A comprehensive guide to batteries for solar panels

If you have a solar PV system, you might be curious to learn more about batteries for solar panels. A solar battery system to complement your solar power production could give you more control of your electricity costs and help you make the most of your investment in solar.

Here's our ultimate guide to the potential benefits of a solar battery system, the types of solar battery technology available, what to look for in a home solar battery and more.

 

How does a solar battery system work?

The short version is this: Your solar panels catch the sun’s rays and your solar PV system generates electricity while the sun is shining on those panels. You can use this electricity produced by your solar PV system while the sun is shining – and any excess is usually fed back to the grid. If you have a solar battery system, excess solar power generated can instead be stored by the battery for you to use when your solar PV system isn’t generating electricity to meet your demand, for example at night or on cloudy days.

For more details on how solar batteries work, check out our guide to solar battery storage.

 

The potential benefits of batteries for solar panels

WA is already making the most of the potential benefits of battery storage technology through the installation of community batteries and large-scale Battery Energy Storage Systems (BESS).

Battery storage for individual homes and businesses isn’t as common as solar PV systems across WA, however it’s likely to become more popular as it becomes more affordable. Here are some of the reasons you might consider a solar battery system for your home. 

  • Make the most of your solar PV system:

    With a home solar battery, you may be able to self-consume more of the solar power your system generates by using the excess stored in the battery when the sun isn’t shining. This means you could require less electricity from the grid, which could help to reduce your electricity costs.

  • Renewable energy:

    Adding solar battery storage to your solar PV system means you could utilise even more of the power you generate from a renewable energy source. Electricity from the grid currently comes from a mix of generation sources, including fossil fuels. Tapping into your battery means you could use more of your solar energy to power your home or business – and this could also help offset your carbon footprint. 

  • Time of use electricity:

    Time of Use (TOU) tariffs are becoming more popular for people who want to take greater control over their electricity costs. TOU tariffs have different electricity prices depending on what time of day you use electricity. Generally, there’s a higher rate during the late afternoon and evening (e.g. 3pm – 9pm) when demand for electricity from the grid peaks. 

  • Backup power:

    Some (but not all) battery technology allows you to back up important circuits in your home. If your solar battery system has this capability, you may be able to keep your essential appliances such as your fridge, lighting and heating and cooling running during a power outage. We take a further look at using your battery as a backup power source in more detail later in this guide.

If you’re considering a home solar battery to disconnect from the grid, it’s important to know that you need to invest in extra equipment. You might also need a petrol or diesel generator as a further backup if you’re looking for a stand-alone power system to disconnect from the grid completely.

 

The most common types of solar battery

These are the two main types of solar battery you might find for home or business use:

  • Lithium-ion – This is generally a reliable type of battery in terms of its lifespan and depth of discharge rate. Lithium-ion batteries are popular for home and business use because they are more compact – but these are more expensive compared to lead acid batteries. Examples of lithium-ion types of solar battery include the Tesla Powerwall and sonnenBatterie. 
  • Lead acid – This type of solar battery has been used for decades and is one of the cheapest varieties. However, some consider that this type of battery technology is becoming outdated – and it has a lower depth of discharge (DoD) rate compared to other battery types.

 

Other types of battery energy storage systems and solar power solutions

Electric vehicles have their own battery technology which could potentially be used as a home battery in the future. This option is not available widely in Australia yet but here’s how it works:

  • Some electric vehicle (EV) manufacturers are creating ‘bi-directional’ EV chargers which can make certain models ‘vehicle-to-grid’ capable. 
  • This means that energy stored in the car’s battery could be used to power the home or sent into the grid for electricity users. 
  • Owners of electric vehicles could then charge their EV from a solar PV system during the day or from the grid overnight when electricity prices may be lower and then tap into the energy stored in their EV battery when electricity prices are higher to power their house.

Other types of solar power solutions are already used in many homes on a small scale. For example, you might have solar powered fairy lights or lanterns. These usually come with one mini solar panel which stores solar energy in an internal battery throughout the day, then the fairy lights or lanterns draw on this battery to light up when the sun goes down. If you can position the charging panel in a sunny spot inside, you may be able use solar powered lighting in this way to add a glow to your home without needing to switch on a lamp.

 

Is it worth investing in batteries for solar panels?

Recent design improvements and price drops in lithium-ion batteries have made energy storage more affordable, but the upfront cost is still relatively high.

With a solar battery system, you can charge your battery with the electricity generated by your solar PV system during the day that you don’t consume at the time. Instead of drawing from the main electricity grid, when your solar PV system isn’t generating you can then use the energy stored in your battery to power your home, before drawing electricity from the grid. This is where your investment in a battery might start to pay off if you draw less power from the grid, reducing your electricity costs.

