Posted:
- Guide
To estimate your solar savings, we take a detailed look at all the different factors that can impact how your system performs, and how efficient it is.
These aren’t just numbers on a page - they’re real details about your home and energy needs. Everything from how much electricity you use, to the type of panels you choose, and even your roof’s position. All of this plays a part in calculating your potential savings. Here’s what we look at, so that we can make sure the estimate is spot on:
How much electricity your home uses each year
The maximum power that can be generated by one solar panel each year
How many panels your home needs to cover your electricity use
How much you'll save from using the power generated by solar panels
How much can you earn from exporting excess power back to the grid
The saving impact of installing a battery with your solar panels
We can then give you a savings estimate. We've included example savings at the end of this guide.
How we calculate your solar savings (step-by-step guide)
Estimating energy usage
Your home’s electricity use plays the biggest role in how much you can save. In our savings estimates, we assume you’re home for half of each day, affecting how much energy you use vs how much you would export to the grid.
Want to get a more accurate savings estimate tailored to your home? You can get a customised free solar panel survey from one of our experts.
Average energy use in UK homes (by property type)
If you don’t have your home’s exact energy use to hand, the table below can help you estimate it. By looking at your home’s size and number of people that live there, you can get a good idea of your typical gas and electricity usage, helping you better plan for your solar panel installation and savings potential:
Source: Ofgem
How to estimate the number of solar panels you'll need
To calculate the amount of panels you’ll need, you can divide your home’s annual energy use by the annual output per panel.
For example, if a home uses 3,000 kWh of electricity each year, and each panel generates 440 kWh per year, you'd need approximately 7 panels to cover all of your home's energy use (3,000 ÷ 440 ≈ 6.82, rounded up to 7 panels)*.
*If kk is 1,000
This table gives you an overview of typical annual electricity use for different UK homes and the number of solar panels they might need:
These estimates are based on the assumption that each 300W solar panel produces approximately 300 kWh per year, though actual production will vary depending on things like roof orientation, shadows, and hours of daylight.
Ready to see exactly how many solar panels you need? Contact us for a personalised quote based on your energy usage and roof conditions
How solar export tariff impact savings
If you’re an OVO customer with solar panels, you can earn money back by exporting the energy you don’t use back to the grid. We include this in our calculations, assuming you benefit from our 20p/kWh export tariff. This is an exclusive rate for people who install their panels and get their energy from OVO.
What is OVO’s export tariff?
OVO’s Smart Export Guarantee allows you to earn money for any extra renewable energy your panels generate and send back to the grid. There are a few options available, including:
Our basic SEG tariff - available to anyone, it doesn’t matter which supplier you’re with
Our Beyond exclusive rate - for users of our free Energy Savings Account
Our exclusive rate for customers who get their panels and battery installed by OVO
Find out more on our SEG options here.
The SEG Install Exclusive tariff can pay up to 20p per kWh if both your solar panels and home storage battery were installed by OVO. See our detailed guide on the Smart Export Guarantee here.
The energy price cap: How it impacts your solar savings
The energy price cap set by Ofgem plays a big role in how much you can save when you have solar panels installed. By knowing how much your electricity costs, we can calculate how much you’re likely to save when you generate your own energy. This price cap directly impacts your potential bill savings. Which is why we factor it into our solar savings estimate.
How is the price cap calculated?
The price cap is based on typical household energy use. The price cap also makes sure that prices for people on a standard variable tariff (default tariff) are fair and that they reflect the cost of energy. The cap is reviewed every three months, with the most recent update in February 2025 setting the price cap at £1,849 per year between 1 April and 30 June 2025 for a typical household that pays via direct debit. That marks a 6.4% increase on the previous price cap set between 1 January to 31 March 2025 (£1,738).
The kK factor
Instead of looking at daily sunlight hours and days in a year, most solar calculators look at what’s called the kK factor - this is location-specific and takes into account:
Solar irradiance levels at the location
Roof angle (variation from 0°)
Roof compass orientation (variation from South)
Here are some location specific kK factors. The higher the kK factor, the more your solar panels can produce in a year.
Roof angle and orientation for solar panels: Is your home suitable?
