Most solar PV system are based on crystalline technology from the mid 80s. Since then manufacturing costs have improved and prices have come down to an average of around $8-10/watt (not including the rebate or installation costs). The quote lifespan of panels are between 25-30 years. An optimally installed system takes over 20 years to payback the initial cost before the electricity becomes 'free'.
Newer generation cells are purporting costs of less than $1/watt (cost-competitive with coal). But due to high demand and limited supply this has not yet translated to reduced prices.
What will be the future of solar technology?
Here is a comprehensive summary about locally available systems (including cost) in Australia:
http://www.ata.org.au/wp-content/renew/ ... _guide.pdf
Here is a discussion about the new generation cells:
http://www.renewzle.com/learn/the-quest ... olar-panel
Here is a local R&D effort on cheaper solar cells:
http://www.originenergy.com.au/1233/SLIVER-technology
Here is a timeline of the different technologies:
http://upload.wikimedia.org/wikipedia/e ... 07%29d.jpg
Here is a general discussion including some information about the economic issues:
http://www.solar.udel.edu/pdf/FAQListfo ... ellsv2.pdf