With a range of options available, how do you know what size solar panel system you need?
There’s no doubt that sizing can be a daunting task. It’s also one you want to get right. And with our help – plus that from your installer – you’ll be able to land on the right size.
So, whether you’re looking to reduce your carbon footprint, cut down on energy bills or achieve a degree of energy independence, this guide will walk you through the different solar panel system sizes available. From compact 3kW setups to larger 6kW arrays, we’ll explain the factors that influence system size selection, compare different options and provide you with the knowledge needed to determine the best fit for your home and energy needs.
Understanding solar panel system sizes
Let’s start off with some of the basics. When reading around, you’ll come across terms and units such as kW (kilowatt), kWp (kilowatt peak) and kWh (kilowatt hour).
The terms kW and kWp are largely interchangeable and are used to refer to the system’s maximum power output under ideal conditions. These standard test conditions are usually done at a solar irradiance of 1,000 watts per square metre and a cell temperature of 25°C.
For example, a 4kW system can theoretically produce 4 kilowatts of power at peak performance. However, it’s important to note that real-world performance often differs from these ideal conditions due to factors such as weather, panel orientation and shading.
Kilowatt hour is a measure of how much energy is used over time – 1kWh is the amount of energy you’d use to keep a 1,000 watt appliance running for an hour.
Common solar panel array sizes
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In the UK, common residential solar panel system sizes range from 3kW to 6kW. You can of course get smaller or larger solar arrays, but these sizes cater for most household energy consumption patterns in the UK.Â
Here’s a quick overview (we’ll go into more detail shortly):
- 3kW systems – Suitable for smaller households or those with lower energy needs
- 4kW systems – A popular choice for average-sized UK homes
- 5kW systems – Ideal for larger homes or those with higher energy demands
- 6kW systems – Designed for large households with high energy consumption
Whilst larger systems have the potential to generate more power, they also require more roof space and come with a higher initial investment. The key is to find the right balance that meets your energy needs without selling yourself short or generating tonnes more energy than you need – although the latter situation is much preferred.
Factors influencing solar panel system size choice
There are a number of factors at play when it comes to selecting the appropriate solar panel system size. Let’s take a look at the main ones in no particular order.
- Household energy consumption
Your annual electricity usage is the number one consideration when sizing a solar array.
To determine this, a top tip is to review your electricity bills from the past year and calculate your average monthly consumption. Multiply this by 12 to get your annual usage in kilowatt hours. A system that can generate 80-100% of this amount would be great.
- Available roof space
The physical area available for panel installation can be a limiting factor. Each kilowatt of solar panel capacity requires about 6-8 square metres of roof space, depending on the efficiency of the panels.
You (or more likely your installer) will have to conduct a thorough assessment of your roof to determine how many panels it can fit on. Roof space may be reduced by the likes of velux windows and chimney stacks.
- Budget considerations
It’s not rocket science, but the larger the system, the higher the upfront cost. With any size system, it’s important to balance the initial investment with long-term benefits. You’ll want to consider factors such as electricity savings, potential earnings from the Smart Export Guarantee (SEG) and the system’s payback period – the shorter the payback time, the better.
- Location and sunlight exposure
Although modern panels can still generate electricity when the sun isn’t shining, the amount of direct sunlight your rooftop receives impacts the system’s efficiency.
It’s not an exact science though. Homes in southern England generally receive more sunlight than those in Scotland. So these systems would potentially generate more energy with the same system size.
Additionally, the orientation and pitch of your roof play a key role too. South-facing roofs at a 30-40 degree angle are ideal, but east or west-facing roofs can still generate good amounts of electricity, with around a 15-20% reduction in energy production compared to south-facing.
For flat roof installations, installers will fit a special type of mounting bracket to get the best angle and orientation possible.
- Future energy needs
Are you planning to switch to an electric vehicle? Install a heat pump? Perhaps extend your home?
All of these factors are likely to lead to an increase in energy consumption. It’s more than possible to add on to an existing solar array and expand it later on, but it makes sense to factor in future needs now so that your system will remain adequate for years to come. This will also reduce installation costs.
Common solar panel sizes for UK homes
Now, let’s take a closer look at each common system size. For each system size we’ll address their specific household suitability, standard energy generation numbers, potential costs and return on investment.
