We have a version of the same conversation most weeks. Someone installed solar eighteen months ago, it does not do what they were told it would, and they want to know whether the panels are faulty.

The panels are almost never faulty. The system was sized against a budget instead of against a building.

How it happens

A buyer asks what a solar system costs. The seller quotes a package: so many panels, an inverter, a battery bank, a price. Nobody asks what the building actually needs to run, for how many hours, or what has to survive overnight. The package is chosen because it fits the budget, and the budget was picked before anyone knew the load.

The system then does exactly what it was built to do, which is less than the owner expected. In month two the batteries are being discharged deeper than they should be, and by year two they need replacing early.

The load assessment is the whole job

Sizing starts with a list. Every item you need to run, its power draw, and the hours per day it runs. Air conditioning, water pumps, fridges and freezers dominate the list in most Nigerian buildings, and they are the loads most often left out of a quick estimate.

From that list you get daily energy in kilowatt hours, peak demand in kilowatts, and overnight energy. Those three numbers size the array, the inverter and the battery bank respectively. Skip the list and all three are guesses.

Air conditioning is where estimates break

Air conditioning is the heaviest load in most buildings and it changes the sizing considerably. A system that comfortably runs lights, sockets, a fridge and a television will not run three air conditioners, and no amount of optimism at the point of sale changes that.

If air conditioning has to run on solar, say so at the start. It is achievable, it costs more, and finding out afterwards is the worst possible order to discover it in.

Batteries: the cheaper option is often dearer

Tubular batteries have a lower purchase price. Lithium tolerates deeper discharge, lasts longer, and works out cheaper per usable kilowatt hour over its life. Which is right depends on your budget and your horizon, but you should see both numbers before you decide rather than only the price on the invoice.

What to ask any installer

Ask them what the system will not run. An installer who will put that in writing has done the load assessment. One who will not, has not.

See our solar range and our solar design and installation service, or send us your load list.