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Janet Richardson

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Jul 24, 2024

Read Time : 9 Minutes

How much Space do I need for Solar Panels? UK Guide 2024

The number of people investing in solar PV is increasing, and inevitably, they will ask, "How many solar panels do I need?

Solar energy benefits both the planet and our bank balance, as the energy produced is free, and the payback period is well within the system's lifespan. However, it's important to determine the number of solar panels needed and the amount of electricity generated per square foot (sq. ft) or square meter (m2) before installation.

In this article we explore how much roof space is required for solar panels in the UK, the electricity output from the panels, and the financial implications.

How Much Space for a 4kW Solar Panel System?

When we talk about solar panels, we usually refer to the power produced in watts (W) or kilowatts (kW). An example of this in context would be that the average household requires a 3.8-6kW system to produce enough electricity to cover most of the electrical requirement. A 5-14kW capacity battery is usually required if you want to cover as much of your electrical usage as possible. 

4kw solar panel system will need to be around 215 ft² or 20 m². This may sound quite large, but when we put it into a different measurement, it only comes out at 15ftx15ft or 4.57x4.57m. This will easily fit on most rooftops in the UK.

The output of your solar panel system will depend on how much space is used, the wattage output of the panels that you have installed, the direction in which the panels face, the pitch of the roof, any shading, and finally, if the suns actually shining! If you want to get the most from your solar panels, they should be facing south and at an angle of 32 degrees with no shade. 

On average, a 4 kW system can cover approximately 50% to 70% of the annual electricity needs for an average UK household.

The table below gives an approximate roof size requirement for solar panel systems up to 6kW. To get accurate, site specific data, you will need to get a professional installer to survey and design a system for your roof. Solar panel sizes and output vary considerably. 

Solar PV System Size  (kW) Roof Space Required  (m²) Roof Space Required  (ft²)
1kW 5 m² 53.82 ft²
2kW 10 m² 107.64 ft²
3kW 15 m² 161.46 ft²
4kW 20 m² 215.28 ft²
5kW 25 m² 269.10 ft²
6lW 30 m² 322/92 ft²

Factors Affecting Solar Panel Output

Wattage Output: The output capacity of the panels.
Panel Orientation: South is optimal, but anything from east to west through south is good. 
Roof Pitch: An angle of 32 degrees is ideal but again, there is some give here. 
Shading: Shade will significantly effect output. Look at micro-inverters if you have some shade. 
Sunlight: The amount of light the panels receive over through the seasons. 

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How Much Electricity per Square Foot or Square Meter? 

The amount of electricity (in kilowatts) that you can expect to generate per square foot of solar panels in the UK can vary based on several factors, including the location's solar irradiance, panel efficiency, tilt, shading, and weather conditions. However, I'll provide you with a general estimation based on typical conditions.

Solar Irradiance: The UK receives less sunlight compared to sunnier regions, which affects the solar panel's output. On average, you can expect around 850 to 1,100 kilowatt-hours (kWh) of solar energy per square meter (approximately 10.764 square feet) annually.

Panel Efficiency: Solar panel efficiency determines how well the panel converts sunlight into electricity. The efficiency of commercially available solar panels is around 15% to 24.5%.

Given these values, we can calculate the estimated electricity generation per square foot of solar panels in the UK:

Estimated electricity generation (kWh/square foot/year) = (Solar irradiance per square meter) x (Panel efficiency) x (Conversion factor)

Conversion factor: To convert square meters to square feet, we use the conversion factor of 1 square meter ≈ 10.764 square feet.

Let's assume an average solar irradiance of 975 kWh/m²/year and a panel efficiency of 17%:

Estimated electricity generation (kWh/square foot/year) ≈ (975 kWh/m²/year) x (0.17) x (1 m² ≈ 10.764 ft²)
≈ 166.275 kWh/square foot/year

Keep in mind that this is a rough estimation, and actual results will vary depending on the factors mentioned earlier. Additionally, solar panel technology is continually improving, so newer and more efficient panels might yield higher electricity production in the future.

How Much Can Solar Save on Your Bills? 

Let's assume you're buying a 4kW solar PV system for £7,000. You're paying £1,750 per kW installed.

Keep in mind that this cost is an upfront investment and does not take into account factors like maintenance, repairs, and replacement costs, which can affect the overall cost of electricity generated by the system over its lifetime.

A 4kW system will not consistently output 4kW; in fact, your installer will likely install an inverter with a capacity to handle around 3.5-3.6kW.

Let's assume an average of 5 hours of full sun per day under optimal conditions. In 2022, the UK average was 4.9 sunlight hours.

Calculate the daily energy generation: Multiply the system capacity (3.6kW) by the average daily sunlight hours (5 hours) to get the daily energy generation in kilowatt-hours (kWh).

Daily Energy Generation = 3.6 kW × 5 hours = 18 kWh

Calculate the annual energy generation: Multiply the daily energy generation (18 kWh) by the number of days in a year to get the total annual energy generation in kWh.

