What Size Solar Battery Do I Need?

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Last Updated on 5th March 2024

What Size Solar Battery Do I Need?

What Size Solar Battery Do I Need?

When considering solar power for your home, selecting the right size solar battery is absolutely necessary to ensure you're making the most of your solar panels. It's all about balance; your battery should match your energy usage and the output of your solar array. It's also not just about storing energy; you also need a solar battery that fits your financial goals and maximises available incentives.

Assessing your daily electricity consumption and the capacity of your solar system can inform you about the size of the battery you need. Remember, a correctly sized battery can enhance your energy independence and provide reliability during times when solar energy is not being produced. Here, we'll discuss the nitty-gritty of choosing the most suitable solar battery size for your home—read on!

Best Battery By Size

Best Battery By Size

When picking a solar battery suited to your home energy needs, consider the size and price point, as well as how long it'll last you before needing a replacement. Battery choices vary widely in capacity and price, so you've got options to match both large and smaller energy requirements. Here's an overview of the best batteries by size on the market today:

For Large Energy Needs:

  • The Tesla Powerwall 2 offers a substantial 13.5 kWh capacity, which is ideal if your house has a high energy consumption. It's one of the larger home batteries available.
  • Puredrive II scales from 5 to an ample 25 kWh, adaptable to both medium and larger homes.
  • The Sonnen Eco sits comfortably in the mid-range, available in capacities from 5 to 15 kWh, suitable for most residential setups.

For Moderate Energy Needs:

  • LG Chem RESU provides a broad span of sizes from 3.3 to 13.1 kWh. These are versatile, allowing for incremental investments based on immediate energy needs.
  • The Plyontech 4.8 is a solid mid-sized choice at 4.8 kWh, fitting well with the average energy requirements of a family home.

For Smaller Energy Requirements:

  • Consider BYD B-Box if you're starting with a small setup or if your energy needs are minimal. These start at a modest 2.5 kWh and go up to 10 kWh.

To make your decision easier, here's a summarised view:

Battery TypeSize (kWh)Average CostLifespan (Years)Cycle Life
The Tesla Powerwall 213.5£6,500 - £8,00010 - 15Up to 5,000
Puredrive II5-25£5,000 - £8,00010 - 15Up to 10,000
The Plyontech 4.84.8£6,500 - £8,00010 - 15Up to 8,000
LG Chem RESU3.3 - 13.1£3,000 - £7,00010-15Up to 6,000
The Sonnen Eco5 - 15£4,000 - £8,00010 - 1510,000
BYD B-Box2.5 - 10£1,500 - £6,00010 - 15Up to 8,000

DISCLAIMER: The provided ranges may not accurately reflect current market prices or regional differences. Prices can fluctuate based on factors like demand, brand, and installer markup.

Remember, your choice depends on how much energy you use and how much you're willing to invest initially. Rather than thinking solely in terms of cost, consider the long-term value and your specific energy demands.

Key Factors Influencing Battery Size Selection

Key Factors

When sizing your solar battery, it’s important to consider your household demands, system specifications, and local climate to optimise energy usage and costs effectively. Let's dive into the specifics:

Household Size and Electricity Needs

  • Your household needs determine the capacity of the solar battery required.
  • Consider the number of people in your home, appliances used, lighting, and other energy-consuming items.

Here is a guide to help you estimate the suggested battery size for different household sizes:

Number of BedroomsAverage Daily Use (kWh)Suggested Battery Size (kWh)

Solar Panel System Specifications

  • The power output and energy production of your solar PV system influence the battery size.
  • A larger solar array means you might benefit from a bigger battery to store excess energy.

Below is a breakdown of recommended battery sizes based on your solar PV system's capacity and average output:

Solar PV Capacity (kW)Average Output (kWh/day)Recommended Battery Size (kWh)
4Roughly 88-9
5Roughly 12-159.5-10
8Roughly 16-2016
10Roughly 20-2520-21

Local Climate and Seasonal Considerations

  • UK weather isn't consistent; your battery size should account for less productive days in winter or when peak sun hours decrease.
  • Planning for autonomy during periods with minimal sunlight can help reduce energy bills significantly.

Below is a table illustrating the effect of seasonal sunlight variations on battery sizing:

SeasonAvg. Sunlight HoursEffect on Battery Sizing
Summer5-6Potentially less reliance on battery storage due to higher solar energy production.
Winter1-2May require increased battery capacity to compensate for lower solar energy production.

Remember, a well-sized solar battery ensures your lights stay on, your energy costs are low, and you make the most out of your renewable investment.

