How Long Can an Energy Storage System Store Electricity?

Did you know that German households waste up to 20% of their solar energy annually simply because their energy storage system isn’t optimally sized? According to the Consumer Advice Center, many could avoid this loss—if they understood how long an energy storage system can store electricity. Whether for photovoltaic systems or backup power, two key questions arise: How long does the energy remain stored without usage, and how long can it be supplied when needed? As an installer, you hold the key to these answers. At Ultimati Energy, your trusted partner for storage solutions in Germany, we help you provide your customers with clear insights and practical advice.

Without Usage: How Long Does Stored Electricity Last?

If an energy storage system isn’t used, how long does it retain its charge? This depends on self-discharge rates, which vary by battery type.

• Lithium-Ion Batteries: These lose only 1-5% of their charge per month. Imagine a 10 kWh battery—after three months, it still retains around 85-90% of its charge. This makes them ideal for customers who want to store energy for extended periods, such as for winter use.
• Lead-Acid Batteries: Studies show these lose around 20% per month. A 10 kWh lead-acid battery would retain only 60-70% after two months, making it more suitable for short-term applications.

Factors Affecting Storage Duration

• Temperature: High temperatures (above 30°C) accelerate discharge, while a cool environment (e.g., 15-20°C basement) minimizes losses.
• Charge Level: Keeping batteries at 100% charge for months can degrade them. Manufacturers recommend maintaining a 40-60% charge for long-term storage.
• Battery Quality: High-end batteries (e.g., Tesla Powerwall) have lower self-discharge rates than cheaper models.

Installer Tip: 

For long-term storage, lithium-ion is the best choice. Lead-acid is better suited for short-term backup applications.

With Usage: How Long Can an Energy Storage System Supply Power?

Once an energy storage system is in use, the duration it supplies power depends on capacity and load. The formula is simple: Time (hours) = Capacity (kWh) ÷ Load (kW) . Let’s examine two scenarios:

Short-Term (A Few Hours):

A family of four with a 5 kWh battery consumes 1 kW for lighting and a refrigerator—giving them 5 hours of power (5 kWh ÷ 1 kW = 5 hours). However, with 90% efficiency and 80% depth of discharge (DoD), the real duration is around 3.6 hours. This is sufficient to use solar power in the evening or bridge short power outages—saving up to 30% on electricity costs.

Mid-Term (A Few Days):

A small business with a 10 kWh battery and a 2 kW load (e.g., office PCs) gets 5 hours of power. If they reduce usage to 0.5 kW, the storage lasts up to 18 hours—almost a full day. For larger households consuming 6-7 kWh per day, a storage system could last 2-3 days in energy-saving mode.

Efficiency and depth of discharge impact actual usage time—high-quality systems effectively utilize 80-90% of their capacity.

Installer Tip:

 Consider efficiency (90%) and DoD (80%) when planning storage systems to give customers realistic expectations.

Comparison of Technologies: What Affects Storage Duration?

Not all storage systems are the same—the technology determines how long energy remains stored and how long it can supply power.

Lithium-Ion Advantages: 

✔ Long storage duration, high efficiency (90%), compact, low maintenance.

Lead-Acid Advantages: 

✔ Lower upfront cost but higher self-discharge and maintenance needs.

Installer Tip: 

For frequent use, lithium-ion is ideal. Lead-acid is a budget-friendly backup solution.

Ultimati Energy: Your Partner for Long-Lasting Storage Solutions

How do we support installers?

✔ Tailored Consultation: We analyze your needs—whether for homes or businesses.
✔ Fast Availability: Our storage solutions are ready for immediate delivery.
✔ Technical Support: From installation to maintenance, we’re your reliable partner.

Our storage solutions are trusted and proven, whether for self-consumption or backup power. Contact us today and let’s help you impress your customers!

Conclusion & FAQs: Everything at a Glance

How long can an energy storage system store electricity? Without usage, lithium-ion batteries last months, while lead-acid batteries last weeks. With usage, storage duration varies from hours (short-term) to days (mid-term) depending on capacity and power consumption. With Ultimati Energy, you can find the perfect storage solution for your customers. And the future? New technologies like solid-state batteries could soon enable even longer storage times.