Homeowner Blog

How Many Solar Panels Are You Allowed on Your House?

George Riley · 01 Jul 2020

Some of our clients are surprised to learn that there can be limits on the number of solar panels they can get on their roof, beyond the obvious physical and cost limitations. In fact, for solar PV systems over a certain size, grid permission is needed before installation can go ahead.

In this post, we’ll explore how many solar panels you’re allowed to install without prior permission, and how we can help you determine the maximum possible allowance for your property.

Why are there system size limits?

The local distribution network operator (DNO) controls the infrastructure between the national electricity grid and your home. When you’re not using much electricity, your solar panels can send power back to the grid. Too much of this power can affect the infrastructure and risk damaging the local network. So it’s important to check the local grid can cope with any additional load during peak generation times.

For DNO permission, the system approval is based on the rating of the inverter. Prior permission is not needed for systems with an inverter up to or under 3.68kW for a single phase supply or 11.04kW for a three phase supply, as you will be generating at or below 16A per phase.

If the desired system is any larger than this, DNO permission is required before installation. This can take up to 11 weeks to be granted, as the DNO will need to assess if an upgrade to the surrounding network is needed prior to the installation.

A battery with backup functionality will always need DNO approval.

How many solar panels can you get without DNO permission?

On a single phase supply, you can have up to a 3.68kW inverter without prior approval from the DNO (as it is granted retrospectively). However, the average domestic solar system is 4kWp, equivalent to roughly 10-13 solar panels.

Because string inverters are often undersized to as much as 120% of the inverter rating, you can still in theory install up to around 4.4kWp of panels to this inverter size (depending how good the inverter is!), but the maximum AC output of the system will always be limited to 3.68kW because of the power of the inverter, even if the system wants to output 4.4kW; this results in system clipping.

lots of solar pv

Can’t you just fit what you want and not connect it to the grid?

Yes you can, but it is an expensive route to go down. The grid is really useful to have as it will make sure you have a source of energy to draw from when it is cloudy, and you can export and sell excess energy when you are over-producing on a sunny day. You can fit the PV system without a battery and still be confident it will work. The caveat to this is the grid needs to sign off on your install before you connect it up.

If you are not going to link the PV panels to your grid connected house, you would need to fit a substantial battery system that is able to store enough excess energy to cover multiple days’ usage, alongside a specialised inverter unit to manage the microgrid. During the depths of winter in the UK there is not enough sun to see you through on solar power alone, so you often need a generator to top you up on those cold dark wet nights in December.

An off-grid battery system and a generator costs far more than a grid application!

Find out how many panels you’re allowed to install

As it can take such a long time to get DNO approval for larger systems (almost 3 months), it can be best to do this early in the planning process. Some of our clients even just want to find out how much solar they can get before deciding whether to go ahead.

For these reasons, we can offer a standalone service to liaise with the DNO, agree on the possible system size for your property and secure DNO permission. You will then have the approval whether you’d like to proceed with the installation or not (or even use a different installer, no hard feelings!).

We can arrange this for a cost of £100 (inc. VAT). If you then choose to go for a Spirit PV installation, this amount would be deducted from the cost of your order.

Just give us a call on 0118 951 4490 or drop an email to info@spiritenergy.co.uk to find out more.

Topics: Solar PV, Inverters