- Site Analysis
- Site Use
- Passive Design
- Material Use
- Space heating
- Lighting design
- Water heating
- Active ventilation
- Electrical design
- Renewable electricity generation
- Bioenergy and Biofuels
- Space heating
- Wet Areas
- Health and Safety
- Other Resources
Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.
Battery banks 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
- Installation requirements
- Maintenance and disposal
Battery storage systems
Battery storage systems require:
- 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 bank will usually cost over $10,000. Batteries require replacement every 5–12 years, depending on the type and how they are used.
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.
Most renewable energy system storage batteries are:
- composed of a number of cells
- supplied as any of 12 V, 24 V, 48 V or 120 V
- built as a block of many individual 2 V cells – though occasionally from mono-blocks of 6 V or 12 V batteries.
Lead acid batteries are most commonly used in renewable electricity systems. 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.
Nickel-cadmium batteries are less common and much more expensive, but last longer.
Rechargeable lithium-ion battery systems are now available in New Zealand from Panasonic, Tesla and other manufacturers. These may be wall mounted or sit on a floor depending on the model or system. The Panasonic system has 8 kWh capacity and the Tesla up to 14 kWh.
- The battery room storage for lead acid batteries must be well ventilated to the outside (using either passive or mechanical ventilation) because batteries contain a flammable and corrosive mixture of oxygen and hydrogen during the last stage of charging. The amount of ventilation needed depends on the size of the battery pack.
- Do not locate electronic components above the batteries as they can corrode or cause an explosion.
- Mount batteries on stands or on thermal insulation if they are floor-mounted – they can react to cold surfaces such as cold floors, causing the electrolytes to stratify, which can reduce battery life and performance.
- Batteries must be able to be readily disconnected for maintenance, repair or replacement by including an isolating switch or fuse between the batteries and the electrical system.
- Locate batteries out of direct sunlight as sunlight can buckle the electrodes.
- Specify drip trays to capture any spilled acid.
- Provide space above the batteries for a hydrometer to check their charge levels.
- Install a cover or shroud over the batteries to prevent accidental shorting.
- Provide an adjacent space to store water and sodium bicarbonate in the event of an acid spill.
Maintenance and disposal
- Maintain battery life and performance by keeping the terminals clean and tight.
- Ensure the electrolyte is above minimum levels using only distilled water.
- Protect against acid burns (for wet lead-acid batteries) by wearing protective clothing and eye protection
- Dilute spilt acid with water and neutralise with sodium bicarbonate.
Disposal of batteries should be at recycling stations, not in landfills (because they contain lead and acid).
Updated: 30 November 2020