Photovoltaic cells
Use the sun's energy to generate electricity for home or business use.
Photovoltaics (PV) are solar panels that generate electricity. They make no noise, produce no emissions and can be mounted on an existing building or on a separate frame.
Unlike wind and micro-hydro, they are suitable for urban use as well as for remote locations.
Up front costs are high, but you should get 20-30 years paying little or nothing on electricity after you've paid off the initial investment.
How does PV power generation work?
A PV system uses solar panels that contain semi-conductor material (often silicon) which creates an electrical current when the sun shines on it. Like the panels used for solar hot water, photovoltaic panels are tilted to make the most of the sun.
Stand-alone or grid-connected
Photovoltaic systems can be connected to the local lines system. This gives you a backup supply for times when the sun isn't shining enough to produce the electricity you need.
It may also allow you to sell electricity back to your power retailer at times when you're generating more than you need.
Alternatively, PV systems can be used as the stand-alone power supply for a property. In this case, the power you generate is stored in batteries for use when the sun is not shining.
For stand-alone systems, PV can generate electricity to run mainly lighting and electronic appliances only. Other forms of energy will be cheaper for higher energy consuming purposes - for example, solar or wetback for water heating, a woodburner for space heating and gas for cooking.
Locating the panels
PV panels can be located just about anywhere that catches sun for most of the day. They're often put on the roof.
They need to face north, and be tilted skywards, to make the most of the sun. The exact angle of the tilt depends on where you live (because the sun travels higher in the sky at higher latitudes). It also depends on the type of system you have. The person who installs your system will be able to explain what is best for your use and location, but generally the ideal angle will be similar to the latitude of your location.
On a grid-connected PV system, the panels can be tilted up more to generate the most electricity during summer when the sun is higher in the sky - since this maximises the total annual amount of electricity generated.
A stand-alone system can be tilted up more, so it catches the winter sun better - this helps to ensure you will get electricity all year round.
Some systems have adjustable frames so you can adjust the tilt depending on the season and others automatically track the sun to gain more energy, but these systems cost more.
It is important to avoid partial shading of the panels. The individual cells in the panel are connected so that shading one cell may turn them all off. Partial shading can also cause hot spots that can cause damage.
How much power can a PV system generate?
About 8m² of PV panels can produce a maximum of about 1kW of power under standard conditions. This is the typical size for a domestic system.
The average New Zealand household uses about 10,000kWh of electricity a year - which equals just under 27.5kWh per day.
Types of PV panel
There are several different types of PV panel available. Talk to suppliers about the best type for your purpose. Aim for the cheapest overall cost per kWh generated. Lower efficiency panels may cost less to buy and install but will produce less electricity.
All PV panels are sealed in waterproof materials to prevent corrosion.
Why use a PV system?
PV systems are used in other countries to provide power for office buildings, schools, factories, farms and some homes. These are normally for demonstrations or have major government support.
Does location matter?
The amount of electricity generated by a PV system will obviously be greatest in areas that receive more sunshine hours.
Cold temperatures don't matter and some electricity will still be produced on cloudy days. Some systems actually work better if the temperature is not too hot. But they cannot work if covered by snow.
Cost-effectiveness
PV systems are expensive. According to the Energy Efficiency and Conservation Authority, a 2kW system will cost well over $30,000 to install.
However, off-setting this is the fact you'll pay very little or nothing for electricity over the 20-30 year life of the system. The batteries will need replacing every 6-8 years, or more often if not properly maintained.
At the moment, the price makes PV systems most economic for people in remote areas who would otherwise have to pay tens of thousands of dollars for an electricity connection.
However, prices will come down. If you're planning a new home, think about installing a PV system in the future. In 10 or 20 years it may be a much cheaper option.
Environmental benefits
PV systems produce no greenhouse gas emissions and they reduce the amount of electricity that needs to be supplied by the local lines system - this means less demand for electricity produced by burning fossil fuels therefore a reduction in greenhouse gas emissions.
The environmental cost of manufacturing PV systems is far less than the benefit they provide, but they will require careful disposal at the end of their life.
Installation
Installation of PV systems should normally be left to the supplier. There are many cases where systems have been badly installed by home owners or unqualified tradespeople.
Electrical work involving mains voltage (230V) must be done by a registered electrician.
Legal
To install a PV system you may need a building consent from your local authority - neighbours may object if it is too close to them.
You'll also need to talk to the lines company and power retailer if you are planning to connect to the local lines network.
Maintenance
Full and clear written instructions must be provided by the supplier. Many homeowners could do most maintenance themselves.
PV systems have no moving parts. Good panels are guaranteed for 25 years without servicing. Rain normally keeps the panels clean, but they need to be checked occasionally.
Future options
You can expect to see more PV systems around in future as technology improves and costs fall.
PV technology is also being put to some innovative uses. For example, transparent solar cells are now being produced for use in windows and skylights: the visible light and the view can still get through, but the ultraviolet light is converted to electricity.
Increasingly, PV technology is being integrated within the cladding and roofing of buildings as they're built. Integrated PV systems look better than add-ons and are safer in high winds.
More information
From Smarter Homes
From ConsumerBuild
From other sites
The Electricity Commission's website has sample contracts for electricity customers, which include clauses relating to sale of electricity back to an electricity retailer.
The National Institute of Water and Atmospheric Research's website has an online map showing mean annual sunshine hours anywhere in New Zealand, and a web page showing monthly sunshine averages.
The Energy Efficiency and Conservation Authority's website has a page about renewable energy and a factsheet Factsheet 6: Standalone Power Systems (PDF, 330KB).
You can also find general information about using PV to generate electricity from the Sustainable Association New Zealand website.
You can read photovoltaic energy case studies on these pages:
- www.electricity.co.nz/solarhome.htm
- solar energy page of EECA's Energwise website.
