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Solar Batteries: Energy Storage for Solar Panels Explained

duracell manufacture solar batteries for storing generated electricity
Duracell's Energy Bank 2 is a new product, replacing the brand's existing solar battery offering. It has launched in Australia and is making its way over to UK shores soon. (Image credit: Duracell)

Solar batteries effectively allow you to make use of the electricity generated by your solar panels when you need it most. While they might sound like a niche purchase, they're actually growing in popularity of late. 

Energy provider Ovo Energy is currently undertaking a solar battery trial with a select group of its customers, for example, to test on a wider scale how solar batteries can be used to not only harness electricity from renewable sources, but better manage our homes usage and even potentially feed back into the grid at times when electricity usage is at its peak. 

If you're investing in solar PV panels, it might seem like an obvious addition to your set-up, but there's certain elements you need to consider before you commit to solar batteries — including the price. 

Get to know solar batteries better in this expert guide, and discover whether they have the potential to offer a real return on your investment. 

What are Solar Batteries?

Solar batteries are often referred to as a home battery — a means of storing electricity produced during the day so that it can be used at a different time. 

The battery is either charged up during the day by solar PV panels or can be charged up during off peak electricity times when the electricity is cheaper.

The generation is either stored as Direct Current (DC) before it gets to the inverter or as Alternating Current (AC) after the inverter. 

If you have a system that pays you incentives for generation then you will have marginal losses if you choose a DC system. 

However, if you are installing a three phase electric supply and a three phase inverter then a DC battery system could be more beneficial.

(MORE: 9 Great Projects with Solar Panels)

solar batteries

(Image credit: getty images)

How Much Energy Can I Store in a Solar Battery?

Solar battery systems for the home come in many different capacities. 

The capacity is measured in kilowatt hours (kWh). 1kWh is a 1000 Watts used for 1 hour. So, in theory, a 1kWh battery would run 20 LED bulbs for around 9 hours, or a typical modern fridge for around 6 hours continuous running. 

Many battery systems have a fixed storage capacity starting at around 2kWh to 14kWh but there are also systems that allow you to add capacity by building extra battery modules on to the system to increase the energy storage. 

How Much do Solar Batteries Cost?

Solar batteries vary in cost depending on their battery capacity and energy rating.

Home solar battery systems start from around £400 per kWh. The Tesla Powerwall 2 is a 14kWh system and you would expect to pay around £5,500 for one.

Other brands can vary in price up to around £800 per kWh but it is important to research each product to see how they work and whether they will be optimised for you. 

The cost can vary depending on:

  • Battery life cycle
  • Storage capacity
  • The usable capacity
  • Chemical materials and how its made

Solar Batteries - Solar Watt Solar Batteries

(Image credit: Solar Watt)

Different manufacturers use different discharge management software that will affect the way the system works. 

Luckily the cost of home battery systems is also due to drop as more electric vehicles go into use and some car manufacturing companies, such as Nissan, are recycling used car batteries into home systems. 

These second life batteries will certainly be the way to make home batteries more affordable.

Pros and Cons of Solar Batteries

There are many reasons a solar battery is a good idea to supplement your solar PV set up:

  • The ability to store surplus electricity generated for future use, rather than being required to export it
  • Reduction in utility bills
  • Store solar electricity can be exported back to the grid, making a small amount of money for the owner
  • Ability to be independent from the electricity grid 

However, there are also some limitations to consider:

  • High end solar batteries have large upfront costs, which will take time to offer a return on investment 
  • Solar batteries have a relatively short lifespan, with some models as low as five years, and others maxing out at 15 years. This is less than half the lifespan of the average solar PV panel
  • Not all electricity suppliers will allow electricity to be exported back to the grid 

Is it Worth Installing Solar Batteries?

As the cost of solar home batteries comes down and the amount of generation we use increases so will the return on investment increase. 

It is worth checking how much export generation you have from your PV panels and then work out how much of that you could actually use if you had a home battery system. 

(MORE: Can You Run a House on Solar Power?)

Tesla's PowerWall solar battery

Tesla's Powerwall reduces your reliance on the grid by storing solar-generated electricity. In case of a power outage, the Powerwall kicks in, seamlessly powering your appliances for up to several days.  (Image credit: Tesla)

What are the Best Batteries for Solar Storage? 

The best home battery for solar storage will depend greatly on what you want to do with the energy. 

Perhaps your car is the best storage battery as the energy goes directly to the car battery from the solar array and you will not need to redeploy it elsewhere. 

It is almost more important to look at the energy management capabilities of the home battery system and make sure that it matches your requirements. 

Optimising Solar Battery Use

Installation Advice

A home battery system must be installed by a suitably-qualified and experienced installer. Different battery systems behave in different ways and they need to be wired and commissioned to best optimise their use and prolong their life expectancy.

The best way to optimise the use of a home battery system is to use the energy stored to run electrical appliances rather than turn it into hot water.

Also make sure that you do not run too many appliances at once as the demand will be higher than the maximum discharge rate. 

By staggering the start up times of different appliances you can then aim to use 1 kWh for four hours which is better than 4kWh in hour hour because the home battery cannot usually discharge 4kWh.

Do I Have to Have Solar Panels for Solar Batteries?

Actually, no. Solar batteries can also work to store electricity bought from the grid. You might be wondering why you need to do this, but it may be useful in the future when time-of-use tariffs become more widely available in the UK. This is where energy providers try to encourage its users to use more electricity at off-peak hours than peak hours with a cheaper price. Your solar battery can take store electricity from off-peak hours to use at peak hours in this instance. 

How Long Will a Solar Battery Last? 

The life expectancy of a solar battery depends very much on how it is used. The storage capacity drops annually and it is expected that the battery will last somewhere between five and 15 years. Keep in mind that the average solar PV panel will last 20-30 years, so you may need to change these twice (or more) in the lifespan of your panels. 

Are Solar Batteries a Good Solution for Off-grid Homes? 

Solar battery systems are the primary solution for off grid homes. The battery systems are, however, set up differently as there is no electricity grid backup. There is more emphasis on appliance and demand management. 

(MORE: Guide to Off Mains Heating)

How Will Electric Cars Affect the Future of Solar Batteries?

Home solar batteries will become cheaper as we see an increase in the use of electric cars. 

Some car manufacturers, such as Nissan, have collaborated with battery suppliers to use the car batteries after they are no longer good enough for the cars. 

The largest home battery systems are around 14kWh but cars start at around 28kWh and can be up to 100kWh plus. 

When the capacity drops the batteries are then used to make home battery systems and this ‘second life’ battery will be significantly more cost effective when the turnover in cars increases. 

(MORE: Charging Your Electric Car at Home

Solar Battery Providers 

Below are some of the most popular solar battery providers that you can look into before buying your battery: 

David Hilton

David is an expert in sustainable building and energy efficiency and is also director of Heat and Energy Ltd.