eco home grey interior battery storage and solar panels

How much battery storage do I need? A Step by Step Guide

Deciding to invest in home energy storage is a major step towards energy independence. But with a growing number of choices, figuring out the right system can feel overwhelming. How much battery storage do I need? Which brands can I trust?

This guide will walk you through everything, helping you understand your needs and compare the best options on the market. We will break down all the factors you need to consider, from your daily electricity habits to your future energy goals. By the end, you’ll have a clear, practical method for determining the perfect battery size for your home.

Step 1: Understand Your Household’s Energy Consumption

Before you can choose a battery, you need to know how much electricity your home actually uses. The most accurate way to find this is by looking at your utility bills. Your supplier provides statements showing your energy use in kilowatt-hours (kWh). Look for your average daily consumption. For most UK homes, this figure is typically between 8 kWh and 10 kWh per day.

If you can’t find a daily average, you can calculate it. Take your monthly or quarterly kWh usage and divide it by the number of days in that period. This number is your starting point—the foundation for all other calculations.

Step 2: Define Your Primary Goal for Battery Storage

Your goal is the most important factor. Investing in a home energy storage system is a significant step, and knowing exactly what you want to achieve with it is key to making the right choice. If you just need to keep the lights on and the fridge cold during a storm, a smaller battery might be enough. If you dream of true energy independence, you’ll need a system large enough to cover your total daily consumption.

Before diving into models and technical specifications, it’s essential to define your primary goal. Are you aiming for greater energy independence, looking to reduce your monthly utility bills, or looking to power your home when power outages occur? By clearly identifying your main objective, you can more easily navigate the options and select a home energy storage system that perfectly aligns with your household’s specific needs.

Maximise Solar Self-Consumption

This is the most common goal. You want to store excess solar energy generated during the day to power your home through the evening and overnight. This allows you to avoid buying expensive electricity from the grid during peak hours.

For this purpose, your battery doesn’t need to be massive. You’re looking to cover your “baseload”—the consistent energy draw from appliances like your fridge, router, and devices on standby—plus your typical evening usage from cooking, lighting, and entertainment. A home energy storage system that matches your average overnight consumption is usually sufficient.

Provide Backup Power During Outages

Sizing a battery storage system to navigate a power cut involves assessing your energy needs and the duration of the outage you want to prepare for. Start by calculating your critical power requirements—list the essential appliances and devices you need to keep running (e.g., lights, refrigerator, medical equipment) and their wattage. Multiply their combined wattage by the number of hours you expect the power cut to last to determine the total energy capacity required, measured in kilowatt-hours (kWh). Factor in inefficiencies, as batteries typically lose some energy during charging and discharging and consider adding a buffer for unexpected needs. Additionally, evaluate the battery’s discharge rate to ensure it can handle peak power demands. For longer outages, pairing the battery with a renewable energy source like solar panels can help recharge it and extend its usability.

Whole home back up and emergency power supply system’s come at an additional cost to your home energy storage system, so if you aren’t affected greatly by power cuts you might not need to install this element. However, with energy security becoming an ever-increasing cause for concern it could prove a beneficial investment to future proof your property and get the most out of your battery storage system.

If you require whole home back-up it is likely you will require a Gateway to transfer the home temporarily off grid allowing your battery storage system to support the home until power is restored. Manufacturers such as Tesla, Sigenergy, Enphase and Hanchu provide gateway or controllers which undertake this function.

Emergency power supplies differ in that they target critical loads such as sockets to provide a limited amount of power during power outages.

Whole-Home Backup System via Gateway

  • Purpose: Provides seamless power to the entire home during an outage, using a home battery storage system.
  • Scope: Powers all circuits in the home, including high-energy appliances like air conditioning, heating, and electric ovens.
  • Setup: Utilizes a gateway (a smart energy management device) that integrates with the home battery system. The gateway automatically detects outages and switches the home to battery power.
  • Advantages:
    • Whole-home coverage ensures no part of the house is left without power.
    • The gateway can intelligently manage energy usage, prioritizing critical loads if the battery capacity is limited.
    • Often works in tandem with solar panels, allowing the system to recharge during daylight hours for extended backup.

