Installing a solar battery backup system is a great solution to keep the lights on during power outages, especially in sunny Australia. But how long does a solar battery last? To get the right battery for your home or camper van you need to know how long you can run it for. We’re going to answer this question in two ways. Firstly, we give you the expected lifespan of a solar battery (both lithium ion batteries and lead acid batteries). Secondly we explain the runtime (how many hours of power) a solar battery will give you in a caravan and a household situation.
Solar batteries: the basics
Solar battery components
Most solar batteries are made up of a solar system plus a battery system. These days the battery system is mostly made from lithium ion. Other solar batteries come with lead acid storage technology.
Before we start, it’s important to understand the components in a solar battery because each component has a different lifespan. The critical components are:
- Solar PV system (portable or grid tied) – made up of solar panels plus the solar inverter (which converts DC type solar power into the AC power your appliances use).
If you have a portable solar system you may also have a solar charge controller (regulator) to manage the voltage the solar panels produce and send into a battery.
- A battery system (or home battery) is the same as a battery energy storage system. A battery system is made up of the battery storage component and battery management system or technology.
There are two main types of battery storage. Lithium ion batteries and lead batteries. Solar power works together with both types. Lithium batteries are a new technology but lead acid has been around for years (like in car batteries).
Common uses of solar batteries
Adding battery storage to solar power, no matter the size, gives you a solar battery. But how can you use them together?
There are 3 common uses for solar batteries:
- Grid-tied solar panels can be used with batteries to form home energy storage systems. This is where the solar and battery power your home alongside or instead of the power grid. Residential solar batteries can be large enough to power your home and send excess energy into the electricity grid. The solar runs your house in the day and charges the battery. You use the battery stored solar power at night.
- You can also use a residential size solar battery backup system to run critical appliances in your home during a power outage.
- Solar battery storage can also be small and portable, which makes it popular for mobile applications (camping and caravans / RVs).
If you want to know more about how you can use solar for backup power, portable power or in your home, read our post on the 6 solar panel uses to secure your power supply and save money.
1. How long does a solar battery last (life span)?
A solar battery can last 3 to 10 years before you need to start replacing system components.
There are two things that determine this broad range:
- the system components and
- the way you use them.
First, let’s break that down to the expected life of key solar battery components.
Solar system life span
A solar system is made up of the panels, a solar inverter, and solar regulator (for portable systems).
The solar PV panels in a home solar system have a life expectancy of 20 to 25 years. Solar owners should be guided by the warranty period here.
A solar inverter will last 7 to 10 years before needing to be replaced.
A solar regulator has a life span of 5 to 10 years.
Battery life span
There are two main battery types for portable and grid tied or residential solar batteries:
- Lithium ion
- Lead acid
Of the two main battery types, lithium ion has a longer expected life.
A new battery that uses lithium ion chemistry has a cycle life of 4000 to 8000 cycles. It will last 5 to 10 years.
A lead acid battery has a cycle life of around 1500 cycles. The average life is around 3 to 5 years.
A battery’s warranty will also give you an idea of its life span according to the manufacturer. Batteries can last longer than their warranty period.
Factors that determine the battery lifespan
Batteries come with a large range in their life span. That’s because a bunch of external factors affect how long they last. These 3 factors influence a battery’s expected life:
How often do you use batteries? – Do you use them according to the manufacturer specifications? The specifications to pay attention to here are the usage cycles and cycle life, as well as the manufacturer’s recommended depth of discharge (dod). Not following these recommendations will shorten your battery life.
Maintenance – the manufacturer will also have a maintenance schedule to follow if you want to maximise the life of your system.
External temperature – extreme temperatures (extreme heat or extreme cold) will degrade your battery and even cause battery failure. Casing, housing and location can help control the ambient temperature around your battery. There are devices that do this also. But they are an expensive addition to your system.
Now you know how long the different components in a solar battery will last before you need to start replace parts.
Next, we will look at how many hours of power a solar battery will give you.
2. How long do solar batteries last (how many hours of power)?
If you want solar battery for backup power, it’s important to know how long it will last.
The size of a solar battery depends on the storage capacity and solar panel size. The battery size and type play a big role in how many hours of power it will give you.
Portable solar batteries (around 1200 watt hours) are much smaller than grid tied / residential solar batteries (around 10,000 watt hours). Buying the wrong size and type of solar battery may mean you can’t power the appliances or equipment you bought the solar battery for in the first place!
