Whole-Duplex or Whole-Office Power on Two Inverters

Savings are the solar energy a system produces and the customer uses, valued at what that energy costs them today. Output is 1,397kWh per kWp a year, the Lagos figure for a well-oriented, unshaded array after system losses; we count 75% of it as used in homes and 90% in businesses, and give the battery no credit for charging from the grid, so the payback is conservative. Generator fuel is derived rather than assumed: litres/hour ≈ 0.25 × kW drawn + 0.037 × rated kVA, at ₦1,920/litre. The second term is fixed burn proportional to the set's size whether or not anything is plugged in, which is why an oversized generator costs more per kWh than one that is worked hard. Most Lagos generators run at 40–70% of rating; across that band fuel alone costs ₦607–₦702/kWh on a well-maintained engine, about ₦640/kWh at a typical 55% load, and around ₦800/kWh on a worn, lightly loaded one. Servicing, overhaul, managed-power premiums and diesel theft add another ₦60–₦120/kWh, which is what takes generator power past ₦700/kWh all-in. Band A grid is taken at ₦210/kWh. Conservative (₦366/kWh blended avoided cost): Band A home, 14–18 hours of mains, load weighted to the evening. Base case (₦531/kWh): Band B/C small business, roughly 10 hours of mains, mid-life generator. Optimistic (₦625/kWh): Band C/D commercial site with minimal grid and heavy daytime load. The more of your consumption falls in daylight hours, the faster the payback.