Types of Solar Battery Storage Systems

Solar battery storage is an often overlooked component of residential renewable energy systems. But battery storage needs to be taken seriously – it’s going to play a vital role in a greener future.  

Solar battery storage provides a way to store excess electricity generated by solar panels when the sun is shining to be used later on. Without good battery storage, you either have the scenario of generating too much electricity that you can’t use or not generating any electricity to use at all.  

Battery storage technology enables both homes and businesses to become less reliant on the national grid, reduce electricity bills and contribute to a greener environment.

This article will inform you all about the main types of solar battery storage. We’ll discuss the pros and cons of each battery type, plus things to consider when choosing the right system for you. 

Understanding solar battery storage systems

If you’re thinking about solar photovoltaic panels, then it’s essential you know about solar batteries too. This is because they can significantly increase the effectiveness of your solar panel array and energy generation. 

A solar battery system is made up of several components that work together to store and manage the energy harnessed from solar panels. 

At the heart of the system is the solar battery itself. It works by storing potential energy in chemical form, ready to be used as electricity around your home.

Depending on the solar battery system you install, some form of inverter is needed to convert the direct current (DC) generated from solar panels and stored in the battery into alternating current (AC) that’s used by appliances in your home and the national grid.

Types of solar batteries

Broadly speaking, there are three main types of solar batteries you should be aware of. Each comes with unique characteristics, pros and cons, plus suitability for different scenarios.

The three main types of solar batteries are:

  • Lithium-ion
  • Lead-acid
  • Flow 

Let’s take a closer look at each. 

Lithium-ion batteries

Lithium-ion batteries have emerged as the dominant storage solution for solar energy systems. In the UK, they are by far the most popular type of solar battery storage. Their energy capacity can range from a modest 1kWh up to 16kWh. 

To put that into perspective, the average home in the UK uses between 6-10kWh of electricity per day. This figure generally doesn’t include the energy required for heating, mainly powered by gas. 

There are sub-types of lithium-ion batteries, including Nickel Manganese Cobalt (NMC) – which is the type used by the Tesla Powerwall – and lithium iron phosphate, often abbreviated to LiFePo4.  

The reason for the dominance since lithium-ion batteries entered the market are clear. They have good power outputs, good depth of discharge, don’t take up too much space, require no maintenance and have a long lifespan. Lithium-ion batteries are generally considered to be the most energy-efficient type. 

As a newer type of technology, they’re generally more expensive than other battery types although this will decrease in the future. But for most people, the higher price point is warranted for the extra benefits they bring.  

Pros:

  • High power outputs – Can supply higher continuous power outputs than other batteries and have a higher depth of discharge at around 80-100% or more.
  • High energy density – They can store a good amount of energy in a relatively small physical space, making them a lighter weight option too.
  • No maintenance – Once installed correctly by a professional, you can leave lithium-ion batteries to do their job with no annual servicing.
  • Long lifespan – Most lithium-ion solar batteries will last between 5-15 years.

Cons:

  • Cost – They generally come with higher upfront costs.
  • Temperature sensitivity – Can be susceptible to overheating. 

Lead-acid batteries

Up until around the mid 2010s, lead-acids were the main choice for battery storage systems. As a well-established battery, lead-acid has a good track record, is reliable and is available at an affordable price.

Despite the positives, they have been quickly overtaken by lithium-ion technology. Almost to the point where lead-acid batteries aren’t really a consideration anymore. 

They’ve fallen as the preferred choice for a few reasons. Lead-acid batteries have a shorter lifespan, lower depth of discharge and have a lower energy density – meaning they take up a lot of space for the same amount of energy storage. They also require maintenance to keep up their effectiveness.

Pros:

  • Affordable – They are less expensive compared to newer lithium-ion technology.
  • Reliable – Established battery type with a long history of solid, reliable performance.

Cons:

  • Lower depth of discharge – Can only discharge around 50% of total energy capacity at a time without damaging their lifespan.
  • Lower energy density – They occupy more space than other battery alternatives for the same amount of energy storage, making them bulkier and heavier.
  • Short lifespan – Generally will last for 3-5 years.
  • Maintenance requirements – Regular maintenance is required to ensure longevity. When disposing, care must be taken as they contain lead, an environmentally harmful, toxic metal.

Flow Batteries

Flow batteries are a type of energy storage system that uses liquid electrolytes to store charge. It’s one of the newer types of technology to enter the scene. 

Due to the way they have been designed, flow batteries can be scaled up quickly. For this reason, they’re often used in grid-scale storage, back up energy systems and other large scale applications. This means they’re not that applicable at the minute to household solar installations. 

They generally have a lower energy density, which means they take up a lot of space for the energy they store. On the plus side, flow batteries have a long lifespan of up to 30 years.

