Why this lesson exists

Most Lagos buyers are sold solar by people who don't fully understand it. The result is undersized inverters, oversized panel arrays, batteries that die in 18 months, and disappointment. This lesson gives you the technically correct mental model so you can challenge any quote.

What a PV cell actually does

A solar photovoltaic (PV) cell uses the photoelectric effect: photons from sunlight knock electrons loose in a doped silicon wafer, and the wafer's P-N junction forces those electrons to flow in one direction — producing direct current (DC) electricity.

Two consequences matter for installers:

• Output is roughly proportional to irradiance (W/m² hitting the panel). Half the sunlight = roughly half the power. Cloud cover, harmattan dust, shading from a single tree branch — all measurable losses.
• Output is inversely proportional to temperature. A panel rated 400W at 25°C cell temperature will produce closer to 340W on a hot Lagos rooftop where cell temperatures hit 60–65°C. The manufacturer's "temperature coefficient" (typically –0.30 to –0.40 %/°C for monocrystalline) is the spec to read carefully.

The four-part system you will install

1. PV array — the panels, wired in series strings to produce a usable voltage (typically 300–600V DC for grid-tied, 150–200V DC for typical residential off-grid).
2. Inverter — converts DC to AC. Modern hybrid inverters also charge batteries and synchronise with NEPA grid power.
3. Battery bank — stores energy for night/grid-outage use. In 2026 the Nigerian market is shifting from lead-acid to LiFePO4 (LFP) for cost-per-cycle reasons.
4. Balance of System (BoS) — DC isolators, AC isolators, combiner boxes, surge arrestors, breakers, cabling, mounting structures, earthing rods. This is where 80% of installation problems live.

What solar will NOT do

A 5kW solar system does not produce 5kW × 24h = 120 kWh per day. On a good Lagos day with optimum tilt and clean panels, expect roughly 4–5 "peak sun hours" of equivalent full-power production. That's 20–25 kWh/day from a 5kW array — and significantly less in the rainy season (June–September). The system you size must match the load you care about during the worst-case month, not the best.

Key takeaways

• Solar produces DC, proportional to irradiance, derated by temperature.
• Real-world output ≈ 4–5 peak sun hours/day in Lagos average.
• The four-part system: array, inverter, battery, BoS. Most failures live in BoS.
• Always size for the worst month of the year, not the best.

Next lesson: panel selection criteria — tier-1 vs tier-2 manufacturers, monocrystalline vs polycrystalline, warranty traps to avoid.