It's a lot of mirrors!

The problem is getting them to align so that they all reflect the sunlight to the same spot. I can already tell that this isn't going to happen but it is interesting to consider why the light has to be focussed on one point in order to boil water. Why can't we simply place a cup of water in the sun. Well a cup does not have a very big surface area so wouldn't absorb much energy. So, how about increasing the area so that the water was in a shallow dish. The problem then is the heat loss. The maximum temperature is reached when the energy absorbed = the energy radiated and the energy radiated depends on the surface area. So a big shallow dish would absorb a lot of energy but would radiate a lot too. By focussing the light we put a lot of energy into a small area. If the area of the mirror is 1m² then we would be shining 1 kW of power onto the focal point.