The 43 yr old, 2000m^2 solar furnace at Odeillo, France is still operating: http://commons.wikimedia.org/wiki/File:Four_solaire_001.jpg Thermodynamics limits its spot temperature to that of the solar "surface". The installation is visitor-friendly and probably has personnel who could enrich this thread. Re double duty solar collectors: Unless you're short of real estate, trying to recover waste heat from a photovoltaic just imposes engineering constraints that cost more than collecting heat separately. Also, electrical energy is much more valuable per watt than heat. This reminds me of my dumb idea to reduce disk seek times with multiple heads per surface. Surface is cheap. --rwg CG>You may find this interesting (and tangentially related in terms of energy output): http://what-if.xkcd.com/13/ Charles Greathouse Analyst/Programmer Case Western Reserve University On Wed, Jul 17, 2013 at 5:07 AM, Simon Plouffe <simon.plouffe@gmail.com>wrote: Hello, I was thinking at how we could pro[d]uce energy in a simple way, like having solar ovens with mirrors and such devices. This lead me to Archimedes and the way he used to 'toast' roman warships from the Syracuse citadel, apparently that idea was somewhat validated once, they found a way to toast a pile of plywood resembling a roman ship with plates of metals used at the time. Anyhow which lead me to think : what about today ?, suppose we would hypothetically having the same kind of threat but from space : an alien warship threatening to zap humans from existence. What about doing the same thing ? Billion of people using mirrors directly aimed at (more or less precisely) at this alien ship : what would happen ? More precisely, what would be the effect in energy having let's say 100 miilion mirrors aimed at one point in space toward one of those things, would it do the same thing ? Is this feasible, we would have one shot at it. This may sound naive, well is it ? Can someone calculate what output of energy this represent ? Best regards, Simon PLOUFF[]E