Battery Storage Calculator

Grid Outages and Energy Resilience

Beyond economics, backup power resilience is a major reason homeowners invest in battery storage. Grid-tied solar panels without batteries shut off during a power outage — a safety requirement to prevent backfeeding electricity to utility workers. Adding battery storage allows your solar system to continue powering your home during an outage, running essential loads like refrigerators, medical equipment, lighting, and device charging.

The value of resilience depends heavily on your location. In areas prone to hurricanes, wildfires, ice storms, or aging grid infrastructure, power outages can last days. In areas with stable grids and rare outages, the financial case for a battery may be harder to justify on resilience alone.

Time-of-Use Rates and Battery Arbitrage

One of the strongest economic cases for battery storage is time-of-use (TOU) electricity rates. Under TOU pricing, electricity costs significantly more during peak demand hours — typically 4–9 PM on weekdays — than during off-peak hours overnight and on weekends. The peak-to-off-peak price difference can be 2–3x in some utility territories.

A battery system can charge overnight at cheap off-peak rates and discharge during expensive peak hours, saving $300–700 per year depending on your rate structure and usage. Combined with solar panels — which generate excess power midday that can be stored for evening use — batteries can shift a substantial portion of your electricity consumption away from peak pricing. If you're on flat-rate pricing, the TOU arbitrage benefit doesn't apply, and the economics for batteries rest primarily on resilience value.

Battery Chemistry and What to Look For

Most residential batteries use lithium iron phosphate (LFP) chemistry, which offers long cycle lives (typically 4,000+ charge cycles), good safety characteristics, and is well-suited for daily cycling. Key performance specs to compare when evaluating batteries: usable capacity (kWh), continuous power output (kW — how many appliances it can run simultaneously), round-trip efficiency (what percentage of stored energy you get back, typically 85–95%), and warranty terms — typically 10 years with a guaranteed minimum end-of-warranty capacity.

For sizing: essential backup only during a typical 8–12 hour outage generally requires 5–10 kWh. Full-home backup or multi-day resilience may need 15–30 kWh or more. Most installers recommend pairing battery storage with solar panels so the panels can recharge the battery each day, enabling extended off-grid operation during prolonged outages.

Battery product prices and specifications change frequently. Verify current pricing and availability with installers before making purchasing decisions.

Solar + Battery: The Ideal Combination

Batteries are most cost-effective when paired with solar panels. Without solar, a battery charges from the grid and can only save money through TOU rate arbitrage — useful but limited. With solar, a battery stores excess midday production for evening use, maximizes self-consumption, and provides backup during outages. In states with below-retail net metering export rates (like California under NEM 3.0), storing solar energy avoids selling it at a discount. Use our Solar Panel ROI Calculator and this battery calculator together to model combined system economics.

Installing Battery Storage: What to Expect

A battery installation typically takes 1–2 days for a single unit. The installer will assess your electrical panel (a panel upgrade may be needed for older homes), determine the optimal placement (usually near the main panel or existing inverter), obtain permits, and coordinate utility interconnection if required. Most jurisdictions require a building permit and utility notification before energizing battery storage — reputable installers handle this paperwork. After installation, most systems include a monitoring app that shows state of charge, charge/discharge history, and backup status in real time.