The grid-tied default: south
For a typical grid-tied home, south-facing maximizes annual kWh production. With net metering, every kWh you produce has equal value (whether self-consumed or exported). So you want maximum production, period. South wins.
South-facing daily production curve: low in morning, peak ~12-1pm, low in evening. The peak is sharp. With net metering, this is fine: excess midday production exports to the grid; you import it back at retail rate.
Why off-grid is different
Without the grid as a buffer, every kWh produced has to either (a) be used immediately or (b) charge a battery. Two off-grid problems:
- Midday clipping. A south-facing array peaks at 100% of nameplate around solar noon. If your battery is full and your load is low, that peak production has nowhere to go — it gets clipped (curtailed by the inverter / charge controller). Wasted energy.
- Battery cycling. Batteries last longer with shallow daily cycles. South-facing forces deep midday-to-evening cycling; east/west smoothes the curve.
The east/west advantage
An east-west split array (half the panels facing east, half facing west) produces:
- Earlier morning startup — east panels begin producing 1-2 hours earlier than south.
- Later evening production — west panels still producing 1-2 hours after south has rolled off.
- Lower midday peak — total production at noon is ~70-80% of equivalent south-facing array, but the curve is wider.
- Total daily kWh typically 5-15% lower than equivalent south-facing in optimal months, but with much better load-matching.
For off-grid where battery isn't infinite and clipping is real waste, the wider production curve is often more useful than higher peak.
When south still wins (off-grid)
- Battery oversized for capacity. If you have 30+ kWh of battery and modest daily load, you can soak up south's peak. South's higher annual kWh wins long-term.
- Winter months at high latitude. Sun stays low in the south sky — south-facing array is more critical because there's no morning/evening sun to capture anyway. East/west panels might produce nothing in December at higher latitudes.
- Heavy summer cooling load. AC compressor runs midday when south peaks. South-facing matches load.
When east/west clearly wins (off-grid)
- Year-round consistent load — refrigeration, well pumping, heat pump heat, lighting. East/west keeps battery topped up across more daylight hours.
- Mild climate, lower-latitude. 35°N or south-of (Phoenix, San Antonio, Atlanta, central CA) where sun arc is wider all year — east/west panels capture meaningful production for 12+ hours.
- Limited battery capacity — small battery + south = midday clipping all summer. East/west reduces clipping.
- Roof orientation forces it. Many homes are oriented with rooflines running north-south, which means the largest available roof faces east or west. Forced east/west is fine for off-grid.
How to decide
- Calculate daily kWh need: ~10-15 kWh for an off-grid cabin; 20-50 kWh for a full-time off-grid home.
- Estimate battery: kWh need × 1.5-3 (depending on autonomy goal).
- Calculate array size needed for daily charge: kWh need / (peak sun hours × 0.85 efficiency).
- Compare: south-facing produces X. East/west produces 0.85-0.95X.
- If your battery is small relative to peak production: east/west wins.
- If your battery is large enough to absorb midday peak: south wins.
Hybrid approach
Many off-grid systems use 60-70% south + 30-40% west (or 30-40% east). Captures most of the midday production benefit while extending the curve. Especially common where the south roof is partially shaded or limited in area.
Physical / engineering considerations
- String inverters: can't mix orientations on a single string — need separate strings or microinverters.
- Microinverters (Enphase) or per-panel optimizers (SolarEdge): handle mixed orientations cleanly — each panel optimizes independently.
- MPPT inputs: hybrid inverters with multiple MPPT inputs can dedicate one to east, one to west, one to south.
Frequently asked questions
I'm grid-tied. Should I still go east/west?
Generally no — for grid-tied with net metering, south's higher annual kWh wins. The exception: if your utility uses NEM 3.0 / net billing where exports are paid below retail, east/west's load-matching advantage starts to matter again.
What about flat-mounting at 0° tilt?
Flat-mount loses 5-10% vs optimal tilt and accumulates dust/snow more slowly to shed. Generally avoid except where building constraints force it (urban roof, ground-mount on flat land with low-tilt economic optimum).
If I'm building from scratch, what orientation should I aim for?
Off-grid in lower 48: 60% south + 40% west (covers afternoon AC peak + evening load). Off-grid in northern latitudes: weight more toward south because winter angle is critical. Grid-tied: pure south.