The chances are you are reading this article because you are considering fitting solar panels to your home or have them already installed and you are researching the most energy efficient systems to help you reduce your energy costs.
In your research, you will have undoubtedly come across the term ‘battery storage’ or ‘solar battery storage’ and want to find out what it is and what it offers the energy conscious consumer when designing the most effective renewable solution.
To help you make the most informed decision you can, we’ve created this short guide to explain what domestic battery storage system is, how it works and why it’s an essential part of any domestic renewable energy solution now and in the future.
How do Solar Battery Storage systems work?
For many people, the problem with solar panels has always been the electricity they create from the shining sun and converted to use in the home by an inverter, all happens during the day when the house is potentially empty and electricity usage is low.
Some saw the advantages of selling any excess electricity generated to licenced electricity suppliers under the Smart Export Guarantee (SEG) scheme, which is then exported back to the National Grid. But for most, it’s complex and brings the owner no closer to the energy independence they seek.
However, with battery storage added to a domestic solar panel array, you have the ability to store the electricity generated during the day for use when your home fills back up with people who need electricity for domestic chores, entertainment or homework.
Being able to store the electricity created by the solar panels in a modern solar battery storage system, will ensure significant reduction in your energy bills, typically over 30% reduction with an integrated modern solar array and battery storage system.
In addition, if there is spare capacity in your battery storage system, at night it can be used to store electricity drawn from the grid at the low tariff rates provided by most electricity suppliers. The savings again could be significant depending on the system and your household usage patterns.
According to MoneySavingExpert, while the average daytime ‘peak’ rates for most suppliers are around 39p–45p per kWh, the overnight ‘off peak’ rate typically drops to from 20% to 50% for the hours from 11pm to 8am, depending on your supplier.
In the winter months when electricity usage in the home increases, with longer need for lighting and hotter heating temperatures, the output from solar panels will drop by as much as 80%, given the shortness of the days and lower energy in the sun’s rays. If there are any in the UK!
Whilst the attraction of solar panels is obvious when the summer sun shines for 16 hours, the real benefits of a system utilising solar battery storage are really felt in the winter. Electricity from weak, short-lived sunshine stored and supplemented by nighttime tariffs will deliver smaller energy bills.
What Is a Battery Storage System?
There are two types of battery typically used in solar battery storage systems, lithium-ion and lead-acid [think car battery], with the former the more commonly used and preferred type by systems installers, for a number of reasons.
The primary reason for the popularity of lithium-ion batteries, the predominant commercial form of rechargeable battery that also features in mobile phones, laptops, etc., is their ability to store more energy, at higher voltage levels, for their size than any other type of battery.
The solar batteries come in a range of sizes and capacities, from as little as 1kWh to as much as 16kWh. Batteries can be coupled together to achieve the optimum arrangement for each unique domestic installation, depending on likely usage in the home and the available budget.
The lithium-ion type most commonly used in solar battery storage systems are made of Lithium Iron Phosphate (LiFePO4), chosen for its performance and safety profile.
Each battery contains an intelligent management system that optimises performance, whilst automatically balancing cells and protecting them from over-charge, over-discharge, over current, short circuit, as well as delivering high and low-temperature protection functions.
How does Solar Battery storage work?
A quick look at the chemistry involved finds lithium atoms in the anode are ionised and separated from their electrons during a discharge cycle. The lithium ions move from the anode and pass through the electrolyte to reach the cathode, where they recombine with their electrons.
A micro-permeable material separates the anode from the cathode, but the lithium ions release free electrons small enough to pass through it and these electrons flow from the negatively charged anode to the positively-charged cathode.
This flow of electrons is what we call the electrical current and it travels in the opposite direction to the flow of electrons. The flow is encouraged by the electrolyte material inside the battery, a lithium-salt, which provides the positive ions needed for the reaction.
When the batteries have released their energy, electricity from the solar panels flows into them and the chemical reaction is reversed. The anode and cathode are restored to their original state, from which they can deliver the electrical current required to power electrical devices within the home.
The Lithium-ion batteries commonly used in solar battery storage systems also possess a good depth of discharge [DoD], which means if a battery has a DoD of 95%, this is the amount of energy the battery can safely supply without being damaged. The DoD should not be confused with the round-trip efficiency of a battery, which is the percentage of the stored energy that can be used.
Of course, when a solar battery storage system is used in conjunction with solar panels, an inverter is still needed to convert the DC electricity discharged from the batteries into the single phase, 240V AC electricity needed by domestic appliances.
We’ve covered the subject of inverters in our useful guide, ‘Solar Inverters: What are they and how to pick the best one?’, to help you understand their importance and how there is no substitute for quality when choosing the right ones for your system.
