Photovoltaic (PV) panels convert absorbed sunlight energy to electricity. They make no noise, produce no emissions and can be mounted on an existing building or on a separate frame.
They are more suited to urban use than wind and micro-hydro, and are also useful for a remote location, provided it’s not shaded. Upfront costs can be high, but provide 20–30 years of close to maintenance-free service. Whether they are a cost-effective investment depends on many variables, including:
- the type of set-up
- the quality of installation
- user behaviour
Solar electricity systems on EECA's Energywise website has useful information.
To assess your specific situation, you can use EECA's online solar calculator
If constructing a house, ask your electrician to make your house solar-ready – this move is likely to save you money down the track when you go to put a system in.
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. Ideally, panels should face north and not be shaded for the majority of the day, but especially around noon.
To maximise their generation capacity, they should be tilted at their latitude angle. While full sun provides the panel with the most ability to harvest energy, the panels will still work, albeit to a lesser degree, on cloudy days.
Stand-alone or grid-connected
The type of system that is going to work best for your home is going to depend on whether the PV system will be a sole or part source of electricity, and how and when the power will be used. There are a number of factors to consider, such as distance of the property from a power connection, the desire for independence or resilience, and the costs and benefits of the different types of systems.
Where there is a need to be independent of the grid, for example rural properties a long way from power lines, a stand-alone system will be needed. Others may want the independence of a stand-alone system but with the backup of the national grid. Where a house will be connected to the national grid, and independence isn’t a primary concern, the most cost-effective option might be a grid-connected system without storage.
Stand-alone and storage systems
PV systems can be used as the stand-alone power supply for a property – particularly where connecting to the national grid is going to be expensive. In this case, the power generated is stored in batteries for use when the sun isn’t shining.
There are three main types of batteries – deep cycle lead acid batteries, lithium-ion batteries or saline batteries. The different types of batteries have different costs, lifetimes and maintenance requirements, so talk to an experienced professional installer about the best option(s) for your particular situation.
For stand-alone systems, it’s important to first make sure that every part of the house is as energy efficient as possible. Other fuels are typically used where a lot of heat or energy is needed, such as hot water, cooking or space heating. This could include using solar hot water, wetback and/or gas for water heating, gas cooking, or a woodburner or gas heating for space heating. This helps to minimise the fluctuations in demand over the seasons, as well as the size of the system you need to install.
Stand-alone and storage systems can also be connected to the grid to export surplus energy, for supplementary power, or as backup during periods with high use and/or low sunshine hours.
PV systems can be connected to the local electricity lines system (ie ‘grid connected’), whether or not there is battery storage. This gives you a backup supply for times when the sun isn't shining or strong 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, but feed-in tariffs are usually a lot lower than what you have to pay for electricity from your retailer.
Grid-connected PV systems are the most economical where you can use as much power generated from them as possible. An electric car can be a great way of maximising the use of your system if your car is at home during the day.
Grid-connected systems (which are by far the most common systems) do not have to have storage, but because the peak production of power is in the middle of the day, the peak output of the system often happens when nobody is home. This often means selling the energy to the grid at a low rate during the day, and buying it back at a high rate at night! Storage-less systems are most suited to households where people are going to be at home during the day on a long term basis.
The more electricity you can use from your system, the more cost-effective it will be. Set timers on your appliances so that they run at times of peak generation – typically around midday to the early afternoon.
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 north-facing slope of the roof, but can also be mounted on stands in open areas.
They need to face more or less north, and be tilted, 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 (for example, Auckland sits at a latitude of about 36 degrees – so the panel should face north and be tilted at an angle of about 36 degrees).
A stand-alone system can be tilted up more than this, so it maximises the winter sun resource better.
On a grid-connected PV system, the panels can be angled to generate the most electricity during summer when the sun is higher in the sky – since this maximises the total annual amount of generated electricity.
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 tend to not to be cost-effective, especially now given the availability of low-cost panels.
It is important to avoid any shading of the panels. The individual cells in the panel are connected, which means that shading one cell may reduce the effectiveness of them all. Partial shading can also cause hot spots to accumulate, and these can cause damage to the panel. Some new panels have 'micro inverters'. If one of these cells is shaded it will not affect the whole panel.
How much power can a PV system generate?
A typically sized domestic PV system of about 20m² of PV panels has a rated output of about 3kW of power during standard sunny conditions. Obviously electricity is only produced when the sun shines on the panel during the day.
According to BRANZ’s PV generation calculator, if installed in Auckland, on an unshaded north facing roof at 30 degrees (ie close to ideal conditions), this will provide around 3,400kWh annually, on average. In an energy-efficient household, this equates to the bulk of the electricity needs, averaged out over the year. An average (non-efficient) New Zealand household uses around 9,000kWh of electricity each year.
Over time most PV panels lose some efficiency. Check the specification sheets, maintenance instructions and warranties given by your supplier.
Types of PV panel
There are two main types of solar panel/module:
- Crystalline silicon solar cells have a solid silicon wafer as the semiconductor. There are two types – monocrystalline (which is more efficient) and polycrystalline.
