Energy

Home battery storage explained

From making the most of your surplus energy to storing cheap, night-rate electricity, our solar battery guide has everything you need to know including how much you can save

What is a home storage battery?

Home batteries store electricity generated from solar panels or other sources, so you can use energy at a time that suits you.

They work just like a rechargeable mobile phone battery and most are made from the same material: Lithium-ion. Batteries can maximise savings and help you make the most of the electricity you generate at home.

You can choose to charge your battery using:

  • Surplus solar panel energy: electricity generated by solar panels during the day can be stored in your battery and released in the evening, to light and power your home.
  • Energy from the grid: if you have a smart tariff and the right type of connection, you can also charge your battery from the grid during off-peak hours when energy is cheaper, for use when electricity is more expensive.

You can also convert electricity to heat, and store it in a heat battery or a hot water tank to heat your home and water.

Why would you need one?

Most homes won’t use all the electricity generated by their solar panels.

This surplus energy can either be sold back to the grid, stored in a solar battery, or - depending on how much surplus energy you produce - both.

Given the high cost of electricity, using energy from your solar battery usually means greater savings in the long run.

Types of batteries

Batteries vary from the material they’re made from, to the type of system you install and how it connects to your home.

There are two main types of battery:

  • Lithium-ion: This is the most popular type of battery, with the longest lifespan and a higher Depth of Discharge (DoD) - they can be more depleted before needing to be recharged.
  • Lead Acid: An older type of battery which doesn’t last as long as lithium-ion, but which is cheaper to buy.

AC vs DC systems

Energy generated by solar panels can not be directly used in our homes.

Our homes and electricity grid use AC (alternating) current, while solar panels produce DC current (direct current. Batteries also store DC current.

The energy is converted before we use it, using an ‘inverter.’ There are two types of batteries which do this in slightly different ways:

DC System

  • Solar panel energy flows to your battery first.
  • As panels and batteries both use DC current, there’s no need to convert energy before it is stored.
  • Before you use the battery’s energy in your home though, it needs to be converted to AC current.
  • As you only need to convert the electricity once, a DC system is more efficient.

AC System

  • Solar panel energy flows to your fuse board first.
  • The panel’s DC current needs to be converted to AC energy before you use it.
  • Any surplus electricity is then stored in your battery, but needs to be converted back to DC current before being stored.
  • This double conversion makes AC systems less efficient.

Which battery storage system is best?

The battery type and system you choose depends on a number of things. They include:

  • Solar panels: If you are adding a battery to pre-existing solar panels, AC systems are easier to retrofit and cheaper to install. If you’re installing new solar panels, a DC system might be a better, more efficient option.
  • Energy goals: Because there is only one inverter in a DC system, it’s easier to obtain permission to connect to the grid. So if you wish to sell surplus energy, a DC system could be a better option.
  • Budget: DC systems are usually cheaper but less versatile than AC systems, especially if you already have solar panels. Older, lead acid batteries are also cheaper than Lithium-ion.
  • Efficiency: DC systems and Lithium-ion batteries are typically more efficient than the other types.
  • EV ownership: DC systems can be used in more applications, such as electric vehicle charging.

Both DC and AC systems can charge from the grid.

How many batteries do you need?

It depends on your energy consumption, solar panel output, the battery’s storage capacity and how many days you’d like your batteries to provide power (called autonomy of power).

But for the average household - consuming 4,200kWh per year with a standard, 13.5kWh battery and allowing for 2-3 days of battery power - two batteries should suffice.

How much do solar batteries cost?

Solar batteries can add between €1,500-€4,000 to the cost of solar panels. A number of things contribute to the cost, including:

  • Capacity: The more energy your battery can store, the more expensive it will be. An 8kWh battery could be sufficient for an average, 3-bedroomed home.
  • Warranty: Although solar battery warranties can last up to 10 years, a shorter warranty is usually cheaper.
  • Type: AC system and acid lead batteries are often cheaper than the other types, but also less efficient.

How much can you save?

