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Domestic properties – installing an additional array

Due to the banding of the UK Feed-in Tariff, and the G83 connection limit of 3.68kWp per phase, most residential PV systems are limited in size to 4kWp.

Whilst a 4kWp system is appropriate for the “average” UK property with an electricity load of 3800kWh per annum, there are many properties with a load exceeding 3800kWh per annum.

In an ideal world, the solar PV system should be sized with a similar level of output to the household consumption. Storage should then be installed with a usable capacity of 1 to 1.5 times the PV output.

For example, in the case study below, a property with an electricity consumption of 7000kWh per annum would benefit from a 6.5kWp PV system producing approximately 6,650kWh, combined with 10kWh of battery storage.

Overall the PV with battery storage will provide approximately 70% of the property’s electricity requirement.

Note that prior DNO permission is required to connect a system to the grid if the system size exceeds 3.68kWp per phase.

Unfortunately, as of January 2016, no tariff is available for extensions to PV systems, but with sufficient on site load, extending the system and installing a battery can still make financial sense.

Peak limiting (export limiting)

If the DNO does not give permission to connect a system of the required size, an export limiter can be installed. The export limiter will prevent the system from exporting excess PV above the agreed DNO limit.

Note that at the time of writing, the installation of an export limiter will still need DNO approval.

Case Study – extension to 6.5kWp + 10kWh battery storage

A householder already has 4kWp of solar installed. The system produces 3800kWh of electricity a year, of which approximately 63% is used on site (2376kWh).  This only represents a third of the household’s 7000 kWh electricity usage.

The householder applies to the DNO for permission to connect 2.5kWp more PV. Permission is granted, and a further 2.5kWp of PV is installed, along with a 10kWh battery storage system to ensure as much as possible of the additional output is used on site.

The on site usage of the PV generation now increases to 78%, with the PV system contributing 4,830 kWh to on site energy usage. Overall the Solar PV now supplies 69% of the on site electricity usage.

Over their 20 year system life, the batteries are expected to discharge over 38,700 kWh of energy.

The household also has an Emergency Power Supply, which it manages via a secondary consumer unit with ‘emergency’ loads.


Please contact us to find out more about being as self-sufficient as possible and we will tailor a proposal to meet your needs!