Types of Battery in Solar Setup: (Components of PV System III) – SS1 Solar Photovoltaic Installation & Maintenance Lesson Note (First Term)

A solar battery is a device that stores electrical energy from the solar panels so the house can use it at night or when the sun is weak.

Behavioural objectives

By the end of the lesson, students should be able to:

1. name the two main types of battery used in solar setups in Nigeria;
2. compare lead-acid and lithium-ion batteries by price, lifespan, weight, maintenance and charging;
3. calculate the total capacity of a battery in watt-hours (Wh);
4. explain depth of discharge and the safe limit for each battery type;
5. state how to care for a solar battery.

What does a battery do in a solar setup?

The battery stores the energy that the panels make during the day.

• Storage: it keeps extra energy from the panels for use when there is no sunlight.
• Night supply: it runs lights, fans, television and other loads after sunset.
• Steady power: it supplies the inverter when cloud cuts the output of the panels.
• Load: the load is the set of appliances the battery must power.

What are the two main types of solar battery?

There are two main types of solar battery in the Nigerian market: lead-acid and lithium-ion.

Lead-acid batteries

Lead-acid batteries use lead plates in acid, and the technology is over 100 years old.

• Tubular: a flooded type, very common in Nigerian homes, and it needs water top-ups.
• SMF/Gel: a sealed type that is maintenance-free, so no water is added.
• Build: heavy, and usually in big white or grey cases.
• Best for: people on a tight budget who can replace the battery every few years.

Lithium-ion batteries

Lithium-ion batteries use lithium chemistry, the same kind of technology as in a smartphone but much bigger.

• LiFePO4: lithium iron phosphate, the type most often sold for home solar systems.
• Build: slim, light and often wall-mounted.
• Smart control: it usually has a built-in battery management system (BMS) that protects the cells.
• Best for: people who want a battery that lasts 10 years or more with no maintenance.

How do lead-acid and lithium-ion batteries compare?

Lead-acid batteries cost less but wear out sooner. Lithium-ion batteries cost more but last longer and need no upkeep.

• Long-term cost: lithium costs more today, but you buy fewer replacements over the years.
• Small flats: lithium suits small apartments because it is light and takes little space.

How do you size a battery?

Sizing a battery means working out the battery capacity needed to carry the house load.

• Ah (amp-hour): the unit used to rate battery capacity.
• Wh (watt-hour): energy used = power in watts × hours of use.
• Battery capacity in Wh: volts × amp-hours.

Step 1: Make the load list

List what you want to use at night, then find the Wh for each item.

• 3 LED bulbs (10 W each) for 10 hours: 3 × 10 × 10 = 300 Wh.
• 1 fan (50 W) for 10 hours: 50 × 10 = 500 Wh.
• Total needed: 300 + 500 = 800 Wh.

Step 2: Find the battery capacity

A 12 V, 200 Ah battery has a total capacity of 12 × 200 = 2,400 Wh.

Step 3: Apply depth of discharge

Depth of discharge (DoD) is the percentage of a battery’s capacity that has been used.

• Formula: DoD (%) = energy used ÷ total capacity × 100.
• Example: using 600 Wh from a 2,400 Wh battery gives 600 ÷ 2,400 × 100 = 25% DoD.
• Lead-acid: use only 50%, so a 2,400 Wh battery gives 1,200 Wh.
• Lithium: use 80 to 90% safely, so a 2,400 Wh battery gives about 1,920 to 2,160 Wh.
• Never use 100%: draining a battery fully shortens its life.

Step 4: Compare usable energy with the load

• Load: 800 Wh.
• Usable lead-acid energy: 1,200 Wh.
• Result: 1,200 Wh is more than 800 Wh, so one battery can carry this load.

Which loads should a small battery avoid?

• Heavy loads: electric irons, heaters and kettles draw very high power and drain a small battery quickly.
• Light loads: LED bulbs, fans and phone chargers use little power and suit a small battery.

How do you care for a solar battery?

You care for a solar battery by keeping it cool, clean, topped up (if flooded) and never fully drained.

In Nigeria, the two biggest causes of early battery failure are heat and neglect.

1. Top up water (tubular/flooded only): check the water level every month and use only distilled water.
2. Avoid tap water and sachet water: the minerals in them damage the plates.
3. Keep it cool: do not place batteries in a hot kitchen or a closed cupboard without air holes.
4. Clean the terminals: switch off the system first, remove the white crust (corrosion) with a toothbrush, then rub on petroleum jelly (Vaseline).
5. Avoid deep discharge: stop using power before the battery runs flat, because frequent draining to 0% spoils it within months.

What are the key terms?

• Ah (amp-hour): the “tank size” of the battery.
• Wh (watt-hour): the unit of energy, found by multiplying watts by hours.
• DoD (depth of discharge): how much of the “tank” has been used.
• Distilled water: mineral-free water used to refill flooded lead-acid batteries.
• BMS: the electronic unit that protects a lithium battery.

Evaluation

1. State two differences between lead-acid and lithium-ion batteries.
2. A 12 V, 200 Ah lead-acid battery has a capacity of 2,400 Wh. How much of this can you safely use?
3. Why must you use only distilled water to top up a tubular battery?
4. Your neighbour uses an electric iron on his small solar battery at night. Is this a good idea? Why?
5. Why is a lithium battery better for saving space in a small apartment?

Assignment

1. A house uses 4 LED bulbs (10 W each) and 1 fan (50 W) for 8 hours at night. Use the load list method to find the total energy needed in Wh.
2. Using a 12 V, 200 Ah lead-acid battery, find the usable energy and say whether it can carry this load.
3. List the five ways of caring for a solar battery.