Pros:

  • Scalability – The energy capacity of flow batteries is dependent on the volume of the electrolytes, making them highly scalable.
  • Duration – Flow batteries can continually discharge energy for long periods of time.
  • Long lifespan – They can undergo many charge cycles with minimal degradation, offering a longer operational life of up to 30 years.

Cons:

  • Lower energy density – Compared to lithium-ion batteries, flow batteries take up much more space for the energy they store.
  • Large scale – For those looking for a home solar battery system, flow batteries are heavy duty and more suited to large scale systems, such as for national grid back up energy reserves.  
  • Cost – Currently the cost of flow batteries is higher than the alternatives.

Overall, the best type of solar battery storage system for residential settings is lithium-ion. These batteries have plenty of benefits and are the most suited for home use. As the technology continues to roll out, prices are continuing to drop, which is great news for the consumer. 

Is the future of battery storage solutions Salt? Or Sodium to be more accurate?

We’re seeing unprecedented research and development in battery technology. So much so that they have now got a commercially ready battery technology base on Sodium (Salt). It’s so abundant and doesn’t need to be mined in the way Lithium does.

We think this could revolutionise how we generate and store energy.

Solar batteries: What to consider

When weighing up the different types of solar battery storage systems, there are a few key factors to consider. You’ll have to look into the different technical aspects and specs, which isn’t as daunting as it sounds. Here are the most important things to look out for. 

Battery size

The size or capacity of a solar battery is measured in kilowatt-hours (kWh). This determines the maximum amount of energy the battery can store. 

Importantly, this is different to the power output of a battery, which determines how much energy can be released at any given time. Different batteries will have different power outputs, as well as different energy storage capacities. 

It’s crucial to understand battery capacity and power because it directly impacts how effective the battery will perform in your home with your personal circumstances. For example, a battery with 260W power output won’t be able to run many appliances in your home compared to Tesla Powerwall battery with 5kW power output.

If there’s a gap between the battery power and the energy needs of your home, the excess energy will have to be pulled from other sources, such as the national grid.

Battery capacity: Measured in kilowatt hours (kWh), this is how much energy a battery can store.

Battery power: Measured in kilowatts (kW), this is how much energy can be discharged at a time. 

Energy density

Energy density is a measure of how much energy a battery can hold relative to its physical size. 

Lithium-ion batteries have a higher energy density than lead-acid batteries. This means they can store more energy relative to its size, making them a more space-efficient choice. When it comes to home solar battery storage systems, this is a major plus point for lithium batteries.

Depth of Discharge

As we’ve all found out with batteries, their ability to hold charge drops over time. Even with rechargeable batteries. 

The depth of discharge indicates how much of the battery’s capacity can be used without adversely affecting its lifespan too much. 

Lithium-ion batteries typically have greater depth of discharge compared to lead-acid, meaning they last longer and are more efficient.

Battery maintenance

For homeowners, maintenance is an important factor. Generally speaking, people want items that require as little maintenance as possible.

Of all of the solar battery storage options, lithium-ion requires the least amount of maintenance. Once installed by a professional, they can be left without requiring a regular service.

Integration with solar panel systems

Integrating solar battery storage systems requires careful consideration of the connection between the solar panels and the battery. This is because a solar panel generates DC electricity but our homes use AC electricity. 

So, somewhere along the line from energy generation and storage to powering home appliances, a solar inverter will have to convert DC electricity to AC. This conversion can happen multiple times depending on the type of battery system you go for.  

There are two main types of systems to pair solar panels with battery storage:

  • AC Coupled
  • DC Coupled 

AC-coupled systems involve separate inverters for both the solar panels and the battery storage. Being separate means they’re typically easier to retrofit into existing solar setups.

But AC systems are less efficient as they have to convert DC to AC then back to DC before it can be stored. It then has to be converted back to AC to be used in your home. In total, there are three conversions with an AC-coupled system. 

DC systems use a single hybrid inverter to manage both solar panels and battery storage. These can be more efficient as DC electricity from solar panels doesn’t need to be converted to AC before it’s stored. The DC electricity either gets sent straight to the battery without conversion, or converted once into AC to power your appliances. 

However, they are generally trickier to install, especially in retrofit situations, and also come with a higher cost. 

Both systems have their own merits and selection will depend on your specific requirements and existing set up.

About the author 

Ben Hardman

Ben is a professional writer and the creator of sustainable living website TinyEco.com.
It's here where he helps people to reduce their environmental impact through simple, everyday choices. Away from the laptop, Ben loves spending time in the natural environment with his young family and Murphy the cocker spaniel.

Experience:
First Class BSc Biology degree (environmental and climate change focus)
Six years of working and writing in the environmental sector, including two years working at an international sustainability consultancy
Written for Ethical Consumer magazine, My Mother Tree, Unsustainable Magazine, Happy Eco News, Emission Index, PeakDistrict.org
Commented in The Independent, The Guardian, GreenMatch. Also featured on Radio 1's environmental special 'Minute of Me'

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