Emergency Power Supply

  • Purpose: Provides power to a limited number of essential circuits during a power outage.
  • Scope: Typically powers only critical appliances or systems, such as lights, refrigerators, medical devices, or a few outlets.
  • Setup: Often involves a manual or automatic transfer switch that connects specific circuits to the backup power source (like a generator or battery).
  • Limitations:
    • Does not power the entire home.
    • Requires careful planning to determine which circuits are prioritized.
    • May not support high-energy appliances like HVAC systems or electric water heaters.

Achieve Near Energy Independence

For those aiming to minimise their reliance on the grid as much as possible, a larger system is required. This means storing enough energy to cover almost all your needs, including running high-demand appliances like heat pumps, immersion heaters, and even charging an electric vehicle (EV).

This approach requires a battery capacity that can meet your entire average daily consumption, with a buffer for cloudy days. These systems often involve stacking multiple battery modules to achieve the desired capacity.

Buying and Storing Cheaper Energy

When paired with time-of-use (TOU) tariffs, home energy storage systems offer a smart and cost-effective way to manage energy consumption. TOU tariffs charge different rates for electricity depending on the time of day, with lower rates during off-peak hours and higher rates during peak demand periods. By using a home energy storage system, homeowners can store energy purchased at lower off-peak rates and use it during peak hours when electricity prices are higher. This approach not only reduces electricity bills but also enhances energy independence and efficiency. The potential savings and usage patterns directly influence the sizing of the battery, as a larger capacity may be required to store enough energy to cover peak periods or multiple high-rate intervals. Properly sizing the battery ensures it aligns with your household’s energy consumption patterns and the TOU tariff structure, maximising financial benefits while minimising upfront investment.

Step 3: Account for High-Demand Appliances

Standard household appliances don’t use much power individually, but some items can drain a battery very quickly. It’s vital to factor these into your calculations.

  • Electric Showers & Immersion Heaters: These devices have a very high power rating (often 7-10 kW). While they only run for short periods, they can overload a smaller battery’s inverter. Ensure your home energy system’s peak output can handle these appliances.
  • Electric Vehicle (EV) Charging: This is the single biggest energy consumer for many modern households. A typical 7kW home charger will draw 7 kWh for every hour it’s active. If you plan to charge your EV from your home energy storage, you will need a significantly larger system. For example, adding 20 miles of range could use 5-7 kWh, which would deplete an average-sized battery.
  • Heat Pumps: Air and ground source heat pumps are efficient, but they have a constant energy draw during colder months. A heat pump can use between 10 to 25 kWh per day, meaning your battery needs to be sized to accommodate this sustained load.

Step 4: Putting It All Together – Sizing Recommendations

Choosing the right battery size isn’t a one-size-fits-all process. It comes down to your daily electricity use, the appliances you need to power, and your ultimate energy goals. Are you looking for a safety net for occasional outages, or do you want to run your entire home on stored energy?

Now let’s translate this into real numbers. Based on household size and energy goals, here are some typical recommendations for UK homes:

how much battery storage do i need
A UK Household Guide: How Much Battery Storage Do I Need

Many modern battery systems are modular. This means you can start with a smaller capacity (e.g., 5 kWh) and add more modules later as your energy needs grow or your budget allows.

  • Small Household (1–2 people): A 5–10 kWh battery is a great fit for providing overnight power and backing up key appliances.
  • Medium Household (3–4 people): A 10–20 kWh system will cover your evening energy needs and offer substantial backup power.
  • Large Household (5+ people)and EV owners: Systems of 20 kWh or more are required for large households or EV Owners. Stacking multiple batteries is a common strategy to meet high demand.

