Easy Way to Size Your Solar Panels (Without Being an Engineer)

How to Calculate Solar Panel Size

Are you thinking about getting solar but not sure how many panels you actually need? Are you sure you are not in the hands of the “Awon I can install” solar engineer that looks at your roof, says, “Hhhmmmm, Oga, you need 50 units of 650W bifacial solar panels”—without doing any calculation? Get one thing straight — solar panel sizing isn’t magic, and you don’t just guess how many panels you need. You calculate it based on what you want to power and your battery bank. Don’t worry, it’s easy maths.

I’ll break it down in plain, everyday English. No big words. No complicated math. Just a clear step-by-step guide that anyone can follow—even if you’re totally new to solar or electricity.

First things first: What is solar sizing?

Solar sizing means figuring out how many solar panels you need to both:

Run what you use during the day, and
Recharge your battery bank so you can use power at night or when the sun isn’t shining.

STEP 1: Find Out How Much Power You Use Every Day

If you use a prepaid meter, note the total units (kWh) you consume in 24 hours. Each unit is one kilowatt-hour (kWh)—that’s just a measure of energy. If you don’t have a bill or meter to read, estimate it manually:

Make a list of the things you want to power, how many watts they draw, and how many hours they run per day. Then multiply to get watt-hours.

Example:

Appliance	Power (Watts)	Hours/Day	Energy (Wh)
4 LED bulbs	10W each = 40W	5	200Wh
Fan	60W	8	480Wh
TV	100W	4	400Wh
Laptop	80W	3	240Wh
Phone charging	20W	2	40Wh
Total Day Use			1,360Wh

So during the day, you use about 1,360 watt-hours (or 1.36 kWh).

STEP 2: Decide How Much Battery Backup You Want

You probably want power at night or during cloudy days. That means your solar has to recharge the battery with enough energy to cover what you used when the sun wasn’t up.

Say you want enough stored to cover the same 1,360Wh at night:

If you use lithium batteries, you can use almost 100% of capacity.
Battery energy needed = 1,360Wh
At 12V: 1,360 ÷ 12 = ~113Ah → get a 12V 120Ah lithium bank (close enough).

If you use lead-acid, you only safely use about 50%:
Needed capacity = 1,360 ÷ 12 ÷ 0.5 = ~227Ah → a 12V 250Ah lead-acid bank.

So your battery must store the night use. That’s 1,360Wh in this example.

STEP 3: Combine Daytime Use + Battery Recharge

Now combine:

Day usage: 1,360Wh
Battery recharge (night use): 1,360Wh
Total energy the panels must supply per day = 2,720Wh

STEP 4: Account for Sunlight (Peak Sun Hours)

Find the average peak sun hours in your area. In many parts of Nigeria, 5 hours is a safe working assumption.

Required panel output = Total daily need ÷ Sun hours
= 2,720Wh ÷ 5h = 544W

So you need at least 544 watts of solar panels to cover both what you use in the day and recharge the battery for night.

STEP 5: Add a Safety Buffer (Losses)

Systems lose power to heat, wiring, inefficiencies in the charge controller and inverter, dust on panels, and so on. Add 30% to cover that:

544W × 1.3 ≈ 707W

Final recommendation: ~750W to 800W of solar panel capacity (round up so you’re not starved on borderline days).

That could be:

3 × 300W panels = 900W (comfortable)

2 × 400W panels = 800W (just enough with buffer)

Mix that fits your roof or mount location

Quick Formula You Can Always Use

(Total daytime use + battery recharge need) ÷ Peak sun hours × 1.3 = Solar panel wattage needed

Bonus: What Else You Need to Make It Work

Charge Controller – manages charging the battery safely. Use MPPT if you have higher voltage panels or want better efficiency.
Inverter – converts stored DC battery power into AC for your appliances. Size it to handle the biggest load you’ll run at once (e.g., if your combined running appliances could draw 1,200W, get at least a 1.5kVA pure sine wave inverter).
Proper Wiring and Protection – correct gauge wires, fuses, and disconnects to keep everything safe.

Final Checklist Before You Buy

Total daily energy use calculated (Wh)
Battery bank sized for night use (Ah)
Solar panel wattage covers both day use and battery recharge (with buffer)
Charge controller chosen (prefer MPPT)
Inverter sized for peak simultaneous draw
Safety gear (breakers, fuses, good cables)

Closing

You don’t need to be an engineer. You just need to know what you use, how much backup you want, and how much sun you get. Do the math once, buy the right pieces, and your system will give you reliable power without the guesswork.

If you’d rather have someone check your numbers or install it properly, Right Click Technologies Ltd can do that for you—no smoke, no overhype. Just real sizing, real components, real power.