How to Calculate Solar Panel Output

The easiest way to calculate solar panel output? Use our solar panel calculator or follow our step-by-step guide.

February 14, 2024
Should I get solar panels?

Wondering how to calculate solar panel output? This guide teaches you how to do exactly that.

The quickest and easiest way would be to use our solar panel calculator - It’s 96% accurate so you can be confident that the calculated output will be similar to what you would expect should you install solar panels. Simply input your postcode and we’ll help you crunch the numbers for your property.

Not only will the calculator save you from having to read this entire article, but it’ll also provide you with estimated costs, savings and how many solar panels you would require.

Calculating Your Solar Panel Output

The easiest way to work out solar panel output is by using our solar panel calculator

However, if you prefer to crunch some very rough numbers yourself, here is required equation:

Note: Our Solar Panel Tool will deliver a far better output so we’d highly recommend using it. The below equation is simplified and will only give a very rough estimate.

Power in watts x Average hours of direct sunlight x 0.75 = Daily Watt-hours.

Power in watts: Each solar panel has a maximum power output under ideal conditions - this is displayed in Watts (W). The solar panels we would recommend to customers have a wattage of 390w. 

Average hours of direct sunlight: You can find the most up to date annual sunshine figures for your city here. Simply divide this figure by 365 to get the average daily sunlight figure.

Why multiply by 0.75? This accounts for factors that may affect the output of your solar panels, including shading, weather conditions, and their orientation/tilt. We’ll dive into this in more detail further in this guide.

Quick Example

For example, if a 390W solar panel receives 4 hours of sunlight each day, then the total power output would be calculated like so:
390W x 4 x 0.75 = 1.17kW per day 

While you can manually crunch the numbers using the formula, we've got a simpler solution for you! Try out our user-friendly solar panel calculator tool, which not only helps you calculate your solar panel output but also provides insights into the cost savings you can expect from switching to solar energy. It's a handy tool for those considering a solar panel installation in the UK.

Why is Calculating Your Solar Panel Output Important?

Solar panel output refers to the amount of electricity that a solar panel system can generate under specific conditions. It is typically measured in kilowatts (kW) or kilowatt-hours (kWh). Here is why working it out is important before you commit to solar panels:

1. Financial Planning: Knowing your solar panel's output helps you estimate the financial benefits of going solar. It allows you to estimate your potential energy savings and determine the payback period for your investment. This information is essential for budgeting and making an informed decision about the size and type of solar panel system you wish to install.

2. Environmental Impact: Solar panels reduce your reliance on fossil fuels and decrease your carbon footprint. By understanding your solar panel output, you can quantify the amount of greenhouse gas emissions you're preventing and contribute to a cleaner, more sustainable environment. 

Factors Affecting Solar Panel Output

There are various factors that can influence how much electricity your solar panels generate. These factors play a significant role in determining the effectiveness of your solar panel system and thus it’s output. They are as follows:

1. Panel Efficiency

Solar panels come in different makes and models, each with varying levels of efficiency (this refers to how well a solar panel converts sunlight into electricity). Higher efficiency panels can produce more electricity for a given area of installation. Opting for higher efficiency solar panels (20% plus) would of course increase your output, especially if your roof orientation or tilt is not ideal (more on this further in this article).

Recommended guide: How Efficient are Solar Panels?

2. Sun Hours

The UK receives an average of approximately 4.9 sun hours per day. The number of sun hours that your location receives directly impacts your solar panel output. Areas with more sun hours will produce more electricity over time, while those with fewer sun hours will generate less. It's important to consider your specific location and use up to date figures when estimating output.

3. Orientation and Tilt

The orientation and tilt of your solar panels can significantly affect their efficiency. In the UK, panels should ideally face south to capture the maximum amount of sunlight throughout the day. However, not all roofs have a perfect south-facing orientation. Panels facing east or west can still generate electricity but at reduced efficiency. Tilt is also important; panels tilted at an angle equal to your latitude will capture the most sunlight. Adjusting the orientation and tilt to match your location can optimise output.

Recommended guide: Best Direction for Solar Panels

4. Weather Considerations

Cloud cover can reduce the amount of sunlight that reaches your solar panels, impacting output. While solar panels can still generate electricity on cloudy days, it's essential to consider potential fluctuations in output due to weather conditions when working out your solar panel output.

Let's take a closer look at how these factors can affect your solar panel system's performance through the use of an example.


Suppose you have a 5 kW solar panel system with highly efficient panels, but your roof's orientation is not ideal, and you experience frequent shading from nearby trees. In this scenario, you may need to adjust your output expectations downward to account for these factors. The impact of shading, orientation, and tilt can reduce your system's efficiency, even with high-quality panels. Our calculator takes all of this into account by using the most recent annual sunshine figures for your specific postcode, allowing us to provide you with a 96% accurate estimate regarding your solar panel’s potential output.

Maximising Your Solar Panel Output

Now that you understand how to calculate your solar panel output, let's explore how to get the most out of your system:

1. Optimal Installation: Position your panels for maximum sunlight exposure. South-facing panels are ideal, but east or west-facing panels can work too. Don’t worry, our solar panel experts will walk you through the best options for your specific roof and our installers with ensure the optimal tilt.

2. Regular Maintenance: Periodically clean your solar panels to remove dirt and debris, ensuring they operate efficiently; and keep an eye out for shading issues caused by new structures or vegetation and address them promptly.

3. Consider Expanding: If your energy needs grow, consider expanding your system to generate more electricity. In most cases, this would be as simple as adding more solar panels.

4. Battery Integration: Explore adding a battery storage system to store excess energy for use during the night or cloudy days, enhancing self-sufficiency.

Our Solar Panel Calculator

If you're considering solar panels for your home in the UK, you're in the right place. At MakeMyHouseGreen, we've developed a user-friendly Solar Panel Calculator that takes the guesswork out of estimating your solar panel output and potential savings.

Here’s what our calculator does:

- Customised Estimates: Our calculator provides tailored estimates based on your location, panel specifications, and energy needs. It's designed to give you a realistic projection of how much electricity your solar panel system can generate.

- Financial Insights: Discover the potential cost savings of going solar. Our calculator considers factors like government incentives (such as the smart export guarantee) and electricity rates to give you a clear picture of your financial benefits.

- Environmental Impact: Understand the positive environmental impact of switching to solar energy. Calculate your greenhouse gas emissions reduction and contribution to a cleaner planet.

Why Choose MakeMyHouseGreen?

- Experience and Expertise: We have a proven track record in solar panel installations. Our team of experts has the experience and knowledge to design and install a solar panel system tailored to your needs.

- Quality Assurance: We use high-quality solar panels and components to ensure the longevity and efficiency of your system.

- Customer Satisfaction: Our priority is your satisfaction. We'll guide you through the entire process, from design to installation, making your transition to solar energy smooth and hassle-free.

Helping make the journey as smooth as possible enabling people to go green.