grid parity, page-28

By my calcs the 85kWhr/sqm/yr are reasonable.

I get for 1 sqm at 8.5% efficiency @ 1/3 sun:

0.085 * 0.333 = 0.0283kW/hr
= 0.226 kWh/day
= 6.793 kWh/Mth
= 81.51 kWh/yr

at 20c / kWh
= $16.30 per year for each m2

I would probably pay about 5 times that on top of the standard roofing cost or an extra $80/m2 - assuming the roof was still producing a reasonable percentage after say 15 years (60% of original efficiency?)