How many solar panels do I need?

It’s one of the first questions people ask us when they start thinking about solar. How many solar panels you need depends on your roof and your household, and we confirm the number at a free on-site survey.

Here’s what goes into that number, how our homepage estimator works it out, and why the survey always has the final say.

How many solar panels you need: two questions decide it

Sizing a solar system means answering two questions at the same time:

1. How many panels can your roof take? That’s down to space, shape, direction and shade.
2. How many does your household need? That’s down to how much electricity you use, and when you use it.

We size each system to what your home actually uses, up to what your roof can take. That’s how we approach every solar panel installation across Dorset. There’s no standard package, and on a big roof the question is often how much of it your usage justifies, not whether solar makes sense at all.

What decides the number, at a glance

What we look at	Why it matters	What it does to the panel count
Roof size and shape	Panels have to sit clear of roof windows, chimneys and vents	Sets the most panels the roof can hold
Which way it faces	South-facing roofs with minimal shading perform best	East or west roofs may need more panels for the same output
Pitch	The angle changes how squarely the panels face the sun	Factored into the layout and the design
Shading	Trees, chimneys and neighbouring buildings cut output	Panels are laid out with it in mind
How much electricity you use	Your bills show what your household gets through in a year	The main thing a system is sized to
What’s coming	An electric car, a heat pump or air conditioning adds to your use	Can justify more panels, if there’s room

Roof size and shape

The usable area of a roof is usually smaller than it looks from the street. Panels have to sit clear of roof windows, chimneys and vents, and a roof broken up by dormers or hips has less unbroken space than a plain rectangle.

That doesn’t rule solar out. At a red-brick home in Christchurch, we fitted a full-width array around two existing roof windows. At the dormer bungalow in the photo above, we used two roof pitches, the main rear-facing slope and a smaller front-facing section, to make the most of a fairly complex roofline. Both are among our solar panel installations in Christchurch, close to our base on Airfield Way.

Bungalow roofs are often a simpler, larger single face that suits a bigger array. That’s typical of Highcliffe, where detached bungalows and chalet bungalows spread across much of the area in the post-war decades. You can read more about solar panel installation in Highcliffe, from those bungalows to the older homes nearer the coast. Older roofs can have irregular pitches or period features to work around.

Which way the roof faces

South-facing roofs with minimal shading perform best. East and west-facing roofs still work, as do most roof types and orientations, but each panel makes less electricity over a year than it would facing south.

So if your roof faces east or west, you may want more panels to make the same amount of electricity, as long as there’s room for them. Using two roof faces is another option, and it’s something we’ll look at on your survey.

Pitch

The angle of your roof affects how squarely the panels face the sun through the year. We check the pitch of each roof face on the survey and design around it.

Shading

Shade from a tree, a chimney or a neighbouring building cuts what the panels in its shadow can produce. We look at what could shade your roof and lay the panels out with that in mind.

How much electricity you use

The roof sets the upper limit. Your usage decides how much of it is worth filling. We look at:

• How much you use: your bills show how much electricity your household gets through in a year.
• When you use it: a household that’s home in the day uses more of its solar as it’s generated.
• What’s coming: an electric car, a heat pump or air conditioning will all add to what you use, so tell us if any of them are on your list. We install air conditioning for Dorset homes as well, so we can size the panels with it in mind.
• Whether you’d add a battery: solar battery storage keeps surplus from the day for the evening, so more of what you generate gets used at home. We fit Christchurch home batteries and battery storage for Poole homes at the same time as the panels or later on.

Bigger homes can change the conversation. Some of the larger detached houses around Poole’s waterside have bigger roof faces and heavier electricity use than a typical semi, so the question becomes how much roof to use. Our Poole solar panel installations include one using Astronergy N7 bifacial panels.

Panel count isn’t the whole story

Panels come in different wattages, so we also talk about system size in kWp (kilowatts peak), the combined rating of all the panels. Two systems with the same number of panels can be different sizes if the panels are different.

Ready to talk it through? Book a free solar survey with our own team and we’ll measure up your roof, talk through your bills and work out how many panels make sense for your home.

How our estimator works out a panel count

The home energy estimator on our homepage gives you a first picture before anyone visits. It sizes a system the same way we do: to your usage, up to what your roof can take. Here’s what each setting changes.

Estimator setting	Changes the number of panels?	What it changes
Your home	Yes	A starting point for how much roof a home like yours usually has
Roof size	Yes	Scales that up or down, shown as “room for” a number of panels
Your electricity bill	Yes	A rough figure for your yearly use, the main thing the panels are sized to
Electric car miles a year	Yes	Adds part of the car’s charging to what the system covers
Which way your roof faces	Yes	How much each panel is expected to make in a year
Who’s home in the day?	No	How much of your solar you use as it’s generated
Battery	No	How much surplus is stored for the evening
How you heat your home	No	With gas or oil heating, a diverter heats your water from surplus sun

A terrace usually has less room than a detached house or a bungalow, so the starting point differs from home to home. Facing east, west or north, each panel makes less in a year, so the estimator suggests more panels for the same usage, up to the room on your roof, and it never suggests more than will fit. “Recommended” in the battery setting picks a size to cover the evening share of your usage.

Change anything and the drawing and the figures follow. Underneath the results, “How we worked this out” lists the main assumptions the estimator uses.

Size decides the grid paperwork too

The size of a system also decides how it’s connected to the grid. A small system is installed and the local network operator is notified afterwards, while a larger one, and many systems that pair solar with a battery, needs the network operator’s approval before it’s connected. We handle that as standard, and our guide to G98 vs G99 explains the two routes.

Why the survey has the final say

The estimator can’t see your roof. It doesn’t know about the roof window, the chimney or the neighbour’s tree, and it works from typical prices and sunshine for a Dorset home rather than your own, which is why our solar panel systems in Dorset are always designed after a survey.

On the survey we check orientation, pitch and shading on your specific roof, look at how your household really uses electricity, and design the system from there. You then get a detailed, fixed quote setting out the panels, the system size and the products in it. Our guide to what happens at a solar panel survey walks through the visit, and if a battery is on your list, read about adding a battery to existing solar panels.

So, how many solar panels do you need?

For most homes, somewhere between 10 and 16. For yours, the honest answer comes once we’ve seen your roof and talked through how you use electricity. Book a free on-site survey and we’ll tell you exactly how many solar panels you need, and why.