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A guide to storage batteries


On a dark and gloomy day, how effective are solar panels? That’s typically the question on everyone’s mind when considering a purchase. Thankfully, we are now being introduced to the world of storage batteries, which can be charged during the day to fully kick in when your solar panels are less effective, giving you a back-up source for when the sun is hidden away. Thanks to this storage, we could see more homes opting for a solar-powered future as well as across-the-board savings on energy bills.

What is a storage battery and how does it work?

Your typical everyday battery consists of several cells and connectors to power various everyday devices, going from your phone to your watch. Just like any other battery, storage batteries consist of three parts, an anode (-), a cathode (+), and the electrolyte. The chemicals inside batteries cause a build-up of electrons at the anode once connected to an electrical circuit. In a rechargeable battery, they produce current in the same way, however, this time the negative-to-positive flow of electrons is reversed to restore charge.

Solar storage batteries rely on solar panels, which contain solar cells on the surface to collect energy from the sun. These photovoltaic (PV) panels convert the sun’s energy by springing electrons into life using photons from sunlight. The same energy is passed through an inverter and converted into power that can be used directly for your home or stored. Storage batteries work by storing excess solar-produced power for use at night or darker days, which is a cost-effective solution as opposed of selling it back to the power grid. In order to decide on a solar-based storage battery, you should take into consideration their useable capacity, cycles and power output.

Choosing a storage battery

To get you on your way to choosing the right storage battery for you, we have listed the key elements below so you know what to look out for:

  • Useable capacity – This refers to the amount of energy (measured in kWh) that the battery can store. You will normally find that some batteries are advertised as being 6kWh when their useable capacity really is closer to 5.5kWh. The reason for this is that none of these batteries should drain to zero, thus reducing the risk of damage.
  • Cycles – One complete discharge and one complete charge is called a cycle. You will find some manufacturers advertise how many times their batteries can be charged, and typically this will be in the thousands. For example, if your phone has an advertised lifetime of 1200 cycles and you fully charge your phone in the morning and use it all day till the following morning, you should expect the battery to last approximately 3 years before it loses its effectiveness.
  • Power output – It’s incredibly important to remember that the power output has to be up to scratch to be able to power even the smallest of devices through to your whole household. If you consider the number of devices and appliances in a typical home, you may be better off going for a larger solar battery to cater to this demand.

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The storage battery market

There is now a growing selection of storage batteries for solar energy on the market brought to you by various manufacturers, all trying to innovate and tackle some of the key challenges within solar power.

The most notable is Tesla, who launched their “Powerwall” storage battery in 2015, which has a storage capacity of up to 10kWh and can power a home for up to 8 hours. Whilst Tesla continues to innovate, they went on to create the Powerwall 2.0 which can store up to 14kWh of power, which is able to power an average household for an entire day. In true Tesla fashion, they have also made the batteries aesthetically pleasing with a simplistic design, moving away from bulkier and bog-standard batteries.

Whilst Tesla makes their Powerwall battery available primarily to US homeowners, it is available to UK consumers too. However, the Powervault is commonly described as our very own UK-based home battery storage alternative to Tesla’s offering. This battery in particular has been built to suit the individual needs of a typical British household, with a capacity of up to 6kWh and a unit about the same size as your typical washing machine. Powervault also claim that they can reduce your electricity bills by 20% as well as the benefit of having the lowest cost energy storage product available in the UK.

SonnenBatterie is another example of storage battery innovation this time brought to you by a German team, with a minimum lifespan of 10,000 charging cycles as well as varying storage sizes from 2 through to 16kWh depending on your household’s energy needs.

What's the cost of a storage battery?

The solar panel battery cost for your home is entirely dependent on the capacity you’ll need to be suitable for an extended period of time. It is also important to note that your household will still be reliant on the national grid’s energy whilst this technology is still being developed, so while you will see a reduction in your monthly energy bills, you will have to wait a few years to see a full return on your investments.

To start off, Tesla’s Powerwall will set you back around £5,400 which includes the installation of a converter as well as the 10kWh battery. In terms of the Tesla Powerwall alternatives, the Powervault costs approximately £2,000 to £2,800 for a battery between 2 and 6kWh. There are also many offers being made available by solar installers in the UK, with a 4kW solar panel system and 4kW energy storage battery costing between £10,000 and £12,000. Whilst this is a large investment, you will see the benefits of investing in a package to be installed together for longevity purposes and investment returns within a few years.

Whilst the technology is still relatively new, it is certain that the cost of a battery as well as installation will also be a lot lower in years to come. We also start to see IKEA starting to innovate within solar as well as battery storage to separate themselves from the competition, which is a clear sign that other companies will follow suit.

Below we have summarised the basic stats for each of these storage batteries:

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 Tesla Powerwall IIPowervaultSonnenbatterie
Storage capacity14 kWh2-6 kWh2-16 kWh
Warranty10 years3,5 or 10 years10 years
Price£5,400£2,000 - £2,800£3,800 - £14,500