The Energy Audit: Understanding Your Usage Profile
Before sizing a solar system, you must understand your household's electricity consumption in detail. Your utility bill shows monthly kWh usage; collect 12 months of bills to capture seasonal variation. A typical US home uses 877 kWh/month (10,500 kWh/year average, EIA 2023), but this varies enormously by climate, home size, and appliances. For accurate system sizing: identify your highest-consumption month (usually summer with A/C or winter with electric heat), as this defines the 'design month' that prevents summer under-production from leaving you with large bills. Identify your largest loads: HVAC (often 30–50% of use), water heater, refrigerator, and EV charging if applicable. A solar offset decision must be made: most homeowners size for 90–100% annual offset, accepting that winter months may require grid power while summer months generate excess. The EV charging load requires special consideration — adding an EV can increase annual household electricity use by 2,500–4,000 kWh, requiring additional solar capacity to maintain offset targets. Use your utility's online portal for exact monthly data. Some utilities (like PG&E and Xcel) provide hourly consumption data, enabling more sophisticated time-of-use analysis that maximizes self-consumption relative to solar production curves.