How to Calculate Home Energy Storage Runtime? A Complete Guide to Power Duration During Outages/Photovoltaic Supply

1. First, Understand: What is Home Energy Storage Runtime?

• Emergency scenarios: The duration it powers "critical devices" like refrigerators, lighting, and routers during outages.
• Photovoltaic (PV) scenarios: The duration it powers home appliances at night using electricity stored from daytime PV generation.

2. Four Key Terms You Must Know for Home Energy Storage

3. Home Energy Storage Runtime: 2 Core Formulas

1. When You Know Total Device Power (Most Common)

Example:

• Energy storage battery: 1200Wh (e.g., a common portable emergency power station);
• Devices: Laptop (80W) + 2 LED bulbs (5W each, total 10W), total power = 90W;
• Theoretical runtime = 1200Wh ÷ 90W ≈ 13.3 hours.

2. When You Know Total Device Current (Less Common, for Users Familiar with Circuits)

Example:

• Energy storage battery: 12V 100Ah (convert to Wh: 12V × 100Ah = 1200Wh);
• Total device current: 7.5A (e.g., 90W device ÷ 12V = 7.5A);
• Theoretical runtime = 100Ah ÷ 7.5A ≈ 13.3 hours (consistent with the result above).

4. Critical Step: Adjust for Actual Household Conditions (Calculate Accurate Runtime)

Using the Same Example as Above, After Adjustment:

• Energy storage: 1200Wh; Efficiency: 90% (0.9); DoD: 80% (0.8, for lithium-ion);
• Total device power: 90W;
• Actual runtime = (1200 × 0.9 × 0.8) ÷ 90 = 864 ÷ 90 = 9.6 hours (nearly 4 hours less than theoretical runtime—this is a significant gap!).

5. Home Energy Storage Calculation: 5-Step Practical Guide

1. Check Energy Storage Parameters: Find the battery’s "capacity (Wh)" or "voltage (V) + Ah" (if no Wh is listed, calculate it yourself: Wh = V × Ah);
2. Make a "Critical Device List": Which devices do you prioritize during a power outage? (e.g., refrigerator, router, 2 lights) Note the power (W) of each device;
3. Calculate Total Power: Add up the power of devices you’ll run simultaneously (e.g., 50W refrigerator + 10W router + 10W lights = 70W);
4. Calculate Theoretical Runtime: Use "Energy Storage Wh ÷ Total Power W" to get the theoretical runtime;
5. Calculate Actual Runtime: Multiply by efficiency (0.85–0.9) and DoD (0.8 for lithium-ion, 0.5 for lead-acid) to get the final usable runtime.

6. Three Real-World Household Scenarios (Direct Application)

Scenario 1: Portable Emergency Power Station for Short Outages

• Energy storage: 1500Wh (lithium-ion, DoD 80%);
• Devices: Router (15W) + 2 LED bulbs (10W total) + phone charging (10W), total power = 35W;
• Inverter efficiency: 90%;
• Actual runtime = (1500 × 0.9 × 0.8) ÷ 35 ≈ 30.8 hours (enough for over a day).

Scenario 2: Solar Energy Storage Powering a Refrigerator (Critical Device)

• Energy storage: 24V 100Ah (24 × 100 = 2400Wh, lead-acid, DoD 50%);
• Device: Refrigerator (average power 60W—note: refrigerators work intermittently; a refrigerator labeled 150W actually has an average power of 50–80W);
• Inverter efficiency: 85%;
• Actual runtime = (2400 × 0.85 × 0.5) ÷ 60 = 1020 ÷ 60 = 17 hours (enough to power the refrigerator for most of a day).

Scenario 3: Large-Capacity Energy Storage Powering Basic Appliances

• Energy storage: 48V 200Ah (48 × 200 = 9600Wh, lithium-ion, DoD 80%);
• Devices: Refrigerator (60W) + router (15W) + washing machine (using "quick wash" for 30 minutes, power 500W—convert to continuous power: 500W × 0.5 hours = 250Wh);
• Inverter efficiency: 90%;
• First, calculate runtime for "continuous devices": (9600 × 0.9 × 0.8) ÷ 75 = 6912 ÷ 75 ≈ 92 hours;
• After adding the washing machine: Total usable energy = 6912Wh - 250Wh = 6662Wh; Runtime = 6662 ÷ 75 ≈ 88.8 hours (the washing machine barely affects continuous power supply).

7. Three Common Pitfalls in Household Calculations

1. Forgetting Total Power of Multiple Devices: Only calculating a single device (e.g., just the refrigerator) without adding the router or lights—resulting in actual runtime being half of what you expected;
2. Ignoring Refrigerator "Average Power": Using the "150W" labeled on the refrigerator directly, without noticing it works intermittently (actual average power is only 50–80W), leading to inaccurate runtime;
3. Overlooking Battery Degradation: A 3-year-old lithium-ion battery may only retain 70% of its original capacity—calculating with its new-battery capacity will leave you short on power.

8. Four Tips to Extend Home Energy Storage Runtime

1. Prioritize "Low-Power Critical Devices": During outages, turn off kettles and air conditioners; only run the refrigerator, router, and small lights. Cutting total power in half can double runtime;
2. Choose "High-DoD Lithium-Ion Batteries": For the same 1000Wh capacity, lithium-ion batteries (80% DoD, usable 800Wh) last longer than lead-acid batteries (50% DoD, usable 500Wh);
3. Find a Good Location for Energy Storage: Avoid placing it on balconies in winter (capacity drops 20–50% below 0°C) or in direct sunlight in summer. A temperature of 20–25°C is most energy-efficient;
4. Charge Storage with PV First: Store electricity generated by PV panels during the day instead of using it directly—save it for powering appliances at night to reduce grid reliance.

9. Household-Friendly Calculation Tools

• Online Tool: Digi-Key Battery Calculator (select the "Household Load" mode, enter Wh and total power);
• Offline Tool: Excel Spreadsheet (create a template yourself—enter storage Wh, efficiency, DoD, and total power for automatic runtime calculation).