Almost every array on a British roof is grid tied, which means the inverter works alongside the mains supply and exports whatever the house does not use. The consequence surprises most owners the first time it matters: when the street loses power, a grid tied system shuts down too, and the roof sits in full sun doing nothing. That is not a fault, it is a safety rule, and getting round it is a different system with a different price rather than a setting somebody forgot to switch on.
The three types of solar energy system a British roof can carry
Grid tied is the ordinary one: panels, an inverter, a connection to the consumer unit, export to the network, no battery needed. Hybrid is the same array with a battery and an inverter that can charge and discharge it, so surplus is stored instead of exported and some of it can be used when the grid is absent. Off grid has no network connection at all, which means a much larger battery, a generator or another source for the dark weeks, and a design that has to carry the worst week of the year rather than the average. Almost nobody with a mains supply chooses the third.
Do solar panels work in a power cut? UK wiring, and what changes it
A grid tied inverter is required to detect loss of mains and disconnect within a fraction of a second. The reason is the engineer working on the fallen line: an inverter that kept pushing power into a dead network would energise the cable they are holding. So the array stops, and it stops whether or not the sun is out and whether or not a battery is fitted, unless the system was specifically designed with a separate backup output. Ask any installer quoting a battery whether the house keeps anything at all in a cut, because the honest answer on a standard hybrid install is often no.
EPS solar backup, the socket that stays live
EPS stands for emergency power supply and it is the feature a hybrid inverter needs for anything to work in a cut. The inverter has a second output, wired to a dedicated circuit or a small sub board, that it feeds from the battery once the mains connection has opened. It is not the whole house unless it was designed and priced as the whole house, and there is usually a short break while the changeover happens rather than the seamless handover a computer room needs. Decide before the quote which circuits matter, because the boiler, the fridge, a router and a few sockets is a very different job from the oven and the shower.
How a solar grid connection is made, and who signs it off
The array is a generator connected to somebody else's network, so the distribution network operator for your area has to know about it. Small domestic installations are normally connected and then notified under the industry's connect and inform recommendation, and larger ones need an application answered before anything is switched on. The installer does this as part of the job. The same installer signs the electrical work off under the electrical safety part of the building regulations and issues the certification, and the MCS certificate is the separate document you will need before an energy supplier will pay for exported units.
What the connection type does to the price and the payback
Grid tied is the cheapest way to fit an array and the one with the shortest payback, because it spends nothing on storage and sells what the house cannot use. Adding a battery and a backup output buys resilience and some self consumption, and it adds a significant sum to the quote for kit that wears out sooner than the panels. Going off grid where a mains supply exists is almost never an economic decision. Price the array first, then ask what the battery and the backup output add as separate lines, so you can see what the resilience is actually costing.
Questions people ask about on grid solar system
Can I add a battery to an existing grid tied array?
Usually yes, either with a battery that has its own inverter alongside the existing one, or by replacing the inverter with a hybrid. Which is cheaper depends on the age of the existing inverter and how the array is strung, so ask for both options priced.
Will a battery keep the whole house running?
Only if it was designed to. Most installs feed a dedicated backup circuit rather than the whole consumer unit, because the whole house needs an inverter sized for the biggest load in it. Decide which circuits you want before anyone quotes.
Do I get paid for what the array exports?
Through the Smart Export Guarantee, if you have an MCS certified installation, a meter that can measure export and a supplier offering a tariff. The rates are set by suppliers rather than by government, so it is worth comparing them rather than accepting your existing supplier's.
Does my network operator have to agree before the panels go on?
For a normal domestic array the installer connects it and then notifies the network operator. Larger systems need the application answered first, which takes time and can come back with conditions, so it is worth asking early if the system is a big one.
Is an off grid system ever worth it on a house with mains power?
Very rarely. Sizing for the worst week of a British winter means a battery far larger than a self consumption battery, and usually a generator as well. Off grid makes sense where a connection does not exist or would cost a great deal to bring in.