Can I Get Solar Panels on an Outbuilding?

Can I Get Solar Panels on an Outbuilding?

When people think about installing solar panels, they usually look straight at the roof of their house.

But what happens if that roof isn’t particularly suitable?

Maybe you’ve got too much shading. Perhaps a dormer takes up most of the usable space. Maybe the roof faces an awkward direction, or you’ve already got solar panels installed and there’s simply no room left for any more.

Then you look down the garden and realise you’ve got a garage, garden room or other outbuilding with a perfectly good roof sitting there doing nothing.

Can you put solar panels on that instead?

In many cases, yes.

Solar panels don’t have to be installed on the main house. Garages, garden rooms, workshops and other suitable outbuildings can all potentially be used for solar.

And importantly, the electricity generated doesn’t necessarily have to stay within that building. Depending on how the system is designed, solar panels on an outbuilding can potentially contribute towards the electricity used by your main home too.

But there are a few things we need to work out first.

The structure needs to be strong enough, the roof needs to receive enough useful sunlight, and there needs to be a sensible way of connecting everything electrically.

So, let’s look at what’s actually possible.

What Types of Outbuilding Can Have Solar Panels?

Potentially, quite a few.

Solar panels can be considered for:

• detached garages;
• attached garages;
• garden rooms;
• garden offices;
• workshops;
• substantial sheds;
• barns;
• other permanent outbuildings.

But there’s an important distinction here.

Just because something is technically an outbuilding doesn’t mean it is automatically suitable for solar.

A substantial brick-built garage with a solid roof is very different from a lightweight timber shed that’s been at the bottom of the garden for 15 years.

That’s why the building itself needs to be assessed before we start talking about how many panels will fit on it.

Got an unused garage, garden room or outbuilding and wondering whether it could be used for solar? JD Allen Solar can assess the building alongside your main house and work out which roof areas actually make sense to use. If you’re in Bromley, Beckenham or the surrounding South London area, get in touch for advice specific to your property.

Why Put Solar Panels on an Outbuilding Instead of the House?

There are a few reasons this can make sense.

Your main roof isn’t suitable

Sometimes the house simply isn’t the best place for solar.

You might have:

• heavy shading from trees or neighbouring properties;
• a dormer taking up a large part of the roof;
• multiple Velux windows;
• chimneys;
• limited usable space;
• awkward roof geometry.

If that’s the case, we wouldn’t automatically conclude that the property is unsuitable for solar.

Instead, we’d look at what else is available.

A detached garage at the side of the house, for example, could have a much simpler and less shaded roof than the house itself.

We’ve covered several of these issues separately in our guides to solar panels on dormer roofs and solar panels on small roofs. 

Your existing roof is already full

This is another increasingly common situation.

Perhaps you installed solar several years ago and your circumstances have changed since then.

You might now have:

• an electric car;
• a heat pump;
• battery storage;
• more people living at home;
• increased daytime electricity use.

Your existing solar array might still be working perfectly well, but you now want to generate more electricity.

If the house roof is already full, an outbuilding can potentially provide the extra space you need.

That doesn’t necessarily mean you can simply connect a few new panels to the existing system — we’ll come back to that later — but it’s certainly an option worth investigating.

The outbuilding might actually have the better roof

This is easy to overlook.

There’s no rule saying your house should be the first place solar panels go.

A garage or garden room might have:

• better orientation;
• less shading;
• a simpler roof;
• more usable space;
• easier access.

In some properties, the outbuilding can actually provide one of the best locations for solar.

The sensible approach is to look at the whole property, not automatically prioritise the biggest building.

Does an Outbuilding Need to Face South?

No.

As we covered in our guide to whether solar panels need to be south-facing in the UK, south is generally the strongest orientation for annual generation.

But it isn’t essential.

East and west-facing roofs can still perform very well.

An east-facing garage will tend to generate more strongly in the morning, while a west-facing one will produce more later in the day.

A flat-roof outbuilding can provide even more flexibility because the mounting system can potentially influence the direction and angle of the panels.

