Sustainability
Solar and battery in a Lagos duplex: the real payback period
Measured against diesel at the price you are actually paying
Most solar payback calculations compare the system against a grid tariff. In Lagos that is the wrong comparison, because the grid is not what you are actually running on for a good part of the day.
Compare against diesel, not the tariff
The honest benchmark is your generator's fuel bill plus its servicing plus the rebuild you are amortising whether you think about it or not. Once the generator is in the comparison the arithmetic changes completely, because diesel is the most expensive electricity in the country.
Where the money actually goes
Panels are the cheapest part of the system and getting cheaper.
The battery is the expensive part and the part that wears out.
The inverter sits in the middle and is where the false economies get made.
Installation and cabling are the line most quotes understate.
You are not buying solar. You are buying storage, and paying for the panels that fill it.
The result for a four bedroom duplex
Sized to carry the house overnight without the generator starting, and measured against the diesel it displaces rather than against the tariff, the payback lands well inside the battery's warranty. Size it to run air conditioning through the afternoon as well and the payback stretches past the point where you are replacing cells, which is where a lot of oversized systems quietly stop making sense.
Size for the load you cannot tolerate losing, not the load you have. That single decision moves the payback more than any equipment choice.