---
title: "What Size Battery Do I Need? | 5kWh, 10kWh or 15kWh?"
url: https://www.greentechrenewables.co.uk/battery-storage/what-size-battery
description: "Find the right home battery size for your solar system. 5kWh suits most 10-panel systems. Use our sizing guide based on solar capacity, usage, and goals."
lang: en-GB
---

Battery Sizing Guide

# What Size Battery Do I Need? Home Battery Sizing Guide

Most UK households need a **5kWh battery** for a typical 10-panel (4-5kW) solar system. This size stores enough surplus solar to cover 4-5 hours of evening electricity usage. Smaller 3kWh batteries suit 6-8 panel systems, while 9.5kWh+ batteries are appropriate for larger 12+ panel systems, EV owners, or households with high evening consumption exceeding 8kWh.

Get Your Personalised Recommendation (https://www.greentechrenewables.co.uk/solar-estimator)

## Quick Battery Sizing Guide

| Solar System | Recommended Battery | Why |
| --- | --- | --- |
| 6 panels (2.8kW) | 3kWh | Matches daily surplus |
| 8 panels (3.7kW) | 3-5kWh | Moderate surplus storage |
| 10 panels (4.65kW) | 5kWh | Optimal balance |
| 12 panels (5.6kW) | 5-9.5kWh | Higher surplus capacity |
| 14+ panels (6.5kW+) | 9.5-13kWh | Maximum self-consumption |

Get Your Personalised Recommendation: https://www.greentechrenewables.co.uk/free-quote

## How to Calculate Your Battery Size

Three factors determine optimal battery capacity: daily solar surplus, evening electricity usage, and your goals.

### Step 1: Estimate Daily Solar Surplus

Solar surplus is generation minus daytime usage—the electricity available to charge your battery.

| Solar System | Daily Generation (Summer) | Typical Daytime Use | Daily Surplus |
| --- | --- | --- | --- |
| 3kW (6 panels) | 12-15 kWh | 4-6 kWh | 6-9 kWh |
| 4kW (8-9 panels) | 16-20 kWh | 4-6 kWh | 10-14 kWh |
| 5kW (10-11 panels) | 20-25 kWh | 5-7 kWh | 13-18 kWh |
| 6kW (12-13 panels) | 24-30 kWh | 5-7 kWh | 17-23 kWh |

Note: Winter surplus is much lower (2-6 kWh/day). Size battery for shoulder seasons (spring/autumn) for best year-round value.

### Step 2: Calculate Evening Electricity Usage

Your battery needs to cover evening consumption—typically 4pm to 11pm.

| Household Type | Evening Usage | Battery Size Needed |
| --- | --- | --- |
| Low (1-2 people, efficient) | 3-5 kWh | 3-5 kWh |
| Average (2-3 people) | 5-8 kWh | 5 kWh |
| High (4+ people, always on) | 8-12 kWh | 9.5-13 kWh |
| Very high (EV charging) | 12-20 kWh | 13+ kWh |

#### How to find your evening usage:

- Check smart meter data via supplier app
- Look at 16:00-23:00 consumption
- Average across several typical days

### Step 3: Consider Your Goals

| Goal | Battery Size Impact |
| --- | --- |
| Maximum self-consumption | Larger (cover all evening use) |
| Best value for money | Moderate (match solar surplus) |
| Backup power priority | Larger (run essentials longer) |
| Budget-conscious | Smaller (capture main surplus) |
| Future EV purchase | Larger (anticipate higher usage) |

## Battery Size by Household Type

### 2-Bed Flat / Small Household

| Typical solar system | 6 panels (2.8kW) |
| --- | --- |
| Daily surplus (summer) | 6-8 kWh |
| Evening usage | 3-5 kWh |
| Recommended battery | 3kWh |
| Alternative | 5kWh (future-proofing) |

A 3kWh battery captures most summer surplus and covers typical evening usage. Smaller households rarely benefit from larger batteries.

### 3-Bed Semi / Average Household

Most Common

| Typical solar system | 10 panels (4.65kW) |
| --- | --- |
| Daily surplus (summer) | 12-16 kWh |
| Evening usage | 5-8 kWh |
| Recommended battery | 5kWh |
| Alternative | 9.5kWh (if high usage) |

5kWh is the sweet spot for most 3-bed homes—enough to cover evening usage without paying for capacity you won't use.

