Solar glossary
Usable roof area: what it means and why it matters
The part of a roof that can carry panels once orientation, shading, setbacks and obstacles are removed.
Why it matters in Nigeria
It sets the hard ceiling on system size. A large footprint with little usable area cannot host the system its bills would justify.
How PureWatts measures it
Total Usable roof
sum_usable_roof_m2
Sum over the buildings in the group. Roof area available for panels after setbacks.
Sum over the buildings in the group.
Total Footprint
sum_footprint_m2
Sum over the buildings in the group. Building footprint.
Sum over the buildings in the group.
Total Roof capacity
sum_roof_capacity_kwp
Sum over the buildings in the group. Largest system the roof can host.
Sum over the buildings in the group.
See these numbers for your area
Every state and local government area page reports usable roof area for its own rooftops. Browse the Nigeria rooftop solar data.
Related terms
How these numbers are produced
Approach A — energy value (upper bracket)
Sizes the system to the building's full latent demand and values that energy at the mixed grid/generator tariff. It answers what the energy is worth — not what anyone currently pays.
Approach B — cash saved (lower bracket)
Sizes the system to demand that is actually served today, values it by merit order (solar displaces generator kWh first) and caps it at current spend. It answers what a building stops paying.
Cohort: Viable rooftops (≥0.6 kWp potential).
- Demand is modelled latent demand, not metered consumption.
- Fuel is priced at ₦1,800/litre (operator-set). NBS reported ₦3,277/litre for May 2026 — on that basis every naira figure here is roughly 1.8× understated.
- Generator ownership is a model output, not a survey result: it follows from the grid-availability scale and the 25% demand-suppression assumption.
- Approach A prices energy nobody currently buys. Its savings must never be read as cash saved.
- Demand is MODELLED LATENT demand, not metered consumption.
- Generator ownership is model output, not survey.
- Medians do not combine across groups — re-derive from the histograms.
- Per-building files are float32 with 4 significant figures; cast to float64 before summing, because polars keeps Float32 sums in Float32.
- Null scenario fields mean the roof cannot host 0.6 kWp, not zero savings.
- `genset` was previously named `diesel` and now uses the segment's real fuel.
- Ordering holds by construction: grid savings < mixed < genset.