Electricity use accounts for about 69% of New Zealand residential energy use by fuel source.

Generating energy from renewable sources

Remote area power systems (RAPs) can be used to meet an individual property or group of properties’ electricity needs, generating electricity close to where it will be used, using sustainable energy sources such as wind, sun and water. Any renewable energy system will involve a significant up-front capital outlay which – depending on circumstances – may be offset by the benefits of self-sufficiency in electricity generation.

Key design decisions

• For renewable electricity generation, key decisions involve:
• which energy source or sources to use – photovoltaic, wind, or micro-hydro
• the capacity of the system – how much electricity is needed to meet peak and overall demand
• what type of electricity storage and/or backup options to specify
• whether to specify a stand-alone or grid-connected system.

Any system will have to be designed to take account of local conditions (rainfall, wind and town planning) and capacity to meet demand (ongoing and peak). Cost-effectiveness and security of supply can be enhanced by also introducing other energy efficiency measures such as use of solar water heating.

Property types

Wind and hydro systems will generally be suitable only for larger rural sites or remote locations, where they may be considerably more cost-effective than getting a connection to the grid. Photovoltaics and some small scale wind generators (if permitted) can be used in urban areas.

Security of supply

All properties need an electricity supply that is available at all times, and can meet peak demand. To ensure security of supply, RAPs should incorporate a backup in the form of:

• batteries
• a diesel generator
• a connection to the grid.

Where properties are connected to the grid, they may be able to sell excess electricity back to their power retailer if permitted under the district plan.

Security of supply for different renewable electricity options:

• Photovoltaic electricity generation is dependent on available solar radiation levels, which means it only generates electricity during the day, and output will vary throughout the day and year. In general, output will be higher in the middle of the day, lower in the mornings and evenings, and higher in summer than in winter. A photovoltaic system can suddenly stop generating if clouds roll over. The best option for photovoltaic systems is for power output to be sent as DC to a battery storage system
• Wind power electricity generation depends on available wind speed, which means its electricity output will be inconsistent. The best option for wind systems is for power output to be sent as DC to a battery storage system. Alternatively an AC supply can be maintained and excess capacity sold (if permitted under the district plan) back to an energy retailer
• Micro-hydro electricity generation depends on a consistent water flow (which can be stored). Its electricity output can be reasonably consistent throughout the day and year (unless its water supply dries up in summer). If the system is large enough to meet peak demand, its electricity output can be sent as AC directly to a home’s electricity supply system. Excess capacity can be sold (if permitted under the district plan) back to an energy retailer.

RAPs may be designed using two or more of these generation options to ensure power will always be available.

Connecting to the grid

With a grid-connected system, the renewable electricity generator can be used to reduce electricity costs rather than replace mains supply altogether. Sizing of the renewable electricity generator is not as critical with the grid as a backup as it otherwise would be.

In a grid-connected system, both the mains electricity and the renewable electricity supplies connect separately into the home’s switchboard. The renewable electricity must be connected as an alternating current supply. Engaging a consultant experienced in switch board design for RAPs is recommended.

In some grid connections, excess supply from the renewable electricity generator can be sold back to the power retailer, if this is permitted by the planning regulations for the area. The power retailer will usually pay a lower rate than they sell electricity for.
When electricity is being sold back to the grid, the electricity meter runs backwards.

To sell electricity in this way:

• control gear (inverters, regulators) are required to convert the renewable electricity and deliver it to the grid at the required voltage and frequency
• a regulator is needed to control the amount of electricity drawn from and fed into the grid
• the property owner will need an agreement with the lines company and the power retailer.