- Amorphous silicon thin film solar cells have silicon in a thin film as the semiconductor usually on a thin metal foil.
Talk to suppliers about the best type for your purpose. Lower efficiency panels may cost less to buy and install but will produce less electricity. But also consider the life expectancy and warranty of the system. Because there are only minimal maintenance costs the cost effectiveness of a PV system is mostly determined by its price, efficiency and life expectancy.
Why use a PV system?
PV systems are a tried and tested technology that can provide you with many years of your own locally generated, renewable electricity. Under some conditions this provides you with more independence from power companies and can be a useful asset as reticulated electricity prices will inevitably increase. A PV system may give a small enhancement to your property value.
Does location matter?
The amount of electricity generated by a PV system will obviously be greatest in areas that receive more sunshine hours. New Zealand’s sunshine hours range from about 1,400–2,600 annually – NIWA provides a solar intensity map for the whole of NZ.
PV panels operate even in cloudy conditions – some electricity will still be produced.
Location of the panels on or around the home is crucial – these need to be in areas that receive year-round sun and are unshaded by trees, chimneys, aerials, or other buildings during their lifetime. There are various low cost apps which provide a good approximation of what a particular sites PV generation potential is, given its specific conditions, which rely on using your smart phone camera.
According to EECA’s solar calculator, a 3kW grid-connected system will currently (2017) cost about $10,000 to install, depending on a number of variables.
If this system is installed in Auckland, on an unshaded north facing roof at 30 degrees (ie close to ideal conditions), this will provide around 3,400kWh annually, on average. In an energy-efficient household, this equates to the bulk of the electricity needs, averaged out over the year.
Although prices have been dropping significantly for several years, solar systems are a long-term investment for most households.
It is best to use independent online tools to determine likely cost-benefits of installing a solar PV system. The EnergyWise solar calculator from EECA is a good example of this. Designed for an average house with typical household energy use patterns, it takes into consideration site aspects, current energy usage, upfront purchase costs, etc.
A 2016 Concept Consulting study [PDF 2.7 MB], available on the Concept website, found that the cost-effectiveness of PV is very sensitive to amount and pattern of power use, panel size and house location. An analysis of over one thousand potential combinations found that cost savings were unlikely in most situations under existing electricity charges, though this is likely to change as panel prices decline further, making self-generation financially viable.
The net environmental benefits of PV systems when examined over their lifetime, is a contentious issue. New Zealand is unusual in that by far the majority of its electricity is sourced via renewable means – some 80 percent currently. This percentage is set to increase to 90 percent by 2025. Thus, there is far less opportunity to reap environmental benefits (specifically those GHG reduction-related) via installing micro-generation systems.
The most comprehensive New Zealand study conducted so far on the issue of CO2 emission reduction was carried out in 2016 by Concept Consulting. They found that the potential for a residential system's PV to reduce electricity generation-related emissions would be small.
They expect that residential solar PV uptake to ‘increasingly substitute for new low emission power stations (such as wind and geothermal) that would have otherwise have been built to meet any growth in demand or retirements of old existing systems’, in the medium term. Even adding batteries to these systems does not alter the results for solar PV itself.
Like any electrical system, they will require careful disposal at the end of their life.
Almost all PV systems require installation by a licensed electrician, or inspector.
Check the manufacturer’s instructions and talk to your licensed electrician or inspector about installation. Ask about their experience in designing and installing such systems and what is the best set up system for your situation going forward.
To install a PV system you may need a building consent from your local building consent authority.
You'll also need to talk to the lines company and power retailer if you are planning to connect to the local lines network. If you wish to supply electricity back to the grid and be paid for it, you may need a contract with your local electricity provider. In most cases they will have standard contracts available.
Grid-connected PV systems must comply with New Zealand requirements, while the solar panels must comply with:
- AS/NZS 5033:2014 Installation and safety requirements for PV arrays
- AS/NZS 1170.2:2011 Structural design actions – Part 2: Wind actions
- The international standard IEC 61730-1:2016 Photovoltaic (PV) module safety qualification – Part 1: Requirements for construction.
Stand-alone PV systems have specific requirements outlined in AS/NZS 4509.1:2009 Stand-alone power systems – Safety and installation. Battery installations must meet AS 4086 Secondary batteries for use with stand-alone power systems.
Full and clear written instructions on panel operation must be provided by the supplier/ installer. Many homeowners can do the basic maintenance themselves – which usually just means making sure that the panels are clean.
PV systems have no moving parts. Good panels are usually guaranteed for at least 25 years without servicing. Rain normally keeps the panels clean, but they need to be checked and cleaned occasionally.
Battery storage systems have differing maintenance requirements and lifetimes depending on the type.
You can expect to see more PV systems around in future as technology improves and costs keep coming down. Even if you can’t install a system yet, it doesn’t cost much to make your house 'solar-ready'. This could save you a lot of money later when you decide to put them on and could make a difference when selling the house.
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 some 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 can bring the initial costs of installation down as some of the costs of the roof or cladding that is not required can be diverted toward the PV system.
More battery storage options are starting to come online, and the costs are changing all the time.