How to decide how many solar panels you’ll need

How to decide how many solar panels you’ll need

For homeowners who are already convinced of the benefits of solar – the challenge isn’t deciding whether to go solar — it’s optimising your solar setup for peak performance. Whether you’re upgrading an existing system or designing a new one from scratch, this guide aims to provide actionable insights for maximising your solar investment.

This article dives deep into the intricacies of determining the ideal type and number of solar panels for your home.

Our follow on article then looks at if you can actually fit the panels your energy usage needs and determines where to place the panels which you can read here.

Assessing Your Energy Needs

A precise solar panel system is tailored to your home’s energy requirements, and the first step toward that precision is having an in-depth understanding of your annual energy consumption. This forms the basis for determining how many solar panels you’ll need and where they should be placed for maximum efficiency.

Many energy retailers provide detailed yearly consumption data via their online customer portals. Logging into this portal will give you a more accurate reading of your energy needs, typically presented in kilowatt-hours (kWh). This data is invaluable for configuring your solar panel system with precision. If you’ve been diligent about keeping past energy bills, you can also calculate your annual kWh usage manually. This gives you a robust dataset to work from and complements the information available from your retailer’s portal.

If you haven’t kept past bills and your online portal only gives you daily kWh usage, you can still get a reasonable estimate of your annual consumption. Simply multiply the daily kWh number by 365 days to get an approximate yearly figure. However, this doesn’t account for seasonal usage changes—such as increased air conditioning in the summer or heating in the winter—so you’ll need to adjust this estimate accordingly.

Energy consumption is not uniform throughout the year. It’s essential to consider the impact of climate on your energy needs. Summer might demand more air conditioning, while winter requires heating. These fluctuations in usage should be taken into account when calculating your annual kWh figure. A buffer for these seasonal variations is advisable for a more accurate solar system sizing.

Once you have reliable data on your annual energy consumption, you’re well-placed to make educated decisions about your solar panel system. This includes not only how many panels you will need but also the most effective orientation and placement to maximise their efficiency. By basing your solar panel decisions on sound data, you’re ensuring a more effective and cost-efficient solar setup tailored precisely to your needs.

Determine Which Solar Panels

When selecting solar panels, it’s not just about quantity but also quality. Consider factors like brands, the colour of panels, and their sizes to find a panel that suits your specific requirements.

Some considerations to take when determining which solar panels to use:

  • Output and Efficiency: When you’re considering which solar panels to install, two fundamental metrics to understand are kilowatts peak (kWp) and efficiency. kWp indicates the maximum power a panel can generate under optimal sunlight and temperature conditions, typically full sunlight at 25 degrees Celsius. The higher the kWp, the more electricity a panel can produce, but remember that real-world conditions often differ. Efficiency, meanwhile, is expressed as a percentage and reflects how well the panel converts incoming sunlight into usable electricity. Higher efficiency generally means you’ll need fewer panels to meet your energy needs.
  • Brand: The kWp and efficiency ratings can vary significantly between brands. Some brands specialize in high-efficiency panels, whereas others might offer a better balance between cost and performance. Additionally, the warranty and insurance options provided by the brand can be crucial factors in your decision-making, ensuring your investment is protected for the long term.
  • Aesthetics: Solar panels aren’t just functional; they’re also part of your home’s visual appeal. Many brands offer panels in different styles, sizes, and colours. Some homeowners prefer the sleek, modern look of all-black panels, while others might be looking for panels that blend seamlessly with their roof tiles. Before you choose, make sure you’re aware of any neighbourhood or local regulations regarding solar panel aesthetics.
  • Panel Size and Configuration: Solar panels usually have standard dimensions, often around 1.6m by 1m. It’s essential to measure your roof’s available space and consider how the panels’ size will affect your installation. The number of panels you can fit is directly related to their kWp and, consequently, how much electricity you’ll generate.

Calculating How Many Panels

To calculate the number of panels you’ll need, first look at the kilowatt-peak (kWp) rating of a single panel. This rating is a measure of how much power the panel can produce under ideal conditions. Multiply this by the average daily sunlight hours your location receives. Then, take that result and multiply it by 365 days to get an annual figure.

Don’t forget to factor in the efficiency of your solar system, as real-world conditions like shade, dirt, and cloud cover will reduce the panel’s output. Multiply your annual figure by the system’s efficiency, usually given as a decimal (e.g., 90% efficiency is 0.9).

Finally, take your annual kWh needs, which you’ve calculated from your energy bills or your energy retailer’s online portal, and divide this by the figure you’ve calculated. This will give you the number of panels you’ll likely need to meet your energy needs for the year.

Example Calculation

  • Annual energy use: 6,500 kWh (found from your energy retailer’s online portal)
  • Panel power rating: 0.3 kWp
  • Daily sunlight: 5 hours
  • System efficiency: 90% (0.9)
  • Daily Output Per Panel: 0.3 kWp × 5 hours = 1.5 kWh
  • Yearly Output Per Panel: 1.5 kWh × 365 = 547.5 kWh
  • Adjusted Yearly Output: 547.5 kWh × 0.9 = 492.75 kWh
  • Number of Panels Needed: 6,500 kWh ÷ 492.75 kWh = 13.2 (round up to 14 panels)

Plug in your own figures to tailor this to your needs. Keep in mind that these calculations provide a yearly average and don’t account for seasonal variations or peak energy requirements. You may need additional panels or a battery storage system to ensure sufficient energy during less sunny months or times of high energy use.


Determining which solar panels and the number you require to offset your energy usage is a multifaceted process which involves understanding your energy needs and other elements such as how you want the panels to look. Once you know how many panels you want/need on your roof – the next step is to actually see if you can fit them and work out the perfect panel placement to maximise your return on investment. You can read our follow on article about how to decide where to place solar panels on your roof here.

Haven’t got a system yet? Get a free quote from Arkana Energy

Get a quote