Solar Sizing — A Worked Energy, Battery and Panel Scenario
A transparent solar-sizing example with corrected connected-load arithmetic, explicit assumptions and limits on surge, battery autonomy and panel recharge calculations.
Updated 2026-09-28
The solar sizing calculator is a preliminary energy-balance tool, not a final electrical design or purchase recommendation. Its example values are assumptions, not measured observations of Nigerian households, weather or product life.
Start with measured loads and product specifications. Have a qualified installer check simultaneous loads, start-up demand, battery/BMS limits, protection, wiring, earthing, compatibility and site conditions. A correct multiplication is not proof that a system will start a motor or run through a cloudy period.
1. Build a load schedule
`` daily energy (Wh) = watts × equivalent full-power hours × quantity connected power (W) = watts × quantity ``
For cycling equipment, use measured energy or a justified duty-cycle estimate. Do not assume every refrigerator compressor runs eight hours, or infer electrical input directly from an appliance's marketing horsepower rating.
The calculator's family-load example, not a representative household, uses:
| Appliance | Assumed W | Qty | Equivalent hours/day | Wh/day |
|---|---|---|---|---|
| LED bulbs | 9 | 8 | 6 | 432 |
| Fans | 70 | 3 | 10 | 2,100 |
| Television | 80 | 1 | 5 | 400 |
| Decoder/router | 20 | 1 | 12 | 240 |
| Refrigerator | 150 | 1 | 8 | 1,200 |
| Charging load | 60 | 1 | 3 | 180 |
| Total | 4,552 |
Connected power is 72 + 210 + 80 + 20 + 150 + 60 = 592 W. Daily energy and instantaneous power are different quantities. The model sums all connected loads; it does not construct a time-of-day simultaneity schedule.
2. Model nominal battery capacity
`` nominal battery Wh = daily Wh × autonomy days ÷ (usable fraction × inverter efficiency) ``
For 4,552 Wh/day, one day of autonomy and an assumed inverter efficiency of 90%:
| Assumed usable fraction | Modelled nominal bank |
|---|---|
| 50% | 4,552 ÷ (0.50 × 0.90) = 10.12 kWh |
| 80% | 4,552 ÷ (0.80 × 0.90) = 6.32 kWh |
The 80% scenario needs 37.5% less nominal capacity than the 50% scenario within this arithmetic. It does not establish that one chemistry costs less or lasts a fixed multiple longer. Confirm permitted depth of discharge, continuous/peak current, warranty cycle conditions and capacity at the expected temperature and load for the actual battery.
Autonomy is a chosen duration at the entered load, not a reliability guarantee. The calculation omits additional capacity margins for ageing, temperature, inverter standby use and other losses unless you allow for them in your assumptions. It does not establish battery string configuration or BMS compatibility.
3. Model daily-energy replacement by panels
`` array power = daily Wh ÷ (peak sun hours × yield factor) ``
Using hypothetical 4.5 peak sun hours and a 0.75 yield factor:
`` 4,552 ÷ (4.5 × 0.75) = 1,348.74 W ``
The arithmetic rounds up to three 450 W panels, or three 550 W panels, when simply dividing by each panel rating. That count does not determine a safe string design, suitable controller or sufficient worst-month output. Near-exact nominal coverage gives very little energy margin.
The 4.5-hour input is not a verified Lagos solar-resource figure. Use evidence for the location, season, orientation and shading, and check which losses the yield factor includes to avoid both omission and double-counting.
Important limitation: the displayed array covers the modelled daily load, not the extra energy needed to refill a depleted battery within a specified number of days. Raising autonomy increases the battery calculation but does not change this simple panel formula. A real recovery-time requirement may need more array capacity, different charging arrangements or backup generation.
4. Treat the inverter figure as a running-power scenario
The tool multiplies connected watts by an editable power margin, then rounds up using its built-in size list.
`` 592 W × example multiplier 1.25 = 740 W next size in this tool's list = 800 W ``
800 W is the model output, not a recommendation to buy an 800 W inverter. The earlier guide incorrectly totalled connected power as 528 W and recommended a 1,000 W unit without a consistent basis; that example is corrected here.
A 25% margin does not model compressor or pump starting current and duration. Check the inverter's continuous output, overload curve, ambient-temperature derating and the appliance's start-up requirements. W and VA are not interchangeable; power factor and the manufacturer's ratings matter. The tool's size list is not a survey of available products.
What to ask an installer
- Which measurements and duty cycles support the daily load estimate?
- What must run simultaneously, and which devices have a starting surge?
- What usable battery capacity and power can the actual battery/BMS deliver?
- What happens during the selected low-yield season and after a multi-day discharge?
- How are panel voltage/current, MPPT limits, charging limits and string design checked?
- What protection, cabling, earthing, installation, commissioning and warranty items are included?
Compare itemised quotes for the same requirements. This guide does not establish a nationwide quote spread, a fixed battery-life range or a universally cheaper chemistry. Use the replacement-aware cost calculator to test specific quoted prices and life assumptions, not to substitute for technical design.
Correction — 28 September 2026
Removed unsupported statements about why most installations fail, typical sunshine by region, universal discharge limits, battery price/life multiples and market quote spreads. Example assumptions are now explicit, the connected-load sum matches the calculator, and both guide and tool distinguish preliminary arithmetic from design approval.