The TV program "mythbusters" did a show about Archimedes / Clarke ship-roasting legend. The participants aimed their mirrors with the aid of a net 1-2 meters in front of them (by shining thru the net, and seeing the lit-up part of the net, they could aim decently) However, I believe their conclusion was, it was not an effective weapon. They could char the ship a bit, and annoy the sailors with the light and heat, at best. For solar energy, mirror-based systems are best used in non-cloudy high altitude locations while photovoltaics are better in cloudy or lower-altitude locations since the latter can use scattered light. Question: what about a combined photovoltaic plus heat-engine/thermal based solar system? Couldn't that achieve greater efficiency than either alone, and why is it not heavily used?