Question 1

What cable size do I need for a battery storage inverter?

Accepted Answer

It depends on the inverter's AC output rating. A 3.6kW inverter draws about 16A and typically needs 2.5mm² T&E on a 20A MCB. A 5kW inverter draws 22A, needing 4mm² on a 25A MCB. For larger 8-10kW inverters, 6mm² or 10mm² cable is required. Always check the manufacturer's installation manual for the specific cable and protection requirements.

Question 2

Do I need DNO permission to install a battery storage system?

Accepted Answer

You must notify the Distribution Network Operator (DNO) of any battery storage installation. If the inverter output is 3.68kW or less per phase, a simple G98 notification form is sufficient. Above 3.68kW per phase, a full G99 application is required, which can take 10 or more weeks for approval. You cannot commission a G99 system until approval is received.

Question 3

What is the typical payback period for domestic battery storage in the UK?

Accepted Answer

Payback depends heavily on your electricity tariff, solar generation, and how much surplus energy you currently export. With typical 2024-2025 electricity prices (24-25p/kWh import, 15p/kWh SEG export), and a well-sized system paired with solar PV, payback is typically 8-12 years. Without solar, payback is longer unless you use an agile tariff to arbitrage cheap overnight electricity.

Question 4

What RCD type is needed for a battery inverter circuit?

Accepted Answer

Most low-voltage (48V) battery systems with standard inverters require a Type A RCD (30mA) as minimum. High-voltage battery systems (around 400V DC) may require Type B RCD, as they can produce DC fault components that a Type A RCD will not detect. Always check the inverter manufacturer's installation guide for the specific RCD requirement.

Question 5

Can I install battery storage without solar panels?

Accepted Answer

Yes. Battery storage can be used without solar to take advantage of time-of-use tariffs like Octopus Agile or Economy 7. You charge the battery at cheap overnight rates and discharge during expensive peak periods. However, the savings are typically less than with solar, as you are still paying for all the electricity - just at a lower rate.

Question 6

How long do home batteries last?

Accepted Answer

Most lithium-ion home batteries come with a 10-year warranty and are rated for around 4,000-6,000 charge cycles. At one full cycle per day, this equates to 11-16 years. Real-world degradation means capacity drops to about 70-80% of original capacity after 10 years. LFP (lithium iron phosphate) chemistry, used by many modern systems, tends to degrade more slowly than NMC.

Question 7

Is battery storage installation notifiable under Part P?

Accepted Answer

Yes. Installing a new circuit for a battery storage system is notifiable electrical work under Part P of the Building Regulations. The work must be carried out by a competent person registered with a scheme such as NICEIC, NAPIT, or ELECSA, or a Building Control notification must be made. Additionally, MCS certification is required if the customer wants to claim Smart Export Guarantee (SEG) payments.

Question 8

What size battery do I need for my home?

Accepted Answer

For a typical UK home using 8-12kWh per day, a 5-10kWh battery covers most evening usage after solar production drops. Pair it with your solar array: a 4kWp system generates roughly 10-11kWh per day on average, of which you might export 50%. A 5kWh battery captures most of that surplus. Larger homes or those with EV charging may benefit from 13.5-20kWh systems.

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