A Guide to Calculating Your Solar Panel Size
- Your average daily energy consumption
- The sun hours in your area
- Your roof size
The average energy consumption - or planned usage - is the most important guideline in determining the number of solar panels that you need. Here, the consideration is the total Kilowatt hours (kWh) you currently use, or intend to use in your home.
The amount of energy solar panels can generate is dependent on sun hours, and is therefore affected by your location. There are varying amounts of sun hours in the UK, which will affect the number of solar panels you will need.
Your roof size is a key factor because it determines the number of panels that can fit on your roof, how much energy will be generated, and the cost. It is also important to consider your roof suitability: whether it can support the weight of the solar panels and how the panels will be angled.
The table below shows approximate amounts of space you need in order to generate a specific amount of energy.
|Size of solar panels||Number of 250W panels||Estimated surface area|
* Table assuming 250Wp Solar Panel dimensions: 1.6 x 1 m = 1.6 m²
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What Is the Average Number of Solar Panels In A UK Home?
One of the determining factors in figuring out how many solar panels you need is the number of people in a household. A 6kW solar panel system is recommended for a home with over five people, while a 5kW solar system is typical for a home with four people. A 4kW solar system is one of the most common sizes for domestic solar systems, as it suits homes with 3 to 4 people.
The number of solar panels you need will vary depending on whether your installation is a 3kW or 6kW, and the size of solar panels you will use. For example, if you install a 3kW solar system using 250W panels, then you need 12 solar panels. A 6kW system would need 24 solar panels.
The average number of solar panels will also be determined by whether you would like your solar panels to generate all your electricity needs, or only a percentage of it.
An average UK home consumes between 3kWh and 6kWh of energy daily, and some UK homeowners use solar energy to power only parts of their energy consumption, which would then reduce the number of solar panels installed.
How to Calculate Your Required Solar System Size
To calculate what solar system size you need, you should first know the amount of energy that you need to generate from your solar solar system daily. The other important things are the sun hours in your area, and your roof space.
Monthly energy bills can provide information on the amount of energy that you consume per day, and therefore how much energy you need to generate daily.
For example, if your monthly consumption is 124 kWh in January, then your daily consumption is 4 kWh. This means that the solar system should generate an average of 4 KWh daily. The 4 kWh can also be referred to as the expected daily solar system power output.
Some people may question if the UK is sunny enough for solar panels. The UK has an average of 4 sun hours daily which means you can certainly benefit from having a solar panel system installed.
It is important to be aware that different regions in the UK have different sun hours per day: England has 4.1, Scotland has 3.7, Northern Ireland 3.2 and Wales 3.3. It is therefore important that you consult your local installer for guidance.
Determining Individual Solar Panel Sizes
To determine the size of the panels that you need for your house, you need to know the following:
- How much energy do solar panels with different capacities generate?
- The capacity of your roof: how much space in square meters is available?
- Dimensions of solar panels per size or brand.
Solar panels generate different amounts of energy depending on their wattage size or rating. A 250 watt panel will generate up to 250 watts per sun hour while a 300 watt solar panel can generate up to 300 watts per sun hour. This is why it is important to know the amount of energy you need before determining solar panel sizes.
In the earlier example with a daily consumption of 4 kWh (4,000 W/hrs), if the homeowner used 250 W solar panels, then they would need to install 16 solar panels (4,000 Wh/250 W). If they used 350 W panel, then they would need 12 solar panels (4,000 Wh/350 W).
The capacity of your roof impacts the number of solar panels you can install and therefore how much energy you can generate. This is also because different solar panel sizes have different dimensions.
Continuing with the previous example, if you are installing 16 250W solar panels, you would require a surface area of 25.6 m².
If you are installing 12 350W solar panels would require a surface area of 22.8 m².
It is therefore important to know how much space you have. The table below outlines the average solar panel dimensions and weight per system size.
|Solar panel size (W)*||Solar panel dimensions*||Weight per panel|
|250||1.6 m x 1 m||18 kg|
|300||1.67 m x 1 m||18 kg|
|350||1.9 m x 1 m||21.6 kg|
*It is important to note that different brands may have different solar panel dimensions.
What Type Of Solar Panels Should I Install?
The choice of solar panel type can be based on efficiency, cost, and available space. Some types of solar panel are more efficient that others, and this would affect the number of panels you need to install.
For example, you need less space to install monocrystalline panels compared to thin film and polycrystalline solar panels.
There are different types of solar panels that can be installed on your roof, but the most commonly installed panels are monocrystalline or polycrystalline solar panels.
Monocrystalline solar panels have the highest efficiency rate of 15 - 20%. This means that they can convert between 15% and 20% of sun energy into usable energy.
This type of solar panel is also space efficient because they generate more energy per area compared to other types. One square metre of a monocrystalline panel will generate 10W more than the same size of a polycrystalline solar panel.
On the other hand, monocrystalline panels are the most expensive solar panel type due to their high efficiency and quality of silicon used.
Due to their high temperature tolerance, polycrystalline solar panels generate more electricity over the year compared to monocrystalline panels.
Polycrystalline panels are a cheaper alternative to its monocrystalline variant. Although both types are made from silicon, in polycrystalline, many fragments of silicon are melted to form the wafers for the panel, while in monocrystalline silicon is formed into bars and cut into wafers.
A downside of polycrystalline panels is that they are less efficient because their silicon material is less pure. You can expect an average efficiency rate between 13-17%.
Cost Of Solar Panels
Naturally, cost is an important determining factor for how many solar panels you need. Solar panel costs depend on several factors that include the size and type of solar panels. The cost ranges from £1,500 to £8,000 for solar panel system sizes ranging from 1 kW to 4 kW.
Other factors that may affect the cost of solar panels include:
- The cost of solar panels in your area
- Brand or supplier costs
- Labour costs in your area
- Site complexities that may require more labour hours
There is also an advantage of getting paid for the energy you generate under the Smart Export Guarantee (SEG), and therefore can result in savings in the long run. Unlike the former Feed-in Tariff scheme, the SEG is a type of solar panel funding that requires that all exported energy is paid by your supplier.
Do I Need a Solar Battery Storage System?
Deciding whether to install a solar battery storage with your solar panels depends on your interests. If you would like to avoid energy bills and reduce reliance on grid power, then installing your solar panels with a solar battery storage is the most appropriate option.However, if your goal is to reduce your energy bills, then installing solar panels without a solar battery storage can be an option.
A solar battery storage has several benefits;
- You can store the unused energy generated by your solar panels
- You will be less reliant on the grid electricity
- You will be more environmental friendly
- You have reduced or no electricity bills
Households that install solar panels with a battery storage, use about 80% of the energy they generate while households without a battery storage use only 40% of energy they generate.
The amount of money you can save by installing your solar panels with a solar battery storage depends on the number of solar panels installed, the size of solar battery installation, and how much the batteries can discharge.
If you would like to save more energy, then you would have to install more panels and more batteries. A solar professional can advise you on different options and costs.
Find an Installer In Your Area
Determining the number of solar panels you need requires key considerations in your current energy consumption, sun hours in your area, and your roof size.
Installing solar panels or a solar system is also a long term decision that is expensive. It is therefore advisable to get relevant information, the right solar suppliers, and professional installers. You should also compare different offers before making a decision.
If you would like more guidance on how many panels you need, fill in the contact form and get up to four tailored quotes from suppliers in your area. The service is free and non-binding!