Annual Energy Generation = 18 kWh/day × 365 days = 6,570 kWh

So, in optimum conditions, a 3.6kW solar panel system could generate approximately 6,570 kilowatt-hours of electricity in a year. The average cost per unit of electricity in the UK is £0.22, so the potential savings, if you used every kWh produced by your panels yourself and didn't send any back to the grid, would be approximately £1,444 per year.

Unfortunately, these calculations are based on a system in optimal conditions, providing the maximum possible output. We've set this out purely as a guideline to start from.

Realistically, a 4kW system in the UK will provide an average of 3,000-3,400 kWh per year due to the factors we discussed earlier; solar irradiation, weather conditions, orientation, pitch, and shading. This works out to approximately 8 to 9.3 kWh per day, or 0.33 to 0.39 kWh per hour, on average over the year.

A standard 4kW solar PV system requires about 20 m² of roof space, resulting in approximately 150-170 kWh per m² of installed roof area annually.

According to Ofgem, the average household in the UK uses approx. 2,900 kWh of electricity per year. So, the average three-bedroom property with 2-3 occupants uses approximately 7.9 kWh per day, so a 4kW solar panel system, with a battery, can often cover all your electricity needs during the summer. In the winter you'll likely be taking more from the grid.

A 4kW solar panel system installed on the average 3-4 bedroom property in the UK will save approx. £704 per year on your energy bills. Average kWh generation x average kWh unit price - 3200 times £0.22 = £704
This calculation assumes you use all the energy your system generates. 

Solar Panel Sizes UK

Solar panel size refers to not only it's physical dimensions and weight but also to it's size in terms of wattage (power output). 

If your solar array is not sized correctly you can end up spending more than necessary, or with a solar system that is too small to meet your needs.

The UK is going 'all electric', so consider future requirements. The government is currently running financial incentives for homeowners switching to heat pumps, electric cars sales are up, and our nation's demand for electricity grows by the day. Whilst your installer is designing your system, if there's space, it's often worth adding extra panels to future proof. 

Below is a table of the 10 best-selling solar panels in the UK, including their size and wattage output:

Solar Panel  Size (cm( Output (W)
Project Solar UK Evo Super Max 455 190.5 x 113.4 455
SunPower Maxeon 7 178.7 x 103.5 445
Jinko Tiger Neo 420 N-Type 54 Cell 172.2 x 113.4 420
JA Solar JAM72D40 Mono PERC Half-Cell MBB 227.8 x 113.4 550
Suntech Ultra V Mini 405Wp 172.2 x 113.4 405
AIKO N-Type ABC White Hole Series 227.8 x 113.4 620
Seraphim SRP-670-BMC-BG 227.8 x 113.4 670
Q Cells Q.Peak DUO BLK ML-G9 174.0 x 103.9 355
Panasonic HIT N340 160.0 x 105.3 340
LONGi Hi-MO X6 Explorer 435W 176.0 x 105.0 435

Let’s take a look at each aspect of a solar panel’s size. 

Solar Panel Physical Dimensions

Solar panels are generally measured in millimetres (mm), centimetres (cm), or metres (m). The physical size of the solar panel is measured by taking the length, width, and height (thickness) of the individual panel including the frame. In terms of dimensions, standard domestic solar panels in the UK are 189cm (length) x 100cm (width) x 3.99cm (height) while standard commercial solar panels in the UK are 195cm x 99cm x 3.81cm. 

However, there is no universal size or dimension for either domestic or commercial roofs. While there isn’t usually much flexibility when it comes to choosing solar panel dimensions it is more important to prioritise the size (power output) of the solar panels over dimensions as this will determine how much energy you generate. The physical dimensions of a solar panel do not necessarily have any bearing on its power output (size). More powerful solar panels may require larger dimensions to accommodate more solar cells.

Physical dimensions need to be factored in to ensure solar panels fit snugly on your roof. The physical dimensions of your solar panels will of course affect how many you can fit on your roof. Once you know how many solar panels will make up your solar system you will need to calculate how much roof space is required. Standard building regulations require solar panel installations to not extend 200mm beyond the edge of the roof or wall; to not be larger than 9m2, to be less than 4m in height, and to be more than 5m away from garden boundaries.

Solar Panel Weight

Solar panel weight is extremely important as it is essential that your roof can bear the weight of your solar installation. If you don’t consider this, you risk damaging your roof which can be both dangerous and extremely expensive. Fortunately, a complete survey is part of your installer’s solar quote process. Your roof’s health and structural status will be assessed during the survey. 

The standard solar panel weight in the UK is 18 – 21kg for residential settings and 22 – 30kg for commercial settings. The weights of the frames and mounting equipment are included in these weights. In most cases, rooftops have a rafter load of 140kg per square metre. To put this in perspective, solar panels usually weigh approximately 20kg per square metre. 

This means that installing panels will increase the dead load by about 15% per square metre. Though the weight of your roof shouldn’t cause you too much worry, all roof structures should be assessed by a professional solar panel installer to make sure your roof is robust enough for the solar panel system.

