Renewable energy storage systems: power for a sustainable future.

It’s generally agreed that greater reliance on renewable energy sources, like solar and wind power, is an essential step on the path to reducing climate change.¹ But generating renewable energy is one thing. In a world that’s becoming increasingly focused on sustainability, finding ways to store that energy is an essential piece of an ever-evolving puzzle. 

Storing power efficiently allows us to make full use of all the renewable electricity we generate, and better yet, reduce our reliance on fossil fuels. In this guide, we’ll explore the benefits of energy storage, how it can be applied to renewables in a changing landscape, and whether it could be right for your home.

What is renewable energy storage?

Renewable energy storage involves capturing the energy we generate from sources like the Sun or the wind, then storing it to use later, when generation dips or demand rises.² 

That’s particularly important where sources like solar and wind power are concerned, which won’t necessarily generate around the clock. By harnessing the on-and-off nature of renewables in a battery storage system, we can make them available on demand for a steady, reliable power supply. That way, they help to balance the grid, reduce our reliance on fossil fuels, and ensure a steady flow of clean energy on tap.³

Solar power is the most common renewable energy generator found in UK homes. So not surprisingly, solar batteries are currently the most common form of renewable energy storage for households. That said, other types of energy storage may be used in industrial applications – for example as part of community energy projects.

How does a solar battery energy storage system work?

Photovoltaic (PV) panels generate clean, renewable electricity onsite, helping to slash a building’s reliance on the grid whilst also shrinking its carbon footprint.⁴ A solar battery storage system works by stockpiling the excess energy that solar panels produce during the day, for use when the Sun isn’t shining. 

There are currently two main battery technologies in use in the UK – lithium-ion and lead-acid. Both are designed to handle the cyclic charging and discharging required for solar energy storage. Here’s how they work:

• Generate: As sunlight hits a solar panel, the cells convert it into electrical energy in the form of direct current (DC).

• Convert and use: This DC electricity flows to an inverter, which converts DC into alternating current (AC) that can be used to power appliances and devices around your home. 

• Store: If the amount of electricity the home demands is less than the amount being generated, the DC can be transferred from the solar panels to charge your battery instead.

• Discharge: Then during the night, when your home needs electricity your solar battery can discharge to power your appliances and devices.

That way, you enjoy the benefits of your solar panels long after sunset.

How much power can a home battery store?

A battery energy storage system (BESS) for use in a typical home can vary in capacity, ranging from about 5 kilowatt-hours (kWh) to over 20 kWh. To determine the right size for your home, there are several factors to consider:

• Your energy use: How much electricity do you normally use on a daily basis?

• Solar system size: How much excess power are you likely to be generating?

• Desired independence: Do you need backup purely for essential appliances, or for partial or even total home coverage?

How long can you store energy in a battery?

Energy storage duration varies with the type of battery and its capacity. 

Lead-acid batteries have a relatively short lifespan and can only store energy for a few hours. But advanced battery technologies, like lithium-ion batteries, can store energy for longer. They have a range from several hours to multiple days, making them the recommended choice for storing solar energy. 

What to expect from your battery storage installation.

You can choose to have solar batteries as part of a new solar panel installation package. Standard installation usually takes about a day. 

You can also add them to an existing solar panel system. When adding a battery to an existing solar array, and in some particularly complex installations, you may also need a new inverter. That’s because the battery system has to be connected to the AC side of the solar system before it goes through the solar array’s inverters. 

If you decide battery storage is right for you, we'll conduct a full survey of your home, to decide on the best place to fit your battery. For practical reasons, it needs to be fairly close to your main consumer unit. That drives the choice of location to an extent, although we’ll normally try to put it somewhere discreet, like a cupboard, garage or utility room.

Solar batteries have an optimal operating temperature of around 25° C. So placing them indoors is a good way to keep them within the right temperature range for maximising their lifespan and their efficiency. 

Will battery storage affect my SEG payments?

The Smart Export Guarantee (SEG) means you can get paid for exporting any surplus solar energy you generate back to the grid. Also known as solar feed-in tariffs, they’re an incentive provided by the government to encourage homeowners to install solar power generating systems. 

Technically, adding battery storage to your system usually reduces the amount you can export with a SEG tariff. But it also means you can use more of your own solar power, reducing your reliance on the grid, and so spend less on electricity.⁵ 

In some cases, adding a solar battery can actually increase your SEG payments by storing excess solar energy and letting you export it during peak periods of electricity demand. However, this would only be the case if your SEG tariff offers different rates at different times of day, and you have the ability to export stored power from your battery. Exporting stored energy may not be eligible for SEG payments from all energy suppliers. So do check with your energy provider about the difference it will make in your particular case.

Can solar batteries be used to charge my EV?

They certainly can. Some battery storage systems have EV charging capabilities built in, while others can be paired with a separate EV charger.

Either means you can conveniently charge your car even at night, using your own stored renewable energy rather than relying exclusively on the grid. That can significantly reduce your electricity costs, and you’ll be contributing to a more sustainable transportation system while you’re at it.

Pros and cons of solar batteries.

Pros:

• Maximise the use of clean, renewable energy you generate with your solar panels.

• Use your solar energy for overnight EV charging.

• Enjoy lower energy bills by reducing the amount of electricity you need from the grid.

• Become more energy independent, making you less vulnerable to the ups and downs of the electricity market.

• Reduce your carbon footprint compared to using fossil fuel-generated power from the grid.

• Support the transition to renewable electricity in the UK.

• Since February 2024, you no longer have to pay VAT when adding a solar battery to an existing solar panel installation (installing a battery alongside a solar installation was already 0% VAT).

Cons:

• They are likely to reduce your SEG payments as you will have less (or even none) excess electricity available to export. 

• The high upfront cost may have a long payback period.

• You may need to install a new inverter if you plan to add one to an existing solar panel installation.

Is solar battery storage right for me?

The decision to install a BESS for your solar array depends on several factors, taking into account your energy needs, financial situation, and your environmental goals. It may well be a worthwhile investment if:

• You already have solar panels: Storing energy can make maximum use of all the solar power you generate - reducing your energy bills and helping to decarbonise your footprint.

• Your energy costs are high: If you use a lot of energy outside peak daylight hours a battery enables you to use stored solar power even after the sun goes down – instead of paying for power from the grid.

• You want to enjoy the convenience of overnight charging for your EV: The excess power stored by your solar batteries can help to charge your EV, even overnight, reducing the amount of electricity you use from the grid.

• You're eco-conscious: By storing renewables, you’re reducing your reliance on fossil fuels and cutting down on greenhouse gas emissions – both of which can help to speed up the all-important energy transition.

So by harnessing the power of batteries and advanced technologies, you’re also helping to create a more reliable, resilient, and environmentally-friendly energy system for generations to come.

The future of energy storage.

In this article, we’ve concentrated on solar power because it’s being widely adopted in homes throughout the UK.⁶ In recent years, electricity storage inventions have grown by 14%⁷, with technological innovations coming on in leaps and bounds. But it’s not all about batteries. 

Other exciting developments include:

• Pumped hydro: Large-scale storage that uses excess energy to pump water uphill, then releases it through turbines when it’s needed.

• Compressed air: Storing excess energy in compressed air form to use later.

• Thermal storage: Storing energy in the form of either heat or cold, for heating and cooling spaces as needed.

Energy storage is the key to unlocking the full potential of renewable energy. As the technology evolves and costs go down, it will become more accessible, and transform the way we produce and consume electricity. 

By creating a grid that’s more reliable, resilient, and sustainable, we’ll be well on our way to a more sustainable future.