Nuts and Volts
Each PV or BIPV (built-in PV) component or ‘module’ is rated on its peak electrical output under standard test conditions, called the Watt Peak, or Wp. Modules are available in sizes from 5 – 300 Wp, with a typical complete domestic system rated at about 1,000 – 3,000Wp. According to The Energy Efficiency and Conservation Authority, a 1kWp solar system costs somewhere between $6,000 and $9,000 to install. According to SEANZ, which surveys NZ installers, the average price in 2011 was around $4,000. According to Kiwi PV installers PowerSmart Solar the average home using 8,500 kwh of power a year could save something like $500 a year if they make the switch, and even more on larger systems. This suggests that a PV system could pay for itself in something like seven years, if grid electricity prices remain constant – and power companies continue to purchase power from small generators at the same price. Given the average power price increase of around 6.5% over the last five years, this time could be shortened. PV systems have an expected lifespan of 25 to 30 years, but they do degrade over time. The best systems are reckoned to only lose about 0.5% efficiency a year, which would mean they should still be 80% efficient if the system itself is still working 40 years from installation.