More than 23,000 new battery storage systems were installed in Australia in 2020. Most of them store solar energy, for their owners to use at night. But exactly how long does a solar battery last at night? We look at 3 different size solar batteries to see how long each will run a typical home overnight. Batteries are expensive. You don’t want to overpay for what you need. So read on to find out how long you can run your home on one, and which size is right for you.

How long does a solar battery last at night? Key takeaways

A small solar battery will last a typical family using 2 kW of power 2 hours a night. A large solar battery can last 6 hours for the same family.

If you’re on the power grid, the right solar batteries can help you save money on power bills. They can also protect you from future power price increases.

And lets face it. With electricity prices going nowhere but up, who isn’t worried about their power bill?

I guess that’s why solar battery installs are booming in Australia.

But there’s nothing cheap about batteries. So unless you’ve got money to burn, you’re probably wanting to know what size battery is right for you and how much nighttime power you’ll get from one. Here are the key takeaways to answer your questions:

Key Takeaways

• Solar batteries store excess solar energy during the day to power your home at night
• The runtime of a solar battery at night depends on its capacity (size) and your energy consumption, plus 2 more critical factors listed below.
• A small battery will power a typical home for 2 hours a night, a medium solar battery for 4 hours and a large solar battery for 6 hours.
• Portable solar battery options now exist for household nighttime and backup power.
• You can get creative with your energy use to reduce the size of battery you need. You’ll save money at the same time.

We explain these takeaways with a close look at three popular batteries below – the Ecoflow Delta Pro (small), the Sonnen Evo (medium), and the Tesla Powerwall II (large).

But first, lets look at solar batteries and the 4 critical elements that control how long they last.

How Does a Solar Battery Work at Night?

A solar battery works by storing the energy generated by your solar panels during the day, allowing you to use this stored power at night when the sun is not shining.

When your solar panels produce more electricity than you need in the daytime, the excess power is directed to charge your solar battery. At night, your home will draw energy from the battery instead of the grid.

So, let’s say you have a sunny day and your solar panels have charged your battery fully. Once the sun sets, your solar battery will begin to power your home, providing electricity to your devices and appliances.

If you have uninterrupted power supply (UPS) capabilities in your solar battery, it can also power your house when the grid goes down completely. With your power stored during the day, UPS can automatically switch your house over to your battery when the grid isn’t available.

So quickly you may not even notice the power is out.

This effectively makes your home an off-grid island, able to function without relying on external power sources.

These 4 things control how long your battery lasts

It’s important to keep in mind that how long your solar battery lasts will depend on four main factors:

1. The type of your battery,
2. The size of your battery,
3. The amount of power you use at night and at once, and
4. Weather and temperature conditions.

Now you might be wondering, how can you ensure your solar battery is storing enough energy to last through the night? And what can be done to extend the runtime of your solar battery? These are great questions, and the answers lie down below.

But first, lets look at each factor and its influence on how long your battery lasts. Because knowing the basics here can help you avoid picking the wrong type of battery for your home.

Battery type – why it matters and which lasts longest?

Battery type is, indeed, another key factor in determining the lifespan and performance of your solar battery. The most common options are lead-acid and lithium-ion batteries.

While lead-acid batteries are generally more affordable, they typically require more maintenance and may have a shorter lifespan and runtime compared to lithium-ion batteries. On the other hand, lithium-ion batteries offer longer lifespans, better efficiency, longer duration, and require less maintenance.

LifeP04 batteries are a new type of lithium battery technology that have a prolonged lifespan and large inbuilt storage capacity. And with batteries, size matters when it comes to duration.

There are a couple of crucial aspects of a battery’s performance that relate directly to the battery type.

The first is its depth of discharge (DoD). This refers to the amount of energy that can be discharged from a battery before it needs to be charged again. A larger number means you can run the battery harder (or longer).

For example, a lead-acid battery has a recommended DoD of around 50%, while lithium-ion batteries have a higher DoD percentage of 80% to 90%.

You’d rather 90% of something good rather than 50%, right? Well the better the DoD, the more energy you can access and utilize before needing to recharge the battery.

The second is its Round Trip Efficiency. This captures how much energy is lost by the system, as electricity passes from the solar panels, to the battery and into your home.

Both of these determine the actual output of your battery. How much energy it delivers into your home. And how long it runs for.

