Energy

Batteries help ensure reliability of power supply for stand-alone renewable electricity generation systems, especially wind or photovoltaic systems which can have periods of low generation.

On this page:

• Battery storage systems
• Charging batteries
• Battery options

Battery storage systems

Battery storage systems require:

• batteries
• a connection to DC electrical cables for input and output
• a regulator or controller on the input side to ensure the batteries are not overcharged
• an associated dummy load for redirecting excess power if the batteries are fully charged (this is usually an electrical element which can get very hot)
• an inverter.

The battery storage capacity should be able to maintain a charge of at least 50%. Rechargeable, deep cycle batteries, which are designed to be discharged to 50% or less without damage, will provide the optimum battery life. A battery will usually cost over $10,000 (and some with larger capacity over $15,000), but there are batteries with a lower capacity that cost less than this. Batteries require replacement every 5–12 years, depending on the type and how they are used.

Charging batteries

When charging batteries, the process requires:

• manual or automatic monitoring of charge level
• protection against overcharging
• supplementary charging when battery charge is low or load is high, e.g. a generator starts automatically
• charge equalisation – often done by a diesel generator
• consideration of the average daily depth of discharge (DOD) – it is lower with a larger capacity battery bank, which gives longer battery life.

A supplementary battery charger may be required.

Battery options

Lead acid batteries were the first type of battery commonly used in renewable electricity systems but are less likely to be installed in a new system today. They are wet batteries, containing sulphuric acid and can be valve-regulated (sealed or gel) batteries. These are very different from car or truck batteries.

Lithium-ion battery systems are available from many different manufacturers and have become the most commonly installed type of battery for new PV systems. Lithium-ion batteries are more compact and convenient and store more energy than the traditional lead-acid batteries.These may be wall mounted or sit on a floor depending on the model or system. The capacity of each main unit typically falls in the range of around 4.5 kWh to around 13 kWh. Some units can be expanded in steps to around 24 kWh or even 48 kWh.

In Australia, the LAVO company is taking orders for what it calls “the world’s first integrated hybrid hydrogen battery that combines with rooftop solar…”

Developed by researchers at the University of New South Wales, it uses high density, solid state hydrogen as the main energy storage medium. Energy is converted to AC power through a hydrogen fuel cell. The system in use produces no carbon dioxide emissions. The cost is around Au$30,000 (excluding installation and maintenance).

Updated: 21 February 2020