A provision shop owner in Surulere told us her business had traded for eleven years without a plan for power. Then the grid failed for two days, the freezer contents spoiled, and the loss was larger than a year of profit on the solar equipment she had been putting off. Businesses are better placed for solar than homes, because they use power during the day. Working out how to size solar for business is harder in one way, because an hour of darkness for a shop is an hour of closed doors.

How to size solar for business starts with a different question

For a home, the awkward part of solar is the night. The array does nothing useful after sunset, so the bank has to carry everything. For a shop, office or workshop, most of the working day sits inside the hours when the panels are producing, so a larger share of the load is served directly. That is a genuine structural advantage and it is worth saying plainly, because it is the strongest argument for commercial solar in Nigeria.

For a business, the other half of the difference is that power cannot be treated as a comfort. A home without electricity is an inconvenience. A shop without it cannot sell, cannot take card payment, cannot keep stock cold, and in some cases cannot open its doors. So the sizing question has a second half: not only how much energy the business uses, but which loads are allowed to fail.

Building the commercial load list

For shops and offices the work is the same as a home with three additions: more load, greater sensitivity to failure, and a supplier more likely quoting a number than a design. A cold room needs its own treatment, covered in sizing solar for refrigeration, and the starting document is the same solar load list used for a home, with one extra column recording whether each load is allowed to stop.

Go through every circuit, not every room. Retail premises accumulate loads over years as things are replaced one at a time, and a second display fridge or a new air conditioner rarely reaches anybody’s list. The table below is an illustrative shop, not a specification.

Load	Watts	Hours a day	kWh a day
Four shop light fittings	40 W each	10	1.60
Display fridge, cycling	150 W	16	0.90
Chest freezer for stock	300 W	14	1.30
Point of sale terminal and printer	60 W	12	0.72
Two desktop computers	150 W	10	1.50
Router plus four CCTV cameras	120 W	14	1.68
Split air conditioner, staff room	1,200 W peak	6	3.60
Water pump	370 W	1	0.37
Outside and security lighting	100 W	12	1.20
Total			12.9

Two of those lines are worth arguing about. The air conditioner in a staff room is not a business-critical load, it is a comfort load, and it is the line that most often turns a sensible design into an unaffordable one. Take it out and the daily total falls by more than a quarter. The cameras and router line is the opposite: small, cheap to run, and losing it can close the business, because card terminals and electronic payment stop the moment the connection dies.

Single phase or three phase, and which one you already have

Nigeria’s premises are commonly served at 230 V single phase, derived from a three-phase network, with 400 V between phases. That distinction decides your options, and you can establish which you have from the meter or the distribution board without guessing. A single-phase shop can be served by a standard single-phase inverter, and there is no reason to pay for three-phase hardware. A premises with a genuinely three-phase supply, where the load is genuinely spread across the phases, is a different proposition.

The three-phase system gives you the same total power over three conductors rather than one, so less current and thinner cable for a given output, and it lets you carry an unbalanced load without pushing everything onto one conductor. The cost is a dearer inverter, a more complicated installation and a maintenance person who understands it. Most small shops do not need it. The national supply standard is what you compare your installer against.

For the shop above, a single-phase inverter of 5 kVA is the sensible pick: the peak combination of lights, computers, point of sale, freezers and air conditioner sits just under 2 kW, and the compressor in the freezer and the air conditioner both draw several times their running current at start. Three-phase becomes worth considering once the simultaneous load passes roughly 10 kW, or where a three-phase supply and its cabling are already in place.

Keeping the till alive: the critical load sub-circuit

Here is the part most installers do not offer, and the part that matters most to a shop. You do not have to keep the whole premises running to keep trading. Divide the circuits into two groups: everything, and the few loads that must not stop. For the shop above that second group is the point of sale terminal and printer, the router, the four cameras, and two lights, together about 260 W.

