08 · Solar, Electrical & Energy
SOL-001: Solar, Battery and Roof Design
Revision 1 · 2026-09-15 · Status: Draft
The recommendation: approximately 5.6–6.0 kW of solar and one 13.5 kWh battery. Develop the 35° roof option — it shifts energy toward winter and gains loft envelope with almost no annual generation penalty.
Household demand
Inferred from six 2026 utility bills (SDG&E):
| Month | kWh | Cost |
|---|---|---|
| February | 768 | $303 |
| March | 874 | $350 |
| April | 712 | $280 |
| June | 997 | $390 |
| July | 1,179 | $460 |
| August | 1,409 | $544 |
Estimated annual consumption: ~11,096 kWh/year (normal weather model). Base load: ~27.4 kWh/day (~1.14 kW continuous). Cooling adds ~1,085 kWh/year.
Solar array
| Parameter | Value |
|---|---|
| South-facing roof area (current concept) | 325 sq ft |
| Panel layout | 18 panels, 6×3 grid |
| Panel rating | 430W |
| DC nameplate | 7.7 kW |
| Roof pitch options analyzed | 30°, 35°, 40° |
Battery and economics
Under NEM 3.0, a battery is strongly recommended — export compensation is much lower than retail rates, so self-consumption is economically superior.
| System | Gross cost | Net (after 30% ITC) |
|---|---|---|
| Solar only (7.7 kW) | $22,330–26,950 | $15,631–18,865 |
| Solar + 13.5 kWh battery | $30,475–39,095 | $21,333–27,367 |
Why 35° roof pitch?
- Nearly identical annual generation to 30° (within 1–2%)
- Shifts production toward winter months when household consumption is less offset by cooling loads
- Gains loft envelope height — more usable storage space
- Better self-cleaning (steeper = less dust/debris accumulation)
Coordination requirements
Before selecting the roof pitch and ordering equipment:
- Obtain a full 12 months of utility bills and interval (green button) data
- Get binding quotes from at least 3 solar contractors
- Confirm the panel layout fits the physical roof (module dimensions + mounting hardware + setbacks)
- Verify the roof structure can carry the PV dead load + wind uplift
- Coordinate the PV mounting system with the standing-seam metal roof specification
- Determine whether a main panel upgrade is needed (owner reports 200A already present)