How long can solar battery last in a blackout?

A battery can continue powering your house during a blackout. But for how long?

Installing a solar array on top of your house gives you the freedom of generating your own electricity. Without the grid. 

But unfortunately, that only lasts during the day.

At night, one of these will happen:

  • You draw power from the grid
  • You draw power from your battery
  • You don’t use any electricity.

If you do decide to get a battery, how long does that last?

Solar Batteries

A battery is a device that stores the unused power generated during the daytime for later usage. If the size of the solar panel and batteries are large enough, then you can shift your home entirely to solar power. Also, using electricity from batteries is much cheaper than using electric power from the grid.

In the case of grid outages or areas where there is an instability of electric power provision, a battery storage system is a huge benefit. This means you can still use your key appliances at home even in the case of a grid outage. If you are looking for some good and budget-friendly solar storage batteries then Goodwe, Growatt, Fronius, and Redback technologies are quite good options for you. Take a look.

How much energy a house uses

You can estimate the daily need of kWh of any device by multiplying its wattage with the number of hours of usage of that device. Wattage rating information is available on the label of the device or it can also be found in the user manual. 

For instance, if the 100-watt bulb is used for 10 hours per day, then the total energy usage by this bulb is 1 kWh

100 watts x 10 hours = 1,000 watt‐hours = 1 kWh

With this simple calculation, you can work out how much energy each device uses around your home. 

Simply add them all up when you’re done, and you should have an idea of your total energy use at home during a particular period. 

Factors affecting how long a battery will last in a blackout

In order to determine how long your battery will last in a blackout situation, the following factors are need to be considered:

  1. The capacity of your battery i.e. how much power can it store?
  2. Which kind of blackout protection do you have i.e. ‘entire house’ or ‘emergency’? ‘Entire house’ keeps the power flowing to the entire house, whereas ‘emergency’ keeps the power flowing to some specific electrical devices in your home. 
  3. How many and what devices are running during power-cut.
  4. The energy efficiency and size of those devices.
  5.  How much battery did the battery have when the grid got down.

Redback and Goodwe technologies have “black start” functionality which means your solar system will remain in operation mode even if there is a full depletion of batteries during blackout. 

Some examples of energy use

Let’s make some assumptions about how much energy you use during a blackout.

Essentials - 0.5kW

You’re aware of the blackout, and want to maximise your battery by using the minimal amount of electricity. If you can limit your home to just the fridge and a few lights, then that would be great.

Medium Usage - 2kW

You need to continue running your home appliances despite a blackout. This could include the usual appliances such as dishwasher, washing machine, fridge and lights.

Heavy Use - 4kW

You could be in a situation where you have a big family with demands on electricity everywhere and because you already have a battery, you’re unaware that a blackout has happened. And so you continue to use electricity as per normal.

Based on these assumptions, here is an estimation of how long your home will last with these batteries (at full charge).

If the battery is fully charged, how long will it last?

As you can see, the more energy you use, the less amount of power you will have available. Alternatively, the higher the battery capacity, the longer you will be able to use your appliances for.

If you switch off everything, and only run the essential appliances and keep total usage is 0.5kW, you would be okay to survive for 14 hours or more on a 7.2kWh battery.

If you are a heavy user, you’re going to need a large battery such as a Goodwe 24kWh battery to ensure you last 6 hours.

Blackouts in Australia

Compared to the rest of the world, blackouts in Australia happen infrequently and are fixed quickly. 

If you have electrical appliances at home that much remain on, you should consider getting a large battery.

But if you live in an area that does not get affected by blackouts often or the impact is low, then a small battery may be all that you need.

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