Stand alone power systems (SAPS)
In situations where there is no connection to the electricity network, micro-generation technologies are often used together as ‘stand-alone power systems' (SAPS).
As connecting properties to the electricity network can cost as much $25,000 per kilometre, a stand alone power system can be an attractive economic alternative.
SAPS may include:
- Solar energy technologies (solar water heating and photovoltaics that convert sunlight to electricity)
- Micro wind turbines
- Micro hydro systems.
Use the links above to find out more about those technologies.
On this page:
The costs of setting up a stand alone power system
Backing up your stand alone power system
Because SAPS are not connected to the electricity network, some form of back-up generation and energy storage is usually required. This is for when the primary generation sources fail to supply the energy needed.
SAPS are often backed up by a diesel or petrol generator for when other generation facilities aren't operating. This back-up may come into play, for example, when solar photovoltaics (that convert sunlight to electricity) encounter a cloudy day or when there is no wind to drive a wind turbine.
The output from micro-generation facilities is usually stored by batteries.
Minimising the need for diesel back up
Diesel generators can result in high levels of greenhouse gas and particulate emissions. Therefore, going ‘off-grid' may not be that environmentally friendly. Staying connected to New Zealand's relatively ‘green' electricity grid could be a better option.
Careful design of your SAPS and close management of your energy use will reduce your overall environmental impact. You can also avoid having to use your diesel generator too often through a greater investment in generation and battery storage.
Operating a SAPS also means you need to pay close attention to how and when you use energy. It's important to reduce your peak electricity demand as much as possible.
It's also important to use alternative energy sources where possible, such as gas, a woodburner, or solar water heating to provide space and water heating respectively.
This way you can minimise the size and cost of the generation system you install.
Batteries
Batteries store the electricity generated so it is available when the sun isn't shining, the wind isn't blowing, or the water isn't flowing.
They also allow you to use more electricity, for short periods of time, than the maximum your generation sources can supply. But it's still necessary to keep the electricity demand of your house within the capability of your battery bank and the amount of generation you have.
Banks of 12V to 48V lead-acid batteries are commonly used. A battery bank can cost anywhere from $10,000 to $30,000, depending on how much energy you need to store.
The batteries will typically need replacing in 5-15 years, depending on quality, sizing and how they are used.
Deep cycle batteries
Batteries designed to be charged and discharged regularly are called deep cycle batteries. Their construction is different from normal car and truck batteries, which are designed to deliver a short burst of current for engine starting.
Normal engine-starting batteries would only work properly for a short period if used in a small-scale generation system.
Use the right sized batteries
Most domestic installations use DC (direct current) voltages between 12 V to 48 V. The individual batteries are usually only between 2 and 12 volts and need to be arranged in an array to give the required voltage and current. Make sure you buy the right sized batteries and battery bank for your situation.
If your battery bank is too small, it may be discharged at a low level too often, which shortens its life. If the bank is too large, it will cost you more and it may not fully charge regularly, which can also shorten its life.
Typically, battery banks for wind and solar systems will be sized for several days storage, depending on the total electricity requirement and generating capacity. Hydro systems may reduce the need for storage if the water supply is reliable.
Your supplier can help you choose the right sized battery bank.
Battery maintenance
Batteries require a small amount of regular maintenance. This usually includes topping up batteries with distilled water (if they aren't sealed) and cleaning away corrosion, dust and dirt. Your supplier should be able to provide a maintenance programme.
Recycling old batteries
Batteries contain hazardous substances such as acid and lead, and need to be disposed of correctly. Most materials used in batteries are suitable for recycling. Take old batteries to a recycling station, not a landfill. Your supplier should be able to advise you on battery recycling options in your area.
Inverters
An inverter converts electricity from direct current (DC) electricity to alternating current (AC), which most household appliances use. There are two types of inverter - one for stand-alone systems and one for grid-connected systems. In both cases, advanced inverters are available that control your generation units and how much electricity your house is using at any time.
Buying an inverter
A number of inverters are available on the market and your supplier can help you choose the right size and type. For a good inverter, you should expect to pay around $3,000 to $10,000. A typical household would require an inverter with a capacity of around 3kW to 5kW.
Check that your inverter is compatible with your appliances. Your supplier should be able to advise you on this.
Costs
The cost of installing and maintaining a stand-alone power system can vary greatly. It depends mainly upon the combination of components installed and the electricity output required.
A middle-of-the-range system, with either solar electric panels or a wind turbine as the primary energy source, typically costs between $15,000 and $25,000.
The set-up costs of a micro-hydro system usually range from $12,000 to $15,000. Of these costs, 20-25% will go on the batteries.
The other major item is the inverter, which can cost from $3,000 to over $10,000, depending on the size, quality and complexity.
Alternatively, to avoid the need for an inverter, DC-powered appliances can be installed but these are generally more expensive and the choice is limited.
A diesel or petrol-fuelled generator will cost between $4,000 and $12,000 installed. The size of the generator will depend on the amount of electricity required to meet demand, the size of the battery bank and the renewable energy sources available at the site.
A system with photovoltaic panels or a wind turbine, micro-hydro generator, batteries, inverter, and a diesel or petrol generator could cost up to $60,000 installed.
Consent requirements
Local and regional councils will each have rules regarding the installation of a stand-alone power system.
For example, local council height restrictions may apply to a wind turbine tower, or a regional council consent may be required to dam or divert a stream. Talk to your local and regional councils about what is required for the system you are planning to install.
In most cases you'll need either a building or resource consent, or both, for your micro-generation system. You need to discuss your consenting requirements with the planning and/or building consent officer at your local council. In some cases your expert will be able to provide advice on your local council requirements. Note that resource consents for hydro generation require consultation with regional councils.
Case studies
High country home goes off grid - case study
More information
Use the following links to find out more about:
- Grid-connected systems are electricity generation systems that may include photovoltaics, micro wind turbines or micro hydro. They are connected to the local electricity network, and can export excess electricity, or use mains electricity as a backup
- Choosing energy options explains what you should consider when deciding on the best generating options for your location
- Solar PV or photovoltaics convert the sun's rays to electricity.
- Micro hydro for households is typically less than 5 kW
- Micro wind energy refers to the use of micro wind turbines typically less than 10 kW
- Micro-generation is one form of distributed generation, which refers to local electricity generation connected to lines networks, rather than the natioal grid.
- More about use New Zealand's use of renewable energy.