3kW systems
A 3kW solar panel system is an excellent entry point for many UK households, particularly those with lower energy needs or limited roof space.
- Suitable for: 1-2 bedroom homes with 1-3 occupants
- Energy generation: Around 2,500 kWh/year
- Number of panels: 8-12, depending on individual panel wattage
- Roof space required: Approx 12-17 square metres
- Cost range: £4,500 – £7,000
- ROI: Around 8-14 years
A 3kW system can cover a significant portion of an average small household’s energy needs. For a home using about 2,700 kWh annually (typical annual electricity use for a medium house according to Ofgem), this system could potentially provide up to 90% of the required electricity.
These systems are particularly beneficial for retirees or small families who are conscious about their energy usage. They offer a good balance between initial investment and long-term savings, making them an attractive option for those looking to dip their toes into solar energy.
4kW systems
The 4kW system is one of the most popular choices for UK homes, offering a sweet spot between cost and output for many families.
- Suitable for: 3 bedroom homes with 2-4 occupants
- Energy generation: Around 3,400 kWh/year
- Number of panels: 10-14, depending on panel wattage
- Roof space required: Approx 16-24 square metres
- Cost range: £5,000 – £8,000
- ROI: Around 8-12 years
A 4kW system can cover the majority of an average UK household’s energy needs. For a home using about 3,500 kWh annually, this system could potentially provide up to 90%+of the required electricity if paired with battery storage that saves all excess electricity produced.
These systems offer an excellent balance between initial investment and energy production. They’re particularly suitable for families who have moderate energy consumption but are looking to significantly reduce their reliance on grid electricity.
5kW systems
For larger homes or those with higher energy demands, a 5kW system offers substantial power generation.
- Suitable for: 4+ bedroom homes with 4-5 occupants
- Energy generation: Around 4,250 kWh/year
- Number of panels: 13-18, depending on panel wattage
- Roof space required: Approx 25-38 square metres
- Cost range: £7,000 – £10,000
- ROI: Around 6-12 years
A 5kW system can often cover all of an average large household’s energy needs, with potential excess during sunny periods. For a home using about 4,100 kWh annually (typical annual usage for a large home according to Ofgem), this system could provide over 100% of the required electricity.
These systems are particularly beneficial for households with high energy consumption, perhaps due to electric vehicles or heat pumps. They offer the potential for significant long-term savings and a higher degree of energy independence.
6kW systems
The 6kW system is designed for large households with high energy consumption or those looking to really maximise and earn from their solar energy production.
- Suitable for: 4+ bedroom homes with 5+ occupants
- Energy generation: Around 5,100 kWh/year
- Number of panels: 16-24, depending on panel wattage
- Roof space required: Approx 38-43 square metres
- Cost range: £8,000 – £11,000
- ROI: Typically 8-10 years
A 6kW system can often exceed the energy needs of even large households, providing ample power for homes with very high consumption. For a home using about 4,500 kWh annually, this system could provide well over 100% of the required electricity.
These systems are ideal for families looking to achieve a high degree of energy independence. During summer months, it’s possible to be entirely self-sufficient and even earn money by selling excess energy back to the grid through the Smart Export Guarantee scheme. It’s worth shopping around for the best SEG rates. Some suppliers offer just a penny or two per kWh exported, but you can get much better. For example, Octopus’ Outgoing Fixed currently pays 15p per kWh exported to the grid.
Comparing system sizes
| System size | Approx energy production (kWh/year) | Costs | Roof space requirements | |
| 3kW | 2,500 | £4,500 – £7,000 | 12-17 m² | |
| 4kW | 3,400 | £5,000 – £8,000 | 16-24 m² | |
| 5kW | 4,250 | £7,000 – £10,000 | 25-38 m² | |
| 6kW | 5,100 | £8,000 – £11,000 | 38-43 m² |
Should you consider battery storage for a solar panel system?
Absolutely, battery storage should at least be a consideration when weighing up system sizes.
Integrating battery storage can significantly improve the benefits and efficiency of your solar system, regardless of the size. Storage batteries allow you to store excess energy for use during low-production periods or at night.