Do You Even Need a Battery? When to Say No

While home energy storage has fantastic benefits, it isn’t the right move for every homeowner. You might be better off without a battery if:

  • Your Grid is Rock-Solid: If power outages are a rare event in your area and your main goal with solar is to save money, net metering programs might offer you a better financial return.
  • Your Energy Use is Minimal: For households with very low electricity consumption, the high upfront cost of a battery system might mean waiting many years to see a return on your investment.
  • You’re on a Tight Budget: Batteries are a significant investment. A smart alternative is to install your solar panel system first and add a battery later when your budget allows.

Comparing the Top Home Energy Storage Brands

Choosing a home energy storage system is a major decision that balances your goals, budget, and lifestyle. By understanding your daily energy use and exploring the top brands, you can unlock energy independence and secure a reliable power source for years to come.

Tesla Powerwall 3

  • Capacity: 13.5 kWh per unit
  • Dimensions: 1100 mm x 609 mm x 193 mm (43.3 in x 24 in x 7.6 in)
  • Key Features: An integrated solar inverter simplifies the system, while seamless backup transition keeps your power on without a flicker. It offers Wi-Fi and app monitoring and is scalable up to 10 units. It comes with a 10-year warranty and a weather-resistant design.
  • Pros: High capacity, sleek all-in-one design, trusted brand reliability.
  • Cons: Higher price point, locks you into the Tesla ecosystem.
  • Best for: Homeowners wanting a premium, integrated system with powerful backup capabilities, especially those with high energy needs or an EV.
  • Tesla Datasheet
tesla powerall installed by e-verve energy externally against red brick wall

Sigenergy (SigenStor)

white sigenergy home energy storage battery installed by e-verve energy against a bare brick wall
  • Capacity: Stackable 5 kWh or 8 kWh modules, expandable up to 48 kWh per stack.
  • Dimensions: Per 5 kWh module: 740 mm x 195 mm x 350 mm (29.1 in x 7.7 in x 13.8 in)
  • Key Features: A 5-in-1 unified system combining the battery, inverter, EV charger, energy manager, and solar input. It’s IP65 weatherproof and highly modular for future expansion.
  • Pros: Extremely flexible and customizable. You can start small and add capacity later. The integrated EV charging is a huge plus.
  • Cons: As a newer brand, it has less name recognition than some competitors.
  • Best for: Anyone who loves customisation. It’s perfect for starting with a smaller system and expanding as your family or energy needs grow.
  • SigenStor Datasheet

Fox ESS Batteries

  • Capacity: Offers a wide range of module sizes, from 2.88 kWh to 28.21 kWh.
  • Dimensions: (ECS2900 model) 480 mm x 165 mm x 465 mm (18.9 in x 6.5 in x 18.3 in)
  • Key Features: Highly compatible with third-party inverters, making it great for retrofits. It boasts high efficiency and can be mounted on the floor or wall.
  • Pros: A very cost-effective and reliable choice. Its flexibility makes it easy to size for existing solar systems.
  • Cons: The design is more industrial, and the smart features and app experience may not be as polished as premium brands.
  • Best for: Budget-conscious homeowners and those looking to add storage to an existing solar setup without replacing other components.
  • FOX ESS Datasheet
2 grey fox ess batteries installed by e-verve energy with solar inverter against white garage wall

Fogstar Batteries

Fogstar stackable batteries
  • Capacity: Various options available, including a popular 5.12 kWh rack-mounted unit that is easily scalable.
  • Dimensions: (51.2V/100Ah rack) 483 mm x 500 mm x 177 mm (19 in x 19.7 in x 7 in)
  • Key Features: Uses safe and long-lasting Lithium Iron Phosphate (LiFePO4) chemistry. Known for its advanced Battery Management System (BMS), technical transparency, and extremely long cycle life (up to 6,000 cycles).
  • Pros: Excellent safety profile and longevity. Highly scalable and customisable, with strong after-sales support.
  • Cons: May require more technical planning to install, making it a favorite of advanced users and DIY enthusiasts.
  • Best for: Users prioritising long-term value, safety, and customisation, especially for off-grid homes.
  • Fogstar Battery Ranges

How do the above models compare to the rest of the market? For a wider brand comparison we’ve put together the table below with the key features of each model

A UK Household Guide: How Much Battery Storage Do I Need

Pairing Your Battery with Your Solar System

To get the most out of your investment, your battery and solar array should be properly matched. A good general ratio is to aim for a battery capacity that is 1.5 to 2.5 times your solar system’s kilowatt (kW) rating.

