Most solar complaints in Nigerian homes come down to one problem: the system was sized for a guess, not for the house. The inverter trips when the pumping machine starts. The battery is flat by 2 a.m. The panels cannot recharge the battery on a cloudy day. None of these are faults in solar technology. They are sizing errors.
You do not need to be an engineer to understand how sizing works. This guide walks through the same logic an installer uses, so you can sense-check a proposal and have a better conversation about what you really need.
Step 1: List Every Appliance You Want to Power
Start with a simple list of the appliances you want on solar, and note two things for each:
- Power rating in watts (W), usually printed on a label at the back or underneath.
- Hours of use per day, split into daytime and night-time if you can.
Be honest about what you will actually run. Many people list an air conditioner "just in case" and then end up with a much larger, more expensive system than they use. It is often better to put essential circuits on solar first and decide on heavy loads separately.
Watch for appliances with motors
Fridges, freezers, pumps and air conditioners draw a surge of power for a few seconds when their motors start, often several times their running rating. Your inverter has to handle that surge, so mark these appliances clearly on your list.
Step 2: Calculate Your Peak Load
Your peak load is the highest total wattage running at the same moment. Add up everything likely to be on together during your busiest period, typically the evening when lights, fans, TV, fridge and phone chargers all run at once.
For example, a home might have:
- LED lights: 10 × 10 W = 100 W
- Ceiling fans: 3 × 75 W = 225 W
- TV and decoder: 150 W
- Fridge: 150 W running
- Wi-Fi router and phone chargers: 50 W
That gives a running peak of about 675 W. The fridge's start-up surge is handled by the inverter's surge rating rather than added straight onto this figure.
Step 3: Choose an Inverter Size
The inverter must comfortably carry your peak load, with headroom. A common rule of thumb is to size the inverter at least 25–30% above your expected running peak, then confirm its surge rating can start your largest motor.
In the example above, a 1.5 kVA inverter would technically cope, but a 2.5–3 kVA unit gives room for a pump or a few more appliances later. Remember that inverters are often rated in kVA, while appliance loads are in watts; depending on the model, a 3 kVA inverter may deliver around 2.4–3 kW of real power. Check the watt rating on the datasheet.
Step 4: Calculate Daily Energy Use
Peak load tells you about the inverter. Energy use tells you about batteries and panels. For each appliance, multiply watts by hours of use to get watt-hours (Wh), then add them up.
Using the same home:
- Lights: 100 W × 6 h = 600 Wh
- Fans: 225 W × 10 h = 2,250 Wh
- TV: 150 W × 5 h = 750 Wh
- Fridge: about 1,200 Wh per day (fridges cycle on and off, so use the energy label or an estimate rather than 24 × running watts)
- Router and chargers: 50 W × 12 h = 600 Wh
That is roughly 5,400 Wh, or 5.4 kWh, per day.
Step 5: Size the Battery Bank
The battery must cover what you use when the sun is not shining. If most of your use is at night, work out the night-time portion of your daily energy, say 3.5 kWh in this example.
Then allow for the battery's usable depth of discharge. Lithium (LiFePO4) batteries are commonly used to around 80–90% of their capacity, while lead-acid batteries last longer when kept to about 50%. That means:
- Lithium: 3.5 kWh ÷ 0.85 ≈ 4.1 kWh, so a 5 kWh lithium battery would be a sensible choice.
- Lead-acid: 3.5 kWh ÷ 0.5 = 7 kWh of nominal capacity, which is a much larger and heavier bank.
If you want backup for an extra cloudy day or long grid outages, increase the battery size accordingly.
Step 6: Size the Solar Panels
Your panels must supply the full day's energy, cover daytime loads and recharge the battery. Nigeria receives good sunshine for much of the year, but output varies by location and season, and the Harmattan haze reduces it further.
A practical approach:
- Take your daily energy use (5.4 kWh).
- Divide by a conservative number of peak sun hours for your location, for example 4.5 hours.
- Add around 25% for system losses, heat and dust.
5.4 ÷ 4.5 × 1.25 ≈ 1.5 kW of panels, which is three 550 W panels at a minimum. Many installers would recommend four to give headroom for cloudy days and future loads.
Common Sizing Mistakes to Avoid
- Ignoring motor surges, which leads to an inverter that trips whenever the pump starts.
- Sizing panels only for daytime use, leaving nothing to recharge the battery.
- Using nameplate battery capacity, without allowing for depth of discharge.
- Forgetting future plans, such as an extra freezer or a home office.
- Mixing old and new batteries, which shortens the life of the whole bank.
Get a Professional Load Assessment
These steps will give you a solid estimate, but every home is different. Roof orientation, shading, wiring condition and how your family actually uses power all affect the final design. If you want to know what a system of your size would cost, see our solar installation cost guide for Nigeria.
7th Breed carries out on-site load assessments and designs systems around real consumption, not guesswork. Request a free quote or browse our solar products to get started.
Sources
- BusinessDay, What it costs to install solar in Nigeria today (February 2026), for typical home system sizes.
- Isaacs, S. et al., Dust soiling effects on decentralized solar in West Africa, Applied Energy (2023), on Harmattan output losses.