According to Purevolt.ie, the total potential savings in one year, based on a typical solar battery installation and on Electric Ireland night and day rates as well as current export payments, are:

  • Solar panel storage: €238.14
  • Grid, night-rate storage: €271.63
  • Annual Total Savings: €509.77*
  • Payback (years): 4.9

Total savings by end of warranty: €4,465.15

Total profit by end of warranty: €1,965.15

*Rates based on Electric Ireland’s Home Electric+ SST, correct as of Jan 2024

What grants are available?

Unfortunately, the government removed the solar panel battery grant in February 2022 due to the introduction of the Microgeneration Scheme. However, you can still get a grant of up to €2,100 for solar panel installation.

Are solar panel batteries worth it?

Solar panel batteries have a wealth of benefits, including energy independence and longer term savings. Whether they’re worth it for you depends on things like your energy usage as well as your budget.

Here’s some pros and cons of batteries:

Pros

  • Lowers bills: Solar batteries can reduce electricity costs by storing surplus solar energy or low-cost, night-rate energy for use during peak energy hours.
  • Provides energy independence: If they’re large enough, solar batteries can provide backup power during outages, and support independent, off-grid living.
  • Reduces carbon footprint: Coupling your solar panels with a battery means using clean, renewable energy more efficiently.

Cons

  • Expensive: Solar batteries can add to the already high cost of solar panel installation; though they can mean longer term savings.
  • Maintenance/replacing: Depending on your battery’s warranty, it will need replacing once every 4-11 years, as well as yearly maintenance.
  • SEAI grant removal: Now that the government promotes ‘Microgeneration’ or selling electricity back to the grid, they have removed the solar battery grant.

Where can you buy storage batteries?

If you’re buying your solar panel battery as part of a package with your solar panels, your solar panel installer should recommend the best type of system for your needs.

Solar panel battery installers in Ireland include:

  • Eco Horizon
  • Electric Ireland
  • Energia
  • Flogas
  • NGR Panel
  • Pinergy
  • Pure Volt

Popular manufacturers used in Ireland include:

  • Tesla Powerwall 2
  • Sonnen GmbH
  • Solarwatt

Tesla powerwall solar batteries

Battery storage vs selling back to the grid

Although batteries have a high up-front cost, given the volatile price of electricity, they could mean greater savings vs selling surplus electricity back to the grid. For example:

  • Sell: Selling surplus electricity to Electric Ireland will get you 21c per kWh
  • Buy: Buying it on Electric Ireland’s time-of-use-tariff would cost around 33c/kWh for 24 hour rate, 40/kWh for day rate, 43/kWh during peak rate and 21/kWh for night rate.*
  • Store: You could save approx20c per kWh just by using energy from your battery during peak hours vs selling it to the grid.

*Prices correct as of Jan 2024

Solar battery installation

Most solar panel installation companies will install a battery with your system if required. Or, you can install your battery separately, at a later stage.

Depending on the size of your home or whether you have solar panels already, your installer will advise what battery storage system is best.

Before choosing an installer, you should ensure they are:

  1. Accredited: Make sure the installer has the correct certifications or is registered as a solar panel installer with the SEAI
  2. Trusted: Check sites like TrustPilot, look for examples of previous work or take recommendations from friends
  3. Offer a fair price: Always compare quotes from multiple installers to ensure you get the best deal

Storage battery FAQs

Should you get a battery with your solar panels?

You can buy your battery as part of a package, with your solar panels, or you can purchase it separately at a later stage.

Can you use a storage battery without solar panels?

Most often, they’re used alongside solar panels, but they may also be useful if you have an energy tariff that offers cheaper electricity at off-peak times.

How long will a 5kWh battery last?

Typically, a 5kWh solar battery can last approximately ten hours when you’re only running a few appliances, such as your TV, and fridge.

A fully charged 10 kWh battery should allow you to power your home for 24 hours.

How much does Tesla Powerwall cost?

Although it varies depending on where you buy it, the Tesla Powerwall can cost approx €7,000, excluding installation.

What is the life expectancy of a solar battery?

Most solar batteries will last between five to 15 years.

Switch and save up to €639 on your energy bills

It only takes a few minutes to find a cheaper deal and start saving