Short version: with state-of-the-art multi-junction (MJ) cells, rooftops go up ~1.8× (no concentrators); deserts with CPV jump ~3.2× per ground area vs today’s Si PV. Net: rooftops ≈1.3–1.6× today’s global electricity; add just 1% of deserts with CPV and you’re at ~5–6×.
Core reasoning (aperture physics)
Under concentration, kWh per ground m² is set by aperture, not cell efficiency:
yield ≈ DNI × optical_eff × packing (GCR) × system_eff.
MJ helps cost/area of cells, not kWh/m²-ground, once concentrated.
Assumptions (explicit)
- Today’s electricity ≈ 30 PWh/yr.
- Rooftop base (Si, fixed-tilt): 20–27 PWh/yr.
- 1-sun MJ modules effective efficiency: ~38% (cell ~39–41%; module slightly lower; ignore cost).
- CPV deserts (two-axis): DNI 2,200 kWh/m²/yr, optical eff 0.80 (concentrator/tracking loss), GCR 0.30, system eff 0.85 (inverter/wiring/soiling).
→ Per ground m²:2200×0.80×0.30×0.85 ≈ 450 kWh/m²/yr
→ 0.45 TWh/yr per km² (vs ~0.14 TWh/yr/km² for today’s Si utility PV). - Hot desert area ≈ 29 million km².
Rooftops with best MJ (no concentrators)
Scale by efficiency ratio vs ~20% Si: ~1.8×.
→ ~36–49 PWh/yr (≈ 1.2–1.6× today’s global electricity).(Concentrators are generally impractical on rooftops; also CPV needs high-DNI. So assume flat-plate MJ on roofs.)
Deserts with MJ and concentrators (CPV)
Per km²: 0.45 TWh/yr.
- 0.1% of deserts (≈29,000 km²): ~13 PWh/yr.
- 1% (≈290,000 km²): ~130 PWh/yr.
- All deserts (29 M km², theoretical): ~13,000 PWh/yr.
Combined impact
- Rooftop MJ only: ~36–49 PWh/yr → ~1.2–1.6× today.
- Rooftop MJ + 0.1% deserts (CPV): ~49–62 PWh/yr → ~1.6–2.1×.
- Rooftop MJ + 1% deserts (CPV): ~166–179 PWh/yr → ~5.5–6.0×.
Key takeaway
- With “best MJ + concentrators,” the big win is deserts: aperture-limited yield rises to ~0.45 TWh/yr/km² even after ~20% optical loss.
- Rooftops benefit ~1.8× using 1-sun MJ, but CPV offers little there.
- Rooftops + just ~1% of deserts with CPV delivers multi-× current global electricity.