So, how long do solar batteries run for?
The best way to demonstrate this is with some common examples.
Caravans, boats & camping – 100 amp hour (AH), 12 volt battery
100 AH 12 volt batteries are popular portable battery sizes. People use them in caravans, RVs and boats, as well as in camping. They come in lithium ion or in lead acid technology. We will factor both into our example.
It’s important upfront to always match your solar battery voltage with the voltage of appliances you want to power. So in this example, you’re running 12V appliances as you have a 12V solar battery.
How long does this 100AH, 12V solar battery last for?
SUMMARY:
100AH, 12 volt solar battery will produce 1200 watt hours of electricty. At 80% DOD you can use 960 watt hours per battery cycle.
To get the battery runtime, add the watts of all of your appliances together (load). Divide this total load number into 960 (available watt hours).
If your load is 110 watt hours, your solar battery will last 8 hours before you need to charge it again.
You’ll need a 300 watt 12V solar panel to charge the battery within a day.
This doesn’t give you any leeway if you have lots of rainy days where the solar isn’t producing power. If that’s you, oversize your battery and solar panels to account for this.
Lets show you how we worked this out by answering 4 simple questions:
Firstly how much power does a 100AH battery provide?
A 100 AH 12V battery will produce 100 amperes of stored energy over one hour (100 amp hours). That’s the same as 1200 watts in one hour (1200 watt hours).
Solar systems come in watts. Converting your battery power from Amps to Watts lets you pair apples with apples. The formula to convert Amp to Watts is *Watts = (Amps x Volts)*Power Factor.
All of our examples assume a power factor of 1 to make it easy.
How much of this power can you use (available energy)?
You can’t routinely discharge your battery until it’s empty. This will ruin the battery. So manufacturers provide a depth of discharge (DOD) recommendation for the battery. It’s usually a percentage of full discharge (the point where the battery is empty).
- Lithium ion batteries depth of discharge is optimised at around 80% (you can discharge the battery to 80% of its full discharge).
- Lead acid battery depth of discharge is only 50% (you can only half discharge it).
So you can use 960 watt hours per cycle for the lithium ion system and 600 watt hours for the lead acid one.
We’re going to focus on the lithium ion example – 960 watt hours.
How many hours will the battery last?
How many hours this 960 watts lasts depends on the appliances you are running and how long you’re using them.
The way to work this out is: Battery runtime = available energy / total load
To calculate ‘total load’, add up the watts for all of the appliance you want to run at the same time.
Lets say you want to run a 12 volt water pump (which uses 60 watts).
Battery life = 960 watts (available energy) / 60 watts (total load) = 16 hours of runtime.
So you could run a 60 watt water pump for 16 hours with this 100AH battery.
If you want to want to run a pump plus an LED TV:
Total load is 60 watts + 50 watts = 110 watts.
Battery life = 960 watt hours / 110 watt hours = 8 hours of battery runtime.
Now that you know how long the battery will last per cycle, let’s look at how you can recharge it between cycles.
What size solar system will charge this battery in one day?
When the battery is discharged, you’ll need to charge it with your solar system (during daylight hours).
Caravan solar power sizes are typically 12V and produce 100 watts. You can get larger ones.
In Australia, we use ratings from the Clean Energy Council to get the average daily power output that a solar system produces. This is measured as the number of kilowatt hours of solar power per kilowatt of solar PV installed.
So using the infographic below, a 5kW (5000W) solar PV in Brisbane will produce 21kWh per day.
This means, in one day a 100 watt solar panel can produce around 400 watt hours (1kW = 1000 watts) in Australia.
So if you want a charge a 1200 watt hour battery in one day, a 1 single 100 watt panel producing 400 watt hours is not enough. You’ll need 300 watts of solar.
Home battery example – 10,000Wh, 240 volt battery
SUMMARY:
10,000 watt hour, 240 volt solar battery will produce 10,000 watt hours. At 80% DOD you can use 8000 watt hours of that (available energy).
To get battery runtime, add the watts of all of your appliances together ( total load). Divide your total load number into 8000 (available watt hours).
If your load to run a fridge and freezer is 1300 watt hours (Wh), your solar battery will last 6 hours before you need to charge it again.
You’ll need a 2500 to 3300 watts of solar panel to charge the battery in one day.
