Batteries and other energy storage devices store energy so that it can be used when needed. In a stand-alone power system, the energy stored in batteries can be used when energy demand exceeds the output from renewable energy sources like solar (e.g. on a cloudy day) and wind (e.g. on a still day).

Inverters and other energy conversion devices turn energy from one form to another. An inverter in a grid connected renewable energy system converts direct current (DC) electricity from solar panels or a wind turbine into alternating current (AC) mains power.

Any renewable energy system also includes switches, circuit breakers and fuses to ensure it is electrically safe and allow major equipment to be isolated for maintenance.

Grid connected systems

A grid connected renewable energy system converts DC electricity from a power source, such as solar panels, to AC mains power and feeds it into the grid. It usually consists of the energy source, an inverter and a meter.

If there is a mains grid power failure, a grid connected renewable energy system disconnects from the grid and energy from solar panels is not available.

Battery banks connected to the grid, with an appropriate inverter, may work as an uninterruptable power supply to make energy available during a power outage for all or some of the electrical loads in a home or business.

Although costs are currently very high and extra components are required, it is technically possible for such a system to enable one of these options:

• energy from the grid to be stored during off-peak times of lower price and supplied during peak times where energy is charged at a higher rate (at homes with a time-of-use tariff for energy)
• surplus energy from renewable energy generators to be stored for use on site (at homes without a premium feed-in tariff for exported energy).

Grid connected system.

Stand-alone systems

A stand-alone power system is used for supplying energy at regional and remote locations where it is more cost effective to have on-site generation than to connect to the electricity grid. Stand-alone power systems typically include a power generation source like solar panels or wind turbines, a battery bank, inverter, battery charger and often a fuel generator for back-up power.

A stand-alone power system is used for supplying energy at regional and remote locations where it is more cost effective than connecting to the electricity grid.

Each system also needs a charge controller/regulator, which can be part of the inverter or other equipment. In a stand-alone system, battery banks and inverters are needed whether the energy comes from solar, wind or micro-hydro.

The exact equipment needed to convert and store energy depends on the energy needs and budget of the user, as well as the available energy resource and physical constraints of the site.

Stand-alone system.