What Size Solar System Do I Need? A Nigerian Sizing Guide

Almost every Nigerian asking this question gets asked one back: "how many kVA do you want?" It is the wrong question, and answering it is how people end up with a system that can run the air conditioner beautifully for forty minutes and then stop.

Sizing solar takes three numbers. They are independent, they are measured in different units, and confusing them is the single most common mistake in this market.

The three numbers

| What you are sizing | Unit | What decides it | |---|---|---| | Panels | kWp | How much energy you use in a day | | Inverter | kVA | How much you run at the same time | | Battery | kWh | How long you want to run without sun |

A 5kVA inverter with a 2 kWh battery and a 10 kWh battery are wildly different systems at wildly different prices. Both are "5kVA".

Step 1: your daily energy, in kWh

Add up, for every appliance: watts × hours used per day × how many you have, then divide by 1,000.

A worked example for a mid-size Nigerian household:

| Appliance | Watts | Qty | Hours/day | Wh/day | |---|---|---|---|---| | LED bulbs | 10 | 8 | 6 | 480 | | Standing fans | 60 | 2 | 8 | 960 | | Fridge | 150 | 1 | 10 | 1,500 | | TV, 32" | 50 | 1 | 5 | 250 | | Decoder | 30 | 1 | 5 | 150 | | WiFi router | 15 | 1 | 24 | 360 | | Laptop | 65 | 1 | 8 | 520 | | Phone charging | 10 | 3 | 3 | 90 | | Pressing iron | 1,000 | 1 | 0.5 | 500 | | Total | | | | 4,810 Wh = 4.8 kWh/day |

Two traps here.

The fridge is not on for 24 hours. A fridge compressor cycles. It draws its rated watts only while running, which is typically eight to twelve hours a day spread across the twenty-four. Putting 24 in that column will roughly double your fridge's contribution and can add hundreds of thousands of naira to your quote. Same for freezers.

Heat is where the energy goes. Notice that a pressing iron used for thirty minutes uses more energy than a TV used for five hours. Kettles, irons, microwaves, cookers and hair dryers are all in the 1,000–2,000W class. The cheapest thing you can do for your solar quote is decide which of them stays on the grid or on gas.

Step 2: your peak demand, in kW

Add up the watts of everything, ignoring hours. For the household above that is 1,540W — but you will never run all of it simultaneously.

The convention is a diversity factor of 0.7: assume about 70% is on at once. That gives 1.08 kW of realistic simultaneous demand.

Then the inverter:

Inverter kVA = peak kW ÷ 0.8 (power factor) × 1.2 (headroom)

For 1.08 kW that is 1.62 kVA, which snaps up to a 2.5 kVA inverter — the next size Nigerian installers actually sell.

The 20% headroom is not padding. Motors — fridges, freezers, water pumps, air conditioners — draw a surge of up to three times their running watts for the first second or two. The diversity factor absorbs a household's worth of that. It does not absorb four air conditioners starting together, so if your load is motor-heavy, size up.

Step 3: your battery, in kWh

This is the expensive one, and it is where you have the most control.

Battery kWh = the energy you want to back up ÷ (depth of discharge × round-trip efficiency)

Depth of discharge is the fraction you can safely use: 80% for lithium (LiFePO4), 50% for tubular. Round-trip efficiency — what you lose putting energy in and taking it back out — is about 95% for lithium and 85% for tubular.

To back up the whole 4.8 kWh day on lithium: 4.8 ÷ (0.8 × 0.95) = 6.3, so a 7 kWh battery. On tubular: 4.8 ÷ (0.5 × 0.85) = 11.3, so 12 kWh.

Nearly twice as much tubular for the same result — which is why comparing the two on price per nominal kWh is misleading. At ₦220,000 per kWh, that lithium bank costs ₦1,540,000; at ₦110,000, the tubular one costs ₦1,320,000. The apparent 50% saving turns out to be 14%, before you consider that you will replace the tubular twice in ten years.

But you probably do not need full-house autonomy. This is the biggest lever on the price of your quote:

| Backup level | Share of daily use | Battery (lithium) | Battery cost | |---|---|---|---| | Essentials only | 35% | 3 kWh | ₦660,000 | | Most of the house | 65% | 5 kWh | ₦1,100,000 | | Full house | 100% | 7 kWh | ₦1,540,000 |

Full autonomy is what makes quotes frightening, and most households do not need it, because the grid is still there for part of the day and the panels are still generating through it.

Step 4: your panels, in kWp

Panel kWp = daily kWh ÷ (peak sun hours × system efficiency)

Peak sun hours vary a lot across Nigeria:

| Region | Peak sun hours/day | |---|---| | South / coastal (Lagos, Port Harcourt, Warri, Calabar) | 4.5 | | South-East (Awka, Enugu, Owerri) | 4.9 | | Middle Belt (Abuja, Jos, Makurdi, Ilorin) | 5.0 | | North-West (Kaduna, Zaria, Kano, Katsina) | 6.0 | | Far North (Sokoto, Maiduguri) | 6.5 |

System efficiency is where we differ from most sizing tools, and it matters. The international default assumes about 14% total losses, of which only 2% is dust. That figure is wrong for Nigeria, and not by a little.

Research published in Renewable Energy measured 68.6% yield loss over seventeen uncleaned months on mono-silicon panels in Northern Nigeria, worst during harmattan. A follow-up soiling map recorded up to 88% optical loss on a horizontal test coupon at Abuja, and stated plainly that the standard global dataset underestimates Nigerian soiling. Panel degradation measured at Maiduguri runs 1.2–1.5% per year against a 0.5–0.8% global norm.

So we use 78% in the south and 74% in the north rather than 86%, and we treat panel cleaning as a real recurring cost — six visits a year in the south, twelve in the harmattan belt.

For our Lagos household: 4.8 ÷ (4.5 × 0.78) = 1.37, so 1.4 kWp — about three 550W panels. The same household in Kano: 4.8 ÷ (6.0 × 0.74) = 1.08, so 1.1 kWp, or two panels. Northern sun is worth roughly a panel.

If an installer's sizing implies better than 78% in the south, ask what they have assumed about dust.

Putting it together

For the household above, in Lagos, backing up most of the house on lithium:

| | | |---|---| | Daily use | 4.8 kWh | | Peak demand | 1.08 kW (1.54 kW connected) | | Inverter | 2.5 kVA hybrid | | Panels | 1.4 kWp (≈ 3 × 550W) | | Battery | 5 kWh lithium (4 kWh usable) | | Estimated cost | ₦2.16 million |

That is a realistic estimate for a real Nigerian household — not a quote, and not a promise, but a figure you can hold up next to what an installer tells you. It sits a long way below the ₦5 million-plus numbers that dominate search results, because it is sized for what the household actually uses rather than for a spec sheet.

A note on what this does not cover

Grid-tied solar and net metering do not exist for Nigerian residential customers. You cannot sell power back. Every system described here is a hybrid: solar and battery carry what they can, the grid carries the rest when it is there, and most households keep the generator for bad days rather than selling it.

That last point matters more than people expect. A 3.5 kVA generator kept for "just half an hour a day" burns close to ₦3.8 million of petrol over ten years at ₦1,250 a litre — often more than the solar system itself. If you are genuinely going to stop using it, the arithmetic changes dramatically.

Do it with your own numbers

The tables above are one household. Yours is different, your band is different, and your pump price is different. Our solar payback calculator does all four steps from your own appliance list, prices the result by component, and tells you the month it overtakes what you currently spend on fuel — including when the answer is that it never does.