Solar Battery Size and Capacity

Understanding Solar Battery Size and Capacity

When selecting a solar battery for your home, it's essential to understand your energy usage, battery capacity, and how different factors like depth of discharge affect a battery's lifespan. Here's how to look into each of them:

Evaluating Home Energy Usage

  • Check your electricity bills: Look at your past electricity bills to find out your daily electricity consumption in kilowatt-hours (kWh).
  • Analyse your solar system's output: Compare this with the electricity generation data from your solar PV system to identify potential surplus energy which could be stored.

To provide a clearer and more contextually accurate overview of home energy usage, here's a table that incorporates the daily measurement timeframe:

Average Daily Electricity ConsumptionEstimated Daily Solar PV OutputPotential Daily Surplus Energy for Storage
10 kWh12 kWh2 kWh
15 kWh18 kWh3 kWh
20 kWh25 kWh5 kWh
25 kWh30 kWh5 kWh
30 kWh35 kWh5 kWh

However, it's important to remember that actual values can vary significantly based on location, the size of the solar system, and individual household appliance usage patterns.

Solar Battery Capacity Explained

  • Battery size is measured in kWh: The capacity of a solar battery tells you how much electricity it can store.
  • Usable capacity vs total capacity: A solar battery’s usable capacity may be different from its total capacity due to battery chemistry.

Understanding the capacity of a solar battery is fundamental to ensuring it meets your energy storage needs. The table below differentiates between total and usable capacity, critical for evaluating how much electricity your battery can realistically store:

Total Battery CapacityUsable Capacity (Approx)
5 kWh4 kWh
6 kWh4.8 kWh
7 kWh5.6 kWh
8 kWh6.4 kWh
9 kWh7.2 kWh
10 kWh8 kWh
12 kWh9.6 kWh
15 kWh12 kWh

Depth of Discharge and Its Importance

  • DoD indicates usable energy: The depth of discharge (DoD) represents the percentage of the battery capacity that has been used.
  • Higher DoD affects battery life: Regularly using a higher DoD can impact the number of cycles, or life expectancy, of your battery.

The following table provides insight into how different DoD levels affect battery life:

Depth of Discharge (DoD)Estimated Battery Lifespan (Number of Cycles)
90%~1,000 cycles
80%~1,500 cycles
70%~2,200 cycles
60%~3,000 cycles
50%~4,500 cycles
40%~6,000 cycles
30%~7,500 cycles

Using this information, you can choose a solar battery that suits your home's energy needs, maximises your solar system's potential and ensures longevity and efficiency in your energy storage solution.

Calculating Battery Capacity

Calculating Battery Capacity

To determine the necessary capacity for your solar battery system, you need to understand your daily power usage, how many days of backup power you require, and the maximum output your battery can deliver. This information helps in calculating the capacity needed to meet your energy requirements effectively.

Key Factors for Calculation

  • Daily Power Requirement: Check your electricity bills for your average daily consumption.
  • Backup Days Requirement: Decide on the number of days you need backup power.
  • Maximum Power Output: Consider the output capacity based on your battery cells.

Calculation Formula

The formula to calculate the required battery capacity is:

Batteries needed (Ah) = (Daily consumption (Ah) X Backup days X Correction factor 1.15) / Depth of Discharge (DOD) %


If your system requires 200 Ah daily, with a need for 2 days of backup, and the batteries provide a 50% Depth of Discharge (DOD), the calculation would be:

Batteries needed (Ah) = (200 Ah X 2 X 1.15) / 0.5 = 920 Ah

This means approximately nine 100 Ah batteries are needed for the specified backup duration.

Financial Aspects and Incentives

Financial Aspects and Incentives

Understanding the financial implications and available incentives is crucial when considering a solar battery. The cost-effectiveness of different battery sizes can be a determining factor in your decision.

Estimating Cost-Effectiveness

  • Estimate daily electricity usage in kWh.
  • Review your solar panel system's capacity and output.
  • Consider the energy demands of specific appliances.
  • Analyze how options like the Tesla Powerwall 2 fit with your energy goals.

Price and Savings Table

Battery Size (kWh)Estimated Price (£)Estimated Savings (£/year)
Small (1-4 kWh)£1,500 - £3,000£200 - £350
Medium (4-8 kWh)£3,000 - £6,000£350 - £500
Large (8-13 kWh)£6,000 - £9,000£500 - £650

This table helps in understanding the potential financial return on different sizes of solar batteries.

Government Schemes and Grants

In the UK, several schemes can make solar batteries more affordable:

  • Look into the Smart Export Guarantee (SEG), which pays you for excess energy you supply back to the National Grid.
  • Investigate any local grants or subsidies that support solar energy installation.
  • Remember, reducing your energy bills and carbon footprint are long-term financial benefits even after accounting for the initial outlay.