### 4-Bed Detached / Large Household

| Typical solar system | 14 panels (6.5kW) |
| --- | --- |
| Daily surplus (summer) | 18-24 kWh |
| Evening usage | 8-12 kWh |
| Recommended battery | 9.5kWh |
| Alternative | 13kWh (if EV or very high usage) |

Larger households benefit from 9.5kWh+ batteries to capture substantial solar surplus and cover extended evening usage.

### EV Owner

| Typical solar system | 10-14 panels |
| --- | --- |
| EV charging need | 7-15 kWh per charge |
| Evening usage (excluding EV) | 5-8 kWh |
| Recommended battery | 9.5-13kWh |

EV owners should size batteries larger to store solar for car charging. A fully depleted EV battery needs 40-60 kWh—stored solar covers a meaningful portion.

## Why Bigger Isn't Always Better

### Diminishing Returns

Doubling battery size doesn't double savings.

| Battery Size | Additional Cost | Additional Savings | Return |
| --- | --- | --- | --- |
| 5kWh baseline | £0 | £350/year | Baseline |
| 9.5kWh (+4.5kWh) | +£2,000 | +£120/year | 6% return |
| 13kWh (+8kWh) | +£4,000 | +£180/year | 4.5% return |

Larger batteries only fill completely on the sunniest summer days. Most of the year, a 5kWh battery captures all available surplus.

### Seasonal Charging Reality

| Season | Daily Surplus | 5kWh Fills? | 9.5kWh Fills? |
| --- | --- | --- | --- |
| Summer | 12-16 kWh | Yes, excess exports | Yes, some excess |
| Spring/Autumn | 6-10 kWh | Yes, mostly | Partially (60-80%) |
| Winter | 2-5 kWh | Partially (40-80%) | Partially (20-50%) |

In winter, even a 5kWh battery may not fill completely. A 9.5kWh battery in winter often sits half-empty.

### Cost-Effectiveness Analysis

| Configuration | Cost | Annual Savings | Payback |
| --- | --- | --- | --- |
| 10 panels + 5kWh | £6,500 | £1,000 | 6.5 years |
| 10 panels + 9.5kWh | £8,000 | £1,120 | 7.1 years |
| 10 panels + 13kWh | £9,500 | £1,180 | 8.1 years |

Smaller, right-sized batteries deliver better returns than oversized systems.

## When to Choose a Larger Battery

Despite diminishing returns, larger batteries make sense in specific situations.

### You Have a Large Solar System

| Solar Size | Minimum Battery | Optimal Battery |
| --- | --- | --- |
| 6kW (13 panels) | 5kWh | 9.5kWh |
| 8kW (17 panels) | 9.5kWh | 13kWh |
| 10kW (22 panels) | 9.5kWh | 13-16kWh |

Large solar systems generate substantial surplus that smaller batteries can't capture.

### You Want Backup Power

Larger batteries run your home longer during power cuts.

| Battery Size | Backup Duration (Essential Loads) |
| --- | --- |
| 3kWh | 2-4 hours |
| 5kWh | 4-6 hours |
| 9.5kWh | 8-12 hours |
| 13kWh | 12-16 hours |

If backup power matters, size battery for desired protection duration.

### You Plan to Add an EV

Future EV purchase increases your electricity needs significantly. Installing a larger battery now avoids retrofit costs later.

### You Use Time-of-Use Tariffs

Tariff arbitrage (charging overnight at cheap rates) benefits from larger batteries that can store more cheap electricity for daytime use.

| Battery Size | Arbitrage Potential (Flux) |
| --- | --- |
| 5kWh | £150-£200/year |
| 9.5kWh | £250-£350/year |
| 13kWh | £300-£400/year |

Learn about time-of-use tariffs: https://www.greentechrenewables.co.uk/battery-storage/time-of-use-tariffs

## Battery Size and Inverter Matching

Your inverter limits how fast the battery can charge and discharge. Ensure compatibility.

### Hybrid Inverter Capacity

| Inverter Size | Maximum Battery Charge Rate | Suitable Battery Sizes |
| --- | --- | --- |
| 3.6kW | 3.6kWh per hour | 3-9.5kWh |
| 5kW | 5kWh per hour | 5-13kWh |
| 6kW | 6kWh per hour | 5-16kWh |

A 3.6kW inverter takes 2.5 hours to charge a 9.5kWh battery—fine for most situations but consider if rapid charging matters.