What actually matters is the combination of:

• orientation;
• roof pitch;
• shading;
• available space;
• expected annual generation.

So don’t rule out a garage or garden room just because it doesn’t point perfectly south.

Is the Outbuilding Strong Enough for Solar Panels?

This is one of the biggest considerations.

Solar panels and their mounting equipment add weight to a roof. The structure also needs to deal with the forces created by wind acting on the array.

That means we need to know whether the building was designed and constructed strongly enough to support the installation.

A substantial garage or well-built permanent outbuilding may be perfectly suitable.

A lightweight shed or garden room may require much more caution.

We would want to consider things such as:

• roof construction;
• supporting timbers;
• condition of the roof;
• mounting method;
• weight of the proposed system;
• wind exposure.

The condition of the roof matters too.

There’s little sense installing a solar system designed to work for decades on a roof covering that’s likely to need replacing in a few years.

It may be better to repair or replace the roof first.

If you’re unsure whether an outbuilding is strong enough for solar, don’t guess based on how sturdy it looks. JD Allen Solar can assess the structure, roof condition and proposed panel layout when determining whether it’s a sensible installation.

Contact us here.

How Much Roof Space Do You Need?

This varies enormously.

A small garden shed might only have room for one or two panels.

A large double garage could potentially accommodate a much more substantial array.

The important thing is to look at usable roof space, rather than simply measuring the total size of the roof.

Panels may need to work around:

• roof edges;
• skylights;
• vents;
• guttering;
• shaded areas;
• access requirements;
• other obstructions.

The exact dimensions of solar panels also vary between manufacturers and models.

This is why we wouldn’t say that a particular size garage automatically fits a certain number of panels without actually designing the system.

And remember: a smaller array isn’t automatically pointless.

If you’ve already got solar panels on the main house, adding a smaller number elsewhere could still increase your overall generation.

If the outbuilding is going to be the only location for your panels, however, we’d want to calculate whether the system you can realistically fit will generate enough electricity to justify the installation.

Can Solar Panels on an Outbuilding Power My House?

This is one of the most important questions.

Potentially, yes.

Putting solar panels on a garage does not necessarily mean the electricity can only be used inside the garage.

A professionally designed system can potentially connect that solar generation into the property’s wider electrical installation.

That electricity could then contribute towards things such as:

• household appliances;
• lighting;
• battery charging;
• EV charging;
• general household electricity consumption.

Exactly how this works will depend on the electrical setup of the property and how the outbuilding is connected to the main house.

This is where a garage attached to the house may be relatively straightforward, while a detached building at the bottom of a large garden can require more thought.

What If the Outbuilding Is Detached From the House?

A detached outbuilding can still potentially be used.

Distance just introduces some additional considerations.

For example, the system design may need to account for:

• cable distance;
• the existing electrical supply to the building;
• cable sizing;
• voltage drop;
• cable routes;
• trenching;
• inverter location;
• consumer unit arrangements.

Imagine a detached garage sitting right beside the house compared with a workshop 40 metres down the garden.

They’re both outbuildings, but the electrical installation could be very different.

Longer cable runs and additional groundwork can also affect the installation cost.

That doesn’t mean a distant outbuilding is automatically unsuitable.

It simply means the further the panels are from the home’s electrical system, the more important the electrical design becomes.

Can I Add Outbuilding Solar to My Existing Solar System?

Often, yes.

But this isn’t always as simple as connecting some extra panels to what you’ve already got.

If you already have solar, we’d need to understand the existing system first.

That includes things such as:

• the capacity of your inverter;
• the existing panel configuration;
• available inverter inputs;
• compatibility between equipment;
• the orientation of the new panels;
• existing battery storage;
• the property’s existing grid connection arrangements.

Your current inverter may have enough capacity and the right configuration to accommodate an expansion.

Or it may not.

In other cases, installing a separate inverter for the additional array could be a more appropriate solution.