Battery size – bigger the battery capacity, the longer it lasts

When it comes to how long a solar battery will last at night, several factors play a role in its performance. First, let’s consider the battery’s capacity, which greatly influences how long it can power your home during the nighttime hours.

Battery capacity is usually expressed in kilowatt hours (kWh).

The higher the capacity, the more kWh, the longer a battery will last.

Energy dense battery technologies contain a lot of power in a small space. Lithium ion batteries are more energy dense than lead acid. And LifeP04 batteries have a high energy density rating, and therefore strong runtime, among lithium battery types.

How weather conditions can leave you with less battery power

A full battery will last longer at night, that goes without saying.

So it’s also true that a day of poor weather will mean you get less power from your battery at nighttime. How so?

Well in poor weather, your solar panels generate less energy. Cloudy conditions can reduce your solar system output by between 60% and 75%. Our 220 watt portable panels, for example, only produces around 60 watts of power (27% of its capacity) in full cloud.

Less juice from your solar panels means less extra power to charge your battery during the day.

And less power available in your battery to use at night.

If there have been consecutive days of poor sunlight, your solar battery may not be fully charged for nighttime use, and could run out of power earlier.

And it’s not just weather that impacts battery run time. Did you know that temperature fluctuations can also impact the efficacy of your solar battery?

Just check the manufacturer’s specs for any battery and it will include temperature limits for the battery to operate efficiently.

Both high and low temperatures can negatively affect the battery’s output and ultimately its lifespan.

For optimal efficiency, most solar batteries should be installed in a temperature-controlled environment. Ensuring your battery is maintained at a consistent temperature can help extend its lifespan and improve its performance throughout the night.

How much power do we use at night?

Understanding your nightly power usage is vital when considering solar batteries for your home. Because your nighttime load is usually powered by your battery. So your power demands at night is where we start.

The thing is, you can’t find this information from your power bill.

What you can find from your power bill is your average daily usage in kWh. Using this, we can estimate how much of that used at night.

The best bill to look at is one for when you use the most power. If you’re in Queensland, that’s summer. In SA, NSW, VIC or TAS, its winter.

Grab a peak season power bill and look at your average daily use figure. Then multiple this by 70%. 70% is what we use at nighttime. It’s an estimate.

Average energy use in Australian homes, by state

In Australia, the average nightly energy use differs by state. The following table shows the estimated power usage for a typical household in different Australian states, as mentioned in this post:

State	Average daily use (peak season)	Nightly Usage
Queensland	16.81 kWh	11.77 kWh
New South Wales	19.18 kWh	13.42 kWh
Victoria	17.46 kWh	12.22 kWh
South Australia	16.28 kWh	11.40 kWh
Tasmania	32.26 kWh	22.65 kWh
ACT	24.10 kWh	16.87 kWh

Now you have an idea of how much energy you use at night, you can start thinking about the right solar battery for your needs. Because how long your battery lasts is a function of how much power you need.

How long does a solar battery last at night for a typical home?

Next, we look at 3 different sized lithium solar batteries, to work out how long they last at night:

1. a small portable backup battery – the Ecoflow Delta Pro 3.6 kWh
2. a medium sized home battery – the Sonnen Evo 11kWh
3. and a larger battery – the popular Tesla Powerwall (II) 14 kWh.

We’re going to work out the duration for each, with some simple calculations.

We use the nighttime load of a typical home in Queensland as an example.

EcoFlow Delta Pro 3.6kWh x 2

1 kW for 5.18 hours, or 2 kW for 2.59 hours of nighttime power

The EcoFlow Delta Pro 3.6kWh stackable solar battery is a LifeP04 battery, with a 3.6kWh capacity per unit. This is a small portable battery. 2 units will make a dent in your night power needs.Here are the key specs for 2 units combined:

• Battery Capacity – 7.2 kWh
• DoD – 80%
• RTE – 90%
• Maximum output (AC) – 7.2 kW (14.4 kW of surge)
• Charged from – the grid, solar panels, EV charge station.

The Ecoflow solar battery will run a typical Queensland home using 2 kW of power for up to 2.59 hours at nighttime:

7.2 kWh x 80% x 90% = 5.18 kWh of actual power

= 5.18 kW for 1 hour, or 1 kW for 5.18 hours, or 2 kW for 2.59 hours, etc

Stackable capacity

The cool thing about the Ecoflow Delta Pro is its stackable battery capacity. You can add units together, to get more power.

