What should I consider before I install panels?

You've decided you want to install solar photovoltaics (PV); and you're happy with the results the tool gives you - maybe it's time to get going? Before you do, there's a few more things that you may want to think about! These are finer points so may not apply to you, but they're things you should check. So read on to become an expert and check that your project is as good as it seems!

In general, many of the considerations will apply to both residential solar projects (putting panels on the roof of your own home) or other projects (such as local authority, or community initiatives). Where appropriate we have highlighted some of the differences here. For more information on larger and non-residential projects, Community Energy London has an excellent guide to community PV projects. While that is London-focussed, most of the information is relevant wherever you are!

Time investment

It is impossible to say exactly how long it takes to install PV, because it will depend on your specific circumstances. A good estimate for a residential solar project is that it will take around six months from deciding you want PV, to generating electricity. However, if your project is more complicated than standard it could take longer. A particular issue that could extend the time it takes is if you require planning permission (see below). Projects which are not on residential properties are likely to take far longer because there are additional complexities such as legal arrangements to sort out. We have written more about the process of getting PV, and how long it could take [[here]].

Project Management

Project management refers to managing all the different aspects of the project. For example, on a residential installation, it would mean coordinating the installers of the panels, the scaffolding, the electrician, etc. to ensure they all arrive when they are needed. In most cases, project management for residential projects will be done by the installers. They will either employ the skillsets needed or should subcontract the work they can't do. This may not always be the case, so make sure you know who will be responsible for what!

On other installations, such as a community project, more involved project management will be involved. Whilst the installers may still handle all the parts of installing the panels - there will be many more moving parts that must be handled. For example, physical and legal access to the installation location and coordination with other organisations such as DNOs. This is not an exhaustive list, and there will be unique aspects to every project. It is up to you how you wish to handle this - do you want to handle this yourself? For example, by nominating a member of a community group as the manager? Or do you want to hire a project manager? Regardless, be clear on who will be managing the project, and for what they are responsible. Decide this early and ensure that the project manager is aware of all their responsibilities - it will be a lot of spinning plates!

Planning permission

Generally, PV panels are considered permitted development for a single dwelling home. This means you don't need to submit a planning application if you and your family occupy the entirety of the building. If you do not - for instance the building is a block of flats, or a maisonette - you may need planning permission. A non-domestic building will almost certainly require planning permission. You may also require planning permission in you live in a 'designated area' - such as a Conservation Area, a National Park, or an Area of Outstanding Natural Beauty. Because there are a huge range of different conditions across the country, and because permissions can always change, it is a good idea to always double check with your local authority before you begin planning.

Local attitudes to PV

While you may not require planning permission to install PV, it is still helpful to know what the local attitude towards rooftop PV is when you're planning your project. It's still best to understand if you're going to annoy your neighbours! If you do require permission, then your neighbours may get to have their say on your project - and could even stop it happening!

Thankfully, there is widespread support for renewable energy projects, with more than three-quarters (76%) of people supporting renewable energy projects in their area.1 Solar is particularly well supported in that study with four in every five people (81%) in favour of solar energy. But those figures show general approval - if you need to get planning permission, you probably want reassurance that your local area also approves. Thankfully, the planning system makes this easy - you can log on to the local authority's planning applications pages and look up details of past solar proposals. This enables you to see objections and restrictions against solar projects in the past. You can then prepare to counter any difficulties in your own proposal.

Housing types

If you are the owner of the building on which you want to install PV (often known as an owner-occupier) then generally the process for installing panels is quite simple. However, if you don't own the building (or don't own it in its entirety), it can be very difficult to install PV - but it is not impossible. We have produced a factsheet that goes into detail regarding how you may be able to find an agreement to install PV on a building you don't own. Find it [[here]].

Roof viability (and pitched roof vs flat roof)

This is one of the most important things to consider before beginning a rooftop PV project. If your roof is damaged in any way, this will need to be rectified before solar panels can be installed. This is because solar panels are very heavy - about 18 kg each. Therefore, they can only be installed on a roof that is strong enough to take the weight. Any damage that is not structural (for example damaged shingles) will need to be repaired prior to installing panels as well. Otherwise the panels will need to be removed to perform these repairs! Even if you are a roofing pro, any reputable solar installer should perform a survey of your roof themselves to ensure it can take the increased weight of the panels.

