Solar and battery systems solve different constraints. Solar is a production source, the battery stores energy, and the inverter determines how much power can flow at one time.
Start with the outage objective
Define whether the goal is overnight backup, several cloudy days, bill shifting, or a whole-home experience. Each goal changes the required energy and power. A system sized for lights and refrigeration is not automatically sized for air conditioning or a well pump.
Use daily energy carefully
Calculate essential kWh separately from total household consumption. Then compare that load with expected solar production after losses. Production averages hide weather and seasonal variation, so include a conservative case for critical backup plans.
Check the bottleneck
A small battery may run out of energy; a small inverter may cap simultaneous loads; a small solar array may not refill the battery. Identify which constraint controls the outcome before increasing one component.
Document assumptions
Record usable capacity, reserve percentage, efficiency, outage duration, peak load, solar resource, and recharging priority. A clear assumptions sheet makes installer proposals easier to compare.
Sources
The figures and rules in this guide are checked against:
- Solar Integration: Solar Energy and Storage Basics — U.S. Department of Energy
- Solar Photovoltaic System Design Basics — U.S. Department of Energy
- Energy Storage — U.S. DOE Office of Electricity
- NFPA 855: Standard for the Installation of Stationary Energy Storage Systems — National Fire Protection Association