Resource Guide · Energy Storage

Solar Battery Sizing Guide

Q: How do I calculate the battery capacity I need for solar backup?

The formula is: Required Ah = (Daily Load in Wh × Backup Hours) ÷ (DoD × Inverter Efficiency × Battery Voltage). Example for a 5kVA system targeting 10h backup: (500Wh/h × 10h) ÷ (0.90 × 0.95 × 48V) = approximately 122Ah. Round up to the next standard size — 48V 200Ah (9.6kWh usable at 90% DoD) is the standard selection for this load profile. Battery capacity, not panel wattage, is the controlling sizing variable for load-shedding applications.

Q: What depth of discharge (DoD) should I use for LiFePO4 solar batteries?

LiFePO4 batteries are rated for 80–90% DoD without significant cycle life reduction. Most BMS settings default to 80% DoD to extend calendar life, but 90% DoD is technically acceptable for occasional deep discharge. Lead-acid batteries should be limited to 50% DoD to maintain cycle life. Using LiFePO4 effectively doubles the usable capacity compared to a same-rated lead-acid bank: a 48V 200Ah LiFePO4 bank delivers 9.6kWh usable vs 4.8kWh for an equivalent lead-acid bank at 50% DoD.

Q: How does load shedding duration affect battery sizing?

Battery sizing is directly proportional to outage duration. For Nigeria (18–20h outage per day), the battery must cover both overnight loads and daytime loads when the grid is off — typically requiring a 10kVA system with 19.2kWh storage. For South Africa (4–8h Stages 2–4), a 5kVA system with 9.6kWh is sufficient for most homes. For Pakistan (12–16h), a 5kVA system covers urban households, while farms or clinics need 10kVA with 19.2kWh. The solar array must be sized to recharge the battery within available sunlight hours (PSH) each day.

How to calculate the battery capacity you need for solar backup — covering load shedding markets in Nigeria, South Africa and Pakistan, depth of discharge, sizing formula and ready-made kit examples.

Battery capacity drives system sizing — not panels

For load-shedding and off-grid applications, the battery bank determines how many hours of backup you can deliver. The solar array must then be sized to recharge that battery within the available peak sun hours (PSH) each day. Getting the battery wrong makes the whole system fail at the worst time — during the outage.

The Sizing Formula

/* Battery sizing formula */

Required Ah = (Daily Load Wh × Backup Hours)

÷ (DoD × Inverter Efficiency × Battery Voltage)

/* Example: 5kVA system, 500W average load, 10h backup */

= (500 × 10) ÷ (0.90 × 0.95 × 48)

= 5,000 ÷ 41.04

= ~122Ah → round up to 200Ah (9.6kWh usable)

DoD

Depth of Discharge

LiFePO4: 90% (use 0.90). Lead-acid: 50% (use 0.50). Using LiFePO4 at 90% DoD effectively doubles usable capacity vs lead-acid at 50%.

Inverter Efficiency

Most hybrid inverters operate at 92–96% efficiency. Use 0.95 as a conservative default when datasheet efficiency is unknown.

Battery Voltage

48V is the standard for residential and SME solar systems. 24V for small off-grid setups; 51.2V nominal for LiFePO4 at 48V bus.

Load Shedding Sizing by Market

Typical battery selections for each market's load-shedding pattern — based on a standard household or small commercial load of 400–800W average consumption.

Market	Outage duration	Typical load	Recommended kit	Battery
Nigeria	18–20h/day	~400Wh/h	10kVA	48V 400Ah (19.2kWh)
Pakistan (urban)	12–16h/day	~500Wh/h	5kVA	48V 200Ah (9.6kWh)
Pakistan (rural/clinic)	16–20h/day	~800Wh/h	10kVA	48V 400Ah (19.2kWh)
South Africa (Stage 2–4)	4–6h/day	~500Wh/h	5kVA	48V 100Ah (4.8kWh)
South Africa (Stage 5–6)	8–10h/day	~500Wh/h	5kVA	48V 200Ah (9.6kWh)

LiFePO4 vs Lead-Acid for Solar Backup

Parameter	LiFePO4	Lead-Acid (VRLA/Gel)
Usable DoD	90%	50%
Cycle life at rated DoD	3,000–6,000 cycles	300–600 cycles
Weight (48V 200Ah)	~45 kg	~260 kg
Temperature tolerance	-20°C to +60°C	0°C to +40°C optimal
Self-discharge	<3%/month	5–15%/month
Maintenance	None	Periodic equalisation required
Cost per kWh (cycle-adjusted)	Lower over lifetime	Higher due to replacement frequency
Sea freight (DG)	UN3480 / UN3481	Non-DG (acid-sealed)

Step-by-Step Sizing Process

Audit the load

List all appliances with wattage and estimated daily hours of use. Sum to get daily Wh consumption. Typical household: lights (200W × 5h) + fridge (150W × 24h) + fans (200W × 8h) + TV (100W × 4h) = ~5,900Wh/day.

Determine required backup hours

Match to your market's load-shedding pattern. Use average outage hours, not the worst-case maximum, to balance cost and coverage.

Calculate Ah requirement

Apply the formula: (Load Wh × Hours) ÷ (DoD × Efficiency × Voltage). Round up to next standard battery size (50Ah, 100Ah, 200Ah, 400Ah).

Size the PV array to recharge daily

Battery kWh ÷ PSH × (1 + system losses ~20%) = minimum PV kWp. A 9.6kWh battery in Karachi (PSH 5.5) needs at least 9.6 ÷ 5.5 × 1.2 = 2.1kWp. Our 5kVA kit includes 4kWp — well above the minimum for rapid recharge.

Select inverter to match loads

Inverter VA rating ≥ peak simultaneous load. Include startup surge: a 1.5HP air conditioner draws ~1,100W running but 3,000W at startup. The 5kVA inverter handles a 1.5HP A/C plus other loads without overloading.

Battery Sizing — Common Questions

How do I calculate the battery capacity I need for solar backup?

The formula is: Required Ah = (Daily Load in Wh × Backup Hours) ÷ (DoD × Inverter Efficiency × Battery Voltage). Example for a 5kVA system targeting 10h backup: (500Wh/h × 10h) ÷ (0.90 × 0.95 × 48V) = approximately 122Ah. Round up to the next standard size — 48V 200Ah (9.6kWh usable at 90% DoD) is the standard selection for this load profile. Battery capacity, not panel wattage, is the controlling sizing variable for load-shedding applications.

What depth of discharge (DoD) should I use for LiFePO4 solar batteries?

LiFePO4 batteries are rated for 80–90% DoD without significant cycle life reduction. Most BMS settings default to 80% DoD to extend calendar life, but 90% DoD is technically acceptable for occasional deep discharge. Lead-acid batteries should be limited to 50% DoD to maintain cycle life. Using LiFePO4 effectively doubles the usable capacity compared to a same-rated lead-acid bank: a 48V 200Ah LiFePO4 bank delivers 9.6kWh usable vs 4.8kWh for an equivalent lead-acid bank at 50% DoD.

How does load shedding duration affect battery sizing?

Battery sizing is directly proportional to outage duration. For Nigeria (18–20h outage per day), the battery must cover both overnight loads and daytime loads when the grid is off — typically requiring a 10kVA system with 19.2kWh storage. For South Africa (4–8h Stages 2–4), a 5kVA system with 9.6kWh is sufficient for most homes. For Pakistan (12–16h), a 5kVA system covers urban households, while farms or clinics need 10kVA with 19.2kWh. The solar array must be sized to recharge the battery within available sunlight hours (PSH) each day.

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