A small second system, sized on its own

Give that group its own small inverter and a small bank, and it will run for hours through an outage that would exhaust the main bank. A 1 kVA unit with a 1.5 kWh bank covers roughly five hours of a 260 W critical load, long enough to finish the trading day and reach a generator. The main array then carries everything else in daylight, and the main bank is reserved for the evening peak. That is far cheaper than doubling the main bank, and it is a design choice rather than a product.

Two cautions. The card terminal needs the data connection as much as the power, so the router and any fibre terminal must be on the critical group. And the point of sale machine is usually a computer with a battery, so a standard uninterruptible power supply may cover the machine itself while the solar sub-system carries the router and the lights.

What business reliability actually demands

A household can accept a system unavailable for a few hours after heavy cloud. A business cannot, so the reliability specification deserves its own paragraph. Three things matter: a transfer mechanism that changes over quickly and safely, a generator as a backstop for genuine bad days, and a way of knowing the state of the installation without driving to the premises.

Transfer, backstop and knowing

The changeover question is bigger than solar. A manual changeover is cheap and adequate for a small shop, but somebody has to be awake to operate it. An inverter that takes over from the grid within a second or two, with the grid kept as a fallback, removes both the outage window and the human being in it. Solar inverter against generator sets out the trade-off, and for most small businesses the honest answer is solar for the base load with a smaller generator retained rather than removed.

For the backstop, match it to the critical group rather than the whole premises, so a small generator can carry the till, the router and the lights. That frees the main bank from covering a week of cloud, which it cannot do at any affordable size. Monitoring matters more in a business than at home because nobody is on site to notice a fault; a unit that reports its own state turns an outage into a phone call rather than a discovery on opening. Inverter security and smart monitoring covers the options.

One last piece of straight talk. Any quotation that promises a payback period without asking what you currently spend on fuel and generator servicing is guessing. Our notes on solar payback period in Nigeria explain why import duty, freight and installation quality all move the answer, and why a figure from a brochure is worth little.

Frequently asked questions

Do I need three-phase solar for my shop?

Almost certainly not. Three-phase is worth considering once your simultaneous load passes roughly 10 kW, or where a three-phase supply and its cabling already exist. Below that, a single-phase inverter is cheaper to buy, cheaper to install and far easier to service locally. Check what you have at the distribution board before agreeing to either.

How do I stop the business closing during an outage?

Split the circuits. Put the till, the router, the cameras and a couple of lights on a separate small inverter and bank sized for a few hours, and let the main installation handle everything else. For a 260 W critical load, a 1 kVA unit and a 1.5 kWh bank is a realistic starting point, and it costs far less than enlarging the main bank to cover a full outage.

Should a shop keep a generator?

Yes, in most cases. Solar is excellent at carrying the daytime load and the evening peak, and a generator is excellent at covering three cloudy days. Keeping a smaller generator matched to the critical loads usually gives better reliability for less money than deleting it, and it keeps the option open for a delivery of frozen or perishable goods.

Is a shop better suited to solar than a house?

Structurally, yes. Trading hours sit inside daylight hours, so a larger share of the load is served by the panels directly and less has to be carried by the battery. The catch is that business loads are more sensitive to failure, so the same installation needs a changeover arrangement, monitoring and a backstop that a home can often manage without.

Key Takeaways

• To size solar for business, separate energy per day from the loads that must never stop.
• Trading hours fall inside daylight, so commercial solar carries more load directly than household solar.
• Most small shops should stay on single phase, and three-phase is justified above roughly 10 kW.
• A small dedicated inverter and bank for the till, router and lights is cheap business continuity.
• Match any backstop generator to the critical loads, not to the whole premises.
• Treat any payback figure offered before your fuel spend is known as a guess.

Once the split between critical and non-critical loads is clear, the arithmetic for the bank is set out in battery bank sizing.

Sources: three-phase electric power; supply voltages by country, including 230 V and 400 V at 50 Hz in Nigeria; the point of sale system and its dependence on power and connectivity; standby generation as a backstop; power quality in distribution networks; uninterruptible power supplies.