How a Solar Panel System is Installed

Get ready for the big day

Scaffolding

Unless you live in a bungalow, the gutter of most houses is at a height of about 5m.

For the roofers who install the solar panels to work safely at that height, a fully-boarded scaffold platform will need to be erected along the gutter.

The length of the platform should be a little wider than the area on the roof where the panels are going.

In addition, there should be ‘edge protection’ going up the roof on each side of the platform. This is to stop the roofers falling off the roof if the panels are close to the edge of the roof (the verge).

The solar panel installers normally arrange the scaffolding. Typically, it goes up a day or two before the solar panel installation.

9 times out of 10, the company that puts the scaffolding up is a sub-contractor to the solar panel installer. This is important. While most scaffolding companies provide an excellent service, some don’t take as much care as they should. Tiles can get broken, garden pots smashed, and so on.

If you notice any damage after the scaffolders have been, but before the solar installation team has arrived, mention this to the person who sold you the solar panel system. They will get it fixed.

Duration of Installation

For small or medium-sized solar panel systems, installation will normally take no more than 1 day.

A small system is 2-8 panels. A medium-sized system is 9-20 panels.

For larger systems, the roofing part of the installation may run into a second day.

It can take even longer if your system is very big, or if your roof covering is difficult technically to mount panels on.

Roofers

The roofers generally climb the scaffold when they first arrive and have a look around.

They check the scaffold is safe. They make sure the scaffolders haven’t damaged the roof. Then they start measuring the roof to ensure the panels will fit on.

Occasionally, the roofers will find the planned panel layout won’t work. It can be difficult to survey the roof from the ground. The original surveyor may have miscalculated.

In this case, the roofers may be able to suggest a new layout. Sometimes a new layout will mean a delay while additional mounting equipment is ordered.

The Inverter

It’s worth spending a good few minutes deciding where the inverter goes.

There are usually several options, for example:

• Attic or loft
• Garage
• Utility room
• Outside wall

Ideally, the inverter should be on the ground floor, though this is not always possible. If the inverter is easily accessible, you can read the display to see how the solar array is performing.

Most inverters are IP65 rated which means they can be mounted on an external wall.

Remember: how a solar panel system is installed is just as important as the technology itself. Better to discuss everything before the electrician gets started.

Cable Run

Once you have worked out where the inverter goes, you then need to discuss with the electrician where all the cables go.

There will be ‘DC’ cables connecting the panels to the inverter.

Then there is an ‘AC’ cable connecting the inverter to your fuse box.

Most home-owners want the cables to be as invisible as possible. Going under floor boards, however, is usually not an option.

Generally, cables are put inside ‘conduit’. This is generally black, plastic trunking if part of the cable run is down one of your external walls.

If inside, the cable is often in white trunking.

Equipment Deliveries

Often the installation team will bring all the equipment with them when they arrive in their vans.

Solar panels, inverter, mounting kit, cables, etc.

Sometimes, though, the equipment will be delivered separately. A truck will arrive on the day of the installation, bringing all the equipment direct from the supplier.

It’s usually a big truck, with a tail-lift, which will block the street for a few minutes while everything is unloaded.

You shouldn’t have to coordinate anything – the roofers / electrician will liaise with the truck driver.

Your contact at the solar panel company may ask if you can receive the main delivery before installation day. This generally only works if you have a big garage.

It can be handy, as it means the equipment is already there when the installers arrive and they can get cracking straightaway.

On-roof v. In-roof

Most solar panel installations are ‘on-roof’.

What does that mean? Basically, the panels are attached to an aluminium frame which in turn is attached to your roof. This means the solar panels are fixed about 10-15cm above the surface of the roof.

On-roof installations allow air to flow beneath the panel array. This keeps the panels cooler which helps them perform a little better. Electrical devices generally work better at lower temperatures.

On-roof solar arrays are cheaper and faster to install than in-roof ones.

