Solar Battery Storage


Solar Battery Storage Explained



You may already have a Solar Photovoltaic (PV) system and be thinking about adding battery storage or be planning to install a new solar panel system and wondering if it worth adding. Our guide is designed to help you decide if you need battery storage and if so, which storage solution is right for your installation.



How does home battery storage work?


Solar Battery systems are designed to store the excess energy from your PV system. They are capable of monitoring the homes usage of electricity.  The internal battery management system will automatically divert the excess energy to your battery, rather than allow it to generate back onto the grid. The battery system will then distribute the stored energy when it detects a demand in the house greater than the PV system can provide.  Or when there is no PV generation, providing there is sufficient energy stored in the battery.


It is important to remember most battery systems give priority to the loads in the house before charging the battery.  However, we are now seeing systems that allow you to choose the priority.



Is Home battery storage right for your property?


It’s a good question and the answer is, it depends on your lifestyle, energy usage and size of PV system.


On average, a household would utilise 35 - 50% of the generated system without a battery.  This would rise if you are in the house for much of the day.  However, battery storage can raise this to 80%.  If you have a system already installed and use all the energy generated from your PV system, then battery storage may not be right for you. However, if there is spare generation, then it could be a great way to further reduce your energy bill.


It is always recommended to look at your inverter monitoring to see how much of the power generated is being consumed during the day, before deciding if battery storage is right for you.



Which size PV system do I need?


Typically, most battery domestic storage inverters / battery managers are manufactured to work with PV systems of 3kW to 5kW.  While it is possible to have smaller (or larger), consideration must be taken to the load and usage.


What Equipment do you require for Solar Power Storage


For a solar battery systems to work, you require a battery manager and batteries. There are two types of battery managers available on the market for grid connected PV systems.


1. Hybrid Inverters, which is an inverter and battery manager combined in the same casing. This is typically installed with new battery systems but is worth considering where you have an inverter nearing the end of its life cycle.  Hybrid inverters come usually as a package and are relatively straight forward to install.


2. AC or DC retrofit unit which is installed alongside your existing inverter on either the Direct current (DC) or Alternate current (AC) side of the inverter. These units can usually be retrofitted to any existing system, with the advantage that they can be more remote from the solar array.


If you are looking for an Off-Grid Solution, then the equipment you require will depend on the loads you are planning to run.


A simple off grid system can be a 100W PV panel with charge controller and battery.  Whereas larger loads would require more PV panels and would need to be installed alongside a generator or wind turbine and are only suitable where there is no, or an intermittent grid.



Lithium Ion Versus Lead Acid


Often, we are asked which battery technology is best for battery storage.


For home storage we would recommend Lithium Ion technology. Whilst more expensive, as an upfront investment the life span of lithium ion by far outweighs the cost of installing lead acid.


Typically, with a lithium battery you are looking at around 6000 cycles at a 90% discharge or 8000 cycles at an 80% discharge.  


This in terms of life span, at a discharge rate of 90% with 6000 cycles, would be around 16.43 years based on one cycle a day, or 8.2 years at 2 cycles a day.


Lithium ion batteries are constantly developing and can come in various sizes, with modular batteries starting at 1.2kWh all the way up to 10kWh batteries.


Despite what we have said above, there is still a role for lead acid batteries which are ideally suited to off-grid applications and are a cost-effective solution where people are using them irregularly.


All batteries need a battery manager, these prolong life and in the case of the Li-Ion, is often built in to the battery. It is important that the battery and any inverter / charger unit are compatible, as this can be the case.



What is a battery cycle?


A battery cycle is simply the battery completing a full charge and discharge (to the set point).  Short cycles will make the battery last longer. An example is if a lithium 5kWh battery with a discharge depth of 90% is drained to, then it would contain 0.5kWh at the shut off point.  It would then be charged back to 100% it would be classed as one cycle.



What size battery should you install?


The size of the battery installed should be matched to your electricity usage and the size of the PV system. Installing too small battery could mean you are not storing as much electric as possible and maximising your self-usage, but too large a battery would mean you would rarely reach maximum battery capacity, and not making full use of the storage you have purchased.


You also must consider the performance of the battery during the winter months when Solar PV generation is at its lowest.


Generally, the smallest lithium battery is 1.2kWh on the market going up to 10kWh. You can also add multiple batteries together to create larger storage systems.


With off grid storage systems, the battery will be matched to the PV array, which is based on the total electrical load you will pull down. If you are not certain, then it is possible to add a battery after the installation to make better use of the storage capability.




How does the system track the power usage?



All of the hybrid systems either use a clamp (CT) that goes around the incoming main grid connection or a special meter (Modbus) installed in the same line. This is connected to the Hybrid or AC coupled unit via a communication cable and monitors which direction the power is travelling. When it detects power going back onto the grid it switches on the battery charge to match it and maintains this until the PV system output drops, or the load rises at which point the charging stops and power is taken from the battery.  In all cases, the system is designed to prevent as little power coming from the grid as possible.


Commercial Battery Storage in the UK


Commercial battery storage on 3 phase installations is more complex than domestic storage solutions. However, there are a growing number of manufacturers with 3 phase storage equipment. If you are looking at commercial storage it is best to store contact an installer with the expertise to design the system.


The difference between 48V battery system v 400v High Voltage (HV) battery system


When looking at lithium batteries, you will find that there are two types of Li-ion batteries available 48V batteries which are typically cheaper and 400V high voltage systems.

