In this 10-minute read, we look at the varying sizes and types of solar panels available for residential and commercial applications in the UK — and how to choose the right solar panels for your project.
Why does solar panel size matter?
If you’re making the switch to solar energy, either in a residential or commercial setting, choosing the correct solar panel size is a crucial factor in ensuring your system is as efficient, cost-effective and productive as possible. It might seem like a simple choice, but the dimensions of the solar panel you use directly influence key aspects of your installation, including:
- Power output: Larger panels produce more total power (measured in watts) per panel installed, and can be more efficient if using microinverters, as they require fewer overall.
- Use of space: Different solar panel dimensions affect how much roof or ground area you’ll need, and how the panels will fit into the available space.
- Installation cost: Choosing larger panels may reduce installation time as you’ll require fewer units, but smaller panels present fewer transport and handling challenges.
- System cost: Depending on your overall requirements, it may be more cost-effective to install fewer, larger panels or multiple smaller panels.
- Maintenance: For the same surface area, larger panels require fewer connectors, which means fewer potential points of failure.
This guide is designed to give you all the information you need to select the optimal solar panel sizes and wattage for your specific project. We’ll look at the standard dimensions of solar panels available on the market, the differences in output and efficiency, physical and structural limitations, and the costs associated with different configurations.
What are the standard solar panel sizes and wattage?
For domestic installations, the solar panels used tend to be smaller and lighter, in order to fit single-home rooftops or garden space, and to make installation easier. In commercial installations, where energy demands are higher and available space is less limited, larger panels are more common, reducing the labour and cost associated with installation.
Common panel dimensions include:
How does solar panel size affect efficiency and output?
Efficiency is typically expressed as a percentage, representing the proportion of sunlight converted into electricity, and as a guide, most modern solar panels have efficiency ratings ranging from 15% to 23%. It’s important to note that the size of a panel doesn’t directly affect its efficiency. For instance, a larger panel with a lower efficiency rating might have the same power output as a smaller panel with a higher efficiency rating.
If you’re looking to maximise the amount of energy you can generate for a given solar panel size or total surface area, then there are a number of factors affecting panel efficiency you should take into account.
Cell technology
Monocrystalline silicon panels generally have higher efficiencies compared to polycrystalline panels, and emerging technologies like thin-film solar cells offer additional efficiency improvements.
Manufacturing processes
Advanced manufacturing techniques and quality control contribute to higher panel efficiency and longevity, although this may be reflected in a higher cost per panel.
Temperature coefficient
Solar panel efficiency decreases as temperature increases, so output is relatively lower on hotter days. Panels with better temperature coefficients maintain higher performance in warmer climates.
Angle of incidence
The angle at which solar panels are installed will affect the efficiency of the panel, and therefore the total output. The optimal installation angle must be calculated based on location and shading patterns.
See how much your business could save each year by switching to commercial solar panels with our easy-to-use online calculator.
How do I calculate the number of solar panels required?
Accurately determining the optimal number of solar panels and the available space you’ll need requires a careful assessment of your energy consumption, the desired system output, and the solar panel dimensions, wattage and efficiency.
Example scenario
Let’s say you run a medium-sized business in London — consuming an average of 50,000 kWh of electricity per year — and you’re looking to install a solar PV system which will provide 80% of your total energy needs. Your target for solar generation is therefore 40,000 kWh per year.
To make a rough calculation of the number of panels you’ll need and the space required to fit them, you’ll need to know the following information.
- Solar panel dimensions (in m²)
- Solar panel peak output (in kWp)
- Peak daily solar hours in your location (in hrs)
In this example, let’s say you’re comparing two types of solar panels — type A producing 0.4 kWp and type B producing 0.5 kWp. Both measure roughly 1 metre by 2 metres, for a total footprint of 2 m². We also know that peak daily solar hours for London are around 3.
First, calculate the yearly output per panel by multiplying the peak output by the peak daily solar hours and multiplying the result by 365 (days in a year)
Then divide your annual target for solar generation by this figure (and round up to the nearest whole number) to reveal how many of each type of panel you would need to meet your energy goals.
And if we multiply the number of solar panels needed by the solar panel dimensions, we can see how much space would be required for each choice.
Of course, there are multiple other factors to consider for an accurate specification — system and transmission losses, panel orientation and shading, and seasonal weather patterns. To design the optimal system for your needs, it’s always best to work with an experienced consultancy that can model each element of the system for the most cost-effective and efficient solution.
Did you know?
JLM offers a free remote energy audit, which examines your energy consumption data, building characteristics, and operational requirements. You’ll receive a personalised report based on your real-world energy usage, with details of the optimal solar PV configuration to meet your needs.
What’s the difference between residential and commercial solar panel sizes?
