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I'd like to say "good idea" but my old physics lessons are saying "Can't see it making enough heat". |
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<frowning> I think it takes about 70KJ of heat energy to change temperature of a mug water from 30C to 100C. PV cells produce a couple of watts each. I'm not going to wrack my brains for conversions and actually fitting these facts together into an argument..I'm just going to look sceptical </frowning> |
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Depending on the resident climate and time of year, I'll take the solar cooling version please. |
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The specific heat of water is 4.18 x10^3 J/kg/degC). |
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Therefore, it would take 1.045 x 10^3 J to heat a standard 250ml cup of water one degree Celsius. |
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I'm not sure how the solar panels would need to be positioned for maximum energy capture. |
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Maybe if you hook up the coffee in the cup with tubes to a solar "water" heater on the roof? |
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[unabubba] Isn't spec heat cap...4190 J/ kg.K? Anyway....point still same in my opinion, to generate the electrical power to heat the water (through an inefficient heating element) there will have to be a much larger surface area of PV cells than you can fit on a mug. |
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I'm with Jinbish on this one, but it's Friday afternoon and I can't be bothered to do the maths. </frowning and scowling>. |
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To change the temperature of a standard cup of water from 22C (295.15K) to 65C (338.15K) (about as hot as you can comfortably drink a liquid) will take 45.008 kJ |
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There is about 3.6 kWh to 1 kJ/h, I think. |
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The very best amorphous silicon solar cells, which return around 30% efficiency, would produce about 0.3kWh/sqm at perpendicular attitude at the equator in perfectly clear conditions, on 22 March and 22 September each year. |
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Assuming you wanted your coffee hot in around 3 mins then the required surface area of the very best PV cells available would mean that that portion of the surface area of your coffee cup, directly perpendicular to the direction of travel of light from the sun, at the equator, on those days, would need to be approximately 108 square metres, or 34 ft x 34 ft. This assumes perfect efficiency in your heat exchanger. |
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Good luck! Welcome to the halfbakery, home of the modern cynics. |
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Why bother with the conversion at all? Just get a glass coffee mug. |
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But remember, the coffee is already hot when put in the mug. All this device does is just keep it warm for ages. so that you can leave the coffee for a couple of hours and it will be still as hot and fresh
(well not really fresh) as it was when you first poured. |
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your mistake [amazing] was to say "heat your coffee" - if you had said *keep* your coffee hot, we would not have got into this maze. only problem is: the sun rarely reaches my little office. |
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There we go, i changed it from to keep at desired
temperature. I think it's better, think...... |
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In that case, all you need do is get a Thermos®. |
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UnaBubba's sight is failing him in his old age, methinks... |
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My coffee never has a chance to get cold. |
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Hmm, the most efficient solar absorbtion transducer would be... Why not just paint it black? |
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