Solar radiation is about 30 MJ per square m.
The man that won the ABC's New Inventors people's vote last year has an interesting setup.
http://www.greenandgoldenergy.com.au/
3 kW / 6,000 kWh* SunCube™ system
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Model GGE3kW
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AU$15,000 inc GST (For Australian customers who use GGE trained solar installers). This price may be reduced by a one time REC (Renewable Energy Credit) rebate of AU$2,250 and a one time PVRP (PhotoVoltaic Rebate Program) installation grant worth upto $4,000. Currently the SunCube system is not qualified for either rebate and the PVRP program is scheduled to finish end June 2007