Your roof’s position isn’t just about looks - it impacts how much sunlight your solar panels get. The better your roof catches the sun, the more energy you can generate. We assume your roof is optimally positioned for solar generation. Our experts will double check your roof's orientation during the free survey.
Can solar panels work on other roof orientations?
East-facing roofs capture more sun in the morning, while west-facing roofs work best in the afternoon. Energy production may be slightly lower than a south-facing roof, but it's still a viable option, especially if it’s not overshadowed. As part of our free survey, our local solar expert will look at your roof and help figure out what will work best for you.
What’s the best roof angle for generating solar?
The best angle for your roof is 35 degrees. This is because it matches the angle of the sun in the UK. This angle helps solar panels get the most sunlight possible, which means they produce more energy. By having the panels tilted this way, they work efficiently all year round, no matter the season.
Roof Shading
Last but not least, we’ll look at how overshadowed your home is, as part of our calculation. We assume no shadows from nearby trees or buildings. Being overshadowed reduces solar panel efficiency, lowering the amount of energy you can create, and money you can save. Even partial shading can significantly impact overall system performance.
Maximum energy output from one solar panel per year
Now that we know all the various factors that impact energy output, let’s put them together.
Let’s assume a 440W panel in the Southampton area with minimal losses.
Maximum energy output = 0.44kW x 1021 = 449.24kWh
How many panels does your home need to cover your electricity use
Now that we understand how to estimate the maximum energy output from one solar panel per year, you can now divide your home’s annual electricity use by the maximum output per panel. This can give you an estimated minimum value of panels enough to power your home.
Note: This estimate is based on the assumption that each 440W solar panel produces approximately 449.24 kWh per year, i.e. a kK factor of 1021 (Southampton area, roof orientation South, 35° roof angle), and minimal losses in efficiency.
Ready to see exactly how many solar panels you need? Contact us for a personalised quote based on your energy usage and roof conditions
How much do you save from using the power generated by solar panels
Now that you can estimate the number of panels your home would need to meet your electricity consumption per year, the question is how much would you save on your bill by consuming power that’s been generated by solar panels.
The answer depends on home occupancy, including how many hours of the day your home is occupied. If the home is occupied all day, you will be able to use more solar power generated compared to if you’re out of home all day. The more power you consume, the more you save from paying to your energy provider.
Here’s some example scenarios for low, medium and high solar PV systems and how much solar power is consumed based on home occupancy.
We then need to apply the electricity cost to this that you would typically pay to your energy supplier. These are usually driven by the energy price cap.
How solar batteries can increase savings
Battery storage plays a major role in maximising your savings. By storing excess energy during the day, you can use it when the sun isn’t shining - like at night or when it’s cloudy.
Usable capacity from battery energy storage
The amount of energy you can use from your batteries depends on four factors:
The size of your solar PV system - the more power that’s generated, the more power available for storage
The size of the battery system - our online solar estimates assume a 5.2 kWh battery storage system
Home occupancy during the day - If your home is occupied, you’ll need more capacity from your battery
Overall electricity consumption - For any given battery capacity, if you consume more electricity, you’ll use more capacity from your battery
Let’s show what usable capacity looks like for a solar PV system generating 3,600 kWh annually, and a battery size of 5.2 kWh.
How much you could save from energy stored in a solar battery
Let’s assume a household with 3,600 kWh of electricity generated by solar in a year, which is largely occupied half the day. The amount of solar power consumed is 905 kWh.
If the installation has no battery, we can assume this power can be exported to the grid at the defined SEG rate. If the installation has a battery, this electricity can be used instead of relying on the electricity supplier. Savings are greater because of the difference in the Ofgem price cap and SEG rates.
Examples of electricity bills after solar panel installation
Let’s take a look at how the savings from solar across the board impact your electricity bill. We’ll make a few assumptions for this scenario:
Medium-sized home with annual electricity usage of about 2,700 kWh
Home is in the Southampton area, roof angle 35°, roof orientation South
Eight panel installation
Home occupied half the day
OVO customer (for applicable SEG rates)
Examples of a full solar install for small, medium, and large homes
The table below walks through the entire calculation for a small, medium and large home. The following assumptions are made:
Home is in the Southampton area, roof angle 35°, roof orientation South
Home occupied half the day
OVO customer (for applicable SEG rates)
Savings related to Ofgem price cap 1 January to 31 March 2025