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Battery Storage and Electric Cars

Electric cars have batteries which store electricity to power their electric motors. But you can also install battery storage at home or at work.

What’s the point of battery storage? Well, if you have solar panels, home battery storage allows you to capture surplus solar electricity for later use.

You can even charge batteries with cheap, night-time electricity and then let it out during the day to replace more expensive day-time electricity.

Energy stored in a home or workplace battery can also charge your electric car. Read on for the full story.

Table of Contents

  • What is Battery Storage?
  • Benefits of Battery Storage
  • How Can I Charge My Car with Battery Storage?
  • What is Solar Panel Battery Storage?
  • Makes and Models
  • Solar Battery Storage System Cost
  • Is Battery Storage Worth It?
  • Battery Storage FAQs

What is Battery Storage?

Battery storage consists of rechargeable, lithium-ion battery cells.

Manufacturers package all these battery cells up into one or more convenient containers to hide all the messy wiring and electrical gubbins.

The battery is connected to your home or work fuse board. There are then two scenarios:

  1. The battery charges with solar electricity – if you have panels installed – and/or cheap electricity from the grid (assuming you have signed up to a tariff with a cheap rate).
  2. The battery then discharges the stored electricity when devices in the home or at work ‘call for’ electricity. This could be you turning the lights on or plugging in your electric car.

Once set up, battery charging and discharging happen automatically.

Electricity stored in the battery will always discharge if you need electricity, replacing electricity from the grid.

When the battery is empty, then all of your electrical needs will be met by grid electricity, until the battery charges up again.

Benefits of Battery Storage

Battery storage is useful for a number of reasons:

  • Capture surplus solar electricity if you have solar panels
  • Store cheap, off-peak grid electricity
  • Discharge stored electricity to your home or work-place
  • Charge your electric car from stored electricity (either solar or grid energy) to save money
  • Power individual devices – or even your whole home – in the event of a power-cut

The last point works a treat if you have power-cuts from time to time. With the right type of battery storage, you won’t even notice there’s been a power-cut. Your lights and electrical equipment will just carry on working until the battery runs out of juice.

How Can I Charge My Car with Battery Storage?

The most environmentally friendly way of charging your electric car is with energy from a renewable source. For most people that means solar panels.

So you get solar panels installed at home. But let’s say you drive your electric car to work every day. You can’t then charge your car with that precious solar energy because your car is in the wrong place! It’s at work rather than at home where your panels are.

The solution? Battery storage. The battery will soak up some of the excess solar electricity generated during the day that your home doesn’t need.

When you come home and plug your car in, that stored solar electricity can then flow out of the battery, through the charging point, and into your car. Bingo!

What is Solar Panel Battery Storage?

Solar panels can be installed either with or without battery storage.

If you have solar panels without batteries, then any electricity you don’t consume at the moment it’s generated by the panels escapes to the national grid.

If, on the other hand, you do have battery storage, then you can store some of that excess solar energy before it escapes to the grid.

Solar panel battery storage is therefore simply a solar panel system combined with battery storage, designed to capture and use as much of the solar electricity as possible.

Want to know more about solar panels? Check out our Solar Panel Guide.

Which Battery Should I Choose?

Makes and Models

There are now quite a few manufacturers of battery storage. Some of the largest and most popular makes include:

  • Tesla
  • Sonnen
  • LG
  • SolaX
  • GivEnergy
  • SolarEdge
  • Alpha

Probably the most well-known of all of these is the Tesla Powerwall. It holds 13.5 kWh of electricity and comes as standard with back-up capabilities in case you lose power.

The average UK home needs about 8 kWh of electricity per day, so a Powerwall could comfortably power your home for a day, with capacity to spare.

Solar Battery Storage System Cost

The cost of lithium-ion battery storage will gradually come down over time, as demand for electric vehicles and both home/work and grid storage increases. Want to give it a go now? Here are some pricing guidelines:

Domestic Battery Storage

The cost of home battery storage depends mainly on the following factors:

  • How much electricity the battery can store, measured in kWh
  • Whether it’s capable of providing emergency power in a power-cut
  • The length of the warranty
  • How much the battery cells will degrade over the warranty period
  • Whether the battery can be mounted outside
  • The quality of the materials

At the premium end of the market, you have the Tesla Powerwall (13.5 kWh). It ticks pretty much all of the boxes and costs around £10,000 to have installed. Alternatively, if you don’t need such a large battery, you could get say the smaller GivEnergy (8.2 kWh). That would cost around £6,000.