The target output for residential solar PV systems is generally much lower than for commercial systems, and this influences the optimal panel size. Smaller panels are usually preferred as they offer more flexibility with the limited roof space available in most domestic settings, and are easier to transport and install. As the total solar panel surface area required for an average home is only around 15-25 m², factors such as installation cost and ease of maintenance do not have a significant effect.
In commercial solar energy projects, larger panels are more commonly used. With fewer space restrictions to consider, they offer several advantages which help to maximise system efficiency, streamline installation and reduce overall project costs.
However, larger panels are not always the best solution for every commercial project. Factors such as roof orientation, shading, and structural considerations can affect the optimal solar panel size for a specific project, and it’s important to undertake a comprehensive site assessment and consultation with experienced solar installers to determine the best configuration.
Thinking about solar panels for your business?
Our 2025 guide to commercial solar energy in the UK has all the up-to-date information you need on commercial solar panel installation, operation, maintenance and financing.
How much space do solar panels require?
Space requirements vary depending on panel size and the desired system output. It’s also important to remember that you may not be able to use 100% of your available roof space (or ground space) to install solar panels — some areas may be too shaded, or may not be structurally capable of supporting solar panels.
Here’s a rough calculation for the space requirements of different types of business, assuming the use of 0.4 kW (400W) panels in a 2 x 1 m form factor.
So, for an office building, in our example, you would need 250 m² of usable roof space — that’s roughly a 16 x 16 m square space. If that’s not available, you have two options. You can go ahead with the maximum installation size possible, which means generating a lower proportion of your total energy needs. Or, you can opt for higher-wattage panels to generate more electricity from the available space.
Here’s the calculation using 0.54 kW (540W) panels in the same 2 x 1 m form factor.
As we can see — choosing the right type of panel makes a big difference in terms of the available space required. For the office building example, we now only require 185 m² — a 13.5 x 13.5 m roof space. This could make all the difference where space is limited. However, it’s important to remember that the higher performance of these panels will usually be reflected in a higher per-unit price.
What are the weight and structural factors to consider?
As solar panels will add significant weight to your roof or mounting structure, it’s essential that you understand the load-bearing capacity of the roof to ensure the system can be installed safely. A full structural assessment may be required, especially for older buildings and for larger installations. Factors to consider when selecting the best solar panel model and dimensions for your needs include:
Weight and handling
Larger panels are usually heavier and therefore present more challenges during transportation, lifting onto roofs, and positioning during installation. This means you may require specialised lifting equipment and additional personnel, which can contribute to higher installation costs. However, some manufacturers offer lighter-weight large-format panels designed to mitigate this issue.
Access and manoeuvrability
Limited roof access or obstacles such as chimneys, vents, or ducts can make it challenging to install solar panels, and the larger the panels, the more this is an issue. One way to address this is to opt for a combined system, where larger panels are used to fill unrestricted space, and then smaller panels can be installed in harder-to-reach areas to maximise overall output.
Roof compatibility
The increased weight of larger panels can put substantial stress on roof structures, and in most cases, a thorough structural assessment is required ahead of installation to ensure the roof can safely support the added load. For roofs with limited weight-bearing capacity, smaller, lighter panels might be a more suitable option. In some cases, regardless of solar panel size, reinforcement or replacement of the roof may be necessary, adding to the installation cost and complexity.
Did you know?
If you require repairs, reinforcement or replacement of your commercial roof — including asbestos encapsulation — to make it suitable for a solar PV installation, you may be able to avoid upfront expenditure by funding the whole project through a Power Purchasing Agreement (PPA).
Ground-mounted systems
While ground-mounted systems offer more flexibility in terms of panel placement and installation, choosing larger-sized panels may still raise some logistical challenges. You’ll need to ensure proper preparation of the site, including suitably robust foundations and access routes (both for installation and maintenance) as well as routing the necessary cabling, usually requiring some excavation work.
Specialised equipment may be needed to transport and position the panels safely. And whether you opt for a roof-mounted or ground-mounted system, the following additional factors should also be taken into consideration.
Wind load
Larger panels present a larger surface area to wind, increasing the risk of damage or detachment, so secure mounting systems and appropriate anchoring are essential. Wind load calculations should be performed before installation to evaluate risk and ensure system stability.
Wiring and electrical connections
Larger panels typically generate higher currents, requiring thicker wiring and appropriately sized electrical components. This can impact the balance of system (BOS) costs. Using higher voltage systems can mitigate this issue by reducing current while maintaining power output.
Choosing the right solar panel size and dimensions for your business
As we’ve seen, designing the most cost-effective and efficient solar PV system for your business requires an in-depth assessment of multiple relevant factors. At JLM, we offer a free remote audit to accurately identify the right solar panels for your needs, based on your current energy usage and available on-premise space.
Following the audit, you’ll receive a personalised system design including details of the type, size and number of solar panels required, full cost breakdowns, annual savings and predicted return on investment.
Contact one of our expert consultants to book your free audit and answer any other questions you may have about commercial solar PV.
