A quick guide to Solar Battery Storage

Electricity is stored as DC (Direct Current) and there are two basic methods of converting solar electricity for storage.

The first method is to simply feed DC electricity directly from the solar array into the battery and then use the existing DC – AC solar inverter to convert the solar power for household use as required. This type of inverter is called a Hybrid, the advantage being that it is cheaper to use a single inverter. The downside is that if you already have a solar system installed the current inverter will require changing. However, if you are having a new solar system fitted or changing an old inverter this makes perfect financial sense.

The second method is an AC side connection which in effect is a complete battery storage system totally separate from the solar array and more expensive because a second inverter is required. If you have a Solar Edge optimized system fitted then this will require an AC side connection as the Solar Edge inverters cannot be exchanged. Also, if you are contemplating storing electricity from the grid at cheap overnight rates this will also require an AC side connection.

Generally speaking an AC side connected battery will discharge at a higher rate than a DC side battery, plus it can be charged from the mains at overnight cheap rates if required.

The next thing to consider is storage capacity and whilst batteries come in many sizes the average household will require a 6 – 10 kWh (Kilowatt Hour) storage battery. As an example the average hot water kettle uses 2 kW and so a 6kWh battery would continuously boil a kettle for 3 hours. Below are some examples of these.

SOLAX 5.8 kWh AC coupled Battery, control equipment and fitting. £4,426.09

(Discharge rate 5.0kW) Existing solar inverter required.

SOLAX 5.8 kWh Second Battery added to an existing system, including Master Box. £2,892.77

TESLA Powerwall II 13.4 kWh AC coupled Battery, Tesla Gateway and fitting. £8,756.25 if purchased with Solar PV or £10,507.50 including VAT at 20% if purchased alone.

TESLA Powerwall II 13.4 kWh Second Battery. £7,787.50

Discharge rate 5.00 kW. (Peak 7.00kW) Emergency back-up and off peak charging capability included.

There are a number of other battery packs on the market and we will be pleased to quote for these however some are composed of batteries and controllers from different suppliers and this can cause issues with warranty work. We feel it better to source a complete package from one manufacturer.

Whilst the main usage of a battery would be at night time when the solar system is not functioning they can also work during the day to smooth out peak usage or when the sun goes behind a cloud. Once the roll out of Smart Meters is almost complete the electricity suppliers intend to introduce varied pricing bands throughout the day and again the battery systems will help to smooth the costly peak bands.