If you’re on a time of use electricity plan, such as our Synergy Midday Saver, you may be able to use your excess electricity generated by your solar PV system that is stored in your battery power during peak tariff times instead of using electricity charged at peak tariffs.  You may also be able to charge your battery during off-peak times, so you are using a mix of stored solar power and off-peak tariff electricity during peak tariff times.  This could help to reduce your electricity costs.

 

Battery details to know: Battery lifespan and depth of discharge

Generally, a battery’s lifespan is somewhere from 5 to 15 years before it needs replacing depending on a variety of factors and how it is used. However, some battery system owners run their battery at reduced capacity towards the end of its life to stretch out its lifespan before they replace it. Always follow your manufacturer’s recommendations.

Depth of discharge (DoD) is a measure of how much a battery can be used (or the amount of power discharged) relative to its total capacity before it is flat. For example, if a battery has a 100% DoD, this means you can use the full battery storage amount (or capacity) to power your home (e.g. for a 2.5kWh battery, you could use 2.5kWh or kilowatt hours) before your battery would need to charge again. If a battery has a 94% DoD, this means you can use up to 94% of the battery capacity (e.g. for a 2.5kWh battery, you could use 2.35kWh) before your battery would need to charge again.

 

Things to look for in a solar battery system

If you decide to make the investment in battery technology, it is worthwhile to do your homework. Make sure you consider the following:

  • Your power needs – Here in Australia, households will generally use up to 20 kW per day, depending on the size of the household and individual electricity requirements. You might use 10 units at night for things like your lights, fridge, TV and cooking dinner. This is without factoring in power-hungry appliances you might have on at certain times of year such as reverse-cycle heating and air-conditioning. You should check that your battery will be large enough to cover your energy needs after the sun has gone down so you can reduce the amount of grid-supplied electricity you need to pay for.
  • Warranty – These are usually given in years or cycles. A solar battery cycle refers to the battery completing a full charge and discharge. The “Cycle Life” of a solar battery is the number of times the battery can perform a full charge discharge cycle before losing performance. For example, a solar battery system might have a warranty of 10 years or 10,000 cycles (whichever comes first).

  • Power capacity – This is the amount of electricity which can be stored in the battery. Many types of solar battery are stackable, which means you can increase your storage capacity with more than one battery.

  • Depth of discharge (DoD) – The higher the DoD, the more power you can draw from that battery. As your home solar battery gets older, the amount of energy you can draw from it will gradually get lower. An older battery, even when it’s fully charged, just won’t have the same amount of power available as when it was new. 

  • Battery technology - Some solar battery systems will come with an app or monitoring tool. This may help you use real-time data to track your system including how much power you generate, store and use to monitor your battery’s performance.

  • Price per kilowatt hour – A battery that might seem too cheap could be worth investigating further. Look at the price per kilowatt hour. Smaller solar batteries can often be priced more competitively but these might not meet your electricity needs.

As with buying a solar PV system, always investigate the quality of the products and the company installing the products itself. Check how long the battery manufacturer has been in the market, especially if it’s a brand you haven’t heard of before. Also consider whether the brand has a local office in Australia you could contact if you need help with service, repairs and warranties.

 

Watch out for cheaper types of solar battery

Solar battery storage is expensive but be careful when considering cheap options. Just as with buying a solar PV system, it’s likely that you’ll get what you pay for.

Lithium based batteries can generally store large amounts of energy. These batteries also generate heat when they charge and discharge and if this process fails or there is an electrical fault, “thermal runaway” can occur and present a fire risk.

There are two common types of lithium battery, the two types are:

  • lithium-ion: NMC
  • lithium-ion: lithium-iron (also called LFP or LiFePo4)

It is important to be aware that NMC solar batteries may catch fire more easily and could burn for longer than lithium-iron batteries.  The bottom line is that it’s not worth risking your safety to save money on a solar battery system. 

 

If you’re considering home solar battery for backup power

Having a solar battery system that provides backup power doesn’t automatically mean that you could “go off the grid” – but it could help keep your lights and other essential appliances or equipment on during an outage.

Here’s a quick guide to the levels of backup power functionality usually  part of a solar battery for your home: 

  • Level 0 – This has no backup power functionality at all.
  • Level 1 – With this level, there’s backup power functionality available but at reduced capabilities (such as lower power output).
  • Level 2 – This level provides backup with the highest level of backup power functionality in the event of a power outage – but your battery can’t charge from your solar PV system when the grid is down. This can be annoying if a power outage hits during the daytime when your electricity storage is running low!
  • Level 3 – This level offers the highest level of backup power functionality, and will allow you to charge your battery from your solar PV system while the grid is down.

Level 3 is generally popular for people who want battery backup. If this is what you need, make sure you advise your installer that you want your battery to charge from your solar PV system when the grid is down. Your solar retailer and installer can help you explore your options and work out if this kind of backup system is a good option for you.

Learn more about battery storage

If a solar battery storage system is something you are interested in investing in as part of your solar PV system, you might like to understand more about how solar batteries work. Learn more about solar batteries and how they could potentially help reduce your electricity costs. 

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