This is particularly relevant if the new panels are going onto a completely different roof orientation.

For example, your existing array might face south on the house while the new garage panels face west.

Those two arrays experience very different sunlight conditions, and the electrical design needs to account for that.

So yes, an outbuilding can potentially be an excellent way to increase an existing solar system.

It just needs to be designed as an extension of the whole energy system, rather than treating the extra panels in isolation.

Already have solar but run out of roof space? If you’ve got a garage, extension or outbuilding available, JD Allen Solar can look at whether it could be used to expand your generation and how the additional panels would integrate with your existing system.

Can an Outbuilding Have Its Own Solar System?

Yes.

There are broadly two ways to think about this.

Connecting it to the main home

For many homeowners, this is likely to be the most useful approach.

The outbuilding provides the roof space, but the electricity contributes towards the wider property’s energy requirements.

That allows the garage, garden room or workshop to become another generation point for the home.

A standalone system

Some homeowners may instead want the solar system purely to serve the outbuilding.

That could make sense for a:

• garden office;
• workshop;
• detached garage;
• building without an existing electricity supply.

But the system needs to be designed around what you’re actually trying to power.

Running LED lighting, a laptop and some small electrical equipment is very different from trying to run electric heating or high-powered workshop machinery.

That’s why we wouldn’t size an outbuilding system simply by asking how many panels fit on the roof.

We need to know what you want the electricity to do.

Do I Need a Battery With Solar Panels on an Outbuilding?

Not necessarily.

If the solar panels are connected into your home’s wider electrical system, battery storage works in much the same way as it would if the panels were on the house.

Excess solar generation can potentially be stored and used later when the panels aren’t producing enough.

With a standalone system, battery storage can become more important.

Solar panels generate during daylight hours. If you want to use the building in the evening, you’ll need another source of electricity once solar generation falls.

A battery can store some of the electricity generated earlier for use later.

But again, we wouldn’t say every outbuilding needs a battery.

Battery capacity should be based on:

• solar generation;
• electricity consumption;
• when the electricity is needed;
• whether the building is connected to the grid;
• what you’re trying to achieve from the system.

What About Solar Panels on a Flat-Roof Garage or Garden Room?

Flat roofs can actually provide some very interesting solar opportunities.

They’re common on:

• garages;
• extensions;
• garden rooms;
• modern outbuildings.

Unlike a pitched roof, where panels generally follow the existing roof angle, flat-roof solar uses specialist mounting systems.

That can give the designer more control over panel orientation and tilt.

However, there are additional considerations.

The system needs to account for:

• structural loading;
• wind uplift;
• mounting or ballast;
• waterproofing;
• spacing between panel rows.

So a flat garage roof isn’t automatically better or worse.

It simply requires a different approach.

We’ve covered this in much more detail in our guide to installing solar panels on a flat roof.

What If the Outbuilding Is Shaded?

This is particularly important with garden buildings.

Because outbuildings are often lower than the main house, they can be more vulnerable to shading from their surroundings.

That might come from:

• trees;
• neighbouring buildings;
• fences;
• the main house itself;
• other structures.

A garage roof might look perfect when you stand beside it at midday, but that doesn’t tell us what happens at 9am, 4pm or during winter when the sun is much lower.

That’s why shading needs to be properly assessed.

If a large portion of the roof spends significant periods in shade, expected generation may be reduced enough that another part of the property becomes the better option.

Again, this comes back to looking at the property as a whole.

Do You Need Planning Permission for Solar Panels on an Outbuilding?

Many domestic rooftop solar installations can fall within permitted development rights, including installations on suitable outbuildings.

However, that doesn’t mean every installation automatically qualifies.

Additional restrictions or considerations can apply depending on the property and installation, particularly with:

• listed buildings;
• conservation areas;
• properties affected by specific planning restrictions;
• unusual panel positions or designs.

So planning should always be checked for the particular property rather than assumed.

For most homeowners, this is something that can be identified during the planning and survey stage rather than something you need to figure out entirely by yourself before speaking to an installer.

