Solar System Calculator

List the appliances you want to power and get the inverter, batteries, solar panels and charge controller you need, sized for your city's sunshine and shown with the full working.

How to size a solar system

A solar power system has four main parts. The inverter turns battery power into 230 V mains for your appliances, the batteries store energy for the night and for cloudy days, the solar panels recharge the batteries and power the house in the day, and the charge controller manages the charging. Each is sized from a different number: the inverter from the power of everything that runs at the same time, the batteries from the energy used during backup, and the panels from the energy used per day.

Worked example: a family flat in Lagos

Eight LED bulbs, three standing fans, a 43 inch TV with a decoder, a medium fridge, a laptop, a Wi-Fi router and three phones, with 10 hours of battery backup at night.

• Running load: 609 W, or 909 W for a moment when the fridge compressor starts
• Energy per day: 4,580 Wh (4.58 kWh); the fridge is counted at 40% of the day because its compressor cycles
• Inverter: 609 W ÷ 0.8 power factor = 761 VA, plus 25% headroom = 952 VA, so a 1 kVA pure sine wave inverter
• Backup energy for 10 hours: 3,572 Wh
• Tubular batteries: 3,572 Wh ÷ (50% usable × 90% inverter efficiency) = 7,938 Wh, which is 331 Ah at 24 V, so four 12 V 220 Ah batteries (two in series, two strings)
• Lithium instead: 3,572 Wh ÷ (80% × 90%) = 4,961 Wh, which is 207 Ah at 24 V, so three 25.6 V 100 Ah batteries
• Solar panels for the rainy season in Lagos (3.5 sun hours): 4,580 Wh ÷ (3.5 × 0.75 × 0.85) = 2,053 W, so five 450 W panels (2,250 W)
• Charge controller: 2,250 W ÷ 24 V × 1.25 = 117 A, so a 120 A MPPT controller, or a hybrid inverter with built-in MPPT

Sized on the yearly average of 4.6 sun hours instead, the same home would need four panels, but it would run short on cloudy days in June to September.

Peak sun hours in Nigeria

Peak sun hours are the number of hours of full-strength sunshine a panel receives in a day. The north gets the most, about 5.5 to 6 hours a day in Kano, Sokoto and Maiduguri. The south gets less, about 4.2 to 4.9 hours in Lagos, Port Harcourt, Ibadan and Enugu, falling to about 3.2 to 3.9 hours in the rainy season. The calculator uses rounded figures from satellite averages for 25 cities.

Why the system voltage matters

Small systems run on 12 V, medium ones on 24 V and large ones on 48 V. Doubling the voltage halves the current, so cables can be thinner, charge controllers smaller and less energy is lost as heat. The calculator picks the voltage from both the inverter size and the size of the solar array, and you can change it.

Tips for a reliable system

• Use a pure sine wave inverter if you run a fridge, freezer, fan or any motor.
• Keep heavy short loads such as pressing irons, kettles, microwaves and pumping machines off small inverters, or run them only in the afternoon sun.
• Replace old bulbs with LED and choose inverter fridges and inverter ACs; saving energy is cheaper than adding panels.
• Fit a fuse or DC breaker close to the battery and keep battery cables short.
• Clean the panels every few weeks during the harmattan, when dust can cut output noticeably.

Frequently Asked Questions

Only need part of the system? Use the Inverter Size Calculator or the Battery Backup Calculator. Your appliance list is shared between all three.