How Much Energy Storage Capacity Do You Really Need?

As solar adoption increases and net metering policies are phased out, more homeowners and businesses are investing in energy storage systems. But a common question remains: how much capacity should your home battery system have? Is 5 kWh enough, or do you need 10, 15, or even 20 kWh? In this in-depth guide, we’ll explain how to calculate the right battery size, what affects your choice, and how to optimize your energy independence, cost savings, and backup capabilities.

What Is Battery Capacity (kWh)?

Battery capacity is measured in kilowatt-hours (kWh). One kWh is the amount of energy needed to power a 1,000-watt device for one hour. For example, a 10 kWh battery could run a refrigerator, lights, router, and other household devices using 1,000W for about 10 hours—depending on efficiency and inverter load.

Average Daily Electricity Use in Europe

• ✔ Single-person household: 4–5 kWh per day
• ✔ Couple without children: 5–7 kWh per day
• ✔ Family with children: 8–12 kWh per day
• ✔ Large home with EV & heat pump: 15–25 kWh per day

Your daily consumption and usage patterns help determine the optimal storage capacity for your energy storage system.

What Factors Influence the Battery Size You Need?

• Solar production: How much electricity do your panels generate?
• Consumption timing: Do you use more power during the day or at night?
• Your goal: Are you optimizing self-consumption, preparing for outages, or aiming for full off-grid living?
• Feed-in tariffs: How much are you paid for exported energy?
• System design: Are you using a hybrid inverter or plug-and-play storage?

Capacity vs. Power Output

Capacity is how much energy the battery can store (kWh), while power is how much it can deliver at a given moment (kW). For example, a 10 kWh battery with a 3 kW inverter can supply 3,000 watts continuously for about 3 hours before being depleted.

Examples by Household Type

1. Apartment with solar (1–2 people)

• Daily usage: 4–6 kWh
• Recommended capacity: 3 to 5 kWh
• Example: Marstek Venus E

2. Medium household with kids

• Daily usage: 8–10 kWh
• Recommended capacity: 7 to 10 kWh
• Example: Felicity ESS 10 kWh with hybrid inverter

3. Large home with EV and heat pump

• Daily usage: 15–25 kWh
• Recommended capacity: 15–20 kWh (or modular)
• Example: Pylontech Force H2 scalable system

Backup Power and Autonomy

If you want to prepare for blackouts or grid outages, battery size becomes critical. During an outage, a typical household might use 500–800 watts continuously for essential loads. A 5 kWh battery could run such loads for about 6–10 hours. Add a hybrid inverter or built-in UPS to support seamless power transition.

Battery Types & Chemistry

The most common chemistry today is LiFePO4 (lithium iron phosphate), offering safety, longevity, and thermal stability. Brands like Marstek, Felicity, Pylontech, and Bluetti all use LFP cells in their storage solutions.

Sizing by Use Case

• Maximize self-consumption: 3–10 kWh
• Backup power during outages: 5–15 kWh
• Off-grid setups: 15–30 kWh (possibly with a generator)
• EV charging support: 10–20 kWh with 5 kW output minimum

Battery Pricing per kWh

Prices vary by brand and configuration. General estimates:

• ✔ Marstek Venus E 5 kWh: €2,950 → ~€590/kWh
• ✔ Felicity 12.5 kWh: €5,500 → ~€440/kWh
• ✔ Pylontech Force H2 15 kWh: €8,500 → ~€566/kWh

Conclusion: What Capacity Is Right for You?

Your ideal battery size depends on your energy usage, solar generation, grid rates, and personal goals. Analyze your smart meter data or energy bills, and plan ahead. Consider modular battery systems that can grow with your needs. At Off Grid Supply, we help you design a system that fits today—and tomorrow.

Need Expert Advice?

Not sure what battery size suits your home? Contact us for a free consultation or visit our showroom in Eindhoven. We offer full service: advice, delivery, certified installation (NEN1010 & NEN3140), and aftercare.