Buying guide

What size inverter do I need?

8 min read · Written by the Sunnovate engineering team

A practical guide to inverter sizing in Nigeria: how to work out the inverter capacity your home or business needs from your actual appliance load and starting current.

The quick answer

Inverter size is set by what runs at the same time, not by the size of your house or the number of rooms.

Add up the running watts of everything that could realistically be on at once, then add surge headroom for your largest motor — a fridge, pump or air conditioner.

A common failure is buying for running load only. The system then trips every time a compressor starts.

Battery voltage, phase and future demand all constrain the choice, so the inverter is picked last, after the load is known.

The Sunnovate system finder does this arithmetic for you in about three minutes.

What an inverter actually does

An inverter converts DC electricity — from your solar panels and your battery bank — into the AC electricity your appliances use. On a hybrid system it does more than that: it decides, moment to moment, whether to draw from solar, from storage, or from the grid, and it performs the changeover fast enough that nothing in the building notices.

That makes it the component every other part of the system depends on. Panels that generate more than the inverter can process are wasted. A battery bank the inverter cannot charge properly will age early. And an inverter that cannot handle your starting loads will shut down to protect itself at exactly the wrong moment.

Running load vs starting load

This single distinction explains most inverter complaints in Nigeria.

Running load is what an appliance draws once it is operating steadily. Starting load — also called surge or inrush — is what it draws for the first moment as a motor spins up. Anything with a compressor or motor draws several times its running figure at startup.

A refrigerator that runs at 150 W can pull well over that on start. A borehole pump rated at 750 W will demand far more for the instant it kicks in. If your inverter was chosen against the running figure alone, the surge exceeds its capacity and it cuts out.

If your inverter trips whenever the pump or fridge starts, it was almost certainly sized against running load and never given surge headroom.

How to size an inverter, step by step

1. List what must run at the same time

Not everything you own — everything that could realistically be on together. Lighting, fans, refrigeration, television, router, and whatever else your household genuinely runs simultaneously.

2. Add up the running watts

Use the rating plate on each appliance where you can find it. This gives you your connected load.

3. Apply a diversity allowance

In practice not everything runs at once, so the full connected total overstates real demand slightly. Sizing applies a diversity factor to reflect that.

4. Add surge headroom for the largest motor

Identify your single heaviest motor load and add headroom on top of the diversified figure — not instead of it. Taking the greater of the two under-sizes any property that has both a large motor and a lot of other connected load.

5. Round up to a real market size

Inverters are sold in standard capacities. The calculated figure is rounded up to the next one that exists, which also leaves a little room for growth.

The system finder performs all five steps from an appliance checklist, so you do not need to find rating plates or do the arithmetic yourself.

Five things that change the answer

Factor

Why it matters

Peak simultaneous load

Sets the baseline capacity the inverter must sustain.

Largest motor load

Determines the surge headroom on top of that baseline.

Air conditioning

A single inverter AC unit can dominate a household’s demand. Declare it at sizing stage.

Single or three phase

Determined by your supply and equipment, not by preference.

Future demand

Specifying headroom now costs far less than replacing the unit in two years.

Common sizing mistakes

Buying by house size. A three-bedroom house with no cooling and the same house running two AC units are completely different electrical problems.

Ignoring the battery relationship. The inverter has to match your bank’s voltage and chemistry. Parts that physically connect do not necessarily work well together.

Oversizing “to be safe”. An inverter far larger than the load costs more up front and can run inefficiently at very light loads.

Sizing before the load is known. The specification should follow the assessment, never the other way round.

What to do next

Run the system finder for an indicative inverter rating based on your own appliance list. Bring that number to the conversation — it makes the quote far quicker and much easier to compare.

If you already know what you need, you can browse inverters or send us your existing setup and we will confirm compatibility before you order, including if the answer is that it will not fit.

Get your inverter size in three minutes

The system finder works out inverter capacity, array size and storage from the appliances you select — including the surge headroom your heaviest motor needs.

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Frequently asked questions

What size inverter do I need for a 3-bedroom house in Nigeria?

There is no single answer, because it depends on what you run rather than how many bedrooms you have. A house without air conditioning and the same house with two AC units need very different inverters. The system finder gives you an indicative rating from your own appliance list in about three minutes.

Why does my inverter trip when the pump starts?

Because it was almost certainly rated for running current rather than starting current. Motors and pumps draw several times their rated figure for a moment at startup, and an inverter without that headroom shuts down to protect itself.

Is a bigger inverter always better?

No. An inverter substantially larger than your load costs more than necessary and can run inefficiently at very light loads. What you want is correct sizing with sensible headroom for growth, not maximum capacity.

What is a hybrid inverter?

A single unit that manages solar, battery and grid together, deciding which source to draw from and handling the changeover. It replaces the separate charge controller and changeover arrangement that older setups used.

Can I keep my existing batteries?

Often yes, but the inverter must match the bank’s voltage and chemistry. Send us details of your existing setup and we will confirm the match before you order.