Again, this doesn’t account for rainy days!
Let’s work it out together next.
Firstly how much power does this battery provide?
A common size of a residential lithium ion battery is 10,000 watt hours (nominal capacity).
This battery is rated to provide 10,000 watts of power over one hour. That’s the same as 41 amps (at 240V) in one hour.
How much of this power can you use (available energy)?
At 80% DOD (because you shouldn’t fully discharge the battery every time), you can use 8000 watts per battery cycle. This is its usable capacity or available energy.
How many hours will the battery last?
Say you want to run a fridge (800 watts) and freezer (500 watts) to keep food cold in a power outage.
Your total load is 1300 watt hours. 8000 / 1300 = 6 hours of runtime.
You can run your fridge and freezer for 6 hours before needing to recharge the battery.
What size solar system will charge this battery in one day?
Rooftop solar panel sizes are typically 300 watts. To charge a 10,000 watt hour (10kWh) battery in one day you would need 2500 to 3300 watts of solar panels depending on where you live in Australia.
2.5kW x 4.2kWh = 10.5kWh (10,500Wh)
That’s 8 to 10 panels at 300 watts each.
Again, we haven’t accounted for rainy days!
Conclusion
A solar battery system will last 3 years (lead acid) to 10 years (lithium ion), depending on the battery type. Lithium ion batteries last longer or allow for more cycles of the battery. But they also cost more. You’ll need to follow the manufacturers instructions on using the battery to get this optimal life span. How long solar batteries last each battery cycle depends on the size of the battery and what appliances you are running. Using the examples above, you can now work out how long a typical size residential solar battery will last between charges. You can also work out the same for a common RV / caravan solar battery system!
FAQ
How long does a 12 volt solar battery last?
To work out how long a 12 volt solar battery will last, you need to know two things about the battery:
– the battery type (which tells you depth of discharge) and
– how many watt hours or amp hours of energy the solar battery will provide.
You can find both of these on the battery nameplate.
A 100 Amp hour 12 volt solar battery will have 19 hours of runtime if you’re just running an LED TV (50 watts) for one hour.
If you want to run a TV and water pump (total 110 watts), you’ll have half the battery runtime (9 hours).
Lets have a look at how we worked this out:
Let’s use the 100 Amp hour lithium ion battery as an example. 100 amp hours is the same as 1200 watt hours.
To convert amp hours to watt hours. The formula is Watt hours = Amp hours x Volts.
100 x 12 = 1200 watt hours.
Assuming the lithium battery can be discharged to a depth of 80%. 1200Wh x 80% = 960Wh of usable energy.
To run your TV for one hour = 960 watt hours / 50 watt hours (TV power use) = 19 hours of run time.
How long does a 24 volt solar battery last?
A 24 volt 100 amp hour lithium ion solar battery will provide 1920 watt hours of ‘stored energy’.
That battery could run a 50 watt TV for 38 hours. Or it could run a 1200 watt kettle for 1 hour and 36 minutes (the same as boiling the kettle 19 times).
Alternatively, it could run a 500 watt deep freezer for over 3.5 hours before the battery needs charging.
The calculations for this are the same as for a 12 volt solar battery (question above).
Do solar batteries expire?
Yes. Solar batteries have an expected life, or lifespan of between 3 and 10 years before you need to replace some system components. Lets have a look at the lifetime of the components that make up a solar battery:
Solar panels have a lifespan of 20 to 25 years, but the amount of solar power they produce degrades over this time.
Solar inverters (that convert DC to AC power) can last 7 to 10 years.
Solar charge controllers have a life of 5 to 10 years.
All batteries degrade over time. The life of a battery system depends on the type of battery, which also determines the battery’s charge cycle (how many times you can charge it).
A lithium ion home battery can have a charge cycle of between 2000 and 8000 times, last 5 to 10 years on average.
A lead acid battery have a charge cycle of 1500 times. It will typically last 3 to 5 years.
Is it worth getting a battery with solar?
Solar systems alone are a worthwhile investment – they pay themselves off well within their expected life. In Australia, a typical 5kW rooftop solar system should pay itself off in 4 to 5 years. After that, it’s all gravy (free power)!
Solar batteries together are not always worthwhile. It depends what you’re paying for power and how you value emergency backup power. Make sure you do the research before you buy. This article will help you determine if a solar battery is worth it or not.
