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Battery Storage – How it Works

Solar home

A solar PV system converts sunlight into electricity which is automatically used to charge a battery storage system and directly power a property, with any excess being routed back to the grid. Any shortfall of power, such as peak use times or at night, is supplied by the battery at first then topped up by your energy supplier if the battery becomes depleted or overloaded by demand.

Solar PV operates on light intensity, not heat, so even if the day seems cold, if there is light the system will be generating electricity, PV systems will therefore generate electricity all year round. Typical usage of PV energy generated is 50%, but with battery storage, usage can become 85% or greater.

Due to the size and weight of the batteries, they often stand on the ground and are secured against walls. This means they are most suited for installation into an attached garage or similar type location, but alternative locations such as lofts can be considered if using specific equipment.

Battery storage systems have no effect on Feed in Tariff incomes as they only act as a temporary store of electricity to be used and metered outside of generation periods. Additionally, as the exported electricity is not metered, but calculated as 50% of generation, this income will remain unaffected.

Terminology

Battery Storage

Watts and kWh – A watt is a unit of power used to express the rate of energy transfer with respect to time. The higher the wattage of an item the more electricity is being used. A kilowatt hour (kWh) is 1000 watts of energy being used/generated constantly for an hour. A kWh is often represented as a “unit” of electricity by electricity suppliers.

Charge/Discharge Capacity – The rate at which electricity can charged into the battery or discharged from it into a load. This value is usually represented in watts, the higher the wattage the more effective it is at providing electricity into the property.

Charge Cycle - The process of charging a battery and discharging it as required into a load. A complete charge and discharge represents a cycle, the lifespan of a battery is often calculated in charge cycles. The life of a battery will be extended by ensuring the battery is utilising the full range of the cycle.

Depth of Discharge – The storage capacity of a battery is represented in kWh, however it cannot discharge all of the energy it stores. Depth of Discharge (DOD) is the percentage of storage which is available to use. A 10kWh battery with 80% DOD will have 8kWh of usable power.

All the solutions CTS Renewables Ltd are providing use Lithium Ion batteries rather than Lead Acid. This is because Lithium batteries are the most energy dense (power/space taken), have improved cycles and have a depth of discharge greater than 80% rather than 50% for lead acid.

The most effective systems have high, Discharge Capacity (>3kW), Charge Cycles (>4000), Storage Capacity (>5kWh) and Depth of Discharge (>80%)

Battery Storage vs Backup

Battery Storage

Battery storage in the context of domestic Solar PV systems, is the process of temporarily storing generated electricity in periods of excess, to be utilised in periods when generation is less than the electrical consumption, such as at night. The system is always connected to the grid and the batteries are designed to be regularly charged and discharged (Cycles). Battery storage enables the cost effective usage of the energy generated.

A battery backup system enables the use of the stored electricity in the event of a power cut. Backup systems are not compliant with UK grid systems (G83/2), and as such require additional measures to manually switch the system off the power grid, to “island” the property. G83/2 ensures that in the event of power cut, all systems which could put power into the grid are shut down for the safety of operatives working on the network.

Once the system is separated from the grid it can be activated to power the home. However, as the output from the battery is limited by its discharge capacity, it is highly recommended to separate high usage circuits within the property to prevent overloading. Backup batteries are designed to store electricity for long periods of time.

When compared against the frequency of grid failure, it is very rare for consumers to opt for backup enabled storage due to the additional measures required.

For more information on the costs and benefits of Battery Storage please click here: or alternatively contact our office Click Here