Is Solar on an Outbuilding More Expensive?

It can be.

But it isn’t necessarily.

The fact that the panels are on an outbuilding isn’t what determines the price.

It’s the complexity of installing and connecting them.

An outbuilding installation might require additional work such as:

• longer cable runs;
• trenching;
• electrical upgrades;
• structural reinforcement;
• specialist mounting equipment;
• an additional inverter.

On the other hand, an outbuilding could also be:

• easier to access;
• lower than the main house;
• simpler in shape;
• easier to work on.

That could make other parts of the installation more straightforward.

So we’d be cautious of anyone giving a blanket answer about whether outbuilding solar costs more or less.

The roof being on an outbuilding isn’t what determines the cost. The complexity of connecting and installing the system does.

When Does Solar on an Outbuilding Make the Most Sense?

There are a few situations where we’d particularly want to investigate it.

Your main house roof isn’t suitable

If the house has significant shade, limited space or awkward geometry but the garage has a clear roof, the garage may provide the better opportunity.

You already have solar and want more generation

If your electricity use has increased since your original installation, another roof could allow you to expand the system.

You have a large detached garage

A substantial garage with good sunlight and plenty of roof space could potentially accommodate a meaningful solar array.

You have a flat-roof extension or garden room

These buildings can provide additional design flexibility where the main pitched roof isn’t suitable.

Your household uses a lot of electricity

If you’ve got an EV, heat pump or generally high electricity consumption, making use of additional roof space could help increase the amount of electricity you generate yourself.

When Might Solar on an Outbuilding Not Be Worth It?

Equally, sometimes it won’t make sense.

We might advise caution if the building has:

• a lightweight or unsuitable structure;
• an ageing roof;
• severe shading;
• very little usable roof area;
• a particularly complicated electrical connection;
• expected generation that is too low to justify the cost.

That’s an important part of assessing any solar installation.

Just because there’s enough physical room for a solar panel doesn’t mean it’s automatically a good place to put one.

If connecting a tiny, heavily shaded garage array requires extensive groundwork and electrical upgrades, the numbers may simply not stack up.

And if that’s the case, we’d rather tell you.

If you’re looking at a garage, garden room or other outbuilding and wondering whether it’s worth using, JD Allen Solar can assess it alongside the rest of your property. We’ll look at the roof, shading, expected generation and electrical connection before recommending anything.

JD Allen’s View: Look at the Whole Property, Not Just the House

When we’re designing a solar system, we don’t think the question should simply be:

“How many panels can we fit on the house?”

We’d rather look at the property as a whole.

That could mean assessing:

• the main roof;
• extensions;
• garages;
• garden rooms;
• other suitable outbuildings;
• different roof orientations;
• shading across the site.

Sometimes the main house will clearly be the best place for the panels.

Sometimes using two different roof areas will create a stronger system.

And occasionally, an outbuilding may provide a better solar opportunity than the main house itself.

The goal isn’t to put panels on a particular roof. It’s to find the best way of generating useful electricity from the property as a whole.

Final Verdict: Can You Get Solar Panels on an Outbuilding?

Yes — solar panels can often be installed on garages, garden rooms and other suitable outbuildings.

They can potentially be used to:

• power the outbuilding itself;
• contribute electricity towards your main home;
• increase the size of an existing solar system;
• provide an alternative when the main house roof isn’t suitable.

But whether it makes sense depends on the building.

You need to consider:

• structural strength;
• roof condition;
• available space;
• orientation;
• shading;
• electrical connection;
• installation complexity;
• expected generation.

So if your main house doesn’t have the perfect roof for solar, don’t assume that’s the end of it.

Look at the rest of the property.

That unused garage, garden room or outbuilding might give you another option.

If you’re based in Bromley, Beckenham, South London or the surrounding areas and want to know whether an outbuilding could be used for solar, get in touch with JD Allen Solar. We can look at the whole property and explain what’s realistically possible before you commit to anything.