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Solar electricity generation (photovoltaics)

New Zealand's sunshine can be harnessed to generate clean electricity for homes and businesses, but it can be expensive

This page covers electricity generation through solar photovoltaics (PV).  Another page deals with using the sun's energy for solar water heating (transferring the sun's thermal heat to water). 

How PV works

PV cells convert sunlight into electricity by an energy conversion process. In most PV cells, photons (light energy) hit the cells, exciting electrons in the atoms of a semi-conducting material. Silicon is the most commonly used semi-conductor. The energised electrons result in the generation of an electrical voltage. In other words, electrons flow, producing direct current (DC) electricity.

PV cells are usually fairly small, with lots joined together to form a PV panel. These panels are then grouped together into PV arrays.

Where PV is used

PV panels and arrays are used in both stand-alone power systems and grid-connected generation systems, as well as in other small applications, like weather stations, some road signs and parking meters.

Key components of PV systems

PV systems are typically made of these key elements:

  • PV panels, cables, and mounting or fixing hardware
  • An inverter and controller 
  • Batteries, back-up generators, and other components in off-grid situations
  • Special electricity meters, in the case of grid-connected systems

Capacity rating of PV panels

Each PV panel (or module) is rated on its peak electrical output under standard test conditions. For example, a module with a 75 Watt peak rating (75 Wp) will have an output of 75 watts under standard test conditions. Modules are available in sizes from 5 Wp to 200 Wp.

A typical domestic system is around 1000 Wp to 3000 Wp. To get a total combined capacity of 1000 Wp you will need to buy a number of smaller modules and connect them to form a ‘solar array'.

How much electricity do PV panels produce?

The amount of electricity a PV system generates depends on the intensity of the sunlight to which it's exposed. PV still produces electricity on cloudy days, but less than with direct sunlight.

Obviously PV panels generate no electricity at night, and less in the morning and evening than in the middle of the day. How much electricity you will get from your PV panels per day can be worked out when designing your system.

In a whole day, a well-located PV panel will typically generate between 2.5 and 5 times its rated power output. So a 1kWp (kilowatt peak) PV panel could produce between 2.5kWh (kilowatt hours) and 5kWh per day, or between 880kWh and 1750kWh per year.

Where can I use PV panels?

PV panels work well in both rural and urban conditions. The best places to use PV is in places that get a lot of sunshine each year and where the sky is generally clear rather than cloudy.

PV works best in north-facing places with year-round sun.  Panels are usually installed on roofs but can also be placed on facades, conservatory roofs, sun shades, garages or specially-built stands on the ground.

Make sure your site:

  • Faces north (south-facing panels are for the northern hemisphere)
  • Is free from shade and exposed to good sun all year
  • Has enough space - a typical 1kW unit needs an area of around eight square metres.

If you are designing a stand alone power system, you will probably need to combine your PV array with other generators - such as a small wind turbine, micro-hydro system, or a petrol, diesel or biodiesel generator.

Costs

The cost of solar panels has fallen significantly in recent years as production expands and technologies improve. However installation and related equipment, such as a battery bank (if required), add to the cost considerably.

Read more on the economics of grid-connected systems and stand alone power systems.

Case studies:

Motukiekie island holiday home generates its own electricity using wind and solar - read case study

Vector is testing the performance and network impact of large-scale thin-film photovoltaic panels on the roof of the Hubbards plant in Mangere, Auckland.  Read more about it on Vector's website.

Related pages:

  • Consumer magazine article on solar PV
  • Stand alone power systems (SAPS) are off-grid electricity generation systems that may include photovoltaics, micro wind turbines or micro hydro, batteries and a back-up generator
  • 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
  • Micro hydro for households is typically less than 5 kW
  • Micro wind energy refers to the use of small 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 national grid.  
  • More about use New Zealand's use of renewable energy including solar energy