In a flat-plate solar collector, water flows through tubes attached to the back of a thin solar absorber plate. If the plate's emissivity and absorptivity are both 0.9, and it's exposed to 500 W/m2 of solar radiation at 0°C ambient temperature, what is the convection heat transfer coefficient at the plate's surface?
a) 5 W/m2·K
b) 25 W/m2·K
c) 50 W/m2·K
d) 100 W/m2·K