If your roof is damaged, this is a costly repair. However, if you can install solar panels at the same time as your roof is repaired, the costs can be shared between the two. This is because the same equipment (such as scaffolding) is required. You could even consider integrated solar panels, or solar roof tiles in such a case! See the guide [[here]] for more information on these choices.

At this point you should also consider how different types of roof may affect the solar installation (particularly its costs). Generally, on a pitched roof, panels will be able to be installed directly on the roof. To do this, the slope will normally need to be about 30° to 40°, and face roughly south - though this is not always the case. Most pitched roofs in the UK will have the correct slope. Flat roofs will require a ballasted (weighted) framework to allow them to point towards the sun. This means that a flat roof installation tends to be more expensive than for a pitched roof. They will also be heavier, and you will also require more space on a flat roof compared to a pitched roof for the same amount of generation. This is because panels on a flat roof need to be spaced out to prevent them shading one another.

Shading

Your solar panels will be affected by shading - even the slightest shadow can reduce the system's output. It's therefore important to understand if, and to what extent, the system will be shaded throughout the year. The tool takes account of this shading - but it can not detect everything (see here for more information).

You should be aware that shading changes throughout the year. In Summer, the sun is high in the sky, and objects cast a short shadow. But in Winter, when the sun is low, the same objects may cast a long shadow. This can mean that a tree that seems fine in Summer may shade your panels in Winter - so it is worth checking year-round!

Shading reduces the output of any shaded cell - but these also “block” the flow of current through the whole system. Sometimes this can even cause damage to panels as this blockage can cause overheating!

There are ways to minimise the loss of energy and risk of damage when designing the system. Some panels contain bypass diodes - which allow current to bypass shaded, weak, or damaged cells. Panels connected in parallel allows shaded panels to be bypassed by the output of other panels - but could require a microinverter for each panel (see here for more information).

Grid connections

How your solar PV will be connected to the national electricity grid is a crucial part of installing PV. Unfortunately, it is rather technical. For a residential system, the vast majority of installations will require a G98 notification, within 28 days of 'commissioning' (finishing the installation of the system). Otherwise, a G98 application (which requires you to get prior approval) or a G99 application may be required. Read on to find out under what circumstances each is required.

A G98 notification is the only requirement if your connection is less than 3.68kW per phase. This sounds very technical but don't worry! For a residential property your electricity supply will most likely be a single phase. So, if the inverter for your PV installation is rated 3.68kW or less, this is all you need! Additionally, in this situation, your installer should handle the process of the notification - but make sure you check when choosing an installer! A non-residential property is more likely to have a three-phase supply (though not always!). In this situation you could have a total generation of 11.04kW - in other words three inverters each rated 3.68kW or less. Further information on the G98 process for a single premises is available here.

There is an exception to the above - if you are connecting multiple generators which would otherwise fall under the requirements above, there are some additional requirements. An example of this would be if a community group was installing multiple arrays on different houses in a street. In this case you must discuss your plans with your distribution network operator (DNO) before installation - the earlier in the planning, the better. If you don't know who your DNO it, you can find out here. Once the plan is complete, you will have to submit a G98 application form - though your installer should handle this process (check before you employ an installer). The DNO will assess your application and produce a 'connection offer' - this will tell you the conditions that must be met for your connection and inform you if you will have to pay a connection charge. Ensure you understand the terms of the offer - and discuss with the DNO if you are unsure. DNOs are becoming more practised at these types of agreement, so should be very willing to help! The process is then the same as for single generators - installation and commissioning followed by a notification to the DNO within 28 days. There is further information on applying under G98 for multiple premises here.

G99 applications will apply in almost any situation not covered by G98. Normally this will be where the generation capacity is greater than 3.68kW per phase. There are a couple of other situations where G99 may applying including higher voltage and non-type tested technology. Due to the additional complexity of these types of application, they will not be covered in detail here. As a brief overview, there are two documents which cover making applications under G99, which are written for general (non-technical) audiences. Under G99, installations are separated into 'types' based on their generation capacity. Type A is generation under 50kW and covered in this document. Types B-D are larger, and covered under this document.

There is one final point to raise about connecting to the grid. In a few situations there may just not be any room at all for your PV. This is very unlikely to happen and is only likely for larger installations. But it can be best to check the available grid capacity with your DNO. First find your DNO, then contact them to ask about capacity if you are planning a larger project. They can then direct you to information regarding their capacity, or give you a direct answer. It is best to do this as early as possible in your project to avoid any costs (or disappointment) if you find out you won't be able to connect.