How big should my solar PV system be?

If you're new to solar panels you might be feeling overwhelmed by options. One of the biggest queries we face as designers and installers has to do with size, and this comes up in a few different ways:

How much energy will my system produce?

Is my roof big enough?

How many panels can I afford?

So let's dive in and figure out what size system is right for you.

Consumption

One of the first questions we ask our customers is how much energy they consume.

While there will be people out there thinking 'I want as many panels on my roof as possible', in some cases this is not actually that cost-effective.

With export rates a fraction of import rates, it makes a lot of sense to maximise your self-consumption (the amount of power going straight from your solar panels to be used in your home) rather than generating more than you can use, exporting it to the grid and watching the pennies trickle in.

So step one in figuring out the size of your system is: know how much energy you need.

This figure can be found on your electricity bill, either as an estimate or actual usage amount for the past year.

From there you can start to design a system that will meet this figure.

Roof size

If filling the roof with panels and hoping for the best isn’t the way forward, then what's the relevance of the size of your roof?

Firstly, not all panels are the same size - either physically or by wattage. Panels are increasing in wattage all the time while staying within recognisable dimensions, giving you more power for the space they cover. 

Also consider the size of your roof in relation to your house - a big house doesn't always mean a big roof. 

Let’s say you live in a bungalow with your partner, and your neighbours are a family of five in a three-storey house. Your homes will have significant differences in energy consumption, but the roofs could be the same size. So you may have more flexibility than your neighbours in designing a system that meets your energy needs.

Roof orientation is also important - but unless you have a single-pitch roof facing north, there will be ways to design a well-performing system whichever way you face. 

We always visit potential customers where possible, or alternatively use our design software with satellite imagery to create a viable proposal - so as long as you have some space on your roof (or ground) for panels, don’t overthink the suitability of your roof.

Cost

This is where many people start out on their solar journey, and understandably so - they want to know how much generating power they can afford. 

However, as long as the previous two points are addressed properly, the equation should be fairly simple. 

Our proposals give an estimate of how long the system will take to pay for itself in savings on your electricity bill (the payback period). So, if you expect to stay in your current home as long as or beyond the payback period, solar is well worth the investment. 

Sample payback illustration from a commercial installation.

And when you consider that solar has been found to add £2,156 to house values (Solar Energy UK), that payback period could end up being a lot shorter. 

So when it comes to thinking about the cost of solar, if you’re staying put for the next few years, solar is very likely to pay you back.

Size is everything

While there’s plenty to consider before taking the plunge into the world of solar panels, we're here to help with honest advice on your specific circumstances. 

Ultimately, the size of your system determines how well it helps you and the planet, and whether it’s a good investment for you. 

There’s lots to say about solar and size, from inverters and battery storage to the merits of ‘oversizing’, so stay tuned for more on this topic!