Home Solar & Battery Storage Installations

Everything you need to know

Installations of home solar PV panels and battery storage systems are on the rise.

Latest MCS figures suggest there are at least 519,409 residential solar installations in the UK. In 2023, annual rooftop solar installations hit a 12-year high with almost 190,000 systems installed. And the number of battery storage systems is catching up, with the MCS noting that 2023 was a “record-breaking” year.

If you’re considering installing a home solar and battery storage system, you’ve probably got a fair few questions.

‘Why do solar panels need batteries?’

‘What’s the right size solar and battery system for me?’

‘Can I DIY install my system?’

‘Does solar and battery storage make financial sense?’

… and probably more.

Here, Dave Roberts, UK MD at energy storage specialist GivEnergy tells you everything you need to know.

Why do solar panels need batteries?

Home solar panels are an affordable and scalable means of generating clean energy. However, while solar panels can generate energy, they cannot store it.

That’s where battery storage comes in. Without it, a lot of solar energy generated can go to waste.

Solar energy generation doesn’t always align with your energy needs.

For example…

… peak hours of electricity usage in the evening typically fall around 4-8 pm. During winter, there is little to no sunlight during these hours. In other words, there’s hardly any solar generation but a lot of electricity demand.

With battery storage, you can store solar energy generated during the day, and then discharge it to power your home during peak hours in the evening.

Strictly speaking, home solar panels can function without battery storage.

However, according to one study, households with standalone solar only use around 30-40% of energy generated. Meanwhile, households with solar and battery storage reduced imports from the grid by up to 84%.

In short, solar is simply not worth it without battery storage.

How to choose the right size solar & battery storage system

Sizing the right solar and battery storage system depends on:

• The size of your home
• Your average annual electricity usage

… among other factors.

Solar

How many solar panels are right for your home?

To answer this, you need to know the capacity of the solar panels you intend to install. Let’s say you opt for 350W solar panels. Under ideal conditions of direct sunlight, one panel will output 350W of energy per hour. Let’s say you get 4 hours of direct sunlight in one day. Multiply 350 by 4 and you get 1.4 kilowatt-hours (kWh) of electricity.

According to calculations by the Eco Experts, below is the ideal number of solar panels, based on average UK household electricity usage:

• 1-2 bedroom house – 3 x 350W panels – annual energy output of 1,590kWh
• 3 bedroom house – 10 x 350W panels – annual energy output of 2,645kWh
• 4-5 bedroom house – 14 x 350W panels – annual energy output of 3,700kWh

Battery storage system

Ideally, you want a battery storage system with enough capacity to store the maximum amount of energy your solar panels can output.

Here’s one way to size a battery storage system.

Let’s say you live in a 1-2 bedroom house with 3 x 350W solar panels. During the height of summer in June-August, you could expect up to 6 hours of direct sunlight per day.

Under these conditions, your panels could generate around 6.3kWh of electricity in a day. So, you may want to consider a battery storage system with a minimum capacity of 6.3kWh.

What about days when your panels generate little to no solar?

Solar generation varies by season. Fewer daylight hours and less direct sunlight in winter mean reduced solar generation. And let’s face it. Some areas of the country are better for solar generation than others.

Let’s say you have a day when solar generation is low and you’re left with a battery with spare capacity. If you’re on a time-of-use electricity tariff, you can consider topping up your battery with cheap off-peak electricity from the grid.

(More details on this below.)

What if solar generation exceeds the capacity of your battery?

Ideally, you’ll have sufficient battery capacity to store all solar energy generated. However, even with the best of calculations, you may find you generate excess solar capacity on some days.

If this happens, you have the option of exporting energy back to the grid and getting paid in return. This is possible under the government’s Smart Export Guarantee (SEG), a scheme in which energy companies are mandated to participate.  

If you find solar generation is consistently exceeding battery capacity, you may want to retrofit additional battery storage.

Installation

Solar

In so far as possible, solar panel installations in the UK should be south-facing. Ideally, panels should be on a roof angled no steeper than 50 degrees.

For a comprehensive overview of the ideal solar panel installation, consider using a solar calculator.