The newer systems offer the High Voltage option as these are more efficient at converting the stored DC to grid power. As a part of the installation they do not need the heavy DC battery cables associated with 48 Volt batteries.


Can battery storage be used for grid backup?


Battery Storage can be used as back-up to the grid. Most storage systems come with a back-up  ouput and most are rated as and uninterruptable power source (UPS).  Meaning that this power is always available but we would recommend making this clear to your installer this is a feature you would like.

It is worth noting that there are two types of battery back-up.  One being a manual back-up where in the event of a power cut you must switch the system into battery back-up mode. Alternatively, a relay which automatically changes the house over to running off the battery can be installed but this will carry an additional cost.


Can you use Economy 7 battery storage?


You can use Economy 7 to charge your battery storage, most manufacturers now include a timer that allows this to take place.  It is possible to charge a battery on Economy 7 alongside a PV system or, with just a battery connected to the grid.


If you receive the FITs tariff you would need to install a smart meter, to comply with regulations therefore on an existing PV system it may be easier to install an AC coupled Inverter / charger



Is Battery Storage Safe?


Both Lithium Ion and Lead Acid batteries are safe as long as they are installed correctly and maintained in the condition recommended by manufacturers.


To ensure Lead Acid batteries are maintained it is important to ensure they are well ventilated and kept at within the temperature parameters.  Most systems have battery temperature monitors.


Lithium Ion batteries pose a fire hazard if not installed correctly, or if you use inferior quality batteries. The reason for this is the chemistry behind lithium ion batteries makes them more prone to thermal runaway, if they are damaged or overheat.  This highlights the importance of the battery management system which monitors all of the parameters as well as the battery temperature and shuts the system down if any faults are detected.


To minimise the risk of thermal runaway it is important to understand the battery you are purchasing. Lithium Ion is the umbrella term used to describe several lithium technologies. The safest lithium technology is Lithium Iron Phosphate (LiFePO4).



Battery Storage Warranty?


Battery storage warranties vary from manufacturer to manufacturer. Usually you will have an initial 5 or 10 years on the hybrid inverter and a separate warranty on the battery.


For a lead acid battery the typical warranty period would be between 1 - 2 years. This would be based on the battery being kept and maintained to the manufacturers specification. 


Lithium batteries, usually come with a warranty of 5 - 10 years or a guarantee of a minimum performance over 10 years.


An example of this would be the LG Chem High Voltage 7.0kWh is warrantied for a total energy throughput of 19.6MWh or 10 years depending which comes first.



Where can I purchase the Tesla Powerwall?


To purchase the Tesla Powerwall you will either have to contact Tesla direct or find an Tesla accredited installer in your area.


Please cleck here to learn more about the Tesla Powerwall


What are the alternative solutions to the Tesla Powerwall?


There are a number of battery Storage options on the market and new products are entering the market all the time. Some of the alternative solutions on the market you may wish to consider are:



SolaX Hybrid and Triple Power battery (HV)

Offering both single phase and three phase solutions the SolaX High Voltage system offers battery storage in either 4.5kWh or 6.3kWh units. These unit can be extended to maximum of 4 batteries.

SolaX offer a range of solutions starting at 3kW inverters up to 10kW 3 Phase installations.


Discover about Solax more by clicking here


SolarEdge Battery Storage with LG Chem or Powerwall (HV)


SolarEdge StoreEdge system is a high voltage system battery system that is compatible with both the LG Chem 7kW and 10kWH batteries. The system can also be installed with the Tesla Powerwall.

Click here to learn more about StoreEdge

Click here to learn more about LG Chem


Solis Hybrid with Pylontech or BYD Batteries (48V)


Solis hybrid are available in 3kW, 3.6kW, 4.0kW and 5.kW single phase options. They are compatible with Pylontech 2.4kWh batteries and 3.0kWh batteries. Pylontechs are scaleable to up to 8 batteries and can be installed on the wall or in a battery storage box.

BYD batteries are a high quality battery manufacturer, who are well know for supplying London transport with their batteries, offering a large range of solutions for both 48V and 400V high voltage systemsSolar-Hybrid-Inverter-Solis-Pylontech-Battery-Storage

Click here to learn more and Solis Hybrid 


Alpha ESS


This unit is a one of a number of competitively priced system now coming onto the market which are a AC coupled inverter / charge with integral 2.9kWh Li-ion battery which is expandable to 15kWh. This unit comes with full monitoring and can be charged through Economy 7.

Click here to discover more about Alpha ESS



Sonnen batteries are manufactured in Germany and offer 10,000+ cycles. Sonnen is a hybrid inverter that comes with a standard 2kW battery which can be expanded to 15kW of storage.

Click here to learn more about sonnen batteries 



Victron Off-Grid solutions

Victron Energy offer a wide range of solutions for off grid power and living. The components required will depend on you the amount of power required. Please bear in mind a lot of off-grid systems will need to work alongside another power source, e.g. a generator or wind turbine.

Click here to learn more about Victron


The cost of home battery storage?


The million dollar question is how much! The answer is very dependant on the system and amount of storage you go for, typically it could be anywhere form £2,000.00 +. We would recommend contacting an installer to get a quote


NuVision Energy is a battery storage company in the UK who supply a wide range of home storage and commercial battery storage solutions. We work with traders throughout the country and are always happy to reccomend an installer to yourself. Please call 01404 891693 or email