Understand hybrid inverters: https://www.greentechrenewables.co.uk/battery-storage/hybrid-inverter

### Battery Discharge Rate

Batteries have maximum discharge rates affecting how much power they can deliver simultaneously.

| Battery | Max Discharge | Can Power |
| --- | --- | --- |
| GivEnergy 5.2kWh | 2.6kW | Most household loads |
| GivEnergy 9.5kWh | 3.6kW | Higher simultaneous loads |
| Tesla Powerwall 13.5kWh | 5kW | Heavy loads including EV |

For backup power during outages, ensure battery discharge rate covers your essential loads.

## Expandable Battery Options

Some battery systems allow adding capacity later.

### GivEnergy

- • Base unit: 2.6kWh or 5.2kWh
- • Add modules: 2.6kWh each
- • Maximum: 15.6kWh (6 × 2.6kWh modules)

Start with 5.2kWh and add 2.6kWh modules as needed.

Read GivEnergy review: https://www.greentechrenewables.co.uk/battery-storage/givenergy-review

### Pylontech

- • Base unit: 3.5kWh (US3000C)
- • Stack up to 4 units
- • Maximum: 14kWh

Modular design allows gradual expansion.

### Non-Expandable Systems

Tesla Powerwall, Sigenergy, and some others are single fixed-capacity units. Choose final size at installation.

View Sigenergy systems: https://www.greentechrenewables.co.uk/systems/sigenergy-installers

## Our Recommendations

Best Value

### 5kWh with 10-Panel Solar

Most households achieve optimal payback with this combination:

- Captures daily surplus in spring/summer/autumn
- Covers typical 4-5 hour evening usage
- £1,000 marginal cost when installed with solar
- 2-3 year payback on battery component

Best for Large Homes

### 9.5kWh with 12-14 Panel Solar

Higher-usage households benefit from increased capacity:

- Captures larger solar surplus
- Covers extended evening usage
- Suitable for EV preparation
- Better backup power duration

Best for Future-Proofing

### Expandable System

If unsure about future needs:

- Start with GivEnergy 5.2kWh
- Add 2.6kWh modules later if needed
- Avoids overspending upfront
- Flexibility as usage patterns change

## Frequently Asked Questions

### Is 5kWh enough for a 3-bed house?

### Can I add more battery capacity later?

### What if I get an EV later?

### Does battery size affect warranty?

### Should I match battery kWh to solar kW?

## Related Pages

Battery Storage Cost UK: https://www.greentechrenewables.co.uk/battery-storage/cost-uk
Battery Storage Savings: https://www.greentechrenewables.co.uk/battery-storage/savings
Is Battery Storage Worth It: https://www.greentechrenewables.co.uk/battery-storage/worth-it
GivEnergy Battery Review: https://www.greentechrenewables.co.uk/battery-storage/givenergy-review
Adding Battery to Existing Solar: https://www.greentechrenewables.co.uk/battery-storage/add-to-existing-solar
Time of Use Tariffs: https://www.greentechrenewables.co.uk/battery-storage/time-of-use-tariffs
Hybrid Inverter Explained: https://www.greentechrenewables.co.uk/battery-storage/hybrid-inverter
Solar Panel Cost UK: https://www.greentechrenewables.co.uk/solar-energy/solar-panel-cost-uk
Solar Estimator: https://www.greentechrenewables.co.uk/solar-estimator
Get Free Quote: https://www.greentechrenewables.co.uk/free-quote

## Get Your Personalised Battery Recommendation

Use our solar estimator or book a free survey for expert sizing advice

Use Solar Estimator: https://www.greentechrenewables.co.uk/solar-estimator
Get Free Quote: https://www.greentechrenewables.co.uk/free-quote

## Accreditations

Image: Our Accreditations: HIES Consumer Code, TSI Approved Code, TrustMark Government Endorsed Quality, Green Deal Approved, MCS Certified, NAPIT (https://www.greentechrenewables.co.uk/assets/solar-accreditations-CbjEg9cO.png)

Public Liability Insurance – Tradesman Saver

£5,000,000 – GREE55TR01

Employers Liability Insurance – Tradesman Saver

£10,000,000 – GREE55TR01

Professional Indemnity – Tradesman Saver

£250,000 – GREE55TR01

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