How to Size Your Home Solar Energy System in Nigeria, Step by Step
A full worked example showing how to calculate your inverter, battery and panel sizes from your own household’s numbers, not a generic lookup table.
Ask three different installers to size your system and you can get three different quotes, because some installers and consumers size off a home-size lookup table rather than your actual usage. Your appliances, your night-time load, and your region’s sunlight all change the right answer, sometimes by a wide margin. This post walks through the real calculation behind any accurate Nigerian solar quote, inverter, battery and array, then runs it on a real household from start to finish so you can see the math work.
Key takeaways
- Inverter capacity comes from your simultaneous load plus your single biggest startup surge, not a flat percentage added to your total load.
- Battery capacity comes from your night-time energy only, divided by your battery chemistry’s real depth of discharge, not your full daily usage.
- Solar array size comes from your daily energy divided by your region’s design peak sun hours, weighted to the worst month, not the annual average.
- A home-size lookup table is a starting point built from these calculations, not a substitute for running your own numbers.
- We work through all three steps on one real Nigerian household at the end, so you can see exactly how the numbers move.
What Actually Determines Your Solar System’s Size?
Two homes with the same bedroom count can need systems that differ by millions of naira, because bedroom count was never really the variable that mattered. What sets your inverter, battery and array size is your appliance list, when you use each appliance, and how much sun your specific location gets in its worst month. Three separate calculations answer those three questions, and running them yourself, rather than reading the answer off a size chart, is the only way to know your system is neither undersized nor needlessly expensive.
Step 1: Size Your Inverter From Simultaneous Load, Not Total Wattage
Start with everything that could realistically run at the same moment, not your full appliance list added up, but the worst-case overlap. A common shortcut is to add a flat margin to your total wattage, roughly 1.2 to 1.25 times, and stop there. That works if nothing on your list has a motor, but compressor and pump-driven appliances change the picture: motors draw 3 to 6 times their running wattage for a second or two on startup, and your inverter has to survive that surge, not just your steady load.
| Appliance | Running load | Startup surge |
|---|---|---|
| Fridge | 150 W | 600–900 W |
| Chest freezer | 200 W | 800–1,200 W |
| 1HP borehole pump | 750 W | 2,200–3,500 W |
| Non-inverter 1.5HP AC | 1,200 W | 4,000–6,000 W |
Add your simultaneous running load, then add the gap between your single biggest appliance’s surge and its own running watts (just the largest one, since surges are brief and rarely overlap). That total is what your inverter’s kVA rating needs to clear, and kVA isn’t the same as kW: most inverters run at roughly a 0.8 power factor, so a 5 kVA unit delivers closer to 4 kW of continuous load. That ratio varies by model, so check your inverter’s datasheet for its actual continuous and surge output rather than assuming 0.8 across the board.
Step 2: Size Your Battery From Night-Time Energy, Not Daily Total
Only the energy you use when the sun isn’t producing has to come from the battery. A common shortcut treats your entire daily usage as the battery’s job and divides it by a flat factor regardless of chemistry. That overstates what a lead-acid bank can safely deliver and ignores that a good chunk of your daytime usage is already covered directly by the sun, before storage even enters the picture.
Split your usage into daytime and night-time hours instead, then divide your night-time energy by your chemistry’s real depth of discharge: lithium (LiFePO₄) gives you 80 to 90% usable capacity, tubular or gel lead-acid only about 50%.
Battery nameplate capacity = (night-time energy × days of autonomy) ÷ depth of discharge
At lead-acid’s 50% depth of discharge, the same night-time load needs roughly double the nameplate capacity that lithium needs at 85%, which is most of why lithium tends to win on lifetime cost despite a higher sticker price.
Step 3: Size Your Solar Array From Design Peak Sun Hours, Not the Annual Average
Nigeria’s solar radiation varies by region, and it varies further by season within each region. A common shortcut applies one flat derate to your region’s annual average peak sun hours (PSH) and calls it done. That skips the bigger swing: which month you’re actually designing for. Sizing off the annual average is the single most common mistake in Nigerian residential solar, because it leaves your system underperforming in exactly the months, typically the June to August rains, when grid supply is also at its worst. Size instead against your region’s design PSH: a conservative estimate of the solar resource available during your worst-performing month, not an average across the year.
Array size (kWp) = daily energy ÷ (design PSH × performance ratio)
The performance ratio accounts for real-world losses, wiring, heat, dust, inverter conversion, typically a 0.75 to 0.82 haircut off the raw sunlight number.
