How to calculate your solar system size?

Fast read

Choosing the solar system and battery sizes (if going with a solar battery combo) that are optimal for your energy needs when preparing to install a solar system is critical.

It is recommended to self-consume the direct energy produced during daylight hours to get the most out of a solar system. Doing so prevents you from paying your energy retailer's high electricity bills.

To determine the size of your solar system, you must first understand your daily energy usage. This can be found by looking at your kWh consumption data from your electricity bill or through a smart meter. The peak hours of sun in your area must also be considered.

To determine the size of a solar battery system, you must first understand why you want one. Common reasons include reducing reliance on the grid, backup energy for power outages, and reducing electricity costs.

What size solar and battery system do I need?

If you are planning on installing a solar system on your roof, the most critical question that should come up is what solar system size you need, and if you are considering purchasing a solar battery combo, what size battery would be best for your energy situation? 

How to size your solar system alone

Let’s first look at solar by itself. To get the most bang for your buck, self-consume the direct energy produced from your system during the daylight hours. This is because using your home’s solar energy allows you to avoid purchasing expensive power supplied by your energy retailer. Although you receive a credit for the energy your system sends back to the grid, this number is usually a lot lower than the energy you buy from retailers, allowing them to increase their profit margins dramatically. 

solar installer working on roof installing solar system
Smart meters can give you accurate energy data to choose an appropriate solar system size

Energy usage

To determine the size of your solar system, you will first need to understand a few main variables, the major one being energy usage on a day-to-day basis. To determine this, you must first gather your kWh consumption data from your electricity bill. It is recommended that you look not only at your recent bill but also at your bills from the past 12 months to gain an overall understanding of consumption. This will allow you to work out your average monthly consumption, which you can then use to work out your average daily consumption.

However, if you have a smart meter, you can find this information much more easily. After this is done, you will want to understand your area’s peak hours of sun. This varies greatly depending on your location, so make sure you put aside a reasonable time for research.

You can then work out your system size by simply taking your daily kWh consumption and dividing it by peak sun hours to work out the kW output. You then divide this number by your solar panel efficiency (the ones you plan to get) to determine how many panels you need. On the other hand, you can use our solar system calculator to estimate solar system sizing accurately.

Solar and battery combinations

So now that you have a general idea of how to determine your solar system size and how many panels you need, let’s explore batteries, as they are usually determined by system size. To size a solar battery system, you must first understand why you want one. In many cases, it’s several reasons. Usually, these are the top three;

  • Reduce reliance on the grid (energy independence);
  • Backup energy for power outages;
  • Reduce electricity bills.

How to size your battery?

If the above cases sound like you, the next step is to determine what size battery you need that works well with your solar system. To size your solar battery system, you need to understand how much energy your solar system produces, how much energy you use, and how much is being sold back to the grid at a low feed-in tariff. So let’s go ahead and explore it in steps.

tesla powerwall on garage
Larger batteries can store extra energy but still rely on the efficiency of your panels to deliver a good output to allow for battery charging
  1. To size your battery system, you must first understand how effective your solar system is. 
  2. This allows you to determine how much energy you use directly during the day from this system. 
  3. After this, you can determine how much energy you sell back to the grid.
  4. Once you understand this number, you can determine how much energy you would be storing in a battery if you purchase one, giving you an estimate of the size of the battery storage system you need. 

In summary

Again, you can also use our battery storage calculator to give you an idea of the battery storage size that would be most appropriate for your home. Therefore, if you are trying to size a solar system or a solar system and battery, you need to make sure you have a thorough understanding of your energy consumption. You must also understand when you use energy during the day and how much energy you are not consuming from your solar system. 

Notify of
Inline Feedbacks
View all comments

Find your local installer