  • 4kW Solar System: A 6–10 kWh battery is a great match.
  • 6kW Solar System: A 9–15 kWh battery will capture most of your excess daytime power.
  • 8kW Solar System: A 12–20 kWh battery system is recommended
  • 10kW+ Solar System: A 15–25+ kWh battery setup will help you maximise self-consumption.

How much battery storage do I need? – Your Next Step!

Answering “How much battery storage do I need?” is a process of self-assessment. Start by analysing your bills, defining your goals, and considering your future needs. With this information in hand, you are ready to have a productive conversation with a professional installer. They can provide a detailed quote and final recommendation to help you make a confident investment in your home energy storage system.

How Can E-Verve Energy Help?

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So now that you understand the key factors and how to calculate your energy needs, take the next step by using our interactive quote tool!

Get your home energy storage cost upfront with no pressure to commit and see how much battery storage could save on your bills! We’re here to help you find the perfect setup for your home.

Yes! You can install a battery and charge it with affordable, off-peak electricity from the grid. Then, you can use that stored energy during expensive peak hours to save money. It also gives you reliable backup power. Here’s how it works and why it might be a good option:

How Home Energy Storage Works Without Solar

  • Grid Charging: The battery charges using electricity from the grid, typically during off-peak hours when electricity rates are lower.
  • Energy Storage: The stored energy can then be used during peak hours when electricity rates are higher, helping you save on energy costs.
  • Backup Power: Home batteries can provide backup power during outages, ensuring that essential appliances and devices stay operational.

Benefits of Home Energy Storage Without Solar

  1. Energy Cost Savings: By charging during off-peak hours and using stored energy during peak hours, you can reduce your electricity bills.
  2. Backup Power: Provides peace of mind during power outages, especially in areas prone to grid instability.
  3. Future Solar Integration: If you plan to install solar panels later, most home batteries are compatible and can be integrated into a solar system.
  4. Energy Independence: Reduces reliance on the grid, even without solar panels.

Things to Consider

  • Battery Size: Choose a battery size that matches your energy needs. For example, smaller batteries (e.g., 5 kWh) are great for essential appliances, while larger ones (e.g., 20+ kWh) can power more of your home.
  • Electricity Tariffs: Check if your utility offers time-of-use (TOU) rates, as this can maximize savings with a battery.
  • Compatibility: Ensure the battery system is compatible with your home’s electrical setup.

Popular Home Batteries for Non-Solar Use

Many brands, like Tesla Powerwall, Duracell Power Center, and GivEnergy, offer batteries that can work without solar panels. These systems are designed to charge from the grid and provide energy storage and backup capabilities.

When answering the question “How much battery storage do I need?” often slightly oversizing your battery can be a smart move. It ensures you have plenty of power for long outages and future-proofs your home for additions like an EV or heat pump. However oversizing your battery too much can also lead to unnecessary costs and inefficiencies. Here’s why and what to consider:

1. Wasted Capacity

  • If your solar panels or energy usage don’t generate enough excess energy to fully charge a large battery, much of the battery’s capacity will go unused.
  • Example: If your solar panels produce 10 kWh of excess energy daily, but you install a 20 kWh battery, half of the battery’s capacity may remain unused most of the time.

2. Higher Costs

  • Larger batteries are more expensive, and if you’re not using the full capacity, you’re paying for storage you don’t need.
  • Example: A 20 kWh battery might cost twice as much as a 10 kWh battery, but if your energy needs only require 10 kWh, the extra cost doesn’t provide additional value.

