Solar Battery Sizing Guide 2026: How to Size a Battery Bank Correctly

Why Sizing a Solar Battery Correctly Matters More Than Anything Else

A solar battery system that is undersized will leave you without power. One that is oversized costs significantly more than necessary. Getting the sizing right — based on real data, not rules of thumb — is the single most important step in any solar project specification.

Step 1: Define Your Daily Energy Requirement

List every load in the system. For each load, multiply power draw (watts) by hours of use per day.

Example — small commercial solar system (resort in the Philippines):

• Lighting (LED, 20 fixtures × 10W × 8 hours): 1,600Wh/day
• Air conditioning (1,500W × 6 hours): 9,000Wh/day
• Refrigeration (200W × 24 hours): 4,800Wh/day
• Wi-Fi and security (100W × 24 hours): 2,400Wh/day
• Total: 17,800Wh/day ≈ 18kWh/day

This is the minimum energy the battery must supply during periods without solar generation.

Step 2: Determine Required Days of Autonomy

Autonomy = number of cloudy days the battery must bridge without solar input.

| Application | Recommended Autonomy | Typical Scenario | |—|—|—| | Grid-tied with backup | 1 day | Grid fails, generator starts | | Off-grid with generator backup | 2–3 days | Multi-day cloudy period | | Remote off-grid (no generator) | 3–5 days | Remote telecom, monitoring station | | Critical infrastructure | 5–7 days | Hospital, data center |

For most commercial solar projects, 2 days autonomy is the practical minimum.

Step 3: Size the Battery Bank for Depth of Discharge Limit

Batteries should never be regularly discharged below their recommended depth of discharge (DoD) limit. Operating beyond DoD dramatically reduces cycle life.

| Battery Type | Recommended Max DoD | Design DoD for Daily Cycling | |—|—|—| | Flooded lead-acid | 50% | 50% | | AGM VRLA | 50–60% | 50% | | OPzV tubular gel | 60–80% | 50–60% | | LiFePO4 | 80% | 80% |

Battery bank size formula: Required bank (kWh) = Daily usage (kWh) × Autonomy (days) ÷ Max DoD

Example: 18kWh/day, 2 days autonomy, OPzV gel at 60% DoD = 18 × 2 ÷ 0.60 = 60kWh battery bank

Step 4: Convert kWh to Battery Units

OPzV tubular gel cells (2V)

For a 48V system: 48V = 24 cells × 2V

To get 60kWh at 48V: → 60kWh ÷ 48V = 1,250Ah required → Recommended: 24 × 2V 1,500Ah OPzV cells

Lead-acid blocs (12V × 4 = 48V)

For a 48V system: 4 × 12V blocs in series

To get 60kWh at 48V: → 60kWh ÷ 48V = 1,250Ah required → Recommended: 4 × 12V 1,250Ah lead-acid blocs (or 4 × 12V 1,000Ah + 8 × 2V cells for a larger bank)

Step 5: Solar Panel Sizing

The solar array must be large enough to recharge the battery each day AND supply the daily load simultaneously.

Recharge requirement: Panel array (W) = Battery bank (kWh) × 1.2 (charging losses) ÷ Peak sun hours × Days to recharge target

For 18kWh/day load in the Philippines (average 4.5 peak sun hours):

• Array needed for daily load: 18kWh ÷ 4.5h = 4,000W
• Array needed to recharge 60kWh bank in 1 day: 60kWh × 1.2 ÷ 4.5h = 16,000W

Minimum recommended array: 16kWp (to fully recharge battery while powering loads on a cloudy day)

Solar Battery Sizing Examples

Residential off-grid (Philippines, family of 4)

Loads: 10kWh/day Autonomy: 2 days Battery: 48V LiFePO4 at 80% DoD → 10 × 2 ÷ 0.80 = 25kWh bank → 48V 400Ah LiFePO4 system Array: 5kW (to recharge in 1 day with loads)

Commercial solar storage (Kenya, safari lodge)

Loads: 30kWh/day Autonomy: 3 days Battery: 48V OPzV gel at 60% DoD → 30 × 3 ÷ 0.60 = 150kWh bank → 48V OPzV system with 24 × 2V 1,500Ah cells Array: 15kW

Telecom tower (Nigeria, off-grid mast)

Loads: 8kWh/day (typical LTE tower) Autonomy: 5 days (remote location) Battery: 48V OPzV gel at 60% DoD → 8 × 5 ÷ 0.60 = 66.7kWh → 48V 1,000Ah OPzV system Array: 4kW with 48-hour recharge target

Key Sizing Mistakes to Avoid

Mistake 1: Not accounting for inverter efficiency Battery kWh ÷ inverter efficiency = usable AC kWh. A 90% efficient inverter means 10% of your battery capacity is lost before it reaches your loads. Size battery and inverter together.

Mistake 2: Ignoring temperature derating Battery capacity falls at low temperatures. A lead-acid battery bank rated at 25°C delivers only 70–80% of rated capacity at 0°C. For outdoor installations in cold climates, increase battery bank size accordingly.

Mistake 3: Oversizing for future loads you never add Adding planned capacity during system design is prudent — but do not double the battery size “just in case.” Size for the loads you actually have, and add a 20% contingency instead.

Mistake 4: Ignoring the charge controller’s current limit A 100A MPPT charge controller can only accept a limited solar array size regardless of battery capacity. Array watts ÷ battery voltage = maximum charge current. Do not exceed the controller’s current rating.

CHISEN Battery Solar Storage Solutions

CHISEN Battery supplies battery banks for solar installations from residential to utility scale:

• OPzV tubular gel series: 2V 100–3,000Ah — the standard for commercial and utility solar storage
• AGM VRLA battery banks: Pre-assembled 24V, 48V, and 96V packs for commercial buildings
• LiFePO4 energy storage systems: 48V residential and custom rack systems for C&I projects
• Containerized energy storage: Complete 100kWh–2MWh container solutions available
• Technical support: Free battery sizing service — send your daily load profile and location for a sizing recommendation
• Certifications: CE, IEC 62619, UN38.3, UKAS, TUV Rheinland (select models)

Send your project specifications for a free battery sizing and quotation: 📧 jack@chisen.cn | WhatsApp: +86 131 6622 6999 | www.chisen.cn