Commercial Battery Storage

Why would a business want to install battery storage?

Most likely if they already have a solar panel array which is generating more electricity than they need. The batteries will capture some of the surplus.

Commercial battery storage systems often comprise the same batteries as you would find in a home system – but more of them.

As companies usually have heavy-weight 3-phase electricity supplies, there will be one or more batteries on each phase.

For example, a Tesla Powerwall system for a business could have 3, 6, 9, 12, etc., Powerwalls depending on how much storage was required.

If it were a 3 x Powerwall set-up, it would cost about £30,000 inc. VAT (i.e. £25,000 + VAT).

Is Battery Storage Worth It?

If you have solar panels and want to be more independent of the national grid, battery storage makes a lot of sense. If energy prices continue to rise, the payback period for battery storage will keep improving. Choose batteries with a strong warranty covering a period of at least 10 years.

Is battery storage worth it overall? Here are some pros and cons:

Pros

  • Capture more of your precious, zero-cost and zero-emissions solar electricity
  • Charge with cheap, off-peak electricity and discharge when rates are higher
  • Get that ‘energy independence’ feeling by importing less energy from the grid
  • Have emergency power if there’s a power-cut (specific models only)

Cons

  • Battery storage is still quite expensive
  • Some warranties are stronger than others – read the small print 


Battery Storage FAQs

Here are Answers to Frequently Asked Questions about battery storage:

Battery storage is basically a type of rechargeable battery.

When charging, it receives electricity which is stored inside the battery. Sometimes an inverter is needed to convert the AC electricity being received into DC electricity that the battery can store. These batteries are known as ‘AC-coupled’.

When discharging, this process happens in reverse. DC electricity flows out of the battery and is converted into AC electricity that the home or workplace can use.

In some types of solar panel installation, the battery is ‘DC-coupled’ and never needs to make AC to DC or DC to AC conversions.

In all cases, charging and discharging happens automatically – no user intervention is required.

Solar panel systems generate electricity when the sun shines on them. However, if you don’t use that electricity at the moment it's generated, the solar electricity will flow out to the grid and you won’t be able to get it back again!

One way to capture some of that surplus solar electricity is to install battery storage. The brain inside the battery will notice that excess solar electricity is about to be exported to the grid and divert it instead to charge the battery.

So solar panels combined with battery storage allow you to capture and consume more of your green, zero-cost, emissions-free solar power.

Good question! This idea is often called Vehicle to Grid or V2G. You will also see it referred to as Vehicle to Home or V2H. It’s an emerging technology which could revolutionise how EVs and homes/workplaces interact.

It’s already possible today with the Nissan Leaf. The Leaf has so-called ‘bi-directional charging’ via its CHAdeMO port. Electricity can either flow from the home into the car, or from the car into the home, as long as you have a special charging point installed.

With bi-directional energy flows, you could indeed use your electric car to power devices in your home. However, it looks as if CHAdeMO is losing the war of the charging standards to CCS. Bi-directional CSS charging is still in its infancy, though it may be possible in the UK when the Ford F-150 Lightning comes over to our shores.

Lithium-based home battery storage is quite expensive. It’s still a relatively new product and manufacturers have not yet achieved economies of scale.

However, the battery cells in home storage are very similar – and sometimes identical – to the cells you find in electric cars. With the imminent exponential growth in EVs, and the corresponding need for batteries to power the cars, battery manufacturing will become a huge growth industry and prices should gradually start to come down.

Battery ‘gigafactories’ are being planned all over the world in the coming months and years. Expect prices to reduce as these giant manufacturing plants come online.

Home and workplace battery storage is mainly made of lithium-ion. However, other chemical elements are combined with the lithium.

For example, the Tesla Powerwall has a lithium nickel-manganese-cobalt (NMC) battery chemistry. Another large manufacturer, Sonnen, uses lithium iron-phosphate.

All these chemical elements have different characteristics: some help make the batteries last longer; some give the battery a higher energy density, and so on.

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