The table below highlights key incentives and their potential benefits, helping you navigate the financial landscape of solar battery installation:

IncentiveDescriptionPotential Benefit
Smart Export Guarantee (SEG)Payment for surplus solar energyOffset installation costs
Local GrantsFinancial support from local authoritiesReduce initial investment
Reduction in Energy BillsSaving on traditional energy costsLong-term financial saving

Remember, while incentives can significantly offset costs, they vary based on your location and the specifics of your installation, so always do your homework.

Case Studies & Customer Testimonials

When you're sizing up a solar battery for your system, Reddit's got a wealth of chatter. Users on subreddits like r/solar and r/solarenergy get into the nitty-gritty of what you might need, offering first-hand experiences and quite the variety of opinions. Here's the lowdown:

  • Battery size calculations: A user from r/solar laid it out pretty simple for a typical scenario. They mentioned, "...amps of charging and/or discharging x 8 = Ah of bank." This means, for a 6kW solar array with a 48V battery bank, you'd need roughly 1000Ah at 48V.
  • Daily energy needs: On r/solarenergy, a user pondering the impact of a 6.4 kWh solar system against 20-25 kWh daily consumption felt that 13-16 kWh battery storage would help dodge peak PG&E rates. The gist is to estimate your consumption first.
  • Panel and battery match-up: A user from r/solar was torn over choosing the right battery for a kit with four 100W panels. They broke down their daily usage including 3 freezers and a well pump and pointed towards at least a couple of 100W panels.

Here's a table summarising the key points from Reddit:

TopicUser Insight
Battery Size Calculation'125A x C/8 = 1000Ah 48V bank' - r/solar
Daily Energy Needs'13-16 kWh needed per day' - r/solarenergy
Panel to Battery Ratios'Minimum 2 100W panels' - r/solar

Sentiment across these discussions leans on the practical side, with Redditors emphasising real-world usage and actual energy needs. There's a general agreement that one size doesn't fit all, and your solar battery should be tailored to your unique setup.

Frequently Asked Questions


How can you figure out the proper size of a solar battery for your home?

To pinpoint the right solar battery size, start by checking your daily energy consumption. Then aim for a battery with at least double this usage to ensure you’re covered, especially during less sunny days.

What is the process for calculating the solar battery capacity needed for a 4kW solar system?

For a 4kW system, work out how much energy you use when the sun's not doing its bit. Let's say it's 4kWh daily. You'll want a battery that can store a day's worth of energy, so look for one with at least 4kWh capacity.

Could you explain how to determine the right solar battery size for a 3kW solar panel setup?

Your 3kW solar panel setup might generate around 12kWh daily. If half of that isn't covered by sunlight, you'll need a battery that can store at least 6kWh to keep the lights on.

How do solar battery sizes relate to their prices?

Battery size is directly linked to cost – bigger capacity usually means a higher price tag. Compare different models and manufacturers to find the sweet spot between battery size and the investment you're ready to make.

Solar Battery SizeCost Range
Less than 1 kWh£230 to £300
3 kWh£2,500 to £4,000
5 kWh£3,500 to £5,000
10 kWh£5,000 to £7,500
15 kWh£7,500 to £10,000

What considerations should you take into account with home battery storage system?

When choosing your battery storage, think about these points: the capacity needed for your home's energy use, compatibility with your solar panel system, warranty periods and, of course, your budget.

ConsiderationDetails to Consider
CapacityMatch to home's energy use
CompatibilityMust work with your solar panel system
WarrantyLonger warranty means better coverage
BudgetKnow your limit and stick to it

How long do solar batteries last?

Solar batteries available in the market today generally have a lifespan ranging from five to 15 years, which means they will likely need to be replaced at least once within the 25 to 30+ year expected lifespan of a solar system. This longevity is considered substantial but requires planning for future replacement to ensure continuous system operation.

What size battery for a 5kw solar system?

For a solar photovoltaic (PV) system of 5 kW with a daily energy consumption of 5-10 kWh, a 4 kWh battery is recommended to maximize returns, while a 35 kWh battery is advised for those looking to maximize energy independence. In cases where daily energy consumption ranges between 11-15 kWh, opting for a 7 kW battery is considered ideal to align with energy needs and system efficiency.

Can I charge my solar battery at night?

Batteries in solar systems offer the advantage of not needing to wait for the sun to recharge. Once discharged, these batteries can be recharged overnight using cheaper, off-peak grid electricity. This strategy allows for the stored energy to be used in the morning, effectively offsetting the more costly on-peak power rates and thus leading to cost savings.

Does a bigger battery mean more power?

The capacity of a battery to store charge is indicated by its ampere-hour (Ah) rating, with a higher Ah rating signifying a larger capacity. However, a battery's power output, which depends on its ability to deliver voltage and current, is not solely determined by its Ah rating. This distinction underscores the importance of considering both capacity and power output when selecting a battery for specific energy needs.