Did you know birds can nest underneath on-roof solar panels? It’s nice and cosy for them. If you want to guard against this, you can ask your installer to put in bird protection around the edge of the array.

In-roof installations, on the other hand, allow the solar panels to lie flatter on your roof.

First, all the tiles where the panels are going need to be removed.

Second, plastic ‘trays’ are laid. Extra wooden battens are often put in at this stage.

Third, the solar panels are put into the trays.

Fourth, the roofers tile up against the panels.

Aesthetically speaking, in-roof installations tend to look better. The panels are almost flush with the roof surface.

Disadvantages include:

• A longer installation
• Higher installation cost
• A slight reduction in solar electricity generated

On-roof Mounting Procedure

In the section above, we touched on how on-roof panels are mounted.

Here is the full story:

1. A roofer measures the roof to make sure the panel layout will work.
2. He then plans where the first row of panels will go.
3. Next he pushes up some tiles to locate the rafters.
4. Now he works out where each metal roof hook will go for the first row of panels.
5. Assuming the panels are in portrait, there will two aluminium rails running across the roof to support the panels.
6. The aluminium rails are attached to the roof hooks.
7. As a rule of thumb, the number of hooks per rail = the number of panels + 1 (so 7 panels in portrait will have 8 hooks on each of the 2 aluminium rails). The exact number of hooks depends on wind loading calculations.
8. The roofers attach the relevant number of hooks to the rafters for the first row of panels.
9. Then they pull the tiles back down, grinding them if necessary (see next section).
10. Now they attach the aluminium rails to the roof hooks.
11. Once this is complete, the roofers go on to the next row of panels above, installing hooks and rail.
12. When all the hooks and rail are in for the whole array, then the roofers start putting panels on.
13. The first panel is laid in the correct position on the aluminium rails.
14. Then the panel is secured in that position with ‘clamps’.
15. ‘End clamps’ secure panels at the edge of the array. ‘Mid clamps’ secure panels where one panel is next to another.
16. The clamps screw into the rail, applying pressure to the edges of the panels to hold them in place.
17. As the roofers secure the panels, they also connect each panel to the other using ‘MC4’ connectors.
18. The panels come with MC4 connectors already attached and the roofers simply click one connector into the next.
19. In this way, each panel is connected to the next electrically and current can flow along the ‘string’ of panels.
20. As they lay the panels, good roofers will also attach the DC cables connecting the panels to the aluminium rail, so that no DC cables lie on the roof. Over time, DC cables on the roof tiles can become degraded. Make sure your roofers attach the DC cables to the rail!
21. Once all the panels are on, the DC cables are usually brought into the attic space, under a tile and through the gap in two sheets of felt.
22. Then the electrician takes over and runs the cables to where the inverter is.
23. Job done!

Roof Covering: Concrete Tiles, Clay, Slate, etc.

What your roof is covered with makes a big difference and affects the overall cost and speed of the installation.

The easiest type of roof covering for solar is concrete tiles. These are very common.

Assuming an on-roof array, the roofers will push a tile up to expose the felt. They will then locate a rafter under the felt in a suitable position.

Next they will drill a metal roof ‘hook’ or ‘anchor’ into the rafter, using two screws. The tile will then be pulled back down to cover part of the metal hook.

Pay attention to this next point!

Very often with concrete tiles, when you pull the tile down, it does not lie flat any more. This is because the metal roof hook can push the tile up a little.

Best practice – we would say essential practice – is to ‘grind’ the back of the tile to create a groove.

When this is done properly, the tiles will then lie nice and flat, eliminating any possibility of leaks in the future.

Lazy roofers don’t bother grinding tiles, even when the tiles don’t lie flat.

Make sure you tell the roofers installing your solar panels to grind the tiles if necessary.

Clay tiles are another type of roof covering. These are smaller tiles, made of clay. They are much more fragile than concrete tiles.

If you install according to the concrete tile method, over time, many of the clay tiles will crack, possibly leading to leads.

