Stand alone power systems (SAPS)
If connecting to the grid is too expensive for you, a stand alone power system (SAPS) is a good alternative. SAPS generally use a combination of renewable generation sources (such as solar PV, wind turbine or micro-hydro), a battery bank, smart controller/inverter and a back-up.
- When to use SAPS
- Back-up generation
- Cost of installing and maintaining SAPS
- Consent requirements for SAPS
- If you live in a remote area - a stand alone power system could be a good way to get your electricity.
- If there is no connection to the electricity network - micro-generation, control and storage technologies are often used together as stand alone power systems.
Connecting your rural property to the electricity network can be expensive - costing as much $25,000 per kilometre. So you don't have to be far from the nearest electricity lines for a stand alone power system to be a better alternative.
Because stand alone power systems aren’t connected to the electricity network, you usually need a back-up generator (diesel, petrol or biodiesel) - for example when it's too cloudy for your solar PVs or there isn’t enough wind to drive your wind turbine.
Minimising the need for diesel back-up
Using a diesel generator can create high levels of greenhouse gas emissions. You can minimise the need for diesel back-up by:
- staying connected to New Zealand's relatively ‘green' electricity grid
- carefully designing your stand alone power systems
- closely managing your energy use
- investing more in generation and battery storage
- paying close attention to how and when you use energy - reduce your peak electricity demand as much as possible
- using alternative energy sources for example gas, woodburners or solar water heating.
Batteries allow you to store electricity from micro-generation so you can use it later. Banks of 12 V to 48 V lead-acid batteries are most commonly used. You need to replace them every 6 to 12 years - depending on quality, size and how much they’re used. You’ll also need a controller and an inverter, as well as a back-up generator.
Batteries of different makes and ages shouldn’t be mixed together, which means it’s important to get the size of the battery bank right to begin with.
Deep cycle batteries
Deep cycle batteries are designed to be charged and discharged regularly. They’re different to normal car and truck batteries, which deliver a short burst of energy to start an engine.
Most households use direct current (DC) voltages between 12 V and 48 V. Individual batteries are usually only 2 V to 12 V, so you’ll need to arrange them to make up the voltage and current you need.
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 to a low level too often, which shortens its life.
- If the bank is too large - it will cost more and it may not fully charge regularly, which can also shorten its life.
Batteries need regular maintenance. This means topping up your batteries with distilled water (if they aren't sealed) and cleaning away corrosion, dust and dirt.
Batteries contain dangerous substances like as acid and lead, so you need to dispose of them correctly - most are suitable for recycling.
Inverters convert electricity from direct current (DC) electricity to alternating current (AC), which most household appliances use. Stand alone power systems and grid-connected systems use different types of inverter. In both cases, advanced inverters control how much electricity you generate and how much electricity you use at any time.
Buying an inverter
Your supplier can help you choose the right size and type of inverter. A typical household needs an inverter with a capacity of around 3 kW to 5 kW.
Check that your inverter is compatible with your household appliances.
The cost of installing and maintaining a stand alone power system can vary a lot - it depends on the combination of the components and the electricity output you need.
- Middle-of-the-range systems, with either solar PV panels or a wind turbine as the primary energy source - usually cost $15,000 to $25,000.
- Set up costs of a micro-hydro based system - usually range from $12,000 to $15,000, with 20% to 25% for the batteries.
- Inverters - can cost $3,000 to over $10,000, depending on the size, quality and complexity. You can avoid using an inverter by using DC-powered appliances but they’re generally more expensive and the choice is limited.
- Diesel or petrol-fuelled generator - will cost $4,000 to $12,000 to buy and install. The size of the generator depends on the amount of electricity you need, the size of the battery bank and the renewable energy sources available to you.
In many cases you'll need either a building or resource consent (or both) for your micro-generation system.
Local and regional councils have rules for installing stand alone power systems, for example local council may apply height restrictions to a wind turbine tower, and you may need regional council consent to dam or divert a stream. Talk to the planning and building consent officers at your local and regional councils about what requirements they have for the system you’re planning to install.