your grid acts as a free battery. Battery makes more sense for backup power or if net metering reforms (like California's NEM 3.0) reduce export compensation.
What's the difference between battery capacity (kWh) and power (kW)?
Capacity (kWh) is total energy stored — how much you can use before recharging. Power (kW) is how fast you can discharge it. Residential batteries typically have a 2-hour discharge rating (a 10 kWh battery delivers 5 kW for 2 hours). Higher kW rating costs more but matters for whole-home backup.
Will battery prices keep falling?
Modestly. LFP cell prices fell 50% from 2022-2024; further drops will be 5-10% per year through 2027, not the dramatic cuts of 2022-2024. Don't wait — incentive availability and installer scheduling matter more to the financial outcome than waiting for a 5% price drop.
Can I add a battery to my existing solar system?
Yes, via AC-coupling. Existing solar inverter stays; a separate hybrid battery inverter handles the battery side. Slightly more complex than installing solar + battery together but routine for most installers. Plan an extra day of installation time.
Related reading
- Solar calculator (PV sizing + payback)
- Solar battery brands US 2026 ranked
- Solar Batteriespeicher Germany 2026
- Best BESS batteries India 2026
- How to choose battery storage (BESS) 2026
- 2-hour vs 4-hour BESS revenue 2026
- C-rate · LFP · Round-trip efficiency
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