The answer is to use a HookStop or equivalent.

These methods replace the clay tile under the hook with something flexible. When the wind blows hard and the panels / mounting frame flex, instead of the metal hooks cracking the delicate clay tiles, the hooks move against rubber or plastic.

Ask your installer what system they plan to use if you have clay tiles.

If your roof is covered in slate tiles, or artificial slate, again your roofers need two employ a special method.

There are four main approaches:

1. Attach Solar Limpets by drilling through the slates and sealing the holes;
2. Use Solar Slate Plates that replace an entire slate with a plastic one;
3. Try an artificial flashing method such as SolarFlash;
4. Use a standard roof hook and traditional lead flashing.

Electrical Installation Procedure

While the roofers are busy on the roof, the electrician will be carrying out the electrical side of the installation.

1. Often he will start by mounting the inverter on the wall. First a small, metal frame is attached to the wall and then the inverter is hung on the frame.
2. Once the inverter is up, the electrician will go to your fuse box and locate a ‘spare way’. This is a gap in your fuse box where there is no trip switch, also known as an MCB.
3. A new, usually 16 amp, MCB will be inserted into the fuse box. This new MCB will control the solar panel system circuit. All the electricity to the house will have to be turned off during this part, so the electrician doesn’t get electrocuted.
4. If your fuse box is already full, the electrician may install a separate mini fuse box often referred to as a ‘garage board’. The garage board is effectively a dedicated fuse box just for your solar panel system.
5. Next, a generation meter will be installed. This is a very important part of the system. It is where every unit of solar electricity generated is recorded. It is basically a government-approved counter that starts at zero and goes up as solar electricity is produced. The generation meter needs to be located where you can see it easily. Once a quarter, you will have to read the meter and send the reading to your feed-in tariff provider — though this only applies if you installed before 1 April 2019 when the feed-in tariff scheme ended. Most installations from 2019 onwards use the Smart Export Guarantee (SEG) instead, which is handled automatically via a smart meter.
6. Now the electrician needs to connect up all the devices.
7. An AC output cable comes out of the inverter and goes into an AC isolator. The isolator allows you to shut the solar panel system off from the rest of the house in an emergency.
8. Then, assuming the inverter is in the attic, the AC cable continues from the AC isolator on its run down through the house to another AC isolator near the fuse box.
9. This second AC isolator allows you to shut the system down from downstairs, rather than having to go up into the attic.
10. When the AC cable leaves the downstairs AC isolator, it then goes into the generation meter.
11. After the generation meter the AC cable goes into the back of your fuse box and is connected to the MCB.
12. At this point, the electrician often asks for a cup of tea. This is because he cannot finish the electrical work until the roofers have installed all the panels.
13. Once the roofers are done, the DC cables will be brought into the attic space and connected to a DC isolator. This isolator permits you to disconnect the electricity from the panels in an emergency.
14. Then the DC cables are continued out of the isolator into the input sockets of the inverter.
15. Finally, all the various isolators are turned to the on position and the inverter is ‘commissioned’. This is just a posh word for turning something on. Actually, the electrician does need to go through a set-up routine on the inverter.

Once that’s complete, your system will be ready and you will be a member of the solar energy club.

Tidying Up

Both the roofers and electrician should take away all their rubbish and leave everything nice and tidy.

As long as you have been supplying the installation team with copious amounts of tea and coffee throughout the day, they can also clean out your gutters – just ask them!

Sometimes they will ask if they can put some of the rubbish in your bins. If you are happy with this, great, if not they can put it in their van.

The Final Steps

Once the whole process is complete, the electrician will normally run through the basics of the system with you.

There is not much to say, as solar PV systems fall into the ‘fit and forget’ category.

The main items are to know where your generation meter is and how to isolate the system in an emergency.

The electrician may also run through some of the menus on the inverter.

Once the installation team has gone, if you have any questions or worries, call the installation company and have a chat.