How Many Solar Panels do I Need? Quick Recap

  • Wattage measures how much electricity a solar panel generates per hour. The higher a solar panel's wattage, the more energy it will produce. The more panels you install the more energy will be generated.
  • How many panels your system will be comprised of will be determined by how much energy you require and amount of suitable roof space you have available. 
  • For example, a regular 4kW solar panel system, which would work well for 1-3 people, will comprise 10, 400w panels and requires approx. 20 m² of roof space. 
  • The average domestic solar system will usually generate an average of 3000 - 3400 kWh of electricity per year. 
  • The average household in the UK uses around 2,900kwh a year, according to Ofgem.
  • How much electricity can a solar panel array produce? In most cases, a 3kW or 4kW will be able to generate enough electricity to provide about 50-70% of the average UK household’s demand while a 2kW will be able to supply around 25-35% of the average UK household demand. 
  • The most common solar panel systems are around 3-5kW. For households of 5 people or properties with high energy usage, maybe a heat pump or an EV, a 6kW+ solar panel system with a battery may well be the best fit.  
  • Based on products from top solar panel manufacturers such as SunPower, Panasonic, and Jinko Solar, the best selling solar panels in the UK range from 340W – 670W.
  • Some properties will be limited by the physical number of panels that can fit on their roof. For example, there may not be enough space on their south-facing elevations. If you don't have much space on your roof, then it's often a good idea to look at panels with higher wattage output. 
  • The UK's best selling solar panels range in size from 1.6x1m - 2.3x1.1m approximately. 

Are there Different Types of Solar PV Panel?

There are three main types of solar panels, monocrystallline, polycrystalline, and thin-film solar panels. Your solar panel installer will advise you on the best type for your home but monocrystaline panels are the most common and efficient. 

Monocrystalline Solar Panels

Made from single-crystal silicon, a monocrystalline solar panel is the most reliable type of solar panel. They are a popular choice for domestic installations and are a uniform black colour with rounded edges. A monocrystalline residential solar panel tends to come in two sizes: 60-cell and 72-cell. The 60-cell panels are about 65 by 39 inches and have a power output of around 280-320 watts, and the 72-cell panels are about 77 by 39 inches and have more power output of around 340-460 watts. Canadian Solar panels weighed in at the heaviest at up to 50 pounds. 

Polycrystalline Solar Panels

Made from melted multiple small silicon crystals these solar panels have a distinctive blue colour. They are slightly less efficient than monocrystalline PV cells but are also cheaper. Polycrystalline panels come in different sizes, from small-weight panel options for portable use to large-weight commercial solar panels. Typical sizes for commercial installations include 60 cell panels and 72 cell panels. The 60-cell panels are 65 x 39 inches with an electrical output of 280-320 watts and the 72-cell panels are 77 x 39 inches with an electrical output of around 340-400 watts. These solar panels are also good for residential solar installations. 

Thin-Film Solar Panels

These solar cells are created by depositing a thin layer of photovoltaic material onto a substrate such as glass, plastic, or metal. They aren’t as efficient as crystalline cells but are a sleek weight, flexible, and can be made in various sizes and shapes. There are two main types of TF solar panels: amorphous silicon and cadmium telluride.

Considering wattage, weight, and dimensions is essential to designing the system that meets the criteria for your ideal system. All these factors are considered during the solar array survey process. 

Advantages of Solar Energy in the UK

  • It’s a renewable energy source. This means it will not run out (at least, not for another 5 billion years or so). It is also a clean source of energy, so does not cause pollution after initial manufacture. 
  • It reduces your electricity bills. The electricity generated by solar panels is technically free as you do not pay for it, reducing the cost of your monthly or annual energy bill. Plus, you can sell the surplus energy back to the grid through the Smart Export Guarantee (SEG).
  • It has diverse applications. It can be used to generate electricity, but also for heating. It can be used in areas that don’t have access to the National Grid or for example, to distill water in regions with limited clean water supplies.
  • Maintenance costs are low. The panels don’t require much maintenance aside from a quick wash a couple of times a year. They last around 50 years, and the warranties tend to cover around half of that time.
  • Constant development. One of the great things about solar technology is the constant research and development going on to make it more efficient, lighter on your roof and more aesthetically pleasing. 
  • When installed specifically for purpose, solar panel systems with batteries can operate in a power cut.  
  • They can potentially remove your reliance on energy companies, or at least protect you from the year-on-year cost increase of electricity.   

Are There Risks?

Solar panels actually tend to be quite low risk because they don’t have any moving parts, aside from a small inverter. This tends to be the part that may need replacing at some point. Plus, they have great lifespans and warranties.

One of the important things to remember is that you should always use an MCS-accredited installer, as not doing so could risk poor installation and also void your warranty. MCS-accredited installers know what they are doing and will ensure it is installed to industry standards, as well as providing you with a guarantee. Without MCS installation, you will also not be eligible for the Smart Export Guarantee, should you want it at any point. 

It is also worth contacting your insurance provider and checking if they require the installer to be MCS certified. 

As a general rule, you should get at least three quotes before you decide on which company you wish to go with.

Want to Know More?

Have you found yourself interested in solar panels? If you want to know more then click the links on the left or visit our online directory of approved installation companies. Alternatively, simply give us a ring using the number at the top of this page and have a chat.

 

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