Clean technology: Is solar right for you?

Photo / Supplied

Back in the 70s, the first photo voltaic solar panels (PV) to produce electricity used to require direct sunlight. These days, modern PV panels produce on even the cloudiest of days.

As those who've been sunburned will attest, we have some serious solar radiation going on here, making our homes prime candidates to be turned into mini electricity generators.

PV has been promoted as an eco-friendly form of energy generation. Studies done in the UK and US suggest that the overall ecological impact of producing, installing and using home PV is much smaller than for large-scale power generation and distribution.

The price of PV panels has plummeted, falling around 60% in the last 18 months.

Along with this the efficiencies in output have increased, and new PV panels can even become the roofing material for your home.

On-site power generation also has the attraction of gaining some insurance from rising power prices. This is either through saving the energy produced by PV panels in large battery banks (which will push the initial capital expenditure up significantly) or, ideally, by selling the power produced on your roof back to the large electricity retailers.

This is, however, provided that the retailers keep agreeing to buy it, something for which they are not legally obliged to do.

Some electricity suppliers currently make this possible, although the prices they pay vary.

The current payment for power delivered to the grid is between $0.10 +GST and $0.15 +GST. This is significantly lower than the retail price, which is about $0.23 +GST.

This is currently under review by the Electricity Authority, which is taking submissions until October 30. Find out more here.

The continuing roll-out of smart meters and its potential to allow more flexible use of the existing power grid could add to these opportunities in the coming years, as could an increase in the use of electric cars whose batteries could also be harnessed to store power for times when the sun isn't shining.

Of course, all these energy calculations entirely depend on a home's energy use, so reducing that use to a minimum should be the priority to minimise financial and environmental cost, whatever system you use to power your home.

All this makes PV solar energy generation well worth considering.

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 theWattPeak, 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.