For smaller systems (3-4kW), a solar storage battery can help maximise self-consumption of generated energy. On a good day, even smaller systems can generate a lot of energy. Why not save this energy up and use it for free during the evening, night or the next morning?
For larger systems (5-6kW), your array can generate so much energy that it’s possible to go off-grid during high-production months with a big enough battery. Read more on can battery storage power a house.
Of course, battery storage does come with an additional cost. However, in the right system this can pay for itself in less than 10 years. You can read more details on the topic of solar panels with or without battery storage to see if this is right for you.
Step by step on how to determine the right size for your home?
Here’s a step-by-step guide to help you make an informed decision:
- Analyse your energy bills – Review your electricity consumption over the past year. Look for both total usage and usage patterns throughout the day and across seasons.
- Assess your roof – Evaluate the available space, orientation and condition of your roof. South-facing roofs are ideal, but east or west-facing roofs can also be suitable.
- Consider future needs -Factor in potential increases in energy consumption, such as switching to an electric vehicle or installing a heat pump.
- Set your budget – Determine how much you’re willing to invest initially. Remember to consider long-term savings and potential SEG earnings.
- Get professional assessments – Solar installers can provide detailed evaluations and recommendations based on your specific circumstances. They can use tools like shade analysis and energy production modelling to give accurate estimates.
- Compare quotes – Obtain multiple quotes from MCS-certified installers. This will give you a range of options and help you understand the cost-benefit ratio of different system sizes.
Common mistakes to avoid
When sizing the system, you have the risk of potentially oversizing or undersizing it.
In general, it’s always better to slightly oversize your solar array. However, although it might seem appealing to generate as much energy as possible, installing a system larger than necessary can lead to excess costs and reduced efficiency. If you’re consistently producing more energy than you can use or store, you’re not fully maximising your investment.
On the other side, undersizing is also something you want to avoid. A system that’s too small may not meet your energy needs, leading to continued reliance on grid electricity and reduced savings from your solar system.
Before you stick a large array on top of your house, make sure the roof conditions have been checked out properly. Failing to consider roof orientation, shading or structural integrity can lead to less than optimal results. In some cases, a slightly smaller system on an ideal roof section might outperform a larger system in a less optimal location.
Neglecting future needs is a common error that can result in a system that quickly becomes inadequate. It’s important to account for potential increases in energy consumption, considering factors like electric vehicle charging or home extensions that might increase your energy needs in the future.
Overlooking energy efficiency is another mistake to avoid. Before sizing your solar system, consider implementing energy-efficiency measures in your home. Reducing your overall energy consumption can allow for a smaller, more cost-effective solar system.
And finally, make sure that you don’t live in an area where you require planning permission for solar panels.
Wrap up on solar panel sizes
There’s no one-size-fits-all solution when it comes to solar energy and the sizes required. Your ideal system size depends on your unique circumstances, including your energy consumption patterns, roof characteristics, future plans and other factors discussed.
By carefully considering these factors and seeking professional advice, you can make an informed decision that maximises the benefits of solar energy for your home. With the right solar system size, you can enjoy reduced energy bills, a smaller carbon footprint and the satisfaction of generating your own clean energy for years to come.
FAQs about solar panel sizes
Q: Can I install a system larger than my current needs?
A: Yes, you can. However, it’s generally more cost-effective to match system size to your actual energy consumption. Oversizing may lead to excess production that you can’t use or store, reducing overall system efficiency.
Q: What if my energy needs change after installation?
A: Many systems can be expanded later. If you anticipate significant changes in your energy needs, discuss this with your installer during the planning stage. They can design a system that allows for future expansion.
Q: Do larger systems always produce more energy?
A: While larger systems have higher potential output, actual production depends on various factors including installation quality, panel efficiency and your local sunlight conditions. A well-designed smaller system could outperform a poorly installed larger system.
Q: Can I install a smaller system now and upgrade later?
A: Yes, many systems are scalable. Discuss this option with your installer to ensure your initial setup can accommodate future expansions. Consider factors like inverter capacity and available roof space when planning for potential upgrades.
Q: How do solar panel sizes relate to energy storage options?
A: The size of your solar panel system should be considered alongside any battery energy storage solutions. Larger systems tend to benefit more from storage, allowing you to use excess energy during low-production periods.