» The Peak Sun Hours Guide has the design PSH bands for every region of Nigeria.
Putting the Three Steps Together: A Worked Example
Here’s how those three calculations play out on an actual household: a 3-bedroom Lagos bungalow with a fridge, a chest freezer, a 1HP borehole pump, lights, fans, a TV, a router, phone charging, and the usual miscellaneous household loads. We’ve left air conditioning out of this particular example so the method stays easy to follow, not because leaving it out is the safe or typical choice; a home running AC would redo Steps 1 and 3 with that load added in.
Daily energy, appliance by appliance:
| Appliance | Rated power | Estimated daily use | Daily energy |
|---|---|---|---|
| Refrigerator | 150 W | ~11h equivalent (compressor cycling) | 1.6 kWh |
| Chest freezer | 200 W | ~10h equivalent (compressor cycling) | 2.0 kWh |
| Lights | 100 W | 6h, evening | 0.6 kWh |
| Fans | 200 W | 9h, mostly overnight | 1.8 kWh |
| TV | 100 W | 5h, evening | 0.5 kWh |
| Router | 15 W | 24h | 0.36 kWh |
| Phone charging | 50 W | 3h, overnight | 0.15 kWh |
| Borehole pump | 750 W | 1.5h, daytime | 1.1 kWh |
| Other loads (standby power, mosquito repellent, misc. charging) | — | — | 1.9 kWh |
| Total | 10.0 kWh |
A fridge or freezer’s real draw isn’t its rated wattage running non-stop, since the compressor cycles on and off; the table uses an equivalent full-power runtime instead of a flat 24 hours.
Fridge and freezer energy splits roughly evenly across day and night, since their compressors don’t track the clock. Lights, fans, the TV, phone charging and most of the standby draw land after dark; the pump and half the router’s day run when the sun is up. Add it up and this household’s night-time energy comes to about 6 kWh of the 10 kWh total, the figure the battery calculation below is built on.
Inverter: Running load is 150 (fridge) + 200 (freezer) + 100 (lights) + 200 (fans) + 100 (TV) + 15 (router) + 50 (phone charging) + 750 (pump) = 1,565 W, assuming the pump can start while everything else on the list is already running, the worst case the inverter has to survive. The pump is the biggest surge risk, jumping to roughly 2,850 W at its midpoint, about 2,100 W above what its running watts already counted for. 1,565 W + 2,100 W surge headroom = 3,665 W of momentary demand, just above the 3,500 W boundary between the 5 kVA and 6.5 kVA inverter classes, making 6.5 kVA the practical choice here rather than a 5 kVA unit. Running a unit continuously at its exact rated ceiling also shortens its working life, so sizing into the class above your number, not right up against it, is the safer call.
Battery: Night-time energy for this household is about 6 kWh, from the appliance breakdown above. At 85% depth of discharge for lithium and one day of autonomy: (6 × 1) ÷ 0.85 = 7.1 kWh of nameplate capacity required, the minimum size that can deliver 6 kWh of usable output at that depth of discharge. Because batteries are sold in standard sizes and usable capacity fades over the battery’s working life, a designer typically rounds up from that minimum rather than speccing it exactly, landing on a 10 kWh nameplate lithium battery for this household.
Array: Lagos sits in the coastal-south band: an annual average of 4.0 to 4.4 PSH, but a design figure of only 3.2 to 3.6 once weighted to the rainy season. Total daily energy for this household is 10 kWh, from the table above. At a 3.4 design PSH midpoint and a 0.8 performance ratio: 10 ÷ (3.4 × 0.8) = 3.7 kWp, round up to a 4 kWp array, about eight 550 W panels.
| Component | This household’s number |
|---|---|
| Inverter | 6.5 kVA hybrid |
| Battery | 10 kWh lithium |
| Solar array | 4 kWp (about 8 × 550 W panels) |
That’s what correctly sizing a system for this exact household looks like end to end, an inverter, battery and array each sized off actual load, night-time energy and regional sunlight, not a bedroom-count chart.
Run This on Your Own Home
Swap in your own appliance list, your own night-time energy split, and your own region’s design PSH, and the same three steps carry straight over regardless of your home’s size. A system that survives the surge, gets through the night, and still charges fully through the rainy season is the actual definition of a solar system that works in Nigeria, not just one that was cheap to quote.
