Difference between Power (kW) and Energy (kWh)


Power and energy, synonyms, right? Wrong! Especially when it comes to shopping around for a solar system or solar battery storage. The two words while interchangeable in some circumstances have two very different meanings and knowing the difference between the two will greatly assist you through the research and purchase stage of a solar system or the addition of solar battery storage.

Power (kW)

energy usage kwh

In simple terms power is how fast work or energy is performed per unit of time or the amount of energy used per unit of time.

For example, a high-powered tap will gush out water fast, at a high pressure filling a bathtub quickly. A low-powered tap may dribble out the same amount of water but over a longer period, meaning you’ll have to wait for your desired soak in the tub.

The power of a solar system is the amount of electricity generated at a given moment. When mentioned in reference to solar or battery storage, power is measured in Kilowatts (kW), 1kW equalling 1000 Watts. This means a 5kW solar system has the capacity in peak weather conditions to push out 5kW of electricity. In not so peak conditions like morning, evening or overcast it may only push out 2kW at a given moment in time.

In reference to battery storage the kW power rating would be how much power can flow into or out of the battery in any given moment.

It’s important to note that a power rating does not cover the storage capacity of a solar system or battery, but only the instantaneous output.

Energy (kWh)

energy meter kwh

Energy is the volume that electricity has been generated, stored, or consumed over time. When referred to in the solar industry, energy is measured in kilowatt hours (kWh). 1kWh is equal to one hour of electricity used at the power of 1kW. So, an appliance with a power rating of 2kW would consume 2kWh in one hour.

Over one day a solar system can generate several kWh from the sun. As an example, a 5kW solar system may produce up to 22kWh over an entire day. How many kWh were produced each hour would vary depending on weather conditions, shading and time of day however the accumulative for the day could be 22kWh.

You’ll notice your electricity bill will state the units of electricity used per day or quarter as kWh. This is helpful when trying to decide how much energy you will need from a solar system to cover the majority of your energy usage.

When referring to a solar battery, kWh are the quantity of energy a battery can store.

Energy and Power For Solar

energy consumption

Being able to distinguish the difference of kW (power) and kWh (energy) when speaking to solar providers and looking at solar systems or battery storage will be extremely beneficial in helping ensure you get the size system or battery required for your electricity usage needs.

These simple dot points will assist you in recalling the differences between the two;

  • The maximum amount of power a system generates at a given moment is referred to as kW. So, a 5kW solar system can produce a maximum of 5kW at any one moment.
  • The energy production of a system is referred to in kWh, so you may ask an installer how much energy they would estimate your 5kW solar system to produce or generate in a day, which they would respond in kWh.

And finally, this equation will hopefully makes calculating your household appliance usage much simpler!

kW (power) x time = kWh (energy).

Now that you understand the difference between Energy and Power you may be interested to see the estimated annual production of kWh that different sized solar systems can produce. Comparing this with the average energy usage on your electricity bills will assist you in finding the right size solar system for your household.

See our Residential Solar System Size page to view estimated prices and annual production or start speaking to accredited installers local to your area who can assist!

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Understanding Batteries

Off-Grid Systems

For some households a battery system can be of great benefit and minimise a home’s reliance on the grid. However, it’s important to understand for a battery to be useful your solar system needs to be generating excess energy for the battery to store, which you can then use at night or when the sun is not out.

When selecting a battery, you’ll want to invest in a system that is most suited to your home and can drive the best return on investment (ROI). Despite a larger upfront cost, a higher quality battery may significantly increase your ROI.

    Battery systems start from $6,000 and costs can vary greatly based on the following factors:

  1. Cycle Life-Time

    The number of times a battery can fully charge and discharge.

  2. Battery Power (kW)

    How fast it can be charged or discharged.

  3. Storage Capacity (kWh)

    The maximum amount of energy a battery system can store.

  4. Battery Management System (BMS)

    An electronic ‘smart’ system that gathers data and manages the battery ensuring it does not overload or operate outside of its safe functioning zone..

  5. Inverter

    Battery systems require their own inverter if your solar system does not have a hybrid inverter.

  6. 'All-In-One Unit’

    A system which includes the battery, BMS and an inverter all in one unit.

  7. Warranty

    Length of time or cycles the battery system is under guarantee.

  8. Blackout Protection/Backup

    It’s important to note this is not a common feature of a battery system and could cost thousands of dollars to include. Blackout protection not only requires additional components but also a specialised installation and rewiring. For grid-connected homes, the cost for blackout protection can outweigh the benefit.

Additionally, if your purpose for adding battery is to go Off-Grid and become completely independent from the grid you will need to ensure your solar system can generate enough energy to power your home and your battery system is large enough to store this energy. For homes in metro areas going Off-grid is not cost effective and is only recommended for those in remote areas with limited access to the grid. Off-grid solar systems with battery start at approximately $30,000.

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