3. Longer Payback Period

  • Oversizing your battery can extend the time it takes to recoup your investment through energy savings. If you’re not using the full capacity, the financial benefits of the battery will take longer to materialize.

4. Charging Inefficiencies

  • A battery that’s too large for your solar system may not charge efficiently, especially during winter or cloudy days when solar production is lower.
  • Example: A small solar system might struggle to charge a large battery fully, leaving it underutilized.

5. Space and Installation Challenges

  • Larger batteries take up more physical space and may require additional installation considerations, such as structural support or ventilation.

6. Maintenance and Warranty

  • Larger batteries may have higher maintenance costs, and if they’re not used efficiently, their lifespan could be affected. Most warranties are based on cycles or years, so underutilizing the battery doesn’t extend its warranty period.

When a Larger Battery Might Make Sense

While oversizing can be inefficient, there are scenarios where a larger home energy storage system could be beneficial:

  1. Future-Proofing: If you plan to expand your solar system or increase your energy usage (e.g., adding an EV charger), a larger battery might make sense.
  2. Backup Power: If you want extended backup power during outages, a larger battery can provide more hours or days of energy.
  3. Time-of-Use (TOU) Rates: In areas with high TOU rates, a larger battery can store more energy to avoid peak pricing.
  4. Seasonal Variations: In regions with significant seasonal solar production differences, a larger battery might help store summer surplus for winter use.

How to Avoid Oversizing

  1. Assess Your Energy Needs:
    • Calculate your average daily energy consumption and solar production.
    • Consider how much energy you want to store for nighttime use or backup power.
  2. Match Battery Size to Solar System:
    • Ensure your solar panels can generate enough energy to charge the battery fully on most days.
  3. Start Small and Scale Up:
    • Many modern batteries are modular, allowing you to add more capacity later if needed.
  4. Consult a Professional:
    • A solar and battery installer can help you size your system based on your energy usage, solar production, and goals.

Final Thoughts

A battery that’s too big for your needs can lead to wasted capacity, higher costs, and inefficiencies. It’s important to strike the right balance between your solar system size, energy usage, and backup needs when answering the question “How much battery storage do I need?” If you’re unsure, starting with a smaller, scalable battery system is often the best approach.

Absolutely. This is a common upgrade called “AC coupling.” It involves installing a battery and its own inverter alongside your current solar setup. It’s a straightforward way to add home energy storage capabilities to your system. Here’s what you need to know:

How It Works

Adding a battery to your solar system allows you to store excess energy generated by your panels during the day. Instead of sending it back to the grid, you can use this stored energy at night or during power outages.

Key Considerations

  1. System Compatibility:
    • Inverter Type: Check if your current inverter is compatible with a battery. If not, you may need to upgrade to a hybrid inverter or add a separate battery inverter.
    • Battery Type: Most modern batteries, like Tesla Powerwall, Enphase, or GivEnergy, are designed to integrate with existing systems.
  2. AC-Coupled vs. DC-Coupled Systems:
    • AC-Coupled: The battery is connected to your home’s AC electrical system. This is easier to retrofit into existing solar systems.
    • DC-Coupled: The battery is connected directly to the solar panels via a charge controller. This is more efficient but may require additional equipment.
  3. Battery Size:
    • Choose a battery size that matches your energy needs. For example, a 10 kWh battery can power essential appliances for several hours, while larger batteries (20+ kWh) can provide more extensive backup.
  4. Backup Power:
    • If you want the battery to provide backup power during outages, ensure it has this capability. Some batteries, like Tesla Powerwall, come with built-in backup functionality.
  5. Energy Monitoring:
    • Adding a battery often includes a monitoring system that lets you track energy production, storage, and usage in real-time.

Benefits of Adding a Battery for Home Energy Storage

  • Energy Independence: Use more of your solar energy instead of sending it back to the grid.
  • Lower Bills: Save money by using stored energy during peak electricity rates.
  • Backup Power: Keep essential appliances running during outages.
  • Future-Proofing: Batteries can integrate with smart home systems and evolving energy technologies.

