Are all home batteries the same?
The simple answer to this question is No, not all batteries are the same. When choosing a battery, the way it performs is vitally important to ensure you get the most out of your system. Your installer should be looking at how you use energy in your home and then choosing a battery based on this, but the majority of installers will have their preferred equipment and offer you this whether its the right choice for you or not. When it comes to price, remember you get what you pay for and most cheaper battery brands perform poorly and will have you importing more electrify from the grid than you would probably expect.
Below is our list of differences and how they can effect your system performance.
Battery Capacity:
The capacity of a battery is the most obvious and easiest performance factor to compare when you are getting quotes, but there are a few things that you need to be aware of. You might be quoted for a 10kw battery, but that doesn’t necessarily mean that you have 10kw of power to use when you need it. It is very typical with Lithium batteries that to help prolong the life of the battery they should never be fully discharged, meaning that you have to leave some power in the battery to protect it from failure. The amount of energy required can vary between manufactures but can be any where from 5% to 15%. This is described as “depth of discharge” and will be the next point we discuss.
Comparing battery capacity is tricky and you should always ask for data sheets for the equipment you are being sold so you can compare what you are getting.
Depth of Discharge:
As mentioned above, the depth of discharge makes a massive difference to how much battery storage you will actually have and the depth of discharge varies between manufactures but can be any where from 85% to 100%. It is important to note that any battery that has 100% DOD is actually just hiding the reserve required to maintain the batteries life. For example, the GivEnergy 9.5kw battery is advertised as 100% depth of discharge but in reality the battery is actually 10.5kw with a 90% Depth of discharge. Where as the Tesla Powerwall is 14kw battery it has a DOD of 96%, so you actually get 13.5kw in reality.
You will need to look at the data sheets of the batteries to understand what capacity you are really being offered.
Charge/Discharge Power:
The charge and discharge power of a battery is probably the most important element of any system design. This describes the amount of power the battery can use to charge up and how much power it can use when needed. A batteries charge and discharge rate are often the same and described in watts or kilowatts. So your cheaper battery may have a charge/discharge rate of 2.5kw, now if you think when you boil a full kettle this is going to use around 3kw, so this battery will supply 2.5kw of power, as this is the maximum it can do and the grid will make up the additional 0.5kw. Where as if your battery has a charge/discharge rate of 5kw then the battery would cover the use of the kettle and more.
So, and here is the really important part, knowing the kilowatt rating of your appliances is really important and your installer should ask about this to help design the best system for you. If all you have is a kettle and an oven then you will need a battery with a charge/discharge rate of around 3kw, but if you have a heat pump or electric shower then you will need the highest battery charge/discharge rate you can get which is around 5kw. Otherwise every time you use these higher rated appliances you will be pulling much more electricity from the grid and you may not see the benefit your organically thought you might see.
Again this information is shown on the equipment data sheets.
Off Grid back up:
A common misconception of having battery storage is that you will have power if there is a power cut. This is not the case for most installations and if this is an important aspect for you make sure you tell your installer as this functionality can be done, but generally not within a standard install.
When you have battery storage, you will have some form of inverter attached to it and this inverter needs power from the grid to work, so in the event of a power cut the inverter switches off and you cant access the electricity within your battery (this could be pretty frustrating if you weren’t told). If you wanted to have backup ability then additional equipment is required to fool the inverter into thinking its still connected to the grid and provide power from your battery and solar.
Talk to your installer about this when they agree to provide a quote.
Location of Installation:
Home battery storage is very new technology as as such regulations are changing quickly to keep up with the risks involved with having large scale lithium batteries within the home. There are currently no restrictions as to where batteries can be located in the home and common locations include lofts and garages.
New codes of practice are suggesting that having batteries located outside is the best solution but this is not a regulation yet.
The main risk of lithium batteries is fire, and this is why installing them in lofts is now considered if no other alternatives are available because areas of the home that are not accessed regularly means issues can go unnoticed for long periods of time and signs of a potential issue could be missed.
It is now a recommendation that smoke alarms are fitted in any room with a battery and ideally these smoke alarms will be radio linked to existing smoke alarms within the house.
An awkward point in this discussion is that batteries need to be located usually within 1m of the inverter, so depending on the home, it is ofter not possible to install the battery externally without also locating the inverter outside too and all batteries also have optimal operating temperatures which need to be considered when locating them outside to ensure optimal performance through the colder months. Housing the equipment in some kind of enclosure is advisable.
Ask your installer on the latest regulations as these will change quickly.
Scaleability:
Working out a homes battery requirement is quite difficult, this is due to there being very little data about the daily usage patterns of a families electricity (this is getting better with smart metering). It is really important that any battery you have installed gets used year round, as any time it becomes empty for long periods of time can have damaging effects. One suggestion is think about scalability, do i need all of the batteries right now? The answer to this is probably, No.
When you have a solar installation, if your installer is any good they will install solar monitoring software for your to access on your phone or PC. This information tracks your energy usage daily and can be a huge help in battery sizing. The sensible option is to get a reasonable sized battery based on your annual usage and then add additional storage over time depending on the detailed reports you have available.
Talk to your installer an ensure the batteries they offer are scalable for future increases in capacity and ask how much extra storage can be added as this varies a lot between manufactures.
Conclusion:
So as you have probably worked out, not all batteries are the same and if you want to maximise the performance of your batteries then spending a bit more money at the installation stage will have a huge impact on how and when you import electricity from the grid especially when you have the power in your battery.