Do solar panels need to be installed by a qualified electrician?

Strictly speaking, you can install solar panels yourself. However, the wiring of your solar panels must be carried out by a qualified electrician to ensure it meets necessary wiring regulations.

What about SEG payments?

To receive SEG payments, your solar panels must be fitted by an MCS-approved solar installer. The only exception to this is SEG payments from Octopus Energy.

Battery storage

Outdoor installations

Installing outdoors is an option, assuming your battery storage system is IP65-rated. Ensure the system is not exposed to direct sunlight.

Indoor installations

Installing indoors – in a garage, main area of your property, etc. – is also an option, as long as your system has sufficient ventilation.

Note that according to updated guidelines from the British Standards Institution (BSI), home battery installations in lofts are not recommended.

Do battery storage systems need to be installed by a qualified electrician?

DIY battery storage installations are not an option. Your home battery must be installed by a qualified electrician to ensure that the wiring meets the necessary regulations.

Does home solar & battery storage make financial sense?

The upfront cost of purchasing and installing a solar and battery storage system can be high. However, given the money that you can save on energy bills, you can make this money back and more in the long run.

You should see your solar and battery storage system as a long-term investment. And like any investment, you want to know what your ROI is going to be.

To determine whether a solar and battery storage system makes financial sense, you need to calculate your system’s payback period.

Let’s say you spend £6k on a new system. And over 8 years, you see £6k in savings on energy bills. That means your payback period is 8 years.

Make this money back over 7 years, and your payback period is 7 years. You get the idea.

Here are a few things you need to consider when calculating your payback period:

• Upfront cost (including the cost of the units and installation)
• Electricity prices (if you plan on charging your battery with cheap electricity from the grid during off-peak hours)
• Average annual usage of electricity
• Solar capacity

Calculating exactly how much money a solar and battery storage system will save you in the long run is nearly impossible. That’s because your calculations cannot always accurately account for changing electricity prices, changes in your energy usage, seasonal variations, etc.

However, by calculating as closely as possible, you can choose a system most likely to give you a good ROI in the long run.

Ultimately, you know your energy needs best. So, it’s down to you to do your research.

Home solar & battery storage myths

Myth no. 1 – solar panels only work in direct sunlight

Reality

Solar panels work best in direct sunlight. However, they will still generate energy under light clouds, heavy clouds, rain, etc., albeit at reduced capacity.

Myth no. 2 – solar panels are time variable, meaning you have to use energy as it is generated

Reality

This is true if you have a standalone solar. However, when coupled with a battery storage system, you can store energy generated during daylight hours. Then, you can discharge to power your home, as and when required, including when little to no solar is being generated.

Myth no. 3 – home batteries are a fire risk

Reality

Some isolated incidents of home battery fires have been linked to battery chemistry prone to thermal runaway. However, home batteries are increasingly moving towards lithium iron phosphate (LiFePO4) – a type of lithium-ion battery with enhanced fire safety.

An alternative to solar & battery storage

Make no mistake. Battery storage coupled with solar PV panels is the ideal choice. This combination gives you the means of generating renewable energy and storing it to use effectively.

However, for those without the means – financial or practical – to install solar panels, a lesser-known solution for reducing energy bills and carbon emissions is available.

Standalone battery storage without solar can be a good option for those on a time-of-use TOU electricity tariff. Here’s how it works.

On a TOU tariff, electricity is cheaper during off-peak hours, such as overnight. Electricity is more expensive during peak hours, such as during mornings and evenings.

With a standalone battery storage system, you can charge from the grid when electricity is cheaper. Then, you can discharge to power your home when electricity is more expensive.

This helps you:

• Cut electricity bills
• Reduce strain on the grid during peak hours, making it less likely that grid operators need to burn dirty fossil fuels to keep the lights on

A standalone battery storage system could be a good choice for those who:

• Cannot afford the upfront cost of solar panels
• Do not have the roof space to install solar

TL;DR

• To work effectively, solar panels need battery storage.
• The right size solar and battery storage system depends on your home’s average electricity usage, the size of your home, and other factors.
• Standalone battery storage without solar is a viable alternative for those unable to install solar panels.