Solar output changes with the weather. In the rainy season, Nigeria can have several cloudy days in a row. A mini-grid still has to keep the lights on through them.
The last few percent are the most expensive
Covering most of the year with solar and batteries is affordable. Covering every day, including a long run of storms, is a different matter. You would need:
- many more solar panels, to recharge on dim days, and
- a much bigger battery bank, to last several days without sun.
For most of the year that extra equipment sits unused, but it still has to be paid for. Customers pay for it through a higher tariff.
The hybrid approach
The alternative is a solar hybrid: solar panels and batteries supply most of the energy, and a small backup generator starts automatically only when the batteries run low after several cloudy days.
Engineers compare these options with modelling tools such as HOMER. Many published studies of Nigerian sites find the lowest-cost design is a solar–battery–generator mix, with solar supplying most of the energy, often around 90–95% in the studies we reviewed. Results depend on fuel prices, weather and load at each site, and some studies do find fully renewable designs work.
Is that still clean energy?
Yes, mostly. A generator running only a small share of the hours burns far less fuel than generators running every evening, which is what many communities do today. As battery prices fall, the solar share can rise further.
Sources and notes
- Frontiers in Energy Research (2024): HOMER study in Nigeria where the optimum was a PV, battery and generator system.
- FUDMA Journal of Engineering and Technology: Nigerian hybrid system study with a 95% renewable fraction.
- The best mix is different for every site. It has to be modelled with local weather, demand and fuel prices.