You do pay for convenience though. The price of one Ecoflow Delta Pro is around AUD$6300 at the time of writing. Two units providing 7.2 kWh will cost a tickle over $11,000.

Or you can get one unit with an EcoFlow smart generator backup that runs on LPG bottle, for just under AUD$9000. For that, you get 20 kWh of total capacity on a standard 9kg gas bottle.

That’s more than enough to run any home overnight, and enough for a full day of backup power in QLD, NSW, and VIC.

Portable solar battery power

In another stroke of genius, the Ecoflow solar battery is portable. It can connect with your home power board with the Smart Panel. But you can easily wheel it away. It’s not just backup power for your home. Its a generator for the home workshop, for your next camping adventure, or to power your tools onsite.

If you want total flexibility of energy supply across sites and circumstances, this is the solar battery for you.

How do the other solar batteries on our list compare to the EcoFlow Delta Pro 3.6kWh? Lets take a look.

SonnenBatterie Evo

2kW for 4.72 hours, or 3 kW for 3.15 hours of nighttime power.

The Sonnen Evo solar battery is a 11 kWh LifeP04 battery made up of two 5 kWh (usable power) battery modules:

• Battery Capacity – 11 kWh
• DoD – 91%
• RTE – 94.4%
• Maximum output (AC) – 5 kW
• Charged from – solar panels or the grid.

The Sonnen Evo will run a typical Queensland home using 2kW of power for 4.72 hours at nighttime:

11 kWh x 91% x 94.4% = 9.45 kWh of actual power

= 2 kW for 4.72 hours, or 3 kW for 3.15 hours.

The Sonnen Evo 10 kWh is around $12,600 at time of writing.

Tesla Powerwall 13.5kWh

2 kW for 6 hours, or 3 kW for 4 hours of nighttime power

The Tesla Powerwall 13.5kWh is a popular and well-known solar battery option. Its a conventional lithium-ion battery and a 14 kWh of capacity.

• Battery Capacity – 14 kWh
• DoD – 96.5%
• RTE – 90%
• Maximum output (AC) – 5 kW
• Charged from – solar panels, the grid.

The Tesla Powerwall II will run a typical Queensland home using 2 kW of power for 6 hours at nighttime:

14 kWh x 96.5% x 90% = 12.15 kWh of actual power

= 2 kW for 6 hours, or 3 kW for 4 hours

The Tesla Powerwall costs around $13,000 in 2023.

How to make your solar battery last longer

How can you make your solar battery last longer at night (and maybe save some money with a smaller battery). The calculations above give you a massive hint.

Manage your energy use

Minimising how much power you use at the one time, will help your battery last longer. You can do this by only running certain appliances together.

It’s easiest if you know the real energy guzzling appliances around your home. Things like a kettle, toaster, iron, vacuum cleaner, fridge, deep freeze, and any form of heating or cooling – all use loads of power. Limit which of these you run at night. And also which you run at the same time.

The Tesla Powerwall for example will last 6 hours if you’re using 2kW of power. But use 3 kW, and you’ll only get 4 hours of charge out your battery.

This is the top tip to do more with a smaller battery. Which hopefully costs you less.

You can also minimise the power demand on your battery with a critical power circuit. It’s just a separate circuit in your home with only critical appliances connected – like lights, your fridge, your freezer, your gas hot water. Your battery is connected to and only runs this circuit.

There’s no need to manage your energy use with this set up. But there’s also less flexibility.

Follow the maintenance schedule

You can also prolong your battery’s usable life with proper maintenance. By proper maintenance we mean regular cleaning, keeping the battery at recommended temperatures, and following the manufacturer’s guidance on discharge and charging regimes.

Consistent upkeep can ensure that your battery functions efficiently, extending its nightly performance and overall lifespan.

Conclusion

When it comes to choosing the right size battery for your needs, it’s important to consider your household’s energy usage as this directly impacts how long a solar battery lasts at night. As a general rule, for a typical household using 2 kW of power a small lithium battery will last around 2 hours. A medium battery will last 4 hours. A large home battery will last about 6 hours. By managing your power use at night you can reduce your solar battery costs. Most batteries these days are stackable or scaleable, which means you can expand or add to them when you have the money. Some are even portable, and can power your home and your next camping trip!

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