Getting the right amount of solar panels for your residential or commercial solar installation couldn’t be more important. The number of panels your array has will directly affect how much power it can generate, and therefore how much electricity you produce yourself on site with solar energy, and how much you need to buy from the national grid.
Still deciding whether solar is right for your home at all? Start with our honest look at the real pros and cons of solar.
To work out exactly how many panels you need you’ll need to think about your current annual energy usage, how much exposure to the sun your panels will get throughout the day, and the size of your roof (which may limit the amount you can have).
Read on to answer the question: ‘How many solar panels do I need?’
Factors Affecting How Many Solar Panels Your System Needs
There are a few different factors affecting how many solar panels you’ll need. Some have a bigger overall impact than others, but all of the factors below are things you’ll need to consider before investing in a solar array:
- Annual energy usage
- Sunlight hours
- Solar panel kWh
- Roof space
- Solar panel size
- Roof pitch & direction
Annual Energy Usage
Most people don’t know their annual energy usage off the bat, but finding out is simple. There are a few different ways to find yours quickly and easily:
| View Your Annual Summary | Most energy suppliers provide their customers with an annual summary of their bills, giving you your total annual energy usage over the past year. |
| Create A Summary Yourself | If you don’t receive an annual summary, you can add up how much energy you used each month for 12 months to get your annual usage. |
| Contact Your Supplier | Not everybody keeps records of their energy bills, and that’s OK, because your supplier will. If in doubt, contact them and they’ll give you your annual usage. |
Knowing your annual energy usage is one of the most important factors because without it, you may buy a solar array that doesn’t cover your needs, or pay more for a larger system you don’t really need.
Sunlight Hours
The amount of direct sunlight your panels get will directly affect the amount of power they can provide, and the difference is by no means small. The same solar panel system installed at identical properties with identical annual usage in south-west England and north-east Scotland could see a difference in production of around 700kWh each year.
To get the same amount, the Scotland home would need more panels. Your location in the UK affects how many hours of direct sunlight your panels are exposed to each year. It’s true that solar panels still work in indirect sunlight on cloudy or rainy days, but they don’t work as efficiently.
Solar Panel kWh
Most domestic solar panels are 350W, but some can be as powerful as 600W. However, how powerful your panels are isn’t the most important thing to know when deciding how many you need. It’s the kWh a single panel can provide per year that matters most.
A standard 350W panel produces around 265kWh of electricity per year. A larger 600W panel could produce around 2.4kWh per day — just over 875kWh per year. An average 3-bed house uses close to 2,900kWh annually, so with 350W panels that household would need 10–12 panels; with 600W panels, 3–4 panels.
Roof Space
The size of your roof will directly affect how many solar panels you can have. Even if you need more panels, your roof will have a limit on how many it can realistically accommodate. And don’t forget about panel weight, too.
Solar Panel Size
The more powerful your solar panel, the more space each panel takes up on your roof — and the more it weighs. Let’s compare average 350W and 600W panels:
| Dimensions | Weight | |
| 350W Panels | 1.9m x 1m = 1.9 square metres | 21.6 kg |
| 600W Panels | 2.4m x 1.1m = 2.64 square metres | 30.5 kg |
A system of 12 x 350W panels would need around 22.8 square metres of roof, minimally. A system of 4 x 600W panels would need 10.6 square metres, but places a significant load in a smaller area due to the increased weight — and not all roofs will support that. As expert installers, we’ll guide you through the best system for you.
Roof Pitch & Direction
You’ll get far more out of your panels on a south-facing roof than a north-facing one. If your roof is east or west facing, expect around a 25% drop in production compared to south facing, and north facing is worse still.
The ideal roof pitch is 30 to 35 degrees, though panels still function (with reduced production) at 15 to 50 degree pitches. Panels on an east-facing roof with a 15-degree pitch will need more panels to match a 30-degree south-facing roof.
Common Solar Systems & Their Number Of Panels
To make things easier, here are some common solar systems and the number of panels they typically use. These are based on average households — yours may differ, which is why we’d always recommend discussing your array with our team first.
| Solar System | Suitable Household | 350W panels | 600W panels | Energy output |
| 1 kW | 1 person flat | 3 | 1 | 800kWh |
| 2 kW | 2 bed house | 6 | 2 | 1,600kWh |
| 3.5 kW | 3 bed house | 10 | 3 | 2,650kWh |
| 5 kW | 4 bed house | 14 | 5 | 3,700kWh |
How Do I Work Out How Many Solar Panels I Need?
A crude way to work it out is to take your annual energy usage and divide it by the expected annual kWh of one panel you’re considering. For example, a household using 3,065kWh a year considering 350W panels (265kWh per panel each year):
3,065 divided by 265 = 11.5, or 12 x 350W solar panels.
A Word Of Warning
That method is fine for a rough idea, but it ignores all the other factors we’ve covered — sunlight hours, roof direction and pitch, and how much roof space you realistically have. To answer the question thoroughly you’ll need a proper survey that breaks down each factor. Our free system size estimator is a good starting point before anyone visits.
How Many Solar Panels Do I Need? Summary
The very best way to answer that question is to speak to our team. We’ll discuss your needs and help you put together a plan for the best solar system for you, your home, and your budget.
Ready to find out exactly what your home needs? As MCS-certified installers across Dorset, Hampshire and Wiltshire, DES Renewable Energy will size the perfect system for your property. Request a free, no-obligation quote.