A roof mounted solar array capable of generating a kilowatt covers about eight square metres. A ground-mounted array needs a little more room for mounts and to prevent shadowing.

For large installations, space is a prerequisite — although States limit the power generation capacity of private renewable installations. In NSW, the limit is 10 kilowatts per registered power line. A farm with separate power lines to bore pumps or sheds can add 10kW per line.

But whether solar power generation represents an opportunity to landholders depends a lot on the State and its policy on “feed-in tariffs”, or how credits on renewable energy fed onto the grid are calculated.

All tariff schemes value renewable energy higher than fossil fuel energy (sold at around 15-19 cents per kilowatt hour), but the multiplier varies between States and power companies.

In NSW, Victoria and ACT, companies are offering feed-in tariff rates of 60-68 c/kwh, but in SA and Qld prices fall to 44-52 c/kwh.

Credits earned through tariffs can either go towards the purchase of mains electricity, or with many power companies can be exchanged for cash.

NSW and the ACT offer gross feed-in tariffs: every kilowatt of energy exported onto the grid is credited, regardless of how much power is drawn back by the household or farm. Returns are guaranteed for seven years in NSW, 20 years in the ACT.

These, according to Mr Gemmell, “are the best systems in the world, on par with Germany and Spain”.

Victoria, South Australia and Queensland have a net feed-in tariff, which provides a credit only on surplus energy fed onto the grid. If a solar installation exports four kilowatts, but the business draws back five, the site only gets a credit for one kilowatt.

The largely identical SA and Qld tariff schemes are now under review—a process that Mr Gemmell suggests should be of keen interest to rural landholders because of the income possibilities from a gross scheme.

Tasmania doesn’t offer a feed-in tariff because it considers its hydroelectricity delivers enough green energy, Mr Gemmell said.

The West Australian Liberals promised a gross feed-in tariff before election, but are now saying that they will only introduce a net scheme.

The inequity between the States is causing renewables money to flow towards NSW and ACT.

Mr Gemmell reported that interstate investors are offering to lease land from NSW farmers to put in solar installations, with the farmer getting free electricity and the investor taking profits from the surplus.

NSW customers represented about 15 per cent of Solar Choice’s base in early 2009. This year they represent 70 per cent.

But the boom may be short-lived, Mr Gemmell said. The NSW Government has said it will review its gross feed-in tariff scheme when uptake represents 50 megawatts.

In Mr Gemmell’s estimation, at current adoption rates that point will be reached by late May or June.

* Solar Choice provides households and businesses with quote comparisons from 65 solar power installers around the country.