A new solar PV system from scratch

The panels are the visible part, but the design choices sit elsewhere. Panels are wired together into strings and feed an inverter, which turns their direct current into the alternating current your home uses. From there a cable runs to your consumer unit, usually through an isolator and a generation meter, and the installer sets up monitoring so you can see what the system produces.

There are three common inverter layouts. A single string inverter is the simplest and usually costs least, and works well on an unshaded roof with all panels facing the same way. Optimisers fitted behind each panel let one shaded or differently angled panel work without dragging the others down. Microinverters convert power at each panel, which removes the central inverter but puts more electronics on the roof. A hybrid inverter can run a battery as well as the panels; if a battery is likely in the next few years, choosing one now can avoid replacing the inverter later.

Most systems are mounted on rails above the existing tiles or slates. In-roof systems replace part of the roof covering with a flashing kit so the panels sit flush. They look neater and are often chosen on new builds or during re-roofing, but they involve more roofing work and the weatherproofing depends on the quality of that work.

Where the roof is too small, shaded or listed, a ground-mounted array in the garden or panels on a garage or outbuilding can be the alternative. In England, stand-alone panels at a house have their own permitted development limits, including a maximum panel area of 9 square metres and height limits that are lower close to the boundary. Larger garden arrays need a planning application.

If the roof covering will need replacing in the next few years, do that first. Removing and refitting panels later means a second round of scaffolding and a second visit from the installer.

A proper survey looks at the roof structure and fixings, the rafters, the condition of the covering, the route for cables, the position of the inverter and the state of your consumer unit. Some older fuse boards have no spare capacity or no suitable protection, and the installer may need to upgrade them before connecting a generator.

Your local network operator has to be told about the system. For smaller systems the installer connects first and notifies the operator within 28 days using the G98 process. Larger systems, and some combinations with other equipment, go through G99, where the installer applies before installing and waits for approval. The quote should say which route applies, because an application can move the start date.

After commissioning, an MCS-certified installer registers the installation and issues the MCS certificate. You need it, together with a meter that records exports half-hourly, to apply for a Smart Export Guarantee tariff with the supplier of your choice.

Source: gov.uk

Solar makes little sense on a heavily shaded roof, on a north-facing slope, or where you expect to move before the system has had time to earn back a good part of its cost. Leaseholders of flats usually need consent from the freeholder, and a tenant needs the landlord's agreement. In a listed building, consent is needed before anything goes on the roof. If you already have panels and simply want more output, extending the existing system is a separate job with different rules.

• the inverter type and whether it can run a battery later without replacement
• on-roof or in-roof mounting, and who is responsible for the roof covering around the panels
• where the inverter, isolators and generation meter will be installed
• any consumer unit upgrade needed before connection
• G98 notification or G99 application, and who submits it
• monitoring set-up and access to the data
• the MCS certificate and the Building Regulations compliance certificate for the electrical work

Once your phone number and email are confirmed, the job appears without your name or contact details to solar installers covering your area. Only one installer can buy it; after that it is gone from the list. The installer pays Offrano for the request, so you pay nothing, and before your details are passed on you get an email with the installer's name, address and phone number.

Nobody is obliged to buy a request, and one that is still unsold after 21 days is withdrawn. You can refuse the quote and ask other firms. Offrano checks that the buyer is a registered business, not how well it installs, so look up its MCS certification yourself before signing.