Installation Process

  1. Assessment: A professional installer will evaluate your current solar system and energy needs.
  2. Equipment Selection: Choose a compatible battery and, if needed, an inverter upgrade.
  3. Installation: The battery is installed and connected to your existing system.
  4. Configuration: The system is configured to optimize energy storage and usage.

Popular Batteries for Existing Solar Systems

  • Tesla Powerwall: AC-coupled, scalable, and includes backup power.
  • Enphase IQ Battery: Modular and integrates seamlessly with Enphase microinverters.
  • GivEnergy: Offers both AC- and DC-coupled options.
  • Duracell Power Center: Affordable and stackable for larger capacities.

The size of your solar panel system plays a significant role in determining the right home energy storage battery for your setup. Your solar array must be large enough to charge your battery while also powering your home during the day. A good guideline is to have a battery capacity that is between 1.5 and 2.5 times your solar panel system’s peak output (kWp).

Here’s how your system size impacts your home energy storage battery choice and what you should consider:

1. Energy Production vs. Battery Capacity

  • Solar Panel Output: The amount of energy your solar panels generate directly affects how much energy you can store in a battery. A larger solar system produces more energy, which may require a larger battery to store the excess.
  • Battery Size: If your solar system generates more energy than your household consumes during the day, a larger battery ensures you can store the surplus for nighttime use or cloudy days.

Example:

  • A 5 kW solar system might pair well with a 10 kWh battery.
  • A 10 kW solar system might need a 20 kWh battery or more to store all the excess energy.

2. Daily Energy Usage

  • Your battery should align with your household’s energy consumption. If your solar panels generate more energy than you use, a larger battery can store the surplus. Conversely, if your energy usage is low, a smaller battery may suffice.

Check your electricity bills to understand your average daily energy consumption in kilowatt-hours (kWh).

3. Solar System Size and Battery Charging

  • Small Solar Systems: A smaller system may not generate enough energy to fully charge a large battery, especially during winter or cloudy days. In this case, a smaller battery is more practical and cost-effective.
  • Large Solar Systems: A larger system can charge a bigger battery more quickly, making it possible to store more energy for later use.

4. Backup Power Needs

  • If you want your battery to provide backup power during outages, the size of your solar system affects how quickly the battery can recharge during the day. A larger solar system can recharge the battery faster, ensuring you have power for extended outages.

5. Time-of-Use (TOU) Rates

  • If your utility uses TOU pricing (higher rates during peak hours), your solar system size and battery capacity should be optimized to store energy during the day and use it during expensive peak hours.

6. Battery Chemistry and Efficiency

  • Lithium-Ion Batteries (LFP or NMC): These are the most common and efficient options, with high energy density and long lifespans.
  • Roundtrip Efficiency: Larger solar systems can benefit from batteries with high roundtrip efficiency (e.g., 90%+), ensuring minimal energy loss during charging and discharging.

7. Scalability

  • If you plan to expand your solar system in the future, choose a battery that is modular or stackable. This allows you to add more storage capacity as your energy production increases.

9. Seasonal Variations

  • During summer, your solar panels may generate more energy, requiring a larger battery to store the surplus.
  • In winter, when solar production is lower, a smaller battery may suffice since there’s less excess energy to store.

10. Budget Considerations

  • Larger batteries are more expensive, so it’s important to balance your solar system size, energy needs, and budget. Oversizing a battery for a small solar system may not be cost-effective.

Final Thoughts

To choose the right home energy storage battery for your solar system:

  • Assess your solar system’s daily energy production.
  • Match the battery size to your energy usage and backup needs.
  • Consider future scalability if you plan to expand your solar system.

While this guide gives you a strong foundation, a certified MCS installer is essential. They will perform a detailed technical survey of your property, analyse your specific energy patterns, and consider factors like inverter compatibility and peak load. This professional assessment ensures you get a system that is safe, efficient, and perfectly tailored to your needs.