Plug-in solar - Batteries

 

As it stands, Plug-in batteries and Hybrid systems (Battery with panels connected) do not comply with UK regulations for Plug-in equipment. As such they can only be used if they are hard wired into your consumer unit.

However, given they will likely be certified in the future, and that they can be installed hard wired, there's a few thoughts worth considering if you plan to go with batteries

Understanding the Spec of kit

There are a number of items in the specification of batteries that can vary from brand to brand. Knowing these is key to ensuring your get the best value from your spend and that the kit meets your needs:

Battery capacity
Usable capacity (taking into consideration the Depth of Discharge
Inverter rating and charge/discharge rates
Warranty in years or cycles

Location of battery install

There is guidance covering where and how batteries should be installed. This guidance is known as PAS 63100 and whilst it is only guidance and not regulatory, it is becoming more embedded in other standards and regulations, so it is well worth noting the key points 

Prohibited Locations: the standard restricts placing home batteries in vulnerable or high-risk areas including:

• Bedrooms and rooms intended for sleeping
• Lofts, roof spaces, and voids
• Escape routes, hallways, staircases
• Cupboards that open directly into bedrooms
• Any room lacking direct access to the outside (ie basements)

Preferred Locations: recommended locations include 

• Outdoors: Preferred option (if the batteries are appropriately IP rated for outdoor use. 
• Outbuildings/Garages
• Setbacks: batteries must be placed safely away from flammable materials, doors, windows, and ventilation openings

Technical and Safety Requirements:

• Ventilation: installation should ensure adequate fresh air exchange (eg to allow cooling)
• Wiring Access: Connections should be limited to reduce accidental or purposeful disconnection or connector damage. 
• Wiring Standards: Must comply with UK wiring regulation, in particular BS 7671 wiring. In particular it is recommended that the battery is wired onto its own appropriately protected (ie RCBO) circuit 

Use cases

Batteries provide power to help run the house in a number of different ways. The optimum use is when the discharge from the battery meets the household demand and when any excess from a separate solar array is being exported. However depending on how your house is wired and other equipment you may have, this may not be an option, so understanding the alternatives available will help you get the best from your battery system

Smart use 

This is achieved by the use of an additional device known as a Smart Meter (this isn't your household Smart Meter, it's a specific device that works with the your battery). Smart meters need to be installed in or near your household consumer unit, with the ability to connect a CT clamp on the house incoming supply. The Smart Meter also requires it's own power, so it will need it's own power socket (in or near the consumer unit) or to be installed in a slot in the fuse box. This mode of operation also allows the battery to charge if excess solar from a separate solar system is being exported 

Non-smart use

In situations where the installation of a Smart Meter is unsuitable or can't be done, then the battery system can (generally) be set to just cover the household base load. So first of all you need to know your households Base Load (see Sizing your system for details on measuring this). Knowing this you can set the battery discharge to just under that value. For example if your Base Load was 200w, setting the battery to discharge at a rate if say 150w. Note that this will require a battery usable capacity of 3.6kwh.

Using a Plug-in battery alongside an existing battery system

Having multiple battery systems that are not from the same manufacturer can lead to conflicts in operation. For example one battery could see a household demand and choose to discharge, whilst the other battery sees that discharge as excess and chooses to charge. There are a number of ways to get around this problem:

1. Use an automation tool like Home Assistant to control when & how batteries discharge 
2. Scheduling battery discharge times - for example one battery set to cover AM and the other one PM
3. Dedicate one battery to a particular workload - For example put the battery CT on the power supply for a large consumer device (ie a Heat Pump) so that it only discharges when there's demand 
4. Use one battery in Non-Smart mode, so that it covers the house base load, allowing the other to cover the rest of the house load

Using the Plug-in battery as an EPS or UPS

Some Plug-in battery systems have a built in AC socket which remains powered in the event the grid goes down. With this the battery will not only power the house, but will in the event the grid drops, this power socket can be used to power critical appliances like a fridge. This gives an Emergency Power Supply (EPS) capability 

Even better, if the appliance is plugged into this socket for normal operation, it will run continuously if the grid goes down until battery capacity until it runs out. This gives Uninterrupted Power Supply (UPS) capability.

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One final note

If this blog has helped and you go on to installing a solar or battery solution, please let me know by leaving a comment and sharing this page as I really like to know I've been able to help. 

If you're considering a move to Octopus to charge your batteries in the darker months, please consider using my referral link below (click on the Octopus) as it will give each of us £50 off our Octopus bill.