Will a Solar Battery storage system power my house in a power cut?
The short answer is yes. The long answer is also yes, but it all depends on the size of the solar battery storage system installed, how much electricity is needed and for how long.
Battery systems are regularly installed in commercial situations, where a power cut causing the instant shutting off of a machine, computers, servers, safety systems, etc., could cause damage to the machines or ruin expensive work if it’s interrupted part way through.
Whilst there are fewer critical applications in the home, a power cut lasting longer than a few hours could be expensive if a freezer full of food is ruined or a TV is smashed by a teenager close to a high score on their favourite game as the screen fades to black.
There is little point over specifying a system to be safe in the most extreme blackouts however, as the high cost of the system would far outweigh any potential damage or inconvenience for members of the household – another reason to have your system designed by experienced professionals.
How long can electricity be stored in a solar battery storage system?
Typically, the charge can be held in solar batteries for anything up to 5 days, before the batteries need to be recharged. This phenomenon is known as self-discharge and is caused by the electrons packed in the battery, still wanting to flow, even when the battery is not in use.
Batteries are never truly off when they still have charge within them. The chemical reaction we exploit to deliver the electricity when we need it, remains active when the battery is not being used, even though the activity is almost negligible.
It is this ongoing low-level activity that can never be stopped in useable batteries that slowly depletes the stored energy over time. The amount and speed of this self-discharge varies according to the batteries being used, their age, the installation, the charge cycle time etc.
Talking about charge cycle time brings us neatly to another important consideration for solar battery storage systems – how long do the batteries last?
There are several factors affecting the life of solar battery storage systems, starting with the quality of the solar batteries and the specification of the installation – batteries required to work too hard will typically have a shorter life, again demonstrating the need for experts to design the system.
The length of service you can expect from your batteries will also be impacted by their cycle life, which is the number of times they are charged and discharged, before any noticeable drop in performance is experienced.
The efficiency of the battery storage solution reduces, rather than the batteries cease to work and the measurements are taken at 90% DoD. High quality batteries will typically achieve a cycle life around 6000, or 16 years if the charge and discharge cycle occurs daily.
A good indication of the quality of the batteries used in well-specified storage systems is the manufacturer’s warranty, which with the best brands such as SolaX Power or Alpha ESS, will be between 5 and 10 years.
Whilst there is not a lot to go wrong in the batteries, you can have confidence that a well-designed and installed system, using high-quality components will give years of good service and smaller energy bills.
Are solar batteries worth it?
Given the dramatic rise in energy prices, the solar battery storage system makes more sense than ever and explains why so many people with solar panels on their rooves are having batteries retro-fitted. But those wanting to fit solar panels to cut their energy bills must really only consider an integrated system that includes solar battery storage. And here’s why:
Use more of the electricity you generate – A battery storage system will allow you to maximise the benefits of your solar panels, using all of the electricity produced, rather than it being left unused or sold to the grid. The surplus energy not used during the day, will be stored in the batteries and available when the sun is no longer shining. And when you use less energy than is stored in your batteries, you will achieve very small bills.
Reduce your electricity bills – A solar battery storage system will undoubtedly lower your energy costs. Many homes use little energy during the working day when solar panels are producing the most electricity and without battery storage, the solar power will be wasted. You can also charge your solar batteries overnight with cheap off-peak tariffs for use during the day if there isn’t sufficient sunshine next day.
Make money from energy suppliers – If you don’t use all the electricity you either produce or buy on a cheap tariff yourself, depending on your energy supplier, you can sell the energy stored in your solar battery storage system back to the grid when electricity prices are high to make a small profit. Some suppliers will even pay you to store their excess electricity in your battery storage system.
Be prepared for outages – With a correctly specified installation that combines solar panels and battery storage, you will not only get closer to energy independence, but when the stressed UK energy grid hits trouble and outages occur, you will be safe for a day or more. You will have time to close down equipment safely and conserve energy to ensure critical elements, such as your fridge freezer stay on
Should I install a solar battery system?
If you’ve done all the research, then if you can afford it, a solar battery system added to your existing panels or purchased as a part of an integrated system makes perfect sense – energy prices are unlikely to fall to previous levels any time soon.
If you’re not entirely convinced yet, then please give us a call so we can talk you through the steps to energy independence and give you a more accurate idea of the likely cost, along with the time it will take for you to see a return on your investment.
And, if after you have all the information, you decide to install solar panels, solar inverters, and battery storage, you will see from our Trustpilot reviews that we are one of the leading system designers and installers, ready to go, please get in touch.